Some problems often encountered in the production process of stamping dies

1 mold failure

Mold failure is the most prone problem in stamping production, often resulting in production downtime, affecting product production cycle. Therefore, the cause of the mold failure must be found as soon as possible, and reasonable maintenance.

(1) mold damage

Mold damage refers to the cracking, breaking, and opening of the mold. To deal with the problem of mold damage, it is necessary to find the reason from the design of the mold, the manufacturing process and the use of the mold.

First of all, it is necessary to check whether the manufacturing material of the mold is suitable, and whether the corresponding hot-buried process is reasonable. Generally, the heat treatment process of the mold material has a great influence on it. If the quenching temperature of the mold is too high, the quenching method and time are unreasonable, and the number of tempering and temperature, improper selection between the elbows, will cause the mold to be damaged after entering the stamping production. The size or depth of the blanking hole is not designed enough to easily block the slot and cause the blanking plate to be damaged. If the spring force design is too small or the height is not equal, the spring will break and the blanking plate will tilt. This will cause overlapping punching and damage to the parts. Improper punching or insufficient screw strength can cause the punch to fall or break.

When the mold is used, the position and orientation of the parts are incorrectly installed or the bolts are not fastened. The working height is adjusted too low and the guide column is insufficiently lubricated. If the feeding equipment is faulty, the press is abnormal, etc., the mold will be damaged. If the foreign matter enters the mold, the overlap of the parts, the blockage of the waste, etc. are not treated in time, and the processing is continued, the blanking plate, the punch, the lower template and the guide post of the mold are easily damaged.

(2) card model

During the stamping process, once the mold clamping is not flexible or even stuck, it is necessary to stop production immediately, find out the cause of the card and eliminate the fault. Otherwise, the fault will be enlarged and the mold will be damaged.

The main causes of the card mold are: poor mold orientation and tilt. Or there is a foreign object between the templates, so that the template can not be flat; the mold strength design is not enough or the force is uneven. The deformation of the mold is caused. For example, the hardness and thickness of the mold base and the template are too small to be easily deformed by external force; the position of the mold is not installed correctly, and the positioning error of the upper and lower molds is excessive. Or the accuracy of the press is too poor, causing the mold to interfere; the strength of the punch is not enough, the size of the punch is too close, and the lateral force of the mold is unbalanced. At this time, the punch strength should be increased to enhance the guiding protection of the discharge plate.

(3) Mold damage and repair

The cost of stamping production is high. Usually the mold cost is 1/5-1/4 of the total cost of the part. This is because, in addition to the difficulty in manufacturing the mold and the high cost. The cost of mold repair and sharpening maintenance after putting into production is also high, and the original cost of the mold only accounts for about 40% of the total mold cost. Therefore, timely repair of the mold to prevent mold damage can greatly reduce the cost of stamping production.

After the mold is damaged, there is a problem with the selection of repair and scrap. Generally speaking. Unnatural wear of stamping dies, such as damage to non-critical parts. And the small punch is broken, the punch is thick and short, the concave template is cracked, the punching edge is cracked, etc. Most of them can be completely restored to the normal state by the maintenance method, and put back into the stamping production. but. When the key parts of the mold are seriously damaged, sometimes the convex and concave molds are damaged at the same time. The one-time repair cost exceeds 70% of the original cost of the die, or the mold life is near. The meaning of maintenance is not great. At this time, the scrap mold should be considered: except for the large mold and the continuous mold with complicated structure. When the mold repair technology is too complicated, the cost of mold repair is too large, the difficulty will inevitably make the maintenance period too long, which will seriously affect the normal production of stamping. It should choose to scrap the scrap in advance and re-manufacture the mold.

Under normal conditions, the main failure mode of the die is excessive wear. Delivered from the manufacture of new molds. Until the burr of the punched part exceeds the standard, the size and shape accuracy of the part are too bad, and the mold can no longer be repaired or has no repair value at all, the mold can only be scrapped. From the time the new mold is put into use to the end of the scrap. It usually takes many repairs and sharpening.

2 Product quality defects

The most common defect in the quality of the part is the size of the product. Only a few products have surface quality problems.

(1) Size is out of tolerance

Out of size is a serious flaw in stamped parts. In this regard, we must first check and check the design of the mold to eliminate the reasons for design and manufacture. If the tolerance is related to the thickness of the material, the thickness, material and hardness of the stamped material should be checked.

In the stamping production process, the size is out of tolerance, mainly due to the wear of the mold, poor positioning and deformation of the workpiece. The edge of the mold is worn out. It will cause the burr to be too large or the shape of the cut to become larger, the punching becomes smaller, and the flatness is too poor. The mold should be sharpened or replaced. Poor positioning and guidance includes no guide, guide pin or other positioning device does not work, the feeder does not relax, the positioning block wears too long, the feed distance is too long, the length of the guide plate is wrong or the guide gap is too large. The parts are deformed during production, mainly including impact deformation. For example, the blowing pressure of the product is too strong or the gravity falls. The impact is too large. When the material is squeezed or deformed during discharge, the discharge position should be cleared or the discharge space should be increased. : Ejection is improperly deformed. For example, when the top pin is improperly formulated, the spring force is not suitable, or the ejection force is too long, the elastic force should be adjusted or the position or the number of pins should be changed; Some curved parts can not allow the material to overlap, and must be dropped every time. When the dish strain occurs, the pressure pad can be used to eliminate it; the punching and shearing deformation is mainly due to the material distortion. The size is increased or the center is asymmetrical; the deformation of the chip is caused by the floating of the scrap or the fines remaining on the die face or the foreign matter and the like.

(2) Surface quality is unqualified

The surface quality of stamped parts is mainly due to excessive burrs. The reason for the excessive burrs of the workpiece is firstly the wear of the die edge. The mold should be re-ground (described below) to ensure sharp edges. Secondly, the interval between the convex and concave molds is unreasonable. If the gap is too large, most of the sides are wiped. If the gap is too small, the secondary shear surface will appear. If the hardness of the material is too high, the material should be replaced or the gap should be increased. When the size of the blanking edge is too small or the material to be trimmed is too small, the material will be pulled into the gap of the mold to become a flash. At this point, it is necessary to increase the size of the punched edge or the trimming margin.

3 mold sharpening

Reasonable sharpening of the mold in stamping production. It can effectively improve the life of the die, save the cost of the mold, and greatly reduce the cost of the product.

When the die edge wears to a certain extent, the original sharp edge becomes dull, which will cause the punching burr to be too large, and the dimensional and shape accuracy will decrease. Therefore, the mold must be sharpened to restore its sharp blanking edge. Reduce the punching burr and the deviation of the size and shape to improve the surface quality of the formed part. If the mold is not sharpened in time, the blunt edge will be subjected to severe friction, such as hard, excessive, and thick burrs, resulting in excessive wear of the vicious cycle of the mold, resulting in several times of sharpening. The amount can restore the sharpness of the cutting edge and greatly shorten the life of the mold. When the burr of the part is about to exceed the allowable burr height, the production should be stopped immediately and the mold should be sharpened. In the actual production, the field workers are accustomed to determine the size of the burr of the workpiece and determine the timing of the sharpening by the hand feeling, so that the operation error is large. It is best to determine the burr height and thickness of the workpiece, the uniformity of the burr distribution, the size of the punching piece and the accuracy of the shape and the quality of the punching surface, etc., to grasp the wear of the cutting edge and the degree of dullness of the blade 121, so as to determine the optimal blade of the die. Grinding time.

The amount of mold sharpening must be determined according to the actual wear of the end face and side of the cutting edge. In addition, factors such as material thickness, die shape structure and sharpening order should be considered. After several times of sharpening of the die, the size will change, especially the punching die designed with the upper and lower large conical die. Since the die edge wall is inclined outward, the upper surface of the die is sharpened. Its horizontal size will inevitably produce an increment. Therefore, before the sharpening, the angle should be calculated according to the angle of the cone. When sharpening, pay attention to the size of the workpiece, and prevent the size increase of the workpiece from being too large due to multiple sharpening, resulting in the product being out of tolerance.