Steering the Market Toward Automotive Casting Opportunities.

A panel of casting experts discusses the automotive market and casting processes used to optimize components, offering examples of current successes and future possibilities.

The dialogue between foundries and end-users is critical to optimizing components. While it is important for foundries to understand the needs and wants of customers, it is equally important for end-users to understand the advantages and limitations of castings and their suppliers.

A discussion of cast components in automotive applications was a highlight of the Society of Automotive Engineers World Congress held in Detroit last year. Four respected metalcasting industry experts talked candidly with automotive design engineers and purchasers, stressing the weight and cost savings automotive companies possible with cast components.

Automotive Casting Overview

Gary Ruff, Intermet Corp., Troy, Michigan, discussed the future of automotive advancement by characterizing current and projected market conditions and forecasting how the engineer/foundry relationship will evolve.

"Today, more than ever, castings are an integral part of the automotive market," Ruff said. "We're seeing a record level of auto production, and there is a renewed drive to reduce weight and cost and increase fuel economy. No matter which way you look at it, castings provide an advantage."

According to the North American Die Casting Assn. (NADCA), steel makes up 56% of an average vehicle, followed by cast iron at 11%, plastic at 10% and aluminum at 6%. Magnesium is starting to take away from plastics, as the magnesium casting market is projected by AFS' 2000 Metalcasting Forecast & Trends report to reach more than 45,000 tons in 2001, up from just over 10,000 tons shipped in 1990. In addition, the metal is forecast to increase to 263,000 tons by 2009, Ruff said. Significant growth in the use of ductile iron also is expected, as ductile iron casting shipments are projected to reach almost 5.5 million tons by 2009.

He explained that the supply chain for automotive casting end-users is evolving. Commodity suppliers are at the bottom of the chain, as they make products to print specifications but add little other value. Above these suppliers are the process-dominant suppliers who add value to components by offering unique expertise. Next on the chain are strategic component suppliers, which offer full-service capability, followed by system integrators/module suppliers that offer the added benefit of assembly services. As vehicle manufacturers look down the chain, those at the bottom are less attractive as suppliers, Ruff said.

Metalcasters are rapidly moving in one of four directions, he said. Those directions are:

* going out of business due to environmental and capital requirements;

* a role as commodity supplier, which in turn makes a foundry an "acquisition target;"

* a role as a system/modules supplier, in which the foundry becomes skilled in assembly, logistics and system design;

* a role as a "master caster," in which the foundry is most attractive as a full-service supplier of state-of-the-science processes and components.

The trend in the industry is for vehicle manufacturers who are outsourcing to require engineering services, system responsibility and modular assembly in addition to manufacturing, Ruff said. This is an opportunity for premium suppliers to take a system focus vs. a component focus and look at manufacturing system functions vs. the component attributes they are trying to impart.

These premium suppliers will be expected to offer components that exhibit the greatest performance characterisitics at the lowest cost as well as a complete complement of product alternatives.

"Full-service capability means meeting all of the customers' criteria as if they designed and produced the part themselves," Ruff said, stressing that these suppliers will boast an unbiased selection of the best material-process combinations for optimum product performance and manufacturability. In addition, suppliers will be expected to stay on top of all stages of manufacturing, including research and development, product engineering and analysis, product design capabilities, casting design and process simulation methods, prototype development, foundry tooling engineering, computer-aided tooling manufacturing, and product testing and evaluation.

A driver for weight reduction in automobiles is fuel consumption and mileage, and market trends to light truck vs. automobiles will require increased weight reduction efforts and opportunities, Ruff said. "With castings accounting for 20% of a vehicle's weight, new and advanced casting materials and processes, along with full-service engineering capabilities, offer an excellent means of achieving weight-saving goals."

An example of advancements in weight reduction is crankshafts. Using stronger materials, such as austempered ductile iron (ADI), and hollow concepts, a cored casting made in green sand can achieve a 20% weight reduction over traditional manufacturing methods, Ruff said. Ford is currently using an upper control arm for its Mustang with independent rear suspension cast in ADI.

Diecasters are producing magnesium structural brackets and suspension components as well as structural components, such as seat frames and support pillars, which, although higher-cost, save weight and increase strength. "Metalcasters refocusing their businesses to modules and systems, or remaining only as commodity suppliers, will not have the proper objectives and discipline to develop highly engineered, optimized castings such as these." Ruff said. "Automotive advancements through total casting solutions only will be provided by those companies dedicated to being a master caster." These master casters will continue to develop lighter iron, stronger aluminum, and cost-effective magnesium components that are sought after by automotive end-users, he said.

Process Perspective

John Jorstad, Formcast, Inc., Denver, covered advantages of casting processes used in the automotive casting arena, including diecasting, low-pressure permanent molding, squeeze casting and semi-solid molding.

The diecasting process provides excellent dimensional control, great detail, small draft angles and features such as tiny holes, all of which aid in meeting automotive objectives, Jorstad said. Magnesium diecasting boasts the manufacturing benefits of longer tool life and shorter cycle times than diecast aluminum. For these reasons, diecasting is the popular casting method for magnesium; however, foundries are exploring other options for producing magnesium components, especially structural components.

Steering wheels are one example of a somewhat thicker, structural component that can be diecast. Thixomolding, which combines semi-solid molding (SSM) (solid magnesium is heated into semi-solid state) and injection molding (similar to injecting plastic into a mold). The process uses solid particulate magnesium, thus scrap/offal is recycled easily. The benefits of Thixomolding include a high cast-to-trimmed weight yield, minimized magnesium reaction with the atmosphere, and integrity and properties that are improved over parts produced by conventional diecasting.

Low-pressure permanent molding in closed systems also is being explored as it also minimizes reaction of magnesium, and produces structurally sound and consistent parts, Jorstad said.

Low-pressure casting, used largely to cast aluminum, is a true "bottom fill" process, which means metal filling the mold will experience little or no turbulence. In addition, hot metal input and shrinkage feeding occur at a common location, meaning easier thermal control and directional solidification. The steel or iron tooling used in low-pressure casting produces small secondary dendrite arm spacing (SDAS) which improves both strength and ductility of aluminum castings. Low pressure produces very high cast-to-trimmed-weight yields, often greater than 98%, Jorstad said. The process has the longest history for mass-produced aluminum structural castings (such as wheels and control arms).

Vacuum diecasting for aluminum has all the normal advantages of conventional diecasting--the ability to produce thin sections, fine detail and excellent dimensions with rapid solidification characteristics and fast cycle times-- but without entrapped gas pores, Jorstad said. He stressed that entrapped cavity gasses are the greatest cause of porosity in conventional die castings; pores compress at the high pressures applied during solidification, thus preventing subsequent high temperature processing such as welding or heat treating without formation of out-gassing and blisters.

Vacuum die castings have excellent strength and ductility. They are both fully heat-treatable (T4, T6, T7) and weldable, Because of their superior soundness, tailored alloys have been developed for vacuum diecasting that are structurally suitable for automotive castings. While vacuum diecasting avoids gas entrapment, it does not aid in feeding shrinkage voids, thus it is best suited to thin, uniform walls.

Squeeze casting is yet another variation on diecasting, and features a bottom, solid-front fill through large gates. The result is no turbulence and no air entrapment, Jorstad said. Because it uses high pressure (1000 bar or more), this process easily feeds remote areas through the large gates, eliminating shrinkage defects, making squeeze casting well-suited for casting thicker parts.

Squeeze casting also uses a steel mold and produces extremely small SDAS at the surface ([less than]15m). Parts produced are heat-treatable (T6, etc.), and the process displays dimensional controls similar to those offered by diecasting.

SSM is a process that is only now coming into its own as a viable manu-facturing method for automotive products. SSM is more than 25 years old, but it has received global manufacturing attention only in the 1990s, Jorstad said. The process features characteristics akin to both squeeze (similar alloys, compa-rable high integrity, heat treatability, high strength and ductility) and vacuum diecasting (section thinness, part complexity and detail). While the process has proven its usefulness to many, it is still somewhat a "novelty" to others ("material having a weird microstructure or "billet that can be cut with a knife"), he said.

SSM features fast cycle rates, long tool life, multiple cavities/mold (cavities below as well as above shot input location), and thin cast sections. Because the metal is 50% solid when it is molded, less heat is transmitted to the die, so solidification time is shorter (5-20 sec), and there is less thermal stress on the tool. In terms of cycle times and long tool life, SSM of aluminum is somewhat analogous to diecasting of magnesium.

SSM produces high-integrity structural components having characteristics similar to squeeze-cast parts. A356/357-T5 heat treatment is able to provide good ductility in SSM-produced components compared to the more expensive T6. In addition, SSM accommodates a number of alloys (beyond those that are readily cast from liquid), including hypereutectic Al-Si, metal matrix composites, alloys that normally are wrought, and 2XX/5XX/7XX-type casting alloys.

Probably the most important benefit of SSM to the automotive community is its ability to produce thin cast sections. The viscous flow of metal in the mold is much less turbulent than 100% liquid, allowing for rapid fill of thin sections (2-3mm) without entrapping cavity atmosphere, Jorstad said, stressing that thin sections translate to reduced part weight.

Advantages in Application

Paul H. Mikkola, Hitchiner Manufacturing Co., Inc., Milford, New Hamp-shire, discussed new automotive casting applications as well as the advantages of using cast components.

"The three biggest advantages to using cast components are cost, cost and cost," Mikkola said, pointing out that cast components allow for consolidation of parts, reducing part inventory and reducing assembly time. In addition, the near-net-shape the casting process is able to achieve means less machining time. Castings offer improved quality, reliability and durability and are designed for manufacturability, Mikkola said, adding that, during the casting process, metal can be impregnated to achieve the desired characteristics of costlier materials at a lower cost than other manufacturing methods.

Despite weight advantages gained from converting from steel or iron to aluminum or magnesium, for total cost and package requirements, it may make more sense to convert from lighter to heavier metals. For example, a steering knuckle may make more sense as a steel component than aluminum. In the 1970s, GM was converting Ford steel pinion gears to austempered ductile iron to gain better overall benefits, Mikkola said.

Metal should be chosen with application in mind--not just weight and production cost. Intermetallics are an emerging material choice for both weight savings and performance characteristics. A titanium aluminite valve actually will get stronger as operating temperature increases. A stainless steel manifold will offer both reliability and durability at high temperatures. A cast rocker arm offers better stiffness and design flexibility over a stamping, however, at a higher cost.

Casting processes also are able to offer operation performance enhance-ments such as higher-strength metal components through grain refinement. Other benefits attainable include components that can endure higher temperature operation, have a greater modulus, as well as the ability to design parts with more freedom.

Through design modification and process refinement, foundries are achieving reduced variation in the parts they deliver. Automotive casters are striving to achieve Six Sigma certification, meaning that there only can be 3.8 rejects for every million components delivered. To obtain this lofty goal, it is integral for the design community to work together with manufacturing, Mikkola said. "The bottom line is that you will see cost savings from less rework and maintaining smaller inventories."

Casting 'Concepts'

Tom Piwonka, Univ. of Alabama, Tuscaloosa, Alabama, spoke on unrealized vision for castings, or concepts for future automotive components. All in all, the forces that will drive casting use in autos, according to Piwonka, are design for performance and cost, recyclability and fuel efficiency.

Total recyclability of a car is beginning to be an issue, in light of European "take-back" laws that impact the international market, Piwonka said. Cast components are durable enough to reuse, and all castings can be recycled to make other castings.

"Today, some truck engine castings are designed for remanufacturability," he said, adding that some castings are remanufactured as many as three times.

"No new casting alloys have been developed for 40 years," Piwonka said. "This suggests that an opportunity exists to develop highly castable ferrous and nonferrous alloys combining high strength, high modulus and good corrosion resistance. One problem is that designers need lots of mechanical property data today to apply these alloys, and data generation is now part of alloy development--an expensive part."

He stressed that there is an opportunity to make thin-wall chassis and body components out of high-strength, low-alloy steels. Use of castings could reduce the use of fasteners, improve crash resistance, and even permit car manufacturers to use modular mold construction to tailor vehicles to specific niche markets. Other opportunities for thin-wall steel castings include one-piece frames, steering and suspension parts, and continuously cast I-beams for truck frames.

There's an opportunity also for fiber-reinforced cast aluminum composites, which combine high stiffness with low weight, Piwonka said. Potential applications include bumpers, transmission cases and body parts.

"Because castings can have complex shapes, they are ideal for styling innovations," Piwonka said "Use of diecasting techniques could make these parts at attractive costs."

In addition, he stressed that thin-wall ductile iron offers the advantage of high fatigue resistance and high temperature strength, which can lead to a new generation of lightweight exhaust manifolds.

Improvements in sand and core techniques are making it possible for sand castings to approach the dimensional control of investment castings at a much lower cost, Piwonka said.

"If you compare life cycle costs of castings with plastics, forgings and welded structures, castings come out looking really good," Piwonka said. "Castings save material, manpower and energy. The untapped potential of castings today is astonishing."