What should be paid attention to in the die casting process of electromechanical aluminum die castings?

The smelting and quality control of aluminum alloys are the basic links to ensure the performance of castings. The smelting process of aluminum alloys needs to be carried out in a high temperature environment of 720℃ to 750℃. This temperature range can effectively promote the full dissolution of alloying elements such as silicon and magnesium, and avoid grain coarsening caused by overburning. Purification of the melt is a key step in this process. Impurities such as hydrogen must be removed by a rotary degassing device to ensure that the gas content of the aluminum melt is controlled below 0.1ml/100gAl. An automobile manufacturer once had pinhole defects in the cylinder casting due to insufficient melt purification, which eventually caused a serious accident of engine oil leakage. In addition, the holding time of the melt must also be strictly controlled between 6 and 8 hours. Too long holding time will lead to component segregation, while too short holding time will not effectively eliminate casting stress.

Mold design and thermal balance management are the core elements of casting molding. The design of the mold cavity requires the use of 3D simulation technology to optimize the filling path of the molten metal to ensure the best match between the flow channel cross-sectional area and the gate speed. For example, in the design of water-cooling runners for battery trays of new energy vehicles, computer-aided engineering (CAE) simulation is required to complete the filling of molten metal within 0.03 seconds while avoiding the problem of air entrainment caused by eddy currents. Temperature control of the mold is also an important technical challenge. The preheating temperature should be stable between 180°C and 220°C. Too high a temperature may cause mold sticking, while too low a temperature may cause cold shut defects. In a certain company, the surface strain rate of the casting increased by 15% due to mold temperature fluctuations of ±10°C. To this end, the mold cooling system should adopt conformal cooling water channels and manufacture complex runners through 3D printing technology to improve the uniformity of cavity temperature and thus improve the overall quality of the casting.

The precise control of die-casting process parameters is a decisive factor in the quality of castings. The injection speed needs to be controlled in stages: in the slow accumulation stage, the speed should be controlled at ≤0.2m/s to effectively exhaust the gas; in the fast filling stage, the speed can reach 40-80m/s, but it is necessary to ensure that the gate speed does not exceed 60m/s to avoid splashing and oxide film entanglement. The selection of injection pressure should be combined with the structural characteristics of the casting. For example, thin-walled parts (≤3mm) need to use 80-120MPa high pressure, while thick-walled parts (≥10mm) can be reduced to 40-60MPa. A company once set the injection pressure too high, causing cracks in the engine cylinder, resulting in losses of more than 10 million yuan. The calculation of the clamping force needs to comprehensively consider the projected area of ??the casting and the fluidity of the alloy. For example, for a motor housing with a projected area of ??0.3㎡, a 4000-ton clamping force device is required.

Post-processing and quality inspection are the final guarantee to ensure the quality of castings. After the casting is demolded, it should be heat treated immediately. The T6 solution plus aging process can increase the tensile strength of the AlSi10Mg alloy to more than 320MPa. In the surface treatment process, the thickness of the anodized film needs to be controlled between 10-20μm. A too thin film layer may lead to insufficient corrosion resistance, while a too thick film layer may cause cracking. Due to the uneven thickness of the oxide film, a certain automobile manufacturer caused red rust on the battery tray in the salt spray test. Quality inspection should run through the entire casting process. X-ray inspection can detect internal defects larger than 0.5mm, while 3D scanners can achieve dimensional accuracy detection at the level of 0.02mm. The artificial intelligence visual inspection system introduced by a certain enterprise can automatically identify surface defects such as microcracks and pores using a deep learning algorithm. Its detection efficiency is more than ten times higher than that of traditional manual methods.

Aluminum Die Castings