Research and Application of Multi-station Progressive Casting Die on Stamping Parts of Automobile Inner Plate

The multi-station progressive die, also known as the continuous die, has two or more stations in the cavity, and these stations are all in a straight line, and can be punched, bent, and finished in one stroke of the press. Various processes such as drawing and forming. It has the characteristics of high efficiency and low production cost. In China, multi-station progressive die is generally used in the field of home appliance steel molds, but it is still less used in the automotive field, especially in the field of casting molds. In this paper, taking a car door sill reinforcement plate as an example, the left and right parts are clamped and produced by the progressive die. From the process arrangement to the mold design, debugging and realization, the relevant personnel are referred to.

First, product process analysis

The material of the product is B250P1, the thickness is 1.4mm, the part size is 320mm×137mm×92mm, and the shape and hole of the part are not symmetrical (see Figure 1). If the part is single-punching, the process route is OP10 blanking→punching→OP20 forming→OP30 flanged→OP40 punching side punching. A total of 7 sets of molds need to be developed. Due to the low production efficiency of the single punch, the capacity requirements are not met. After the evaluation, the multi-station progressive die with the left and right parts is clamped. Because the mold size is large, the mold type is cast.

Second, the strip design

In the multi-station progressive die, each step of the strip is fed by the feeder to send a step to reach different stations, and the work content of each station is different. Before completing all the processes, the process parts Not separated from the strip.

The strip chart design is to determine the processing content of each station. The strip chart design is the key to the multi-station progressive die design, and is also the basis for the die structure design. Once the strip chart is determined, it also determines the tool number, step size and material utilization rate of the product. When designing the strip chart, pay attention to the following items: 1 The center of the press should be basically the same as the center of the mold to ensure the balance of force. If the consistency cannot be guaranteed, the eccentricity should not exceed 100mm. The empty station can be set appropriately for later product design. Change or avoidance involves ensuring a balance of forces. 2 In order to make the belt positioning reliable, generally, some process holes can be punched in the first station as the rear station positioning holes. When the holes are close to the shape surface, the holes can be punched first, and the back holes are punched to the large holes of the required size. Or after forming and punching. 3 Waste and finished parts should be able to drain smoothly, and the feeding needs to be smooth. 4 Both formed and curved workpieces are formed and bent first to avoid the influence of material flow on the shaped surface. 5 need to consider the convenience of mold manufacturing and maintenance. 6 The carrier must have sufficient strength to be smoothly fed in the process.

The material belt designed in this case is shown in Figure 2. The carrier is selected as the double medium carrier. The software used for material development is AUTOFROM. The selected punching machine is a 6300kN press with continuous punching function.

Third, the positioning design of the parts

In the multi-station progressive die, in order to ensure the accuracy of the relative position between the convex and concave die and the process component, a reliable and accurate positioning device must be provided, and the positioning is mainly set in three directions, namely, the X direction, the Y direction and the Z direction. Usually, the guiding pin and other coarse positioning methods are used together. The guiding pin guiding is to use the guiding hole mounted on the guiding pin of the upper die to ensure the uniform position of the strip in the die. In this paper, the process guide hole is punched out at the station 1, and the X and Y directions are precisely positioned by the guide pin in the station 2~6. The full position is used to position the Z-direction with the floating pin pin, and the guide plate is used to assist the positioning. Y direction and Z direction. Then punch out the product hole at the position of the guide hole in station 7, as shown in Figure 3.

Fourth, the structure of the design

Mold structure

In order to reduce the size of the mold, this stage of the mold does not use the guide leg guide structure of the conventional mold, but uses four guide column guides, the length of the mold is thus reduced by about 750mm, and then the embedded lugs are used, and the width is also reduced. About 400mm, the final die size is 2575mm × 1020mm × 800mm. The mold is mainly composed of upper mold base, unloading plate, lower die base, pallet, various forming and trimming convex and concave molds, and various standard parts.

2. Unloading device

The unloading device is an important component in the multi-station progressive die. On the one hand, the strip is pressed before the stamping is started, the strip is prevented from being shaken, and on the other hand, the unloading is ensured and the punch is protected. The pressure of the stripping plate of the stripper plate is generally about 5% of the punching force. Its calculation formula is

F=tLÏ„

Where t-material thickness (mm);

L—cut length (mm);

Τ—cutting strength (kg/mm ² ).

In this paper, three strips are used and guided by guide pillars. Considering the space and service life, a nitrogen gas spring is selected as the pressure source of the pressure plate. In order to balance the pressure and find the problem in time, the nitrogen gas springs are connected in series and a visual pressure gauge is installed outside the mold.

3. Feeding device

The multi-station progressive die is automatically fed according to the design step by the feeding device. After the tape is formed by the punching, the tape will have different degrees of deformation in the direction of the material thickness. In order to smoothly feed the material, the formed material must be formed. The belt is raised to make the belt slightly higher than the working part of the lower mold. In this paper, three pallets are used in the repairing station. One supporting core (lower dead bottom) and eight floating top pins are used in the forming station. All the feeding devices are guided by the guide bushing.

4. Design considerations

When designing a multi-station progressive die structure (see Figure 4, Figure 5), you should also pay attention to the following:

(1) Because the punching cycle is very high, the punching waste may bring out the surface of the mold and damage the mold, so the punch selected for the positive side punching should be the topping type punch.

(2) In order to facilitate processing and maintenance, all the repairing cutter blocks shall be designed as a block type, and the block forming type shall be in the form of block type, because the product material is high-strength plate and the material thickness is 1.4mm, all repairing and forming The cutter blocks are all made of Cr12MoV and the quenching hardness is above 55HRC.

(3) In order to protect the convex and concave molds, all the discharge plates and the lower mold movable blocks need to be guided by the guide pillars to ensure the high motion precision, and when the mold precision requirements are higher, the guide pillar guide sleeves should also use the balls. formula.

(4) All punching die uses standard die sets for easy maintenance and replacement.

(5) The stripper should be pressed against the sheet before forming, and all the strips should be in contact with the strip at the same time. The stroke must be exactly the same. The travel of the safety screw is 5~10mm longer than the stroke of the working screw. The discharge screws should be symmetrically distributed, and the discharge screw with the sleeve should be selected, which can be used in conjunction with the stroke adjustment collar to extend the stroke.

(6) In order to reduce the friction between the belt and the punch, the material should be lifted by the supporting plate or the floating device, and the height of the ejection should be higher than that of the lower forming block.

(7) In order to make the scrap fall automatically, the scrap sliding angle should be no less than 25° and there is enough space for rotation.

5. Processing and debugging of progressive die

The progressive die not only requires the precision of the finished stamping parts to be qualified, but also ensures the high-speed running precision of the die. The progressive die has high requirements for the precision of CNC machining and the positional accuracy of each part of the die. At this stage, the parts with high positional accuracy, such as forming and punching punches, are assembled on the mold base, and then processed together with the mold base on a high-precision CNC machine tool. The movable parts such as the billet core are machined to the coordinate reference. After the hole is established, the coordinate coefficient control processing is completed. After the various inserts and the block are machined out, the coordinate system is processed by the assembly surface.

After the mold is finished and assembled, it needs to be debugged. In the first stage, the moving parts of the mold such as the wedge, the feeding plate and the unloading plate are operated smoothly and without interference. In the second stage, the research rate and the production rate of the formed parts are improved, and the guarantee parts can be produced. The third stage is to improve the precision of the stamping parts and eliminate burrs and other surface problems.

Before the mold leaves the factory, static and dynamic inspection of the mold, inspection of the surface quality of the stamping parts and inspection of the pass rate are required.

Mold static inspection mainly detects whether the casting is defective, whether the profile, the quality of the sliding surface, the hardness, etc. meet the technical requirements. The mold inspection mainly detects whether the components are running smoothly, and the working portion is combined (the paint is coated with the paint to detect the bonding area with the mold). The surface quality inspection of stamping parts mainly checks the surface quality defects such as brushing, dark injury, wrinkling, burr, cracking and crushing of stamping parts. The pass rate check is performed on the gage with the stamping reference book to check the accuracy of the stamping. After 4 months of tooling factory debugging, the first-level die was successfully released, and the stamping parts and molds were all qualified and entered the stamping factory production base.

6. Multi-station progressive casting mold realization

After the mold entered the field, after one month of matching and rectification of the press and the mold, the mass production status was fully achieved, and the mass production tact was 40 times/min, the production efficiency was significantly improved, and the production personnel and equipment were reduced.

The mold can realize the automatic, high-speed and safe realization of the high-strength board of the inner panel of the automobile in the progressive casting mold, and the left and right parts are clamped, which overcomes the defects of manual feeding of the traditional mold, low efficiency and high cost, and has good application value. And promote value.

references:

[1]WU Yu-nong, YANG Wei, YUAN Gen-hua. Improvement of Stamping Process for Upper and Lower Beams of Refrigerator and Design of Multi-station Transfer Die[J]. Forging & Stamping Technology, 2012, 37(6): 91-95.

[2] Chen Wenlin. Plastic forming process and mold design [M]. Beijing: Mechanical Industry Press, 2007.

[3]Chen Yanwei. Multi-station progressive die design manual [M]. Beijing: Chemical Industry Press, 2012.

About the author: Liu Dixiang, Huang Dingshe, Cui Lichun, He Cheng, Cao Longbing, Jianghuai Automotive Technology Center, Process Engineering Institute, Stamping Technology Department.