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How can I increase the tolerance of laser welding to joint fit-up?


Frequently Asked Questions

Laser welding has been used in the automotive, aerospace, shipbuilding and heavy manufacturing industries to join a variety of materials. The main advantage of laser welding is that it can produce a narrow weld at high speed with low heat input and distortion. High quality welds can be produced on joint configurations such as butt, T-butt, lap seam, lap fillet and lap edge. However, the small spot of the laser beam means that the process has restricted tolerance to joint fit-up compared with conventional arc welding processes. Typically, gaps of less than 10% of material thickness for butt joints must be maintained to avoid weld defects. Good joint fit-up is therefore essential to achieving good weld quality. Tolerance to fit-up can be enhanced by correct clamping, process control and improved laser welding techniques.

Use of appropriate clamping systems is the key to achieving the correct fit-up for autogenous laser welding of thin sheet metals. Proper clamping fixtures should be used to hold the sheet in position and close any gaps during welding. There are two types of clamping system: fixed clamps, and moving clamps. Fixed clamps hold the component in place prior to welding; both downward and sideward forces may be applied to achieve good fit-up. Moving clamps apply pressure locally to the weld area by using a roller system to achieve close fit-up.

Fit-up tolerance can also be improved through the use of wire feeding. This reduces welding speed and increases the heated area but tolerance to fit-up is improved to about 100% of sheet thickness for steels up to 6mm thick. Laser welding with wire feed has been used for welding of steels, aluminium alloys and dissimilar materials for tailored blank manufacturing in the automotive industry.

Arc augmented laser welding (hybrid laser-arc welding) also has a greater tolerance to joint fit-up. Combining the two energy sources can give higher welding speed, deeper penetration and greater tolerance to variation in joint fit-up, resulting in reduced requirements for edge preparation accuracy. Hybrid laser welding processes are being used in the automotive, shipbuilding and heavy construction industries.

Beam weaving or spinning is another method of widening the heated area to overcome poor fit-up. The laser beam is either scanned across an area at, for example 50Hz, or spun using rotating optics. Both techniques produce welds at a lower speed than conventional autogenous laser welding (for a given power) but increase the tolerance to gaps to about 20-30% thickness. Beam weaving is used in production for the manufacture of tailored blanks in the automotive industry.

Tolerance to joint fit-up can also be improved by twin-spot welding (dual-laser beam) in which two laser beams interact in a common weld pool either side by side or in tandem. Two laser beams arranged side by side can substantially increase tolerance to joint fit-up.

Further information

How does laser welding work?
What is plasma augmented Nd:YAG laser welding?

For further information see Joining Technologies or please contact us.

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