Buildings and Industry

Powder Metallurgy at Automotive Parts Plant

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Summary

Stackpole Limited has developed high quality, low cost automotive parts using a process called powder metallurgy (P/M), a process well known for converting fine metal powders into solid products. It is particularly useful for manufacturing complex shapes to close tolerances in high volumes and at relatively low production costs.

By eliminating the casting, forging and machining operations of conventional fabrication processes, Stackpole's P/M process provides energy savings of approximately 500 TJ each year and decreases cycle times. Stackpole began to develop its P/M technology in 1982 and continues to improve the technique to obtain stronger, higher tolerance and lower cost parts.

Aim of Project

Metals in powder form have been used for many centuries; however, modern P/M technology came into its own during World War II, and since that time has grown more rapidly than any other metal fabricating process. The principal reason for this growth is that the P/M process is an economic high-production method for making parts exactly to final dimensions and finishes with little or no waste.

In 1982, Stackpole saw the potential of powder metallurgy and undertook not only to use the technology, but to continue to refine it to higher levels of performance in order to be a stronger company offering a cutting edge, globally competitive and desirable product. The goal was to produce high quality, low-cost automotive parts using powder metallurgy.

The Principle

The conventional method of manufacturing automotive parts involves numerous operations, including casting, metal forming (with presses, drop hammers and forging machines), drilling, boring, turning, milling, planing and grinding. The formed part may be heat-treated to develop the final properties of the material. All of these procedures are energy intensive. Much energy is wasted simply to produce and remove metal by machining that ultimately becomes scrap.

Powder metallurgy uses a blend of metal powders that are carefully selected for the size and shape of the particles. The mixture's main constituent is iron powder, to which small quantities of other elements are added to produce alloys with specific properties (tensile strength, toughness, hardness, etc.) The first main step of the P/M process is the blending of these powders and the addition of a lubricant. Step two involves the compaction of the mix under high pressure in a shaped die to form a "green"component which is strong enough to be transported to step three, sintering. In the sintering furnace, when a critical temperature is reached, the balance of the surface energy on the particles is activated and the final intimate bonding between the metal particles takes place. The temperature of the furnace must be kept well below the melting point of iron or the part will lose its shape.

After sintering, the parts undergo a variety of secondary operations, including cold sizing (coining) which improves dimensional accuracy and increases surface density, heat treating to improve tensile strength and hardness.

The Situation

Stackpole followed a long term R&D strategy to create new markets for P/M by improving mechanical properties, in particular the fatigue endurance strength of P/M. The company has been able to progressively enhance the properties of its products to higher levels since the beginning of the project. Significant, patented technical innovations using advanced alloying, high temperature sintering and selective densification for very high dynamic strength have been developed.

These new technologies have opened new markets, allowing Stackpole's advanced P/M parts to replace conventional machined cast and wrought steels, with considerate cost and energy savings. The majority of these automotive technology components are exported.

The development of its P/M technology has allowed Stackpole to expand its product line to high performance components such as selectively densified engine balancer gears, transmission sprockets with unique, phased teeth, and synchronizer assemblies for manual transmissions. Under a project running from 1996 to 2001, the company is developing new high-density materials and processes to achieve high core densities in products such as helical gears. These novel shape processes represent the last phase in the long term mission to develop P/M components with dynamic properties at least equivalent to high strength, low alloy steels.

Aside from the reduction of fabrication steps and energy savings, powder metallurgy also benefits the environment in several ways. First, by eliminating the melting and hot forging operations, air pollution is reduced and fewer combustion gases are released. Second, there is less waste: because P/M parts are near final form, cutting and machining operations are eliminated or reduced, which means that less scrap is produced. Third, machine oil used in conventional processes is no longer a disposable problem.

By using P/M in place of conventional manufacturing techniques, Stackpole is saving an estimated 500 TJ each year, or about 82,000 barrels of oil equivalent (BOE). This is equivalent to an annual reduction of 26,000 tons of CO₂ emissions. If the technologies being developed in this project are applied to the manufacture of automotive transmission gears and connecting rods, energy savings could amount to an additional 1.6 PJ per annum, or 270,000 BOE. In this case annual CO₂ emission reduction would be about 83,000 tons.

The Company

Stackpole operates four separate facilities in Canada. The company's high strength parts plant in Mississauga, Ontario, among the most modern in North America, is producing more than 500,000 parts each week for the North American automotive industry. In 1991, capacity was doubled to more than 19,000 square meters (200,000 square feet) to accommodate the increased production. Additional production capacity was added at the Stratford Division, Ontario in 1998.

Economics

Stackpole's total investment in the powder metallurgy technology is expected to be about CAD 65 million with an additional CAD 6 million invested by Natural Resources Canada's Industrial Energy Research and Development (IERD) program.

Implementation of the technology has allowed the company to produce a wider range of higher quality products at globally competitive prices. The target market for these advanced technology products is mainly in the automotive area, for example, transmission gears and connecting rods. These areas, traditionally dominated by machined, heat-treated steels, represent a new market potential for P/M of over CAD 1 billion.