Common problems and solutions of stamping dies

1、 Causes of cracking and bursting of stamping die template
It mainly includes the following:
1. Unsmooth blanking: there is no leakage, or rolling and blocking, or foot blocking when assembling the mold. This is the most common. If the assembly master does not pay attention, such as when there are many blanking holes, or when the mold has a cushion block, this situation is most likely to occur
2. Design process: the strength of the mold is not enough, the spacing between the knife edges is too close, the mold structure is not reasonable, and the number of template blocks is not enough without base plates and feet
(1) Layout and lapping: unreasonable reciprocating feeding layout method and too small lapping value often cause sharp wear of the mold or gnawing of the convex and concave molds. Reasonable selection of layout method and lapping value can improve the die life.
(2) Precision of die guide mechanism: accurate and reliable guide has a great impact on reducing the wear of die working parts and avoiding the gnawing of convex and concave dies, especially for blanking dies without gaps and small gaps, compound dies and multi-station progressive dies. In order to improve the service life of the die, it is necessary to correctly select the guiding form and determine the precision of the guiding mechanism according to the requirements of the process nature and the precision of the parts.
(3) Geometric parameters of die (male and female die) edge.
3. Heat treatment: deformation caused by improper quenching and tempering process
Practice has proved that the hot working quality of the die has a great impact on the performance and service life of the die. According to the analysis and statistics of die failure causes, the "accident" of die failure caused by improper heat treatment accounts for more than 40%.
(1) Forging process: This is an important link in the manufacturing process of die working parts. For the mould of high alloy tool steel, technical requirements are usually put forward for the metallographic structure such as carbide distribution of the material.
(2) Preparation heat treatment: annealing, normalizing or quenching and tempering and other preparation heat treatment processes shall be adopted according to the different materials and requirements of the die working parts to improve the structure, eliminate the structural defects of the forging blank and improve the processing technology. After proper preliminary heat treatment, the high carbon alloy die steel can eliminate the network secondary cementite or chain carbide, spheroidize and refine the carbide, and promote the uniformity of carbide distribution, which is conducive to ensuring the quenching and tempering quality and improving the die life.
(3) Quenching and tempering: this is the key link in die heat treatment. If overheating occurs during quenching and heating, it will not only cause greater brittleness of the workpiece, but also easily cause deformation and cracking during cooling, which will seriously affect the die life. During die quenching and heating, special attention should be paid to prevent oxidation and decarburization. The heat treatment process specification should be strictly controlled. If conditions permit, vacuum heat treatment can be used. Tempering shall be conducted in time after quenching, and different tempering processes shall be adopted according to technical requirements.
Analysis of the causes of the bursting of the stamping die, which the die maker must know
(4) Stress relief annealing: After rough machining, die working parts shall undergo stress relief annealing treatment to eliminate the internal stress caused by rough machining, so as to avoid excessive deformation and cracks during quenching. For molds with high accuracy requirements, after grinding or electric machining, they need to undergo stress relief tempering treatment, which is conducive to stabilizing the mold accuracy and improving the service life.
4. Die grinding flatness is not enough, resulting in deflection and deformation
The surface quality of die working parts is closely related to the wear resistance, fracture resistance and adhesion resistance of the die, and directly affects the service life of the die, especially the surface roughness value. If the surface roughness value is too large, stress concentration will occur during working, and cracks will easily occur between its peaks and valleys, which will affect the durability of the die and the corrosion resistance of the workpiece surface, and directly affect the service life and accuracy of the die. For this reason, the following items should be noted:
(1) During the processing of die working parts, it is necessary to prevent grinding from burning the surface of the parts, and strictly control the grinding process conditions and methods (such as grinding wheel hardness, grain size, coolant, feed rate and other parameters);
(2) During processing, it is necessary to prevent macro defects such as knife marks, interlayers, cracks, impact marks, etc. on the surface of the working parts of the mold. The existence of these defects will cause stress concentration, become the source of fracture, and cause early failure of the mold;
(3) Use grinding, grinding, polishing and other finishing and fine processing to obtain a smaller surface roughness value and improve the service life of the mold
5. Improper wire cutting: wire cutting by pulling wire, the gap is incorrect, and the angle is not cleared
The wire cutting was artificially pulled, and the wire cutting gap was not properly treated, and the angle was not cleared and the metamorphic layer of wire cutting was not affected. The cutting edge of the die is mostly processed by wire cutting. Due to the thermal effect and electrolytic effect of WEDM, a certain thickness of metamorphic layer is produced on the surface of the die, resulting in the reduction of surface hardness and the appearance of micro-cracks, which leads to the early wear of the die processed by WEDM, which directly affects the maintenance of the die blanking clearance and the easy edge collapse, and shortens the service life of the die. Therefore, in the process of online cutting, a reasonable electrical gauge should be selected to minimize the depth of the metamorphic layer.
6. Selection of punch equipment: punch tonnage, insufficient blanking force, too deep mold adjustment
The punch tonnage, the punching force is not enough, and the mold is adjusted too deeply. The precision and rigidity of stamping equipment (such as press) are extremely important to the life of the die. The precision and rigidity of the stamping equipment are high, and the die life is greatly improved. For example, the die material of complex silicon steel sheet is Crl2MoV, which is used on ordinary open press, and the average regrinding life is 30000 to 30000 times; When used on the new precision press, the regrinding life of the die can reach 6-120000 times.
7. Unsmooth material removal: no demagnetization treatment and no material removal tips before production; There are stuck materials such as broken needle and spring in production
8. The mold material is not good, and it is easy to break in the subsequent processing
9. Production awareness: lamination stamping, positioning is not in place, no air blowing gun is used, and the formwork is cracked and still continues to be produced
2、 Die life analysis
When it comes to die life, it is more reasonable to say that die failure form
The failure forms of the die are mainly wear failure, deformation failure, fracture failure and gnawing failure. However, due to different stamping processes and working conditions, there are many factors affecting the life of the die. The following is a comprehensive analysis of the factors affecting the die life in terms of the design, manufacture and use of the die, and the corresponding improvement measures
1. Stamping equipment
The precision and rigidity of stamping equipment (such as press) have an extremely important impact on the life of the die. The precision and rigidity of the stamping equipment are high, and the die life is greatly improved. For example, the die material of complex silicon steel sheet is Crl2MoV, which is used on the ordinary open press and has an average regrinding life of 30000 to 120000 times, while the regrinding life of the die can reach 60000 to 120000 times when used on the new precision press. In particular, the press with high precision and good rigidity must be selected for small clearance or no clearance die, carbide die and precision die, otherwise, the die life will be reduced, and even the chess set will be damaged.
2. Mold design
3. Stamping process
(1) Raw materials of stamping parts
In actual production, the raw material thickness tolerance of external pressure parts is out of tolerance, material performance fluctuation, surface quality is poor (such as rust) or not clean (such as oil stain), which will lead to the adverse consequences such as increased wear of mold working parts and easy to crack. Therefore, it should be noted that: ① raw materials with good stamping process shall be used as far as possible to reduce the stamping deformation force; ② Before stamping, the brand, thickness and surface quality of raw materials shall be strictly checked, and the raw materials shall be wiped clean, and the surface oxide and rust shall be removed if necessary; ③ According to the stamping process and the type of raw materials, softening treatment and surface treatment can be arranged if necessary, and appropriate lubricants and lubrication processes can be selected.
(2) Layout and lapping
Unreasonable reciprocating feeding and layout method and too small lapping value often cause sharp wear of the die or gnawing of the convex and concave dies. Therefore, while considering improving the utilization of material judgment, the layout method and lapping value must be reasonably selected according to the processing batch, quality requirements and die fit clearance of parts to improve the die life.
4. Mold material
The influence of die material on die life is a comprehensive reflection of material type, chemical composition, microstructure, hardness and metallurgical quality. Die life of different materials is often different. For this reason, two basic requirements are put forward for the materials of working parts of stamping dies:
① The service performance of the material shall have high hardness (58~64HRC) and high strength, high wear resistance and sufficient toughness, small heat treatment deformation and certain thermal hardness;
② Good process performance. The processing and manufacturing process of stamping die working parts is generally complex. Therefore, it must have adaptability to various processing technologies, such as malleability, machinability, hardenability, hardenability, hardenability, quenching crack sensitivity and grindability. Generally, die materials with excellent performance are selected according to the material characteristics, production batch, precision requirements, etc. of stamping parts, while taking into account its process and economy.
In short, formwork cracking and bursting must be treated with caution, because there are certain safety hazards in production
3、 Let me show you the mold foundation: 17 typical mold problems and 17 solutions!
1. Scrap jumping
A. If the punch length is not enough, replace the punch according to the cutting edge of the punch cutting into one material thickness of the concave die plus 1mm
B. The clearance of the concave die is too large, and the gap can be reduced by cutting the insert or by using the draper
C. The punch or template is not demagnetized. Use demagnetizer to demagnetize the punch or template
2. Scrap plugging
A. The blanking hole is small or the blanking hole is offset, and the blanking hole is enlarged to make the blanking smooth
B. The blanking hole has a chamfer. Increase the blanking hole to remove the chamfer
C. The knife edge is not laid with a taper line to cut the taper or expand the hole on the reverse side to reduce the length of the straight wall position
D. The straight wall position of the knife edge is too long and the reverse side is drilled to shorten the straight wall position of the knife edge
E. The edge is broken, resulting in a large edge, and the edge is reground due to material blockage
3. Poor front
A. The edge of the blade is broken, resulting in excessive edge and regrinding the edge
B. The clearance between the punch and the die is too large. Cut the wire into the block and re-arrange the clearance
C. Poor finish of concave die knife edge polishing straight wall position of knife edge
D. The clearance between the punch and the female die is too small to save the die and match the clearance
E. If the jacking force is too large, pull out the draper reversely to change the spring to reduce the jacking force
4. Uneven trimming
A. Positioning offset adjustment positioning
B. One-sided forming, material pulling and pressing force increase, and positioning adjustment
C. Design error, resulting in uneven tool connection, cutting edge insert
D. Feeding is not allowed to adjust the feeder
E. The feeding step calculation is incorrect. Recalculate the step and reset the tool position
5. The punch is easy to break
A. The closing height is too low, and the punch cutting edge is too long. Adjust the closing height
B. Improper material positioning, resulting in unilateral cutting of punching punch, adjustment of positioning or fracture of feeding device due to uneven stress
C. The cutting edge is blocked by the lower die waste, which causes the punch to break, and the large blanking hole is drilled again to make the blanking smooth
D. The fixed part of the punch (splint) and the guide part shall be repaired or the wire shall be cut into the block again to make the punch move up and down smoothly (punch)
E. The punch is not well guided, which causes the punch to be forced on one side to re-repair the punch clearance
F. The punch knife edge is too short, and it interferes with the punch plate to replace the punch and increase the length of the knife edge
G. The punch is not fixed well, and moves up and down. Fix the punch again to prevent it from moving up and down
H. The punch edge is not sharp and regrind the edge
I. The surface of the punch is strained, and the stress is uneven during stripping. Replace the punch again
J. The punch is too thin, too long, and the strength is not enough. Change the punch type again
K. The punch hardness is too high, the punch material is not correct, the punch material is changed, and the heat treatment hardness is adjusted
6. Iron filings
A. Rebar dislocation Recalculate the rebar position or bending position
B. If the bending clearance is too small, extrude the scrap iron to readjust the clearance, or grind the formed block, or grind the formed punch
C. Bending punch is too sharp to repair R angle
D. The material of the knife edge is too small to reconnect the knife edge
E. If the rib is too narrow, regrind the rib
7. Poor sprouting
A. The center of the bud bottom hole does not coincide with the center of the bud punch to determine the correct center position, or move the position of the bud punch, or move it to the position of the bud - edge high - edge low or even break dynamic pre-punch, or adjust the position
B. Uneven gap of the female die, resulting in sprouting - high side - low or even broken sprouting gap during repair
C. The sprouting bottom hole does not meet the requirements, resulting in the sprouting height and recalculation of the bottom hole diameter, and the pre-punching increases or reduces the diameter deviation, or even cracks
8. Poor molding
A. The forming die punch is too sharp, which causes the material to crack. The forming punch is trimmed with R angle, and the knife edge is properly trimmed with R angle
B. The forming punch length is not enough, resulting in the failure to calculate the correct length of the punch and adjust the actual length of the punch to meet the forming requirements
C. The forming punch is too long and the material at the forming part is deformed, so it is necessary to determine the correct length of the punch, and adjust the actual length of the punch to meet the requirements until the punch breaks
D. The material at the forming part is not enough to cause tensile crack, calculate the expanded material, or repair the R angle, or reduce the forming height
E. Poor positioning, resulting in poor molding adjustment positioning or feeding device
F. The forming gap is too small to cause cracks or deformation
9. Bending dimension
A. The mold is not adjusted in place, resulting in angle error, resulting in size deviation, poor closing height or poor angle difference
B. Poor angle caused by insufficient elasticity leads to dimensional deviation. Replace the spring
C. The material does not meet the requirements, resulting in poor angle, resulting in size change of material or re-adjustment of gap deviation
D. Poor angle caused by material thickness deviation, resulting in size deviation, material thickness determination, material replacement or re-adjustment of gap difference
E. Size deviation caused by improper positioning Adjust the positioning to make the size OK
F. The design or processing error caused intermittent repair welding and grinding between the bent male blocks, eliminated the gap between the blocks, and led to the small bending size~
G. The molding tool has no R angle, and the bending height is too small under the angle and other normal conditions
H. The bending size on both sides is too large for compression reinforcement
I. Size instability caused by unilateral bending and drawing increases spring force and adjusts positioning
J. Unreasonable clearance, resulting in poor angle and dimension deviation, repair clearance
K. The height of the bending tool is not enough, and the bending punch is too short to close the bending tool, which increases the height of the bending tool, so that the bending punch can close into the position of the bending tool as much as possible, resulting in more bad angle
L. The bending speed is too fast, which causes the deformation of the bending root. Adjust the speed ratio control and select a reasonable speed
M. The structure is not reasonable, the folding knife is not inserted into the fixed template, and the groove is milled again. When the folding knife is inserted into the template for stamping, the gap becomes larger
N. The hardness of the molding male heat treatment is not enough, resulting in the collapse of the pressing line or the flattening of the reshaped male pressing line
10. No unloading
A. Improper positioning or feeding Adjust the positioning or feeding device
B. The avoidance position is not enough to be polished
C. The inner guide pillar is strained, which causes the board to move slowly. Replace the inner guide pillar
D. The punch is pulled or the surface is not smooth. Replace the punch
E. Reasonably rearrange the position of the ejector pin
F. The jacking force is not enough, or the stripping force is not enough. Replace the jacking spring or stripping spring
G. The punch and the splint are not matched smoothly. Repair the splint and the splint to make the punch fit smoothly
H. The formed slide block is not smoothly matched. Trim the slide block and guide groove to make it fit smoothly
I. The heat treatment of the plate is not suitable, and the plate is deformed after stamping for a period of time. Grind the plate again and correct the deformation
J. The punch is too long or the length of the ejector pin is not enough. Increase the length of the ejector pin or replace it with a punch with appropriate length
K. Replace the punch when the punch is broken
L. The template is not magnetized, and the workpiece is brought up to demagnetize the template
11. Unsmooth feeding
A. The mold is not aligned, resulting in that the material belt is not in the same line with the feeder and the mold is not aligned with the mold or adjusted feeder
B. The belt is not flat, adjust the leveling machine or replace the material
C. Non-discharging causes irregular feeding. Refer to non-unloading solutions
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D. The positioning is too tight. Adjust the positioning
E. The guide pin is too tight or the straight wall position is too long. Adjust the guide pin
F. The punch is not fixed properly or is too long and interferes with the strip to change the length

12. Poor riveting
A. The closing height of the mold is not correct. The riveting is not in place. The closing height is not adjusted
B. The workpiece is not placed in place, and the positioning deviation is adjusted
C. Before riveting, if the workpiece is defective, confirm the sprout hole, and refer to the solution for the defective sprout hole to confirm whether the riveting hole is chamfered. If there is no chamfer, increase the chamfer
D. If the riveting punch length is not enough, replace it with a punch with appropriate length
E. Confirm that the riveting punch does not meet the requirements and use the riveting punch that meets the requirements
13. Missing or installing
A. Be careful when assembling and erecting
B. Punch has no direction mark. Punch with direction shall be marked
14. Install the wrong screw
A. Do not know the thickness of the formwork. Know that the thickness of the formwork is too long or too short
B. Not careful and experienced enough to select proper screws
15. Disassembly and assembly of mold
A. If the pin hole is not cleaned, clean the pin hole and pin. When removing the mold, remove the locating pin first, which is easy to damage the mold. When installing the mold, use the screw to guide it first, and then punch the locating pin hole
B. Do not damage the pin hole when the pin is knocked down due to incorrect mold assembly and disassembly procedures
16. Locating pin
A. When the hole wall is roughened and scratched, resulting in too tight mold assembly, carefully check whether the pin hole is roughened, otherwise the pin hole that cannot be punched out should be reamed again
B. The pin hole is out of position or there is no escape hole below, and the locating pin escape hole is added
17. The spring is too long
A. The depth of the spring hole was not measured, and the compression of the spring was calculated. The spring could not be pressed down after re-selection
B. Inadequate care and experience, suitable lower dead center of spring