Before assembling aluminum wire and cable harnesses, engineers must carefully consider several important factors, such as the size of wire and type of terminal being used. For instance, because aluminum is not as strong as copper, termination connections cannot take as much pull force.
Small aluminum wire under 2.5-square millimeters poses many challenges. “Processing changes are required in feeding, cutting and stripping, but the biggest challenges lie in crimping,” notes Rob Boyd, crimping product manager at Schleuniger Inc.
When feeding aluminum wire, straightening must be handled differently. “For instance, the standard wire straightener is a series of offset rollers that bends the wire forward and back and up and down in two planes to remove memory from the wire,” Boyd explains. “For the most part, with copper wire, if you need more of a straightening affect, you tighten the rollers.
“However, with aluminum, if you tighten too much, the conductor can actually stretch because it is so soft,” warns Boyd. “Therefore, resulting wire lengths may be longer than normal. Finding the correct settings for aluminum wire can be tricky; you want to straighten the wire, but not stretch it.”
Cutting aluminum wire may require different blade geometries and spacing, because the material is so soft. Aluminum does not shear the same as copper and is more likely to leave burrs on the wire. “This is because the metal can ‘ooze’ between the blades during the cutting process,” Boyd points out.
Stripping aluminum wire can be a challenge, as well. Because the conductor strands are so soft and fragile, it's easy to tear strands if there is too much adhesion of the insulation to the strands. Nicking or scraping strands with copper can sometimes be allowed, because the material is stronger. With aluminum, any nicks or scrapes in the strands will easily break either during or after the crimping process.
According to Boyd, presenting aluminum wire to processing stations is not really an issue for most machines, because the bend radius is large enough. However, the crimping process is quite different and unique compared to that for copper.
“A correct crimp involves the ‘system’ of the wire, the terminal and the crimping method,” says Boyd. “You can’t just crimp any terminal onto an aluminum wire with the same tooling and expect the crimp to perform the same.”
When crimping aluminum wire, the two main challenges are corrosion and relaxation of the crimp. For instance, crimping a copper terminal onto an aluminum wire will not work. Copper and aluminum cause a chemical reaction that causes the aluminum to erode. The effect is that the crimp corrodes from the inside-out.
“Eventually, the wire will be able to fall out of the crimp,” claims Boyd. “However, most terminals are plated, so this effect is minimized. But, finding the optimum chemical make up of the tin is also critical in preventing corrosion.
“Aluminum oxidizes almost immediately,” Boyd points out. “Oxidation on the wire forms a barrier between the wire and terminal. Barriers increase resistance and resistance results in heat. The more the corrosion-oxidation, the more heat is generated.” Some companies have been experimenting with a post-crimping or precrimping chemical process to prevent corrosion of aluminum wire. A
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