Adriaan Spierings

Influence of the particle size distribution on surface quality and mechanical properties in AM steel parts

Purpose – A recent study confirmed that the particle size distribution of a metallic powder material has a major influence on the density of a part produced by selective laser melting (SLM). Although it is possible to get high density values with different powder types, the processing parameters have to be adjusted accordingly, affecting the process productivity. However, the particle size distribution does not only affect the density but also the surface quality and the mechanical properties of the parts. The purpose of this paper is to investigate the effect of three different powder granulations on the resulting part density, surface quality and mechanical properties of the materials produced.Design/methodology/approach – The scan surface quality and mechanical properties of three different particle size distributions and two layer thicknesses of 30 and 45 μm were compared. The scan velocities for the different powder types have been adjusted in order to guarantee a part density≥99.5 per cent.Findings ...

Comparison of density measurement techniques for additive manufactured metallic parts

Purpose – In the optimisation of processing parameters for additive manufactured parts using, e.g. selective laser melting (SLM) or electron beam melting, the measurement of the part densities is essential and of high interest. However, there is no common standard. Different institutes and system providers are using their own principles and guidelines. This study investigates the accuracies of the three measurement principles: Archimedes method, microscopic analysis of cross sections and X‐ray scanning.Design/methodology/approach – A total of 15 test samples on five density levels (densities between 90 and 99.5 per cent) were produced using the SLM process. The samples are analysed regarding the accuracy of the measurement principles and their reproducibility taking into account influencing parameters like the buoyancy of a sample in air (Archimedes method) or different magnifications of a cross section.Findings – The Archimedes method shows a very high accuracy (±0.08 per cent for high densities) and rep...

Fatigue performance of additive manufactured metallic parts

Purpose – Additive manufacturing technologies such as, for example, selective laser melting (SLM) offer new design possibilities for a wide range of applications and industrial sectors. Whereas many results have been published regarding material options and their static mechanical properties, the knowledge about their dynamic mechanical behaviour is still low. The purpose of this paper is to deal with the measurement of the dynamic mechanical properties of two types of stainless steels.Design/methodology/approach – Specimens for dynamic testing were produced in a vertical orientation using SLM. The specimens were turned to the required end geometry and some of them were polished in order to minimise surface effects. Additionally, some samples were produced in the end geometry (“near net shape”) to investigate the effect of the comparably rough surface quality on the lifetime. The samples were tension‐tested and the results were compared to similar conventional materials.Findings – The SLM‐fabricated stain...

An integrated cost‐model for selective laser melting (SLM)

Purpose – The integration of additive manufacturing (AM) processes into a production environment requires a cost‐model that allows the precise estimation of the total cost per part, although the part might be produced in the same build job together with other parts of different sizes, complexities and quantities. Several cost‐models have been proposed in the past, but most of them are not able to calculate the costs for each single part in a mixed build job or are not suitable for Selective Laser Melting (SLM). The purpose of this paper is to develop a cost model, including all pre‐ and post‐processing steps linked to SLM.Design/methodology/approach – Based on collected data and the generic cost model of Alexander et al., an adapted model was developed for the SLM process including all required pre‐ and post‐processes. Each process was analysed and modelled in detail, allowing an evaluation of the influences of the different geometries on the cost of each part.Findings – By simultaneously building up mult...

Processing of metal-diamond-composites using selective laser melting

Purpose – The purpose of this paper is a feasibility study that was performed to investigate the basic processability of a diamond-containing metal matrix. Powder-bed-based additive manufacturing processes such as selective laser melting (SLM) offer a huge degree of freedom, both in terms of part design and material options. In that respect, mixtures of different powders can offer new ways for the manufacture of materials with tailored properties for special applications such as metal-based cutting or grinding tools with incorporated hard phases. Design/methodology/approach – A two-step approach was used to first investigate the basic SLM-processability of a Cu-Sn-Ti-Zr alloy, which is usually used for the active brazing of ceramics and superhard materials. After the identification of a suitable processing window, the processing parameters were then applied to a mixture of this matrix material with 10-20 volume per cent artificial, Ni-coated mono-crystalline diamonds. Findings – Even though the processing...

Optimization of SLM productivity by aligning 17-4PH material properties on part requirements

Purpose – The purpose of this study is the development of a global SLM-manufacturing optimization strategy taking into account material porosity and SLM process productivity. Selective laser melting (SLM) is a master forming process generating not only a near net shape geometry, but also the material with its properties. Research focuses primarily on optimal processing parameters for maximised material properties. However, the process allows also designing the material structure by internal porosity, affecting global material properties and the process productivity. Design/methodology/approach – The study investigates the influence of the main SLM process parameters on material porosity and consequently on the static mechanical properties of hardened SS17-4PH material. Furthermore, a model for the SLM scanning productivity is developed based on the SLM processing parameters. Findings – The results show a clear correlation between porosity level and mechanical properties. Thereby, the mechanical strength a...

Integrating Fiber Fabry-Perot Cavity Sensor Into 3-D Printed Metal Components for Extreme High-Temperature Monitoring Applications

This paper reports the methods of embedding into 3-D printed metal components a fused silica capillary designed to accept an in-fiber Fabry–Perot cavity-based extreme high-temperature sensor. The components are manufactured in stainless steel (SS316) by additive manufacturing using selective laser melting (SLM). The temperature sensor consists of a standard single-mode optical fiber with the F-P sensor located at the distal end of the fiber with the fiber being inserted into the capillary. The capillary is either directly embedded into the structure during the SLM build process or brazed into the structure in between the SLM build process, and the advantages and disadvantages of these two manufacturing approaches are discussed. Temperature sensing of up to 1000 °C inside the metal with an accuracy better than ±10 °C is reported. The capillary can be directly embedded in the component, which needs to be monitored, or it can be embedded in a metal coupon, which can be attached to a component by conventional welding technology, including the use of laser metal deposition (LMD). In the case of LMD, the sensor coupon can also be fully encapsulated by over cladding the coupon.

Approaches to minimize overhang angles of SLM parts

Purpose For geometries exhibiting overhanging surfaces, support structures are needed to dissipate process heat and to minimize geometrical distortions attributed to internal stresses. The use of support structures is often time- and cost-consuming. For this reason, this study aims to propose an approach which minimizes the use of such structures. Design/methodology/approach For minimizing the use of support structures, process parameters in combination with a contour-like exposure strategy are developed to realize support-less overhanging structures of less than 35°. These parameters are implemented in a shell-core strategy, which follows the idea of applying different processing strategies to the critical (overhanging) shell and the uncritical core of the part. Thereby, the core is processed with standard parameters, aiming a dense material. On the critical shell, optimized processing parameters are applied, reaching good results in terms of surface quality, especially at extreme overhang situations. Findings The results show that the selective laser melting (SLM) technology is able to realize support-less overhanging surfaces by choosing suitable scan strategies and process parameters. Particularly good results are always obtained when the exposure direction of the shell is parallel to the contour of the sample. Originality/value The validity of the results is demonstrated through the successful reproduction of the build strategy on two commercial SLM machines, reaching support-free builds of surfaces with an angle to the horizontal of less than or equal to 30°.

Temperature Monitoring of an SLM Part with Embedded Sensor

Selective Laser Melting (SLM) offers various new possibilities for the production of metallic components with respect to their design and complexity. The manufacturing process in layers enables accessibility and the possibility for manipulation and modification to each section of the part’s geometry. Hence the integration of sensors into the component during its manufacturing process is feasible. This approach is of enormous interest for various industrial sectors since sensor integration is a key enabler of industry 4.0. A sensor that has been embedded into a part during SLM production process facilitates not only a monitoring of this metallic part during its use phase in general but a monitoring of a spatially well-defined location within this part. The work presented in this paper specifically targets the integration of a temperature sensor into an SLM part. The sensor is embedded in a section of the part which is not accessible after the production process any more. Different concepts and strategies of sensor positioning and integration are investigated, focussing on an evaluation of the operating ability of these sensors after their embedding with the SLM process. Thus different methods to attach the sensor to the metallic part are presented. Furthermore the paper reports on the analysis of the influence of geometrical design features on the response behaviour and accuracy of the temperature measurement compared to conventionally conducted reference measurements.

Gute Poren – Erwünschte Porosität in SLM-Werkstücken

RTeJournal - Fachforum fur Rapid Technologie, Vol. 2015, Iss. 1 - Das Selective Laser Melting-Verfahren birgt enormes Potenzial fur Anwendungen im Werkzeugbau. So konnen durch den schichtweisen Aufbau sehr komplexe Werkzeug-Geometrien hergestellt werden. Auch eine konturnahe Kuhlung thermisch stark beanspruchter Flachen lasst sich mittels SLM umsetzen. Wahrend diese Vorteile aktuell vor allem im Kunststoffspritzguss bereits ausgenutzt werden, beginnt sich mit der Umformtechnik ein weiterer, bedeutender Industriesektor fur additive Fertigung von Metallbauteilen zu interessieren. In der Umformtechnik spielt nebst der Werkzeug-Temperierung vor allem deren Schmierung eine wichtige Rolle. Hier kommt eine weitere Starke des SLM zum Tragen: Materialeigenschaften in einem SLM-Werkstuck konnen durch eine entsprechende Prozessfuhrung gezielt gesteuert und so hinsichtlich ihres designierten Einsatzgebiets optimiert werden. Es wird gezeigt, dass sich entgegen dem eigentlichen Ziel des Prozesses – Bauteile mit moglichst hohen Dichten zu erzeugen – auch Strukturen generieren lassen, welche eine definierte Porositat aufweisen. So erlaubt eine Variation der Prozessparameter, solche Strukturen flexibel zu designen. Diese Poren konnen als Mikrokanale dienen und ermoglichen somit, dass einzelne Bereiche eines Umformwerkzeugs von einem Fluid durchstromt oder mit einem Fluid benetzt werden. Verschiedene derartige Stromungskorper werden vorgestellt, wobei neben der Prozessfuhrung speziell auf die Resultate ihrer Durchstromungsversuche eingegangen wird. Ausserdem werden Schwierigkeiten und Einschrankungen bei ihrer Fertigung erlautert.