Automated, diodelaser-based brazing of carbide tips for optimised saw blade fabrication

To increase wear-resistance, circular saw blades are equipped with carbide tips with different compositions. At present, inductive brazing is the only joining process which can be used to achieve sufficient connection characteristics between the tool steel master blade and the carbide tip. For induction brazing, a typical, wide thermal load on the saw tooth increases hardness and thus a negative effect on the mechanical properties. Moreover, thermal distortion of the saw blade makes additional, expensive straightening process necessary. Laser beam brazing is characterised by a local and temporally precise, controlled energy input, resulting in almost no hardness increase of the saw tooth and with increased strength of the connection. Laser brazed saw blades showed good properties regarding the tool service life. Due to this, a conventional induction brazing machine was altered to accomodate laser-based brazing. The induction coils were dismantled, the tooth support and -mounting plate changed and a fibre-coupled diode laser with a one inch optic processing head and a high-power laser mirror were integrated into the machine. The laser beam is projected onto the cutting face of the carbide tip, so that the brazing zone is heated uniformly by heat conduction. This brazing strategy allows a much smaller heat input into the master blade, compared to conventional inductive brazing. Moreover, a reduction of production time could be achieved, based on this new laser process. The test results show a brazing time reduction of 33%. The metallographic investigations of brazing zone cross-sections exhibit much smaller heat affected zone. Degradation of mechanical properties of the master blade can be completely avoided by adapting the parameters.