Cold stamping mould: the reasons that affect the life of the die and the measures to improve the life of the mould!

2021/07/06


To improve the quality of the mold, materials must be selected reasonably, and the corresponding heat treatment process and optimized processing technology for different materials can be used to improve the manufacturing accuracy and service life of the mold and avoid early failure of the mold. Based on this, this article mainly analyzes the factors that affect the life of cold stamping dies and the measures to improve the life.

 

 

1. Analysis of factors affecting the life of cold stamping die

 

In today's rapid economic development, cold stamping dies are widely used in the mass production of mechanical parts by enterprises. At the same time, in order to get the greatest benefit, companies generally pay more attention to the service life of cold stamping dies. To

1.1. Stamping production process and mold design

In actual production, the main factors that affect the work of the mold are the poor surface quality of the stamping material, large tolerances, unstable material properties, and impurities on the surface, which will lead to accelerated mold wear. In the drawing die, the most important factors affecting the size of the die punching load and the degree of adhesion tendency are the forming ability, thickness, and surface quality of the material to be drawn. In the production mold, because the integral mold will have concave and convex corners, it will cause the phenomenon of stress concentration and cause the mold to burst. In addition, the shape and fillet radius of the concave and convex mold have a greater impact on the wear of the mold. For example, in the drawing mold with a relatively small fillet radius, it will increase the flow resistance of the billet, and continuously increase the friction force to make the mold Wear or break the punch. To

 

 

1.2 Mold material

(1) Mold material affects mold life

The mold material has the greatest impact on the life of the mold. The material properties of the mold greatly affect the life of the mold. For example, if Cr12MoV steel is used in the production of drawing dies, it is prone to seizure and napping, but the use of GT35 steel is hard. The alloy production can greatly reduce the seizure tendency and increase the service life of the mold.

 

 

(2) The working hardness of the mold affects the life of the mold

The increase of mold hardness mainly refers to the compressive strength, wear resistance and seizure resistance of mold steel, but it also reduces mold toughness, cold and heat fatigue resistance and grinding performance. In the practice of production and life, the common form of failure is that the hardness is too high to cause the mold to break, and a very small amount of deformation and wear will occur.

(3) The metallurgical quality of mold materials affects mold life

The metallurgical quality of mold materials primarily affects those mold steels with large and medium cross-sections and mold steels with high carbon and alloying elements. The actual performance is non-metallic assimilation, carbide segregation, looseness, etc., for those high-carbon and high-alloy steels. , It is easy to cause the mold quenching cracking and the initial damage of the mold.

 

 

1.3. Heat treatment process of mold

Pre-heat treatment, stress relief annealing after rough machining, quenching and tempering, stress relief annealing after grinding or electrical machining, etc. are all heat treatment methods for molds. The heat treatment quality of the mold also has a great impact on the performance and service life of the mold. A large number of facts have proved that the poor heat treatment process of the mold can directly lead to the quenching deformation and cracking of the mold workpiece and the early fracture during use.

 

 

1.4. Mold processing technology

Cutting, grinding and EDM are the necessary processing techniques for making molds. During production, the wear resistance, fracture resistance, and strength of the mold are affected. If the processing method is improper, the processing quality is prone to problems.

 

 

 

(1) The influence of grinding

Improper grinding processing will cause the fatigue strength and fracture resistance of the mold to decrease due to grinding burns and grinding cracks.

(2) The influence of EDM

Improper EDM will reduce the toughness and fracture resistance of the mold. The primary reason for this phenomenon is that EDM will produce an EDM burn layer, which has a large tensile stress, and when the thickness is large, microcracks will appear.

 

 

2. Measures to improve the life of cold stamping dies

 

Through the analysis of the influencing factors of the cold stamping die life, it can be seen that there are many factors that affect the die life. These factors should be comprehensively considered when designing the mold, so as to design a more economical and efficient mold. For special-purpose cold stamping dies, should Combine its own requirements to design economical and applicable molds.

2.1, the correct choice of mold material

The working condition of the punch is worse than that of the female mold, and the material of the punch is better than that of the female mold. When blanking in large quantities, it is necessary to pay attention to the selection of mold materials that have high strength, good wear resistance, and good toughness.

2.2. Reasonable cold stamping die design structure is an essential prerequisite to ensure the service life of the die

The service life of cold stamping dies has a great relationship with reasonable structural design. At the beginning of the design, other design requirements of cold stamping dies are guaranteed. The toughness, rigidity and strength of the die must be guaranteed to ensure that the convex, concave and other structural parts of the die during the blanking process of the cold stamping die will not be deformed, damaged or increased wear due to the impact of the blanking force. The mold design should use guided mold design as much as possible, and the mold design gap should also be considered. If the design gap is too small or too large, it will increase the degree of wear of the convex and concave molds, which will lead to mold damage and reduced service life.

 

 

2.3. Use maintenance molds reasonably

In the stamping process, the cold heading blank should be phosphated or copper-plated in order to reduce the frictional resistance during work and prevent the adhesion of the mold. Therefore, the metal plate must be preheated to improve the processing performance of the material before cold heading. Reduce the possibility of cracks and extend the life of the mold. Lubrication during cold heading is also a good method. Good lubrication can obviously increase the surface finish of the sheet metal, reduce frictional resistance, reduce wear, and extend the service life of the mold. When cold heading parts with complex shapes, lubrication becomes even better. Is important. To

When the mold is stored, a certain gap should be maintained between the upper and lower molds to protect the cutting edge from damage. When punching, the depth of the punch into the concave mold should be controlled well to avoid aggravated wear. In the stamping practice, after punching and stamping for a period of time, the edge of the concave and convex die will be worn and worn out. If the mold is repaired at this time, it will not only reduce the frictional resistance and prevent cracks caused by wear groove marks, but also avoid the additional bending moment caused by the uneven gap between the die and the punch after the wear, and extend the use of the mold. life. After the cutting edges of the concave and convex molds are ground again, the gap between the cutting edges will be more uneven. At this time, the cutting edge should be carefully ground and polished with fine oil stone to remove the grinding burrs. Generally speaking, the surface roughness value should reach Ra0.10μm, so as to eliminate the hidden danger of edge wear of the concave and convex die immediately.

 

 

2.4Good lubrication conditions

Good lubrication can prevent molds from rusting, reduce frictional heat, friction, and punching force, reduce mold wear, and extend mold life. For example, when punching silicon steel sheets in transformers, if the lubrication is good, the life of the mold is about 15 times that of the mold with poor lubrication. In addition, the proper use of lubricants can also extend the life of the mold.

 

2.5, the processing and assembly quality of cold stamping dies

The service life of a cold stamping die is directly proportional to its machining accuracy and quality. The higher the accuracy and quality, the longer the service life. In the process of mold installation, we must strictly control the gap between the male mold and the female mold to reduce wear.

2.6. Use and maintenance of cold stamping dies

The correct choice of the right, high-precision stamping equipment, and the right pressure can effectively extend the service life of the mold. At the same time, in order to reduce wear and tear, suitable lubricants can be applied to the stamped sheet, and the mold should be sealed and stored when not in use, and properly protected.

 

 

With the continuous development of modern industrial technology, the structure and performance of industrial products are becoming more and more complex, and the high temperature, high speed, high friction and corrosive working environment has an increasing demand for high-performance materials. Cold stamping dies have the unique advantage of high production efficiency, so they are widely favored by enterprises. However, the working environment of cold stamping dies is very bad, so there are very strict requirements for the working performance of cold stamping dies. The mold must be high in the production process. Life, high precision and high performance. The economic cost of product processing and the economic benefits of product processing are determined by the service life of cold stamping dies. The service life of cold stamping dies is the main indicator to weigh the degree of cold stamping die manufacturing in a country.