processing, less floor space, consumables and maintenance, higher design criteria possible, process flexibility, reduced material costs, and stronger safer design through the use of custom weld shapes and patterns. Examples of Remote Laser Use Two examples of automotive manufacturers replacing traditional RSW with traditional fixed optic laser welding and eventually with remote laser welding are detailed below. The first example, as shown in Fig. 6, is a laser welding cell that required four robots and five weld guns to complete 34 spot welds in 35 s. It was replaced by one robot, one PFO 33, and one TruDisk 4002 laser, which still put down 34 laser C welds (comparable to RSW), requiring 13 s. Processing was reduced by nearly three times, and three fewer robots were required to complete the task, saving capital expenditures and valuable floor space. The second example, shown in Fig. 7, displays a progression through three different methods. The original part using RSW took 30 s to complete the welds. The first evolution was to use a laser and replace the weld gun with traditional fixed optic laser welding head and laser connected to the same robot cell, which achieved nearly a 25% reduction of cycle time. The next step replaced the fixed optic weld head with a remote scanner (PFO), and utilized the “welding on the fly” process to achieve the maximum benefit of the PFO. The final processing time was five s with a final 84% reduction of cycle time, which is a 600% increase in production capacity. Remote Laser Welding Is Not without Challenges Metal Vapor During the welding process, a metal vapor fume rises up from the key hole and gets in contact with the laser beam. This ionized metal vapor plume, which arises above the welding seam, leads to a reduction of the laser power, to a deformation and enlargement of the focus diameter, and finally to a fluctuating welding process. The solution is the usage of process jets to blow the metal vapor out of the laser beam, stabilizing the welding process — Fig. 8. This can also be achieved by extensive and elaborate cross-jets on the fixture near the weld areas. Overlap Welding of ZnCoated Material Another very common issue with traditional or remote laser welding is Zncoated material. Due to different melting points and gases released during the weld process, if the two pieces of material are tightly clamped together as they should be, the only place for these gases to escape is through the melt pool. This results in very poor quality welds both in appearance and strength. The best solution to manage this problem is to introduce a controlled gap into the process; this can be achieved by mechanical methods in fixturing and part stamping or by laser methods of creating small dimples approximately 0.15 to 0.20 mm high. This controlled gap then allows enough area for the gas to escape without blowing up through the melt pool of the weld, and the gap is small enough not to cause weldgap issues — Fig. 9. Additionally, other coatings and oxide layers can cause problems with weld quality such as cracking, porous welds, weak welds, and brittleness just to mention a few. Remote Vapor Pressure Melt Cutting The remote laser welding process is flexible. Many times a stamping die was missing a hole in early production, or 52 JANUARY 2013 Fig. 9 — Overlap issues with Zncoated material.
Welding Journal | January 2013
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