| A aluminum gearbox of yacht underwater outer chord machine is taken as the research object,and the problems existing in the actual production of the casting are analyzed.The casting simulation software MGAMASOFT is used to simulate the casting filling and solidification process.Improvement suggestions of the overflow discharge and cooling system for this casting have been provided by analyzing the simulated filling and solidification process.The effects of casting temperature,die-casting working temperature,injection speed and slow/fast injection speed on the filling and solidification quality of castings were studied,and we selected the optimal process parameters.A high pressure die casting mold for this gearbox has been designed by using NX 8.0.The underwater gearbox of the yacht external stringer is an important part of the outboard motor of the yacht.Its quality directly affects the normal operation of the propeller and even the safety of the entire yacht.The main problems that occur in the actual production process of the casting are as fllows :(1)The local area of the horizontal wing of the gearbox has turbulent flow during the filling process,and the air pressure at this part is relatively large and the tendency to generate the air hole is large;(2)The liquid and air contact time is longer during the filling process of the two sides of the middle part of the gearbox body,causing the probability of generating oxidized slag is high;(3)The solidification pressure of the installation cavity of the box propeller is small,and the central portion of the section has shrinkage and shrinkage defects;(4)The center of the thick part in the gearbox has a shrinkage hole defect in the center.Based on the results of the simulation analysis,suggestions for improvement of the cooling and overflow system are proposed:(1)The diameter of 10 cooling channels located in the thick part of the middle of the gearbox increased from 10 mm to 12mm;(2)The thickness of the overflow at the horizontal wing of the cabinet is increased from the original 1.2 mm to 1.8 mm.The simulation results are as fallows: During the fillingprocess,the turbulent flow on the surface of the horizontal wing of the box is obviously weakened,and the air pressure is reduced;The air contact time on both sides is shortened;The shrinkage and shrinkage defects of the thick part of the casting are obviously reduced,but the change in solidification pressure of the propeller mounting cavity area in the cavity is small.When the die-casting pressure is sufficiently large,the castings will leak during the pressure test,which is related to the low density of the castings caused by the poor pressure transmission effect of the die-casting.The injection pressure is transmitted to the alloy liquid in the cavity through the gate,and as long as the gate is solidified,the die casting pressure cannot be transmitted to the alloy liquid in the cavity.Increasing the transfer efficiency of the die casting pressure can increase the solidification pressure of the alloy liquid in the cavity,extend the infusion gate solidification time to make full use of the die casting pressure,both can increase the density of castings.The influence of pressure casting process parameters on the pressure transmission of die casting is complicated.The effects of "casting temperature","die-casting working temperature","fast injection speed" and "slow/fast injection switching position" on the filling process were studied by orthogonal test method,which includes air entrainment conditions,solidification pressure distribution,ingate solidification time,and shrinkage porosity shrinkage defects.The simulation analysis results are as follows:(1)The effect of die-casting working temperature on the setting time of the inner gate is greater than the pouring temperature,and it is more effective to increase the solidification time of the inner gate by increasing the temperature of the die-casting type;(2)The die-casting working temperature is 180°C,the pouring temperature is below 650°C,the solidification pressure is very low;the die-casting working temperature is increased by 200°C from 180°C,the solidification pressure is obviously increased,and when the temperature is continuously increased to 220 °C,the solidification pressure is decreased;(3)Increasing the pouring temperature significantly increases the probability of shrinkage defects of the casting,and the working temperature of the die-casting type is increased from 180 °C to 220 °C,which has little effect on the shrinkage defects of the casting;(4)Increasing the fast injection speed and the early slow/fast injection speed conversion all contribute to the increase of the solidification pressure.The effect of the rapid injection speed is greater than the slow/fast injection speed switchingposition,followed by the die-casting working temperature and the pouring temperature;(5)The increase of the fast injection speed and the slow/fast injection speed position have little effect on the shrinkage defects of the casting;(6)When the rapid injection speed is more than3.5 m/s,the turbulent flow during filling is more obvious.When the slow/fast shot speed is switched between 535 and 545 mm,the filling process is the smoothest.According to the results of the simulation analysis,the optimal process parameters are determined as follows: casting temperature 650 °C,die-casting working temperature 200 °C,fast injection speed 3 m/s,slow/fast injection speed switching position 535 mm.The optimized process parameters were optimized and verified.The optimization results are as fallows:(1)The filling process of the gearbox is stable and basically no turbulence is generated.;(2)There is no obvious shrinkage and shrinkage defect in the thick part of the casting;(3)The solidification pressure of the cabinet propeller installation cavity area is obviously improved.The actual production verification results show that there are no obvious shrinkage and shrinkage defects in the thick part of the casting,no porosity and oxidized slag defects,and no gas leakage occurs in the pressure test.Finally,UG NX 8.0 is used to design the mold,the mold has been designed including molded parts such as cores and inserts,moving stencils,fixed stencils,mold bases,push rods and push plates,and other accessories,auxiliary mechanisms such as core pulling mechanism,push core mechanism and guide bush guide sleeve,and mold check. |
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