Regular readers will be familiar with our previous predictions that one result of the seemingly relentless rise in copper prices compared to some competing metals like aluminum is the inevitability of product substitution. Some applications are easier than others in which to substitute copper, and one of the hardest has been electrical wiring. Even though aluminum has many advantages, not least being it now costs a third the price of copper, substitution on a large scale has so far been limited largely to long-distance suspended power transmission cables where the lower weight of aluminum has been a major benefit even before metal cost is taken into account.
Understandably the more critical the application, the greater the challenges that need to be overcome. Automotive cabling is one such application. Copper in car cabling is a tried and trusted technology that has proved reliable over the 10+ year life cycle of a modern car. Components may fail but the wiring loom rarely does; if there’s a problem, it is usually a design fault and not a material failure. But engineers at BMW in conjunction with the University of Munich (TUM) are working to find solutions to a number of challenges in using aluminum not just for conventional autos, but more importantly, for fully electric vehicle applications where demands and temperatures may be even higher.
Some of the issues the team is addressing are related to the way aluminum behaves over time. For example, as a TUM press release states, aluminum has a tendency to creep particularly at high pressure, meaning connectors would loosen over time. Even at lower temperatures, a paper by Austin Weber in Assembly Magazine explains that aluminum will flow when placed under constant pressure, so even if secured under twice the crimping pressure of copper, in time it will become loose as the metal flows from the pressure points.
Another issue is oxidation. Wherever it is exposed to the air, aluminum will oxidize; indeed, it is one of its strengths in that the oxidation layer protects the metal against further corrosion — unlike rust on steel, which remains porous. But oxidized aluminum does not conduct as well as pure aluminum, so conducting surfaces need to be formed in such a way that an oxidation layer cannot form. The BMW/TUM team are putting a lot of work into connection boundaries and are coming up with some innovative solutions that they believe will provide reliable wiring configurations over a minimum ten-year vehicle life span.
Nor should the efforts being expended be seen simply as a drive to reduce metal costs. The team firmly believes the lower weight of aluminum will allow the reduction of vehicle weights resulting in lower fuel consumption and emissions. Although an approximately 60% greater cross section of aluminum wire is required than copper for the same conductivity, the weight reduction is still about a third. Nevertheless, so demanding are the approval processes, the team believes it could still be the latter part of this decade before we see all aluminum-wired electrical vehicles on our roads.
In the meantime, Sumitomo is starting small and working its way up. An article in Interconnection World reports on how Sumitomo Electric has already developed low-voltage aluminum-wired harnesses for use in Toyota’s new Ractis line of conventionally powered sub compacts. The Sumitomo Group says it developed the lightweight wiring harnesses using thin aluminum wires with twisted wire structures to ensure reliability of electrical connection. As so often happens, where Toyota leads others eventually follow, and it seems probable we should factor in automotive wiring to become a major driver of aluminum consumption in the years ahead.
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