Defect-free joining of zinc-coated steels by bifocal hybrid laser welding

Abstract

Laser welding of zinc-coated steels in an overlap setup is prone to weld defects and seam expulsion reducing in particular the properties in mechanical loading and in general the deployability of such weldments in industry. Several laser welding process technologies failed to created defectfree welds in zinc-coated steels. This paper renders the welding of zinc-coated steels by the novel technology of bifocal hybrid laser welding. The zinc-coated steels under consideration are DX56D ? Z, DC04 ? ZE, and HXT700D. The bifocal hybrid laser system is realised by combining an Nd:YAG laser with a high power diode laser, both of 3 kW maximum output power. The beam parameter product (BPP) of the employed Nd:YAG laser of 25 mm mrad translates with an optical system of focal length f = 150 mm into a circular focus of diameter 0.45 mm, whereas the BPP of the HPDL of 85 mm 9 200 mm mrad can achieve a rectangular focus of 0.9 mm 9 3.7 mm. The optical system allows the respective focal plane and relative position of the foci to be independently vertically and horizontally positioned. This paper presents research into the causes of instabilities in laser welding of zinc-coated steels. Experimental evidence is considered and presented to establish the need for an empirical process model for stable laser welding of zinc-coated steels. The increase of process robustness is discussed.

Microstructural Aspects of Bifocal Laser Welding of Trip Steels

“…Multi-beam laser welding can be conducted using two laser heads or a special optical module [3]. Presently, twin-spot laser welding is tested in relation to joining galvanised sheets [4] or light metal alloys [5,6]. Important materials for the automotive industry include advanced high strength steels (AHSS), i.e.…”

Disk Laser Welding of Car Body Zinc Coated Steel Sheets / Spawanie Laserem Dyskowym Blach Ze Stali Karoseryjnej Ocynkowanej

“…Sheets of this type are used in the manufacture of automobile bodies in high volume production because of excellent corrosion resistance and relatively low costs [1][2][3][4][5][6][7][8][9][10].…”

“…The basic, conventional and used for many years method of joining of the car body parts is a resistance spot welding (RSW) [7][8][9][10][11][12]. In the case of car body parts with larger thicknesses, also the method of gas metal arc welding (GMAW or MIG/MAG) is used.…”

“…That is how there are a lot of research on vibrations [43][44][45][46][47][48] and it should be analysed during the welding process as well in term of influence on the propagation paths. In addition to laser welding technology, the welding-brazing, hybrid welding, cold joining by forming and clinching, structural adhesive bonding are becoming increasingly important [1,8]. Laser welding offers many benefits such as high welding speed, low heat input, narrow weld and narrow heat affected zone (HAZ), high precision, reliability, high efficiency, and high productivity, and improved corrosion resistance of welds, compared to the conventional welding methods [5,6].…”

“…For example W. Chen et al proposed pre-drilling by a pulsed Nd:YAG laser to form vent holes along the weld line and then seam welding in the lap-joint configuration using a continuous wave CO 2 laser [6]. J. Milberg and A. Trautmann produced defect-free overlap joints of galvanized steel using bifocal hybrid laser welding by combining an Nd:YAG laser with a high power diode laser [8,[18][19][20][21][22][23][24][25]. S. Iqbal et al elaborated the novel method of dual beam laser welding [9].…”