Figure 1 shows an engine connector contact piece part, which plays the role of connection and signal transmission in the engine. The material of the parts is phosphor bronze with C5210 and the thickness of the material is 030mm, high hardness, good fatigue resistance, corrosion resistance, and good elasticity. The bending focus of the part controls the dimensional tolerance of 003mm, the angle tolerance is 1°, the parts and the engine base can not be abrasion, deformation, need to meet the elastic requirements, the relative position without deviation. The production batch of parts is 10 million pieces, the punch speed is 200 times, the service life of the mold is 20 million strokes, the shape of the parts is complex, the precision requirements are high, the production batch is large, and the convex and concave die inserts are required to be easy to disassemble and have good interchangeability in the mold manufacturing. 
The right end of the part is an "M" shaped card slot, and a convex hull is formed in the middle, which is convenient for clamping the pin, so the material elasticity is required. The part is free to pop open the mouth, and the mouth is fit and elastic after assembly. The shape of the parts is complex, the key control size tolerance requirements are high, the surface needs to be clean, there should be no scratches and abrasions, and there should be no cracks and wrinkles at the bends. Due to the high bending height of the parts, the lifting height is also high, and the die punching speed is controlled at 200 times, in order to ensure the forming quality and production efficiency of the parts, it is decided to use the progressive die for production. (1) Fig. 2 shows the local shape of the part, the left and right bending feet have been interfered with, so there are requirements for the sequence of bending forming, and the "U" shape needs to be formed in advance, but the "U" shape is completely formed in place in advance and will cause the die strength to deteriorate when the final bending is made, so only the punch-free insert can be used to bend when the final forming. 
2) The difficulty of forming the local shape of the part shown in Figure 3 lies in the high bending height of the supporting foot, resulting in the high lifting height of the mold, and the mold bending and core pulling are more, and the core pulling stroke is long. 
In order to improve the material utilization rate, the oblique arrangement method is selected first, and the parts to be formed are rotated by 10° 30°, and the arrangement of the station is considered when the parts are core-pulled. The position of the carrier is selected in the flat area without bending, and it is necessary to ensure that the carrier has sufficient strength to ensure the stability of mold production, and the local nesting scheme is shown in Figure 4. 
The overall nesting of the part is shown in Figure 5, the part to be formed is inclined 20°, and the forming process includes blanking, downward bending, core pulling downward bending, lever upward bending, shaping, core pulling forming, side bending forming, etc. In order to ensure the strength of the carrier and maximize the connection area of the carrier, the "frame" structure is also adopted to make the carrier form a closed frame to ensure the reliability of lifting, feeding and forming. Due to the large forming step distance of the parts, the forming station is arranged to correct the nail for correction; In order to ensure the key bending size, a fine-tuning mechanism is set at the forming station of the important size of the part. The main forming process of the part is shown in Figure 6 and Figure 7. 
1) Downward bending: forming a "U" shaped bend on the middle and middle legs. (2) Pendulum bending: Using the swing bending structure, the downward forming is 87° through two actions. (3) Core pulling bending: the downward bending die adopts a movable structure, because the parts are wrapped on the outside of the die after forming, in order to realize the lifting and feeding after the mold is opened, the die is designed as a mobile structure. (4) Lever bending: the bending is upward bending, the stripper is pressed first, and the unloading stroke is used to transmit to the lever to achieve upward bending. (5) Bending: Downward forming the "M" card slot and the middle side of the foot. (6) Downward bending: Downward forming of the inner leg in the "M" card slot. (7) Core bending: The downward bending die adopts a movable structure, which is convenient for lifting and feeding. The mold structure is shown in Figure 8, the guide pillar adopts a ball guide pillar, in order to realize the rapid replacement of convex and concave die, the punch adopts a pressing plate structure, and the discharge spring is installed on the upper supporting plate, and the stripper plate can be directly removed to replace the punch without taking the discharge spring. The die insert is pressed down with a side guide, and the die insert can be removed by tapping the hole from the back after removing the corresponding side guide. Due to the fact that the parts are bent more and the tolerance requirements are high, the parts have a micro-adjustment structure after bending, which is convenient for size adjustment. When the mold is closed, after the strip is corrected and attached to the concave template, the wedge moves downward with the upper die, pushing the core-pulling die on the slider to put it in place, and the upper die continues to drive the forming punch downward to complete the bending. After that, the bending punch retreats, the wedge retreats, and the slider drives the die inserts to exit under the action of the return spring, and the material is lifted and fed. In order to shorten the mold discharge stroke, the strip is first corrected and pressed on the surface of the die by using the pressure rod, the wedge pushes the slider to drive the core-pulling die insert in place, and the stripper plate presses the strip and begins to bend. The core pull and pressure bar structure are shown in Figure 9. When there is a short leg in the bending, and the bending angle is less than 90 °, the conventional structure cannot be formed at one time, so the pendulum rod mechanism is adopted, as shown in Figure 10. 
The forming steps are decomposed as follows: the first step swing punch realizes the bending of the part to be formed under the guidance of the stripper; The second step punch continues to move downward, and the swing bending is realized under the contact of the inclined plane of the die insert, and the structure is simple, and the adjustment is convenient and reliable. The material of the mold plate is SKD11, the fixed plate, the stripper plate and the concave template type hole are processed by slow wire, and the guide pillar and guide sleeve hole are processed by coordinate grinder, with an accuracy of 0002mm。The punching and forming parts in the mold are made of imported powder high-speed steel, which are processed by slow wire walking, forming grinding and optical curve grinding, with an accuracy of 0002mm。As shown in Figure 11, the bending punch adopts powder metallurgy high-speed steel, which has the advantages of high material hardness and fine particles. Wire cutting, forming grinding and optical curve grinding are used, and the roughness value of the forming place is Ra01 m, after grinding and polishing, it is ground and polished by fitters, and then DLC coating (diamond-like coating), which can prolong the service life of the bending punch, reduce bending abrasion, and improve the forming quality of the parts. 
The parts are typical representative parts of the connector, and the mold structure has been improved and optimized, which solves the problems of high bending feet, high lifting and large unloading stroke. Verified by production practice: the mold production is stable, the action is reliable, and it has a certain reference role for the forming of similar parts. Original authors: You Jian, Zhu Xun, Hou Yi.
Author's Affiliation: Chengdu Hongming Shuangxin Technology Co., Ltd. ***