Partitioning of laser energy during directed energy deposition

An energy balance that describes the transfer of energy is proposed for the laser-based directed energy deposition process. The partitioning of laser energy was experimentally measured and accurately validated using a special process calorimeter for Ti-6Al-4V and Inconel 625™ alloys. The total energy provided by the laser was partitioned as: the energy directly absorbed by the substrate, the energy absorbed by the powder stream and deposited onto the substrate, the energy reflected from the substrate surface, and the energy reflected or absorbed and lost from the powder stream. Titanium alloy Ti-6Al-4V showed higher overall or bulk absorption than the Inconel 625™ alloy. Processing with powder resulted in lower laser energy absorption within the substrate than without powder, due to the “shadowing” effect of the powder stream within the beam and loss of energy representing unfused powder. During processing at a laser power of approximately 1 kW the total energy absorbed during the deposition process was found to be 42% for the Ti-6Al-4V alloy and 37% for the Inconel 625™ alloy. Under these conditions 14% of the total energy was lost by the Ti-6Al-4V unfused powder; whereas only 11% was lost by the Inconel 625™ powder.