Casting market focus: auto: the automobile depends on castings, from the engine to the brakes. It also presents a platform for casting design to shine.

Excuse the pun, but it is entirely accurate to say that motor vehicles "drive" the metalcasting industry. In any given year, the passenger car and light truck market can represent one-third of the total casting shipments in the U.S., with about an equal percentage of all U.S. metalcasting operations serving this industry. Since the days of the first horseless carriage, engineers have relied upon the metalcasting process to power, control and stabilize their ever-demanding vehicles.

Dealing with a dual-front of reduced weight (for fuel economy) at lower costs has proven to be a challenging environment for both automakers and their suppliers. Where the "rubber meets the road," these two objectives rarely go hand in-hand, and exchanging one material tot another often comes with a cost and property penalty. For the casting industry, however, these challenges have stimulated new progress and manufacturing advancements that are being to put to use not only in automotive castings, but also being rolled out across all applications.

In a recent Society of Automotive Engineers (SAE) publication, committee chairmen Martin Myers of Cummins Engine and Edward Vinarcik of Robert Bosch Corp. described how the automotive industry previously looked upon castings as simply a commodity item. "Perceiving castings in this manner trivializes the complex engineering solutions that can be achieved through excellent casting design within the automotive industry," they wrote.

"Rapid changes in the automotive industry are leading designers and product engineers to reconsider traditional notions in the design of both new and existing components. The paradox of removing weight to meet pollution control regulations while designing higher performance vehicles is a major challenge confronting the automotive engineer of today. In many cases, engineered cast metal components provide the flexibility needed to meet these difficult challenges by consolidating parts into a single net shape which virtually eliminates the need for secondary machining of assembly processes."

Changing Times ...

After the average vehicle weight fell significantly from the 1970s 1990, the average vehicle weight has actually in creased again every year since (due in large part to new safety and crashworthiness features). To address this, the Big Three established lofty targets for mass reduction through their Partnership for the Next Generation Vehicle.

Ultimately, they aimed to develop the technology and manufacturing expertise required to build and market midsize vehicles that could achieve a nearly threefold improvement in the current corporate average fuel economy standards. To achieve this 80 miles/gal target, they determined that mass must be reduced by 50% in chassis, body and interior subsystems. Further, the vehicle must be affordable without sacrificing safety, comfort, ride of performance. The casting industry has been involved in this project through a U.S. Dept. of Energy program.

Changed Castings ...

The move toward lighter vehicles has resulted in material changes; some simply reduce weight while others (like iron bedplates) are required to provide greater support to lighter components.

Iron remains the most widely cast material in automotive, applications, but its influence on a per vehicle basis is lessening. (Gray iron by itself saw 650 lb/vehicle in the early 1980s; today it is about 280 lb). While ductile iron and compacted graphite iron have gained automotive applications, total iron weight is expected to continue to decline particularly with the conversions of the main gray iron parts to cast aluminum.

Much of the "headline news" has been on light metals such as aluminum and magnesium. Cast aluminum has long been used for mass reduction in powertrain and transmission applications, but structural applications have grown only in the last decade or so. Cast aluminum is rapidly posting high penetration rates among engine blocks and cylinder heads while also finding significant gains in differential carriers and suspension parts. It too, however, faces potential losses on existing components such as the intake manifold, as well as emerging conversions to magnesium.

Cast magnesium is also on a rapid growth trend. While its application is minor today, shipments are forecast to grow at an annual rate of 13% over the next 10 years. It is rapidly replacing zinc and aluminum parts because of the further weight reduction possibilities it offers.

While the conversions of many of the heavier castings have already left the gate, ferrous metalcasters have responded, pushing the envelope on what they can bring to the lightweighting table. While benefits in cost, stiffness, damping, machinability, thermal expansion and fastening are documented, cast iron has reaped lightweight solutions of its own through design innovation and part consolidations.

In addition, the American Foundry Society's Thin-Wall Iron Group is conducting research projects to foster the specification and production of thin-wall cast iron, which would offer significant weight reductions in powertrain and chassis components. Advances by ferrous casting producers have kept components and systems in iron that were previously targeted for material conversions.

The next sweeping change on the automotive horizon, and one that will certainly impact all castings, may be the automakers' move toward an automotive engine design that uses hydrogen fuel cells (water-only emissions) in lieu of the internal combustion engine. Many metalcasters ate closely watching this trend, as well as looking to identify what role advanced castings may have in the car of the future.

A Vital, Viable Solution

Despite the ongoing trend for automakers to shed non-core responsibilities, each of the major automakers have made significant recent investments in their own internal casting operations. This affirms the importance and proprietary interest each places on certain cast components in improving and differentiating component systems for the final vehicle.

The wide variety of casting processes and alloy options gives today's engineer a limitless pallet of casting choices. Beyond the weight issue, castings are given the nod for their role in reducing noise, improving strength, inventory piece reductions (consolidations) and near-net shape advantages to reduce downstream processing, to name a few. Metalcasting's ease in recyclability is also growing in importance.

Within this article, you've seen a series of proven cast designs and applications. Some offer simple enhancements, while others illustrate a pushing of the capabilities. At any rate, each has contributed to a cost-effective, highly engineered solution.

Aluminum Rapidly Gaining Share in Engine Blocks

The engine block is one of the most rapidly growing applications for cast aluminum. While an estimated .i5% of engine blocks in 2004 will be cast aluminum, this figure is forecast to increase to 60% by 2006. Two highly advanced casting processes are currently being used to produce these engine block castings.

General Motors Powertrin Defiance is utilizing the lost foam casting process to produce the inline 4-cylinder block for its new Vonec 2800 (2.8 l) light truck engine. This design, at 74.5 lb, is 15 lb higher than the comparable iron design, but its true benefits in lost foam came in the elimination of processing functions. As an example, the design featured a cast-in main oil passage (675 mm long) and numerous other features that eliminated costly and time-consuming machining functions. Compared to the engine it is replacing, this block improved fuel economy, reduced emissions, improved horsepower (50) and torque (35 pounds/ft), and reduced noise and vibration. At full production, this component represents a $1 million savings in manufacturing costs.

On the other hand, the Precision Sand Process (often called the Cosworth process by the group that developed it for Formula One racing engines) is also employed for engine block production. It utilizes chemically bonded sand cores that are assembled into a single core/mold package, which then receives molten aluminum via a special pumping mechanism. Using this process at Nemak, this 3.9-liter, V-8 cylinder block offered significant machining cost reductions, including the full elimination of internal machining of oil galleries. At 83 lb, it also saved 104 lb over the previous iron design.

For More Information

"Design and Product Optimization for Cast Light Metals," USMP-LMD 210 Project, U.S. Dept, of Energy. Published by AFS (supported by Aluminum Division Committee 2-C), Des Plaines (2001).

Designing and Achieving Lightweight Vehicles, Society of Automotive Engineers, Warrendale, PA, 2002.