This paper deals with various selective laser melting (SLM) processing strategies for aluminum 2618 powder in order to get material densities and properties close to conventionally-produced, high-strength 2618 alloy. To evaluate the influence of laser scanning strategies on the resulting porosity and mechanical properties a row of experiments was done. Three types of samples were used: single-track welds, bulk samples and samples for tensile testing. Single-track welds were used to find the appropriate processing parameters for achieving continuous and well-shaped welds. The bulk samples were built with different scanning strategies with the aim of reaching a low relative porosity of the material. The combination of the chessboard strategy with a 2 × 2 mm field size fabricated with an out-in spiral order was found to eliminate a major lack of fusion defects. However, small cracks in the material structure were found over the complete range of tested parameters. The decisive criteria was the elimination of small cracks that drastically reduced mechanical properties. Reduction of the thermal gradient using support structures or fabrication under elevated temperatures shows a promising approach to eliminating the cracks. Mechanical properties of samples produced by SLM were compared with the properties of extruded material. The results showed that the SLM-processed 2618 alloy could only reach one half of the yield strength and tensile strength of extruded material. This is mainly due to the occurrence of small cracks in the structure of the built material.

The aim of this study is to observe the effect of process parameters on residual stresses and relative density of Ti6Al4V samples produced by Selective Laser Melting. The investigated parameters were hatch laser power, hatch laser velocity, border laser velocity, high-temperature preheating and time delay. Residual stresses were evaluated by the bridge curvature method and relative density by the optical method. The effect of the observed process parameters was estimated by the design of experiment and surface response methods. It was found that for an effective residual stress reduction, the high preheating temperature was the most significant parameter. High preheating temperature also increased the relative density but caused changes in the chemical composition of Ti6Al4V unmelted powder. Chemical analysis proved that after one build job with high preheating temperature, oxygen and hydrogen content exceeded the ASTM B348 limits for Grade 5 titanium.

Kurzfassung: Der Vorgang der Erstarrung hat einen wesentlichen Einfluss auf die Mikrostruktur und die Hochtemperatureigenschaften von Stählen. Besonders bei Prozessen des Form- und Stranggusses ist die Gewinnung von Materialkennwerten an der Gussstruktur direkt nach dem Aufschmelzen und Erstarren von großer Bedeutung. Weiters kann man die Heißrissbildung im Laborversuch mit einer vorhergehenden Aufschmelzung realitätsnäher untersuchen. Es werden konventionelle Versuchsmethoden zur Bestimmung von Hochtemperatur-Materialkennwerten wie der Duktilität und Festigkeit von Stählen und eine neue Methodik zur Aufschmelzung von Heißzugproben vorgestellt. Die Aufschmelzung der Proben erfolgt bei dieser Testmethode ohne eine konventionelle Schmelzbadsicherung. Eine ungestörte Temperaturmessung während des ganzen Versuches ist damit gewährleistet.

Selective Laser Melting (SLM), as a fast-growing metal-based Additive Manufacturing technology, allows to produce high strength parts with complex geometries. However, limited part properties in the as-built condition require effortful post-processing tasks (e.g. milling, drilling, polishing) to meet technical specifications and tolerances. This significantly increases the manufacturing costs of SLM parts. To address this problem, the concept of Direct Machining is presented. Direct Machining is defined as the post-processing of SLM parts via machining without prior removal of the parts from the build platform to achieve economic benefits. For this, the support structures have to withstand the occurring cutting forces during machining — a task for which they were not initially designed. The aim of this study is to investigate the load capacity of 316L SLM support structures. For this, machining experiments on a five-axis milling machine were conducted. Cutting parameters, support geometries and support volume were varied and the cutting forces were measured to investigate their influence on the stability of the support structures. Results show, that deliberate SLM support structures allow precise machining directly on the build platform. Furthermore, a theoretical load model of Direct Machining is developed. Based on this, further optimization of the support structures regarding cutting force absorption and material volume are presented.