Arc welding as a production process took a long time to become established, but has nevertheless been around since the 1940s. Although the laser was only invented in 1960, it quickly became established as a production process and by the 1980s was starting to be used in high volume manufacturing. Recent advances which have improved the beam quality and efficiency of lasers, make the laser an even more advantageous solution to high volume or automated industrial joining.
Weld quality and consistency
Laser welding enables the quality and consistency of welding to be readily controlled and consistently maintained. Since the laser head makes no contact with the workpiece and there is no electrode which can become worn, eroded or damaged there is no need for a tool change where the electrode needs to be reground or sharpened, as is the case with TIG. The lack of electrode dressing in laser welding results in higher uptime and longer time between maintenance interventions. Also, there is no risk of contamination of the weld material with Tungsten from the TIG electrode tip when striking the arc.
Lower heat input
With laser welding the heat input to the metal being welded is lower which means there is a smaller heat affected zone (HAZ) and the distortion of the assembly is vastly reduced making complex and accurate assembly more achievable, especially in an automated setting.
TIG welding (left) typically exhibits higher heat input into the surrounding material – Laser welding (right) is capable of finer welds, with a much smaller heat-affected zone
In addition, the lower heat input means that a weld can be placed close to sensitive electronics or other heat-sensitive materials without risk of damage or failure. An example of this is in cardiac pacemakers and defibrillators where the external weld seam is directly above a heat-sensitive battery and micro-electronics which cannot withstand a temperature over 80 degrees C.
Throughput – higher welding speed
Weld speeds are generally higher with laser welding, especially with modern high power continuous wave (CW) fibre lasers. A high welding speed sometimes means that the motion system, for example the CNC system or robot contouring speed, is the limiting factor on cycle time rather than the process.
Cost per metre of weld
In processes where throughput is high it is common to find that the laser solution is more efficient and results in a lower cost per metre of weld. Interestingly, there are processes which combine laser and arc welding to achieve deeper penetration and higher welding speeds. These hybrid processes typically use a combination of laser welding to heat the metal efficiently to melting point and arc welding to provide deposition of droplets into the weld pool and enhanced penetration and weld strength over either process as a stand-alone procedure.
No finishing of the weld
With inert gas shielding, a laser weld in stainless steel or aluminium normally requires no post-processing (grinding or dressing) after welding, the weld finish is bright and oxide free and can be typically coated or painted without further cleaning steps.
Access difficult areas
Since the laser beam is a “line of sight” process, the laser can pass through gaps in a structure to weld areas from the rear, where it would not be possible to introduce a TIG electrode. Using a camera to view through the laser optics, it is easy to align the beam to a precise feature and perform welds in difficult-to-reach parts of the structure.
What about gaps?
One disadvantage of laser welding is that it tends to rely on good contact and minimum gap between parts to be joined. With either a laser process or a TIG weld, there is a need to ensure that gaps are minimised or avoided to ensure good results. With the addition of wire feed, which adds a certain complexity to the process, it is possible to fill gaps or build up areas for additional strength.
For ease of automation, consistent quality and lack of post-processing there are clear advantages to using laser welding. Where welding is to be applied manually, TIG welding has greater flexibility and lower capital cost for the equipment.