The main goal of this study is to present the process characteristics to be used in designing the process parameters of the complex high pressure diecasting through 3D-fluid and solidification simulation. A complex high diecasting comprises vacuum diecasting, local squeezing diecasting and hot sleev...
The main goal of this study is to present the process characteristics to be used in designing the process parameters of the complex high pressure diecasting through 3D-fluid and solidification simulation. A complex high diecasting comprises vacuum diecasting, local squeezing diecasting and hot sleeve diecasting and it has been widely used in manufacturing relatively high functional components, thanks to the complex benefits obtained from its component processes. But, complex high pressure diecasters have also had difficulties in casting design and setting process parameters like other castings. In this study, by building a new numerical analysis model and using of commercial simulation code, the process characteristics of its comprising processes were investigated respectively.
1. Flow characteristics of molten metal in vacuum diecasting
To investigate flow characteristics of molten metal in the mold cavity (of total volume: 397㎤, average thickness: 2㎝) of vacuum diecasting, a new vacuum numerical analysis model was built. For validation of the numerical analysis model built, various vacuum degrees of no vacuum, 650, 500, 250 and 60mmHg were artificially applied in the mold cavity and the filling behaviors of molten metal with the applied vacuum conditions were simulated and compared with those of experiment. The results showed that molten metal was partially filled into cavity when vacuum pressure was applied and the simulated filling behaviors of molten metal were apparently similar to those of experiment, indicating the numerical analysis model developed in this study is highly available. The filling length of molten metal in cavity is increased by the ratio of 0.15 with the increasing applied vacuum pressure. And the filling velocity at final filling area is increased with ratio of 2.317, while at boss area is increased by relatively low ratio of 0.1953.
The gas quantity of the product was gradually decreased with the increasing applied vacuum pressure. Especially, in the case of 60mmHg, the gas quantity was significantly reduced by 15cc/100g (final filling area) and 11cc/100g (boss area) respectively. Finally, with the modification of vacuum gate system by filling simulation, the big reduction by 30% in gas quantities was obtained and it can be seen that the optimization of vacuum casting design by vacuum filling simulation developed in this paper is possible and efficient.
2. Solidification characteristics of molten metal in local squeezing process
The effects of local squeezing pressure and time-lag in LSVD (Local Squeezing and Vacuum Diecasting) were investigated. Measurements of specific gravity with the changes of local squeeze pressure and time-lag showed that the local squeezing effect can be increased by increasing squeeze pressure and decreasing time-lag. In this paper, for reaction shaft support, the optimized condition of local squeezing was experimently obtained as 2,000kg/㎠ for local squeeze pressure and 1.0sec for time-lag.
The ratio of retained melt per total volume (Vr-m/Vt) of the cylinder shaped local squeezing area was obtained (Vr-m/Vt: 0.9) through solidification simulation result by applying the optimized time-lag(1.0sec). And it was adopted in solidification analysis for complex shape component, gear housing. By applying the time-lag obtained from the solidification simulation result, the internal defects of casting were found to be minimized by computerized tomograph(CT), implying that as the optimal local squeezing time-lag for the product.
3. The behaviors of chill layers with temperature variation on shot sleeve
The effects of chill layers occurred in shot sleeve on the molten metal filling were analyzed through computer simulation. And the behavior of chill layers with temperature variation of shot sleeve set from 200 to 280℃ was also investigated. The simulation results showed the chill layers set in the in-gates during the injection process changed the main filling direction and caused turbulent flow pattern, resulting in porosities inside the castings. And the temperature profile on the shot sleeve set from 200 to 280℃ during diecasting process was investigated. The highest temperature on shot sleeve during diecasting process is 450℃ at T1 position (molten metal pouring area) when the molten metal is poured and shot sleeve is heated by 280℃, while the lowest temperature is 140℃ at T2 (platen adjacent area) under the waiting stage and shot sleeve is not heated artificially. So, it can be seen the T2 position acts an extensive place of chill layers occurrence during diecasting processes.
The amount of chill layers with the increasing temperature on shot sleeve was considerably reduced. Particularly, at the setting temperature of 280℃, the big reduction in chill layers, excellent trimmed surface, the highest density of 2.722 g/㎤ and the best creep property of rupture time 69 hours were achieved, suggesting that as the optimal sleeve condition in aluminum high pressure diecasting.
The main goal of this study is to present the process characteristics to be used in designing the process parameters of the complex high pressure diecasting through 3D-fluid and solidification simulation. A complex high diecasting comprises vacuum diecasting, local squeezing diecasting and hot sleeve diecasting and it has been widely used in manufacturing relatively high functional components, thanks to the complex benefits obtained from its component processes. But, complex high pressure diecasters have also had difficulties in casting design and setting process parameters like other castings. In this study, by building a new numerical analysis model and using of commercial simulation code, the process characteristics of its comprising processes were investigated respectively.
1. Flow characteristics of molten metal in vacuum diecasting
To investigate flow characteristics of molten metal in the mold cavity (of total volume: 397㎤, average thickness: 2㎝) of vacuum diecasting, a new vacuum numerical analysis model was built. For validation of the numerical analysis model built, various vacuum degrees of no vacuum, 650, 500, 250 and 60mmHg were artificially applied in the mold cavity and the filling behaviors of molten metal with the applied vacuum conditions were simulated and compared with those of experiment. The results showed that molten metal was partially filled into cavity when vacuum pressure was applied and the simulated filling behaviors of molten metal were apparently similar to those of experiment, indicating the numerical analysis model developed in this study is highly available. The filling length of molten metal in cavity is increased by the ratio of 0.15 with the increasing applied vacuum pressure. And the filling velocity at final filling area is increased with ratio of 2.317, while at boss area is increased by relatively low ratio of 0.1953.
The gas quantity of the product was gradually decreased with the increasing applied vacuum pressure. Especially, in the case of 60mmHg, the gas quantity was significantly reduced by 15cc/100g (final filling area) and 11cc/100g (boss area) respectively. Finally, with the modification of vacuum gate system by filling simulation, the big reduction by 30% in gas quantities was obtained and it can be seen that the optimization of vacuum casting design by vacuum filling simulation developed in this paper is possible and efficient.
2. Solidification characteristics of molten metal in local squeezing process
The effects of local squeezing pressure and time-lag in LSVD (Local Squeezing and Vacuum Diecasting) were investigated. Measurements of specific gravity with the changes of local squeeze pressure and time-lag showed that the local squeezing effect can be increased by increasing squeeze pressure and decreasing time-lag. In this paper, for reaction shaft support, the optimized condition of local squeezing was experimently obtained as 2,000kg/㎠ for local squeeze pressure and 1.0sec for time-lag.
The ratio of retained melt per total volume (Vr-m/Vt) of the cylinder shaped local squeezing area was obtained (Vr-m/Vt: 0.9) through solidification simulation result by applying the optimized time-lag(1.0sec). And it was adopted in solidification analysis for complex shape component, gear housing. By applying the time-lag obtained from the solidification simulation result, the internal defects of casting were found to be minimized by computerized tomograph(CT), implying that as the optimal local squeezing time-lag for the product.
3. The behaviors of chill layers with temperature variation on shot sleeve
The effects of chill layers occurred in shot sleeve on the molten metal filling were analyzed through computer simulation. And the behavior of chill layers with temperature variation of shot sleeve set from 200 to 280℃ was also investigated. The simulation results showed the chill layers set in the in-gates during the injection process changed the main filling direction and caused turbulent flow pattern, resulting in porosities inside the castings. And the temperature profile on the shot sleeve set from 200 to 280℃ during diecasting process was investigated. The highest temperature on shot sleeve during diecasting process is 450℃ at T1 position (molten metal pouring area) when the molten metal is poured and shot sleeve is heated by 280℃, while the lowest temperature is 140℃ at T2 (platen adjacent area) under the waiting stage and shot sleeve is not heated artificially. So, it can be seen the T2 position acts an extensive place of chill layers occurrence during diecasting processes.
The amount of chill layers with the increasing temperature on shot sleeve was considerably reduced. Particularly, at the setting temperature of 280℃, the big reduction in chill layers, excellent trimmed surface, the highest density of 2.722 g/㎤ and the best creep property of rupture time 69 hours were achieved, suggesting that as the optimal sleeve condition in aluminum high pressure diecasting.
주제어
#수치해석 복합고압주조법 3차원 유동 응고해석 3D-fluid solidification simulation complex high pressure diecasting
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