The most direct judgment of the quality of the mold is based on its service life. At the same time, the performance of the mold is inevitably reflected in the failure form and failure characteristics of the mold. In order to analyze the performance requirements of various types of molds for mold surfacing materials, and reasonable selection of surfacing materials, failure analysis of various types of molds should be carried out to find out the failure law.
1. Failure mode of hot work die
The failure modes of hot work die mainly include fractures (including overall cracking, local fracture and mechanical fatigue cracks), deformation, thermal fatigue cracking, thermal wear, and thermal melting loss. Generally, the hot work die has a low die life when the fracture fails, and is regarded as an early failure mode of the mold. This form of failure is technically considered an unacceptable form of abnormal failure, which is mainly caused by improper selection of mold steel grades or unreasonable heat treatment processes. Wear failure, deformation failure and thermal fatigue failure with longer die life are generally considered to be normal failure of the mold. With the continuous development of mold technology, the failure modes of various hot work molds are constantly transformed from abnormal failure forms to normal failure forms. The task of mold surfacing technicians is to study the high-performance surfacing materials on the basis of studying the failure rules of various types of molds, and to match the corresponding surfacing welding process, in the case of reducing the early failure of the mold to improve the service life, try to Improve mold surfacing efficiency.
The failure mode of the mold reflects the different properties of the material. For hot work dies, the performance requirements of the mold for the material under high temperature conditions are highlighted.
Fracture failure: There are two root causes: (1) The load stress of the mold exceeds the high temperature fracture strength of the material in the whole range or local position; (2) The instantaneous impact load of the mold exceeds the high temperature toughness index of the material.
Collapse failure: The cause of the collapse failure is: (1) the material is lower than the load stress level of the mold, and the plastic deformation is accumulated. (2) The thermal stability of the material cannot be adapted to the high temperature conditions for long working hours.
Thermal fatigue failure: Thermal fatigue failure is mainly determined by the high temperature yield strength of the material, and also related to the high temperature impact toughness and thermal stability of the material. That is, the more difficult the material is to deform, the higher the toughness and the better the thermal fatigue resistance.
Thermal wear failure: For most hot work die steels, improving the material's high temperature yield strength, thermal stability and oxidation resistance can improve thermal wear resistance. However, the thermal wear resistance of different materials is more related to the structure of the material, especially the type of carbide inside the material.
Hot melt loss effect: The heat flux loss effect is directly related to the chemical affinity of the mold material and the casting liquid under different temperatures and stresses.
2. The failure shape of the cold work die
Common failure modes of cold working die include: edge cracking, edge smashing, edge cracking; overall cracking of the mold, partial fracture; edge wear and collapse; draw rib face and adhesion; wear of die R Grooves appear at the corners; deformation and cracking of the unloading plate. General delamination, drop or cracking is considered early failure, and mold deformation failure is considered normal failure. Among the above failure modes, the blanking die is mainly characterized by cracking, smashing and abrasion of the cutting edge; the most common form of scrapping of the drawing die is wear, adhesion and draw rib face. Cold molds and cold extrusion molds are often unusable due to wear, deformation and fracture damage.
For all types of cold work dies, although they work differently, the failure modes are different, but they have the same requirements for certain properties of the mold, such as surface hardness, wear resistance and toughness. That is to say, if the material studied has high hardness, wear resistance and excellent toughness, it can be used to manufacture all kinds of cold working molds, but different cold working molds may have higher requirements for a certain performance. . However, the high hardness and excellent toughness of the material are a contradiction. In other words, to increase the hardness of the material, it is generally necessary to lose some toughness. Therefore, people are studying the cold-worked mold surfacing materials, selecting cold-worked mold surfacing materials or formulating heat treatment. Different measures should be taken for different failure modes of different types of cold working dies in the process.
3. Failure mode of plastic mold
Since the degree of heat, stress, and wear during the working process of the thermosetting plastic mold is relatively serious, the probability of failure is higher. The failure modes of plastic molds are mainly: wear, deformation, corrosion and cracking. For example, the injection molding aperture of the plastic mold is enlarged, pits appear on the surface of the liquid material or the oak scouring mold, the compression mold is broken, and the convex portion is worn, which are typical examples.
references
[1] "Alloy Steel" writing group. Alloy steel. Mechanical Industry Press, 1976
[2] Economic and Technical Consulting Department of China Die & Mould Industry Association. Mould Materials and Heat Treatment, 1995
[3] Department of Metallurgy, Tianjin University. Mold Heat Treatment. Tianjin People's Publishing House, 1974
[4] Beijing Institute of Mechanical and Electrical Engineering, Shanghai Materials Research Institute, etc. Technical Summary Report on “Study on Performance and Application of Hot Work Die Steelâ€, 1991
[5] Yuan Yusheng. Surfacing welding process and economic benefit analysis of cast iron cold die. Welding machine. 1989.9
[6] Jiang Yucheng. Surfacing welding process of cold stamping die. Welding. 1989.9
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