Application of Vacuum PVD Coating Technology in Die Casting Mould

The friction coefficient of the surface of the vacuum PVD coating is small. The friction coefficient of the surface of the polished metal material to the steel is generally about 0.9. The friction coefficient of the vacuum PVD coating to the steel is between 0.01 and 0.6. The friction coefficient of PVD coating materials (AlCrN, AlTiN) is generally 0.4-0.6. The low friction coefficient reduces the surface friction between the vacuum PVD coated mold and the processed parts during processing, and the surface quality of the parts is better than that without coating. The parts are produced by the layers of the mold.

The production conditions of die-casting molds are the most severe. The metal solution at a high temperature of 600-800°C is injected under high pressure, and the surface of the mold continues to expand and contract, resulting in very short service life of the die-casting mold. Repair and maintenance are required. The main causes of failure of die-casting molds are cracks, erosion, stickiness, and deformation.

Since the mold cavity works at a high temperature, the improvement of the performance of the die casting mold needs to have the following characteristics. During the service life of the mold, the cavity surface accuracy and deformation amount must be maintained under the alternating conditions of high temperature and low temperature. Therefore, in addition to the characteristics of plastic molds, the material of die-casting molds should also have excellent high-temperature resistance, hardness, oxidation resistance, tempering stability, and impact toughness, as well as good thermal conductivity and fatigue resistance. The die-casting mold adopts the processing technology of quenching, tempering, and polishing, which has a limited increase in the hardness of the material itself. At the same time, because the working temperature is close to or exceeds the tempering temperature, it is easy to cause the secondary tempering of the mold to reduce the hardness of the mold and deform the mold.

Vacuum PVD coating can solve the problems encountered by some die-casting molds. By depositing a layer of coating on the surface of the mold, this type of coating is characterized by high thickness and high-temperature resistance. Vacuum PVD coating The addition of TiO2 can effectively improve the high-temperature resistance, surface hardness, and oxidation resistance, and the vacuum PVD coating on the surface can resist the impact of impacting metal liquids. Common die-casting mold coatings include TiAlN, AlCrN, and AlTiCrN. The common idea is to use a harder vacuum PVD coating to resist the high temperature brought by the metal liquid and the erosion of the mold.

The above coatings all have good high-temperature resistance and friction coefficient against steel below 0.5, which can effectively solve the deformation caused by sticky materials and sudden cooling and sudden heating. At the same time, the hardness of several coatings is higher than HV3000, and the hardness can be effectively maintained at high temperatures, which can resist the stress deformation caused by high-temperature metal liquid to the mold.

A coating company has developed a new technology for the pretreatment of vacuum PVD coating in response to this problem. Combined with other surface technologies and the composite effect of vacuum PVD coating, it has achieved certain results in improving liquid metal mold sticking and thermal cracking. For example, HVAC has developed a device that can complete the soft nitriding + vacuum PVD coating of die-casting molds at the same time, which effectively solves the problem of poor bonding force between traditional coatings and nitrided substrates, and further improves the use of die-casting molds. life. Most companies use the concept of thick coating to increase the life of the mold by depositing a coating of sufficient thickness. I analyze the processing technology of die-casting mold coating here.