Controlled metal transfer from a wire by a laser-induced boiling front

Abstract

The addition of wire is an option during laser welding, laser cladding or laser additive manufacturing. By high speedimaging of leading wire addition during fibre laser keyhole welding it was observed that for the 40 experiments underconsideration the wire tip always established a concave boiling front. The front appears similar to a keyhole front and issort of a continuation of the keyhole, owing to the leading wire employment. For most of the parameters the melt istransferred downwards from the wire tip into the melt pool surrounding the keyhole front. In other words, hardly anyuncontrolled spatter to the sides was observed. A trailing wire would normally tend to a completely different behaviour.Typical as well as limiting phenomena of the wire melt transfer mechanism are presented and discussed. Controlledvertical melt transfer of the wire through the ablation pressure from a laser-induced boiling front, either in contact withthe workpiece surface or positioned higher above, can be a desirable mechanism of metal deposition for the differenttechniques, namely welding, surface treatment or LAM. By suitable choice of the laser power density above the boilingthreshold, the here observed mechanism can be applied in a controllable manner. An interesting technique option islateral beam oscillation for example by a galvanometer optics which shears off the melt in a manner similar to remotefusion cutting. The process limits become different to the static technique. The wire melt transfer technique has thepotential to be developed further towards a highly controllable remote drop transfer, e.g. in terms of direction.Upprättat; 2016; 20151117 (alka)</p