Welding’s different with the laser

All thermal bonding processes use energy in order to melt the workpieces and join them. At one time, the smithy fire was the only energy source for this. Later, the gas burner replaced the hearth. Gas fusion cutting – also called autogenous welding – was among the first welding processes. the filler material. The molten metal resolidified and left the welded seam behind.

In sheet processing today, MIG and MAG as well as TIG welding are standard. In addition, there is an increased use of laser welding. Spot and projection welding are attractive because they only involve pressure and electrical current. Plasma and electron beam welding hold a secondary place. They are used for special purposes. In some cases soldering is used as well, where materials with different melting points are in contact.

Thats how it works

Heat exchangers are welded together from two parts and then “pumped up.” In spite of the enormous stress of “pumping up,” the seams must remain absolutely liquid-tight.

In laser welding, the focused laser beam serves as the energy source. The laser beam is bundled in the welding head by means of a mirror or lens. The crossjet, a stream of gas flowing across the laser head, prevents dirt from falling on the mirror or lens.

Where the bundled laser beam hits it, the workpiece melts. Focus diameter, focus position, laser power and welding speed are the important parameters determining the depth and width of the seam. During processing, the welded seam is usually shielded against reactions with the air by a protective gas. Other gases - the so-called assist gases - can support and control the welding process. Depending on the type of seam to be welded and how large the gap between the components is, filler metals are used.

Precision and Quality

Arrangement for laser welding of pipes: the sensor in the black housing follows the position of the joint and regulates the position of the optics accordingly.

At the focus, the diameter of the laser beam is only a few tenths of a millimeter. Only the smallest gap may remain between the components that are to be joined. Moreover, the width of the gap should be constant. For this reason, in laser welding the preparation of workpieces and positioning are comparatively complex. Sensors assure constant quality. Sensors that follow the course of the seam recognize deviations from the programmed path and regulate the position of the laser beam. They equalize edge and positioning precision. Other sensors measure the expansion of the weld pool to determine whether the welding process is proceeding within the defined limits. Sensors can be added to monitor the hardened welded seam and distinguish good seams from bad.

Large range of applications

Low distortion, high process speeds, flexibility and fine welded seams are the advantages of laser welding. Laser-welded seams generally do not have to be reworked and they are gas- and liquid-tight. The main materials welded are metallic materials such as structural steel and stainless steel, aluminum and aluminum alloys, titanium and titanium alloys, and non-ferrous and noble metals.

This opens a large range of applications for laser welding; from the fine weld spots in a halogen incandescent lamp, to the welded seam in a fire extinguisher, to the meters-long welded seams in machines or airplanes. Laser welding is usually performed in automated laser welding plants or by means of welding robots. Smaller welding tasks with individual spot welds or short seams can also be performed at manual welding stations.

Points win

Bonding with laser beams has many advantages over conventional welding processes that use an arc:

Targeted energy impact on a small area, thus low thermal stress and very small heat-affected zone and very small amount of warpage.
Narrow seam geometries and smooth surfaces decrease or eliminate reworking.
Great strength with low seam volume: Workpieces can subsequently be formed by bending or hydroforming
Good possibility for integration: laser welding can be combined with other production steps; for instance, alignment or bending.
Only one side of the joint has to be accessible.
High process speeds assure short process times (cycle times).
Laser welding can be automated very well.
Good process control: machine control and sensor system monitor process parameters and assure quality.
The laser beam welds without touching and exerts no pressure on the workpiece.