High Pressure Die-casting Process Simulation And Mold Design For A Aluminum Alloy Cylinder Block

The high pressure die casting defects of an aluminum alloy cylinder block used in a generation device has been analyzed. The filling and solidification processes have been simulated by casting simulation software MAGMA soft. Improvement suggestions of the high pressure die casting technique for this casting have been provided by analyzing the simulated filling and solidification process. Important casting process parameters have been optimized by orthogonal simulation method. The optimized technique has been used in products to verify the beneficial effect by comparing the quality of castings. A high pressure die casting mold for this cylinder block has been designed by using NX8.0.The currently defects of this cylinder block casting are 1-2mm diameter shrink hole in the central axis hole and the inner of cylinder, blow hole and oxidation slag in the machined surface of cylinder, air leakage in the oil road area near central axis hole in 0.52MPa pressure test.The filling and solidification processes for this high pressure die casting using the present technique have been simulated and analyzed. Simulation results show that there are turbulences in filling process, feeding channel blocking in solidification process, shrinkage defects and low density in the position of casting central axis hole where shrinkage defects and leakage exists in products. Gas blocking and a long air contact time of melt are observed by simulation on both sides of cylinder port where blow hole and oxidation slag exists in products. Simulation results also show that switch position of slow/high injection velocity is before the ingate and mold erosion exists near the ingate. Improvement suggestions are given as follows: (1) Increasing the cooling channels diameter near cylinder and central axis hole of casting and adjusting pouring temperature and mold temperature in order to improve the feeding effect, (2) Increasing the thickness of 7 vent grooves outside of the cylinder to improve exhaust situation, (3) Increase the closing parameter time, (4) Adjusting the injection velocity and (5) Adjusting switch position of slow/high injection velocity.Four parameters of "fast plunger injection velocity", "pouring temperature", "mold temperature", and "switch position of slow/high injection velocity" are optimized by orthogonal test simulation. Three assessment criteria are identified. First is the pressure distribution in the oil road area near central axis hole of castings at the end of the filling process which reflect the transfer efficiency of injection pressure and the higher the pressure, the better effect of feeding and higher density of casting after solidification. Second is solidification time, and the shorter solidification time, the higher production efficiency. Third is the defect score from 1 to 10 that is according to the shrinkage defects of the simulated casting by MAGMA soft, and the higher the score, the smaller tendency of shrinkage porosity defects. The results are as follows:(1) Effect of process parameters on the pressure distribution of cylinder casting from strong to weak is in the order of "fast plunger injection velocity", "mold temperature", "pouring temperature" and "switch position of slow/high injection velocity". The pressure increases along with the increase of "fast plunger injection velocity". The pressure is maximum when "mold temperature" is 180 ℃. There is a little effect of "switch position of slow/high injection velocity" on the pressure.(2) Effect of process parameters on solidification time from strong to weak is in the order of "mold temperature", "fast plunger injection velocity", "switch position of slow/high injection velocity" and "pouring temperature". With the decreases of "mold temperature", "fast plunger injection velocity" and "pouring temperature", and moving forward to injecting plunger for "switch position of slow/high injection velocity", the solidification time decreases.(3) Effect of process parameters on defect score from strong to weak is in the order of "fast plunger injection velocity", "pouring temperature", "switch position of slow/high injection velocity" and "mold temperature". The defect score is maximum while "fast plunger injection velocity" is 3m/s and the defect tendency of castings is minimum. The defects score increases with the decrease of "pouring temperature". With the increase of "mold temperature", the defect score increases first and then remains unchanged. There is little effect of "switch position of slow/high injection velocity" on the defect score.Based on the impact of the four process parameters "fast plunger injection velocity" A, "pouring temperature" B, "switch position of slow/high injection velocity" C and "mold temperature" D on the three assessment criteria, and giving priority to defect score, the optimized test level A2B1C3D2 has been selected, with "fast plunger injection velocity" 3m/s, "pouring temperature" 635 ℃, "switch position of slow/high injection velocity" 580 mm and "mold temperature" 200 ℃.The high pressure die casting filling and solidification processes for the aluminum alloy cylinder block have been simulated using the optimized technique. The simulation results showed that mold erosion near the ingate is remarkably reduced, air contact time of melt near cylinder port is shortened that reduces slag oxidation tendency, no obvious shrinkage defects are observed near central axis hole, there are also shrinkage defects near cylinder still, but remarkably reduced and the solidification pressure significantly increases by the same injection pressure, which indicates injection pressure transmission effectively. The practical production using the optimized technique show that there are no shrinkage defects near the central axis hole, the shrinkage defects reduces apparently near the cylinder area, blow hole and oxidation slag in the machined surface of cylinder decreases and no air leakage in pressure test of the casting products.According to the optimized high pressure die casting technique of the aluminum alloy cylinder block, the mold has been designed including molding department, mold frame department, side core pulling mechanism, casting push up and reset mechanism, mold thickness calculation, stroke checking for movable mold plate, minimum distance of die closing, maximum distance of die opening and the maximum profile checking. Three-dimensional modelings have been given using NX8.0.