Power Supply Expansion at the Bergen County Utilities Authority

Lost Foam Casting

Mercury Marine established a lost foam casting operation at its outboard engine manufacturing plant in Fond du Lac, Wisconsin, in 1985 to supplement its established die casting shop. The company uses the process to make engine blocks for three two-stroke engines. In lost foam casting, a machined foam pattern is coated with a thin ceramic film to prevent hot metal, from penetrating it and then placed in dry sand that is compacted around it by vibration. Molten metal is poured onto the foam through a sprue, melting and subliming the foam and taking its place in the mold. Mercury opted for lost foam casting, rather than for expanding its conventional die-casting operation, to reduce costs and enhance design capabilities. Lost foam casting allows an engine block that formerly consisted of 125 assembled pieces to be cast as a single part. It also allows the design of more-complex shapes. Machining and assembly were eliminated for the lost foam parts, production rates increased by several times, metal waste and energy use decreased, and wear on dies was virtually eliminated, according to a company spokesman. The tooling for a lost foam setup costs about 750,000 USD, compared with about 1 million USD for tools for a die casting setup. The machine tools for a lost foam line generally have a virtually infinite useful life, while die casting tools must be replaced after about 200,000 parts. Although energy savings were not specifically measured at Mercury, the spokesman said the electrical load from several pieces of machining equipment was eliminated. (A comparison of energy usage conducted for the U.S. Department of Energy by the University of Alabama at Birmingham shows lost foam casting consumes about 27% less energy than conventional sand casting.) Mercury Marine expects to expand its use of lost foam casting.

Technical Data

Mercury installed a lost foam casting line that pours about 20 flasks of metal per hour. Lost foam casting is used to make blocks for three different engines: a 2-cylinder 40 hp and a 3-cylinder 60 hp engine-both with integral heads, water heads, and exhaust chests designed into one casting-and a 3.0-L V-6 250 hp engine. At a line speed of 20 flasks per hour, the lost foam casting line can produce 40 V-6 engine blocks per hour, compared with 12 blocks using die casting, and about 60 3-cylinder blocks vs. 15 or 16 per hour with die casting. The use of low-expansion sand as a molding medium enables lost foam casting to achieve the dimensional precision of high-pressure die casting. The use of 10 atmospheres of pressure during solidification results in order-of-magnitude decreases in porosity, 100% increases in elongation, and 10% increases in ultimate tensile strength.

Energy Data

A comparison of energy usage conducted for the U.S. Department of Energy by the University of Alabama at Birmingham shows lost foam casting consumes about 27% less energy than conventional sand casting. It reduces the energy required for melting metal by about 30%, for a potential savings of 37 trillion Btu per year. A Mercury spokesman said the reduction in machining requirements in that plant has produced significant energy savings. The electrical load from five or six machines, each driven by a 50-hp motor, has been eliminated.

Environmental Data

Use of the lost foam casting process led to a 17% reduction in distortion scrap by one foundry participating in the University of Alabama study. In another, the scrap rate dropped from 5.5% to 0.25%. Because dry sand with no bonding agents is used for lost foam casting, it can be reused instead of being disposed of as solid waste.

Economic Data

A product line that would cost about 15 million USD in die casting machine tools would require about 10 to 11 million USD in lost foam casting tools. The associated machine tools for the lost foam line cost about 750,000 USD; the tools for a die casting line would cost about 1 million. The lifetime of lost foam tools generally is several times that of conventional casting tools. The parts produced with lost foam casting are highly accurate and the process does not leave blemishes or surplus metal that must be machined away. Although a lost foam casting line costs approximately twice as much as a large die casting machine, its production volume may be three to four times higher, and more features are designed into the casting.

Contacts:

Mercury Marine

Tom Schmidt

P.O. Box 1939

Fond du Lac, WI 54936-1939

920-929-5000

920-929-4914 (Fax)

http://www.mercurymarine.com

Vulcan Engineering Company

Bryan Baker

1 Vulcan Drive

Helena, AL 35080-0307