Strut housing used on GT-R manufactured by Nissan is made by high vacuum die casting, improving excellent car body stiffness and controllability. The following are the processing of strut housing used for GT-R.
1. Feasibility of die casting
Strut housing on GT-R transfers 15 parts on strut and wheel house into once die casting, connecting with parts of R-SIDEMBR, DASH-LWR, HOODLEDGE, COWLTOP in three-dimension, effectively dispersing pressure from tires. It is a key procedure for realizing linearization of car body deformation without liberation. So, on the base that transfers the structure that multi parts stamped, welded into once forming structure, it needs to eliminate sealing lumen structure having influence on demolding, wiping out unnecessary thickness. Meanwhile, homogenize the whole thickness of products. Besides, to improve production efficiency, simplifying mold paring, ensuring the position of kicker pin and mold cooling space should be taken into consideration. Finally, determine the shape of strut housing parts meeting requirements. The performances required for high vacuum die casting is that yield strength is higher than 140Mpa and elongation is higher than 10%.
2. Development of production technology.
Use Vacural die casting machine supplied by Muller Weingarten. The feature is that molten aluminum is poured rapidly quantificationally under vacuum differential pressure; use thermal insulation stripping lubricant for heat preservation of filling molten aluminum. Vacuum management of mold can prevent air from involving furthest. Use cast aluminum alloy having high toughening pressure developed by company. Clamping force of die casting machine is 40000kN and the material is Al-10Si-0.35Mg. Strut housing is large thin-walled part, having long filling flow length. The test result shows that the molten aluminum should be completely filled within 23ms, otherwise, bad filling may be caused. The measurement is reducing backpressure inside cavity. Seal holding furnace and mold. Meanwhile, to delay setting time, adiabatic release agent is used. However, air entrapment and shrinkage are still caused on the parts of casting far away from ingate. The strategies for air entrapment are: one, optimize technique through numerical simulation; two, change oily lubricant on punch into powder lubricant; three, change fabric sealing between pressure chamber and punch into metal sealing. The effectiveness is that vacuum degree of cavity is maintained below 3kPa. Measures for shrinkage is setting high speed partial pressure device. Strut housing has high requirement for precision of parts. Aiming at high deformation during solid solution and water quenching of heat treatment on T6, measure are taken respectively. In terms of deformation caused by dead weight during solid solution, the best support zone of heat treatment can be acquired through computer simulation. Meanwhile, optimizing setting not only controls deformation, but also meets solution temperature and conditions of mechanical properties. Changing water quenching in air quenching can reduce deformation caused by quenching. Moreover, using stiffener can improve stiffness under high temperature. Strut housing should be combined with steel plate when installed on vehicle. Dimensional deviation can be caused by electrochemical corrosion and temperature difference during car body coating. The measure for electrochemical corrosion is carrying out electrostatic coating on single part of strut housing, then sear glue on the combination of steel, completely isolating aluminum from steel. Use stationary fixture to restrain dimensional change during car body coating.
3. Mass production
For high vacuum die casting parts, management of vacuum degree and ensuing of dimension precision are very vital. Management of vacuum degree is not only the assurance the internal quality of castings, but also the necessity for pouring quantity management of high vacuum die casting machine and stability of equipment operation. In actual production, with the temperature of mold rising, vacuum degree of mold cavity decrease gradually and quantity of defective goods is increasing. The reason is that spreader and insert are separated for cooling. Temperature difference exists between spreader and insert. The measure is to optimize cooling of mold, preventing temperature on joint face from growing and maintaining temperature. Use simple automated dimensional checking device to ensure dimension precision, reducing human error and improving qualification rate.
GT-R is a new generation sport car developed by Nissan. The application of aluminum alloy die casting is the key technology for body having high stiffness and high precision. It is integration of high vacuum die casting technology. Compared with original model, using aluminum die castings on strut housing can significantly improve controllability of car. Therefore, using aluminum alloy die castings can not only reduce weight, but also improve performance of car.