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3D LASER WELDING
Laser welding exploits the capability to concentrate high energy in a punctiform and very small spot, melting the material of the parts and creating a highly stable and resistant joint between them. The energy brought to the part is focused on the joint and therefore the heat affected zone and the part distorsion are minimal.
The are two kinds of welded joints: lap joints or butt joints. In any case, and in particular for butt joints, the quality and the presentation of the edges to be welded is of the greatest importance: they must be accurately prepared, referred, joint and clamped during the process. Often it is better to make some tack-welds to be sure that the edges are kept joint during the process. This means that reference and clamping devices play a leading role in the welding process, much more than in the cutting one. Generally, laser welding is autogenouos. Sometimes, for metallurgical reasons (e.g. for some kinds of aluminium) or when the joining is not perfect and needs to be filled, filler material can be used. The laser welded joints are generally thin and can be cleaned and/or smoothed more easily than the joints obtained with other welding techniques. Consequently, laser welding is particularly suitable when the appearance of the articles is essential (e.g. tableware, kitchenware, furnishing) or for hygenic reasons (e.g. gaps or extra material which can become "biological traps" in the food or medical industry). It has already been mentioned the importance of referencing and clamping systems: with conventional tools the fixtures complexity and costs can be very high. With a laser system, on the contrary, it is often possible to precess the workpiece in a single phase. In fact, since the laser head can move around the part in any of its sides, there’s no need to reposition the piece. This drastically reduces the number and the complexity of the fixtures needed. In 3D applications lap welding is almost always used. The parts are often formed and, therefore, the fixture must force the parts in their nominal position, overcoming spring-backs. The fixture must refer, force and keep the parts joint during the process, while the laser head moves along the path to be cut. On the weld stitch it is usually brought an inert gas (usually Nitrogen or Helium or Argon) in order to avoid the welded joint oxidation. Usually, this gas is brought through a nozzle, coaxial to the focused laser beam. When the gas is not required or it can be brought through the fixture, the nozzle is not necessary. This technique is called HOW (“Hands Off Welding”) and it is available on PRIMA INDUSTRIE 3D laser machines. It consists in the "remote" welding (at a distance of 150÷200 mm): no need to bring the laser head near to the part to be processed. The fixtures become simpler and the cycle times are sensibly reduced. In the automotive sector for car body parts it is used the stitch welding (more or less similar to classic spot welds): with any technology most time is spent to move the machine (or the robot) from one stitch (or spot) to the next one. With the laser the so called "remote welding" is possible, keeping the machine head far away from the part (till one meter or more) and guiding the focused laser beam with oscillating mirrors. The repositioning time from one stitch to the next one is virtually eliminated (less than 0.1 socond on average), allowing very short cycle times. The AGILASER by PRIMA INDUSTRIE is today the largest and fastest remote welding system available on the market. It is worth mentioning that all PRIMA INDUSTRIE welding machines can be turned into cutting machines, replacing in few seconds one part of the focusing head. For 3D welding PRIMA INDUSTRIE offers: RAPIDO OPTIMO AGILASER |
