The JTEC/WTEC team visited two plants of the Toyota Motor Corp. -- the Tahara plant and the Myochi plant. The former is a state-of-the-art aluminum casting plant that produces automotive engine blocks and heads using metal mold processes; the latter, the Myochi plant, has three different casting plants: two produce iron castings and the third plant produces aluminum. The Myochi plant produces cylinder blocks, differential carriers, cylinder heads, and cross members. The cylinder heads and cross members are made from aluminum. Nonetheless, ductile iron is the largest production at the site.
Die casting is the preferred metal mold technology used by Toyota for auto chassis, powertrain, and body component applications. Aluminum suspension members are manufactured via low pressure die casting while aluminum wheels are manufactured using high pressure squeeze casting. As discussed in Chapter 2, all the dies used at Toyota are made in-house with an extensive infrastructure for die maintenance and inventory control.
Hitachi Metals has made a strong commitment to and shown an interest in R&D in metal mold casting technologies. Some of the achievements during the last seven years include the practical application of super heat-resistant steel (NSHR-F) for high-power engine exhaust components, the establishment of flash-free casting technology, the development of "HIPAC11" for premium quality aluminum alloy castings, the development of a computer-aided solidification simulation system (SCAST), the development of the practical use of new cast steel exhaust parts for clean auto engines, and the development and practical use of new pressure reduced atmosphere casting (HMRAC) using sand molds.
Die cast and permanent mold casting technologies are used for aluminum. There is a very strong automotive focus at Hitachi for specific applications such as intake manifolds, engine blocks, and chassis components. The development of a flash-free casting technology has been quite a benefit for the metal mold casting process.
Ahresty is significantly involved in high pressure die casting. Ahresty operates mostly in the cell configuration. Castings are moved from die cast machines of varied size by overhead-mounted robots or extractors. These control the complete cycle from casting design via computer work station to die construction on site. Dimensional tolerancing of castings is done via coordinate measurement machines with computer-aided tomography used to measure internal wall thickness.
Many advances in high pressure die casting are already developed at Ahresty:
Ahresty is a leader in the application of technology to high pressure metal mold casting operations. However, its business has been reduced as a result of the decrease in automotive production in Japan.
Ryobi has a major involvement in high pressure die casting. For example, at the Shizuoka plant alone there are 35 die casting machines, four of which are 3,500 ton machines. Seventy-two percent of the high pressure die castings produced by Ryobi are for automotive applications. Altogether 88% of all the Shizuoka plant's products are used in the transportation industry.
Like other metal die casters, Ryobi produces all of its dies in-house and maintains them rigorously. Ryobi's management believes that squeeze casting may be better than conventional die casting for high performance components. However, squeeze casting is more expensive. At present, wheels, cross members, and certain components for high performance cars like the Mazda RX7 are being produced by squeeze casting. There are no specific weight reduction goals in Japan like the Corporate Average Fuel Economy (CAFE) regulations in the United States. Ryobi has not embraced squeeze casting as a whole; however, Tokyo Light Alloy, a company associated with Ryobi, has two 1600 ton medium pressure squeeze casting machines made by Toshiba. In addition, a smaller squeeze casting machine is being used to produce automotive components at Ryobi's Mitsugi plant.
Ryobi uses slower shot speed, which enhances laminar flow and also helps with heat treatment and defect reduction. This increases the propensity of cast components to be heat treated for structural applications. All die temperatures are monitored through infrared measurements to maintain good process control of the operation. RIC cores are being used at Ryobi operations; these are sand cores that have a special resin coating, which prevents the liquid metal from impregnating the core.
As previously discussed in Chapter 2, both of these corporations have made a commitment to the metal casting industry and in particular to develop ceramic materials as enabling technologies for the die casting industry. They produce advanced silicon nitride materials for specific die casting applications such as ladles, stalks, and die cast sleeves. Kyocera has a working relationship with Toshiba Metals; their joint activity is in the area of hot chamber die casting machines.
Kubota, in addition to producing silicon nitride materials, commercially produces a titanium matrix composite with applications for transfer ladles. Kubota has a relationship with Ube Corp., a producer of die casting machines, in the field of squeeze casting. Kubota is also working with Toshiba developing advanced transfer tubes.
Most interesting for the die casting industry are the porous metals that Kubota produces. This is a significant enabling technology for metal mold casting with potential use as die materials and core boxes. This technology may lend itself to the removal of entrained air as well as for venting purposes.
It is quite clear that the growth of squeeze casting has slowed in Japan; however, it has not stopped. The interest is very much present, and attempts to optimize the process are being made. The cost of the process is a barrier for its expansion. There are two major machine manufacturers of squeeze casting systems in Japan -- Ube and Toshiba.
Metal mold casting is the process of choice in Japan for aluminum. There is very limited activity in sand casting, ceramic mold casting, or lost foam.
The market growth in Japan is limited and is not expanding as in other parts of the globe. The automotive business is moving from Japan to off-shore locations such as the United States and China. Japanese foundries being established in the United States will be competing seriously with U.S. foundries.