Efficiencies that used to be limited to factories are now commonplace in garage workshops. Machine tools such as welders, metal saws and even plasma cutters have become relatively affordable. With your ability to fabricate metal, you'll need to be able to efficiently bend metal. You can build bending tools yourself, either for one specialized job or for repetitive production

Read more: Homemade Metal Rod Bending Jigs | eHow.com http://www.ehow.com/info_8744553_homemade-metal-rod-bending-jigs.html#ixzz25P8f5zgw

he possibilities of a Semi-Circular Bending (SCB) test onsemi-cylindrical specimens is investigated as an alternative tothe Indirect Tensile Test (ITT) to determine the flexural strength,stiffness and fatigue behaviour of asphalt concrete. Finite elementanalysis relations for the stresses and deformations under SCBhave been derived. Based on these relations the tensile strengthand fatigue behaviour of two asphalt mixes were determined withlaboratory tests. These results have been compared with ITT resultson the same mixes.

It can be concluded that the SCB gives results comparable withITT for the tensile strength. The determination of stiffness requiresaccurate measurement of the relatively small vertical deformationsunder loading. Fatigue tests can also be carried out. The SCBtest can be used as a mix design test for performance relatedspecifications and a reliable quality control test for mix productionand road construction. A standard test set-up is proposed.

Tube bendingFrom Wikipedia, the free encyclopediaJump to: navigation, search

Bent tubing

Shown is a trombone, it displays some U-bends

Tube bending is the umbrella term for metal forming processes used to permanently form pipes or tubing. One has to differentiate between form-bound and freeform-bending procedures, as well as between heat supported and cold forming procedures.

Form bound bending procedures like “press bending” or “rotary draw bending” are used to form the work piece into the shape of a die. Straight tube stock can be formed using a bending machine to create a variety of single or multiple bends and to shape the piece into the desired form. This processes can be used to form complex shapes out of different types of ductile metal tubing.[1] Freeform-bending processes, like three-roll-pushbending, shape the workpiece kinematically, thus the bending contour is not dependent on the tool geometry.

Generally, round stock is what is used in tube bending. However, square and rectangular tubes and pipes may also be bent to meet job specifications. Other factors involved in the tube bending process is the wall thickness, tooling and lubricants needed by the pipe and tube bender to best shape the material.

Contents 1 Geometry 2 Processes

o 2.1 Press bending o 2.2 Rotary draw bending o 2.3 Three-Roll Push Bending

2.3.1 Roll bending o 2.4 Heat-induction o 2.5 Roll benders o 2.6 Sand-packing/hot-slab forming

3 Mandrels

o 3.1 Bending springs 4 References 5 External links

GeometryA tube can be bent in multiple directions and angles. Common simple bends consist of forming elbows, which are bends that range from 2 to 90°, and U-bends, which are 180° bends. More complex geometries include multiple two-dimensional (2D) bends and three-dimensional (3D) bends. A 2D tube has the openings on the same plane; a 3D has openings on different planes.

A two plane bend or compound bend is defined as a compound bend that has a bend in the plan view and a bend in the elevation. When calculating a 2 plane bend you must know the bend angle and rotation (dihedral angle).

One side effect of bending the workpiece is the wall thickness changes; the wall along the inner radius of the tube becomes thicker and the outer wall becomes thinner. To overcome this the tube may be supported internally or externally to preserve the cross section. Depending on the bend angle, wall thickness, and bending process the inside of the wall may wrinkle.

ProcessesTube bending as a process starts with loading a tube into a pipe bender and clamping it into place between two dies, the clamping block and the forming die. The tube is also loosely held by two other dies, the wiper die and the pressure die.

The process of tube bending involves using mechanical force to push stock material pipe or tubing against a die, forcing the pipe or tube to conform to the shape of the die. Often, stock tubing is held firmly in place while the end is rotated and rolled around the die. Other forms of processing including pushing stock through rollers that bend it into a simple curve.[2] For some tube bending processing, a mandrel is placed inside the tube to prevent collapsing. The tube is also held in tension by a wiper die to prevent any creasing during stress. A wiper die is usually made of a softer alloy i.e. aluminum, brass to avoid scratching or damaging the material being bent.

Much of the tooling is made of hardened steel or tooled steel to maintain and prolong the tools life. However wherever there is a concern of scratching or gouging the work piece, a softer material such as aluminum or bronze is utilized. For example, the clamping block, rotating form block and pressure die are often formed from the hardened steel because the tubing is not moving past these parts of the machine. On the other hand, the pressure die and the wiping die are formed from aluminum or bronze to maintain the shape and surface of the workpiece as it slides by.

Pipe bending machines are typically human powered, pneumatic powered, hydraulic assisted, hydraulic driven, or electric servomotor.

Press bending

Probably will be the first bending process used on cold pipes and tubing. In this process a die in the shape of the bend is pressed against the pipe forcing the pipe to fit the shape of the bend. Because the pipe is not supported internally there is some deformation of the shape of the pipe giving an ovular cross section. This process is used where a consistent cross section of the pipe is not required. Although a single die can produce various shapes, it only works for one size tube and radius.

Rotary draw bending

Rotary draw bending (RDB) is a precise technology, since it bends using tooling or "die sets" which have a constant center line radius (CLR), alternatively indicated as Mean Bending Radius (Rm). Rotary draw benders can be programmable to store multiple bend jobs with varying degrees of bending. Often a positioning index table (IDX) is attached to the bender allowing the operator to reproduce complex bends which can have multiple bends and differing planes. Rotary draw benders are the most popular machines for use in bending tube, pipe and solids for applications like: handrails, frames, motor vehicle roll cages, handles, lines and much more. Rotary draw benders create aesthetically pleasing bends when the right tooling is matched to the application. CNC rotary draw bending machines can be very complex and use sophisticated tooling to produce severe bends with high quality requirements.

The complete tooling is required only for high-precision bending of difficult-to-bend tubes with relatively large OD/t (diameter/thickness) ratio and relatively small ratio between the mean bending radius Rm and OD[3].

Full tooling for rotary draw bending

The use of axial boosting either on the tube free end or on the pressure die is useful to prevent excessive thinning and collapse of the extrados of the tube. The mandrel, with or without ball with spherical links, is mostly used to prevent wrinkles and ovalization. For relatively easy bending processes (that is, as the difficulty factor BF decreases), the tooling can be progressively simplified, eliminating the need for the axial assist, the mandrel, and the wiper die (which mostly prevents wrinkling). Furthermore, in some particular cases, the standard tooling must be modified in order to meet specific requirements of the products.

Three-Roll Push Bending

The Three-Roll Push Bending (TRPB) is the most commonly used freeform-bending process to manufacture bending geometries consisting of several plane bending curves. Nevertheless, a 3D-shaping is possible. The profile is guided between bending-roll and supporting-roll(s), while being pushed through the tools. The position of the forming-roll defines the bending radius. The bending point is the tangent-point between tube and bending-roll. To change the bending plane, the pusher rotates the tube around its longitudinal axis. Generally, a TRPB tool kit can be applied on a conventional rotary draw bending machine.

Three roll push bending process

The process is very flexible since with a unique tool set, several bending radii values Rm can be obtained, although the geometrical precision of the process is not comparable to rotary draw bending [4] .

Bending contours defined as spline- or polynomial-functions can be manufactured.[5]

Roll bending

Main article: Roll bending

Three roll bending of tubes and open profiles can also be performed with simpler machines, often semi-automatic and non CNC controlled, able to feed the tube into the bending zone by friction. These machines have often a vertical layout, i.e. the three rolls lay on a vertical plane.

Heat-induction

An induction coil is placed around a small section of the pipe at the bend point. It is then heated to between 800 and 2,200 degrees Fahrenheit (430 and 1,200 °C). While the pipe is hot, pressure is placed on the pipe to bend it. The pipe is then quenched with either air or water spray. Heat-Induction bending is used on large pipes such as freeway signs, power plants, and petroleum pipe lines.

Roll benders

During the roll bending process the pipe, extrusion, or solid is passed through a series of rollers (typically 3) that apply pressure to the pipe gradually changing the bend radius in the pipe. The pyramid style roll benders have one moving roll, usually the top roll. Double pinch type roll benders have two adjustable rolls, usually the bottom rolls, and a fixed top roll. This method of bending causes very little deformation in the cross section of the pipe. This process is suited to producing coils of pipe as well as long gentle bends like those used in truss systems.

Sand-packing/hot-slab forming

In the sand packing process the pipe is filled with fine sand and the ends are capped. The pipe is then heated in a furnace to 1,600 °F (870 °C) or higher. The pipe is then placed on a slab with pins set in it. The pipe is then bent around the pins using a winch, crane, or some other mechanical force. The sand in the pipe minimizes distortion in the pipe cross section.

MandrelsA mandrel is a steel rod or linked ball inserted into the tube while it is being bent to give the tube extra support to reduce wrinkling and breaking the tube during this process. The different types of mandrels are as follows.

1. Plug mandrel, a solid rod used on normal bends.2. Form mandrel, a solid rod with curved end used on bend when more support is need.3. Ball mandrel without cable, unlinked steel ball bearings inserted into tube, used on

critical and precise bends.4. Ball mandrel with cable, linked ball bearings inserted into tube, used on critical bend and

precise bends.5. Sand, sand packed into tube.

In production of a product where the bend is not critical a plug mandrel can be used. A form type tapers the end of the mandrel to provide more support in the bend of the tube. When precise bending is needed a ball mandrel (or ball mandrel with steel cable) should be used. The conjoined ball-like disks are inserted into the tubing to allow for bending while maintaining the same diameter throughout. Other styles include using sand, cerrobend, or frozen water. These allow for a somewhat constant diameter while providing an inexpensive alternative to the aforementioned styles.

Performance automotive or motorcycle exhaust pipe is a common application for a mandrel.

Bending springs

These are strong but flexible springs inserted into a pipe to support the pipe walls during manual bending. They have diameters only slightly less than the internal diameter of the pipe to be bent. They are only suitable for bending 15-and-22 mm (0.6-and-0.9 in) soft copper pipe (typically used in household plumbing) or PVC pipe.

The spring is pushed into the pipe until its center is roughly where the bend is to be. A length of flexible wire can be attached to the end of the spring to facilitate its removal. The pipe is generally held against the flexed knee, and the ends of the pipe are pulled up to create the bend. To make it easier to retrieve the spring from the pipe, it is a good idea to bend the pipe slightly more than required, and then slacken it off a little. They are less cumbersome than rotary benders, but are not suitable for bending short lengths of piping when it is difficult to get the required leverage on the pipe ends.

Bending springs for smaller diameter pipes (10 mm copper pipe) slide over the pipe instead of inside.

References1. ̂ Todd, Robert H.; Allen, Dell K.; Alting, Leo (1994), Manufacturing Processes

Reference Guide (1st ed.), Industrial Press Inc., ISBN 0-8311-3049-0.2. ̂ Pipe Bending Methods, retrieved 2009-02-01.3. ̂ Mentella, A.; Strano, M. (10 October 2011). "Rotary draw bending of small diameter

copper tubes: predicting the quality of the cross-section". Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture 226 (2): 267–278. doi:10.1177/0954405411416306.

4. ̂ Strano, Matteo; B.M. Colosimo, E. Del Castillo (2011). "Improved design of a three roll tube bending process under geometrical uncertainties". Esaform. AIP Conf. Proc. 1353: 35-40. doi:10.1063/1.3589488.

5. ̂ Engel, B.; Kersten, S.; Anders, D. (2011), "Spline-Interpolation and Calculation of Machine Parameters for the Three-Roll-Pushbending of Spline-Contours", Steel Research International 82 (10)

2. Table of Factors and Terms For Bending Formulas3. B = degree of bend4. E = feathered edge thickness5. Fb = bend difficulty factor6. Fd = "D" of bend7. Fw = wall factor8. Kr = constant for rigidity9. Ks = constant for minimum clamp length10. Kz = constant for feathered edge11. Lc = clamp length12. Lp = pressure die length13. Mb = mandrel ball diameter14. Md = mandrel nose diameter

15. Mm = mandrel body diameter16. Mr = mandrel nose radius17. Pe = percentage of elongation at arc18. Pt = percentage of wall-thinning19. Pw = wall thickness after thinning20. R = centerline radius21. Ri = inside radius22. Ro = outside radius23. S = maximum set-up depth24. T = tube outside diameter25. Ti = tube inside diameter26. W = wall thickness27. Wi = thickness of inside lamination28. Wo = thickness of outside lamination29.

30. Tube inside diameter:31. Ti = T - ( W x 2 )32.

33. Inside radius:34. Ri = R - ( T / 2 )35.

36. Outside radius:37. Ro = R + ( T / 2 )38.

39. Wall factor:40. Fw = T / W41.

42. "D" of bend:43. Fd = R / T44.

45. Bend difficulty rating (the higher the value, the more difficult the bend is to make; rule of thumb only):

46. Where "Kr" = a constant for material rigidity (assign the same value to "Kr" as you would to calculate pressure die length; a value of 2 is suitable for most applications; click here for more information) and "n1" through "n4" are values to adjust the weight of each factor in the equation (see below for our recommended weighting):

47. General formula:  Fb = [ ( n1 x Kr ) + ( n2 x Fw ) + ( ( n3 x B ) / 180 ) ) ] / [ n4 x Fd ]

48. Formula with recommended weighting:  Fb = [ 2Kr + .2Fw +  ( B / 180 ) ] / [ Fd ] 49. Note: A bend difficulty rating (calculated with our recommended weighting) of 7 or

less indicates a bend that is relatively simple to produce with the rotary-draw

method.  Factors in excess of 7 typically require either additional precision in set-up or close attention during production in order to hold the set-up parameters.

50.

51. Wall-thinning of extrados at outside radius after bending (rule of thumb only):52. Where "Pt" = percentage of wall-thinning and "Pw" = targeted thickness of wall after

thinning out from bending:53. Pt = ( Ro - R ) / Ro 54. Pw = W x ( 1 - Pt )55.

56. Percentage of elongation at arc of the bend (rule of thumb only):57. Pe = ( Ro / R ) - 158.

59. Mandrel nose diameter for single-wall tubing:60. Md = T - ( W x 2.21 )61.

62. Mandrel nose diameter for double-wall tubing:63. Where "Wo" = wall thickness of outside lamination and "Wi" = wall thickness of inside

lamination:64. Md = ( T - ( Wo x 2 ) ) - ( Wi x 2.21 )65.

66. Mandrel nose radius:67. if Fw < 50 then Mr = Md x .1 else Mr = Md x .0268.

69. Mandrel body diameter:70. Mm = Md x .99571.

72. Mandrel ball diameter:73. Mb = Md x .99874.

75. Maximum set-up depth of mandrel nose relative to the line of tangency, as measured from nose end (including nose radius):

76. S = [ ( R + ( T / 2) - W )2 - ( R + ( Md / 2 ) )2 ]1/2 + Mr

77.

78. Wiper feathered edge thickness (simple-sweep geometry only):79. Where "Kz" = a constant approaching zero depending upon limitations of material

and method of manufacturing (with current technology, a value of .0025 is reasonable for "Kz"):

80. if T x Kz > .006* then E = T x Kz else E = .006*81. * Inches.  For metric applications, substitute .15 millimeters.

82.

83. Clamp length:84. Where "Kr" = a constant for material rigidity (assign a value of 2 to "Kr" for most

applications; click here for more information) and "Ks" = a constant limiting the minimum clamp length depending upon the surface of the cavity (assign to "Ks" the value of 2 for smooth cavities and 1 for serrated cavities; click here for more information):

85. if ( T x ( Kr x 2.5) ) - R < T x Ks then Lc = T x Ks else Lc = ( T x ( Kr x 2.5) ) - R86.

87. Pressure die length:88. Where "Kr" = a constant for material rigidity (assign a value of 2 to "Kr" for most

applications; click here for more information):89. Lp = ( R x 3.14 x ( B / 180 ) ) + ( T x Kr )90.

91. Springback and radial growth:92. We are frequently asked for formulas to calculate springback and radial

growth.  While there are rules of thumb -- e.g., a radius will increase 1% for every "D" of bend -- they are not effective, as a true formula would be, in reducing the prove-out needed to lock in the parameters of a machine set-up.

93. Unfortunately, effective formulas for springback and radial growth have not been developed, because the factors involved include not only tube and bend specifications but also machine settings -- especially the radial pressure and axial pressure applied by the pressure die to the tube and the placement of the mandrel nose relative to the line of tangency.  How an operator sets these things on a particular make and model of machine alters where the neutral axis of a tube bend lies in relationship to the centerline of the radius, and it is the location of the neutral axis that determines how much springback and radial growth there will be.  Moreover, springback and radial growth are the result of fundamentally non-linear processes, which would make any effective formula that does account for all these factors fairly complex.  Presently, finite element analysis (FEA) is the only tool up to this task, and it is not yet practical for everyday use in the bend shop.

94. Fortunately, the trial-and-error needed to adjust for springback and radial growth does not have to be repeated for every set-up of a tube bend.  By using the "Four-Step Set-Up Method" to employ the "forward mandrel, low pressure" set-up for rotary-draw tube-bending, the parameters of a successful set-up can be recorded and then duplicated with little or no trial-and-error to prove out future set-ups of the same or similar tube bends.

Pipe bending machinesPipe bending made simple: With its comprehensive and efficient range of pipe bending machines, transfluid® offers unlimited bending options for all purposes. This range includes mobile pipe bending machines, compact and stationary mandrel bending machines and high-performance CNC bending machines.

These perfected pipe bending solutions from transfluid® can be customized to individual customer requirements. transfluid® pipe bending machines are available in semi-automatic or fully automatic versions and can be hydraulic or servo electric driven. Depending on their configuration these pipe bending machines can bend pipes to the left or to the right, to the left and to the right right, or in free-form. The pipe bending machines can be loaded and the bent pipes removed either by a fully automated handling system or by robots. 

With t control, transfluid® offers a powerful software package for its pipe bending machines and pipe forming machines to ensure efficient and reliable processes. Isometric drawings can be easily imported from all current CAD systems. This allows t control to offer a significant advantage for online design and enables secure planning even before pipe bending takes place. The software calculates the exact cut lengths, documents all pipe data and tests the pipe geometries for practicability in advance. This prevents collisions with the pipe bending machine, the tools or other elements.

3" Metal DIE PIPE TUBING BENDER New US $99.99

Tubing Bender Tubing benders come in many sizes, for use in everything from heavy construction to auto building to home landscaping. They range from a 16-ton hydraulic pipe bender to a handheld bender for small-gauge copper and aluminum tubing. All of them, however, use one of four basic methods.Ram bending is the cheapest and easiest method. The tube is restrained at two ends and a ram deforms the pipe in the middle. This is suitable for light gauge tubing only. Rotary draw bending is the most commonly used method, and maintains the diameter of the pipe without deformation. In this method, the tube is drawn through a stationary counter-bending die onto a forming die of a specified radius.Mandrel bending is used in the formation of exhaust pipes, process pipes, and any aluminum or stainless steel application where interior deformation can't be tolerated. Mandrel bending is similar to rotary draw bending, except that the interior of the tube is supported by a flexible mandrel. The mandrel bends with the tube, ensuring that the interior diameter is not deformed. Ring roll bending is used for bending pipes and tubes with a large diameter. There are three rollers, two on the bottom and one on the top. As the pipe is rolled through, the top roller exerts a downward pressure, bending the pipe. The pressure of the top roller can be adjusted manually or hydraulically, and either two or all three rollers can be powered. This method is used to make drum barrels, awnings, and other circular shapes.

g

Pipe and Tube Bending Principles

Bending is an important step in the process of manufacturing industrial pipes and tubing, which serve a vital role in both construction and the transportation of materials. Most bent pipes and tubes function as structural components or as “passageway” units that facilitate the transfer of substances. Structural tubing includes items such as handrails, handlebars,

furniture frames, and automobile roll cages, while passageway tubing is found in fuel and water lines, hydraulic systems, and exhaust lines. Tube and pipe bending can be accomplished through a number of different processes, including draw, press, ram, and roll bending, but each method is based upon the same fundamental concepts. Bending principles such as elongation and bend radius, as well as the tool functions of mandrels and wipers, form the foundation for most tube and pipe bending operations. These principles intersect in several ways that influence the effectiveness of pipe and tube manufacturing. Bending Forces As a tube or pipe is being bent, the exterior wall at the point of the bend begins to stretch and thin out. Simultaneously, the corresponding interior segment of the workpiece becomes thicker and more compressed. Controlling these degrees of physical deformation is important for creating a smooth rounded bend. Thick walled tubes bent at a wide radius are likely to have a relatively low degree of deformation, but thinner tubes may not. Bending services typically measure the wall factor, which is the ratio of a tube’s wall thickness to its external diameter, in order to determine whether a tube should be treated as a thin or thick workpiece. A similar comparison is made between the centerline radius and the tube’s external diameter to determine if a bending radius is tight or wide. The combination of the bending radius and the wall factor is used to designate the complexity of the bend. Under

parameters in which the interior and exterior walls would not be seriously comprised, a standard bending procedure can be performed with a basic die set, such as a bend, clamp, and pressure die array. The clamp die holds the tube in position, while the pressure die forces it against the bend die to curve into the desired shape. Mandrel Functions In many cases, the tubing workpiece does not fit the ideal criteria and cannot be properly shaped using a basic die set apparatus. As the wall factor measurement grows larger from the external wall thinning, the bend radius also grows tighter and increases the chances of producing a flattened bend. This usually occurs if the wall is too thin to maintain its integrity at the angle of the bend. A mandrel is often used to compensate for this weakness. The mandrel is a device that can be affixed to the interior of the tube at the point of the bend to provide support throughout the operation. It can be designed as a single plug or a sequence of balls that flex and adjust according to the bend. Aside from providing internal support for thin tubes, a plug mandrel can also be used to exert additional bending force on thicker tubes that are more difficult to shape. The Wiper Die Under more severe bending conditions, like those involving thin tubing undergoing a tight bend radius, internal wall compression may develop unevenly, resulting in a wrinkle defect. A wiper die may be necessary in order to reduce the risk of wrinkling on the workpiece. This wiper is designed to be wedged into the groove between the tube and the bending die, and it has a thin tip that reaches to the point where the tube will start to bend.  The wiper completes the gap between the bending die and the tube, leaving the tube constricted and removing any space for a wrinkle to develop. Wipers are often used in conjunction with a mandrel to further reduce the potential for deformation. Elongation 

Elongation is the degree to which a tube can stretch before undergoing structural failure or cracking. Given that material stretching occurs in essentially all tube and pipe bending procedures, elongation can be an important concern for manufacturers. In general, as a bending radius grows tighter, the material will stretch more. In some cases, material selection is dictated by the expected level of elongation. For example, stainless steel has a higher maximum elongation than other grades of steel, making it easier to bend without fracturing along a tight radius.