Material of plate A is SAPH440, and material thickness is 2.0mm.Original structure of part is shown in Figure 1. Forming height is about 80mm. When drawing, height dimension is larger than contour dimension of punch parting line, and forming is difficult. After avoidance shape is added to vertical wall, since forming of avoidance shape belongs to local forming, when mold closes to complete closure, it is difficult for material in this area to be replenished from periphery of vertical wall that has undergone large deformation, and risk of local thinning or even cracking increases. Therefore, how to form avoidance shape in original process is the key to stamping process.

 

In order to demonstrate reliability of part structure change scheme, it is necessary to correlate part structure change with stamping feasibility certification. Automobile main engine factory provides limit position of bushing of interference part for mold company as a design constraint. As shown in Figure 2, interference position between bushing and A plate is near steep vertical wall, and space safety margin of original part is about 4mm. Considering difference in attitude of stabilizer bar during driving, safety margin of this space is insufficient. When designing void on vertical wall of A-plate, space safety margin and relationship between formability should be considered comprehensively, and dimension of void should be increased as much as possible under premise of ensuring that forming is feasible. When optimizing design of part structure, in order to ensure minimum safety margin of 10mm proposed by automobile OEM, outer surface of shaft sleeve is first offset by 5mm as limit position, then offset surface is extended vertically downward to intersect bottom surface of part. Take intersection line as section line of drawn surface, and design drawn surface as main surface of avoidance shape according to draft angle of 8°~10° with drawing direction, then match and connect with surrounding shape. Shape of part after rounding is shown in Figure 3 and Figure 4, finally safety margin of part avoidance space is increased to about 13mm.

 

Before optimal design of part structure is finalized, feasibility of part structure needs to be verified. In order to obtain stable samples, mold companies use simple forming molds to form avoidance shapes. Since avoidance shape is pressed on A-plate stamping, in order to ensure pressing effect of simple forming die and stability of forming, simple forming die adopts stamping angle shown in Figure 5, and forming angle is an open "V" shape, which is flatter than original process forming angle, but it cannot match forming angle of original mass production die. Therefore, sample formed by simple forming mold can only verify whether modified structure of part meets loading requirements . Simple forming die pressed 50 sets of samples, and there was no abnormal sound after loading, confirming that part structure after improved design can meet loading requirements. Stamping manufacturability of mass-produced parts is not considered in forming of prototypes. Feasibility of mass-produced stamping will be analyzed below.

 

Since plate A has already been mass-produced with molds, in order to save costs, original stamping process of plate A was maintained in process design, as shown in Table 2. In order to analyze risk of mold improvement, it is necessary to consider how to decompose avoidance shape into original stamping process. One solution is to complete forming of avoidance shape in one process, and arrange it in later process as much as possible. Considering convenience of mold improvement, try to put all avoidance shapes in process ③ to complete shaping, drawing die does not need to be improved, and mold after process ③ can only increase avoidance space, so that workload of mold improvement is minimal; another solution is to put all avoidance shapes in drawing process to complete, and increase avoidance space for mold in other subsequent processes, and workload of mold improvement is relatively small. Stamping simulation analysis of these two schemes, both produce forming cracks as shown in Figure 6. Try to decompose avoidance shape into step-by-step forming in process ② deep drawing and process ③ shaping, preform part of shape in drawing process, and realize final forming in shaping process. After trying to distribute forming amount, with the help of stamping forming simulation analysis, optimized step-by-step forming scheme eliminates risk of forming cracking. Simulation results after process optimization are shown in Figure 7. After confirming that improved part structure and formability are feasible, automobile main engine factory made a final confirmation on improved shape of plate A, corresponding mold company modified original drawing die and shaping die of plate A. Process mold design avoids space, and modified mold can meet mass production.

 

Changing shape of plate A to A1 also takes into account formability and punchability of high-strength plate. As shown in Figure 8, deep-drawing process is carried out on vertical wall of area 1, vertical wall of deep drawing is moved outward and draft angle is increased, rounded corner of drawing punch is enlarged relative to part, main shape of part is formed first, then the final shape is obtained through shaping and flanging process, which improves formability of drawing and manufacturability of trimming; splicing area 4 of left and right parts is gently connected to increase smoothness of trimming. There is room for optimization in stamping process of original A-plate. Formability can be improved by setting process holes of deep-drawing blank. Trimming angle of vertical wall of deep-drawing can be further optimized by adjusting forming process and optimizing forming surface, can reduce trimming process. Improvement of mold is based on original process and mold. Except for difference in avoidance shape, stamping process and process content of A plate and A1 plate are same, and step-by-step forming of A1 plate realizes safe forming of avoidance shape.
(1) Process ① Blanking and punching. Plate A is same as deep-drawn blank of A1 plate. Blank is equipped with 3 special-shaped process holes, which is conducive to flow of intermediate materials to both sides and reduces risk of cracking. According to on-site process verification, sheet with process holes can save material in symmetrical direction compared with sheet without process holes, which is conducive to improvement of material utilization. Considering addition of avoidance shapes on A1 plate, there is room for optimization of hole shape and position of the largest process hole at big end of blank, but it is necessary to modify structure of existing blanking punching die, resulting in high modification costs, so drawing blank is not modified.
(2) Process ② deep drawing. This process adopts paired deep drawing, symmetrical area 4 is spliced with a gentle profile, vertical wall where area 1 is located is expanded from center to outside and upper and lower fillets are enlarged (over-drawing method) to form general shape of A plate and A1 plate, then through shaping and flanging process to make it in place; trimming line of deep-drawing process is on a gentle profile that is conducive to trimming, so as to avoid punching at a steep angle. When forming avoidance shape of A1 plate, step-by-step forming is adopted, part of avoidance shape is preformed in this process, then formed in place in process ⑤ shaping and flanging.
(3) Process ③ Shaping. In this process, attachment surfaces of two flanging shown in areas 2 and 3 are shaped in place, which is beneficial to step ⑤. Shaping and flanging can be formed after attachment surface is formed and material is stably pressed.
(4) Process ④ trimming and cutting. Two sets of closed trimming blades are used to cut into independent left and right process parts. Disadvantage of this process is that deep-drawing vertical wall area is shaped to shape of part, resulting in a steep vertical wall trimming. According to analysis, stamping direction of this process can be slowed down by 6°~10° according to punching specification to improve punching quality and prolong service life of die.
(5) Process ⑤ shaping and flanging. This process completes shaping of two flanges in areas 2 and 3 shown in Figure 8 and shaping of area 4 (docking part of left and right parts). Attachment surface of two flanges has been completed in process ③, and forming is relatively stable. Shaping of butt joint parts of left and right parts in area 4 is completed in process ⑤ shaping, in order to slow down bevel angle of this part in process ④, and vertical wall area of area 1 has been shaped in process ③.

 

(6) Process ⑥ trimming. Complete fine trimming of plate A and area 1 of A1. Design of this process is not optimized enough. This process can be canceled or combined with process ⑦ punching, but trimming needs to use wedges. Punching, punching angle is rotated close to 90°, but this is not conducive to automatic production.
(7) Process ⑦ punching. Complete processing of all holes of plate A and plate A1. Except for two holes sharing one die insert, punching die adopts standard die inserts for quick change. Referring to process analysis of process ⑥ trimming, it can be considered to combine process ⑥ and process ⑦, but it must be trimmed with a wedge, and standard die insert cannot be used at trimming of wedge due to limited space.

In the development of another model, automobile OEM designed a new stabilizer bar reinforcement plate (B plate) with reference to structure of A1 plate (see Table 1). Structure of B plate is similar to that of A1 plate, and same avoidance shape is adopted. Since mold is newly developed, stamping process and mold development of plate B draw on development experience of plate A1. After process research and stamping simulation analysis and verification, it is determined that there are 6 stamping processes for B-plate (see Table 2), and key points of B-plate stamping process are shown in Figure 9.

 

 

(1) Process ① Blanking and punching. Number, size and position of process holes were optimized through stamping forming simulation, and 3 process holes in original drawing blank were changed to 4, and positions of 2 lateral holes were closer to those shown in Figure 9. Area 1 makes it easier for material to flow to vicinity of avoidance shape and fillet area of vertical wall of large end, reducing risk of cracking and transitional thinning.

 

(2) Process ② deep drawing. Deep-drawing process inherits original process method. Basic shape of B-plate is formed by slowing down profile and enlarging rounded corners by over-drawing, avoiding shape and completing part of shape in deep-drawing process, leaving a shaping allowance for process ③ shaping and process ⑤ shaping and flanging, purpose is to decompose large amount of deformation in process ② deep drawing and process ③ shaping, and at the same time satisfy trimming line on a gentle profile that is conducive to trimming, avoiding steep punching.
(3) Process ③ Shaping. Complete part shape of other marked areas except marked areas 1 and 4, including avoidance shape and process it to part position. Unlike A1 board, vertical wall shape shown in area 1 is not shaped into part shape in this process, and a more gentle punching angle is provided for the process ④ trimming. After trimming is completed, trimming line of process ④ needs to be grasped near surface area 1 of process, trimming line is determined by reverse calculation of stamping forming simulation and corrected during debugging.
(4) Process ④ trimming and cutting. Two sets of closed edge trimming knives are used to cut out left and right process parts. Unlike A1 board, punching direction of B board in this process is about 8° slower than punching position of process ②, ③, ⑤. Vertical cutting part shown in area 1 is not shaped to position of part, so as to improve trimming conditions. This process does not leave trimming amount for subsequent process, so that bad trimming angle is improved from about 20° of A1 board to 30°, saving finishing process of A1 board. After trimming line optimization and back calculation, grab trimming line near area 1 of shaped surface in process ③, as shown in Figure 9.
(5) Process ⑤ shaping and flanging. This process completes shaping and flanging of 4 marking areas. Conventional flanging process is generally to form attachment surface of flanging first and then perform flanging, that is, forming of attachment surface and flanging based on this surface are generally not arranged in same process. Difference from A1 board is that vertical wall of B board area 1 is shaped to shape of part in this process. During forming process, material on flanging attachment surface of area 2 will be in a flowing state. It is necessary to discuss stability of pressing material and flanging , but also need to grab position of trimming line. After stamping simulation, shaping and flanging of these two areas can be formed in same process. Composite forming process is shown in Figure 10. Trimming line of composite forming area is obtained through stamping simulation and meets size of formed part.

 

(6) Process ⑥ punching. Complete all punching in this process to ensure accuracy of hole position of part. It is also considered to combine local finishing of B plate area 1 corresponding to A1 plate process ⑥ with punching, so that B plate process ④ only needs rough trimming in this area. edge (no need to grab trimming line). However, considering that partial trimming requires use of oblique wedges, and edge of trimming blade is close to punching blade, it is impossible to use quick-change die inserts, which is not convenient for mold manufacturing and maintenance. In addition, use of oblique wedges will cause positioning and removal. Due to inconvenience of parts, size of press table and size of mold will be increased, so it is more appropriate to set process ⑥ as a single process punching.

Stamping process of stabilizer bar reinforcement plate and some process methods involved in optimization of mold structure, such as over-drawing, step-by-step forming, composite forming of shaping and flanging, and connection method between processes have a certain reference effect on stamping process development of high-strength pickling plate parts. Above case also applied method of synchronous development, organically related optimization of structure of parts with optimization of stamping process and mold, improved development speed and quality of parts. This synchronous development mode of close cooperation between mold manufacturers and OEMs is also worthy of promotion in the industry.