Laser beam heat treatment in large-scale additive manufacturing

Abstract

Large-scale additive manufacturing (LSAM) has been developing a huge potential to address certain tasks in industrial applications over the last years. Particularly granule extrusion technologies enable the processing of an enormous variety of materials but also introduce new challenges in printing large-scale parts. Compared to fused layer modelling and due to larger nozzle diameters as well as higher extrusion rates strand geometry and consequently, process-related voids are enlarged. A promising approach to improve part quality is the integration of carbon dioxide laser (CO2) radiation into the additive manufacturing process to weld deposited strands by increasing the interface temperature. Experiments are conducted for polymethyl methacrylate (PMMA) and styrene-acrylonitrile (SAN) which are very good absorbers of the wavelength 10.6 µm. Due to the locally defined heat treatment, merely certain areas of the strands are heated to a desired temperature. This leads to a more complete diffusion. At the same time, temperature gradients in the overall part are avoided. By means of a thermographic camera, the temperatures at the re-melting process of deposited strands can be precisely monitored. Therefore, the relation between laser intensity and resulting temperature can be transferred into a repeatable process window. The interaction between laser and deposited material leads to a wider contact area between stacked strands. While flexural strength is not significantly affected, compared to specimens manufactured without any heat treatment bending force is increased by 66% (PMMA) and 48% (SAN), respectively. In addition, voids between adjacent strands are reduced by up to 57%.