What are the reasons for the damage of the die casting mold?

Design and development of zinc alloy die-casting molds. Die-casting is a precision casting method that uses high pressure to force molten metal into a metal mold with complex shapes. It is a precision casting method. In China, the zincIn die-casting production, molds are often broken. The common form of die-casting molds is cracks. Stress is the main cause of mold damage. Thermal, mechanical, chemical and operational shock are all sources of stress, both mechanical and thermal.

First, the mold manufacturing process

1. Burr forging quality problems

Some molds only produce a few hundred molds, so there will be cracks. Although only external dimensions may be guaranteed when forging, loose defects in the steel such as dendritic crystals, carbide mixing, shrinkage holes and air bubbles extend along the machining method, creating streamlines.

2. The cutting stress generated in the finishing process such as lathe, milling and scraper can be eliminated by intermediate baking.

3. Grinding stress is generated when grinding hardened steel, friction heat is generated in the grinding process, softening layer, decarburization layer occurs, thermal fatigue strength is reduced, and hot cracks and premature cracks are easily caused. For H13 steel, heat to 510-570°C after grinding for 1 hour per 25mm thickness for stress relief and baking.

4. EDM stress. The surface of the mold produces a white layer rich in electrode elements and dielectric elements, and the hard and brittle layer itself has cracks and stress. During the EDM process, high frequency must be used to minimize the white layer, polishing methods are removed, tempering is carried out, and it is carried out at a tertiary tempering temperature.

2. Mold processing

If the heat treatment is not suitable, cracks in the mold can be quickly discarded. In particular, we only use quenching and tempering, without quenching, and carry out a surface nitriding process. After thousands of die castings, surface cracks and cracks appear. The stress generated during the quenching process of steel is the result of the superposition of thermal stress during the cooling process and the structural stress during the phase transformation process. The quenching stress is deformed, leading to cracking, and the solid must be tempered to eliminate the stress.

3. In the process of die casting production

1. Type temperature

The mold must be preheated to a certain temperature before production. Severe cooling occurs in the high-temperature metal liquid-filled mold, the temperature gradient inside and outside the mold increases, thermal stress is formed, and the mold surface has cracks and sometimes cracks. During the production process, the mold temperature continues to rise, and when the mold temperature is overheated, sticky molds are prone to occur, and the failure of moving parts leads to damage to the mold surface. Install a cooling temperature control system to keep the working temperature of the mold within a certain range.

2. Charging type

The metal liquid fills the mold under high pressure and high speed, which inevitably causes severe impact and brushing on the mold, resulting in machine stress and thermal stress. During the impact process, metal liquids, impurities and gases also produce complex chemical interactions that together with the die surface accelerate corrosion and cracking. When the metal solution contains gas, the low pressure area first expands in the cavity, and when the gas pressure increases, the inner gas rupture occurs, causing damage by pulling out the metal mass points on the surface of the cavity, and corrosion leads to cracks.

3. Mould

Mechanical stress can occur if certain elements are deformed during the process of pulling out the core and opening the mold.

4. Production process

During the manufacturing process of each die casting, the heat exchange between the mold and the metal solution causes periodic temperature changes on the mold surface, resulting in periodic thermal expansion and contraction, resulting in periodic thermal stress. If the mold surface is under compressive stress when heated while pouring, open the mold and push out the casting, the mold surface will be under tensile stress to reduce the temperature. When this AC stress is repeatedly cycled, the accumulated stress inside the mold becomes larger and larger, and when the stress exceeds the fatigue limit of the material, cracks appear on the surface of the mold. alloy die-casting industry is mainly concentrated in the Pearl River Delta and Wenzhou, Zhejiang. However, in terms of technological maturity and the entire post-processing level, the Pearl River Delta is still far stronger than Wenzhou. Industry insiders analyzed that it is not enough to have a good die-casting machine to make a good die-casting product. It must be the combination of the mold, the die-casting machine and the die-casting process to make a good product. The product characteristics of zinc alloy die castings are as follows:

1. The specific gravity is large, the weight is more textured, and it is stronger than plastic injection molding.

2. Good casting performance, it can die-cast precision parts with complex shapes and thin walls, and the surface of the castings is smooth.

3. Surface treatment is available: electroplating, spraying, painting.

4. It does not absorb iron during melting and die-casting, does not corrode the molding, and does not stick to the mold.

5. It has good mechanical properties and wear resistance at room temperature.

6. Low melting point, melting at 385℃, easier to form than aluminum alloy die casting