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Bending working procedure arrangement

The bending times and working procedure arrangement of the bending parts must be considered comprehensively according to the complexity of the shape of the workpiece, the performance of the material, the level of the precision requirement and the size of the production batch. Bending process arrangement for Stanzpresse is reasonable, can reduce the bending times, simplify the mold structure, improve the quality of the workpiece and labor productivity; If the arrangement is improper, it will lead to poor quality of the workpiece and scrap rate.

Principle of working arrangement of bending parts

1. Bending parts with simple shape, such as V-shaped, U-shaped and Z-shaped parts, can be formed once. Bending parts with complex shape usually need to be formed twice or several times.

2. For large batch and small size of the bending parts, in order to make the workers easy to operate, safe, to ensure the accuracy of the bending parts and improve productivity, should be used as far as possible progressive die or composite die.

3. When multiple bending is required, the bending order is generally to bend the two ends first and then the middle part. In the previous bending, it should be considered that the latter bending has reliable positioning, and the latter bending can not affect the previous bending shape.

4. When the geometrical shape of the bending parts is not symmetrical, in order to avoid the deviation of the billet during bending, the process of bending in pairs and then cutting into two pieces should be adopted as far as possible, as shown in Fig. 1-1.

Work arrangement of typical bending parts

Fig. 1-2~ Fig. 1-5 are examples of primary bending, secondary bending, tertiary bending and multiple bending forming workpiece respectively. For some small and thin elastic contact parts with complex shape, one—time composite bending forming should be adopted to make the location accurate.

the typical structure of the bending die

Structural design of bending die

Bending die is the blank or semi-finished parts along the bending line bent into a certain Angle and shape of the stamping die.

1. Billet preparation and working procedure arrangement.

• The bending line of the blank in the bending process should be perpendicular to the direction of the material fiber or form a certain angle.

• When bending, the bending crack of the billet is often in the inside of the bending parts.

• Bending process should first bend the outer end of the Angle, after the inner Angle, and the previous bending must have a suitable positioning benchmark for the next process, after the bending should not damage the accuracy of the previous bending.

2. To prevent billet deviation in the bending process.

• Part of the billet before bending should be in elastic compression state, and then bending.

• As far as possible to use the workpiece of the hole positioning.

3. To prevent the Verformung of the workpiece in the bending process.

• The mold structure design should prevent the obvious thinning and scratching of the local material. For the multi-angle bending, die design to make the multi-angle bending not at the same time, there should be a certain time difference.

• The bending effect should be corrected as far as possible when the mold is bent to the BDC.

• Structural design to eliminate the springback of parts should be considered.

• The structural design of counteracting the lateral forces of asymmetrical parts should be fully considered.

• The stiffness and service life of the die should be fully considered.

4. Matters needing attention.

The following points should be paid attention to when the structure of the bending die is designed.

• The blank must be placed on the mold to ensure correct and reliable positioning.

When there are holes in the workpiece and allow them to be used as locating holes, the locating of the holes in the workpiece should be used as much as possible. If there is no hole on the workpiece but it is allowed to punch the process hole on the blank, it can be considered to design the positioning process hole on the blank.

If the workpiece is not allowed to have a process hole, the positioning plate should be considered to locate the shape of the blank, and the pressing device should be set to press the blank to prevent the deviation of the blank in the bending process.

• when using multiple processes bending, each process as far as possible using the same positioning datum.

• To design the mold structure, attention should be paid to the operation of putting and taking out the workpiece to be safe, rapid and convenient.

• When determining the accurate rebound value of elastic material, it is necessary to correct the convex and concave die through die test, so the die structure design should be easy to disassemble.

Design of forming bending die

1. V-shaped bending die

Fig. 1-6 (a) shows a simple V-shaped bending die, which is characterized by simple structure and good versatility. But the billet is easy to deviate when bending, which affects the precision of the workpiece. Fig. 1-6 (b)~ (d) are respectively the mold structure with positioning tip, ejector rod and V-shaped roof, which can prevent the blank from sliding and improve the precision of the workpiece. V-shaped bending die, as shown in Fig. 1-6 (e), can effectively prevent the deviation of bad material during bending due to the roof and fixing pin, and obtain the workpiece with side length deviation of ± 0.1mm.

The function of the counterweight block is to balance the horizontal lateral force generated by the left side bending.

Fig. 1-7 shows the basic structure of the bending die for V-shaped parts. The advantages of the die are simple structure, convenient installation and adjustment on the press, lax tolerance requirements on the material thickness, the workpiece at the end of the stroke to get different degrees of correction, so the rebound is small, the flatness of the workpiece is better. The jacking rod 9 not only plays the role of jacking material, but also plays the role of pressing material, which can prevent material deviation.

2. Bending die for U-shaped parts

According to the requirements of bending parts, the commonly used U-shaped bending die has several structural forms as shown in Fig. 1-8.

Fig. 1-8 (a) shows an open bottom die for parts where flat bottom is not required.

Fig. 1-8 (b) shows bending parts for which bottom level is required.

Fig. 1-8 (c) shows the zero bending parts for which the thickness tolerance is large and the outer dimension is high. The punch is a movable structure and the lateral dimension of the punch can be automatically adjusted according to the thickness of the punch.

Fig. 1-8 (d) is used for bending parts with large tolerance of material thickness and high requirement of inner dimension. There are movable structures on both sides of the die, and the transverse dimension of the die can be automatically adjusted according to the material thickness.

Fig. 1-8 (e) shows a U-shaped fine bending die. The movable inserts of the die on both sides are hinged to the roof by rotating shafts respectively. Bend the front jacking rod to push the roof out of the die surface, and at the same time, the roof and the die movable inserts are formed into a plane, and the inserts are provided with positioning pins for the positioning of working parts.

When bending, working parts and die movable inserts move together, so as to ensure that the holes on both sides are coaxial. Fig. 1-8 (f) shows a bending die with thinned wall thickness on both sides of the bending part.

Fig. 1-9 shows the basic structure of the bending die for a general U-shaped part. Material along the concave die fillet sliding into convex, concave die clearance and bending, punch back up, the ejecting plate will work piece out. Because of the elasticity of the material, the workpiece is generally not wrapped on the punch.

3. Bending die for Z-shaped parts

Z-shaped parts can be formed by bending once. As shown in Fig. 1-10, when bending Z-shaped parts, bending the left end or the right end of the Z-shaped parts first depends on the elastic force of the rubber on the supporting plate 2 and the elastic force of the springboard device on the roof.

If the elastic force of the rubber on the supporting plate 2 is greater than that of the elastic device on the roof, then bend the left end of the Z-shaped piece first and then bend the right end; If the elastic force of the rubber on the supporting plate 2 is less than that of the elastic device on the roof, then bend the right end of the Z-shaped piece first and then bend the left end. Fig. 1-10 illustrates the action process with the example of turning the left end first and then the right end.

Before bending, the punch 6 and the end face of the movable punch 7 are flush due to the action of rubber 3. During bending process, the movable punch 7 and the roof 1 will clamp the blank, because the elastic force of the rubber on the supporting plate 2 is greater than the elastic force of the elastic device on the roof, forcing the blank to move downward, and completing the left end bending first.

When the top plate 1 contacts the lower die base 8, the movable punch 7 stops descending, and the upper die continues to descend, forcing rubber 3 to compress, and the punch 6 and the top plate 1 complete the bending at the right end. When the pressing block 4 touches the upper die base 5, the whole workpiece is corrected.

4. Bending die for concave parts

Concave parts can be bent either once or twice.

Fig. 1-11 shows the primary forming bending die for concave parts. As can be seen from Fig. 1-11 (a), in the bending process, because the punch shoulder obstructs the rotation of the blank and increases the friction force of the blank through the rounded corners of the die, the side wall of the bending part is easy to scratch and thin, and the two shoulders of the workpiece are not easily parallel to the bottom surface after forming, as shown in Fig. 1-11 (c). Especially when the material is thick, the straight wall of the bending part is high and the fillet radius is small, this phenomenon is more serious.

As shown in Fig. 1-12, the bending die for the concave part in one—time composite forming is shown. Before bending, the billet is positioned by the positioning plate. When bending, the punch die 1 down, first make the blank in the die 2 bending into a U shape, punch die 1 continue to go down with the action of the active punch 3, and finally bend into a concave part. At the end of bending, 4 jacking rod jacking workpiece

As shown in Fig. 1-13, the bending die is formed twice. Since two sets of dies are used for bending, the defects as shown in Fig. 1-11 are avoided and the quality of bending parts is improved. However, it can be seen from Fig. 1-11 (b) that only when the bending part height H> (12~15)t can the die maintain sufficient strength.

5. Bending die for circular parts

The size of the round piece is different, and the bending method is different. Generally, it is divided into two kinds: small round piece and large round piece according to the diameter.

• Small round parts with diameter d≤5mm

For small round parts with diameter d≤5mm, the U shape is usually completed first. And then the U shape is completed to the circle. Fig. 1-14 shows a primary bending die for a small circle. Before bending, the blank is positioned by the positioning groove of the concave die fixed plate 1.

When bending and the upper die down, the spindle punch 5 and the lower die 2 will first press the blank into a U shape. The upper die continues to go down, the spindle punch 5 and the press plate 3 do not move and the stroke of the upper die is used for the compression spring. And then the upper die 4 will finally bend the workpiece to form.

After the return of the upper die, the workpiece is left on the punch of the core shaft, the punch of the core shaft is pulled out, the workpiece falls automatically, and the spring on the core shaft automatically resets the core shaft.

• Large round parts with diameter D ≥20mm.

For large circular parts with diameter D ≥20mm, it can be bent once or repeatedly. Fig. 1-15 shows a primary bending die with a swing die. The billet is positioned on both sides of the positioning plate and the upper end of the swing concave module 3.

When bending, the punch 2 presses the billet into a U shape first, and then the punch 2 continues to go down, and the bottom of the swing concave module 3 is pressed down, so that the swing concave module 3 oscillates axially inward around the pin, and the workpiece is bent into a circle.

At the end of bending, push support 1 to the right and remove the workpiece from the punch. This method has higher production efficiency, but because the upper part of the cylinder part has not been corrected, the rebound is larger, and there are gaps and a small number of straight edges in the joint of the workpiece.

6. Hinge bending die

Hinge bending forming is generally divided into two processes, the end of the flat billet will be pre-bent into a circular arc, and then roll round. The method of pushing round is usually used for hinge round forming. As the hinge rebound increases with the relative bending radius ratio, the size of the die should be smaller than the outer diameter of the hinge 0.2~0.5 mm.

Fig. 1-16 shows the hinge bending roll round die, Fig. 1-16 (b) shows the structure of the vertical hinge bending roll round die. Which is suitable for the dumpling chain with thicker material and shorter length, the structure is simpler and the manufacture is easy. Fig. 1-16 (c) shows the structure of the bending and winding die of horizontal hinge. The inclined wedge 3 is used to push the concave die 4 of the bending and winding die in the horizontal direction, and the punch 1 is also used as the pressing part. This kind of die structure is more complex, but the quality of the workpiece is better.

7. Composite bending die

For small bending parts, you can also use composite die, that is, within a stroke of the press, several different processes such as blanking, bending and punching can be completed in the same position of the die. Fig. 1-17 (a) and (b) are the structural sketches of the composite cutting and bending dies. Fig. 1-17 (c) shows the compound die of blanking, bending and punching. The die structure is compact and the workpiece accuracy is high, but it is difficult to repair and grind the convex and concave dies.

8. Universal bending die

For small batch production or trial production of the workpiece. Due to small production, many varieties and shape and size often change, so in most cases can not use special bending die. But if manual processing is used, it will not only affect the processing accuracy of the workpiece, but also extend the production cycle of the product and increase the cost. Therefore, general bending die is generally used.

The general V-shaped bending die is shown in Fig. 1-18. The die is composed of two pieces, which have four working faces for bending at various angles. The punch shall be replaced according to the bending Angle and fillet radius of the workpiece.

Using the general bending die can not only produce the general V-shaped parts, U-shaped parts, but also can produce the complex workpiece with low precision requirements. An example of a complex part manufactured by multiple V-bending is shown in Fig. 1-19.

The general bending die for a bending machine is shown in Fig. 1-20. Several notches suitable for bending workpiece are produced on the four surfaces of the die, as shown in Fig. 1-20 (a). There are two types of punch: straight arm type and curved arm type. The working fillet radius can be made into several sizes to be replaced according to the needs of the workpiece, as shown in Fig. 1-20 (b) and (c).