Hongping Gu

A practical use of humping effect in laser beam welding

The humping effect in laser beam welding has long been recognized as an adverse effect that limits the achievable welding speed in high power laser beam welding applications. By nature, this effect results in a rough weld bead in laser beam welding and affects the weld integrity. In the past, efforts have been made to suppress the humping effect in laser welding. However, it has been found that the humping effect can have a practical use during the preprocess stage for generating “dimples” for laser beam lap welding of zinc coated sheet metals. Remote laser welding takes advantage of less mechanical movement and better accessibility of the beam to the workpiece, thus fast processing speed can be achieved. Furthermore, currently remote laser welding is mostly suitable for lap joints. However, laser beam lap welding of zinc coated steel components is not a straightforward process and it requires a special procedure to provide proper venting for the zinc vapor which is generated in the interface during weldi...

Hybrid welding of galvanized steel sheet

Laser lap welding of galvanized steel sheets under zero gap conditions using an Nd:YAG laser is difficult since there is a considerable amount of Zn vapor generated between the metal sheets which must be vented out of the weld pool. Compared to a high power CO2 laser, a 3 kW Nd:YAG laser does not have enough energy density to keep the keyhole open for a sufficient time for Zn vapor to escape. By combining a YAG laser with a TIG welding process, the additional energy from the TIG plasma helps to sustain the keyhole during welding and improve the weld quality.Laser lap welding of galvanized steel sheets under zero gap conditions using an Nd:YAG laser is difficult since there is a considerable amount of Zn vapor generated between the metal sheets which must be vented out of the weld pool. Compared to a high power CO2 laser, a 3 kW Nd:YAG laser does not have enough energy density to keep the keyhole open for a sufficient time for Zn vapor to escape. By combining a YAG laser with a TIG welding process, the additional energy from the TIG plasma helps to sustain the keyhole during welding and improve the weld quality.

Laser localized coating of corrosion resistant metal over a steel weld bead

Coated steel sheet is one of the most important raw materials for the automotive industry. The commonly used Al or Zn based coatings on steel sheet provide a physical barrier and/or galvanic protection, and thus prevents a corrosive attack of the steel substrate. In order to make complex component or assembly, several steel sheets of various sizes, shapes, or thicknesses are welded together before or after being formed. Unfortunately, the process of welding together the precoated steel sheet pieces results in the formation of a weld joint that is devoid of anticorrosion protection. Re-formation of the protective coating over the weld joint could greatly improve the final products quality in terms of resistance to corrosion. In this investigation, recoating of aluminum-silicon over laser weld joints has been explored by laser beam heating and powder injection. Precise coating over the weld joint was achieved. The produced coating on the welding bead is smooth when proper processing parameters are employed.

Feedback control of processing temperature in laser beam hardening of production dies

Automotive draw and line dies are often subject to high wear and tear in the areas with convex radii during volume production and require heat treatment to improve the mechanical properties in these areas in order to increase the operating life of the die. Laser beam transformation hardening has been proven to be a viable technology for such type of heat treatment. It has been demonstrated that laser hardening process provides better overall hardness and more consistent levels of quality compared to conventional heat treatment processes. Experimental results show that the processing temperature during laser beam hardening is one of main key factors in achieving the highest hardness on the die surface. At Magna, a laser processing system has been integrated for implementation of laser beam hardening of dies, which includes expanded beam spot, precise processing temperature control, as well as off-line programming and automatic tool path generation. This paper describes the practice of laser hardening dies, including influence on the process of different types of material, analysis of laser hardened materials, the effect of the geometry of processing area on the processing temperature and the requirement for temperature control in process.Automotive draw and line dies are often subject to high wear and tear in the areas with convex radii during volume production and require heat treatment to improve the mechanical properties in these areas in order to increase the operating life of the die. Laser beam transformation hardening has been proven to be a viable technology for such type of heat treatment. It has been demonstrated that laser hardening process provides better overall hardness and more consistent levels of quality compared to conventional heat treatment processes. Experimental results show that the processing temperature during laser beam hardening is one of main key factors in achieving the highest hardness on the die surface. At Magna, a laser processing system has been integrated for implementation of laser beam hardening of dies, which includes expanded beam spot, precise processing temperature control, as well as off-line programming and automatic tool path generation. This paper describes the practice of laser hardening dies,...

Remote laser welding of zinc-coated sheet metal component in a lap configuration utilizing humping effect

With the advancement of high power fiber-delivery lasers, remote laser welding becomes a reality and more and more systems have been introduced into production lines. Remote laser welding takes the advantages of less mechanical movement and better accessibility of the beam to the workpiece, thus fast processing speed can be achieved. In most cases, remote laser welding involves lap welding. Laser beam lap welding of zinc coated steel components is not a straightforward process and it requires a special procedure to provide proper venting for the zinc vapour which is generated during welding in the interface. Although there are many approaches to address this issue, many of the approaches are either impractical or too costly to apply to remote laser beam welding in production.Humping effect is an adverse effect that limits the achievable welding speed in laser beam welding. However, it has been demonstrated in the experiment that the height of the protuberance in the humping effect can be controlled via proper process parameters and an optimal height in the range of 0.1 – 0.2 mm can be achieved to meet vapour venting requirement. In reality, the optimum gap size is depending on material thickness and coating type. As a result, the high-speed humping effect can be advantageously used as a pre-process to provide proper gap for laser beam lap welding of zinc coated sheet metals. Furthermore, this pre-process can be naturally implemented in the remote laser welding process flow. The whole process is very flexible and can be achieved at very high speed.With the advancement of high power fiber-delivery lasers, remote laser welding becomes a reality and more and more systems have been introduced into production lines. Remote laser welding takes the advantages of less mechanical movement and better accessibility of the beam to the workpiece, thus fast processing speed can be achieved. In most cases, remote laser welding involves lap welding. Laser beam lap welding of zinc coated steel components is not a straightforward process and it requires a special procedure to provide proper venting for the zinc vapour which is generated during welding in the interface. Although there are many approaches to address this issue, many of the approaches are either impractical or too costly to apply to remote laser beam welding in production.Humping effect is an adverse effect that limits the achievable welding speed in laser beam welding. However, it has been demonstrated in the experiment that the height of the protuberance in the humping effect can be controlled via pr...