Use of 450-808 nm diode lasers for efficient energy absorption during powder bed fusion of Ti6Al4V

The additive manufacturing process selective laser melting (SLM) uses a powder bed fusion approach to fully melt layers of powdered metal and create 3D components. Current SLM systems are equipped with either single or multiple (up to four) high-power galvo-scanning infrared fibre laser sources operating at a fixed wavelength of 1064 nm. At this wavelength, a limited laser energy absorption takes place for most metals (e.g. alloys of aluminium have less than 10% absorption and titanium 50-60% absorption). The lower absorption of 1064-nm laser sources requires higher laser powers to compensate for the loss of energy due to reflectivity and fully melt the feedstock material. This makes the use of 1064-nm lasers within current powder bed fusion SLM systems energy inefficient. Further to this, there is limited potential for scale-up of these laser sources within an SLM system architecture due to physical space requirements and high economic cost, placing further limitations on current state-of-the-art SLM productivity. This research investigates the use of low power, highly scalable fibre coupled diode laser sources and the influence of shorter laser wavelengths (450–808 nm) on material absorption and processing efficiency using a diode area melting (DAM) approach. It was found that when processing Ti6Al4V, absorption was 11% higher using 450-nm lasers when compared to using 808-nm lasers and 14% higher than 1064-nm lasers. The maximum powder bed temperature for irradiation at 450 nm and 808 nm was 1920 0C and 1760 0C respectively when using only 3.5 W of laser power. Due to the speed at which the DAM process scans the powder bed, the melt pool cooling rate was much slower (750–1400 0C/s) than traditional SLM (105–106 0C/s). This encouraged the development of β phases within the formed Ti6Al4V component. The low power, low cost, highly compact short wavelength diode laser is viable energy source for future powder bed fusion additive manufacturing systems, with potential for productivity scale-up using a DAM methodology.