GB2344546A

GB2344546A - Bend forming apparatus

Info

Publication number: GB2344546A
Application number: GB9827242A
Authority: GB
Inventors: Ronald Arthur George King
Original assignee: BELSIZE ENGINEERING Co LI
Current assignee: BELSIZE ENGINEERING Co LI
Priority date: 1998-12-10
Filing date: 1998-12-10
Publication date: 2000-06-14
Also published as: GB9827242D0

Abstract

A cold-forming press form tool for bending a workpiece 106 about a predetermined bend axis, comprising: top and bottom clamping tools 100, 101 with parallel-opposed clamping surfaces for holding therebetween the workpiece on one side, the inside, of the intended bend; a folding ram mounted to the bottom clamping tool for rotation about a support axis parallel to the bend axis and on the inner side of the bend axis, adjacent the clamping surfaces, the folding ram 105 having a flat abutment surface for engaging a portion of the workpiece projecting from the clamping surfaces on the other side, the outside, of the intended bend, the arrangement being such that the abutment surface can rotate in a folding path about the bend axis progressively as the folding ram rotates in the same sense about its support axis; and means for driving the folding ram along its said folding path to fold the workpiece about its intended bend on the bend axis, whereby in use there is minimal tendency for sliding movement of the folding ram over the workpiece during folding, and the folding pressure is spread over the flat surface.

Description

Bend forming apparatus The present invention relates to bend forming apparatus, and is especially useful for cold forming sheet metal blanks.

Figures 2a to 2c show an example of a known clapper box tooling method for cold forming bends in sheet metal workpieces. The method involves placing a sheet metal workpiece 203 between a punch 201 and the base 204 of a clapper box having hinged sides 202. The base 204 is itself supported by a ram 205. Figure 2a shows the situation when two workpieces 203 are placed into the clapper box ready for bending. The workpiece 203 protrudes from the punch and extends over a respective clapper box side 202. Each side 202 rests on a respective cam 206. The punch 201 drives the clapper box down relative to the cams 206 to the position shown in Figure 2b, where a bend is partly formed in each workpiece 203. This downward motion relative to the stationary cams 206 forces the sides 202 to rotate about their hinges as illustrated, and in tum the sides 202 bend the protruding workpieces 203. Figure 2c illustrates the situation when a complete bend has been formed.

There are several problems with the clapper box method and with other known methods of cold forming bends in sheet metal. For example, wipe, score, rolling or forming marks are often created on the workpiece as a result of the bending process. Also, the clamping pressure provided is typically inadequate. Further, it is not easy to bend short legs in workpieces because too little projects from the clamp. If the workpiece has surface features such as half shears these are difficult to accommodate either on the clamped or the formed leg and extrusions of the metal on the outside of the bend often occur. Another problem is that irregular leg lengths may result from the bending process and it is difficult to hold tight tolerances on the bends and legs. As well as this, a high rate of tool wear typically results.

It is accordingly an object of the present invention to provide a bend forming apparatus which overcomes or at least mitigates one or more of the problems noted above.

According to a first invention, a cold-forming machine tool for bending a workpiece about a predetermined bend axis comprises : top and bottom clamping tools with parallelopposed clamping surfaces for holding therebetween the workpiece on one side, the inside, of the intended bend; a folding ram mounted to the bottom clamping tool for rotation about a support axis parallel to the bend axis and on the inner side of the bend axis, adjacent the clamping surfaces, the folding ram having a flat abutment surface for engaging a portion of the workpiece projecting from the clamping surfaces on the other side, the outside, of the intended bend, the arrangement being such that the abutment surface can rotate in a folding path about the bend axis progressively as the folding ram rotates in the same sense about its support axis; and means for driving the folding ram along its said folding path to fold the workpiece about its intended bend on the bend axis, whereby in use friction between the workpiece and the folding ram tends to drive the workpiece towards the top and bottom clamping tools for at least the first half of a folding operation.

A corresponding method of cold-forming a workpiece to bend it about a predetermined bend axis, using a cold-forming machine tool as described immediately above, comprises clamping the workpiece in between the top and bottom clamping tools and then operating the tool to cause the driving means to drive the folding ram along its folding path to fold the workpiece about its intended bend on the bend axis, such that friction between the workpiece and the folding ram tends to drive the workpiece towards the top and bottom clamping tools for at least the first half of a folding operation.

According to a second invention, a cold-forming machine tool for bending a workpiece about a predetermined bend axis comprises: top and bottom clamping tools with parallel-opposed clamping surfaces for holding therebetween the workpiece on one side, the inside, of the intended bend; an articulated folding ram comprising a folding body with a flat abutment surface connected pivotally to a linkage which is connected pivotally to the bottom clamping tool for rotation about a support axis parallel to the bend axis and on the inner side of the bend axis, adjacent the clamping surfaces, the flat abutment surface being suitable for engaging a portion of the workpiece projecting from the clamping surfaces on the other side, the outside, of the intended bend, the arrangement being such that the abutment surface can rotate in a folding path about the bend axis progressively as the folding body rotates in the same sense about its support axis; and means for driving the folding body along its said folding path to fold the workpiece about its intended bend on the bend axis.

The second invention also provides a corresponding method of bending a workpiece using such a tool, comprising clamping the workpiece in between the top and bottom clamping tools and then operating the machine tool to cause the driving means to drive the folding body along its folding path to fold the workpiece about its intended bend on the bend axis.

The inventions make it is possible to form a bend in a metal blank or workpiece where one leg of the intended product is too short to be held or formed using any of the conventional bending processes or where the surface characteristics of the workpiece are such that existing techniques cannot be applied. In this way workpieces such as automotive gear selector forks are manufactured at economic speeds and volumes. Because the friction between the workpiece and the folding ram tends to drive the workpiece towards the top and bottom clamping tools, for at least the first half of a folding operation, this makes the workpiece more secure in its location in the clamp and enables short workpieces to be folded.

A preferred embodiment of the inventions will now be described, by way of example only, with reference to the accompanying drawings in which: Figures 1a to 1c are vertical cross sections through a cold forming press form tool embodying the present invention, showing two workpieces clamped into the assembly, Figure 1a showing the workpieces prior to bending, Figure 1b showing the two workpieces partly bent, and Figure 1c showing the two workpieces fully bent; Figures 2a to 2c are vertical cross sections through a press with conventional clapper box tooling, showing two workpieces clamped into the assembly, Figure 2a showing the workpieces prior to bending, Figure 2b showing the two workpieces partly bent, and Figure 2c showing the two workpieces fully bent; Figure 3 is a cross section through a cam block; and Figures 4a to 4c are the same as Figures 1 a to 1 c but show a coining or kicking block.

Figures 1a to 1c are vertical cross sections through the centre of an hydraulic fine blanking press form tool 10 at various stages in the process of cold forming a bend in workpieces 106 which in this example are metal blanks. Figure 1a illustrates the situation when two identical workpieces 106 are clamped between a top clamping tool or form punch 100 and a bottom clamping tool or seating pad 101 prior to bend formation. Figure 1b illustrates the situation when a bend has been partly formed in each workpiece 106 and Figure 1 c illustrates the situation when the bends are fully formed.

As shown in Figure 1, the press form tool 10 comprises a top die set 20, the form punch 100, the seating pad 101, and a bottom die set 102. The seating pad 101 is provided below the form punch 100 and one end of each workpiece 106 is clamped between the seating pad 101 and the form punch 100 as shown.

The press form tool shown in Figure 1 illustrates an arrangement that allows pairs of components to be worked on simultaneously. This is provided by providing symmetry in the assembly about the median plane on the central punch axis A-A. This helps to balance out the assembly and to allow side loads on the form punch 100 and seating pad 101 to be equalised. However, it is not essential to do this: the assembly may simply comprise the parts shown on one side of the vertical line A-A.

At each side of the press form tool 10, a folding ram comprising a roller 105 journalled between a pair of spaced parallel linkages 104 is provided. One end of each linkage 104 is pivotally connected to the seating pad 101 via a pin 107 on a horizontal support axis which is substantially parallel to the axis of the bends to be formed in the workpieces. Each roller 105 is generally cylindrical, but a central, working portion is formed with a flat as shown in the drawings, giving the working portion a D section. The flat working or abutment surface of the roller 105 contacts the underside of the leg of the workpiece that protrudes from the form punch 100 and the seating pad 101. It is not essential for the roller to be generally cylindrical in shape ; any other suitable shape with a flat working surface can be used.

Each linkage 104 has an arcuate shape, its inner edge surface being a 90 bend with a radius corresponding to the intended outer radius of the bent workpiece 106, so that each linkage 104 will abut the finished component as shown in Figure 1c. It is not essential for the inner edge surface of the folding links to form a 90 bend ; any other suitable curved surface can be used depending on the desired shape of bend to be produced.

As shown in Figure 1b, each fixed cam block 103 has a sloping surface 108 facing the respective roller 105. The sloping surface 108 has five flat contiguous sections 108a to 108e, and the cam block 103 has this same section all along its length. The five flat contiguous sections 108a to 108e are shown in more detail in figure 3. The first 108a and fifth 108e sections are vertical; the second 108b and fourth 108d sections are inclined at about 45 and 50 respectively to the horizontal, and the middle, third section 108c is inclined at about 20 to the horizontal. These inclinations provide an appropriate cam action driving the roller 105 as described below.

The cam blocks 103 rest on a fixed die set 102, with transverse shoulders locking them in place and preventing them sliding outwards. The seating pad 101 is sized and shaped to fit into a channel in the bottom die set 102 through which it slides. Shoulders 110,111 are provided on the seating element so that the seating element cannot pass through the vertical channel in the bottom die set 102. Shoulders 112 on the bottom die set 102 are also provided which engage with shoulders 110 on the seating element as shown in Figure 1c.

In one embodiment the top and bottom clamping tools are connected or integrated into an hydraulic control system (not shown). In an alternative embodiment only the top clamping tool is provided with hydraulic control and the bottom clamping tool rests on an air cushion or other fluid cushion.

Another embodiment is shown in figures 4a to 4c. A coining or kicking block 400 is fixed to the die set 102 and extends along the die set 102 parallel to the roller 105 and behind the linkage 104. The coining or kicking block 400 has a protruding edge which extends along its length. This protruding edge has an approximately 45 degree surface which slopes towards the seating pad 101 as shown in figures 4a to 4c and which is shaped to fit against the workpiece towards the end of the bending process. However, the protruding edge of the coining or kicking block may have different shapes depending on the desired final form of the workpiece after bending. The coining or kicking block 400 does not touch the roller 105 at any stage in the bending process.

The bending process is commenced by loading the two flat workpieces 106 onto the seating pad 101, the horizontal flats of the rollers 105 and the upper surfaces of the cam blocks 103, which are all at the same height. The punch 100 is lowered onto the workpieces 106 to clamp them. The weight of the seating pad 101 and the workpieces 106, and the downward force of the punch 100, are balanced by the reaction force from the sliding pad 101 slides through die set 102.

Increased ram or punch 100 pressure causes the seating pad 101 to move downwards with the form punch 100 relative to the cam blocks 103. The reaction from the inclined surfaces 108 of the cam block and thus on the rollers 105 causes a torque on the respective linkages 104, and the rollers 105, whose flats engage the workpieces 106 without sliding, bend the workpieces about their clamped edges. The linkages 104 rotate progressively as the seating pad 101 slides down relative to the bottom die set 102. Thus each roller flat rotates in a folding path about the bend axis progressively as the folding ram 104 rotates in the same sense about its support axis 107. Also, the folding rams rotate about pins 107 through about 30 to 40 , only a fraction of the 90 angle of rotation of the roller flats along their folding paths. The cold forming press form tool 10 does not create any significant scores, wipes or other marks on the workpiece surface because the roller flats do not move along the surfaces of the workpieces and the folding force is spread over the surface area of the roller flats. Also, the folding rather than wiping action provides a more consistent bend radius and less extrusion on the outside of the bend and consequently a stronger and more accurate bend.

As the seating pad 101, form punch 100 and workpieces move downwards relative to the fixed cam blocks 103, the rollers 105 also move along the sloping cam block surfaces 108. As described above, the sloping cam block surfaces have five flat contiguous sections 108a to 108e and these provide an appropriate cam action to drive the roller 105. At the start of the bending process, as shown in Figure 1a, the roller 105 rests against surface 108b (which is at 45 to the horizontal) and surface 108c (which is at 20 to the horizontal).

Together surfaces 108a, 108b and 108c form a concave surface which act to cup and hold the roller 105 so that the roller flat is against the underside of the workpiece 106 as shown.

As me seating pad 101, form punch 100 and workpieces move downwards relative to the fixed cam blocks 103, the roller 105 rolls without sliding over cam surfaces 108b and 108c and towards cam surface 108d which is at 50 to the horizontal. The cam surfaces drive the roller 105 so that the roller rotates and the roller flat contacts the underside of the workpiece 106 as shown in Figure 1 b. As the roller 105 moves over the cam surface 108d onto the end of the sloping cam surface 108e (which is vertical) it rotates to its fullest extent and folds the workpiece to create a substantially 90 bend as shown in Figure 1c. The parts of the workpiece that are bent upwards eventually abut the sides of the form punch 100 as shown and this helps to create the desired bend in the workpiece.

The friction between the workpiece and the roller flat creates a force whose component along the workpiece is directed towards the punch 100 and seating pad 101 for at least the first half of the folding operation. It is only towards the end of the operation that the workpiece has bent so far that the inclination of its contact surface with the roller causes the force component to tend to pull the workpiece out of the clamp; but by then the clamp is well able to counter such a force by the reaction force it exerts on the workpiece near the bend. The inward direction of the force along the workpiece is advantageous because the workpiece is driven towards its location between the punch 100 and seating pad 101 and is held securely in place during at least the first half of the folding operation, in which the major part of the work to fold the workpiece occurs. This improves the performance of the cold forming apparatus and enables the pressure applied to the punch 100 and seating pad 101 to be reduced. This saves operating costs.

The roller flat engages the workpiece over a strip equal to the length of the Dshaped flat (from left to right in Figure 1a), the inner edge of this strip being very close to the seating pad 101 about which the component bends. This ensures that a folding force is applied close to the desired bend which helps to minimise extrusions around the bend region. Also, the concave arcuate shape of the linkages 104 enables the folding rams to rotate close to the bend axis without interference. A small degree of overbend is often applied to provide for a small amount of spring back. For example, an initial bend of 91.5 may be created in order to achieve a final 90 bend.

During the folding operation there is (despite the friction therebetween) some minimal sliding movement between the roller flat and the workpiece. Because this sliding movement is minimal, wipe, score, rolling and forming marks on the workpiece are substantially reduced or eliminated. Also the rate of tool wear is reduced. The amount of this sliding movement, i. e. the distance of relative movement along the contact surface from beginning to end of the folding operation, varies according to the thickness of the workpiece and the following measurements of this sliding movement have been obtained empirically:

Thickness of workpiece (mm) Amount of sliding movement between the workpiece and the roller flat that occurs in one folding operation (mm) 4 14. 2 6 16. 0 8 17. ~~ The region of contact between the roller and the sloping cam surface 108a to 108e is at a radius from the support axis 107 which decreases progressively as the roller is turned along its path to fold the workpiece, thereby progressively decreasing the mechanical advantage of the cam action. When the press is controlled hydraulically, the speed of the clamping tools can be controlled by the relative hydraulic pressures of the form punch 100 and the seating element 101.

Once the bend has been formed in the workpiece 106, the top die set 20 is retracted. This allows the workpieces 106 to be removed from the press. In the embodiment where the form punch 100 and seating pad 101 are both hydraulically controlled this process is particularly effective because the seating pad 101 can be raised hydraulically to allow removal of the workpieces.

In the embodiment shown in figures 4a to 4c the coining or kicking block 400 is used to aid the bending process. As the ram or punch 100 pressure increases, the seating pad 101 moves down relative to the cam blocks 103 and the coining or kicking blocks 400. The cam blocks 103 act on the rollers 105 whose flats engage the workpieces 106 to bend the workpieces. Towards the end of the bending operation the bending force of the roller flats on the workpiece 106 is reduced. This is because when the roller flats are closer to the bend point the moment of the force from the roller flats on the workpiece 106 is reduced. By using a coining or kicking block 400 an additional force is applied to the workpiece 106 at the stage when the force of the roller flats on the workpiece 106 is reduced. Towards the end of the bending process, as the seating pad 101 moves down relative to the cam blocks 103 and the coining or kicking block 400, the protruding edge of the coining or kicking block eventually contacts the underside of the workpiece around the bend region. The ram or punch 100 pressure forces the workpiece down onto the protruding edge of the coining or kicking block, which produces a reaction force on the workpiece and aids the bending process. By using different shapes of protruding surface on the coining or kicking block, different effects can be achieved. For example, if the protruding surface is shaped so that it extends around part of the leg of the workpiece that is being bent, then the coining or kicking block helps to overbend the workpiece.

The bending assembly can be used to form automotive gear selector forks and detent levers for automatic gearboxes. The workpiece or blank material is, for example, steel and the thickness can range from around 3 mm to around 10 mm. However, this range varies according to the characteristics of the material used.

Surface features on the clamped leg of the workpiece such as half shears can easily be accommodated within the punch 100 and seating pad 101. Significant half shears and holes in the clamped part of the workpiece can help location and clamping of the workpiece.

The configuration of the press allows an earlier bend on a different axis of the workpiece 106 to be accommodated by carefully arranging the location of the folding rams 104,105 and providing clearance on the form punch 100. For example, two 90 bends on different axes of a gear selector fork can be formed by successive bending processes.

The embodiments described are press form tools although the invention could equally well be implemented using any suitable type of cold-forming apparatus, such as a hydraulic or mechanical fixture which has more than one working force direction.

Claims

Claims 1. A cold-forming machine tool for bending a workpiece about a predetermined bend axis, comprising: top and bottom clamping tools with parallel-opposed clamping surfaces for holding therebetween the workpiece on one side, the inside, of the intended bend; a folding ram mounted to the bottom clamping tool for rotation about a support axis parallel to the bend axis and on the inner side of the bend axis, adjacent the clamping surfaces, the folding ram having a flat abutment surface for engaging a portion of the workpiece projecting from the clamping surfaces on the other side, the outside, of the intended bend, the arrangement being such that the abutment surface can rotate in a folding path about the bend axis progressively as the folding ram rotates in the same sense about its support axis; and means for driving the folding ram along its said folding path to fold the workpiece about its intended bend on the bend axis, whereby in use friction between the workpiece and the folding ram tends to drive the workpiece towards the top and bottom clamping tools for at least the first half of a folding operation.
2. A cold-forming machine tool for bending a workpiece about a predetermined bend axis, comprising: top and bottom clamping tools with parallel-opposed clamping surfaces for holding therebetween the workpiece on one side, the inside, of the intended bend; an articulated folding ram comprising a folding body with a flat abutment surface connected pivotally to a linkage which is connected pivotally to the bottom clamping tool for rotation about a support axis parallel to the bend axis and on the inner side of the bend axis, adjacent the clamping surfaces, the flat abutment surface being suitable for engaging a portion of the workpiece projecting from the clamping surfaces on the other side, the outside, of the intended bend, the arrangement being such that the abutment surface can rotate in a folding path about the bend axis progressively as the folding body rotates in the same sense about its support axis; and means for driving the folding body along its said folding path to fold the workpiece about its intended bend on the bend axis.
3. A cold-forming machine tool according to Claim 2, in which the drive means comprises a cam block outside the bend axis, having a cam surface extending parallel to the bend axis and facing the folding body, the cam surface being inclined to a machine tool axis along which the top and bottom clamping tools are moveable relative to the cam block, such relative movement causing the cam block, in use, progressively to drive the folding ram along its folding path.
4. A cold-forming machine tool according to Claim 2 or Claim 3, in which the folding body is a roller with a flat providing the flat abutment surface, the roller being joumalled for rotation on the linkage.
5. A cold-forming machine tool according to Claim 2,3 or 4, in which the articulation is such that the linkage rotates through a fraction of the angle of rotation of the flat abutment surface along its folding path.
6. A cold-forming machine tool according to any of Claims 2 to 5, in which the linkage is concave to the bend axis to enable it to rotate close to the bend axis without interference.
7. A cold-forming machine tool according to any preceding claim, the arrangement being such that the flat abutment surface tums substantially through a right-angle along its folding path to produce a right-angle fold.
8. A cold-forming machine tool according to Claim 3 or any preceding claim dependent on Claim 3, in which the cam surface is inclined such that its region of contact with the folding body, in use, is at a radius from the support axis which decreases progressively as the folding body is turned along its path to fold the workpiece, thereby progressively decreasing the mechanical advantage of the cam action.
9. A cold-forming machine tool according to Claim 8, in which the cam surface is polygonal in section.
10. A cold-forming machine tool according to any preceding claim, the machine tool being an hydraulic fine-blanking press having top and bottom hydraulic rams acting in opposite directions respectively on the top and bottom clamping tools.
11. A cold-forming machine tool according to any of Claims 1 to 9, in which the top clamping tool is driven by an hydraulic ram and the bottom clamping tool is biased upwardly by a fluid cushion.
12. A cold-forming machine tool according to any preceding claim, in which the clamping surfaces are arranged to accommodate two balanced workpieces disposed side by side, and comprising opposed pairs of the said folding rams and drive means.
13. A cold-forming machine tool according to any preceding claim, whose components are configured so as to accommodate a workpiece of which the projecting portion already contains a bend.
14. A machine tool for bending a workpiece, substantially as described herein with reference to the accompanying drawings.
15. A method of cold-forming a workpiece to bend it about a predetermined bend axis, using a cold-forming machine tool according to claim 1 or any preceding claim dependent on claim 1, comprising clamping the workpiece in between the top and bottom clamping tools and then operating the machine tool to cause the driving means to drive the folding ram along its folding path to fold the workpiece about its intended bend on the bend axis, such that friction between the workpiece and the folding ram tends to drive the workpiece towards the top and bottom clamping tools for at least the first half of a folding operation.
16. A method of cold-forming a workpiece to bend it about a pre-determined bend axis, using a cold-forming machine tool according to claim 2 or any preceding claim dependent on claim 2, comprising clamping the workpiece in between the top and bottom clamping tools and then operating the machine tool to cause the driving means to drive the folding body along its folding path to fold the workpiece about its intended bend on the bend axis.