Reducing the variations in laser welding

Key Points

• The operator's dexterity has a real influence upon laser welding quality but this can be reduced when the choice of welding parameters has been optimized.

• It is possible to avoid the empiric choice of irradiation parameters (energy, pulse duration, power) to improve the welding procedure and get a full penetration depth of the laser beam in the dental alloy used.

• Adequate combination of energy and pulse duration using a power set around 1 KW has been performed on different diameters of FeNiCr orthodontic wires. A classification of welding parameters have been performed for that kind of material and for this type of pulsed Nd-Yag laser, so that the operators can optimize their laser welding procedure.

• Unfortunately, changing the composition of the alloys requires another systematic study.

Abstract

Objective Interactions between lasers and materials are very complex phenomena. The success of laser welding procedures in dental metals depends on the operator's control of many parameters. The aims of this study were to evaluate factors relating to the operator's dexterity and the choice of the welding parameters (power, pulse duration and therefore energy), which are recognized determinants of weld quality.

Design In vitro laboratory study.

Materials and methods FeNiCr dental drawn wires were chosen for these experiments because their properties are well known. Different diameters of wires were laser welded, then tested in tension and compared to the control material as extruded, in order to evaluate the quality of the welding. Scanning electron microscopy of the fractured zone and micrograph observations perpendicular and parallel to the wire axis were also conducted in order to analyse the depth penetration and the quality of the microstructure. Additionally, the micro-hardness (Vickers type) was measured both in the welded and the heat-affected zones and then compared to the non-welded alloy.

Results Adequate combination of energy and pulse duration with the power set in the range between 0.8 to 1 kW appears to improve penetration depth of the laser beam and success of the welding procedure. Operator skill is also an important variable.

Conclusion The variation in laser weld quality in dental FeNiCr wires attributable to operator skill can be minimized by optimization of the physical welding parameters.

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