Investigation on Occurrence of Elevated Edges in Selective Laser Melting

Selective laser melting (SLM) is a layer-wise material additive process for the direct fabrication of functional metallic parts. During the process, successive layers of metal powder are fully molten and consolidated on top of each other by the energy of a high intensity laser beam. The process is capable of producing almost fully dense three-dimensional parts having mechanical properties comparable to those of bulk materials. However, one of the problems encountered in SLM process is the occurrence of elevated ridges of the solidified material at the edges of the successive layers. Those ridges reduce the dimensional accuracy and topology of the top surface. The edge-effect problem is encountered not only in SLM, but also in other production techniques applying melting processes such as LENS® (The Laser Engineered Net Shaping) and EBM (Electron Beam Melting). In this study, the reasons for elevated edges and solutions to this problem are investigated and reported. Different scan strategies as well as different hatching and contour parameters are tested to reduce the edge-effect problem. Besides, the influence of applying laser re-melting in combination to selective laser melting has been investigated. It turns out that re-melting layers deposited by SLM improves the part density and surface roughness, but creates on its own elevated edges.Mechanical Engineerin

Rapid Manufacturing Research at the Catholic University of Leuven

Additive layer manufacturing (LM) is commonly used for manufacturing prototypes (RP), tools (RT) and functional end products (RM) in a wide range of industries including medicine, automotive and aerospace industries. One of the key advantages of RM over conventional machining is the elimination of molds, dies, and other forms of tooling, and the consequent eradication of tooling restrictions. Moreover, almost infinite geometrical complexity, mass customization, individualization and material flexibility give RM other superior properties. For RM to prosper, the limitations of existing additive processes must be overcome, e.g. limitations such as repeatability, reliability, surface finish, material properties and productivity. At the University of Leuven, selective laser melting/sintering (SLM/SLS) of metals, ceramics and polymers is studied aiming to develop the process to a level enabling RM of complex and customized parts in a competitive way. In order to achieve this overall goal, a monitoring and control system of SLM/SLS for metals is installed in an in-house developed machine to process metals. Laser re-melting and selective laser erosion (SLE) are employed during or after SLM/SLS in order to improve surface quality and density as well as to modify the microstructure and mechanical properties. For medical applications, design and manufacturing of scaffolds and dental prostheses with required mechanical properties are conducted including the investigation of the influence of structural parameters (porosity, cell size and cell shape) on the cell growth. In order to widen the palette of applicable materials, K.U.Leuven does not only focus on metallic materials, but also on direct or indirect SLM of ceramics as well as machine modifications such as pre-heating modules and deposition systems necessary to handle ceramics.status: publishe

Improving Productivity Rate in SLM of Commercial Steel Powders

Selective laser melting (SLM) is a powder-based additive manufacturing process capable to generate 3D parts from a CAD model. The competitive advantages of SLM are geometrical freedom, shortened design to product time, mass customization and material flexibility. Recent technical improvements have made a shift of the process applications from rapid prototyping to rapid manufacturing. Currently there is a growing interest in industry for applying this technology for generating high geometrical complexity and low quantity parts, among them are medical parts and tooling inserts. To turn the SLM process into a production technique for real components, some conditions have to be fulfilled. Productivity is one of those conditions that plays a key role for further applications of this process and that is discussed in this paper. However, compared to selective laser sintering (SLS), the productivity rate is lower because SLM is carried out at scanning speeds much slower than the speed range normally used in SLS. This study attempts to improve the SLM parts productivity rate for commercial steel powders, 316L stainless steel and DIN 1.2709 maraging steel. The influences of processing parameters on the parts' relative density as well as surface quality are investigated. A wide range of scanning speed, scan spacing and layer thickness as well as part shape's effect are considered. The effect of particle size on the results is also investigated.status: publishe

Fused Deposition Modeling and Fabrication of a Three-dimensional Model in Maxillofacial Reconstruction

The utilization of customized three-dimentional (3D) models based on patient's computed tomography (CT) scan data and by assistance of additive manufacturing/rapid prototyping (AM/RP) techniques for 3D reconstruction is one of the applicable trends for reducing the errors and time saving during surgeries. In the present study, the methodology of the fabrication of a custom-made 3D model based on converting CT scan data to standard triangle language (STL) format for a 33-years old male patient who was suffering from an accident trauma was described. The 3D model of the patient’s skull was fabricated and applied in preoperative planning. It was used for designing a comprehensive plan for rehabilitation of the damaged orbit to restore the appearance and bone reconstruction of the patient. Before fabricating the model, the accuracy of protocols used in converting CT scan data into STL file was evaluated. Then, the model was fabricated by a fused deposition modeling (FDM) machine. Using this procedure led to a maximum of 1.4% difference between the virtual model in the software and the fabricated 3D model in the fracture site. The present technique reduced operation time significantly. In addition, following eight months from the operation, the treatment approach ensured the patient's fractures healing process

MICROSTRUCTURAL ANALYSIS AND PROCESS OPTIMIZATION FOR SELECTIVE LASER MELTING OF AlSi10Mg

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Part and material properties in selective laser melting of metals

Recent technical improvements of additive manufacturing (AM) have shifted the application of these processes from prototyping to the production of end-use parts either as customised or series. Selective laser melting (SLM) holds a special place within the variety of AM processes due to the flexibility of materials being processed, and the capability to create functional components having mechanical properties comparable to those properties of bulk materials. The process, however, is characterized by high temperature gradients and densification ratio that in turn may have significant impact on the microstructure and properties of SLM parts. This article presents the state of the art in SLM and aims at understanding the SLM part and material properties specifications to form a picture of potential application of this process. The paper demonstrate that, although SLM can result in functional parts with controlled microstructure, there is still a long way to go in tuning the process parameters and building patterns in order to achieve the desirable grain structure and properties.status: publishe

Additive Manufacturing: Selective Laser Sintering & Selective Laser Melting

Additive Manufacturing: Selective Laser Sintering & Selective Laser Melting: robustness, reliability and flexibility.status: publishe