The quality of the stamping die is directly proportional to the quality of the product, so the die is very important for the stamping process in metal forming. The improvement of the quality of the die must be reasonable choice of materials, for different materials using the appropriate heat treatment process and optimization of the processing technology, can improve the manufacturing accuracy and service life of the die, to avoid early failure of the die. Based on this, this paper mainly focuses on the factors affecting the life of cold stamping die and measures to improve the life of the analysis.
First, the impact of cold stamping die life factors in the rapid development of the economy today, cold stamping die is widely used in the mass production of mechanical parts, while in order to get the maximum benefit, enterprises will generally pay more attention to the service life of cold stamping die.
1, stamping production process and mold design
In actual production, the factors affecting the work of the mold are mainly poor surface quality of the stamping material, large tolerances, unstable material properties and impurities on the surface, which will lead to accelerated wear of the mold. In deep-drawing dies, the most important factors affecting the size of the stamping load of the die and the degree of adhesion tendency are the forming ability of the sheet being deep-drawn, the thickness, and the surface quality of the material. In the production of molds, due to the integral type mold will exist concave and convex corners which will cause stress concentration phenomenon leading to mold cracking. In addition to the wear of the mold has a greater impact on the shape of the concave and convex die and the size of the corner radius, for example, in the deep drawing die is relatively small in the corner radius, it will increase the embryo material flow resistance, and constantly increase friction and thus make the mold wear or make the punched parts fracture.
2, mold material:
(1) mold material affects the life of the mold on the mold life of the greatest impact for the mold material, mold material performance greatly affects the service life of the mold, for example, in the production of deep-drawing die such as the use of Cr12MoV steel is very easy to bite and pulling the hair phenomenon, but the use of GT35 steel junction tungsten carbide production can greatly weaken the tendency to bite and improve the service life of the mold.
(2) mold hardness affects the life of the mold
Mold hardness improvement mainly refers to the mold steel compressive strength, wear resistance and anti-clenching ability, but also reduces the mold toughness, hot and cold fatigue resistance and grindability. In production life practice, the common form of failure is too high hardness leads to mold fracture, very few will appear deformation and wear.
(3) the metallurgical quality of the mold material affects mold life
The metallurgical quality of the mold material is the primary impact of those large and medium-sized cross-section of the mold and the high content of carbon and alloying elements of the mold steel, the reality of the performance of non-metallic assimilation, carbide segregation, intermediate loosening, etc., for those high carbon and high alloy steel, wherever easy to cause mold quenching and cracking and mold quenching of the initial damage.
3, mold heat treatment process
Pre-heat treatment, rough machining stress relief annealing, quenching and tempering, grinding or electrical machining stress relief annealing belongs to the mold heat treatment, mold heat treatment quality of mold performance and service life has a great impact, a large number of facts have proved that the mold of the heat treatment process is poor can directly lead to the mold workpiece parts of the quenching deformation and cracking as well as the use of the process of the early fracture. The quality of heat treatment has a great influence on the performance and service life of the mold.
4, mold processing technology
Cutting, grinding and EDM are necessary for the manufacture of mold processing technology, production impact on the mold wear resistance, fracture resistance, strength, if the processing method is not appropriate, processing quality is prone to problems.
(1) The impact of grinding
Improperly processed grinding will cause the fatigue strength of the mold and fracture resistance is reduced, due to grinding burns and grinding cracks.
(2) The impact of electric discharge machining
Improper EDM processing will reduce the toughness of the mold and fracture resistance, the primary reason for this phenomenon is that EDM processing will produce EDM burn layer, burn layer tensile stress is greater, when the thickness is greater will appear microcracks.
Second, improve the cold stamping die life measures:
By analyzing the influencing factors of cold stamping die life, it can be seen that the factors affecting the life of the die are manifold, and these factors should be taken into consideration when designing the die, so as to design a more economical and efficient die, and for the special-purpose cold stamping die, it should be combined with its own requirements for designing an economical and applicable die.
1、Correct selection of mold materials
The working condition of convex mold is worse than that of concave mold, and the material of convex mold should be better than that of concave mold. When large quantity punching, pay attention to the selection of mold material should be high strength, good wear resistance, good toughness of the mold material.
2、Reasonable cold stamping mold design structure is to ensure that the mold service life of the necessary prerequisites
The service life of the cold stamping mold has a great relationship with the reasonable structure design, the beginning of the design in the cold stamping mold to ensure that other design requirements. Must ensure that the toughness of the mold, steel and strength to ensure that the cold stamping die in the blanking process mold convex, concave die and other structural components are not affected by the blanking force and the occurrence of deformation, damage or increase the degree of wear and tear. Die design should be used as far as possible with guided die design, should also consider the die design clearance, design clearance is too small or too large will also increase the degree of wear and tear of the convex and concave die, which leads to damage to the die, the service life is reduced.
3, to use reasonable maintenance mold
In the process of stamping, the cold heading blank should be phosphated or copper plated in order to reduce the friction resistance when working and prevent the die from adhering to the bite, so the metal plate must be preheated before cold heading to improve the processing performance of the material, so as to reduce the possibility of cracks and prolong the die's so life. Lubrication is also a good method when cold heading, good lubrication can obviously increase the surface finish of metal plate, reduce friction resistance, reduce wear and prolong the service life of the mold, when cold heading complex shape parts, lubrication is more important.
When the mold is stored, there should be a certain gap between the upper and lower molds to protect the edge from being damaged. When stamping, the depth of the convex die into the concave die should be controlled to avoid increased wear. In stamping practice, blanking, stamping for a period of time, the concave and convex die edge will appear wear, wear groove phenomenon. If the mold repair at this time, not only to reduce the friction resistance, and at the same time to prevent the wear of cracks caused by grooves, but also to avoid additional bending moment due to uneven gap between the edge of the concave die and the convex die after abrasion, to extend the service life of the mold. After the edge of the concave die and convex die are ground again, the edge clearance is even more uneven, and at this time, the edge should be carefully ground and polished with a fine oil stone to remove grinding burrs, and in general, the surface roughness value should reach Ra ≤ 0.10 μm or less, so as to instantly eliminate the hidden danger of concave-convex die edge abrasion.
4、Good lubrication conditions
Good lubrication, you can mold with anti-rust function, but also reduce frictional heat, friction, stamping pressure, reduce mold wear, mold life extension. Such as in the blanking transformer in the silicon steel sheet, if the lubrication is good, mold life is about 15 times the poor lubrication of the mold. Also, the use of the right type of lubricant can also extend the life of the mold.
5, cold stamping mold processing and assembly quality
The service life of cold stamping die is directly proportional to its processing precision and quality, the higher the precision and quality, the longer its service life. During the installation of the mold, we should strictly control the gap between the convex die and the concave die, so as to reduce the wear and tear.
6、Use and maintenance of cold stamping die
Correct selection of appropriate, high-precision stamping equipment, as well as the appropriate pressure can effectively extend the service life of the mold. At the same time in order to reduce wear and tear can then be coated with suitable lubricants on the stamping plate, molds in the non-use of time to be sealed and stored, properly protected.
With the continuous development of modern industrial technology, industrial product structure and performance is more and more complex, and high temperature, high speed, high friction and corrosive working environment on the demand for high-performance materials is also more and more high. Cold stamping die has the unique advantage of high production efficiency and widely favored by enterprises, but the working environment of the cold stamping die is very harsh, so the working performance of the cold stamping die has very strict requirements, the die in the production process must have a high life, high precision and high performance. Processing economic costs and economic benefits are closely related to the service life of the stamping die, the service life of the stamping die is weighed in a national mold manufacturing degree of the main indicators.