During a recent panel discussion at the 12th annual National Electrical Wire Processing Technology Expo in Milwaukee, automotive engineers discussed the challenges involved in transitioning from copper to aluminum.
The “Automotive Aluminum Wire…In Your Future?” session was moderated by Don Price, connectors and components technical specialist at Ford Motor Co. and the automaker’s liaison to EWCAP. He was joined on the panel by Kurt Seifert, crimp technology and contact physics supervisor at Delphi Corp., and Rakesh Patel, a Ford engineer who serves as chairman of the ISO Automotive Electrical Cables Committee, which is currently developing a new aluminum cable standard.
According to Seifert, many people still associate aluminum wiring with house fires. Back in the 1960s, when copper prices spiked to record highs, homebuilders rushed to aluminum alternatives.
Underwriters Laboratories actually approved aluminum for use in housing as early as 1945. “But, there were several rules to using and applying it,” says Seifert. “For instance, you needed to upsize the aluminum conductor, but you also had to use approved switches, outlets and termination systems.
“The problems in the housing industry were largely caused by people who did not follow the correct guidelines,” adds Seifert. “If you’re going to use aluminum cables for any application, whether it’s houses or automobiles, you must use the right technologies and guidelines. You must also be aware of potential problems, such as oxides that can build up with aluminum and create opportunities for corrosion.”
“Today, the volatile price of copper is the key driver behind increased interest in aluminum,” says Price. “Weight reduction due to aggressive CAFE standards (which call for 36 mpg by 2016 and 54 mpg by 2025) is another major force. Aluminum offers a lower cost per amp and provides up to 48 percent mass reduction over copper. Aluminum is also lighter, which makes assembly easier, because it’s easier to pick up and handle than copper wire and cable.”
Seifert says aluminum makes a lot of sense as an alternative to copper, because it’s the most abundant metal in the earth’s crust. “Copper is getting harder to find and there’s a much larger demand for copper in the building industry,” he points out. “That’s why copper is so volatile and aluminum is fairly steady, with only slight fluctuations in price.”
Today, European and Japanese automakers are further along on the aluminum conversion process than the Big Three. The trend started in Europe 12 years ago and aluminum battery cable is already used in several vehicles by Daimler and other companies. Japanese automakers are close behind and hope to reduce vehicle weight by up to 40 pounds by replacing copper with aluminum in various wiring harness applications.
Price predicts that U.S. automakers will soon catch up to their overseas rivals. “The motivation is there and the legislation is there, but we still have challenges that need to be addressed,” he points out.
“Aluminum is not copper,” adds Seifert. “Engineers need to consider six challenges.”
Aluminum is not as conductive as copper. It’s only about 60 percent as conductive as copper. So, to replace a copper wire, engineers need to upsize the aluminum conductor about two gauge sizes. For instance, a 20-gauge copper wire would be replaced with an 18-gauge aluminum wire.
Aluminum is not as strong as copper. It has less tensile strength. Engineers need to make sure that there’s enough tensile strength to handle plugs, terminals and connectors. “We’re currently only
using 18-gauge and larger for aluminum wire,” says Seifert. “Different application guidelines may allow us to use smaller sizes in the future.”
Aluminum develops thicker oxide layers than many other metals, far more than copper. “Whatever termination system you use needs to break through these oxides so that you have good metal-to-metal contact between the conductor and the terminal,” warns Seifert.
Aluminum has different coefficients of thermal expansion. “You need to make sure that you design all your termination systems to take this into account, so that when you have thermal shock cycles, your aluminum wire and your terminal stay in contact with each other and you have low resistance,” Seifert points out. “If you do not design a robust system, you can end up with repeated thermal shocks cycling, causing voids that increase resistance and create heat.”
Whenever any two dissimilar metals, such as aluminum and copper, contact each other, there’s a risk of galvanic corrosion. The larger the separation
between the two materials, the more likely it is that you’ll experience galvanic corrosion. When using aluminum wiring, engineers need to inhibit galvanic corrosion. “Depending on the application, you may need to seal your interfaces or your terminations,” says Seifert.
Aluminum tends to relax more over time, which can result in higher resistance. “Whatever termination system you design has to be robust enough to take into account aluminum stress relaxation and creep,” explains Seifert.
“There are a lot of different solutions out there,” warns Seifert. “It’s not easy; it’s a challenge. Depending on the cable size, no single termination process may be applicable to all cable sizes.” Small, medium and large wires each need their own technologies.
“There are ways to screw up aluminum,” adds Price. “We’re not quite at the tipping point yet.” But, he believes that upcoming standards will help spur development efforts.
“The goal among the Big Three is to get some standards in place,” says Price. “For instance, we need to determine whether crimping or welding will be used for terminations.”
The EWCAP standard aluminum termination initiative started on April 24 and will finish on Oct. 1. “We’re working with suppliers and looking into standards to accelerate technical development, improve quality, reduce cost and provide common methods to foster growth,” says Price. “This initiative to standardize processes, methods and equipment will make aluminum wire implementation easier.”
Another step on the road to standardization is the new ISO 6722-2 aluminum cable standard, which is in the final stages of approval. “It is a continuation of the existing German standard (LV112-2) for aluminum cables,” says Patel. “However, the new ISO standard will be used globally. And, the new standard uses the same sizes and dimensions as ISO 6722-1, which covers copper cable.”