Two-color mold-electric tool housing two-color mold
Several common errors in stamping processing, see if you have ever occurred
In the process of stamping, there will be more or less various problems, and a large part of these problems are caused by very low-level errors. This reflects that our basic knowledge of stamping processing is not good enough. The following Kechuang summarizes some common basic errors in the stamping process:
1, the depth of the upper die into the lower die is too large during stamping
When punching, the depth of the upper mold entering the lower mold should not be too large. Generally, it is better to just break the sheet. The depth can be 0.5-1mm. If the upper mold enters the lower mold too deeply, the wear of the upper mold and the lower mold will be aggravated. In the case of poor mold guiding and punching accuracy, the cutting edge of the mold will be damaged, especially for punching thick materials and punching small holes. In high-speed stamping, the depth of the punching upper die into the lower die cannot be too large. In order to prevent the upper mold from entering the lower mold too deeply, a limit sleeve can be installed on both sides of the upper mold to limit the depth of the upper mold entering the lower mold. When grinding the upper mold, the limit sleeve is also ground to the same amount of grinding.
2, there is an eccentricity between the stamping pressure center and the punching pressure center
The point of action of the resultant punching force is called the punching pressure center. If the punching pressure center and the punching pressure center (usually located on the axis of the die shank hole) are not on the same axis, the punch slide will bear an eccentric load, which will cause abnormal wear of the slide rail and die guide part, and damage the movement accuracy of the punch , Reduce the life of the mold, and even damage the mold. Therefore, determining the stamping pressure center is an important task of mold design. For a workpiece with a simple and symmetrical shape, the resultant stamping force is at its geometric center, and the center of pressure does not need to be calculated. For workpieces with complex shapes and multi-process continuous stamping dies, the method of finding the combined force point of the parallel force system should be used to determine the stamping pressure center.
3, the punching force exceeds the nominal pressure of the punch
The choice of stamping press is mainly based on the pressing force. The principle is that the punching force cannot exceed the nominal pressure of the punch. The main factors affecting the punching force are the material thickness and mechanical properties, the peripheral length of the stamping part, the size of the die gap and the sharpness of the cutting edge. When stamping high-strength materials or workpieces with large thicknesses and large contours (such as thick plate stamping), the required punching force is often close to or exceeds the nominal pressure of the punching machine, and when the number of punching machines available in the factory is limited, this is the case. It is necessary to consider trying to reduce the punching force from the mold structure. The main methods to reduce the punching force are: oblique edge punching method, step upper die punching method, part step punching method, heating punching method and so on. The oblique edge punching method is to make the cutting edge of the upper die (when punching) or the lower die (when blanking) into a shape inclined to its axis at an angle, this angle is less than 150 degrees, generally 80~100 degrees and the oblique blade shear The cutting is similar, the entire cutting edge is not in contact at the same time, but the material is punched step by step, so the punching force is significantly reduced, and the vibration and writing noise during punching can be reduced. Heating stamping is when the material is stamped under heating (or called red stamping). Since metal materials generally have a significant decrease in shear strength under heating, the stamping force can be effectively reduced. However, the disadvantage of this method is that the material is heated to produce oxide scale, which affects the surface quality of the parts. Therefore, it is generally used for thick plate stamping or stamping of parts with low size and surface quality requirements. In addition, the cutting edge of the die is dull, chipped or not sharp, which will also significantly increase the punching force. Therefore, maintaining a sharp edge is one of the conditions for the normal working of the stamping die. In order to keep the edge of the die sharp, the edge of the die should be sharpened after a period of time.
4. There is a large cavity under the die base in the fixed upper mode fine blanking die
The structure type of fine blanking die can be divided into fixed upper mode fine blanking die and movable upper mode fine blanking die. Different mold structure forms require corresponding punching table structure to match. For the movable upper mode fine punching die, the working table of the punching press is required to be a floating hydraulic working table composed of annular oil cylinders and plungers around the center and fixed and resistant. For the fixed upper mode fine punching die, a plunger cylinder is required in the middle of the worktable of the punch press, as shown in Figure 3-29. The characteristic of this kind of mold structure is that the upper and lower molds are fixed on the lower mold base, and the blank holder keeps relative movement with the upper and lower molds through the force transmission rod and the mold base. The fixed upper mode fine punching die should not have a large cavity under the die base. This is because: when the upper die is pressed, the hydraulic cylinder moves downward under the action of the force transfer rod, so a large cavity appears under the die base. Hole, and all the punching force acts on the top of the cavity, which causes the upper and lower molds to bend, which is very unfavorable. Under the action of increasing punching force, the lower part of the upper and lower molds will be broken due to bending. Danger. In order to avoid this situation, when the punching force is high, a special joint ring is required to improve the supporting conditions of the lower mold base, and avoid the occurrence of a big grab and the upper and lower molds to bend. Due to the development of fine blanking technology to large-scale and composite processes, it is necessary to punch holes or larger inner contours, and the punching force is very large, and the required blank holder force and back pressure are both large. Therefore, the center of the punching table is required.
5, the active upper mode fine punching die punching parts with multiple holes or large internal contours
The upper and lower molds of the movable upper mode fine blanking die are directly fixed on the center of the worktable, and the supporting conditions are good. The characteristics of this mold structure are: the upper and lower molds are movable relative to the mold base, and the upper and lower molds are guided by the inner hole of the mold base and the blank holder. The lower mold and the blank holder are respectively fixed on the upper and lower mold seats. The upper and lower molds are kept in relative positions through the blank holder and the lower mold. Therefore, the gap between the upper and lower molds and the lower mold is required to be smaller. Long orientation and correct positioning can ensure alignment. Therefore, the movable mode fine blanking die cannot punch parts with multiple holes or large internal contours. Because the mold assembly is difficult to align and the gap is difficult to ensure, it is mainly suitable for fine blanking of small and medium-sized parts.
6, the heat treatment hardness of the upper and lower die of the stamping die is lower than 55HRC
The upper die and the lower die of the stamping die are in contact with the stamping material, which is subject to greater force and wears quickly. Therefore, the upper and lower dies 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 and the more wear-resistant. Different die steel materials have different heat treatment processes and hardness. Cold work die steel Cr12MoV, high-speed steel W18Cr4V2, high heat treatment hardness, good hardenability, small quenching deformation, no cracking, suitable for stamping parts with complex shapes, and T8A has good hardenability, but poor hardenability, and easy quenching deformation Cracking, often used to punch simple and soft parts. Since the processing of the lower mold is relatively difficult to the upper mold, the hardness of the lower mold is higher than that of the upper mold, generally 2-3 Rockwell hardness higher, that is, the heat treatment hardness of the upper mold is generally 58~60HRC, and the heat treatment hardness of the lower mold is 60~62HRC.