| Squeeze casting process is a technic that high mechanical pressure are conducted on the liquid or semi-liquid metal in the cavity to make it fully filled and go through small plastic deformation. Porosity and shrinkage defects could be effectively reduced or even avoided. The castings with refined grain, homogeneous structure, complex-shaped and good mechanical properties can be achieved. However, domestic squeeze casting technology mainly focuses on experimental research on small-dimension, simple and low performance components and small-lot production, the confirmation of treatment regulation of material deterioration, process parameters, and gating system structure is guided by the experiences of high-pressure casting design, whether it is suitable for squeeze casting or not needs to be verified. This paper develops auto parts airbag bracket weighing 7.3 Kg with thickness 11-38 mm, large-dimension, complex and high-performance by using horizontal precision squeeze casting machine HVSC-1250PL, the influence of recession laws of modifier Sr in A356.2 and gating system structure pressure transmission is studied, meanwhile, the influence of casting process parameters on casting structure and mechanical properties is explored combined simulation with trial-production method. The main research contents and conlusions are as follows:(1) The comparison on recession speed difference of modifier Sr at various initial Sr content, P, B content, temperature was made, the inoculation and fading laws of it were studied, and the influence of Sr recession on casting mechanical properties was tested. It comes to a conclusion that the initial Sr content should be within 150-200 ppm, the grain refiner B is not suggested, the time interval between two modifications should be 40 hours when the pouring temperature is 680-690℃ and P content of 30 ppm.(2) The structure and mechanical properties of casting casted by two different structure gating systems (long sprue short handle material and short sprue thick handle material) were mainly compared and analyzed, the results illustrated that thick handle material took advantage of pressure feeding characteristics of squeeze casting and owned better casting properties.(3) The mold filling and solidification process during squeeze casting were simulated based on Anycasting. Based on simulation model, several main casting defects were forecasted, the reason for defects generation were analyzed, the preliminary optimization of process parameters and mold structure were made to prevent the generation of defects, and the overall plan of airbag bracket squeeze casting was designed.(4) Testing the casting performance and running statistics on casting defects of trial-production airbag support arm, it could be found that several casings appeared to be shrinkage cavity, shrinkage porosity, slag inclusion in the local area. When it compared to simulation results, the reason for casting defects generation was analyzed and the reasonable improvement program was put forward, the casting process parameters were finally confirmed:specific pressure of 70 MPa, early fast mold-filling velocity of 150 mm/s, interim ingate-filling velocity of 70 mm/s, late slow fast mold-filling velocity of 90 mm/s, pouring temperature of 680～690℃, the casting properties could be:σb>300 MPa, σ0.2>220 MPa,δ≥ 8%, no fatigue bench defect time ≥100 h. The productions delivery to customer smoothly and they has been installed and performanced. The qualified rate of products are apparently improved, and reliable casting defects prevention and control programs are put forward, and finally the mass production realized. |
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