Die casting is a metal type pressure casting on a die casting machine, which is the casting process with the highest production efficiency at present. Die casting machines are divided into hot chamber die casting machines and cold chamber die casting machines. Hot chamber die casting machine has high degree of automation, less material loss and higher production efficiency than cold chamber die casting machine, but limited by the heat resistance of the machine, it can only be used for the production of low melting point materials such as zinc alloy and magnesium alloy. The aluminum alloy die-casting parts widely used today can only be produced on cold chamber die-casting machines due to their high melting point.
The main feature of die casting is that liquid metal fills the cavity under high pressure and high speed, and forms and solidifies under high pressure. The shortcomings of die casting parts are:
1. In the process of filling the cavity with liquid metal under high pressure and high speed, the air in the cavity is inevitably wrapped in the inside of the casting, forming subcutaneous pores, so the aluminum alloy die casting is not suitable for heat treatment, and the zinc alloy die casting is not suitable for surface spraying (but can be painted). Otherwise, the internal pores of the casting will expand when heated by the above treatment, resulting in deformation or bubbling of the casting.
2. The mechanical cutting allowance of die casting parts should also be smaller, generally about 0.5mm, which can reduce the weight of castings, reduce the amount of cutting to reduce costs, and avoid penetrating the dense layer on the surface, exposing the subcutaneous pores, causing the workpiece to be scrapped.
Die casting machines are generally divided into two categories: hot press chamber die casting machines and cold press chamber die casting machines.
Cold press chamber die casting machine is divided into horizontal die casting machine and vertical die casting machine (including full vertical die casting machine) according to its press chamber structure and arrangement.
1. Hot press chamber die casting machine (hot air die casting machine)
The pressure chamber is immersed in the liquid metal of the thermal insulation crucible, and the injection parts are not directly connected with the frame, but are installed on the crucible. The advantages of this die-casting machine are simple production process and high efficiency; Less metal consumption, stable process. However, the pressure chamber and injection punch are immersed in liquid metal for a long time, which affects the service life. And easily increase the iron content of the alloy. At present, the hot press chamber die casting machine is mostly used for die-casting low melting point alloy castings such as zinc alloy, but it is also used for die-casting small aluminum and magnesium alloy die-casting parts.
2. The press chamber of the cold chamber die casting machine is separate from the heat preservation furnace. During die casting, the liquid metal is removed from the holding furnace and poured into the press chamber for die casting
With the rapid development of automobile, motorcycle, household appliances and other industries, the shape of industrial products in meeting the performance requirements at the same time, becoming more and more complex, and the manufacturers of these products do not open the mold, which requires the mold manufacturing industry to produce the mold at the fastest speed, the lowest cost, the highest quality. In order to meet the above requirements, mold enterprises can only use advanced management methods and integrated manufacturing technology in order to be invincible in the fierce market competition.
So in the production of die casting, it is inevitable to encounter such problems. The following two points of knowledge are emphasized to illustrate.
Why can’t the hole processing allowance of aluminum die casting exceed 0.25mm?
In order to be suitable for die casting, humans add a lot of silicon (SI) to the aluminum alloy used in die casting. When the aluminum alloy condenses in the mold, this silicon will float to the surface, forming a thin silicon film Aluminum die castings. This silicon film is very hard and very wear-resistant. Some OEM designers take advantage of this feature. The inner surface of the hole of the die casting is directly counted as the bearing surface. This silicon surface layer is generally only 0.2 to 0.9mm. Too much processing will shorten the life of this bearing surface.
Why aluminum die casting, when polishing, there will be black spots?
There are several reasons for this. It could be the formation of silicon oxide, or aluminum oxide. The solution is simple: use fresh aluminum ingots. However, the most likely source is the release agent. Maybe. We sprayed too much release agent. It is also possible that the organic content of the release agent is too high. At the temperature of hot molten aluminum, some of these organic compounds are reduced to carbon elements, and some become organic macromolecular polymers. The mixture of these carbon molecules and polymers, when the aluminum casting is formed, is contained in the surface layer and becomes the dark spot we see. We can start by reducing the concentration of the spraying agent, switching to another spraying agent, or lengthening the blowing time after spraying. To reduce the formation of carbon elements and prevent the accumulation of macromolecular polymers.
