Castings will play major role in the future of transportation.

Ecology concerns and the need for fast, economical manufacturing will drive transportation industries toward structural castings.

On a recent sojourn into some Alcoa company history, I came across an article in a 1900 trade journal that contained one of the earliest proposals for the application of lightweight metals in the transportation industry...wagon frames.

Today, we are producing the first commercial castings for automobile frame applications - vacuum diecast nodes that lend stiffness to the Audi A-8's multi-product spaceframe. For another application - this one in the air - we developed one of the world's largest thin-walled structural castings, the F-16's vertical stabilizer.

However, we are far from maximizing the potential of casting technology, even after so many years of experience. This is especially true in structural applications for the world's transportation industry.

As you well know, castings have traditionally been used in non-highly stressed roles. Though, as quality improved, they have been applied in areas where heat resistance was necessary, consideration of castings for structures where high stress and strain performance is mandatory is fairly recent. This increasing use of castings in structural roles has been driven by the transportation industry's push for cost-effective, high-performance structures that are highly engineered, increasingly large, net-shaped and lightweight. However, the application of castings in a lightweight structure demands wrought strength, toughness, fatigue resistance and durability, all in a reasonable economic package.

The powerful ability of castings to create extreme geometries with designed reinforcements for stiffness or strength without incurring additional part, die or joining costs is beginning to allow designers to create castings that offer higher quality at lower costs. The name of the game in today's transportation industry is design flexibility and performance.

Castings can bring both to the party. But they are not cheap dates, and require the development of improved casting alloys and processes. They demand control technologies that far exceed those that have in the past characterized the foundry industry. And they demand a very high level of customer and market understanding.

Environment

There is a need to balance economic growth with the absolute requirements of sustainable biosphere for our children and grandchildren. This is pertinent to transportation because no other industry so epitomizes the need for such balance. The era of energy profligacy and environmental excess that the automobile has come to symbolize is at an end.

We have the ingenuity and the technology to defeat the spiral of increasing weight and fuel consumption that has been driving the automotive industry the past 10-15 years. Lightweighting the world's transportation fleet is essential if we are to move people and goods in a fuel-efficient and environmentally acceptable manner. Lightweighting is about the future and about the future of castings as tools to save energy and reduce emissions.

Bob Eaton, Chrysler's CEO, has observed that in the 20th Century, the automobile dramatically influenced society...but that in the next century, society will dramatically change the automobile. He couldn't be more correct. Here are a few facts as to why:

The global motor vehicle fleet exceeded 700 million for the first time in 1994, including more than 405 million cars. That total number grows by more than 17 million per year. In the U.S. alone, drivers fill up 191 million times a week, and for every 15 gal of gas, about 300 lb of carbon dioxide is eventually released into the atmosphere. Around the world, motor vehicles account for about one-third of oil consumption and 14% of carbon dioxide emissions. The World Bank has noted that by 2030, emissions from these vehicles will quadruple [ILLUSTRATION FOR FIGURE 1 OMITTED]. Automobiles are not benign participants in global climate change, particularly in greenhouse warming.

Lightweighting is one of the most important innovations in improving fuel economy and reducing vehicle emissions. Taking the weight out while meeting consumer demands for performance, comfort, safety and cost may be the most critical challenge - and opportunity - facing today's transportation industry.

Manufacturing Economy

In addition to curbing their impact on the environment, there are other global forces driving the transportation industry.

First, and most significant, is the need to reduce manufacturing costs. This is stimulated by a need for part consolidation and larger, more highly engineered, net-shape structural components, along with a corresponding emphasis on reducing the number of machining and fabricating steps in final assembly operations. In the automotive industry, these trends support the development of multi-product spaceframes in both steel and aluminum. In aerospace, the search for lower-cost aircraft has become the dominant theme for the '90s.

Strategically integrated global partnerships are also becoming a way of life, as OEMs and Tier 1 and 2 suppliers integrate product and process design. These partnerships are facilitated by the worldwide ubiquity of information technology, and its unprecedented dispersion of scientific and engineering know-how. In my view, the rapid application of technology is already determining winners and losers in the competitive arena.

The only rival of consequence to cost is speed, and product development cycles are telescoping dramatically. Windows of opportunity for the application of a new material or a new casting are opening and closing faster than ever. When they open, you must be ready. If you aren't, traditional materials or product forms will be modified and used instead. OEMs will not wait for suppliers.

Product quality, consistency and uniformity demands are also increasing, and meeting them will require unprecedented attention to process understanding and control technologies. This has stimulated an upsurge in process modeling and simulation. Today, casting parameters such as filling and solidification rates are routinely modeled in conjunction with factors like mold and metal temperatures, process pressures, thermal conductivity and heat transfer.

Casting Improvements

All these forces are substantially altering customer perceptions about the role of castings and about the casting industry itself. The image many have of castings is evaporating in the presence of castings that can compete in strength and ductility with sheet metal and many forged products.

Alcoa is making castings with 12-18% elongation, as well as castings that fold instead of shatter. This is accomplished through a combination of process control to eliminate porosity and metallurgical design to manage precipitate formation and spacing. Thermal treatments and welding are freely employed.

As negative images of the product are disappearing, so is the perception of the foundry industry as the last bastion of black art, where trial and error are the key technology drivers. Increasingly, the modern foundry is characterized by modeling and simulation, by sensors for process control, and by SPC and real-time feedback systems.

This is not to say, however, that the old ideas have been completely replaced - the continued existence of the casting factor in the aerospace industry shows there is still some heavy baggage standing in the way of lightweighting aircraft with castings.

Fortunately, the automotive design community places no such constraints on castings. Take, for example, the Alcoa spaceframe in the Audi A-8, and in 1997, the Plymouth Prowler [ILLUSTRATION FOR FIGURE 2 OMITTED]. These structures reveal the strength and ductility potential of castings, as well as a revolution in automotive structural manufacturing. This spaceframe embodies the design flexibility and weight savings capabilities of castings that today are unique, but will, I believe, become the design and performance standards of the future.

The Alcoa spaceframe features straight and curved extruded sections joined by high-ductile diecast nodes at key intersections. These vacuum die castings stiffen the structure and act as distribution points for forces within the frame. They are highly engineered to meet local performance applications, such as suspension and engine mounting points where high-strength is essential. Through their design flexibility, these castings bring local reinforcement without requiring multiple parts, and we have been able to build attachment points directly into the spaceframe. The requirements for the spaceframe cast nodes are listed in Fig. 3.

The extrusions and castings in the spaceframe have impressive mechanical performance and energy absorbing characteristics. In the A-8, they offer a minimum of 46% weight reduction in the body and an increase in energy-absorbing capability compared to today's steel monocoque body structures.

The success of the Alcoa spaceframe is a threefold event tied directly to an understanding of product, process and materials design. Understanding one of these areas was not enough. To get to part manufacture, we had to integrate all three and address some key assembly issues.

This integration capacity defines the paradigm for competitiveness that I believe is crucial for success in the materials business in the years ahead. It is applicable to the foundry industry and has been a guide for the development of Alcoa's capabilities. I'd like to discuss this model in relationship to the design of casting materials, products and processes.

Controlling the Process

In the area of material design, the dominant metallurgical issues revolve around control of the microstructural evolution during solidification. Alloy flexibility, freezing range and volume change on solidification are essential for optimizing alloy systems.

Alcoa is now in its second and third generation of alloy development for cast spaceframe nodes. The first generation low-iron alloy, C-119, had the requisite high-ductility and toughness, but suffered from die erosion problems as the program progressed. We have developed a new alloy that we feel solves this problem, and are on the homestretch to a third generation - a nonheat treatable alloy that will eliminate distortion in the cast nodes associated with downstream thermal treatment.

Our current progress in understanding and controlling the processing-microstructure performance continuum has led us to the point where we are working to enable the design of structural castings by optimizing material microstructure. This is being approached by linking fatigue and durability performance requirements with predictive models of porosity formation and cooling rates.

These models give us the ability to take a specified fatigue life and predict a desired microstructure for a targeted level of stress performance. Conversely, we can also predict fatigue life based on a given microstructure. The scientists and engineers doing this work are making real the concept of using "microstructural models to provide a quantitative link between casting process design and component fatigue design." It is not an overstatement to say we're very close to the capability of tailoring microstructures within a component to save weight and achieve our customer's fatigue and performance requirements.

A tremendous amount of attention is being paid to casting process design. Metal cleanliness, porosity formation, process models, closed-loop process control, sensing technologies, and mold and die design are areas Alcoa feels require much more attention.

At the quantitative level, models and simulations have been successfully employed to increase the performance of cast components and reduce mold costs and proofing trials by integrating filling and thermal simulations with die design.

In the area of product design, we're seeing these design strengths being applied to new opportunities for several metals. I am not as familiar with steel, magnesium and titanium as with aluminum, but I do know of some interesting progress in each.

For instance, steel founders understand the lightweighting issue and are working hard to improve their products in this respect. New alloys are being developed, along with vacuum-assisted investment castings for large, thin-walled aerospace parts. I suspect we will see an increased use of magnesium diecastings for secondary structures in the auto industry. Promising applications right now appear to be door and window frame components, seats and instrument panels.

In aluminum, we're going to see multiple casting processes producing primary and secondary structures for the automobile, including chassis and suspension components, strut and shock towers, engine and suspension cradles, steering knuckles and door structures. Railway bogie systems are re-emerging as candidates for aluminum casting, particularly in Europe and Japan.

I fully expect to see castings emerge in the primary structural applications in commercial aircraft. Alcoa produced a bulk head door for a passenger aircraft that is capable of replacing $100,000 built-up assemblies for about 75% less. The trend toward large, complex structural castings - 6-10 ft sections - as a part-consolidation, lightweighting and cost play has begun.

We must improve the dimensional tolerances of cast components. A key element in meeting this goal is eliminating the need for thermal treatment to achieve desired mechanical properties. As an industry, we must move aggressively to bring part design, tool and die design and process design onto common ground. Those who learn to integrate these functions will create a significant advantage for themselves.

Lightweighting is about the future - about the growth of industries, such as transportation, that are essential for the prosperity of the world's economies. It is about developing and applying scientific and engineering knowledge to regularly, rapidly and seamlessly integrate materials, product and process design to produce consistently high-performance and cost-effective castings for all industries. It is about a future where economic and ecological sustainability are complementary.

But most of all, it's about our children and grandchildren. If we act now, they will be able to have the same opportunity and enjoy the quality of life offered to you and me.

RELATED ARTICLE: Fig. 3. This list shows the important requirements for castings used in the Alcon spaceframe.

Spaceframe Cast Node Requirements

* Thin-wall sections ranging from 2-4 mm in diameter;

* Complex geometries featuring multiplanes, holes and tabs;

* DIN 1688 dimensional tolerances;

* Yield strengths between 17-29 ksi;

* Tensile strengths between 29-43 ksi;

* Tensile elongation greater than 15 percent;

* Fatigue strength of 12 ksi at 5 million cycles;

* Toughness of 90 KJ per square meter;

* Weldability by standard processes; and,

* No susceptibility to stress corrosion cracking.

Lightweighting the Transportation Fleet