ORIGINAL ARTICLE

Automated setup and fixture planning system for box-shapedparts

Michael Stampfer

Received: 18 September 2008 /Accepted: 16 February 2009 /Published online: 4 March 2009# Springer-Verlag London Limited 2009

Abstract The topic of the research is related to the domainof computer-aided manufacturing process planning. Thispaper deals with the problem of setup and fixture planningfor the machining of box-shaped parts on the horizontalmachining centres. The setup and fixture planning involvesthe definition of setups, the setup sequence and conceptualdesign of fixtures for each setup. The central topic of thisresearch is the automation of the conceptual design offixtures. This topic is interconnected with the setupplanning, and accordingly, the aim of the author has beenthe integrated handling of tasks of setup and fixtureplanning and the finding of solution in an integratedsystem. Based on the workpiece model, the developedsystem automatically determines the setup sequence, thecontent of setups and the conceptual solution of fixture foreach setup. The paper presents the problems of fixturesolutions and the partial tasks of workpiece holding, thetypical solution of partial tasks and the conditions of theirapplication and finally offers a new method, which makesthe integrated handling of tasks of setup and fixtureplanning and finding solution in an integrated systempossible.

Keywords Process planning . Fixture planning

1 Introduction

The technological planning can be broken down intoseveral steps (Fig. 1): (1) setup planning and conceptual

design of fixtures; (2) operation planning; (3) fixtureconfiguration and design.

The setup planning and conceptual design of fixtures isone of the most complex intellectual tasks in the process ofindustrial design and can be automated only with greatdifficulty. Human process planners very often find thesolution relying on their experience and engineeringintuition.

This means that there is a small number of researcherswho are engaged in the conceptual design of fixtures,especially in the case of prismatic workpieces. The reasonis perhaps that the existing knowledge for the fixturesolution is not available in explicit form as formulas, logicaldiagrams or well-defined processes. It restricts the devel-opment of the appropriate fixture planning methods incontrast with another design task.

The attempt to automate fixture design activities is not anovel idea, nor is it the first attempt. Researchers havealready recognised the necessity of the development ofplanning systems in order to solve the problem ofconceptual design of fixtures. Some of the major achieve-ments in this field are listed below.

Boerma [1, 2] presented the FIXES system for setup andfixture planning for prismatic parts. In this system, first thefeatures have to be selected, which are meant for candidatemachining in one setup. Then, the suitable surfaces forlocating and clamping are selected. The system searchesclamping surfaces only on the opposite face to the planelocating face of the workpiece. It is a subsystem of thePART CAPP system, which is the first complete expertprocess planning system to be commercialised and coversmost of the process planning functions. Giusti et al. [3]introduced the planning system KAPLAN. This is aknowledge-based approach to process planning of rotation-al parts. It selects the machine tools interactively, while the

Int J Adv Manuf Technol (2009) 45:540–552DOI 10.1007/s00170-009-1983-1

M. Stampfer (*)Faculty of Engineering, University of Pécs,Pécs, Hungarye-mail: smihaly@witch.pmmf.hu

tools, the machining sequence and clamping devices areselected automatically. Quick Turnaround Cell [4] wasdeveloped by Chang and is an integrated planning systemcapable of designing, process planning, cell control andvisual inspection. It is designed to create one-of-a-kindprismatic parts, which are machinable on vertical machin-ing centres where the clamping device is a vice. Trappey etal. [5] set out to find the locating and clamping points. Inthis setup, the orientation of the workpiece is handled asinput data. Their approach is based on an analysis of theworkpiece projection onto the fixturing base element. Inthe first step, the algorithm selects the locator points onthe base element. In the next step, it defines thecoordinates of the two-point locating and finally thecoordinates of the one-point locator. Two algorithms arereviewed for the clamping points definition, one for theclamping in the projection direction and one for theclamping in the perpendicular direction. Cai et al. [6]proposed a new method, called the Robust FixtureConfiguration Design for fixture configuration, whichminimises the locating errors. As input data, the followingare used: the geometric model of workpiece, initial locatorpositions, orientation and value of the clamping force. Thesystem keeps changing the initial locator positions until thelocating errors are at the minimum. Joneja et al. [7]

provided a short description of a Setup planner and a moredetailed description of a fixture planning program. They arepart of an integrated process planning system. The Setupplanner first groups the surfaces to be machined intodifferent setups, then defines several setup sequences andselects the one with the minimum number of setups. TheFixture planner first determines the clamping method (viseor modular fixture), selects the feasible features forlocating, supporting and clamping, checks tool interference,then builds the entire assembly and finally checks stability.Ma et al. [8] presented an automated fixture design system,in which the fixturing surfaces are automatically deter-mined based on geometric and operational information.Horváth et al. [9] offered a method for setup planning andsetup sequence optimising by applying genetic algorithms.Champati et al. [10] and Marefat et al. [11] applied case-based reasoning for process planning for prismatic partswhere the clamping device is a vice. Cecil [12] selected theclamping areas by a geometrical approach to cutteraccessibility in addition to the mechanical stability analysis.Paris et al. [13] developed a method, which deals withsimultaneous grouping of machining operations in the setupand selects adapted fixturing solutions. The process plan iselaborated in three steps. The first step consists offormatting the basic data of process planning system. Theseare the set of machining features, the manufacturingfacilities and the set of fixturing features. The fixturingfeatures are defined as a combination of three locatingfeatures and at least one clamping feature. The fixturefeatures are built interactively. The second step deals withthe association of machining processes with machiningfeatures. The third step consists of organizing the globalplan of the machining of the whole workpiece. Bansal et al.[14] presented an integrated setup and fixture planningsystem. The program reads the STEP file, reconstructs andmodifies the model, slices it at different heights and tries toestablish acceptable locating points, checks accessibilityand stability and selects the solution that gives the listtolerance deviance. Several researchers have employedmodular fixturing principles to generate fixture designs[15–17]. These systems are comprised by three modules:(1) module for selecting of modular fixture elements, (2)module for assembly of fixture elements and (3) module forinterference checking. The conceptual design of fixture ishandled as input data or it is solved interactively.

Although numerous Computer Aided Fixture Designtechniques have been proposed and implemented, fixturedesign still continues to be a major bottleneck in theintegration of CAD and CAM activities [18].

With the review of the new method for fixture planning,developed for box-shaped parts machined on four-axishorizontal machines, I wish to contribute to overcoming thedifficulty.

Fig. 1 Integrated process planning and fixture planning system

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2 The basic function of fixture and the typified solutions

For machining box-shaped workpieces, the most suitablemachine tool is the horizontal machining centre. The majorcharacteristics of horizontal machining centres are suitabil-ity for diverse manufacturing operations, tool-magazine andwith the help of a revolving or NC-machine table, all thefour faces of workpiece are machinable in one clamping.Depending on workpiece complexity, the manufacturingoperation of complete machining can be done in one or twoclampings.

The basic functions of the clamping fixture are locatingand clamping of the workpiece. Locating can be brokendown into plane locating (supporting) and side locating,while side locating is further reduced to endwise locatingand guiding (Fig. 2).

Due to the great variability and complexity of prismaticparts, typifying the whole fixture is impossible. However,the solutions of partial fixture function can be typified.

With the consideration of technological facilities ofhorizontal machining centres and analysis of existingclamping fixtures, according to the position of planelocating surface of workpiece, there are three types ofplane locating established (Fig. 3): (1) horizontal (denotedwith “pos1”), (2) vertical (“pos2”), (3) vertical with partialmachining of the locating face (“pos3”).

There are four basic types of side locating established(Fig. 4): (1) side locating by using surfaces, which are onthe adjoining faces of the plane locating face; (2) sidelocating by using two boreholes on the plane locating face;(3) side locating by using one borehole on the planelocating face and a surface on one of the adjoining faces;(4) side locating by using two screws and threaded joints onthe plane locating face.

According to the direction of clamping forces, clamp-ing can be perpendicular to the plane locating surface(type s1) or parallel with the plane locating surface (types2). The basic type s1, depending on the location ofclamping faces, can be further divided into subtypes s11,

s12 and s13. In the case of s11, the clamping surfacesare on the adjoining sides of the plane locating face. Inthe case of s12, the clamping surface (or surfaces) is onthe opposite side of the plane locating face, and withtype s13, the clamping is on the opposite face andhappens through the borehole. One of the specific waysof clamping is clamping by screws and threaded jointson the plane locating face and it is called type s3(Fig. 5). The number of clamping points is also a veryimportant attribute of clamping. According to the numberof clamping points, we differentiate between clamping inone, two, three and four points. Adding these to theprevious basic types, the possible clamping types are asfollows: s11_2, s11_3, s11_4; s12_2, s12_3, s12_4;s13_1, s13_2; s2_1, s2_2; s3_2, s3_3, s3_4. In this list,the last number means the number of clamping points.

3 Suitable surfaces of workpiece for locatingand clamping

Besides the presented systematisation of the solutions ofpartial tasks of workpiece holding, there are criteriaestablished for determination of the workpiece surfacesuitability for supporting, side locating and clamping.

3.1 Suitable surfaces for plane locating

The suitability of surfaces for plane locating depends on theshape and dimension of the surface. Based on their shape,the following surfaces are suitable for plane locating: planarsurfaces, intermittent planar surfaces, a group of planarsurfaces in the same plane, a group of planar surfaces intwo different planes, cylindrical surfaces (with parallelaxes), a combination of cylindrical and planar surfaces.

The surfaces (features) listed so far are not equallysuitable. The suitability decreases in the order of enumer-ation. In the expert system prototype, only the first threefeatures are built-in.

Apart from having an appropriate shape (feature), theplane locating surface must be sufficient in size in orderto be applicable for plane locating. The dimensions of

Fig. 3 Plane locating types

Fig. 2 Locating

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candidate features for plane locating must be comparedwith the three overall dimensions of the workpiece(Fig. 6).

3.2 Surfaces suitable for side locating

The suitable features are established by each side locatingtype.

3.2.1 Suitable surfaces for side locating type p1

Side locating can be divided into guide locating andendwise locating. Hence, suitability tests are to beperformed separately for guiding and for endwise locating.

Suitability for guiding must be tested from three aspects,i.e. according to shape of the surface, dimension andposition of the surface.

Fig. 5 Types of clamping

Fig. 4 Types of side locating

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Suitability for endwise locating must be tested from twoaspects, i.e. according to shape of the surface and positionof the surface.

3.2.2 Suitable surfaces for side locating type p2

According to the shape of the surface, there should be twoholes on the plane locating face. The typical dimension isthe distance between holes, and they must not be less than35% of the longest side of the plane locating face.

Suitable surfaces for other side locating types are definedin a similar way.

3.3 Suitable surfaces for clamping

The suitability of surfaces for clamping must be tested fromfour aspects, i.e. according to shape of the surface, position ofthe surface, clamping force flow and dimension of the surface.

Suitable clamping surfaces have been established forevery clamping type [20].

4 The necessary inputs for setup and fixture planning

It seems that the feature-based workpiece model isunavoidable by the technological process planning. Forthe conceptual design of fixtures, however, besides the localdata of features, the workpiece model must contain theglobal structure of the workpiece and must be given thepossibility of the description of relationships betweenfeatures as locating tolerances and dimensional tolerances.This problem is solved in a way that the whole workpiece isfirst reduced to six faces (top, bottom, left, right, front,back), and to each face, there is one or more equidistantplane designated, the position of which is determined by thedistance to the workpiece’s zero point (Fig. 7). Each featurehas a reference point the position of which is defined withtwo coordinates. That way, each feature position is definedto the workpiece zero point (and hereby also to each other).

The distance tolerances and locating tolerances of thefeatures themselves (Fig. 8) are vital parts of the workpieceof the model. The tolerances between features (which“interconnect” features) can be divided into loosely andstrictly tolerance-related connections.

The group of loosely tolerance-related connectionsconsists of accuracy-related requirements, which can beactualised relatively easily even in cases when theconnected surfaces are machined in two separate clamp-ings. In the case of these functional connecting types, thefixture accuracy is critical only with respect to parallelismor perpendicularity to the machine table. In this group, thefollowing types of tolerances have been determined:

1. Locating tolerance

(a) Parallelism or perpendicularity between two planesurfaces.

(b) Parallelism or perpendicularity between the planesurface and axis.

2. Distance tolerance

(a) Between two plane surfaces if the tolerance zone isT≥0.2 mm.

(b) Between the plane surface and axis if the tolerancezone is T≥0.2 mm.

The group of strictly tolerance-related connectionsconsists of accuracy-related requirements, which can beactualised with difficulty in cases when the connectedsurfaces are machined in two separate clampings, respec-tively; they need high accuracy of fixture and locatingelements of the workpiece. This group contains thefollowing types of tolerances:

1. Locating tolerance

(a) Parallelism, concentricity or perpendicularity be-tween two axis.

Fig. 7 Definition of the feature position. W workpiece zero point, Rreference point of the feature

Fig. 6 Comparison of the dimensions of candidate plane locatingfaces with the three overall dimensions of workpiece

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2. Distance tolerance

(a) Between two parallel axis.(b) Between skew axis.(c) Between the plane surface and axis if the tolerance

zone is T<0.2 mm.(d) Between two plane surfaces if the tolerance zone

is T<0.2 mm.

With these connecting types, the connected surfacesneed to be machined in one clamping or rather suchsurfaces are machined in two separate clampings, onlywhen there is no other solution.

These attributes are extended also to the workpiece faces,so the faces of the workpiece which contains strictly connectedfeatures are strictly connected, and faces which contain onlyloosely connected features are loosely connected faces.

The feature-based workpiece model is created primarilyby recognition and has to be extended by an expert.

5 Setup and fixture planning

Most researchers divide the fixture planning process intoseveral steps: (1) setup planning, (2) conceptual design offixture, (3) fixture configuration [8, 15, 21].

In the author’s opinion, the setup planning and theconceptual design of fixture are so interconnected that thepractical planning tasks cannot be divided into separatefixture or rather setup planning tasks. The new methodmakes the integrated handling of tasks of setup and fixtureplanning and finding a solution in an integrated systempossible.

Fig. 8 Interconnected surfaceswith locating and distancetolerance

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It is assumed that the machining is carried out on thehorizontal machining centres. At best, four faces of theworkpiece are machinable on the horizontal machiningcentres in a one setup. Since one box-shaped workpiece hassix faces, so it is almost always machinable in two setups.The question is which faces must be machined in one setupor to paraphrase it, how does one select the workpieceposition in the workspace of machine tool? These questionscan be answered only by analysing the accuracy require-ments of the workpiece. It is obvious that the moststraightforward way to the realisation of the prescribedtolerances is to machine those feature in one setup, whichare interconnected by tolerance.

The definition of the workpiece position in the work-space of machine tool, and the setup definition must bedone according to the location of the functional (connected)features in the structure of the workpiece. However, theworkpiece position selected in this way can be acceptedonly when it is suitable for fixture solution (namely suitablefor supporting, locating and clamping). This fact necessi-tates the integrated approach of setup planning and theconceptual design of fixture.

The setup, i.e. clamping, in which the functional surfacesor most of them are machined is denoted by main clamping,while the setup in which the rest of the surfaces aremachined is called additional clamping. Regardless of theclamping sequence, it is the main clamping, which is solvedprior to the additional clamping.

Based on the above statements and restrictions, the setupand fixture solution consists of the main clamping andadditional clamping solution (Fig. 9).

6 General solution concept of main clamping fixtureand operation sequence

When solving the main clamping, one must try to find aposition of the workpiece in the workspace of machiningcentres in which the machining of all connected faces ispossible. In this way, we can reach great accuracy of theworkpiece, and at the same time, the accuracy requirementand the complexity of fixture are minimal. This position ofthe workpiece is denoted by the “technologically idealworkpiece position”. The fixture received this way is thebest possible fixture solution.

However, in several cases, the disposition of connectedfaces is such that the workpiece cannot be held in atechnologically ideal workpiece position. In this case, onehas to aim at finding a position of the workpieces in whichat least the machining of strictly connected faces is possiblein one clamping. In other words, the loosely connectedfaces in this stage are disregarded. This way, the fixturesolution is still “fair”, but the accuracy requirements refer

only to the parallelism or rather to the perpendicularity ofany fixture surfaces (see Section 4).

If this attempt is not successful, then one must give upthe idea of machining all of the strictly connected faces inone clamping. At the same time, there are cases when notthe entire face but the strictly connected features (holes) onthe face are workable in one clamping with other strictlyconnected faces (see Section 6.3).

Lastly, when none of enumerated attempts are success-ful, one is forced to machine the strictly tolerance-relatedfeatures in separate clampings. In this case, the accuracyrequirements of the fixture are very high.

Taking into consideration the above-mentioned aspects,four strategies are devised for solving the main clamping(Fig. 9):

& Fixture solution for technologically ideal position of theworkpiece

& Fixture solution based on disregarding the looselytolerance-related faces

& Fixture solution based on the reduction of a strictlytolerance-related side into loosely tolerance-relatedsurfaces and strictly tolerance-related surfaces

& Fixture solution by disintegration of strict functionalrelationships

The strategies stated so far do not yield solutions equallysuitable for the fixture. The best results are obtained byapplying the first strategy. The second strategy is applied

Fig. 9 A part of the AND–OR graph for setup and fixture solution

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only in cases when the first strategy fails to produce asolution, etc.

6.1 Main clamping fixture solution for technologically idealposition of the workpiece

This strategy is aimed at finding the position of theworkpiece in the machine workspace, which would allowthe machining of all connected faces in one clamping. Thepotential position of the workpiece in the machine work-space is determined by the requirement that all connectedfaces should be machined in one clamping. Depending onthe plane locating type, this can be formulated as follows:

& In the case of the horizontal plane locating type—pos1—the plane locating face and its opposite face must not betolerance-related faces because it is not possible tomachine them together with other faces in the sameclamping.

& For a vertical plane locating type—pos2—the planelocating face, the face which is facing the machine table

and its opposite face, must not be tolerance-relatedfaces.

Since the horizontal plane locating (pos.1) allowsmachining of four faces and the fixture construction issimpler, the system first attempts to generate a fixturesolution for the horizontal plane locating type. If thatattempt fails, a second attempt is made at solving the fixturefor the vertical plane locating type.

In order to finally adopt the selected workpieceposition, it should be suitable for the workpiece fixturesolution. A certain position of the workpiece is suitablewhen it is easy for plane and side locating and clamping(Fig. 10).

The selected workpiece position is suitable for planelocating if the plane locating face contains surfaces, whichare suitable for plane locating. When in the analysedworkpiece position there is no appropriate feature for planelocating, then this position is unfeasible for fixture solution,and in this case, one must select a new workpiece position.If the workpiece position is suitable for plane locating, then

Fig. 10 A part of the AND–ORgraph for fixture solution in atechnologically ideal workpieceposition

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in the next step, a suitability check for side locating isperformed.

The selected workpiece position is suitable for sidelocating if for some of the possible types of side locatingthere are suitable surfaces on the appropriate workpiece face.In the next step, the suitability for clamping is checked.

If, for some of the possible types of clamping, there aresuitable surfaces on the appropriate workpiece face (orfaces), then the supposed workpiece position is consideredto be suitable for clamping. Since suitability for planelocating and side locating has already been checked for inthe previous stages, the fixture solution has been reachedfrom the point of technologically ideal workpiece position.If the supposed workpiece position is not suitable forclamping, the position is eliminated, and a new position isselected, which is again checked for plane locating, sidelocating and clamping suitability.

Considering that the workpiece is six-sided and that, inprinciple, any one of the faces can be chosen for the planelocating face, the workpiece has six possible positions inthe machine workspace for each of the plane locating types,pos1 and pos2. If none of the possible workpiece positionsmeet the discussed requirements, the fixture solutionstrategy based on the ideal workpiece position cannot yieldsolutions and should be abandoned.

6.2 Fixture solution based on disregarding the looselytolerance-related faces

Since the first strategy, namely the assumption that allconnected faces must be machined in one setup, has failedto produce a fixture solution, one is forced to reduce thisrequirement and be content with the workpiece positionwherein the machining of all strictly tolerance-related facesis possible in one setup. This strategy is similar to theprevious one, with the exception that the loosely tolerance-related faces are omitted during the process of selection ofthe workpiece position in the machine workspace. This canbe formulated in the following manner:

& In the case of the horizontal plane locating type, theplane locating face and its opposite face must not bestrictly connected faces.

& For vertical plane locating, the plane locating face, theface which is facing the machine table and its oppositeface, must not be strictly connected faces.

In order for the assumed workpiece position to beadopted according to the previous requirement, it has tobe suitable for plane locating, side locating and clamping.With this strategy, main clamping is always the secondone, which implies that only finished surfaces can be usedfor locating. Suitability of a workpiece position is checkedin the same manner as with the first strategy.

6.3 Fixture solution based on the reduction of a strictlytolerance-related side into loosely tolerance-related surfacesand strictly tolerance-related surfaces

This strategy is resorted to in cases when the first twostrategies fail. The main point of this strategy is to find sucha fixture solution, which enables the machining of at leastall strictly connected features in one setup, if the machiningof all strictly connected faces of the workpiece is notpossible. It employs the analysis of strictly tolerance-relatedfaces in order to find such a face, which, besides strictlytolerance-related holes, also includes tolerance-unrelated orloosely tolerance-related faces, which are suitable forlocating and clamping. If such a face exists, then all theincluded surfaces, except the strictly tolerance-related ones,are machined in additional clamping. That face will be theplane locating face in the main clamping where all thestrictly tolerance-related workpiece surfaces, includingthese on the plane locating face, will be machined. Sincein this case some surfaces on the plane locating face aremachined, the plane locating type is always vertical withpartial machining of the locating face (pos3). A moreprecise definition of the workpiece position follows fromthe condition that the face facing the machine table and itsopposite face must not be strictly tolerance-related. Thelogic behind this strategy is portrayed with the AND–ORgraph in Fig. 11. This fixture solution allows machiningaccuracy without special requirements in respect to fixtureaccuracy but nevertheless increases fixture complexity.

6.4 Fixture solution by disintegration of strict functionalrelationships

Should none of the discussed strategies succeed ingenerating the desired solution, one is forced to resort tomachining the strictly tolerance-related surfaces in separateclampings. For this reason, the fixture for the secondclamping must be highly accurate, which often presents akey issue in the process of meeting workpiece accuracydemands. By now, one needs to analyse only the workpiecepositions where the plane locating face is one of the strictlyconnected faces. Namely, the other possible positions of theworkpiece are already analysed through the application ofthe first three strategies, but no solution has been found.The first step involves an attempt to find by horizontalplane locating such a workpiece position in the machineworkspace, which ensures that the face opposite the planelocating face is not strictly tolerance-related. If this attemptfails, then both the plane locating face and its opposite faceare allowed to be strictly tolerance-related. The selection oftype of side locating must be done with special attention,performed on the basis of the type of strict face connection.This strategy is described in greater detail in [19, 20].

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6.5 Definition of the content of setups

Upon solving the main clamping fixture, the following factshave become known: plane locating type, plane locatingface of the workpiece in main clamping, plane locating

surfaces, side locating type, guiding and endwise surface,clamping type and clamping surfaces. Based on these facts,it is possible to reduce technological operations to main andadditional clamping. Thus, it has to be defined whichfeatures are machined in the main clamping and which inthe additional clamping. This task can be relatively easywhen the plane locating type in main clamping is horizontalor vertical. In these cases, it is sufficient to define the faces(and certainly all features which belong to some face),which will be machined in the main clamping or rather inthe additional clamping. When the plane locating type isvertical with partial machining of the plane locating face,then the reduction of technological operation to main andadditional clamping presents a more complex task due tothe fact that the main clamping plane locating face has to bepartially machined in both main and additional clamping.For this reason, it should be precisely defined whichsurfaces on the plane locating face should be machined inthe main clamping and which should be machined in theadditional clamping (Fig. 12).

Sequentially ordered, with the exception of one case, theadditional clamping takes precedence. The main clampingtakes precedence in that case when the fixture solution isdone in a technologically ideal workpiece position but inthis position, the workpiece has only rough surfacessuitable for plane locating.

7 Conceptual solution of fixture for additional clamping

The conceptual solution of fixture for additional clampingfollows after the reduction of the technological operationsto main and additional clamping. At first, one must have alook at the necessity of additional clamping because suchsituations may occur, when the workpiece contains onlyfour or less faces for machining, and they can be machinedin the main clamping. The workpiece position within themachine workspace is selected in such a way as to allow

Plane locating type in the main clamping

Machining in the main clamping

Machining in the additionalclamping

Horizontal

Four faces The plane locating face in the

main clamping and its opposite face

Vertical

Three faces The plane locating face in the

main clamping, the face facing the machine table and itsopposite face.

Vertical with partial machining of the locating face

Three whole faces and the strictly connected holes on the plane locating face

The face facing the machinetable and its opposite face as well the partial plane locating face in the main clamping

Fig. 12 Reduction of techno-logical operation into clampings

Fig. 11 A part of the AND–OR graph for fixture solution based onthe reduction of a strictly tolerance-related side into loosely tolerance-related surfaces and strictly tolerance-related surfaces

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machining of those workpiece faces, which are scheduledfor machining in additional clamping. With auxiliaryclamping, horizontal and vertical plane locating types maybe applied. The assumed workpiece position has to meetplane locating, side locating and clamping requirements.

8 Implementation and test examples

The Integrated Process Planning and Fixture PlanningSystem are made up of several modules presented inFig. 1. The module for Setup and Fixture Planning isimplemented in Visual Prolog programming language. Thefeature-based workpiece model, which is created in modulefor CAD model post-processing, is the input of the FixturePlanning System. Based on this input, the system generatesan acceptable solution for fixtures and setup definition.Search for a fixture solution is carried out automatically, butin certain cases, the solution offered by the system must beapproved by the user by pressing the “Y” key or rejected bypressing “N”. This may primarily be necessary regardingthe selection of the clamping points, as it may happen thatthe clamping element obstructs the machining, and at itscurrent level of development, the system is unable to detectinference.

The system for fixture solution generates output basedon the facts, which are grouped into associative triples:

fixture solution < object >; < attribute >; < value >ð Þ;

where the object can be one of the following: mainclamping fixture (m_clamp) or additional clamping fixture(ad_clamp).

8.1 Test example

The approach described above has been tested on industrialparts. Presented in Fig. 13 is an example of a typicalworkpiece. The surfaces (features) of the workpiece aremarked with numbers on the drawing. With geometricaland tolerance analysis of the workpiece, the following factsare known: Strong connected features of the workpiece arethe features marked with the numbers 2, 3, 12 and 13.Loose connected features are marked 1 and 11. Respec-tively, the front and the back faces are strong connectedfaces and top , bottom , left and right faces are free faces.

Fig. 13 Test example

Fig. 14 The realised fixture for the main clamping, which enables themachining of high accuracy holes on the plane locating face throughthe opening in the fixture body

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In the first step, the system tries to solve the main clamping,applying the first strategy, namely the main clamping fixturesolution for the technologically ideal position of the work-piece. The workpiece can be placed in the workspace of themachine tool in the technologically ideal workpiece positionif, for example, the plane locating face is at the bottom becausethe bottom face and top faces are not tolerance-related faces,but the bottom face is not suitable for plane locating (seeFig. 10). Hence, this attempt will fail. The same problemoccurs by supposing the plane locating face is the top, left orright face. That is why this strategy must be skipped and thesecond strategy be applied.

By using the second strategy, namely the Fixturesolution based on disregarding the loosely tolerance-related faces, the same problems are likely to occur as withthe first strategy.

After the failure of both the first and second strategies,the system will apply the third strategy, which is the Fixturesolution based on the reduction of a strictly tolerance-related side into loosely tolerance-related surfaces andstrictly tolerance-related surfaces (shown in Fig. 11).According to this strategy, the plane locating type isvertical with partial machining of the locating face (pos3),see Fig. 3. The system checks the suitability of possibleworkpiece positions for locating and clamping. If it isassumed the plane locating face is for example, the leftface, the attempt will fail because the left face is not astrictly connected face. If it is assumed that the planelocating face is the front face, the system will yield thefixture solution for the main clamping on the basis ofreasoning, as presented in Fig. 11. The plane locatingsurface is the feature marked by number 1. The side

Table 1 The output created by the expert system for setup and fixture planning

Partial output based on the facts Meaning

Fixture for main clamping

fixture_solution(m_clamp, seque, second) The main clamping is the second clamping

fixture_solution(m_clamp, plane_loc_type, pos3) The plane locating type is vertical with partial machining of thelocating face (pos3), see Fig. 3

fixture_solution(m_clamp, face_to_table, bottom) The face facing the machine table is the bottom face

fixture_solution(m_clamp, plane_loc_face, front) The plane locating face is the front face

fixture_solution(m_clamp, plane_loc_surf, 1) The plane locating surface is the feature denoted with number 1

fixture_solution(m_clamp, side_loc_type, p4) The side locating type is p4 (see Fig. 4)

fixture_solution(m_clamp, guid_loc_surf, 4) The guiding surface is the feature number 4

fixture_solution(m_clamp, endw_loc_surf, 5) The endwise locating surface is the feature number 5

fixture_solution(m_clamp, clamp_type, s3_4) The clamping type is s3_4 (see Fig. 5)

fixture_solution(m_clamp, clamp_surf1, 4) The clamping surfaces are the features with number 4, 5, 6 and 7

fixture_solution(m_clamp, clamp_surf2, 5)

fixture_solution(m_clamp, clamp_surf3, 6)

fixture_solution(m_clamp, clamp_surf4, 7)

Fixture for additional clamping

fixture_solution(ad_clamp, plane_loc_type, pos2) The plane locating type is vertical (pos2), see Fig. 3

fixture_solution(ad_clamp, plane_loc_face, back) The plane locating face is the back face

fixture_solution(ad_clamp, plane_loc_surf, 11) The plane locating surface is the feature denoted with number 11

fixture_solution(ad_clamp, side_loc_type, p3) The side locating type is p3 (see Fig. 5)

fixture_solution(ad_clamp, guid_loc_surf, 12) The guiding surface is the feature number 12

fixture_solution(ad_clamp, endw_loc_surf, 20) The endwise locating surface is the feature number 20

fixture_solution(ad_clamp, clamp_type, s13_1) The clamping type is s13_1 (see Fig. 6)

fixture_solution(ad_clamp, clamp_surf1, 10) The clamping surface is the feature with number 10

Operation scheduling

schedule(machining_in_ad_clamp, front) The front face is machined in additional clamping (partial)

schedule(machining_in_main_clamp, back) The back faces is machined in main clamping

schedule(machining_in_main_clamp, front) The front faces is machined in main clamping (partial)

dekomp(machining_in_main_clamp, 2) The features denoted with numbers 2 and 3 are machined in main clamping

dekomp(machining_in_main_clamp, 3)

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locating is possible by using two threaded joints denotedwith numbers 4 and 5 on the front face (type p4 presentedin Fig. 4). The clamping is done by screws and threadedjoints on the front face denoted with number 4, 5, 6 and 7(type s3 presented in Fig. 5). The features on the front facedenoted with number 1, 4, 5, 6 and 7 will be machined inadditional clamping, while the strong connected features 2and 3 will be machined in the main clamping together withthe other strong connected features of the workpiece. Thisis possible only through the opening in the fixture body(Fig. 14).

The test results of the expert system are presented inTable 1 in the form of facts. With the help of the post-processor, this output in the form of facts can be presentedin another form, as well.

9 Conclusion

The definition of the typical partial task of the fixture,the definition of suitable surfaces for locating and forclamping, the discovered logical connection, practicalrelationships, and the presented new method for setupand fixture planning make the automation of theconceptual design of fixtures and the integrated handlingof tasks of setup and fixture planning possible. Theconfines of this article do not allow the presentation ofthe entire developed system.

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