A future in FLUX

A number of industries are rethinking the metals they use and how they use them. Coil springs for automotive applications were once always steel, but now titanium ones are in use on one production car.

Biodegradable inserts may take the place of titanium in some medical procedures, and new alloys may soon be common in keyhole surgery.

The call for ridding electronic components of lead gained additional momentum when newly proposed standards were released.

The 2000 Lincoln LS contains over 200 lb of aluminum. Meanwhile, experts predict magnesium auto parts, like this prototype, will become increasingly common in the not-too-distant future.

In most industries, there is a material of choice. For the electronics industry, it's lead and copper; the medical field, it's titanium; automotive, it's steel; for aerospace, it's aluminum. But now these key industries are either eliminating their commonly used materials, finding new applications for them, or experimenting with completely different ones. And the resulting benefits range from lead-free electronics and better surgical techniques to more fuel-efficient automobiles and safer airplanes.

Currently, there is a push to eliminate the use of lead in electronic equipment, and that movement is gaining momentum through the efforts of three companies. Infineon Technologies of Munich, Germany, Philips Semiconductors in Eindhoven, Netherlands and STMicroelectronics, out of Geneva, have developed standards for defining and evaluating lead-free semiconductors. The primary barrier to eliminating lead in the electronics industry to date was a lack of internationally agreed upon standards for evaluating lead-free components. That stumbling block may well have ended with these newly proposed standards. Adopting them, say the trio, will result in better environmental protections, increased recycling, and easy disposal of electronic devices.

Lead, along with tin, is a critical component of the solder used for printed circuit boards. The metal is also widely used in semiconductors to coat the leads of packages, in power IC packages, and for the balls of ball-grid-array (BGA) packages.

"Many different kinds of lead-free solder alloys and soldering processes are already under investigation around the world," says Carlo Cognetti, vice president for New Package Development at STMicroelectronics. Combinations of tin, silver, copper, bismuth, indium, and zinc, all of which require increased temperature profiles when compared to tin-lead solders, are possible replacements for lead.

While many explore ways to get lead out of electronics, others are looking for better ways to get copper into the process. Copper plays a vital role in high-speed semiconductors as the connection between transistors, but placing copper by electroplating, especially on thin wafers, is a time-consuming and sometimes difficult process. However, a new technology, electrochemical mechanical deposition (ECMD), promises to change that.

With the ECMD process, it is possible to deposit planar copper films on the surface of wafers at extremely low film thickness, 50% of the feature depth or less. The process reduces copper chemical mechanical polishing (CMP) costs, decreases cycle times, and yields more parts. In addition, ECMD cuts down on the dishing and erosion of semiconductors. The use of this technology comes at a good time, as the market size for copper electroplating systems is expected to approach $500 million by 2003.

Metals in medicine
On the medical front, titanium has long been a standard for several types of surgical pins and inserts. The metal has a proven track record in the field. It is strong, durable, and perhaps most importantly, noncorrosive. However, there are changes happening.

Recently, two San Diego plastic surgeons performed a type of facial reconstruction that always called for the insertion of titanium pins to hold bones in position. But instead, the two used an amorphous polylactic acid copolymer produced by Macropore Inc., of LeFort Ill.

This new material retained approximately 70% of its initial strength after 9 months and 50% after 12 months. And unlike titanium pins, Macropore implants are metabolized by the body, over time, into carbon dioxide and water. So, they do not have to be removed.

With Macropore's material, say the surgeons, there was a reduction in surgical time, the product was easy to use, and there was a less invasive follow-up for the patient. The question remains though, though, whether or not biodegradable materials will actually replace titanium in medical procedures.

While titanium may see less use in some medical procedures, that same metal is looked upon as a vital part of another new type of surgery.

According to the Wellcome Trust, a UK-based medical research charity, titanium is a key component of alloys that "remember" their shape. This ability may make minimally invasive, or "keyhole," surgery easier to perform. Already, a range of new surgical tools is being developed that make use of a titanium-nickel blend and its special properties.

At low temperatures, the titanium-nickel alloy is soft and pliable. Surgical tools, inserts, or sutures constructed from it can be easily placed and positioned through small incisions. At high temperatures, such as body temperature, the blend becomes rigid, which is ideal for a number of surgical procedures. Most useful, however, is that the alloy not only become rigid, but also has a memory of its a original form.

Automotive
No other industry uses more metal than automotive manufacturing, and, perhaps, in no other sector have more changes in metal use taken place. Only a generation ago, cars were nearly all steel from bumper-to-bumper.

Today, automakers, because of a number of economic factors, including Federal fuel-mileage standards, are looking for ways to decrease the weight of automobiles. And obviously that means means using lighter metals. The current is toward aluminum, magnesium, and titanium.

Once reserved for wheels and trim pieces, aluminum is now used for hoods, doors, fenders, and more. Ford leads the way in the use of automotive aluminum. For example, its 2000 Lincoln LS contains over 200 pounds of aluminum. The lightweight metal comprises the vehicle's rear deck, hood, and front fenders as well as some of the sedan's cross members. And aluminum isn't just on the outside. The Lincoln has an aluminum engine block as well as aluminum alloy cylinder heads and a structural cast-aluminum oil pan that strengthens the bottom of the block.

Experts predict that aluminum will eventually be found in other automotive components as well. Already, new casting techniques let Ford make aluminum struts, control arms, and steering knuckles. Drivetrains may soon follow suit and be constructed of aluminum or aluminum-based alloys.

Expectations are that other automobile manufacturers will phase in more aluminum parts over a multiyear period, giving parts suppliers the time to invest in the tooling needed to machine the metal and establish optimum production techniques.

Aluminum isn't the only metal that has caught the eye of automobile manufacturers. Magnesium has also become more popular, and several auto producers are using it to build parts such as seat supports, floor pans, various brackets, and lock housings. In the future, transmission housings and engine blocks may also be made of magnesium.

The reason for the magnesium's rise in popularity is a direct result of its low density. In fact, an equal volume of aluminum weighs 1.53 more than magnesium; zinc weighs 4 more, and iron and steel weigh 4.5 more.

One company that sees magnesium use growing in the automotive sector is Thixomat. The Ann Arbor-based company has developed a metal injection molding process to design and mold magnesium-alloy parts for automotive applications.

"It's conceivable that in the not-too-distant future, we will see major component parts, such as trunk lids, hoods, and other chassis parts being made with this process," says Dr. Stephen LeBeau, Thixomat vice-president of sales and marketing of his company's production techniques. LeBeau also believes that there will be magnesium chassis parts produced within the next five years.

Currently, there are only about 7 lb of magnesium in the average vehicle, but the industry expects that total will reach about 50 lb per vehicle by 2019.

The benefits of magnesium are not limited to those using injection molding, however. For those choosing to make chips or cast magnesium, the metal offers several benefits. For example, a low-heat content means faster production cycles, and some magnesium parts can be die cast up to 50% faster than the same parts in aluminum. In addition, magnesium machines at high speeds using greater depths of cut and faster feedrates as compared to other structural metals. And the power requirements for removing a given amount of material is lower for magnesium than other metals, resulting in longer tool life.

Most often associated with aerospace applications, which still use 60% of the titanium sold, the exotic metal was once seen as too expensive and too hard to machine for use in the auto industry. However, new alloys make this durable metal both cheaper and easier to use, and some 2001-model Corvettes sport titanium exhaust systems.

The use of titanium in the automotive field has grown. The latest Volkswagen Lupo FSIs, available in Germany, are the first production cars to have titanium coil suspension springs.

Within two years, Timet, Denver, Co., a supplier of automotive titanium, expects more automakers will begin using the metal in their coil springs and exhaust systems. In addition, the use of titanium in brake caliper pistons, drive shafts, connecting rods, and a host of other automotive applications are being explored.

Also experiencing greater use in the automotive industry recently has been powdered metals. Mixing selected metal powders and then compacting them at room temperature in a precision die makes powder metal parts. The parts are then sintered, ensuring the bond between powder particles. According to Dymet Corp., a maker of powder metal parts based in Muskegon, Mich., there are several attractive features of the technique. There is little waste, fewer manufacturing steps, and less expense. In addition, the powder-metal process offers a wide range of alloys, composites, and associated properties. A slew of designs and shapes are produceable, and the process is well suited for any run size. Already such parts are vital in a number of automobile engines, transmissions, and chassis assemblies

Aerospace
Aluminum continues to be the most commonly used material in the commercial aerospace industry. The vast majority of aircraft are built from aluminum sheets with a thickness of about a millimeter. While aluminum is good for airplane fuselages, it does have some drawbacks, including the speed at which it transfers heat.

Recently, a new material was introduced to the aerospace industry. Developed by the Faculty of Aerospace Engineering, Delft Aerospace, Belgium, the material, which uses aluminum in a new way, is called Glare. With Glare, a layer of fiberglass is sandwiched between two layers of thin aluminum. Sometime called ply-metal, the material is more protective in case of fire and is more resistant to metal fatigue.

A variant of the new material was used in the freight door of the USAF's C-17 transportation aircraft. And preliminary designs call for Glare to be the principal material used on the A3XX from Airbus.