In the process of stamping processing more or less will appear a variety of problems, and a large part of these problems are caused by very low-level errors. Reflect our basic knowledge of stamping processing is not up to scratch. Here are some basic mistakes that are common in stamping:
1, when stamping the upper die into the depth of the lower die is too large when stamping, the upper die into the lower die depth should not be too large. Generally to just punch the plate is appropriate, this depth is desirable for 0.5-1mm. If the upper die into the lower die depth is too large, it will aggravate the wear of the upper die and the lower die. In the case of mold guidance and punch motion accuracy is not good, it will also bite the edge of the die, especially when punching thick material, punching holes and high-speed stamping, the depth of the stamping die into the lower die can not be too deep. To prevent the upper die from going too deep into the lower die, a limit post can be installed on either side of the die to limit the depth of the upper die into the lower die. When grinding the upper die, the limit sleeve is also grinding to the same amount of grinding.
2, stamping pressure center and punch pressure center of eccentric punch pressure force of action known as the stamping pressure center. In Deep Draw Stamping small punch, for example, if the pressure center for stamping and punching pressure center (usually located in the mold handle hole axis) is not in the same axis, press the slider will be under eccentric load, will cause the slide guide rail and mould guide part is not normal wear and tear, damage the movement precision of press, reduce the die life, even damage the mould. Therefore, determining the center of stamping pressure is an important work in die design. For a workpiece with a simple and symmetrical shape, the point of force is in its geometric center, and the pressure center is not calculated. For the workpiece with complex shape and the continuous stamping die with multiple processes, the method of finding the joint force point of parallel force system should be adopted to determine the center of stamping pressure.
3. Punching pressure exceeds the nominal pressure of punching press. The choice of punching press is mainly based on punching pressure. The principle is that the punching pressure should not exceed the nominal pressure of the punch. The main factors affecting the punching pressure are the thickness and mechanical properties of the material, the length around the stamping parts, the size of the die gap and the sharpness of the cutting edge. When the stamping high-strength material or thickness, the stamping contour around the workpiece (such as thick plate stamping), the required punching pressure is often close to or more than the nominal pressure of the punch, and the factory is limited to choosing from the punch, then it is necessary to consider from the mold structure to try to reduce the punching pressure. The main ways to reduce the punching pressure are: inclined edge stamping, step stamping, step stamping, heating stamping, etc. Helical blade on stamping method is to die (punching) or lower die (blanking) axis parts made with the shape of a tilt Angle, the Angle is less than 150 degrees, usually take 80 ~ 100 degrees as a oblique shear blade, the blade is not contact at the same time, but gradually die cutting materials, therefore had significantly lower impact force, and can reduce the vibration of the stamping when writing noise. Heating stamping is the material in the heating state of stamping (or red punching), because metal materials generally in the heating state shear strength decreased significantly, so it can effectively reduce the punching pressure. However, the disadvantage of this method is that the oxide skin is produced after the material is heated, which affects the surface quality of the parts. Therefore, it is generally used for the stamping of the thick plate or the parts whose size and surface quality are not high. In addition, the die edge blunt, broken or not sharp, will also significantly increase the impact pressure, therefore, maintaining a sharp edge is one of the conditions for the normal work of stamping die. In order to keep the edge of the die sharp, after stamping the die for a period of time, the edge should be polished.
4. When the upper die is fixed, the fine punching die has a large cavity under the die base. The structure types of the fine punching die can be divided into the fixed upper mode fine punching die and the movable upper mode fine punching die. Different die structure forms, the punch table structure is required to match with it. For the movable fine punching die, the workbench of the punch press is required to be a floating hydraulic workbench composed of an annular cylinder and plunger in the center. For the fixed upper mode fine punching die, the middle of the punch table is required to have a plunger cylinder. This mold structure is characterized by: the upper and lower die fixed on the lower die base, blank holder through the force transfer rod and die base, and the upper and lower die to maintain relative motion. Fixed on the model, precision punching die in the bottom of the mold base should not be a big hole. This is because: when the mold, hydraulic cylinder under the action of dowel bar moves down, and in the bottom of the mold base appears very empty, and all burst pressure above the hole, the lower die bending, this is very bad, and day. Under the action of increasing punching pressure, the lower part of the upper and lower dies will be bent, resulting in the risk of tension cracking. In ORDER TO AVOID THIS SITUATION, WHEN THE PUNCHING pressure is high, it is necessary to use special joint ring to improve the supporting conditions of the lower die seat, to avoid the occurrence of large rinse and make the upper and lower die bend. Due to the development of fine blanking technology to large and composite process, the need for porous or internal shape of the larger, the punching pressure is very large, the need for blank holder force, back pressure are large, therefore, the requirements of the middle of the punch table.
5. The upper and lower dies of the movable fine punching die are directly fixed in the center of the workbench, and the supporting conditions are good. This mold structure is characterized by: the upper and lower die relative to the die base is movable, the upper and lower die by the die base and the blank holder inner hole guide. The lower die and the blank holder are respectively fixed on the upper and lower die seat. The upper and lower die keep the relative position through the blank holder and the lower die. Therefore, the gap between the upper and lower die is smaller. Therefore, the movable fine punching die can not punch the parts with holes or large inner profile, because the assembly of the die is difficult to center, clearance is difficult to ensure, so it is mainly suitable for the fine punching of medium and small parts.
6, the heat treatment hardness of the upper die and the lower die of the stamping die is lower than 55HRC. The upper die and the lower die of the stamping die contact with the stamping material, the force is larger, and the wear is faster. Therefore, the upper and lower die of the stamping die must be heat treated, and the hardness cannot be lower than 55HRC, because the higher the hardness, the higher the strength of the die, the more wear resistant. Different die steel materials, heat treatment process and hardness are different. Cold working die steel Cr12MoV, high speed steel W18Cr4V2, high hardness of heat treatment, good hardenability, small quenching deformation, no cracking, suitable for complex shape stamping parts, and T8A hardenability is good, but poor hardenability, quenching deformation is easy to crack, commonly used in punching simple shape and soft parts. Because the processing of the lower die is more difficult than that of the upper die, the hardness of the lower die is higher than that of the upper die, generally 2-3 Rockwell hardness higher, that is, the heat treatment hardness of the upper die is generally 58~60HRC, and the heat treatment hardness of the lower die is 60~62HRC.