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.
One of the problem areas that has existed in applying lasers in some sheet metal applications has been where two galvanized surfaces need to be joined. At issue here, Havrilla explains, is that because the zinc on the steel has a comparatively low boiling point, it melts and leads to porosity problems. However, this problem has been solved through the use of remote laser welding. In this case, a laser scans the surface of one of the materials to be joined so that there are melted protrusions of a repeatable size generated (known in the industry as "laser dimpling"). Then the second sheet is laser welded onto it. The little humps provide an escape route for the melted zinc, to the sides, which keeps the porosity blowouts from occurring.
Says Havrilla, "People need to rethink design in order to appropriately apply lasers to the manufacturing arena." He explains that it isn't a matter of just taking lasers and replacing spot welding equipment, because that's not particularly advantageous to realizing the benefits that lasers can provide. But by taking another look at what lasers can do-think only of the elimination of the ditch, which is still a "feature" on even some of the latest cars-aesthetic and economic benefits can be realized.
Creating Plastic-Metal Hybrid Components
Plastic-metal assemblies can be produced with a process developed by the Fraunhofer Institute of Technology (www.ilt.fraunhofer.de; Aachen, Germany). In the process, laser radiation is combined with mechanical pressure. The laser radiation passes through the plastic piece; the metal part to be attached is pressed onto the plastic and heated. It is then pushed into the plastic. Assuming there is appropriate geometry involved, and that the metal part has a higher melting point than the plastic, once there is cooling, there is a solid bond. (In addition to metal, the process, called LIFTEC, also works with ceramics and temperature-resistant plastics.)
Fast Stainless Marking
According to application engineers from Laser Photonics (www.laserphotonics.com; Lake Mary, FL), Q-switched fiber lasers are superior for marking on stainless steel than CO2 lasers. The reason: because stainless steel is reflective, it is necessary to coat the stainless steel surface with a “laser marking material” (LMM). This is sprayed on, allowed to dry, then the CO2 lasing commences. Afterward, the surface has to be cleaned. However, with a Q-switched fiber laser, such as the company’s 20-W FiberTower XP, no LMM is required, so the marking process is fast. In one application, they were able to mark at a rate of five inches per minute.
System for Welding Plastic Housings
Laser welding is an alternative that can offer higher weld quality and higher yields, according to LPKF Laser & Electronics (www.lpkfusa.com; Tualatin, OR). It has developed a diode-laser based off-the-shelf laser welding system for processing such things as electronic enclosures and sensor housings. The system is available with 30 to 600-W laser power; it adheres to Class 1 laser safety rating. The maximum part size that can be handled is 9 x 9-in. There is a rotary table that can be manually or automatically loaded. With standardized fixture adapters, retooling changeovers can be accomplished in 10 minutes or less.