Design of punching die for welded pipe

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Design of punching die for welded pipe Abstract: the characteristics of punching for welded pipe are analyzed, and the design idea of punching die for welded pipe is introduced through an example

key words: welded pipe; Punching die: process analysis

1 introduction

our company has recently received a batch of lamp tube processing tasks. The parts are shown in Figure 1. There are thousands of similar processing tasks from time to time. Process requirements: the elbow is in the same plane, the two screw holes are in the inner side of the elbow and the axis is in the same plane. Since the wiring is required in the lamp tube, it must be ensured that the lamp tube is not out of round and the burr is small

2 process analysis

according to the previous process: blanking - bending - Drilling - tapping - surface treatment - finished product

in the above processes, the most difficult to guarantee the quality is the drilling of holes. In the past, the drilling mold was made and the holes were drilled by fitters. Because the operation quality of this process has a great relationship with the quality of workers, the drill bit is easy to slip when drilling on the round pipe when using the drilling die. Even if the falling point is the same, the small deviation will make it difficult to ensure that the two screw hole shafts are on the same plane. According to previous production experience, the yield is about 70%, the production efficiency is low, and the material consumption is large

if the punch is used for punching, it can ensure that the two holes are in the same plane, and the perpendicularity can be accurately guaranteed by the limit. However, the common punching die uses the female die to ensure that the lamp tube does not lose its groove and the burr is small. Although this hole does not have high requirements for punching clearance, such a long cantilever beam structure is unsafe in operation. Another adverse factor is that the weld is relatively high (as shown in figure 1, the weld in the pipe is about 0.5mm high), and it is difficult to make the weld at the same position of the elbow when bending. Due to the uncertainty of the weld position, The core mold can not accurately avoid the weld, so the common punching method is not reliable

since the lamp tube is round, it is not easy to deform as long as the annular force is applied, and plastic deformation is easy to occur when the material is charged under pressure, although the usage of plastic bags can be reduced. The author makes the following design after comprehensively considering various factors according to the above ideas

3 mold design

due to the small number of single batches of this part, first of all, from the perspective of cost saving, it is decided to use the open simple mold. It is convenient to align the die by using the shape of the pressing plate and the die. The mold structure is shown in Figure 2

in order to ensure the feasibility of the scheme, necessary feasibility analysis shall be carried out for the design scheme. Since the minimum equipment of the company is a 25t punch, the punching force can not be calculated for punching such small holes. Punch mainly has the following forms, one is flat bottom punch, the second is pointed punch, and the other is ball head punch. If the flat bottom punch is used, the sharpening sequence can be reduced, but because there is no concave die, it is easy to cause out of round, inside out and burr; Generally speaking, the common pointed punch and spherical punch are mostly used for turning holes and other molds, but in this mold, which punch can successfully punch qualified products

stress analysis: when punching, first press the material plate 7 downward to press the lamp tube. The lamp tube is subject to elastic deformation, which is limited by the circumference of the lower formwork, resulting in circumferential compression stress. For example, the flat bottom convex is used. 3. Test run: after the air leakage switch is turned on, the force on the lamp die is as shown in Figure 3a. The downward force T1 plus t pressure will make the lamp tube out of round and turn inward, and even if the punching is successful, large burrs will occur. For example, if the punch is changed to the pointed form in Fig. 3b, T1 can be decomposed into T2 and T3, which not only reduces the tendency of inversion, but also makes the deformation area in a favorable plastic deformation condition of compression: obviously, the stress of the spherical punch is between the flat punch and the pointed punch, which is not as good as the pointed punch. Therefore, the punch adopts the pointed punch form

determine the specification and size of the punch after determining the form of the punch. The diameter of the punch shall be selected according to the standard of elbow 3 × screw hole bottom hole ∮ 2.5mm; The angle of sharp angle can be selected from the following aspects: ① in order to minimize out of round, varus and burr, T2 and T3 should be parallel to t pressure as much as possible (that is, the sharper the punch is, the better); ② Keep the punch rigid; ① The length of the tip shall not be greater than the inner diameter of the pipe. According to the above theoretical demonstration, it is decided to use a 60 ° sharp angle punch

4 practical demonstration

the sample of the first mold test obtained almost 100% bright band without burr. Formula: This is because the material has enough time for plastic deformation due to multiple punching, and it also shows that the stress analysis is correct. In the formal production, the holes and blanking as shown in Figure 4 were obtained, and more than half of the bright strip. This is due to the high speed of the punch, the material did not have time for plastic deformation, and was torn when the material deformation exceeded 1/2. The size of the bright strip is ∮ 2.5mm, which meets the product requirements. After tapping m3mm teeth, it meets the requirements through the force measuring wrench test

after the production of about 2000 pieces, it was found that the punched bottom hole was too large, and it was easy to slip after tapping. Some parts were unqualified after the force measuring wrench test. Through inspection, it is found that the height of the bright band (∮ 2.5mm part) of the hole is only about 0.5mm, less than one effective tooth, and the size of the big end of the tear band is about ∮ 2.75mm, which is certainly unqualified after tapping. After removing the mold, it was found that the punch was no longer sharp after punching nearly 2000 pieces, that is to say, it could not fully meet the function of the sharp corner punch as the original design. At the same time, it is found that the lamp tube is not seriously out of round (there is a slight angle collapse r at the punching position


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