Hybrid Laser Manufacturing-State of the Art and Benefits

摘要

This presentation summarises recent developments in hybrid laser manufacturing processes. These include hybrid la-ser/MIG/MAG/TIG welding. Hybrid laser/EDM/mechanical/chemical machining and hybrid laser/flame/plasma/sol-gel coating. Most of the examples given are based on the work carried out by staff and students in the author's research centre. The process characteristics, key benefits and drawbacks are discussed. Future prospects are proposed. 1. Hybrid laser-arc welding Hybrid laser and arc welding was first reported in 1978 by researchers at Imperial College, UK. There had been a long pause in further development of the technology until 1990's. The first industrial application of a hybrid laser-MIG welding system was demonstrated in 2000 for oil tank manufacture in Germany. Since then, hybrid laser-MIG, laser-MAG and laser-TIG welding research and applications have progressed considerably. Key benefits of the hybrid laser-arc welding processes include: higher welding speed, better joint fit-up, deeper weld penetration, better fatigue properties, higher energy efficiency and lower production costs. As the hybrid process is more complicated than autogenous laser welding or arc welding, scientific understanding/modelling of the process and better control of process operating parameters to achieve optimum welding performance for various engineering materials have been the major focus of the scientific research. 2. Hybrid laser machining This involves the combination of a laser beam with another form of medium (e. g. electrical, chemical, mechanical, physical) for the removal of materials effectively. The main problem of laser machining is the generation of a heat affected zone and recast layers. Although the emergence of femtosecond and picosecond lasers has enabled high quality machining to be carried out with little heat affected zones, the material removal rate is generally low. A number of approaches have been taken to use nanosecond pulsed lasers to machine metallic and ceramic materials with the aid of another medium to achieve high quality and high material removal rate in the machining processes. Fig. 1 shows the configuration for chemical assisted laser machining. With the aid of a salt solution, laser machining of stainless steels has been demonstrated to achieve high material removal efficiency and at the same time recast layer presence has been eliminated. Other hybrid and sequential laseron-laser machining processes include laser-EDM machining, lasermechanical machining and water assisted machining. Fig. 3 shows an example of water assisted laser machining of coronary stents used as medical implants. 3. Hybrid laser surface modification and coating leaser coating of ceramics materials normally results in cracks due to high thermal stress and brittleness of the material. Conventional thermal spray is more efficient, but bonding is poor and density is low. By combining laser and flame spray, high density, crack-free ceramic coatings with fusion bonding to the substrate has been demonstrated with high coating efficiency. Fig. 4 shows an example for hybrid laser/flame spray coating of Al3O3 on a refractory brick substrate for waste processing furnace linings.