It has proved possible to combine the advantages of a fully digital MIG/MAG process with those of laser welding in a single process. This process, known as LaserHybrid, combines the excellent gap-bridging properties and simple seam preparation of MIG/MAG welding with the advantages of laser welding, such as focused heat input, good weld depth and speed. As soon as the laser beam impinges on the material surface, it vaporises a spot on the surface. The result is an extremely intense column of vapour that has the desired effect of creating a deep and narrow heat-affected zone. In the LaserHybrid process, the use of expensive laser energy is restricted almost exclusively to this deep-weld effect, which also permits thicker sheets to be joined. The remaining energy requirement is met by the cheaper MIG/MAG process, whose melting electrodes at the same time provide better gap-bridging capabilities. As both processes focus their energy on the same process zone, weld depth and speed and significantly improved compared to the individual processes.
At the heart of the LaserHybrid system is a compact LaserHybrid head with an integral MIG/MAG torch and laser optics. A robot holder forms the link between the LaserHybrid head and a standard industrial robot. This gives the LaserHybrid head the flexibility it requires to access difficult-to-reach areas of the workpiece. The filler wire can be placed in any position with respect to the laser beam, thus enabling the joining process to be adapted precisely to the wide variety of seam preparations, outputs, wire types, wire grades and joining tasks.
A coated protective glass is required to protect the laser optics from welding spatter damage. The LaserHybrid head uses what is known as a CrossJet unit to ensure that the protective glass itself remains clean, undamaged and translucent for the laser. An air flow very effectively diverts any spatter into an extraction channel at supersonic speeds. The air flow itself is also extracted before it can reach the weld area and interfere with the work of the shielding gas. The work area remains free of contaminants and welding fumes. The integral MIG/MAG torch has a dual-circuit cooling system and draws its welding current from a fully digitised inverter power source, which also controls the associated wirefeeder. Standard laser output is presently 4000 W, although applications with 6000 W will soon be available.
Application and advantages
LaserHybrid welding is particularly suitable for applications that use industrial robots, as the potential offered by this high-performance process can only be exploited by automated applications, and only a robot is able to take full advantage of the flexibility offered by the compact welding head. The process is extremely competitive, despite the expensive laser. A comparison of the costs involved in joining 2 mm sheets using LaserHybrid and MIG/MAG welding has been carried out. The LaserHybrid process was six times faster than the MIG/MAG process and made do over the same period with one third of the amount of shielding gas. In terms of seam length, the amount of shielding gas required was reduced to one eighth. The lower heat requirement of the MIG/MAG process also meant that much less filler wire melted. There was far less excess weld metal, and the seam surface exhibited much reduced swelling. The high weld depth resulted in a stronger seam, especially with fillet welds, compared with, for example, laser welding with no additional MIG/MAG process. Alternatively, the seam volume can be reduced. Both effects, less excess weld metal and optimised weld depth, also contribute to substantially reduced wire consumption. Taking all these factors into account, the cost of joining one metre of material using LaserHybrid welding came to 1.20 Euro, while the figure for MIG/MAG welding was 1.80 Euro.
Although weld seams with very good gap-bridging capabilities are cheaper if welded exclusively using the MIG/MAG method, the speed and productivity benefits of the assisted laser process come to the fore when gaps are narrower. The greatest commercial benefits of the LaserHybrid process are achieved when the gap to be bridged is between 0.3 and 0.5 mm, as in this range welding performance increases nearly four-fold (up to 6 metres per minute) compared with pure MIG/MAG welding. The process can be adapted to a very varied range of applications by modifying the proportions of laser and MIG/MAG welding. For example, the laser can be switched off temporarily for seams that involve the bridging of large gaps.
The LaserHybrid process will be of particular interest to those sectors in which the investment can be quickly recouped through increased production levels of weld-intensive components. The automobile industry and its suppliers immediately spring to mind, though manufacturers of containers, pipework and pipelines, for instance, will also be interested. The LaserHybrid process is suitable for a wide range of materials and thicknesses. It is advantageous in a large number of aluminium applications, particularly those where component tolerances and preparation times make them unsuitable for laser welding. Another positive aspect of the LaserHybrid process is the relatively low heat input required. On the one hand high-strength materials exhibit hardly any loss of strength, while on the other the low levels of thermal delay mean improved component precision.
Improved competitiveness is the result of a whole package of advantages. The versatility of the LaserHybrid process opens up a broad range of joining applications. The best chances are felt to be in areas where wide gap-bridging requirements do not permit the exclusive use of laser welding, or only if the appropriate investment is made. A saving in laser output promises reduced investment costs. Newly exploited application areas and optimised performance increase productivity. Synergy effects also increase the efficiency of the process. LaserHybrid once again demonstrates the expanded horizons of the new thermal joining processes with regard to cost-effectiveness, seam quality and process reliability.
