Aluminum die-casting molds are widely used in the current stage of society. Because of the long production cycle, high investment and high manufacturing precision, their cost is relatively high, and the service life of aluminum die-casting molds is relatively high. However, due to a series of substantial factors such as materials, machining and use, the molds often fail prematurely and become scrapped, leading to great waste. After analyzing the selection, design, manufacturing and use of the mold, the main factors affecting the service life of the aluminum die and related precautions.

The role of mold material on mold life is reflected in three specific aspects: whether the selection of mold material is appropriate, whether the material is reasonable and whether it is used correctly. When the process of opening the mold and the top part is carried out, the surface of the cavity will bear a large compressive stress. After thousands of die castings, various defects such as cracks will appear on the mold surface. At the current stage, the aluminum die-casting mold material is H13 steel, which corresponds to the domestic grade 4Gr5MoV1Si, and has become a widely used mold material. This is a hot work mold steel with high thermal fatigue resistance, fracture toughness and thermal stability.

Factors affecting the life of aluminum die casting molds

⑴Structural design

In the mold design manual, there are related precautions for the design of aluminum die-casting molds. It should be emphasized that the design of the mold structure needs to try to prevent sharp rounded corners and excessive cross-sectional changes. The stress concentration caused by sharp rounded corners can reach 10 times the average stress. At the same time, it is necessary to pay attention to the deformation and cracking of subsequent heat treatment due to unreasonable structural design. In order to prevent heat treatment deformation and cracking, the cross-sectional dimensions should ensure uniform shape and simple symmetry. Blind holes should be formed as through holes when necessary. Process holes can be opened below.

⑵Machining

Inappropriate machining can easily lead to stress concentration. When the decarburization layer formed by rolling and forging is eliminated completely and uniformly with insufficient finish and machining, it may cause early failure of the material. At the same time, in the specific process of processing the mold, the thicker template cannot be superimposed to ensure its corresponding thickness. In the process of processing the cooling channel, attention should be paid to maintaining concentricity during the two-sided processing. If the heads have corners and cannot be concentric with each other, in actual use, cracks will occur at the connected corners.

⑶ Grinding and EDM

Grinding time is likely to cause local overheating of the metal surface, resulting in high surface residual stress and structural changes, which may promote the generation of grinding cracks. At the same time, when the original structure is improperly pretreated, carbide segregation, coarse grains and insufficient tempering will cause grinding cracks. Therefore, under the condition of ensuring the material, care should be taken to select the appropriate coolant to control the cooling of the grinding process. EDM can produce a bright white hardened layer of quenched martensite on the surface of the mold after quenching and tempering. The corresponding thickness is determined by the current intensity and frequency during the machining process.

⑷ Heat treatment

Improper heat treatment is the main cause of early failure of the mold. The deformation phenomenon of heat treatment is mainly caused by thermal stress and structural stress. If the stress exceeds the yield strength, the material will undergo plastic deformation, and if the stress exceeds the strength limit, it will cause the parts to quench. The following aspects should be important in the specific heat treatment of aluminum die-casting molds.

①Spheroidizing annealing should be carried out when the forgings are not cooled to room temperature.

②After roughing and before finishing, quenching and tempering should be added.

③ Pay attention to the heating temperature and holding time of the steel during the quenching process to prevent the austenite from coarsening.

④ Pay attention to the decarburization and recarburization of the cavity surface during the heat treatment process.

⑤ During the nitriding process, it should be noted that no oil contamination is allowed on the nitriding surface.

⑥ Between the two heat treatment processes, when the temperature of the previous one drops to the touch of the hand, the next one can be carried out.

⑦Use various methods such as static quenching, salt furnace quenching and special fixture quenching to reduce heat treatment distortion.

⑧ Tracking adopts advanced heat treatment equipment and technology, which can improve the surface finish of the mold and help control heat treatment deformation.

⑸Production operation

When the aluminum die-casting mold determines the injection speed, the corresponding speed should not be too high. Too high a speed will cause corrosion of the mold and increase of deposits on the cavity and core. However, if it is too low, it will easily cause defects in the casting. Therefore, the minimum injection speed for aluminum die-casting molds should be 18m/s, the corresponding maximum injection speed should not be greater than 53m/s, and the average injection speed should be 43m/s. During the specific use of the mold, the casting process should be strictly controlled. Within the allowable range of the process, the casting temperature and injection speed of the molten aluminum should be reduced, which is beneficial to increase the preheating temperature of the mold.

There are many reasons that affect the actual service life of aluminum die, which involve many specific aspects. For the manufacturing industry, the mold structure should be correctly designed, the mold parts should be manufactured accurately, and reasonable and effective heat treatment process standards should be formulated. The mold is used in a reasonable and standardized process, and can be repaired and maintained in time, which can give full play to the relevant properties of the mold material and effectively improve the quality and service life of the aluminum die.