chapter ring rolling en

1 Ring Rolling

Ring Rolling Ring rolling

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Table of Contents1.1. Ring rolling ................................................................................................................................. 2

1.1.1. Model setup ...................................................................................................................... 21.1.1.1. Preface: Incremental forming processes ....................................................................... 31.1.1.2. Different types of rollers and their modeling ................................................................ 41.1.1.3. Special Controls ...................................................................................................... 61.1.1.4. Detailed explanation of the needed features ................................................................ 181.1.1.5. Further elements of modelling .................................................................................. 231.1.1.6. Special features of Postprocessing ............................................................................. 301.1.1.7. Potential problems, solutions and trouble shooting ....................................................... 311.1.1.8. Final remarks to the model setup .............................................................................. 32

1.1.2. Demos&Examples ............................................................................................................ 33

1.1. Ring rolling

Figure 1.1. Ring rolling (example)

1.1.1. Model setupKeywords

Ring rolling (hot and cold), axis of rotation, free rotating dies, local coordinate systems, table press, process control,simufact.kinematics, RAW, MERW

Objectives

This chapter will show in general how to set up a ring rolling model in simufact.forming. For this purpose both theindividual components of ring rolling simulation models and the required parameters are explained. In addition specialinstructions for enhanced analysis of results are given.

Preconditions

Ring Rolling Model setup

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Practical experience and/or insight of real ring rolling processes, basic knowledge in simufact.forming - correspondingto Quickstart and chapters 1 to 6 of the simufact.forming Tutorials, preferably some training with simufact.formingand first practical experiences to model and run simulations.

Some features introduced in this chapter require special licences and are not included in the basic packageof simufact.forming.

1.1.1.1. Preface: Incremental forming processes

All rolling processes including ring rolling are incremental forming operations. Final shape of the parts is not generatedby transformation of a die contour into the part (such as closed/impression die forging) but by sequential, repetitivelocal interaction of dies with simple geometries to the part. Depending on the process (flow rolling, radial forging,ring rolling, open die forging, axial die rolling) some thousands of cycles may occur. For simulation purposes thosereal working cycles again have to be divided into small incremental time steps. Despite optimized and simplified setupthis will lead to a very high number of incremental steps to be calculated.

Additionally plastic zones of incremental forming processes (the zone where the part is interacting with the tools) arevery small compared to the overall part size and need to have an appropriate mesh size resolution. Such plastic zonesare moving often through the part volume in a cyclic manner. Due to the fine mesh requirements an appropriatelyhigh number of elements is used.

In order to minimize the real process loads (forces, moments), often a high number of cycles combined with highprocess velocities (e.g. high rpm) are used. Especially for rotating parts this may cause problems. In such cases onehas to take care not to exceed a maximum displacement of an element edge per time step. Beside all other effectsmentioned before, this will determine the number of time steps to be calculated.

Thus simulations of incremental forming processes like ring rolling are very sophisticated. In order to get a stableand fast simulation with accurate results, please read carefully the following instructions and adjust all the describedparameters to your special application. Parameters in this tutorial are recommendations only.

"Standard forming process"

• large deformation zone ("contact area")

• shape formation by transforming the geometries of the dies into the part

• several operations (if necessary)

• large process loads (forces, moments, ...)

Incremental forming process

• small, moving deformation zone (small "contact areas")


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--> highly sensitive parameters

• large free surfaces

--> impact on convergence, geometry when remeshing

• stepwise forming by moving simple dies, numerous types of kinematics

--> input, display, calculation

--> many small time steps

1.1.1.2. Different types of rollers and their modelingBasic idea

In fact ring rolling devices consist of different types of rollers. First of all their model generation is introduced. After-wards one will find common control settings as well as complementary modules of a complete setup. The objectiveis to give the right understanding of the several setup modules and hence to individual ring rolling devices as well asenabling the user to model several rolling processes respectively.

Types of rollers

In this context, types of rollers means types of kinematics and not the different functions like e.g. king roller, axialroller, etc. In terms of different kinematics one knows:

• stationary and moving rollers:

referring to the displacement (translation) of the axis of the roller, not to rotational movements

• moving rollers:

• with defined movements (direction and velocity)

• self-controlled moving paths, especially controlled by:

• springs

• by given process control

• engine-driven and driven by friction (drag-rollers):

referring to rotational movements of rollers

• orientation and location of roller axis:

• ... identical to global coordinate axis

• ... parallel to global coordinate axis

• ... non-parallel to global coordinate axis

Of course all roller types can be combined in one project.

Modeling features for rollers

All previously mentioned types of rollers can be described by using the following features (for further details pleasego to Section 1.1.1.4). The extent of features needed depends on your process.

• Table Presses (insert: Press -> Manual -> Press Type "Tabular Motion (Translation & Rotation)")

In simufact.forming rigid dies move neither translationally nor rotationally unless one defines a motion by a Pressor special kinds of mounting are enabled using Die Inserts. While most of the predefined presses pretend a purelytranslational motion in global Z- direction (by defining velocities, strokes, energies), table presses offer a broader


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range of motions to be applied: one can determine simultaneous translational motions in all main directions andone driven rotation by using tabulated time-velocity, stroke-velocity and time-stroke dependencies with nearly anunlimited number of sampling points. Furthermore one can define a tabulated diameter-velocity function whereasthe diameter corresponds to the actual measured diameter of the ring determined by one of the Special Controlsmentioned below. Last but not least table presses enables to describe force-velocity dependencies. Please notethat this type of table press supports translational motion in global Z- direction only! Hence its application andcombination with other important ring rolling features is restricted. This table type is often used to characterizehydraulic presses for non-incremental bulk forming operations.

• Rotation Axes

If one wants to define an engine-driven rotation by using a table press, a Rotation Axis is needed to define the axisused for the rotation and the sense of rotation. Rotation axes can be either identical to or parallel to or non-parallelto the global coordinate system. Each rotation axis is coupled with the geometry of the die it belongs to per user'sdefinition and will move during the simulation along with the die translationally, but not rotationally.

Frictionally driven rotations do not need a rotation axis but will be defined using a global or local coordinate system.

• Die Inserts

In simufact.forming rigid dies move neither translationally nor rotationally unless one defines a motion by a pressor special kinds of mounting are enabled using Die Inserts. Mounting a rigid die is possible for each of the 3translational directions (along X-, Y-, Z- direction) as well as for each of the 3 rotatory directions (around X, Y, Z-axis) individually and enables for all those directions to determine whether the rigid die is freely moving, whetherthe motion is determined by a press or whether the movement is controlled by the force of a generic spring or whetherthe rigid die is stationary, i.e. not moving in selected directions. Freely moving dies will be moved (translational orrotatory) by contact with the workpiece and/or deformable tools. A typical application for such dies are drag-rollers(driven by friction). One can combine die inserts with presses or generic springs if applicable.

• Local Coordinate Systems

Clear definition of directions of both translation and rotation will be done by a coordinate system. Unless thereis no other definition present, this is stated to be the global, cartesian coordinate system. And this is valid for allbodies unless specified differently. This global coordinate system can be visualized by fading in "zero planes". Theorientation of the system is to be seen on its symbol down left in the graphics window. More flexibility especially fordefining several motion directions which are not parallel to the global system is given by local coordinate systems.In such one can define a coordinate system being valid for a given rigid die only. It can be used for easy setup oftable presses, die inserts or generic springs, if the direction of motion is not parallel to the global axes. Each localcoordinate system is coupled with geometry of the rigid die it belongs to per user's definition and will move duringthe simulation along with the die translationally, but not rotationally. Each geometry can own one local coordinatesystem only, whereas translation or rotation can be activated independently.

A table press can operate different dies with different local coordinate systems. For instance one can define inverselymoved dies in one table press. Another typical application are drag-rollers (driven by friction) with non-parallelcoordinate systems compared to the global one. Engine-driven rotations with non-parallel axis for dies without dieinsert need to have a rotation axis, for those with die inserts a local coordinate system. Rotation axes and localcoordinate systems are defined in the same sub-menu.

Local coordinate systems are valid for FE- simulations only. FV- simulations are not supported. Please run ringrolling simulations only with FE. All kinds of post-processing data refer to the global coordinate system. Localcoordinate systems are always cartesian ones and follow the right-hand-rule (notation conventions for vectors inthree directions).

• Springs

There are two different types of springs to define position-dependent forces on rigid tools in simufact.forming:

• Springs ("Die type" -> "Die spring"): acting translationally only in one global coordinate direction that can beselected. Deflection is limited in both directions (compression, release), spring definition orientated on applica-tion. The position of the spring-mounted die can be relative to a second one if applicable. Combinations with a


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die insert or a local coordinate system, and thus the flexibility resulting form this, are not supported. For instanceone cannot model a drag-roller (driven by friction) by using springs. As substitute one can assume frictionlessconditions without rotation.

• Generic springs ("Die type" -> "Generic spring"): acting in up to 3 translational and one rotatory direction in thelocal coordinate system. If there is no local coordinate system present or an existing one is not activated, genericsprings act per definition in the global one. Deflection of generic springs is unlimited in principle but genericsprings tend to reach the minimum absolute value of force. The definition of generic springs is mathematicallyorientated. The position of the die with a generic spring is always relative to its initial position. Generic springsneed to be combined with a die insert. Like this generic springs can e.g. be used to model drag-rollers.

Both types of springs are described separately in another chapter in more detail. Thus they will not be discussedhere any further. Possible applications of springs for ring rolling simulations can be a) to define a self-controlledmotion of measurement rollers for the Special Controls mentioned below, b) to approximate the rotational motionof rollers with unknown kinematics by using torsion springs (e.g. axial rollers) or c) to center a ring by using spring-loaded rollers. In such cases please note that two identical springs working in opposite direction do not effect anystabilizing or centering because the total sum of forces is equal to zero (forces compensate each other completely).

• Special Controls

Above mentioned modelling features define a die motion either by (fixed) given characteristics or tool motionresults from current contact conditions or resultant forces acting on the tools (process-controlled motion). However,both control mechanisms do not have any feedback-control-circuit (closed-loop-control) to the current process state,especially to the ring diameter. To integrate this closed-loop-control into a model (because real ring rolling processeswork that way), simufact.forming offers special controls for axial-radial ring rolling as well as for radial-profilerolling. Those kinds of controls have to be added to the model similar to a press (Press / Kinematics / RAW andMERW) - how to set up such closed-loop-controls is explained in the next paragraphs.

The usage of such special controls is an option for ring rolling simulations. If you have a chance topredefine all movements in a proper way, it is recommended to use your known kinematics. Especiallywhen starting to simulate ring rolling processes it is clearly recommended to simulate known processesnot using a special control first. This way material behavior, thermal effects and all other settings canbe checked, adapted and optimized. For this you can use recorded logger data from your machine inthe simulation using table presses. Later on you can start to implement advanced settings and controls.

Ring rolling processes have to be simulated in 3D. Hence, all subsequent informations, settings anddefinitions refer to 3D- modelling. There are many other rolling applications that can be simulatedmuch faster and much more effectively in 2D. For all special settings, particularities and peculiaritiesof 2D- simulations (i.e. mesh types) please refer to the related tutorials.

1.1.1.3. Special Controls

Typically the translational and rotational velocities of the dies are used to calculate the finite element solution. Butfor most incremental forming processes the velocities are usually not predefined for the whole process. Within thereal machine the current status –positions, dimensions and forces – is continuously measured and used to calculateupdated speeds and feeds using closed-loop control. For industrially relevant simulations of such processes the samecontrol loop must be implemented in the simulation. Simufact.kinematics, an optional model of simufact.forming,contains two such control-loops. To enable process control within each increment, the whole control algorithm wasintegrated into the finite element solver, including the required measurement of positions, dimensions, forces andother status quantities. This avoids the typical division of a finite element simulation in setting the velocities duringthe preprocessing, analysis in the postprocessing and repeated preprocessing to adjust the velocities. The result is afast and robust closed-loop process control. In the preprocessing you are using application-orientated higher-ordersettings, the rest is done by simufact.kinematics.


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Figure 1.2. Closed-Control-Loop of simufact.kinematics

Control-loops in simufact.kinematics do not comply with real device controls exactly but fulfill theneeds of the selected control type with a specially developed algorithm accordingly in a common sense.This algorithm is mostly based on a geometry only. Hence one will detect sometimes deviations to realkinematic behavior.

Simufact.kinematics contains different control approaches for all applications - like ring rolling - wherespecial kinematics are not known (because they are process-controlled) or preparation of known kine-matics is too costly - i.e. some open die forging applications - or predefinition with supported functionsis not possible (i.e. orbital forging).

1.1.1.3.1. Radial-Axial-Ring Rolling (RAW)

For Radial-Axial-Ring Rolling one defines typically the rotational speed of main rollers, the translational motion ofthe dragged mandrel and the axial motion of the axial rollers. The rotational speed of axial rollers and their radialmotion is often controlled by machine controllers internally. Additionally the ring will often be guided by one ortwo dragged centering rollers. Herewith position of ring centre can be stabilized and controlled displacement of ringcentre can be used to influence fill-up of profiled rings. Centering rollers move on a circular path whereas their currentpositions are based on current ring diameter - this is controlled by the machine. In simufact.forming those controlswill be done by simufact.kinematics "RAW".

In order to add an RAW-control, please select Insert (or "right-mouse-click" the inventory window) / Press / Kine-matics and then select RAW. Please press OK. Following dialog appears:


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Figure 1.3. Dialog for RAW-control

This dialog contains 5 areas:

• General settings for main rollers and determination of ring diameter

• Settings for the control of centering rollers

• Settings for the control of axial rollers

• Settings for the control of the mandrel

• Settings for the control of the remesh

All four control algorithms of the RAW - centering rollers, axial rollers, mandrel and mesh - can be activated/deacti-vated independently. After setting the parameters and closing this dialog, the RAW control will appear in the inventorywindow like a press object and can now assigned to the process. Typically centering rollers will be assigned to theRAW control within the process tree. If no centering rollers are used or if they are not controlled by RAW, the RAWcontrol can be used for the process without any die assigned to it - please compare the paragraph "diameter-tables"below.

Models containing an RAW control have to be oriented as shown in the dialog pictures thus: ring axisparallel to global Z-axis and all translational motions of mandrel in Y-direction must have a positiveorientation (increasing values). Otherwise simulation will not work and may abort with ambiguous errormessage.

General settings

Please assign herein the main roller. If required for the determination of the ring diameter, one can and has to specify

diameter of main roller. If the option is activated, the maximum roller diameter will be taken auto-matically from the roller geometry and used in the dialog-box. By defining an Start increment one can decide when


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RAW-control shall start. Before the RAW-control starts, all specified axial and center rollers will not be moved duringthe simulation in the controlled translations and rotations. But they are present for the simulation and all other settingsand specifications (i.e. dragged rotation) are active. Depending on the stability of initial contact situation it may makesense to start RAW-control or main roller rotation or both after a certain time delay compared to the start of mandrelfeed. This may support formation of stable initial contact areas.

is a help to specify the diameter automatically for one time only. If one is changingdiameter in the model after using this feature, the new value will not be taken over automatically. It hasto be done manually. Therefore it is clearly recommended to build up the complete geometrical modeland to define all object names before running RAW-dialog.

option always determines maximum diameter based on XY- dimensioning in the in-ventory window. If the assigned roller in the model (in the process tree) has been rotated around X- orY- xis, the feature does not work properly and should not be used.

In order to determine ring diameter including calculation of ring centre point one can select between two options,which shown in the next figure:

• Bonding Box (enveloping cuboid)

Bonding Box is called the smallest enveloping cuboid of a body having side faces parallel to global cartesiancoordinate system. The edge length in Y-direction of this enveloping cuboid around the ring will be used as currentring diameter during simulation. Use this very simple approach especially in case of centering rollers spanningwhole axial height of the ring, thus guiding the ring on its largest diameter accordingly. But you can freely definethe Z-dimensions of the bonding box and thus determine the ring diameter for a specific area only. This makessense in particular case of centering rollers having smaller axial height than the ring and shall guide a profiled ringonly in specific areas of its axial hight. For this specify Z min. and Z max. accordingly. If Z min. and Z max.are equal, for example the preset 0, the Z-dimension of the bonding box is unlimited and thus the complete axialhight of the ring is considered.

The Bonding Box method does not require any further consideration in the model setup.

Figure 1.4. Determining ring diameter for RAW-control

• Metering Roll

By using this approach ring diameter will be calculated from diameters of main roller and metering roll and fromtheir distance. In order to use this option one has to assign within the RAW dialog one die of the process tree tothe metering roll and to specify the diameters for both main roller and metering roll. Especially for profiled ringsaccurate selection of the related diameters is needed to gain an exact positioning of the centering rollers. This methodis very useful for profiled rings, if centering rollers shall touch the ring in a given height only or if improved andcloser guidance is needed when outer profile of the ring gets filled continuously. Measuring roller can be profiledas well. Compared to Bonding Boxes this method is more accurate in terms of measuring changing local diameters(local profile - also dependent on local profile fill-up), but it will consume more CPU- time.


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Metering rolls are defined as rigid dies that shall contact the ring at the defined position without affecting diametergrowth of the ring. Best way to do this is to use spring mounted bodies. If the metering roller rotates (draggedroller) a generic spring with suitable die insert has to be used. But in most cases the rotation of the metering rollis not needed and frictionless contact can be assumed. Then a die spring can be used. When defining the spring,please take into account that for profiled rings the outer local diameter does not grow necessarily all the time, itmight become smaller while rolling occasionally. Only once if fill-up of the profile has been reached, it will growcontinuously and can become larger than initial diameter. Normally, modelled initial position of metering roll is asmuch in -Y that even if the maximum ring diameter has been achieved, the metering roll can't reach this position.Die spring used for the measuring roller is in compressed condition with +Y given as direction of elongation. Themaximum elongation has to be defined in such a way that measuring roller can be moved to the smallest possiblediameter of the ring all the time. Within the first solver increment measuring roller will get contact with the ringand will after this move along with ring (diameter) by keeping contact.

Please define for generic springs as well as for die springs a spring force and spring stiffness with more moderatevalues in order to avoid any negative impact on the rolling process (metering roll shall not effect any deformationon the part). On the other hand please don't define values close to zero - this may cause numerical problems. Onlyin particular cases spring force should drop 100 N and stiffness 1 N/mm. Please set heat exchange to workpiece tozero. There is no need to define a local rotation axis or local coordinate system unless measuring roller is definedas drag-roller.

Please make sure that the diameter of the metering roll is large enough compared to the ring diameter.In simufact.forming contact between workpiece and die is calculated based on element nodes of theworkpiece and the die faces not considering the element faces of the workpiece - hence small diametersof the metering roll lead to fluctuating ring diameters measured (comparable to a gear wheel). Thiswill cause an instable calculation. Following figure shows such unsuitable conditions - there is nopenetration present but improper combination of geometries and mesh-sizes.

Normally there is no need that the metering roll rotates. If the metering roll does not rotate, there isno need to use a circular round one. In such a case one can use also flat, square or similar designs.This will lead to stable contact conditions and accurate diameters measured if the ring moves in X-direction. If using non-circular round designs please define in the RAW dialog the Y-dimensioningof the measuring tool instead of a diameter.

Figure 1.5. Too small measuring roller

If applicable one can measure ring diameter and ring centre point also by using two metering rollspositioned opposite to each other. One may place the second metering roll at the same side like mainroller (rigid tools are allowed to penetrate each other). Within the RAW-dialog please select thissecond die as main roller and specify its diameter as main roller diameter accordingly. The "real" mainroller does not have any other meaning for the RAW-control than determining the diameter. This isnot valid for MERW-control where the main roller will be fed by the control-algorithm.

Control of centering rollers

The RAW-control permits up to two centering rollers and can position them corresponding to the current ring diameterin such that they are touching the ring very precise and herewith centering and stabilizing the ring. This can be done


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by using an offset value if applicable. This kind of control is purely geometrical based. For positioning purposes ofcentering rollers it is assumed that their center points are moving on an arc which is given by a radius and a centerpoint (please see figure below). Within the RAW-dialog one activates centering rollers and defines their diameter.

For this, one can tick on optionally. Please describe the arcs by specifying Length and Height ofcenter point and Radius of the arc. Please note that length and height are related to signs (+/-) and herewith theirpositions in +X and -X will be defined. This must correlate to their positions into the model. Centering rollers can't be

positioned by penetrating the ring during the simulation. While animating the kinematics ( ) centering rollers willfollow the predefined arc. Center points and radiuses will be shown as a spoke. Heights of centering points have to bealways +X or -X but never equal to zero. If necessary please specify a very small height.

Figure 1.6. Specifying centering rollers for Radial-Axial-Ring Rolling

By using an offset, one can regulate how close the ring shall be guided. The offset value will be added to the currentring diameter by taking into account the sign before the new position of centering rollers will calculated. Positive signslead to a more loose guidance. By defining a negative offset for one centering roller and a positive one for the oppositeone it is possible to shift the centre point of the ring and hence influencing profile fill-up.

Activate in order to position the centering roll like the RAW-control would do in the beginning of asimulation. Positioning within the model visualizes all the parameters selected and makes sure that centering rollersare positioned properly at the right side of the ring. Having centering rollers in their initial position before simulationstarts may stabilize the initial contact formation (especially if one has defined a start increment - time delay - for theRAW-control or for the rotation of the main roller using a suitable table press). In other situations it may be betternot to start with positioned centering rollers.


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is supporting the setup one time only. Subsequent changes on inputs or model will notbe updated automatically. This has to be done manually. It is clearly recommended to build up the model

first and define RAW-control afterwards. works only when RAW was assigned to aprocess already.

By using Switch force threshold one can switch-off position control of the related centering roll if the absolute forcein global X-direction exceeds the given maximum value. Once position-control was switched-off it can't be activatedagain even if the force drops below the limit. Once the position control has been switched-off, the force in globalX-direction on the particular centering roll will be maintained at the specified force. At the same time translationalmovements remain possible in global X-direction only. Movement and position of the particular centering roll resultfrom this. If you switch both centering rolls from position control to a constant force, please consider that oppositeforces on the ring neutralize each other and do not have any centering or stabilising effect.

Centering rollers need to have a rotation axis. Its position will determine the centre of the roller used by the RAW-control. Centering rollers can be either free driven drag-rollers or assumed to be frictionless. If being a drag roller(with rotation) all degrees of freedom need to be fixed in the die insert. Only rotation around Z-axis is to be allowed.Centering rollers are not allowed to have a (activated) local coordinate system - hence free rotation is possible aroundaxes parallel to the global Z-axis only.

If simulation aborts after the very first increments this might be caused by unsuitable settings of centeringroller control. In such cases one can find error messages like "iterative penetration checking" within thelog-file. To check this, one may shift centering rollers to +Z-axis as long as the rollers do not touch thering anymore. Doing this enables one to check by postprocessing first increments whether the positioningwas carried out properly. In order to get a fast responses please specify output divisions with a largenumber (compare the forming control dialog).

Control of the axial rollers

Up to two axial rollers can be controlled either translational or rotatory (or even in mixed condition) independently.Please assign the die to the axial rollers and activate Mill stand position and/or Rotation roll as required.

Mill stand position shifts the related axial roller translational in global Y-direction depending on the displacement ofring centre point. If the (missing) top of the axial roller is positioned on the axis of the ring, compare the followingfigure, the tangential velocity of the axial roller slows down linear in the same extent as the tangential velocity of thering. This makes it much easier to define rotation speed for the axial roller and enables a slip less dragged rotation.Using "automatic with positioning" the particular axial roll will be moved in the first calculation increment (or in thespecified start increment) such that this condition is fulfilled. The movement is done with complete contact and frictioncalculation, thus it can be very instable when bigger distances are used. Using"automatic without positioning" thispositioning of the axial roll in the first calculation increment is omitted and the shift of the axial roll depending onthe movement of the ring centre starts once the condition for the position of the (missing) top of the axial roll hasbeen fulfilled by the ring growth.

Because rigid bodies are allowed to penetrate each other there is no need to do collision checks with mandrel or otherbodies. For stability reasons the axial rolls are only shifted in -Y-direction and do not follow an interim reduction ofthe ring diameter or temporary shift of the ring center to the main roller.

Rotation roll controls the number of revolutions of axial rollers depending on the tangential velocity of the ring basedon its outer diameter with contact to the axial roller. To do so, axial rollers need to have an axis of rotation which isproperly oriented with respect to the sense of rotation. They are not allowed to have die inserts and local coordinatesystems. One can combine RAW-control for rotation with a table press for translational motions.


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Figure 1.7. Axial roller for RAW-control

Control of the mandrel

Normally the translational movement of the mandrel in the model will be predefined using a table press. But in realitythe feed of the mandrel is frequently determined or limited by the maximum force on the mandrel. To model thisbehaviour in the simulation, activate the control of the mandrel in the RAW dialog, select the die used as mandrel andspecify the switch force threshold. With this the mandrel is initially moved in global Y-direction as defined in themodel. Once the specified switch force (absolute value) is reached for the first time, a one time switch is done and theforce on the mandrel will be maintained at this constant value. Movement and position of the mandrel will then resultform this. It will never be switched back to the movement defined in the model. The process ends once the processtime specified in the table presses or in the forming control is reached. The complete stroke of the mandrel will thengenerally not match the target of the table press, but it will be bigger or smaller.

Control of the remeshing

To mesh the ring a special ringmesher is provided (please compare Section 1.1.1.5). It enables to use different meshsizes in tangential (rolling) direction for a "critical part" and for the rest of the ring, with the position and size of acritical part defined by the user. This enables to mesh the radial rolling gap with a finer mesh than the rest of the ring.This is especially use full if considerably more forming is done in the radial rolling gap than in the axial rolling gap("axial corrective stretching"). This will support the reduction of overall number of elements and will shorten CPUtime consumption.

The RAW-control can be used to start remeshing if the predefined zone with finer mesh size has nearly passed theradial roll gap (see next figure). When activating this feature please specify the sense of rotation of the ring basedon the definition inside the RAW-dialog. Positioning and dimensioning of the critical part of the initial mesh need tobe done by your self matching this setting. Taking over the initial mesh settings for the remeshing, the critical partwill be located properly after every remeshing operation. RAW-controlled remeshing acts additionally to the standardsettings of the remeshing object and becomes active only if the predefined zone has nearly passed completely theradial roll gap. Independent on RAW-controlled remeshing it may happen, that reaching any other remeshing triggercriterion a remeshing starts even if the predefined zone has not yet reached its "remeshing position".


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Figure 1.8. Remeshing based on RAW-control (Overview)

In any case there are three things should be attended to:

1. The selected critical part with the finer mesh should be large enough to avoid too much time-costly remeshingoperations. If its too small, additional time needed for remeshing operations may over-compensate time savingsobtained by reducing number of elements. To get an optimum approach for a model one can check within theLOG-file, when and why remeshing took place. If remeshing operations are carried out based on other remeshingcriteria or if so called "forced remeshing" occurs before the specified zone of the ring has passed the radial roll gap,RAW-control does not have any influence. Regarding forced remeshing more details can be found at: separationin Section 1.1.1.5 (see below).

2. Do not specify tangential element size in the rest of the ring too large. It may cause problems to calculate contactconditions to the different rollers used (axial rollers, centering rollers, metering roll) properly. Please comparerelated topic to Figure 1.5 above.

3. For every remeshing operation with different tangential mesh sizes, state variables need to be transformed from finerto coarser elements. In principle this will lead to inaccuracies and averaging. But this influence is quite marginal forstable simulations and tangential results that are distributed uniformly. Additionally minimal interpolation errorsmay occur when mapping state variables from an old to a new mesh. Normally this influence can be neglected too.Nevertheless one should check calculated force distribution for the presence of discontinuities after remeshing ifapplicable. Micro-structural related state variables may react sensible on interpolation errors caused by frequentrepeating remeshing operations, too.

Diameter-tables

As soon as RAW-control is activated in the model, the current ring diameter can be used to control translational androtational velocities of rigid tools. This is also valid if non of the four control-algorithms mentioned before are used.Differing to the standard rule that the moving tools have to be assigned to the presses, in this case the RAW-controlcan be assigned to the process without specifying a tool belonging to it.

To make use of this feature one has to define a table press (Insert or right-mouse-click the inventory-window / Press/ Manual ... / Press-Type "Tabular Motion (Translation & Rotation)") and select Table type "Diameter/Velocity" todefine a diameter-dependent velocity. Please make sure, that an ascending order of the diameter values is specifiedherein. Doing so, the defined table press can be used like any other table press in the model. It can be combined withdie inserts and/or generic springs, too, to enable highest possible flexibility.

1.1.1.3.2. Radial-Profile-Rolling (MERW)

Specific radial-profile-rolling processes can be subdivided into the three phases inner profile fill-up, outer profile fill-up and calibration as shown in the figure below. Often radial infeed-velocity is controlled depending on which ofthe three phases is currently present. The transition between the phases are determined by specific outer ring diam-eters. Following description of such MERW-controlled radial-profile-rolling assumes a machine with locally fixedmandrel and translational as well as rotational driven main roller. The model may optionally contain a centeringroller that moves on an arc like shown above for RAW-control. In simufact.forming the "MERW" feature of thesimufact.kinematics module will realise that. It's named by the machine type used to develop the control.


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Figure 1.9. Process phases and infeed control for radial-profile-rolling

Basic idea of MERW is a linear slow down of radial infeed-velocity of the main roller, starting at initially smallouter ring diameter and ending at a larger ring switch diameter. Initially outer ring diameter may decrease caused bybeginning of profile fill-up. While the current outer ring diameter is smaller than at the beginning of the process, initialinfeed-velocity is active (phase 1). As soon as ring diameter starts to increase, infeed velocity will slowed down linearly(phase 2). When reaching the predefined switch diameter, infeed velocity will slowed down to the smaller calibrationvelocity (phase 3). This process runs until desired final outer diameter has reached. Afterwards some revolutionswithout any infeed motion will occur. Following figure shows the dependencies of MERW-control described herein.

Figure 1.10. Radial infeed-velocity of MERW-controlled main roller


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Determination of current outer ring diameter and of ring centre point is always made by a metering roller. The currentring diameter is calculated by using the initial ring diameter and the displacements of metering and main roller inY-direction. Hence diameter of both metering and main roller will not be considered. With increasing profile fill-up the contact point (or area) between ring and main roller might change. Hence, current diameter calculated mayslightly deviate from the real one. This can be observed on real machines which are working with the same measuringprinciple, too. With increasing fill-up, measured ring diameters tend to be smaller than the real ones. Hence guidanceprovided by centering rollers becomes closer while rolling. Rolled rings may become slightly larger as given by theMERW-controller. By adapting initial ring diameter one can compensate this if required. Guidance of centering rollerscan be influenced by an offset additionally.

In order to set up MERW-control please select Insert (or right-mouse-click the inventory- window) / Press / Kine-matics. Select MERW from the list and press OK. Following dialog appears:

Figure 1.11. MERW-control dialog

Models containing MERW-control have to be oriented like shown in the dialog pictures, thus: ring axisparallel to global Z-axis, all motions of main roller in Y-direction and centering point of the mandrelhas to be equal to X=0 and Y=0. Otherwise simulation will not work and may abort with ambiguouserror messages.

By defining a Start increment one can decide when MERW-control of the centering roller shall start. Before that in-crement has reached during the simulation, centering rollers will hold its position defined in the model. After reachingthe specified increment centering roller will be positioned by MERW-control. This time delay may support stabilizingof the process until a definite, robust and proper contact situation between ring, main roller and mandrel has reachedand ring has started to rotate. Infeed-motion and rotation of the main roller will be started always at the beginningof the solver run.

Radial infeed of the main roller can be specified by defining Start velocity of roll, End velocity of roll and Calibra-tion velocity. Direction of main roll determines its infeed direction. Positive means motion in global +Y and negativein global -Y- direction. Nr. Rotations specifies the number of revolutions after calibration cycle without any infeed


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motion. Max. press time determines the end of the process (time limit): the process stops, even if the desired finalring diameter including the specified number of roll-out rotations has not yet been reached. On one hand it makessense from technological point of view to limit rolling time. It enables to use known values from shop-floor and toomuch cooling of the ring will prevented. On the other hand it is a safety-setting to avoid endless simulation loops incase the desired ring diameter cannot be reached under the conditions selected. Percentage-value of the simulationprogress relates always to this time limit. Simulation succeeds (exit 3004) if either the final diameter (after absolvingthe given numbers of roll-out rotations after calibration) or if the maximum time limit has reached. This means thatreaching the time limit is not an error in the sense of the simulation. Please input a constant Rotation speed for themain roller. Sense of rotation is given by definition of the axis of rotation in the model.

Specify Initial outer diameter of the workpiece, Switch diameter of the workpiece and Final outer diameter of the

workpiece to complete the settings for the control of Figure 1.10 (above). By activating this option: maximum diameter will be determined automatically from the model and will be used in the dialog.

The MERW-control allows an optional centering roller and can position it corresponding to the current ring diameterin such that it is touching the ring very precise and herewith centering and stabilizing the ring. This might be doneby using an offset value if applicable. This kind of control is purely geometrical based. For positioning purposes ofcentering roller it is assumed, that the centering point is moving on an arc, which is given by a radius and a centeringpoint (please see MERW-dialog figure above). Within the MERW-dialog one activates centering roller and defines

its diameter. For this one can tick on optionally. Please describe the arc by specifying Length andHeight of center point and Radius of the arc. Please note that length and height are related to signs (+/-) and herewiththeir positions in +X and -X will be defined. This must correlate to their positions into the model. Centering roller can't

be positioned by penetrating the ring during the simulation. While animating the kinematics ( ) centering roller willfollow the predefined orbital path: Centering point and radius will be shown as a spoke.

is a help to specify the diameter automatically for one time only. If one is changingdiameter in the model after using this feature, the new value will not be taken over automatically. It hasto be done manually. Therefore it is clearly recommended to build up the complete geometrical modeland to define all object names before running MERW-dialog.

option always determines maximum diameter based on XY- dimensioning in the in-ventory-window. If the assigned roller in the model (in the process tree) has been rotated around X- orY-axis the feature does not work properly and should not be used.

Please specify the names of Main roll, Metering roll and Centering roll in the lower part of the dialog. AssignMERW-control to a process and afterwards main roller to MERW-control. The metering roll has to be a rigid body andto be positioned in the model in such, that it is contacting the ring at a desired location without influencing ring growth.For this it is recommended to use a spring loaded body. Shall the metering roller be dragged (by friction) please use aGeneric Spring with proper die insert. But mostly there is no need for rotating this roller, hence frictionless contactcan be assumed. In that case you can use a Die spring. As the current ring diameter will be determined base on thecurrent displacement of the metering roll relative to its initial position, it is necessary to have contact between ringand roller as a starting condition. Thus the "Die spring" die is in released condition with same direction of motion asmain roller (+Y or -Y). The maximum elongation has to be defined in such that it allows measuring roller to be shiftedto the maximum possible ring diameter. Please note that typically such "Die spring" dies are not able to keep stablecontact in the early beginning of the process, characterized by decreasing diameters of profiled rings. The diametermeasured in that phase tends to be slightly too large but it is always smaller than the initial one. It does not play anyrole for infeed-velocity control cause it will start only then if the diameter measured is larger than initial one. But theguidance of the ring by centering roller might be less closer than normal.

Please define for Generic springs as well as for Die springs spring force and spring stiffness with more moderate valuesin order to avoid any negative impact on the rolling process (metering roll shall not effect any deformation on the part).On the other hand please don't define values close to zero - this may cause numerical problems. Only in particularcases spring force should drop 100 N and stiffness 1 N/mm. Please set heat exchange to workpiece equal to zero. Thereis no need to define a local rotation axis or local coordinate system unless measuring roller is defined as drag-roller.

Please make sure that the diameter of the metering roll is large enough compared to the ring diameter.In simufact.forming contact between workpiece and die is calculated based on element nodes of the


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workpiece and the die faces not considering the element faces of the workpiece - hence small diametersof the metering rolls lead to fluctuating ring diameters measured (compare to a gear wheel). This willcause an instable calculation. Figure Figure 1.5 shows such unsuitable conditions - there is no penetrationpresent but improper combination of geometries and mesh-sizes.

Normally there is no need that the metering roll rotates. If the metering roll does not rotate, there is noneed to use a circular round one. In such a case one can use also flat, square or similar designs. This willlead to stable contact conditions and accurate diameters measured if the ring moves in X-direction. Ifusing non-circular round designs please define in the RAW dialog the Y-dimensioning of the measuringtool instead of a diameter.

1.1.1.4. Detailed explanation of the needed features

Following informations refer to and shall give a more detailed insight on this topic, except for springs and specialcontrols. Springs will be described in another chapter of this tutorial. Special controls have been described abovealready.

1.1.1.4.1. Table press

To add a table press please select Insert (or right-mouse-click the inventory- window) / Press / Manual ... and selectfrom Press type menu "Tabular Motion (Translation & Rotation)". Following dialog appears (see next figure). Afterconfirming your setting by clicking OK, a new press symbol appears in your inventory window. One can assign nowthe press to the related process as well as the related tools (one or more) to the press. It is possible to assign more thanone press to a process and to combine it with RAW- or MERW-control if required. Even combination of table presseswith another press type in one process is possible. In some cases this may lead to constraints for the table press, thusyou need to check on this in you particular case. Normally the combination of table presses with other press types isnot relevant for ring rolling applications. Like many other objects table presses can be stored within simufact.formingdatabase and be used for other projects as well.

Figure 1.12. Table press dialog

First of all please select Table type. Names of the selectable types stand for their special dependencies included(y=f(x)) and are valid for all three possible translations as well as the rotation. Possible dependencies are: time-velocity,


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stroke-velocity or time-stroke and above mentioned diameter- velocity. Table presses enable force-velocity functionstoo. This type of table press supports translational motion in global Z-direction only. (Combination with typical ringrolling features is restricted. It is widely used for hydraulic presses (for non-incremental processes)). Please selectUnits for the given table columns according to the table type and all other requirements. For time-stroke dependenciesplease specify any rotation as cumulated angle - multiple values of 360° are possible and make sense. Stroke of a dieis always relative to its initial position in the model.

Fill in related values line-by-line and confirm after each line by clicking Add. Repeat whenever needful. By clickingModify or Delete one may correct input values or change table properties accordingly. Values of the first columncan't be change. One have to delete complete line and add corrected one. But one can also change all Values in the line- even in first row - and afterwards add this line before deleting the old line. Every line has to be completed, so everycolumn has to be filled. It is not possible to use different times or strokes in the first column for separate directions.If required you have to prepare your data accordingly.

One can import table values also from csv-files. csv-files must use commas as separator between columns and point-sign as decimal separator. Every csv-file contains 5 columns and as many lines as needed according to the table format.It is not allowed to contain headers, only values are permitted. To read in a csv-file please click Read and selectrelated file from browser. Check the table type and the units after the import! This information is not included in thecsv-file. The import of a csv-file always deletes al existing table data. Importing of table values is a very comfortableoption especially when importing a large number of lines (i.e. machine data-logger to simulate an existing process tocalibrate simulation settings and parameters). By clicking Write you can export defined tables back to a csv-file.

When setting up complex kinematics for different directions you may ask what kind of table press shouldbe used. Simufact.forming processes all types of table presses properly. For internal use all definedtables will be converted lossless. For all dies without die insert a time-velocity dependency will beused internally, for those with die inserts a time-stroke dependency accordingly. (This does not applyto diameter and force dependent table functions). Thus you may be able to save some back and forwardcalculation.

All table presses used in a process need to have the same overall process time. By definition this time describes thesimulated time of the process. One can reduce this time by changing it inside the forming control under stroke (asusually default setting "0" does not mean zero but the time is determined by the table press(es)). Special controls aswell as abort criteria may shorten this time too.

Table presses are independent from the predefined step control used inside the forming control. Especially all giventimes, strokes and velocities (sample points) do not interact with calculation of time increments of the solver run.Hence they may not be meet exactly (i.e. one defines a sample point at 1 s process time but the solver uses internallytime increments at 0.99 s and 1.01 s). The smaller the step size, i.e. the more time increments are used, the smaller apossible deviation. For ring rolling applications normally a large number of time increments will be used, hence thisis usually not an issue. Tables with a large number of sample points for a steady kinematic function in principle leadto very small deviations and in most cases the exact compliance of each value is not needed.

Usually table presses will be combined with fixed number of time steps. Following this logic one may ensure exactmatch between given and used sample points: For the initial time of each calculation increment the current velocityof the die will be determined from the table - if required by linear interpolation between to sample points. Duringduration of a running increment this velocity is kept constant. By synchronizing the given times in the table (whereapplicable indirectly based on the stroke) with step control it is possible to get identical points. In a "theoretical" tablehence the given moments of time are multiples of the time step. But in the "practical" table used in simufact.formingtime sample points should be shifted about 10% of the time step to early times while keeping all other values constant(time = theoretical time - 0.1 x time step). This ensures that a the begin of each calculation increment the table valuesfor the new increment are used.

1.1.1.4.2. Rotation axes and local coordinate systems

Rotation axes and local coordinate systems define translational as well as rotational directions in which table presses,die inserts (see next paragraph) and generic springs affect rigid dies. Following dependencies exist:

• rigid dies without die insert and with table press


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• Translation

• parallel to global coordinate system: no local coordinate system necessary

• non-parallel to global coordinate system: can be transformed by superimposing translations within global co-ordinate system -> must have for Finite Volume, for FE problems is better to use local coordinate system anddie insert

• axis of rotation without any influence

• Rotation

• only driven rotation possible, always with axis of rotation, no local coordinate system necessary, sense ofrotation is given by direction of axis of rotation

• rigid tools with die insert

• Translation

• parallel to global coordination system: neither axis of rotation nor local coordinate systems necessary

• non-parallel to global coordinate system: local coordinate system should be used, for table presses as wellas for generic springs - but not for die inserts - transformation by superimposing translations within globalcoordinate system possible too, must have for Finite Volume (only table presses, no generic springs)

• axis of rotation without any influence

• Rotation

• driven (by table press or by generic spring) or dragged around global coordinate axis: neither axis of rotationnor local coordinate system necessary, sense of rotation is positive (mathematically) around global coordinateaxis, please adjust signs of table press or springs if applicable

• driven or dragged around axis parallel to global coordinate system: axis of rotation is sufficient (origin of the3 possible axes parallel to the 3 global coordinate axes is the initial point of defined axis of rotation), localcoordinate system possible, sense of rotation is positive (mathematically) around selected coordinate axis,please adjust signs of table press or springs if applicable

• driven or dragged around non-parallel axis: local coordinate system necessary, sense of rotation is positive(mathematically) around local coordinate axis, please adjust signs of table press or springs if applicable

Axis of rotation and local coordinate system are geometry related properties but not die related ones. They can bedefined within the same dialog. To call this dialog please select within inventory or process window a geometry, right-mouse-click, and select Rotation axis / local System .... Following dialog appears:


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Figure 1.13. Dialog for axis of rotation and local coordinate system

By activating one can define axis of rotation by three mouse clicks and local coordinate system by afourth one. All mouse-clicks will be assigned to the corner points of the selected stl- facets of the geometry. Firstthree clicks form a circle. Axis of rotation will go through the centre point of the circle described and will be orientedorthogonally to it. Length of axis will be chosen automatically so that it will exceed boundaries of the geometry onboth sides. Typically one places mouse-clicks on peripheral curves of either a cylinders front face, a cones bottomface or similar suitable surfaces of the geometry selected. Fourth mouse-click defines the X-direction of the localcoordinate system. Z-direction corresponds to axis of rotation and origin to the initial point of axis of rotation. Positionsof selected points will be shown as numbered ones in ascending order. By using < and > one may select, which pointwill be set with next mouse-click, hence a click can be repeated and the old point will be overwritten.

If is not activated, one may define coordinates of initial and end point of axis of rotation manually aswell as local coordinate system. Origin of the local coordinate systems should always be the initial point of axis ofrotation. Orientation of this local coordinate system (X-, Y- and Z-axis) will be given by three vectors starting in the

origin. These vectors need to be cartesian ones and must follow right-hand-rule. Inactive enables oneto correct all values created by mouse-clicks afterwards, i.e. to assign them to their exact position. Adjust length canbe used to define length of axis of rotation in such that it exceeds both sides of the selected geometry a little bit.

(upper left corner) turns the direction of the axis of rotation (and herewith sense of rotation) as well as Z-direction

of the local coordinate system. (upper left corner) deletes both axis of rotation and local coordinate system.

After defining local coordinate system one has to activate or deactivate use for Translation and/or use for Rotation.Use for rotation is activated by default but not use for Translation. Hence one can describe translation and rotationindependently in global or local coordinate systems. But please note, it is not possible to use different local coordinatesystems for translation and rotation.

After definition of axis of rotation and/or local coordinate system has been finished, the symbol for the geometry

selected gets changed within inventory- and process-window from to . Please select button from "Dis-


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play"-toolbar to visualize defined axis of rotation (will be shown as black arrows with red arrowhead). again can beused to make the local coordinate system visible inside the model-window by a black arrow with yellow arrowhead. Ifthe local coordinate system is not activated for both rotation and translation one can see inside the model-window twodifferent coordinate systems which are slightly shifted to each other and will have different orientations. Visualizationof local coordinate systems will determined by the die insert. Freely moving systems are to be seen as drawn lineswith arrowheads, other motions by broken lines without arrowhead.

Because axis of rotation and local coordinate systems are properties assigned to a geometry, each geometry can beused within a project with consistent axis of rotation and local coordinate systems only. If necessary one has to importor create a geometry several times if different approaches regarding axis of rotation or local coordinate systems shallbe used.

For the same reason axis of rotation and local coordinate systems will shifted along with the geometry if this ismoved by translation or rotation during the model setup. Hence definition may differ dependent on where the selectedgeometry is located - either in the process- or in the inventory-window. One may take advantage of this by selectingthat geometry (either within process- or inventory-window) which is more suitable positioned for planned definitionof axis of rotation and local coordinate system. This is recommended especially if one wants to input the related valuesmanually.

All orientation statements during postprocessing always relate to global coordinate system. Local defi-nitions will not considered.

1.1.1.4.3. Die Inserts

In previous chapters and paragraphs the terms dies with or without die insert have been used. Die inserts define specialmountings of a rigid die. With them one can define individual motions in each of the three translational as well as foreach of the three rotational degrees of freedom (DoFs) of rigid dies. Possible definitions are:

• Fixed, hence no motion in the defined direction is allowed,

• Press, hence determination of a motion by a press which is assigned to the same rigid die,

• Generic spring, hence determination of a motion by the reaction force of the generic spring which is assigned tothe same rigid die (note: Finite Volume does not support generic springs).

• free motion, hence a motion which is determined by forces affecting the rigid tool in given direction. By definitiona free motion is given if neither Fixed, nor Press nor Generic spring are selected for a direction.

To add a die insert please select Insert (or right-mouse-click the inventory-window) / Die type / Die insert / Manual ...The following dialog appears wherein above mentioned motions can be defined. Please note that not all combinationsare possible. One may observe that activating one option may deactivate another one. Before pressing OK pleasecheck all settings finally. For all Finite Volume applications (not to be used for ring rolling) one has to specify themass of die. For all Finite Element simulations this setting will not be taken into account.


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Figure 1.14. Die Insert dialog

Die inserts are marked in the inventory and in the process window with the symbol . They are assigned to rigid dieson their own or in combination with generic springs or presses. If a local coordinate system is activated, the directionsrefer to it. If not they refer to the global coordinate system.

Reminder:

In simufact.forming rigid dies will neither move translational nor rotatory unless there is assigned pressmotion and/or "die insert" definition. There is no need for "die insert"-definition if either the die hasbeen fixed in all directions or it moves by given press-definition in one direction and all other directionsare fixed.

Hence this definition is necessary for special combinations of motions only. Generic springs alwayshave to be combined with such "die insert" definitions.

Technical background for former users of simufact.formingGP:

By assigning a "die insert"-definition to a tool it becomes a load controlled body. All other rigid toolswill be treated as velocity or spring controlled bodies internally.

1.1.1.5. Further elements of modelling

Only kinematic settings of ring rolling applications were discussed so far. In addition to this important issue one hasto know further aspects of modelling and simulating ring rolling that shall be described now. All informations referto Finite Element (FE) simulations (FV is not used for ring rolling). Please select only FE when defining the processand related properties (Process Definition / Solver).

1.1.1.5.1. Meshing

Simufact.forming offers a powerful and specifically developed mesher for ring rolling, the Ringmesher. It is clearlyrecommended to use only this mesher for both initial meshing and remeshing operations defined within the remeshobject. Ringmesher creates a consistent hexahedron mesh which is oriented to the ring in axial, radial and tangentialdirection accordingly. It enables to create high quality meshes with the most accurate element type for such kind ofprocesses - the hexahedron element - whereas the number of elements used is less compared to other types of elements


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and hence the calculation time is reasonable with respect to the complexity of the process. Tetrahedrons should notbe used for ring rolling.

Next picture shows the principle of the ringmesher: First of all a cross section is meshed with Quad-elements (2D) -subsequently rotated by 360° to get a 3D- mesh out of hexahedron elements. Finally cross sections will be adapted tothe shape and roundness of the ring accordingly without changing element structure.

Figure 1.16 compares obtained results of meshing a simple rectangular ring between standard mesher (overlay-hex)and ringmesher. Uniformity of the ringmesher can be seen.

Figure 1.15. Functional principle of Ringmesher

Figure 1.16. Comparison of hexahedral meshes createdby Overlay HexMesher (left) and RingMesher (right)

Ringmesher works completely different to Overlay-Hex-mesher with cylindrical basic coordinate sys-tem and should not be confused. Both are using axial, radial and tangential orientations of the mesh butstarting mesh creation and further meshing principle is completely different (overlay-hex creates firstof all mesh-core which is then projected onto surface of geometry to be meshed). This is well suitedfor nearly round structures, round structures with radial holes or material accumulation. Ringmesherenables to create better, high-quality meshes for rings and much more flexibility in terms of ring axis.


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As well ringmesher shall not be confused with "overlay-hex-mesher with template". This kind of ringtemplate is the precursor of the ringmesher, uses an other projection and adaption of the base mesh tothe geometry and is provided only for compatibility to old models. It is not supported anymore. To getoptimal results again use the ringmesher.

To create an initial mesh (double-click or right-mouse-click followed by Show / Create Mesh ... on the meshing-sym-

bol assigned to the workpiece or ) and select first of all Ringmesh as Mesher (given by default when using theprocess type ring rolling). The initial 2D-mesh of the cross section can be checked by pressing Preview before onestarts with 3D mesh creation. This option enables quick check whether the used settings create a suitable mesh interms of shape quality (ring profile) and number of elements. Advanced enables to do additional settings as follows:

• General

Given element sizes in axial, radial and tangential directions determine how many elements one will create. Asknown this has a huge influence on CPU-time will consumed later on. For tangential direction element size canbe different for "critical" and "uncritical" parts (deformation zone). Please compare "Control of the remeshing" inSection 1.1.1.3.1. Maximum allowed ratio of tangential element size to radial/axial element size is allowed to exceedfactor 1.3. Related warning messages when start the simulation can be ignored. Edge angle determines the minimumangle which has to be there to detect an edge and to consider it during meshing. For ring rolling applications largevalues (80°) are recommended to make sure that only (real) rotary edges (circumference) will detected.

• Rotation

Ring centre point is recommended to be determined automatically, cause it will change while rolling. Please checkproper orientation of ring axis (X, Y, Z). On demand size and position of "critical" part and its deviating elementsize can be defined herein.

• Quality

Maximum refinement level and outline quality affect only the cross sectional 2D-mesh not its 3D-rotation andadaptation of roundness and profile/shape of the ring. Maximum refinement level defines how often radial and axialelement size are allowed to be halved to get an exact cross section of the ring. Outline quality is an abstract teststatistic - default is 0,0001. This should be changed by decimal powers on demand. For suitable combination withmaximum refinement level smaller values will lead to improved mapping of ring contour. To check impact of thesesettings one can use above mentioned preview feature.

• Refinement box

Refinement boxes affect only the cross sectional 2D-mesh not its 3D-rotation and adaptation of roundness andprofile/shape of the ring, too. Dimensioning of the box in axial (U) and radial (V) direction will be defined withincross sectional plane relative to - automatically determined - centre point of the ring. Usage of such boxes is limiteddue to changing diameters of the ring. It can be used to define it for outer diameters of profiled rings to get moreaccurate results.

Initial Meshing starts by clicking - after the meshing process is ready - OK - mesh will transferred to the model.Thereby a remesh object with the selected settings will created and assigned to the workpiece. It is labelled within

inventory- and process-window as: - all settings can be found at Advanced. Remeshing criteria can be differ fromthose of the initial meshing i.e. to start with coarser mesh for the first increments and to become finer if needed atthe end of simulation. The remesh object contains also information when remeshing shall start. By default it starts ifstrain change exceeds 0.4. One may input higher values due to the uniform deformation process, i.e. 0.6. There areother criteria available but normally not used.

Changed settings of the remesh object will not be overwritten necessarily when creating a new initialmesh and assigning this to the workpiece. All settings, even refinement boxes, meshing and remeshingcriteria will be overwritten not before one has answered Yes to the question: "Do you wish to use theinitial mesh parameters for remeshing?". Be careful when answering this question: Yes will overwriteall settings of the remesh object, including the remesh criteria. In doubt select No and check and adaptthe remesh object manually.


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If CAD-data of the final ring geometry or intermediate stages are available it may make sense to loadthis data also and to mesh them in a dummy process. It enables to check mesh settings for this geometriesin terms of number of elements used as well as proper shape mapping, especially for profiled rings.

Tubular rings with locally nearly constant wall thickness (which can change with time) can be meshedalso effectively by using the sheet mesher. For thinner wall thicknesses it creates less number of elementsthan ringmesher. There is one precondition before just trying: it must exist definite edges between front/end surfaces and circumferential surfaces.

1.1.1.5.2. Stabilizing

In general in simufact.forming mass-dependent inertial- and dampening-effects will not be considered. Normally theirimpact on forming processes (excluding some special cases) is marginal. This leads especially for ring rolling simu-lations to tilting and wobbling of the ring which is maybe higher than compared to reality. It may cause deviationswhile ring starts to enter profiled shape of rollers too. Full consideration of inertial and dampening effects is possiblein general. But this approach would consume multiples of CPU-time.

For ring rolling applications there are two much more effective approaches to avoid over scaled tilting and wobbling

of the ring. Next figure shows the two different approaches. Both can be defined by opening the forming control ( in the process window - either double-click the symbol or tag it, then right-mouse-click and select Properties). Allsettings are described herein are options - if the ring is stable in the simulation, there is no need to use these optionsand you can simulate without stabilizing.

• Weight force can be considered as a volume-related load and holds down the ring (by using the weight force but notby inertial effects). If simultaneously a bolster plate (rolling table) is integrated into the model an explicit stabilizingeffect can be observed. Main disadvantage of this approach is the costly calculation of large contact areas to thebolster plate. On the other hand with this friction and heat transfer between ring and bolster plate can be considered.If this is not desired, no friction and no heat transfer can be assumed. But the ring may contact the bolster plateonly sporadic and short time in many real processes. Stabilizing the ring by using this approach may not modelreality in a proper way in this cases.

• Very effective and fast is the usage of special stabilizing springs. These springs will increase the (internal) stiffnessof the model without creating continuously acting forces. Doing so there is no need to insert a bolster plate. One candefine either springs operating downwards to a "virtual" bolster plate and hold down the ring as a whole or stabilizingsprings within the ring which act on nodes facing each other. This suppresses relative movements between thenodes along ring axis and hence tilting of the ring. How strong this stabilizing shall work can be influenced by themagnitude of spring stiffness.

To model the heat transfer, the bolster plate can be positioned in the model in such that there is no (mechanical)contact to the ring. Then the heat transfer can be modelled by using the "near contact tolerance" option of the contacttable (pure thermal contact).


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Figure 1.17. Available approaches for stabilizing and guiding the ring

Weight force can be activated inside the forming control under Advanced / Miscellaneous...Gravity. Please do notforget to select the right Direction.

Stabilizing springs can be set in the forming control under Advanced / Stabilizer. Please check right orientation ofaxis of rotation and select a suitable Stiffness for the different spring types. This has to be calibrated by testing severalvalues from case to case. Please vary the stiffness by changing order of magnitude by some decimal powers. Oneshould consider that stabilizing springs do affect not only undesired wobbling and tilting but also the desired "filtering"of the ring into profiled rollers in the early phase of the process. One has to find the right compromise between theseobverse effects. In general an over scaling of the stabilizing effect should be avoided.

1.1.1.5.3. Step control

Usually for ring rolling simulations a fixed number (manually defined by user) of time steps is used. As a thumb-rulethe number of time steps should be defined in such a manner that tangential motion of a driven roller with contact tothe ring does not exceed one third of tangential element length of the ring per time step. Number of time steps can

be defined in the forming control dialog: symbol in the process window - either double-click the symbol or tag it,then right-mouse-click and select Properties / Step control. Select mode "Fixed time steps" and activate Fixed -afterwards specify desired number of time steps. By clicking the button ... right next to the input field one can activatea sub-dialog to calculate the number of time steps based on the above mentioned thumb-rule (see next figure).


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Figure 1.18. Calculation of the number of timesteps based on tangential element length of the ring

Please follow this sequence of actions to be done: select drop down list Point of the Press --> this point has to bedefined previously by using main menu Tools / Define points ... The point should be located on a representative outerdiameter of the driven main roller. To define the point open the dialog, click on a desired point of the main roller,select Add and Close the dialog. <-- previously defined point will appear in the drop down list, select it. Next step isto check the Distance per step. This value is calculated already as one third of tangential element length of the criticalpart of the ring. All other setting are taken over automatically and can't be changed. By confirming OK the calculatednumber of steps will be set to the forming control. Calculated value can be overwritten all the time.

Herein described sequence is a help only to support completion of the forming control. Calculated num-ber of time steps will taken over one time only. If one changes whatever setting is influencing this valueit will neither calculated again nor overwritten automatically. It has to be done manually.

One-third-thumb-rule keeps users on the save side (no slippage is assumed). Dependent on the de-sired accuracy of the results one may run a simulation also with explicit less number of time steps. Itcan be stated that using a tangential distance step is equal up to a half of the tangential element size maynot lead to any problem. In some cases two thirds are possible, too. Be careful when trying to set highervalues than mentioned. It can cause problems.

Calculation of time steps does not consider radial and axial infeed-velocity. Number of time steps ishence dependent on number of revolutions but not from local deformations. In case of fast rotating rollerssimulations become particular costly. Increasing motor speed at constant infeed-velocities (hence realprocess time keeps constant too) will lead to an increase of time steps and CPU-time consumption. Butthere should be a reasonable amount of forming left within each time step to achieve a stable simulation.

1.1.1.5.4. Friction

Caused by locally small contact areas, which are characterised by the discretization, i.e. the meshing, the frictionmodelling of ring rolling processes is based on more the demands of the simulation than on possibly existing measuredfriction values. In general friction of the driven rollers should be defined as high as needed to ensure a stable rotationof the ring. Dragged-rollers should be modelled with low friction. The upper friction value is limited by possiblyoccurring local distortions of the element. This is especially applied to rollers with (local) slippage, i.e. profiled rollersor axial rollers. In case of profiled rings a too large friction value may affect material flow in radial and axial directionand hence lead to underfill problems of the ring.


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Typically Coulomb-friction value of 0.4 for driven rollers and 0.2 for dragged-rollers should be used combined witharctan- friction approach. If local element distortions within contact zones occur or improper material flow in profiledareas can be observed, one may decrease these values or change over to the shear-friction approach. In case of thering does not rotate stably, one option is to change over to the - more costly - bilinear friction approach. Bilinear or

arctan-friction approach can be selected in the forming control: - either double-click the symbol or tag it, then right-mouse-click and select Properties... / Friction. The usage of the combined friction law is possible too. Suitability ofthe IFUM friction model is not yet approved.

If one has underfill problems with profiled rings in reality and simulation shows the same effect, the friction values areadjusted and calibrated well. When using dragged-rollers one should check whether they can approximated as non-rotating and frictionless. This will help to stabilize simulation and saves CPU-time.

1.1.1.5.5. Contact and separation

Detection of contact and loosening of contact - so called separation - influence stability, CPU-time as well as results

of ring rolling simulations particularly strong. Related parameters can be found in the forming control: - eitherdouble-click the symbol or tag it, then right-mouse-click and select Properties... / Contact and possibly additionallywithin the optional contact table.

Contact detection can be adjusted by the parameters contact Tolerance and contact BIAS. Normally one can usedefault settings (typified by "0"). If the simulation is not converging properly or separation is delayed, it might beuseful to set contact-BIAS to large values of 0.95 ... 0.995. This will shift contact tolerance into the dies. Delayedseparation can be seen through element distortions at the roll-gap. But it may caused by other factors (i.e. friction),too. Poor convergence can be seen through high number of iteration cycles (check sts-file) and related messages whichrefer to penetrations (check log- and/or out-file). It may help to define a fix contact value manually. Default value is atwentieth of smallest tangential element length. For test purposes try to set a twentieth of axial or radial element sizeby consideration of refinement level. Enlarging this contact tolerance value may help to overcome bad performingsimulations.

In order to achieve stable conditions a force, larger than zero, has to pull away a node from the die for contact separationto occur. Separation is especially needed for all nodes passing the roll-gap exit. Separation can be influenced bydefining Separation type and maximum number of Several releases / increment. One should check these values.Separation type determines either which force, stress or portion of flow stress have to be exceeded to separate thenode from the die. To use a stress-based criteria is recommended because it is independent mesh fineness compared toforce-based criteria. Usage of flow-stress based criteria may make sense to reduce influence of material characteristicson separation but there is not so much experience with that. Several releases / increment determines how often thecontact status of a node can be changed within one increment. Use either very small values of 0 ... 5 possibly 10 ora high value of about 100.

Generally speaking "difficult made" and "few" separations will shorten CPU-time but there is increasing danger of"bad" results and aborted simulations due to mesh distortions. Too large separation stresses lead to spotted stress-,strain- and temperature values at the surface, hanging nodes, distorted meshes (and herewith more remeshing opera-tions) and may cause simulation abort. Too small separation stresses may lead to instable and slow simulations. Theinfluence of several releases per increment can be discussed in similar way. High separation criteria and high numbersof releases per increment often result in the same outcome like the combination of their low/low- values. But to uselower values for both saves CPU-time and is recommended herewith.

Separation does not only influence the local results, but the ring growth, too. Particularly within the calibration phase,thus at low ring growth velocities, a too difficult separation can restrain the ring growth. In this case, use very lowseparation stresses, if needed well below 1 MPa. The maximum number of releases per increment may be kept below10 at the same time.

Surface facets

Another important aspect for every contact calculation is the shape and quality of surface facets of rigid rollers. Amore uniform facet distribution and facets with similar edge lengths help to improve contact algorithm. If you haveanalytical CAD-data, thus no STL but STEP, IGES or a native format, it can be imported by using the option "qualityfacets" and a Facet Sag which tends to be small. To do so please select Insert (or right-mouse-click the inventorywindow) / Model / CAD import ... activate "Quality facets" and try out (by pressing "Preview") different settingsof Facet sag. Note that too small values of facet sag will lead to too many surface facets.


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Within simufact.forming one can create uniform surface facets by right-mouse-clicking a geometry within the inven-tory-window followed by Modify geometry / Surface remesh. A new geometry with different surface facets willbe created. Compared CAD import with the option "quality facets" one can use additional refinement boxes to main-tain a low number of surface facets. Doing that, one should have in mind that an already discretized surface will bediscretized again what may lead to quality issues.

1.1.1.5.6. General aspects

Heat transfer

There is no special aspect of modelling heat transfer for ring rolling applications. Caused by typically long processtimes one should check very carefully calculated temperatures. Calibration of processes should always contain tem-peratures. Because of large free surfaces of the ring the influence of heat transfer to environment and emissivity ontemperature calculation is stronger than for other forming processes.

Symmetry

Any symmetry axis orthogonal to ring axis extremely supports stable calculations. This requires not only a symmetricring but also an axial ring growth which develops symmetrically - please check this carefully before using it. In additionstabilizing effects might become too strong and hence suppress real tilting or "hide" wrong kinematics.

Flow lines and particles

... can be used as usual. Flow lines particularly support the user to check whether the cross sections of the ring remainplanar.

Previous and next stages

Within a simufact.forming project the ring rolling stage can be combined of course with previous or next stages. Pleasetake the possibility of transformation from axial-symmetric (2D) - often used for previous upsetting - into 3D- modelinto consideration. With Release 11 also vice versa transformation can be used, thus e.g. finished rings can be forgedaxial-symmetric again.

Combination with cooling-, heating- or heat treatment stages is possible, automatized stage controls, too..

Solver

Most of the time ring rolling simulations are stable enough to use the fast Iterative-Sparse-Solver. If problems occurthe Multifrontal-Sparse-Solver can be tested on demand. Feel free to try other solvers - even if no general experienceexists.

Parallelizing features

CPU-time consumption can be reduced by using parallel-computation. Unless the Iterative-Sparse-Solver is used twooptions are available: Domain-Decomposition-Method (DDM) and Multithreading. Multithreading is not available forthe Iterative-Sparse-Solver, but DDM is. Especially the DDM-method can induce speed-up factors of 2 or more. Butplease keep in mind that the calculation time of ring rolling simulations results from the high number of calculationincrements. The models them self normally have a rather moderate size. These are not the ideal preconditions forparallel-computing using many domains.

1.1.1.6. Special features of Postprocessing

It the model contains either a RAW or a MERW-control, ring diameter and ring growth velocity can be plotted for the

workpiece with a history plot (open of the "result actions" toolbar). To check kinematics, translational motion ofaxes can be plotted based on position and velocity of related reference points. Plotting rotation speed of drag-rollersenables one to assess stability of ring rotation.

Thickness evolution of the ring is possible by using contour plots or animations. In order to enable that, one has to

activate it before starting the simulation within the forming control: - either double-click the symbol or tag it, thenright-mouse-click and select Properties... / Output results -> Thickness.


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Usually ring rolling processes will performed with a high number of output results (output divisions) - also to beset within the forming control - in order to check frequently progress of the simulation and to get results close to apossible abort or other problems. Hence the result folder becomes extremely large. One may open properties of results

(symbol within process tree) to select and delete results on demand. This is very efficient for the SPR-files, whichare needed only for a restart or a next stage.

1.1.1.7. Potential problems, solutions and trouble shootingSeveral problems and possible model errors were discussed already in previous paragraphs. Following bullet pointswill summarize these issues along with their causes and possible solutions:

• Poor convergence at early beginning of simulation or early abort (within first 50 increments) - first incrementsmight be critical with respect to stable contact conditions and initialization of ring rotation.

• Check initial positioning inside the model (at least 3 contact points, no penetration (consider the mesh), positionof edges, ...), adapt model accordingly

• Infeed tools first of all without rotation of driven rollers, start rotation slowly not before stable contact is present

• For RAW- and MERW-controls check initial position of centering roller with contact to the ring and/or startcontrol with a time-delay and/or change contact by using off-set (closer or farther)

• For RAW- and MERW-controls shift centering rollers up in +Z-direction as long as there is no more contact tothe ring - check positioning

• Start with many output divisions (one result file per increment) to enable more detailed analysis

• Check given kinematics - review used units

• Ring does not start rotating or sticks during simulation

• Increase friction, check friction law (Coulomb) and friction approach (bilinear)

• Infeed-velocities and strokes too large?

• Temperature evolution realistic? Temperature too high?

• Check material data

• For RAW- and MERW-controls check guidance of the ring by centering rollers - use positive off-set for looserguidance

• Review kinematics - if driven rollers were approximated as dragged ones (i.e. axial rollers with unknown rotationspeed) - change approach - use instead transformation of rotation speed of the ring (possible with Release 11)or predefine either rotation speed or torsion spring

• local mesh distortions in contact areas, hanging nodes, ring surface after roll-gap exit very rough, spotted stress-,strain- or temperature values on the surface

• Separation too difficult: decrease separation stress, increase number of several releases per increment

• "Too much contact": increase Bias (approx.. 0.995 or higher but smaller than 1), decrease contact tolerance

• Friction creates local deformation or temperature spots: reduce friction, test shear-friction law and arctan-ap-proach, reduce if necessary amount of dissipation (Forming-control / Friction), i.e. the fraction of the frictionwork converted into heat, but the influence of this tends to be low

• Check temperatures and heat transfer coefficients

• Check material data

• Review kinematics: can slippage be seen where slippage is in reality?


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• Remeshing problems, inconsistent cross sections after remeshing

• Increase edge angel within remeshing object

• In general poor convergence, contact problems

• Import rollers by using "Quality Facets“ option combined with small "Facet Sag" or remesh surface insimufact.forming

• Vary contact tolerance and BIAS

• Vary step control

• Change to Multifrontal-Sparse-Solver, test different solvers

• When using DDM: try another number of domains, another decomposition method or deactivate DDM for testpurposes

• Review kinematics, check initial position of rollers

• instable simulation, ring "flutters", non-circular or wrong shape

• Review kinematics, check initial position of rollers, if the same happens in reality - try to optimize the process(a kinematics that will not or only badly work in reality, will not work in the simulation, too)

• Check material data and temperatures

• Check friction, contact, separation and time step settings

• Check stabilizing settings

1.1.1.8. Final remarks to the model setup

Recommended steps for beginners

Ring rolling indeed is one of the most complex and sensible processes in both reality and simulation. It will take time(and one should take it) to set up a model, check the model finally and calibrate the process. One has to develop stepby step a feeling for this kind of simulation. Don't start with a ring which failed several times already in the shop-floor and needs to be delivered tomorrow.

Better to start with a stable and well known process. Often this enables to predefine all motions and simulate firstof all the process without any kind of control. Please use existing logger-data and import them as a table press forinstance. Thus one can test first of all basic settings like material data, friction, thermal properties and adjust it tothe process if necessary.

Second step could be to simulate afterwards a similar ring (in terms of material, dimensions and shape) which wasfailed in the shop-floor (underfill, ...). Is it possible to simulate the failure / defect? With the same settings? Can thedesired final diameter be reached?

Third: add now suitable control if applicable. Does reality and simulation still match? Have the control setting to beadjusted? Does is match to real control settings?

After getting satisfying results in all test runs one can trust now the settings and start to simulate more complex partsor even new and unknown geometries. Always consider that real machines often use much more sensors and actuatorsso that simulation maybe will not match exactly (especially for roundness) . Small deviations are normal.

What's to do if rotation speeds are unknown?

If one have a driven roller with unknown rotation speed and what can't be controlled by RAW axial roller control andif one know that rotation drive power is less than compared to other rollers, then proceed as follows:

First of all assume the roller as a dragged one. If results do not match, please analyze the calculated rotation speed,correct it if required (smoothen, increase, decrease, ...) and define by using a table press desired rotation speed. Similar

Ring Rolling Demos&Examples

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way is to use a generic torsion spring in order to enforce related rotation speed what can be used after analyzing andadjusting the values as a table press.

Final remark

It can be stated in general: ring rolling processes that do not work in reality, won't work in simulations too. It followsvice versa: a simulation does not run properly either uses wrong settings and assumptions, inputs are missing or realprocess does not work at all.

If real process works well and simulation fails, mostly the assumptions are wrong, data are not complete, used mea-suring devices may not work properly, material types were interchanged, data are from different batches, recordedkinematics and initial positions do not match, etc. Please check again carefully all settings step by step.

1.1.2. Demos&ExamplesCompared to other chapters of this tutorial one will not find for ring rolling simulations any step by step or click byclick instruction to build up a model (there are too many different subtypes and possible combinations of the process).But one can find in simufact.forming "Demos & Examples" a number of different ring rolling models, showing theright application of all features and settings mentioned in this tutorial. It enables all users to adapt their own models totheir specific process. Basic handling of simufact.forming and model setup are described in chapters 1 to 6. Chapter7 and following contain more detailed step by step instructions for several types of models. Further information andtips are provided with the simufact.forming manual.

Demos & Examples is one of the available applications of the simufact.forming program group and can be found in the

Windows start menu: . Application examples of ring rolling processes are located in "AdvancedExamples" / "Ring Rolling", see next figure. The installation of Demos & Examples is optional. If you can't find ityou can install it separately from your DVD.

Figure 1.19. Ring rolling applications in Demos & Examples

Ring Rolling Demos&Examples

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Following models for ring rolling applications are included in simufact.forming Demos & Examples:

• 01 ring rolling 3D FE

Basic and simple example with rectangular ring - no control is used.


Fictitious process for rolling an inner roller-bearing-ring. Contains two table presses but no control. Axial rollersare free-rotating around a non-parallel axis (related to ring axis).


General process example for RAW control with rectangular ring. Diameter calculation uses a bonding box. Axialrollers are driven translational and rotatory by table presses and will fed in radial direction simultaneously with themandrel. Upper axial roll will be moved in axial direction additionally.

• Exercise 1:

Convert the model to axial rollers being dragged but still can be moved translational. Minimize number of tablepresses used in the model.

Tip: Define local coordinate system for rotation but not for translation. Define mounting / die insert, deleterotation from table press, use one table press for mandrel and lower axial roller if possible.

• Exercise 2:

Use measuring roller for diameter calculation..

Tip: add new die, read in / create measuring roller geometry and assign it, create spring and assign it, don't forgetto define thermal and friction parameters, decide to use either free-rotating (dragged) or frictionless conditions,adjust RAW-control settings.


Example for a process using a table press with diameter-velocity-dependency. The diameter is determined using aRAW-control with measuring roller. For demonstration purposes a relatively small freely rotating measuring rolleris used. In a "proper simulation" a measuring roller with bigger diameter or a non rotating measuring beam - asexplained earlier - should be used.

• 05 ring rolling 2D3D FE

Example for a process chain consisting of upsetting, preform operation, piercing and result transfer from 2D to 3D.The ring rolling process uses an RAW-control and is very similar to "03 ring rolling 3D FE".


Basic example for MERW-controlled process. Ring to be rolled has inner and outer profile.


Advanced example for RAW-process: ring with rectangular cross section. Please have attention to the translationalmotions of the axial rollers. We are allowed to show an animation only.

In addition one should have a look to "Basic examples" / "Rolling" and "Advanced examples" / "Rolling", i.e. for :

• 01 rolling 3D FE

Axial-die-rolling of a profiled ring. Ring tilts while rolling temporarily out of the die. This is not by accident andmay not be suppressed by stabilizing features. Hence stabilizing is inactive. Because there is an equal sense ofrotation for both die and roller, application of the calculation of time increments based on one-third-rule does notmake sense.

chapter ring rolling en

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