Effect of Stainless Steel Additive Manufacturing On Heat Conductivity and Urea Deposition

Abstract: Hydroforming is the manufacturing process that Scania uses to produce exhaust pipes with complex shape and high durability.  Selective Laser Melting is the process used by designers to print prototype pipes and perform emissions tests before mass production. Results from previous tests at Scania showed superior performance of 3D printed pipes compared to hydroformed components during emissions test as the 3D printed pipes were able to transfer heat faster than hydroformed pipes.  To understand the reason behind this mismatch, the effect of selective laser melting parameters on energy density, relative density, grain size and thermal conductivity are investigated.  These properties have direct impact on heat transfer. Ten samples were fabricated using the same laser power and layer thickness but different combinations of scanning speed and hatch distance.   Samples were then subject to microstructural analysis using an optical microscope and average grain size measurement using image analysis software called Imagej. The  density  of  each  sample  was  measured  using  the  Archimedes  method. Moderate correlation is found between energy density and relative density. No ranking of the selective laser melting parameters with respect to forming the highest density was achieved because of the high uncertainties involved with the density measurement technique.  Thermal conductivity was measured us- ing the one dimensional heat flow equation with an appropriate experimental set up. Thermal conductivity seems to be more influenced by relative density and direction of printing layers than the energy density and grain size.  This conclusion is not statistically significant due to high uncertainty involved in the measurement of thermal conductivity.  More advanced and accurate tech- nologies need to be used in the future to measure both density and thermal conductivity in order to find the most suitable selective laser melting parameters for Scania’s prototype pipes. The findings of this research can be used as a foundation for future research related to urea deposition on 3D printed pipes.