Causes of Problems in Die Casting and Solutions
1. The appearance of die castings often has mildew spots, which seriously affects the appearance quality of castings, mainly the composition of demoulding agent. At present, there are a large number of large and small manufacturers producing demoulding agents on the market. Many of them have various quality problems. The most important thing is that the corrosion effect on die castings will occur. Generally, die-casting factories do not pay much attention to it. If the time of die-casting is longer, there will be white spots on the surface (frost-like, black after removal), which have actually been corroded. It is mainly the component of release agent which can cause corrosion effect. Therefore, the choice of release agent must not only pursue low price, but also pay attention to cost-effective.
The release agent will not be immersed in the die castings. However, the residual demoulding agent will corrode the appearance of the die castings and soak into the interior. In addition, if the amount of gas released by the demoulding agent is large, it will be involved in the inner part of the die castings to form blowhole. If the paint such as demoulding paste is used improperly, slag inclusion and other shortcomings will occur.
2. The appearance peeling phenomenon of die castings often occurs after shot blasting, which is generally composed of the following reasons: 1. the mould or injection chamber (melting cup) is not cleaned up; 2. the injection pressure is not good (whether the dynamic model is yielding when injection is needed to be noticed); 3. there are some problems in the opening of the casting system, the turbulent flow of alloy liquid into the cavity; 4. the temperature of the mould; 5. the liquid metal during injection; The splash was severe.
3. Foaming in zinc alloy electroplating. Poor plating can be caused by factors such as plating process and surface quality of die castings. Die castings should ensure good appearance quality, without looseness, cracks, air holes, bubbles, shrinkage holes, cold lines, pinholes and other shortcomings. Otherwise, the surface of the castings after electroplating is easy to foam, and the electroplating layer is separated from the matrix. When grinding and polishing before plating, be careful not to grind excessively. Because in the process of condensation, the exterior of die castings forms a fine hard and cold layer due to rapid cooling, while the interior arrangement may have some shortcomings, such as blowhole, shrinkage hole and so on. When grinding, do not grind off this good surface, otherwise the electroplating will present pits, bubbles and so on. In addition, the polishing wheel should not be pressed too tightly and overheated to avoid adhesion between abrasives and products, which constitutes poor electroplating of products.
4. There are small knots on the surface of die castings after electrostatic spraying. How to deal with them? The reason is the quality problem of the die casting itself. 1. Purity of zinc alloy raw materials; 2. Refining degassing and slag picking during die casting production; 3. Exhaust of mould and release agent. The problems mentioned above must be noticed when the zinc alloy die castings need surface treatment, which is different from that of aluminium die casting. In addition, the instantaneous maximum temperature of molten zinc alloy should not exceed 450 degrees, and the pouring temperature should be 400 degrees. Regardless of the external treatment method, the temperature should not exceed 150 degrees.
Fifth, there are air holes in die castings, and the causes are as follows: 1. The metal flow direction is incorrect, and the casting cavity has a positive impact, eddy current occurs, which surrounds the air and produces bubbles; 2. The inner gate is too small, the metal flow rate is too high before the air is swept away, the exhaust holes are blocked prematurely, so that the gas remains in the casting; 3. The cavity is too deep, and the ventilation and exhaust system is difficult; The plan is unreasonable, and the adjustment method of exhaust gas is difficult. 1. Revise the size and shape of diversion cone to avoid the impact of metal flow on the cavity; 2. Increase the inner gate appropriately; 3. Improve the mould planning; 4. Plan the exhaust slot rationally and add air holes.
6. The metal liquid splashes out in the process of die casting. The causes are as follows: 1. The closure between the moving and fixing moulds is not tight and the gap is large; 2. The clamping force is not good; 3. The die casting machine is not parallel to the fixing device plate; 4. The span of the supporting plate is large. The jacket plate is deformed by the injection force. Spraying occurred. Adjustment methods: 1. Re-install the die; 2. Increase the clamping force; 3. Adjust the die casting machine to keep the moving and fixing device plates parallel to each other; 4. Adding support plate to the moving die and stiffness of sleeve plate.