Improving die quality requires reasonable selection of materials, the adoption of appropriate heat treatment processes and optimized processing techniques for different materials, which can improve the manufacturing accuracy and service life of the die and prevent premature failures.
Based on this, this article mainly analyzes the factors that affect the service life of cold stamping dies and measures to improve their service life.
I. Analysis of factors affecting the service life of cold stamping dies
Today, with the rapid development of the economy, cold stamping dies are widely used in the mass production of mechanical parts by enterprises.
At the same time, to obtain maximum benefits, companies generally pay more attention to the service life of cold stamping dies.
1. Stamping and die design production process
In actual production, the factors that affect the operation of the die mainly include poor surface quality of the stamping material, large tolerances, unstable material properties and impurities on the surface, all of which will accelerate the wear of the die.
In the case of drawing dies, the most important factors affecting the die drawing load and the degree of adhesion are the formability, thickness and surface quality of the drawn material.
In the production of matrices, due to the existence of concave and convex angles in the integral matrices, stress concentrations may occur and cause the matrix to explode.
Furthermore, the shape and radius of concave and convex dies have a great influence on die wear.
For example, in a drawing die, a smaller radius of curvature can increase the flow resistance of the blank, continuously increase the friction force, and thus cause die wear or stamping fracture.
2. Matrix materials:
(1) The influence of die materials on the die life
Die material has the greatest impact on die life. The properties of the die material greatly affect the service life of the die.
For example, in the production of drawing dies, if Cr12MoV steel is used, it is easy to produce sharp and drawn hairs, but if GT35 type steel with a hard alloy structure is used, the tendency to bite can be greatly reduced and the service the life of the die can be improved.
(2) The working hardness of the die affects the service life of the die
Improving the hardness of the matrix mainly refers to the compressive strength, wear resistance and anti-bite ability of the matrix steel, but will also reduce the toughness, cold and hot fatigue resistance and machinability of the matrix.
In production and daily life, the common form of failure is high hardness, leading to matrix fracture, with deformation and wear occurring only in very few cases.
(3) The metallurgical quality of die materials affects the service life of the die
The metallurgical quality of die materials mainly affects large and medium-sized sectional dies and die steels with high carbon and alloy element content.
Real-world manifestations include assimilation of nonmetals, segregation of carbides, and intermediate looseness. For high-carbon, high-alloy steels, this easily leads to quench cracking and initial matrix damage.
3. Matrix heat treatment process
Preheat treatment, stress relief annealing after rough machining, quenching and tempering, stress relief annealing after grinding or electrical processing, etc. are all heat treatment methods for the matrix.
The quality of die heat treatment also has a great impact on the performance and service life of the die.
A large number of facts have proven that poor die heat treatment can directly lead to quenching deformation and cracking of die parts, as well as early failure during use.
4. Die processing technology
Cutting, grinding and electrical discharge machining (EDM) are machining processes required for die manufacturing. In production, these processes affect wear resistance, fracture resistance and matrix strength.
If processing methods are inadequate, problems with processing quality are likely to occur.
(1) The impact of grinding
Improper grinding can reduce the fatigue strength and fracture toughness of the die, as a result of grinding burns and cracks.
(2) The impact of EDM
Inadequate EDM can reduce the toughness and fracture resistance of the matrix. The main reason for this phenomenon is that EDM can produce EDM-burned layers, which have large tensile stress. When the thickness is large, microcracks will appear.
II. Measures to improve the service life of cold stamping dies
Through the analysis of the factors affecting the service life of cold stamping dies, it can be seen that the factors affecting the service life of the die are multifaceted, and these factors should be comprehensively considered when designing the die, so to design a more economical and efficient matrix.
For special-purpose cold stamping dies, economical and applicable dies should be designed based on your own requirements.
1. Correctly select matrix materials
The working conditions of convex die are worse than those of concave die, so the material of convex die must be of better quality than that of concave die.
When stamping in large quantities, attention should be paid to selecting die materials with high strength, good wear resistance and toughness.
2. Reasonable design structure of cold stamping dies, which is a necessary prerequisite to ensure the service life of the dies
The service life of cold stamping dies is closely related to the reasonable structural design.
At the beginning of the project, other design requirements of cold stamping dies must be guaranteed.
It is necessary to ensure the toughness, rigidity and strength of the die to ensure that the convex and concave dies and other structural components of the die are not deformed, damaged or increased in the degree of wear due to the impact of stamping force during the stamping process.
The matrix design should adopt a design with guidance elements as much as possible, and the design slack should also be considered. If the design clearance is too small or too large, it will also increase the wear degree of the convex and concave dies, causing damage to the die and reducing the service life.
3. Rational use and maintenance of the matrix
During the stamping process, the cold drawn billet must be phosphorized or copper coated to reduce frictional resistance during work and prevent die adhesion and biting.
Therefore, the metal plate before cold drawing must be preheated to improve the material processing performance, reduce the possibility of cracking, and extend the service life of the die.
Lubrication during cold drawing is also a good method. Good lubrication can obviously increase the surface smoothness of the metal plate, reduce frictional resistance, reduce wear and tear, and extend the service life of the die.
Lubrication is even more important for complex shaped parts during cold drawing.
When storing the die, a certain space must be maintained between the upper and lower dies to protect the cutting edge from damage.
During stamping, the entry depth of the convex mold into the concave mold must be well controlled to prevent wear from becoming more severe.
In stamping practice, after a period of punching and stamping, wear marks and grooves will appear on the cutting edge of the die.
At this time, repairing the die can not only reduce friction and resistance and prevent cracks caused by wear and groove marks, but also avoid additional bending moments caused by uneven clearance between the concave die cutting edge and the die convex after wear, and prolong the service life of the die.
After the cutting edge of the concave and convex dies is ground again, the cutting edge gap becomes more uneven.
At this time, the cutting edge should be carefully sanded and polished with a fine oil stone to remove grinding burrs.
Generally, the surface roughness value should reach Ra ≤ 0.10μm or lower, in order to timely eliminate the hidden dangers of cutting edge wear of concave and convex molds.
4. Good lubrication conditions
Good lubrication can provide the die with rust prevention function, reduce frictional heat, friction and stamping force, and reduce die wear, thereby prolonging the service life of the die.
For example, when punching silicon steel sheets in a transformer, if the lubrication is good, the service life of the die is about 15 times longer than that of the die with poor lubrication. Furthermore, proper use of lubricants can also extend the life of the die.
5. Processing and assembly quality of cold stamping dies
The service life of cold stamping dies is proportional to the processing precision and quality, and the higher the precision and quality, the longer the service life.
During die installation, we need to strictly control the gap between convex and concave dies to reduce wear.
6. Use and maintenance of cold stamping dies
Correct selection of suitable and high-precision stamping equipment and appropriate pressure can effectively extend the service life of the die.
At the same time, to reduce wear, appropriate lubricants must be applied to the stamped metal sheets, and the die must be sealed and stored properly when not in use.
With the continuous development of modern industrial technology, the structure and performance of industrial products are becoming more and more complex, and the demand for high-performance materials in high-temperature, high-speed, high-friction and corrosive working environments is also increasing.
Cold stamping dies have unique advantages in high production efficiency and are widely preferred by companies.
However, the working environment of cold stamping dies is very harsh, so the working performance of cold stamping dies has very strict requirements, and the die must have high service life, high precision and high process performance of production.
The economic cost and processing efficiency are closely related to the service life of stamping dies. The useful life of stamping dies is an important indicator for evaluating the level of die manufacturing in a country.
