Some tips for punching die repair

Continuous mode maintenance must be done with careful patience and step-by-step procedures. Do not engage blindly. Repairing the mold due to a failure requires the use of tape to facilitate the query of the problem. Open the mold, check the tape, check the condition of the mold, confirm the cause of the failure, identify the problem, and clean the mold before removing the mold. When the mold is removed, the force should be uniform. For the mold structure of the feed spring between the fixed plate and the stripper plate and the stripping spring directly on the inner column, the removal of the stripper plate must ensure the balanced stripping of the stripper plate. The tilting of the stripper plate may cause cracking of the punch in the mold.

Male and female die maintenance

When the male and female molds are disassembled, they should pay attention to the original conditions of the molds so that they can be easily restored during the subsequent mold installation. There must be pads or shifts to make the thickness of the gaskets on the parts and make records. Replace the punches to try to remove the material. Whether the block die is smooth and whether the gap between the test plug and the die is uniform, and whether the replacement of the die must be even if the clearance between the punch and the punch is uniform. For the trimming of the punch, the back die needs to be padded to achieve the required length. Should check the effective length of the punch is sufficient. Replace the broken punch to find out the reasons, at the same time to check whether the corresponding die die edge, whether the need to grind the edge. Assembly punch to check the punch and fixed block or fixed Whether the gap between the plates is enough, there is a press block to check whether there is an active margin. The assembly die should be placed horizontally, and then use a flat iron block placed on the surface of the die and tap it in place with a copper rod, must not Inclined strong hammering, the bottom of the die should be chamfered. After installation, check whether the die surface is flush with the die surface. After the punch die and the core are assembled, check the tape to check if necessary. Or install the opposite, check if the die and the die pad are reversed and the blanking hole is blocked. Whether or not to change the parts need to steal material, need to steal the material is enough, the mold needs to lock the locking position is not locked. Note that the screws to remove the material to confirm the lock, the lock should be from the inside to the outside, balanced cross-force locking, can not be Tighten one of the screws and tighten the other to prevent the tilt of the stripper causing the punch to break or reduce the accuracy of the mold.

Detaching plate maintenance

The removal of the stripper can be balanced with two drivers, and then the force is taken out by balancing with both hands. When the removal is difficult, the inside of the mold should be checked to see if it is cleaned and the locking screws are completely removed. Die damage, identify the cause and then do the appropriate treatment, must not blindly dispose. When assembling the stripper, first clean the punch and the stripper, add lubricant to the guide post and punch injection, and put it smoothly. With both hands pressed in place, and repeated several times. If too tight should identify the reasons (guide pillar and guide sleeve guide is normal, whether the various parts of the damage, whether the new replacement punch can smoothly pass the position of the stripper board) check Observe the reasons for the corresponding treatment. Fixed plate with a briquette to check whether the material on the backing plate is sufficient. The material contact surface between the stripper plate and the die, stamping for a long time to produce indentation (demolition plate and die The gap between the material and material is generally 0.03-0.05mm thick. When the indentation is severe, it will affect the pressing accuracy of the material and cause the product dimension to be abnormally unstable. It is necessary to perform repair or re-grinding on the material insert and stripper plate. The contour sleeve should be checked for accuracy. It will cause the stripper to tilt when it is not equal. Obliquely, its precision-guided smooth ejection function will be destroyed and must be maintained.

Guide site inspection

Guide column guide sleeve with clearance, whether there are burns or wear marks, the mold guide the oil state is normal, should be checked. The wear and precision of the guide part is destroyed, so that the precision of the mold is reduced, all parts of the mold will appear Problems must be properly maintained and replaced on a regular basis. Check the accuracy of the guides. If the guide pins are worn out, the accuracy and function of the guides must have been lost and must be replaced. Check the condition of the springs. Top-feed springs, etc.) To see if it is broken or used for a long time Although not broken, but fatigue has lost the original strength, regular maintenance and replacement must be done, otherwise the mold will be damaged or the production will not be smooth.

Die clearance adjustment

The core positioning holes are worn due to the frequent combination of the cores, resulting in large gaps after assembly (loose after assembly) or uneven gaps (caused by positioning deviations) that will result in poor shape of the cross-section after punching. The mold is easy to break, resulting in burrs, etc. It is possible to make proper clearance adjustments by checking the cross-sectional condition after punching. When the clearance is small, the section is small. When the clearance is large, the section is more and the burrs are larger. It is obtained by shifting. Reasonable clearance, after adjustment, should be properly recorded, can also be marked in the die edge, etc., in order to follow-up maintenance operations. Daily production should pay attention to the original material collection and preservation of the mold when the tape is better, such as follow-up production is not smooth When the mold is mutated, it can be used as a reference for mold repair. In addition, whether the auxiliary system such as the top material pin is worn or not, whether the material can be topped, and whether the guide pin and the sleeve are worn, should be checked and maintained.

What are the main reasons for mold burst?

Due to different stamping processes and different working conditions, the causes of die burst are many. The following is a comprehensive analysis of the reasons for the die burst in the design, manufacture, and use of the die and the corresponding improvement measures.

(1) mold material is not easy to crack in subsequent processing

Dies of different materials often have different life spans. For this purpose, two basic requirements are put forward for the working part material of the die: 1 The performance of the material should have high hardness (58~64HRC) and high strength, and have high wear resistance and sufficient toughness, heat treatment deformation is small, there is a certain Hardness; 2 process performance is good. Die processing parts manufacturing process is generally more complicated. Therefore, it must have adaptability to various processing techniques such as malleability, machinability, hardenability, hardenability, quench cracking sensitivity, and grinding processability. Usually based on the material characteristics of the stamping parts, production volume, precision requirements, etc., select the mold material with excellent performance, taking into account its craft and economy.

(2) Heat treatment: Improper deformation due to quenching and tempering

Practice has proved that the hot processing quality of the mold has a great influence on the performance and service life of the mold. From the analysis and statistics of the cause of the failure of the mold, it can be known that the “accident” caused by improper heat treatment accounted for about 40% of the failure. The quenching deformation and cracking of the working parts of the mould and the early fracture of the working process are all related to the hot working process of the fixture.

1) Forging process:

This is an important part of the manufacturing process of mold working parts. For the tooling of high-alloy tool steels, the technical requirements for the metallographic structure of the material, such as the distribution of carbides, are usually put forward. In addition, the forging temperature range should be strictly controlled, the correct heating specification should be established, the correct forging force method should be used, and the slow cooling or timely annealing after forging should be adopted.

2) Preparation heat treatment:

The annealing, normalizing, or quenching, and other preliminary heat treatment processes should be adopted separately depending on the materials and requirements of the working parts of the mold, in order to improve the organization, eliminate the defects of the forging blanks, and improve the processing technology. The high-carbon alloy die steel can eliminate meshed secondary cementite or chain carbides after proper preliminary heat treatment, so that the carbides are spheroidized and refined, and the distribution of carbides is promoted. This will help ensure the quality of quenching and tempering and improve the life of the mold.

3) Quenching and tempering:

This is a key part of the mold heat treatment. If overheating occurs during quenching and heating, not only the workpiece will cause large brittleness, but also it will easily cause deformation and cracking during cooling, which will seriously affect the life of the mold. Special care should be taken to prevent oxidation and decarburization when the die is quenched and heated. Strictly control the specification of the heat treatment process. If conditions permit, vacuum heat treatment can be used. After quenching, it shall be tempered in time, and different tempering processes shall be adopted according to technical requirements.

4) Stress relief annealing:

The mold working parts should be annealed and annealed after rough machining. The purpose is to eliminate the internal stress caused by rough machining so as to avoid quenching and excessive deformation and cracking. For molds with high precision requirements, after stressing or electro-machining, they need to undergo stress-reducing and tempering treatment, which will help stabilize the accuracy of the mold and increase the service life.

(3) The flatness of the mold is not enough to produce deflection

The pros and cons of the surface quality of the working parts of the mold have a very close relationship with the wear resistance, fracture resistance and anti-adhesion ability of the mold, and directly affect the service life of the mold. In particular, the surface roughness value has a great influence on the die life. If the surface roughness value is too large, stress concentration will occur during operation, and cracks will easily occur between peaks and valleys, which will affect the durability of the die, and will also affect the The corrosion resistance of the workpiece surface directly affects the service life and accuracy of the die.

To do this, pay attention to the following:

1) During the processing of mould working parts, it is necessary to prevent grinding of surface parts of burned parts, and the grinding process conditions and technological methods (such as hardness, particle size, coolant, feed amount, etc.) of the grinding process should be strictly controlled;

2) During the machining process, the tool marks on the surface of the working part should be prevented. Interlayers, cracks, impact scars and other macro defects. The existence of these defects will cause stress concentration and become the source of the fracture, causing early failure of the mold;

3) The use of grinding, grinding, polishing and other fine processing and fine processing, to obtain a smaller surface roughness value, improve the service life of the mold.

(4) Design process: mold strength is not enough, knife-edge distance is too close, mold structure is irrational, number of template blocks is not enough, there is no padding foot, mold guide is inaccurate, and clearance is unreasonable.

1) Nest and tie.

Unreasonable reciprocating feed layout methods and excessively small bridging values ​​often result in rapid wear of the mold or bruising or denting of the mold. Therefore, in consideration of improving the material utilization rate of the material, it is necessary to reasonably select the method of layout and the margin value in accordance with the processing volume, quality requirements of the components, and the clearances for the mold assembly, so as to increase the service life of the mold.

2) The accuracy of the guide mechanism of the mold.

Accurate and reliable guidance is more effective in reducing the wear of mould working parts and avoiding the great influence of convex and concave die bruising. In particular, gapless and small gap blanking die, compound die and multi-position progressive die are more effective. In order to improve the life of the mold, it is necessary to correctly select the guide type and determine the accuracy of the guide mechanism according to the requirements of the nature of the process and the precision of the parts. Under normal circumstances, the accuracy of the guide mechanism should be higher than the convex and concave mold fitting.

3) Die (convex, concave die) edge geometry.

The shape of the convex and concave molds, the fit clearance, and the radius of the fillet not only have a greater impact on the stamping part, but also have a great influence on the wear and life of the mold. For example, the clearance of the mold directly affects the blanking quality and die life. For those with higher accuracy, smaller gap values ​​should be selected; otherwise, gaps can be appropriately increased to increase die life.

(4) Wire cutting process:

Man-made pull line cuts, wire cut gaps are not handled correctly, and are not affected by the metamorphic layer of clear corners and wire cuts.

Die cutting edge more use of wire cutting. Due to the thermal effect and electrolysis of the wire cutting process, the deformed layer with a certain thickness is produced on the surface of the die, resulting in a decrease in the surface hardness and the appearance of micro-cracking, etc., resulting in early wear of the die for wire cutting and directly affecting the blanking gap of the die. Keeping and cutting edge is easy to collapse and shorten the service life of the die. Therefore, reasonable electrical specifications should be selected during on-line cutting to minimize the depth of the altered layer.

(5) Selection of punching equipment: punch tonnage, punching force is not enough, mold adjustment is too deep.

The precision and rigidity of the pressing equipment (such as a press) have an extremely important influence on the die life. The stamping equipment has high precision and rigidity, and the life of the die is greatly improved. For example, the complex silicon steel die material is Crl2MoV. It is used on ordinary open presses and has an average regrinding life of 1 to 30,000 times. However, on the new precision press, the resurfacing life of the die can reach 6 to 120,000 times. In particular, small gaps or gapless dies, hard alloy dies and precision dies must be selected with high precision and good rigidity. Otherwise, the life of the dies will be reduced. In serious cases, the chess pieces will be damaged.

(6) Stamping process:

Excessive tolerances in raw material thickness for stamped parts, fluctuations in material properties, poor surface quality (such as rust), or uncleanliness (such as oil stains) can result in increased wear of the mold's working parts, and can lead to chipping and other undesirable consequences.

1) Use stamped and processed materials as much as possible to reduce stamping deformation force;

2) Before the stamping, the grade, thickness and surface quality of the raw materials should be strictly inspected, and the raw materials should be wiped clean. If necessary, the surface oxides and rust should be removed;

3) According to the stamping process and the type of raw materials, if necessary, softening and surface treatment can be arranged, and appropriate lubricants and lubrication processes can be selected.

(7) Correct use and reasonable maintenance of production operations.

1) The material is not discharged smoothly: There is no demagnetization before production and there is no feed tip; there are broken springs and other cards in the production.

2) The blanking is not smooth: There is no leakage during the assembly of the mold, or the roller is blocked and the feet are blocked.

3) Awareness of production: Laminated stamping, positioning is not in place, air blow guns are not used, cracks in the formwork continue.

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