What Designer Should Know About Lasers

While the design of the 2009 Cadillac CTS is remarkable and renowned, there is something that doesn't meet the eye about it.

 

Look carefully at the photo of the CTS (below). What do you see? And what don't you see? What you do see is a decklid that has a rather substantial angle. It is the sort of shape that would take considerable deep drawing to achieve-assuming it could be achieved at all. And deep drawing is a time-consuming operation that requires serious presswork and tooling.

 

Then consider the roof. More specifically, focus on the area where the roof meets the body side. If you look at most cars, you'll see something else there. You'll see a bit of trim on both sides, running along that mating edge. That's because there is a ditch where the roof meets the body side. An unsightly, long divot. It's formed to accommodate roller resistance welding that's performed to join the roof to body side. Then it is filled with a sealant so as not to leak. Then the trim is added on top. Yet there's nothing there on the roof of the CTS.

That is an example of how lasers can help improve vehicle design, points out David Havrilla, product manager, High Power Lasers, TRUMPF, Inc.

 

In the cases of both the decklid and the roof of the CTS, laser brazing is deployed. The trunk is produced with two pieces, with the seam invisible where the horizontal piece meets the vertical piece. The ditch joint is eliminated by simply laser joining the roof to the body sides. The seam is sealed so that there's no need for the sealant, no need for the trim.

 

Havrilla says that this is becoming more common on European automobiles (and realize that one of the things that Cadillac engineers set out to do was develop a car that could compete with the BMW 5-Series with a price-point of the 3-Series). For example, at Audi they actually have a term for the laser brazing process that is used even on vehicles as big as the Q7 SUV: the "zero-gap" look. (In all, Audi engineers utilize more than six meters of laser welding on the Q7.) And at the rear, some European cars have a laser brazed license plate inset, which would otherwise be another deep drawing challenge and that would require multiple sets of tooling to accommodate different plate sizes in Europe.

 

The point is, designers at places like General Motors and Audi are taking advantage of laser processing, as are those at Volvo (e.g., C-70) and Volkswagen (e.g., Passat). But there are some significant opportunities for those at other companies to do the same.

 

Flange elimination.
For example, Havrilla says that another area where there can be weight, cost and aesthetic advantages, and even improved safety through increased driver visibility, offered by lasers versus traditional resistance spot welding is in the elimination of flanges that are found in various areas on vehicles-such as below the rocker. The flanges, which are generally on the order of 16 to 18 mm in width, are sized to accommodate the tip of the spot welding gun. This, he claims, can be cut in half through the use of a laser. Which results in savings of time and money. Or because lasers make it possible to vary the length of the welds-from stitches that are analogous to spots all the way to continuous seams-it is possible to eliminate some structural reinforcements: Consider the door opening on a body-in-white; by running a continuous seam where the door will be attached, but stitches elsewhere, a reinforcement can be eliminated, thereby providing savings.

 

Audi is using this process in a processing cell in its Ingolstadt facility for producing the doors of the A4 and Q5. In the first step, a 7-kW laser fires pulses on the surface of the door inner to produce 0.15-mm high bumps. In the second, the second piece, the frame, is added, and a robot with an optical focusing system moves around such that 48 welds are produced. It is done so quickly that cycle times for each door are cut in half.