Laser welding dissimilar materials

Laser welding of dissimilar materials is a good example where both laser sources can play very important role. The use of dissimilar material joints is expanding in the rapidly growing advanced energy sector including batteries, large scale energy storage, fuel cells, Gen IV nuclear power, and solar power; as well in advanced oil and gas, and fossil fuel power systems.

Today’s requirements on vehicles with internal combustion engine are characterised by more sophisticated emission regulations, rising fuel prices and higher driver’s demand on driving dynamic, comfort in line with increased environmental awareness. For that reason, more and more car manufacturers throughout the world are focusing on electric vehicles. The battery technology currently in use is lithium ion batteries because these are smaller and lighter than current automotive power batteries (generally, Nickel Metal Hydride). This technology can provide power equivalent to current technology at a smaller size and lighter weight, or more power at an equivalent size and weight.

The batteries used in the electric vehicle batteries (EVB) are constructed from a combination of different materials and these materials and poses particular challenges to be joined together. In battery and pack manufacture there are a number of similar and dissimilar materials that need to be joined The result show that pulsed Nd: YAG lasers (125-300W) with its pulse shaping capabilities and high peak power can either spot or seem weld a range of materials up 3m thickness, whereas with SM fibre laser it was only possible to join thin material sections up to 2mm thick stainless steels and <1mm with reflective materials i.e. copper and aluminium alloys. The average power needed to join reflective material was 400W and because of its small spot size i.e. 43μm, a greater attention was paid to the jigs and fixturing to make sure that fit of the parts was good. For spot welding applications of reflective materials, pulsed Nd: YAG laser was better than the SM fibre laser. Pulsed laser produces spot welds with large interface width, which is very import to produce strong welds.

Whereas the pulsed Nd: YAG is very good for spot reflective materials, SM fibre laser is best suited for spot welding thin stainless foils. Laser spot welding (20-200um) sheets of stainless steel, which are extensively used extensive, used in electronic industry welding hard disc drive flexures. An essential component of hard drives, suspension assemblies are used in virtually every size and model on the market today. The disk drive flexure components are thin 300 series stainless steel parts with spot welds that join the separate pieces via lap welds. For a number of years lamp pumped pulsed Nd: YAG lasers with an adequate beam quality have been the laser of choice for spot welding Flexures (weld dia approx. 120μm). However, as these devices are getting smaller and smaller, it is very important to have a laser, which has a very good beam quality to produce small spot size to weld these small parts (weld dia <110μm) with consistent weld quality. Because of the high beam quality of the fibre laser, a scanning head can fitted to the laser for this application and this will reduce the cycle time compare to laser/welding solution. The spot welding tests carried out with a SM 100W fibre laser in thin (20-150μm) 304 stainless foils show that with proper optimisation of laser and processing parameters, it was possible to produce spot welds of various diameters without any spatter.