MELTING AND HANDLING -- INDUSTRIAL PRACTICE

The industrial practices observed are described specific to the sites visited. The Japanese sites precede the European ones.

Japan

The Japanese sites visited pertaining to melting and handling are Daiki Aluminum, Ryobi, Ahresty Corp., Toyota Motor Corp., Kubota Corp., and Kyocera. These are briefly described below, followed by overall impressions.

Daiki Aluminum

Daiki Aluminum is the largest and oldest supplier of secondary aluminum in Japan. At about 160,000 tons per year, it serves the die casting industry, the casting industry, and other related secondary aluminum users. Daiki operates four plants in Japan and has headquarters and laboratory facilities in Osaka. The raw material -- the aluminum -- is melted in open well furnaces although rotary and induction furnaces are also used. Major R&D efforts are aimed at reducing costs and investigating defects in castings. Hard spots and inferior machinability are the leading matters of concern. It is interesting to note that the delivery of molten metal to various casters is not practiced in Japan as it is in the United States. Each casting operation melts its own metal. The WTEC team learned that environmental laws in Japan prohibit carrying molten metal over public highways.

Ryobi

The Ryobi group is a conglomerate of 40 companies that form the backbone of Ryobi Ltd. The Shizuoka operation, which the WTEC team visited, got started in 1962 and is intensely invested in die casting. In 1984, a joint venture with Ford Motor Co. was formed with the objective of producing transmission cases. Four 3,500 ton machines were used for this activity. Production for Ford is now being done in the United States in a 100% Ryobi-owned plant. The 3500 ton machines at the Shizuoka plant now are used to supply domestic customers.

At Ryobi, there is no extensive molten metal treatment. The melt is neither routinely degassed nor filtered via ceramic foams or rigid media. Fishnet type "filters" are used during ladle filling to remove dross prior to filling the die cavity. No grain refining or modification of the aluminum melt is carried out. Furthermore, no quality measurements of the molten metal, such as hydrogen level and inclusion content, are carried out on a routine basis. Similarly, no thermal analysis of the aluminum is carried out on a routine basis to monitor quality.

Ahresty Corp.

Ahresty Corp. is an integrated die casting company. Its principal products are aluminum die castings, secondary aluminum, ingot, free access floors, garden tools, and peripheral equipment for die casting machines. Ahresty operates six casting plants, five sites for die manufacturing and a secondary aluminum operation.

Ahresty has developed processes to improve the quality of high pressure die castings through rapid melting furnace technology, automated aluminum scrap sorting, and enhanced molten metal handling. At Ahresty, molten metal is transferred to each die casting machine. Subsequent to casting, an automatic extractor places the castings into a trim press to remove the flash.

Ahresty uses CT scanners to measure interior casting dimensions, and infrared temperature sensing devices are used to monitor die temperature. Critical process parameters are measured and stored; the data are analyzed for quality assurance purposes.

Toyota Motor Corp.

Toyota operates both iron and aluminum casting operations. It operates both sand cast and die cast shops to produce parts for its auto manufacturing. Cast components are used for chassis, power train, and body applications.

Many advances in both product and process have resulted from Toyota's commitment to foundry engineering. Some of the most recent are the TDP aluminum cylinder block production, Toyota's new differential pressure casting process, aluminum suspension members produced by low pressure die casting, aluminum wheels produced by high pressure casting, automatic core transfer and setting, automatic core delivering, and automatic coating of investment casting molds.

Toyota Motor Corp. has an advanced materials handling system in place. Secondary aluminum is melted in a rapid manner and delivered to each casting unit. It is interesting to note that zinc is removed from auto body scrap prior to melting.

Toyota practices advanced molten metal processing technologies; in particular, inclusions are removed prior to casting. Electromagnetic and centrifugal forces are applied to the melt to separate the inclusions out before transferring the melt to the mold.

Kubota Corp.

Kubota is a major corporation committed to materials, and it continues to invest in materials research and development. The main sectors of the corporation are in agriculture, water supply, housing, and the environment. It is interesting to note that Kubota Corp. has made a commitment to the development of materials for the metal casting industry and specifically as a resource for enabling technologies for the foundry industry.

Kubota has a very intense development and presence in the use of ceramics for advanced die casting processes. Kubota's ceramics have higher strengths and toughness as well as higher corrosion resistance against molten aluminum compared with the traditional ceramic refractories used in the industry. Maximum dimensions of Kubota ceramics for the die casting industry are a length of 50 in, a diameter of 20 in, and a thickness of 2 in. Kubota is working with end users and customers in producing state-of-the-art ceramics for the die casting industry, and has a very good array of such products. Kubota is a key player in the development of enabling technologies for the metal casting industry in Japan, as well as globally. It is producing Si3N4 material and composite material (titanium matrix containing ceramic particulates) for die casting applications. These include transfer ladles for Ube squeeze casting systems, transfer tubes for Toshiba electromagnetic pump systems, riser stalks for low pressure die casting, heater element tubes for holding furnaces, thermocouple protection tubes, nozzles, and a variety of other applications. The titanium composites are used as short sleeves for high pressure aluminum die casting, for both horizontal and vertical machines. These composite ceramics have very high insulation properties as well as high corrosion resistance to molten aluminum.

Kubota also produces porous metals. These are produced via powder metallurgy -- a special sintering process unlike traditional sintering processes. The porosity is controlled within the range of 15-30%. The size of the pores and their distribution are independently controlled to between a 20-100 µm diameter. It is clear that Kubota also controls the size of the initial powders, the raw material used in the development of porous metals. The porous metals are made out of H13 steel as well as AISI 1304, and have applications in aluminum die casting and plastic injection molding. These porous metals also have potential applications as die materials and core boxes; this is a major enabling technology for the metal casting industry.

Regarding metal handling, Kubota is producing skid buttons (which are used in the steel industry to support reheated slabs). These buttons are produced by Kubota from chromium matrix alloy using hot isostatic pressing (HIP), and are four times more wear resistant than those made of cobalt matrix heat resistant steel material. This new material is anti-oxidizing and can be utilized for temperatures in the vicinity of 1350°C. The melting point is 1250°C for conventional buttons. Kubota is supplying skid buttons to most of the major steel producers of Japan, having manufactured over 4,000 pieces since 1988.

Kyocera Corp.

Kyocera is a well established powerhouse in the field of ceramics. Kyocera ceramics are used in a variety of applications in the chemical industry, in the semiconductor industry, and in wire drawing equipment, automation components, communications, engine components, etc. Like Kubota Corp., Kyocera Corp. has made a commitment to the metal casting industry in that it is producing advanced ceramics for die casting manufacturing applications. These are thought of as enabling technologies for the foundry industry. The fine ceramics division has advanced facilities with cold isostatic pressing (CIP) for making Si3N4 components, for slip casting, and for state-of-the-art grinding and machining operations. Kyocera's Si3N4 is based on its own proprietary technology. The stalk tubes produced by the Kyocera materials have demonstrated a 2 year life during industrial applications.

Kyocera's products for metal casting applications include ladles, die cast sleeves, stalks, thermocouple protection tubes, submersible heater protection tubes, heater tubes, degassing pipes and rotors, fixtures for wetting processes, pumps, etc.

In the past, Kyocera has worked with Toshiba to develop a die casting hot chamber machine, and has manufactured ceramic components that are used in the hot chamber casting machine.

Overall Impressions

Europe

The European sites this panel visited pertaining to melting and handling are BMW, Buhler, and Pechiney Aluminum. These are described below, followed by overall impressions.

BMW Foundry Division

The BMW aluminum casting operation is located in Landshut, Germany. It is the largest low-pressure, semipermanent mold aluminum foundry in the world. This is are a captive shop, currently manufacturing parts only for BMW, but plant managers are interested in expanding their casting sales. This modern aluminum manufacturing plant employs high pressure die cast, gravity, and low pressure permanent molding, sand casting, and a lost foam development cell. The site is a multilevel foundry with varied operations on each level. All equipment is monitored by a computer information system that reports both inventory control and manufacturing process data.

The process begins by either melting aluminum or purchasing liquid aluminum from the secondary industry. Unlike Japan, molten aluminum is transported by trucks in high temperature ladles over highways for as far as 200 miles. The aluminum is held in gas-heated furnaces until needed at the casting machines, at which time the fork trucks transfer it via ladles.

Casting production of transmission cases, motorcycle cylinder blocks, and oil pans is done on high pressure die cast machines. More complex cylinder heads and engine blocks are made using the low pressure, semipermanent mold process. The molten metal is degassed prior to casting; however, no extensive quality measurement devices are utilized.

Buhler Ltd.

Buhler is a worldwide engineering group active in the design and construction of plants and equipment with headquarters in Switzerland. Buhler has a very strong expertise in die design and manufacture and is one of the leading producers of die casting machines. Buhler's modular design and flexibility of apparatus allow control of the pressure and velocity profiles during operations.

Buhler has made a major investment in semisolid processing of materials by producing a new die casting machine -- the SC model -- wherein semisolid billets are placed into the die. With respect to molten metal handling, Buhler's approach completely changes the paradigm in that there is no liquid metal handling. Buhler heats slugs cut from rheocast billets via induction, and subsequently these heated billets are transferred into the cavity and injected. Under pressure or shear, the heated rheocast slug flows into the cavity. This is an exciting new development offering most interesting cast properties.

Pechiney Aluminum

Pechiney, a large private corporation in France, has corporate axes in the packaging industry and in metal production -- including magnesium, aluminum, and other refractory materials. Pechiney is one of the few, if not the only, primary producer of aluminum that is also heavily committed and involved with secondary aluminum production. This may be a resource for the metal casting industry in that there exists a great deal of technology derived from primary production of aluminum that can be used in secondary production of aluminum and subsequently in metal casting.

Pechiney's group in melting and solidification research is very strong in personnel, equipment, and intellectual property. The staff is very much involved in recycling and thus has developed a great deal of expertise and proprietary information in melting, removal of secondary phases (inclusions), degassing of molten aluminum, fluxing, etc. Moreover since they are integrated in the corporation with an end product such as the packaging industry, they can assess the performance of the metal they produce in the marketplace. For example, the refining techniques used during casting and the resultant performance in the beverage can industry can be measured under one umbrella at Pechiney.

There is a great deal of effort at Pechiney in semisolid processing, specifically in the production of thixotropic materials. The R&D program is now at the commercial stage, exemplified by the production of thixotropic billets as well as the development of the thixoforming processes. The product name of the thixotropic billet they produce is ALTHIX; these are now being produced commercially on an industrial scale and distributed in North America by Oremet. Their products -- A356 and A357 -- are currently available in 3 in diameter billets. Larger diameters are also being developed. The corporate philosophy is that Pechiney Aluminum will supply billets to independent companies and will provide technical assistance to its clients. The goal is to contribute to the development of thixocast parts, especially for the automotive industry.

Overall Impressions

In comparison to Japan, there is more of an infrastructure for the secondary aluminum industry in Europe. The various casting houses and casting operations do not rely on melting their own aluminum and their own metal but rather purchase it from the secondary aluminum industry. In most instances, a combination of both in-house melting and purchase of secondary aluminum takes place. In Europe there is a greater consciousness of the quality of the molten metal and implementation of molten metal processing technologies such as degassing and filtering than in Japan. However, neither Japan nor Europe is using measurement devices to control the quality of the molten metal as fully and extensively as is the case in the United States.

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Published: March 1997; WTEC Hyper-Librarian