In order to prevent early failure of the mould and effe […]
In order to prevent early failure of the mould and effectively extend the service life of the mould, corresponding preventive measures are mainly taken from the following aspects.
1. Mould material.Since the cold work mould bears a large unit extrusion force, high-performance mould materials with high strength, good toughness and good wear resistance should be selected; because the working conditions of the convex mould are more susceptible to eccentric force than the concave mould Therefore, the wear resistance of the male mould material should be higher than that of the female mould material.
2. Heat treatment.Die heat treatment includes: timely tempering of cold-worked die blanks after forging to refine grains, tempering after rough machining to eliminate stress, and stress-relieving low-temperature tempering after electric spark and wire cutting. Experience has shown that moulds with a diameter of ≤80mm should be directly machined with bar stock, without forging, because improper forging will cause defects such as over-sintering, coarse crystals, segregation, etc.
Attention should also be paid to the heating rate, holding time, quenching temperature, cooling rate, number of tempering, surface hardness, etc. during mould quenching and tempering. Excessive temperature during mould quenching and heating can easily cause mould overheating and overburning, decrease impact toughness, and cause early fracture. If the quenching temperature is too low, it will reduce the hardness, wear resistance and fatigue resistance of the mould, and easily cause plastic deformation and wear failure of the mould. When quenching and heating, it is necessary to take protective measures to prevent surface oxidation and decarburization. Decarburization will cause quenching soft spots and soft areas, reduce the wear resistance and fatigue strength of the mould, and affect its service life.
If the quenching cooling rate is too fast and the swimming temperature is too low, the mould is prone to quenching cracks. If the tempering temperature is too low and insufficient, the residual stress in the quenching process will not be eliminated, the toughness of the mould will be reduced, and early fracture will easily occur.
3. Mould design.The structure of the cold work mould must have sufficient strength, rigidity, reliability and good guidance, but the unreasonable structure of the mould will directly affect the service life of the mould. The working part of the mould should be designed with a large enough fillet radius to avoid stress concentration caused by sharp corner transition. The width of the ligament should be designed reasonably according to the metal flow condition to minimize the friction force, generally between 1.5-3.5.
4. Mould processing. In the die cutting process, the following measures should be taken; improve the surface roughness, the micro-crack marks formed by grinding, the transition part should be smooth, and the knife marks and small defects cannot be processed organically to prevent stress concentration during use and cause cracks. .