Papers by Keyword: Laser Re-Melting

Abstract: Laser metal deposition (LMD) is an additive manufacturing process highly adaptable to medium to large sized components with bulky structures as well as thin walls. Low surface quality of as-deposited LMD manufactured components with average roughness values (R_a) around 15-20μm is one of the main drawbacks that prevent the use of the part without the implementation of costly and time-consuming post-processes. In this work laser re-melting is applied right after LMD process with the use of the same equipment used for the deposition to treat AISI 316L thin walled parts. The surface quality improvement is assessed through the measurement of both areal surface roughness S_a(0.8mm) QUOTE and waviness W_a QUOTE (0.8mm) parameters. Moreover, roughness power spectrum is used to point out the presence of principal periodical components both in the as-deposited and in the re-melted surfaces. Then, the transfer function is calculated to better understand the effects of laser re-melting on the topography evolution, measuring the changes of individual components contributing to the surface roughness such as the layering technique and the presence of sintered particles. Experiments showed that while low energy density inputs are not capable to properly modify the additive surface topography, excessive energy inputs impose a strong periodical component with wavelength equal to the laser scan spacing and directionality determined by the used strategy. When a proper amount of energy density input is used, laser re-melting is capable to generate smooth isotropic topographies without visible periodical surface structures.

Abstract: Ti-Nb based alloys have the potential to be used as structural implant materials due to their excellent bio-compatibility and ability to reduce stress shielding. The idea to additively manufacture Ti-Nb based alloys using selective laser melting (SLM) technology can further improve the resultant implant quality. However, the lack of economically sound and readily available pre-alloyed powder has pushed for the usage of composite powder as a means to hasten research pace in fabricating new alloy systems via SLM. The usage of Ti-Nb composite powder can lead to several problems, particularly the issue of macro-segregation. Hence, this paper presents the potential of laser re-melting scanning strategy to address macro-segregation without sacrificing (or even improving) density of parts fabricated by SLM.

Abstract: The surface of Al2O3 coating sprayed on 40Cr substrate was re-melted with high power continuous CO2 laser, and its micro-hardness and residual stresses were measured, respectively. The strengthening mechanism of Al2O3 coating by laser re-melting was analyzed and discussed. The experimental results shown that the surface of Al2O3 coating by laser re-melting is neat and smooth, and its compositions are even, its structures are compact, and Al2O3 coating is evenly distributed in its surface with grain forms, and its micro-hardness increases about 200%; Residual stress of Al2O3 coating by laser re-melting is changed into compressive stress from tensile stress, which is benefit to improving bonding strength of coating-substrate interface.

Abstract: This paper presents the results of a recent comprehensive investigation of selective laser melting (slm) of prealloyed gas and water atomised M2 and H13 tool steel powders. The objective of the study was to establish the parameters that control the densification of single and multiple layers with the aim of producing high density parts without the need for infiltration. Powders were processed using continuous wave (CW) CO2 and Nd:YAG lasers. Relationships between alloy composition, powder particle size and shape, flowability, microstructure (phases present, their size, morphology and distribution), track morphology, post scanned density, surface finish and scan conditions (Laser power, spot size and scan speed) are discussed for single track, single layer and multi-layer (up to 25 layers) constructions. Processing with a Nd:YAG laser with powders placed on substrates rather than on a loose powder bed gave more stable builds than with the CO2 laser. Using the Nd:YAG laser densities up to ~90% relative were possible with H13 powder compared with a maximum of ~70% for M2 in multi-layer builds. Maximum density achieved with CW CO2 processing was only ~60%, irrespective of powder composition. The paper compares the processibility of these materials with stainless steel powders processed to higher densities (up to 99% relative) under similar conditions. The results of the work show that a crucial factor for high density processing is melt pool wettability and this is controlled largely by carbon content; low carbon contents producing better wettability, flatter tracks and higher densities. The significance of this observation for the processing high alloy steels by slm will be discussed.