Layer Formation Studies in Selective Laser Melting of Steel Powders

This paper advances the findings of the selective laser melting (SLM) of tool steel and stainless steel powders. The distinguishing feature is the melting of single layers in deep powder beds by a continuous CO2 laser. First, effect of process parameters on the surface roughness for each material is investigated. Based on these results combined with visual observation of the solidified tracks, the question is then discussed as how the processability of various type of steels is changed. The results show that surface morphology of layers is affected strongly by scan spacing, thereby giving a lower average roughness at reduced scan spacing. The effect of scan speed is also remarkable. In addition, other roughness parameters such as the peak height and skewness are found to be useful tools for evaluation of laser melted surfaces.Mechanical Engineerin

Further Developments in Process Mapping and Modelling in Direct Metal Selective Laser Melting

This paper advances previous reported work on the mapping and modelling of single tracks and layers produced in powder beds of tool steel and stainless steel powders by a CO2 laser. For single tracks it reports on predicted and simulated track masses. It validates the simulations, including the use of absorption close to 1.0 when cylindrical tracks are formed. It also reports on melt pool temperature calculations and estimated melt pool dimensions which are used, in conjunction with bed physical properties, to explain why the single tracks form as either continuous with a crescent shape cross-section, continuous with an elliptical section, discontinuously irregularly broken, discontinuously balled or only partially melted as scan speeds and laser powers change. It then extends its scope, experimentally, to consider effects of scan spacing on single layer formation.Mechanical Engineerin

Direct Selective Laser Sintering of Tool Steel Powders to High Density: Part A - Effects of Laser Beam Width and Scan Strategy

This paper describes progress on the Direct Selective Laser Sintering of M2 and H13 tool steel powders, comparing this with previous and further observations on stainless steel powders. The distinguishing feature is the melting of single tracks and layers in deep powder beds. The paper focuses on changing characteristics of the melt pool (mass, volume, aspect ratio, stability) and laser-powder interactivity as the laser beam width, power and scan speed change. It also compares the melt pool of neighbouring tracks during single layer construction. Simulations from a computer model to predict melt pool shape and dimension show reasonable agreement with experimental results at low scan speeds (0.5mm/s). But unexpected increases in melt depth above 1.0mm/s have been observed, suggesting higher values and more variability in laser absorptivity than expected, even approaching 1.0 for the CO2 laser radiation used in this work.Mechanical Engineerin

Micro-dimple rolling operation of metallic surfaces

The presence of micro-dimples on the surface of workpieces has long been known to have a positive impact on the friction control and wear resistance at the sliding surfaces. Several manufacturing processes have been used to generate micro-dimples on the surfaces of parts subjected to mechanical contact. Among those methods, metal forming-based techniques have received little attention in the literature mainly due to the challenges present in formation of sub-millimetre dimples using these processes. In this study, a micro-dimple rolling apparatus was developed to rapidly generate dimples with square cross-sections and side dimensions of smaller than 200 μm. The dimples were formed on the surface of a low-carbon structural steel and the effect of generated texture on friction and wear was studied through pin-on-disc test. In comparison with untextured surfaces, the results proved that the dimples formed by the proposed system could effectively reduce the friction coefficient by up to 23% and weight loss due to wear by up to 50%

Process Optimization and Microstructural Analysis for Selective Laser Melting of AlSi10Mg

AlSi10Mg is a typical casting alloy which is, due to its high strength/density ratio and thermal properties, highly demanded in aerospace and automotive industries [1]. The alloy combination of aluminium, silicon and magnesium results in a significant increase in strength and hardness which might even reach 300 MPa and 100 HBS, respectively, by applying a proper heat treatment [2]. Selective Laser Melting (SLM) of AlSi10Mg, may be interesting to open new application areas such as heat sinks with complicated geometry [3], and therefore is taken under investigation in this study. The process optimization of SLM for this alloy is not straightforward due to high reflectivity and conductivity of the material. In this study, the main goal is to optimize the process parameters, namely scan speed, scan spacing and laser power, to achieve almost full density and good surface quality taking productivity as a key issue. A relative density up to 99% is achieved with an average roughness (Ra) of about 20 µm measured on horizontal top surfaces while the scanning productivity is about 4.4 mm3/s. The reasons spherical and irregular porosity formed are investigated. Moreover, microstructural analysis of the SLM samples is conducted.Mechanical Engineerin

Process optimization and microstructural analysis for selective laser melting of AlSi10Mg

AlSi10Mg is a typical casting alloy which is, due to its high strength/density ratio and thermal properties, highly demanded in aerospace and automotive industries [1]. The alloy combination of aluminium, silicon and magnesium results in a significant increase in strength and hardness which might even reach 300 MPa and 100 HBS, respectively, by applying a proper heat treatment [2]. Selective Laser Melting (SLM) of AlSi10Mg, may be interesting to open new application areas such as heat sinks with complicated geometry [3], and therefore is taken under investigation in this study. The process optimization of SLM for this alloy is not straightforward due to high reflectivity and conductivity of the material. In this study, the main goal is to optimize the process parameters, namely scan speed, scan spacing and laser power, to achieve almost full density and good surface quality taking productivity as a key issue. A relative density up to 99% is achieved with an average roughness (Ra) of about 20 μm measured on horizontal top surfaces while the scanning productivity is about 4.4 mm3/s. The reasons spherical and irregular porosity formed are investigated. Moreover, microstructural analysis of the SLM samples is conducted.status: publishe