Using the process plan of (2), before the punching process, because the hole is large, it cannot be guaranteed that the existing holes will not be deformed during the deep drawing, so the dimensional accuracy of the hole during punching cannot be ensured, so In order to ensure that the size of the punching hole remains unchanged, the punching process must be placed after the drawing process, so the process plan of (2) is not feasible.
Now let’s analyze whether the process plan of (3) is feasible. Judging from the process of (3), after punching, the size of the hole is guaranteed to be no problem after drawing. After drawing and punching, trimming is performed, so that the vertical edge size is 10+0125 after flanging. -0150mm is not a problem, it seems that the process plan of (3) is feasible.
Now let’s analyze why the boss cracks during forming. During stamping, the blank may be subjected to compressive stress or tensile stress. It is impossible to crack under the action of compressive stress, only wrinkles may occur. It is only possible to crack due to tensile stress, and it is not cracked due to tensile stress. Only when the tensile stress in the blank exceeds the tensile strength of the material, the crack can occur.
It seems that when the process plan of (3) is adopted, the blank is subjected to tensile stress exceeding the tensile strength of the material during deep drawing. Why is there a tensile stress in the blank that exceeds the tensile strength of the material during deep drawing? It can be understood by analyzing the structure of the part. The length between the left and right sides of the boss and the width between the front and back are compared with the outer dimensions of the boss. Are relatively small, and when the ratio of the size of the blank outside the deformation zone to the size of the deformation zone is greater than 3, only bulging deformation can occur, and drawing deformation or deep drawing deformation and bulging deformation will not occur. At the same time.
Here, the ratio of the size outside the deformation zone to the deformation zone (range of the boss size) is calculated to be greater than 3. Therefore, only bulging deformation occurs in the boss area, and no drawing deformation or drawing deformation and deformation are caused. Bulging deformation occurs at the same time. Because the inside of the blank in the bulging deformation zone is subjected to bidirectional tensile stress, the crack of the boss exceeds the tensile strength of the material due to the bidirectional tensile stress. Now, through the above analysis, it is easy to know the cause of the boss crack. If you can find a way to reduce the internal tensile stress of the blank or increase the tensile strength of the blank, the problem can be satisfactorily solved. Then, first look at whether it is feasible to increase the tensile strength of the blank, because the tensile strength of the blank is related to the type of material. Once the material is determined, its tensile strength is also determined.
So what should I do? The reason for the crack at the boss, we know from the previous analysis, it is completely because of the bulging deformation that occurs at the boss, which causes the internal tensile stress of the blank to exceed the tensile strength of the material, so why is it convex? Bulging deformation occurs at the platform. This is because the deformation zone is too small and the outer size is too large. When forming, the outer material cannot flow to the deformation zone, which leads to insufficient material supply in the deformation zone, and the rounded corners of the boss The internal tensile stress of the material exceeds the tensile strength of the material, and the material is cracked, causing the parts to be scrapped. Since the insufficient material supply in the deformation zone causes the internal tensile stress of the material to exceed the tensile strength of the material, the blank is stretched. , If we can find a way to make the material around the boss flow to the boss when forming the boss, the problem will be solved.
According to the structural characteristics of the part, the resistance of the metal flow to the boss is very large, especially when the stroke is close to the bottom dead center, the sheet is basically on the bottom of the punch, and the bottom of the die and the turning point are tightly pressed , The material is difficult to flow to the rounded corners. Therefore, in the drawing die design, the top rounded corner radius was increased from R4mm to R8mm, and the turning point at A was designed to be a straight line, and the final size of the part , The shape is further processed by the flanging shaping process to meet the dimensional accuracy requirements of the parts, and to obtain a convex boss with a clear outline.
At the same time, the boss part of the punch adopts the inlaid combined structure, the purpose is to bring convenience to the trial and maintenance. This part belongs to the stamping and forming of medium and thick plates with large forming force. Generally, multi-point crank presses or hydraulic presses are often used to protect the accuracy of the mold and ensure the quality of the stamping parts, and improve the dimensional accuracy of the stamping parts. However, due to the limitation of factory conditions, processing can only be carried out on a friction press, and the working characteristics of the friction press bring certain difficulties to the design of the blanking die and the drawing forming die. Among the above-mentioned problems, only measures can be taken in the part’s processing technology plan and mold structure design. The working characteristic of the friction press is that the closing height of the mold cannot be accurately controlled. The improvement of the mold structure is now used to overcome the above shortcomings to achieve the ideal blanking effect.
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