1. Overview
The method of metal mold casting for aluminum alloy parts is widely used because of its high productivity, clean working environment, smooth surface and compact internal structure. Especially for automobile engine parts, many industrial developed countries such as Japan, the United States, Britain, Germany and Italy use metal mold gravity casting method to produce automobile engine aluminum cylinder block, aluminum cylinder head and aluminum piston. In recent years, many manufacturers in China have introduced advanced metal mold equipment or self-made equipment to produce aluminum castings such as cylinder head, intake pipe and piston of automobile engine. Metal mold casting aluminum technology is also widely used in aviation, aerospace, high voltage electrical appliances, electrical machinery and instrumentation industries. Compared with other casting methods (such as die casting, low pressure casting and sand casting), the metal mold casting of aluminum alloy parts in Dongguan CNC processing plant has the following advantages
1) The overall quality of geometric dimension and metallographic structure is good.
2) The low pressure and high pressure casting process is flexible and can produce more complex castings.
3) More conducive to mass production, to achieve a high degree of automation and simplify maintenance; Under the same production scale, compared with high and low pressure casting, the one-time investment of casting equipment and metal mold tooling is lower.
2. Metal mold casting technology of aluminum alloy parts
(1) Metal mold casting process design of aluminum alloy parts in Dongguan CNC processing plant: the key of metal mold casting process design is the determination of casting pouring position, the design of pouring system and the control and adjustment of mold working temperature.
l) Casting pouring position: it is directly related to the number of metal core and parting surface, the position of liquid metal leading in, the unobstructed degree of exhaust and the complexity of metal mold structure, so as to determine the difficulty of metal mold processing and operation and the distribution of casting cooling temperature, and then affect the production efficiency, dimensional accuracy and other internal and external quality of castings. Therefore, the casting pouring position is the first important part of casting process design.
2) Gating system: the design of gating system determines the internal and external quality of castings. The pouring system should have the functions of skimming slag, exhausting gas and feeding. At the same time, it should ensure the reasonable solidification and cooling temperature field of castings. The correct and reasonable pouring system can not only be estimated by experience, but also be directly predicted by computer numerical simulation during solidification process of castings, which can show the dangerous parts of castings that may produce shrinkage porosity (hole). The processing of precision parts can guide the process design, and by adjusting the structure and size of pouring system, the structure of metal mold, the thickness of casting surface, the thickness of casting surface, the thickness of casting surface, the thickness of casting surface, the thickness of casting surface, the thickness of casting surface, the thickness of casting surface, the It is difficult to adjust the temperature field and eliminate casting defects by controlling the cooling rate or adjusting the thickness of coating layer. For example, for the blank of automobile engine aluminum cylinder head cast by bottom injection, it is difficult to adjust the reasonable temperature field by setting a large riser at the top and forced water cooling at the bottom, It is difficult to eliminate the shrinkage defects caused by overheating around the bottom gate. This pouring system is used in the aluminum alloy metal mold casting machine imported from SIFA company of France, and the production process is unstable. One hundred percent of the cylinder head needs to be infiltrated. For the cylinder head with serious shrinkage, even if it is infiltrated, it can not meet the pressure requirements; The aluminum liquid is directly injected from the riser, and the aluminum liquid is purified by the ceramic filter before entering the mold cavity, which ensures the reasonable cooling gradient of the casting, that is, the sequential solidification mode from bottom to top, eliminates the shrinkage defects, and significantly improves the yield of cylinder head. Foseco company has done detailed research and comparative test on the two casting methods, and called the latter dypur method. This method makes the mold simple and compact, saves liquid aluminum and has high yield of castings. With this method, even a small amount of inclusion defects caused by high drop of molten aluminum have little effect on the mechanical properties and air tightness of castings. Of course, the location, structure and size of the pouring system should not only consider the solidification temperature of the casting, but also consider the complexity of the mold, whether the liquid metal filling is stable, whether it has the functions of skimming and exhaust.
3) Working temperature of metal mold in precision parts processing: similarly, working temperature of metal mold and temperature difference of each part play an important role in cooling temperature field of castings. Forced water cooling and air cooling in the local overheated area of metal mold is to ensure the normal working temperature of the area, improve the production efficiency, eliminate overheating and ensure the normal cooling temperature field. The metal mold working temperature control is more advanced and effective means is to control the cooling water outlet temperature, which is regulated by the cooling circulating water circulation speed. For example, the metal molds designed and manufactured by fata company of Italy and SIFA company of France have advanced water and air cooling devices. In addition, metal inserts with high thermal conductivity or large heat storage capacity can be embedded in the local thick hot spot, or the thickness and type of coating can be adjusted to ensure that the casting forms a reasonable cooling temperature gradient and eliminate local shrinkage (porosity) defects.