According to the different materials, shapes and sizes of the parts, a variety of different squeeze casting forming processes are studied, and the optimal matching scheme of process parameters is selected to achieve the dimensional accuracy and performance of the parts. In recent years, a lot of research and experiments have been carried out on the process parameters of squeeze casting, such as pouring temperature, injection speed, extrusion pressure, mold temperature and holding time.
Wang Jiaxuan et al. Carried out comparative experiments on squeeze casting process of 5083 aluminum alloy, and adopted orthogonal experiment method on pouring temperature, specific pressure and holding time. Through range analysis and experimental comparison, the optimum squeeze casting process conditions for microstructure and mechanical properties of 5083 alloy were obtained as follows: specific pressure 125mpa, holding time 15s, pouring temperature 670 ℃. Skolianos, Stefanos M. et al. Studied the squeeze casting process of AA6061 aluminum alloy. The mechanical properties and microstructure of AA6061 aluminum alloy were tested under different extrusion pressures. The results show that the extrusion pressure is 60 ~ 80MPa The results show that the tensile strength can be improved obviously by squeeze casting, mainly because it reduces the size and volume of micro pores in the casting, and the dendrite and intergranular zone become smaller, and the microstructure is more compact. Wang xiansong et al. Carried out the orthogonal test of squeeze casting process parameters of Al Cu alloy and analyzed it by Taguchi method. The results show that the process parameters of squeeze casting parts to achieve the best mechanical properties are: pouring temperature 730 ℃, extrusion specific pressure 75mpa, holding time 45s and mold preheating temperature 200 ℃. Li Qingfeng et al. Studied the aluminum copper alloy by indirect squeeze casting process. The results showed that when the specific pressure was 100MPa, the metal mold temperature was 200 ℃, the holding time was 16S, and the pouring temperature was 750 ℃, the mechanical properties were the best and the hot cracking tendency was low. Maleki, A. et al. Studied the squeeze casting process of lm13 alloy under different extrusion pressures. The results showed that with the increase of extrusion pressure, the microstructure of the parts became finer and the hardness increased gradually. When the extrusion pressure exceeded 100MPa, there were almost no shrinkage cavity, porosity and porosity in the parts. The results show that the best mechanical properties can be obtained when the die preheating temperature is 150 ℃ and the squeeze casting pressure is 106mpa. Yang Wen et al. Used the image analysis method to analyze the squeeze casting parts of A356 solidified under different specific pressures. The results show that the size and volume fraction of micro holes decrease with the increase of specific pressure. Yang, 50. J. the different pouring temperatures of al-13.5si alloy squeeze casting were studied. It was found that the mechanical properties of the bottom section of the squeeze casting parts were good when the pouring temperature was 660 ℃. The mechanical properties of the top section of the squeeze casting parts were better when the pouring temperature was 690 ℃. The mechanical properties of the bottom section of the squeeze casting parts were better when the pouring temperature was 660 ℃ The results show that the solidification time at the bottom of the squeeze casting cavity is shorter, and the mechanical properties of the cross-section specimen of the bottom part are better. The results show that the microstructure and mechanical properties of al-5.5si-4cu alloy do not increase and change obviously when the specific pressure exceeds 50MPa. When the specific pressure is 0 ~ 50MPa, the grain structure and eutectic Si can be improved obviously with the increase of extrusion pressure The results show that the morphology of phase, the mechanical properties of the alloy are obviously improved, and the grain is refined. The best squeeze casting specific pressure is 50MPa. The results show that the specific pressure of squeeze casting is 75 ~ 100MPa, the preheating temperature of die is 200 ~ 250 ℃, the pouring temperature is 680 ~ 730 ℃, and the extension time before pressing is less than 12s At the same time, the experimental results show that higher die temperature and pouring temperature can make the grain coarsening phenomenon, and the increase of extrusion specific pressure can refine the grain, but when the specific pressure is greater than 25MPa, there is no obvious refinement phenomenon, and the macro segregation of Cu is restrained. The results show that the maximum tensile strength of al-4.5cu-1mg alloy can reach 288.8mpa when the injection pressure is 70MPa, The hardness of HRB can reach 48.3% and the elongation can reach 12.8%. The mechanical properties of the alloy increase with the increase of specific pressure. When it reaches 70MPa, the increase of pressure has little effect on the properties of the alloy. At the same time, it shows that the density of the alloy increases gradually with the increase of pressure. When it reaches 70MPa, there is no big change. Li Rongde et al. Studied the squeeze casting process of ZA27 alloy casting with large height diameter ratio (M = H / D = 7), analyzed the microstructure and mechanical properties of the alloy squeeze casting parts. The results show that the casting defects can be eliminated when the specific pressure is 750MPa, pouring temperature is 600 ~ 630 ℃, mold temperature is 170 ~ 200 ℃ and holding pressure is 45s, and good mechanical properties can be obtained.
With the development of squeeze casting technology, a lot of exploration and research have been carried out in equipment and new technology. In the early stage, the general hydraulic equipment was mainly used, and in the later stage, the special squeeze casting machine was developed gradually to intelligent control, but the development of squeeze casting equipment in China is still not enough. Ouyang Ming invented a vacuum squeeze casting device, which is equipped with a vacuum pumping system and runner seal. When the liquid metal starts to fill the mold, the vacuum system is opened, and the injection punch is used to complete the mold filling in the vacuum state. In the final stage, the master cylinder and auxiliary cylinder are fed to complete the whole vacuum squeeze casting process. It is characterized by indirect squeeze casting, which can reduce oxidation Inclusion, but the disadvantage is that pores may be formed during filling.
In 2005, Li Yuanfa and others proposed the liquid casting forging double control forming technology. Luo Shoujing of Harbin Institute of technology and other scholars jointly designed the first domestic casting forging double control forming machine, which was successfully developed and patented. Liquid casting and forging double control forming technology is a combination of squeeze casting and liquid die casting technology, which has the excellent characteristics of forging and die casting. The defects of shrinkage porosity and shrinkage cavity often appear in die casting are basically restrained. At the same time, the difficulty that forging can not produce complex high-precision blanks and parts is solved. Its essence is to apply a common pressure immediately when the liquid metal in the cavity has not been completely solidified As a result, the solidified dendrite structure will be broken and the alloy melt will be strengthened by fine grains, which can significantly improve the properties of squeeze casting parts. The most critical process parameter is to control the delay time of die forging, that is, to control the state of metal in the cavity during die forging. The delay time of die forging directly determines the plastic deformation state of metal melt after solidification. At the same time, FLOW3D is used The results show that the double control forming technology of liquid casting and forging can overcome the shortcomings of liquid die casting, and the parts with fine grain, compact structure, no segregation and high mechanical properties can be obtained. The results show that the tensile strength and elongation of AZ91D magnesium alloy are increased by 84.39% and 101.76% respectively, and the microstructure is fine and dense.
two thousand and eight In, Qi PI Xiang and other scholars put forward the concept of double squeeze casting. They thought that the double squeeze casting process with feeding system essentially belongs to continuous casting and forging. The specific process of double squeeze casting is as follows: after the extrusion die is closed in advance, a closed casting cavity is formed, the lower extrusion hammer is pressed upward to keep the casting pressure, and then the upper extrusion punch is pressed further to keep the casting pressure For aluminum alloy, the suitable forging ratio is between 3% and 6%, and PLC is used The computer control system precisely controls the extrusion time, and puts forward the principle of controlling the second extrusion time, that is, when the metal or alloy melt has been filled and is still in the semi-solid state, it is the best time to start the second extrusion. When the extrusion casting is completely solidified, the extrusion is also in place simultaneously. The delay of the second extrusion will make the deformation resistance surge and the extrusion pressure increase, such as the second extrusion In addition, the secondary extrusion can be divided into local extrusion, integral extrusion or multi-point extrusion.
The excellent characteristics of the process are as follows
a. The upper and lower extrusion heads realize extrusion (forging), and the product has high density;
b. The reduction (forging pressure) of the upper extrusion head can be controlled, the casting size can be accurately controlled, and the surplus metal remains in the injection gate;
c. It can be used not only for casting alloy, but also for high strength deformation alloy;
d. The probability of abnormal segregation in squeeze casting is small;
e. It can form complex casting parts;
But its disadvantages are also very obvious
The process is complicated and needs complex die structure. Three sets of extrusion cylinders need to be installed on the press for closing die, extrusion filling and re extrusion forging, and the time sequence of action should be strictly controlled.