Optimization of Scan Strategies in Selective Laser Melting of Aluminum Parts With Downfacing Areas

Selective laser melting (SLM) is an additive manufacturing technique in which metal products are manufactured in a layer-by-layer manner. One of the main advantages of SLM is the large geometrical design freedom. Because of the layered build, parts with inner cavities can be produced. However, complex structures, such as downfacing areas, influence the process behavior significantly. The downfacing areas can be either horizontal or inclined structures. The first part of this work describes the process parameter optimization for noncomplex, upfacing structures to obtain relative densities above 99%. In the second part of this research, parameters are optimized for downfacing areas, both horizontal and inclined. The experimental results are compared to simulations of a thermal model, which calculates the melt pool dimensions based on the material properties (such as thermal conductivity) and process parameters (such as laser power and scan speed). The simulations show a great similarity between the thermal model and the actual process

Development of a Smart Selective Laser Melting Process

The main objective of this dissertation is to improve the quality and robustness and to be able to estimate the quality of the Selective Laser Melting (SLM) process. This is realised by carefully examining the complete SLM process chain and by improving the intelligence of the system by predicting the quality and improving the robustness. To improve the robustness and quality, the job preparation is implemented in an in-house developed software to create job files for an SLM machine based on a 3D CAD model. Combining the recognition of critical zones with optimised parameters for each zone results in a higher local and more repeatable quality level for the production of these features. This software is tested for overhanging structures and thin wall structures. The methodology however is generic and can in future be implemented for any possible feature. This improved intelligence is combined with the developed monitoring system to make a first step in the field of automated quality estimation. By transferring logged data into maps and comparing them with CT images of the produced parts some correlations between the two images could be detected. These correlations are however influenced by a lot of different phenomena which make that the automated quality control needs further research to be applicable in industry.General introduction Selective Laser Melting Research objective and motivation Methodology Experimental Set-up Feature Optimization Quality Control Conclusionnrpages: 204status: publishe

Homogenizing the melt pool intensity distribution in the SLM process through system identification and feedback control

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A priori process parameter adjustment for SLM process optimization

Selective Laser Melting (SLM) is a layerwise production technique enabling the production of complex metallic parts. In the SLM process parts are built by selectively melting subsequent layers of powder by a laser beam. Nowadays a SLM machine is provided with a fixed scan strategy (laser power, scan velocity and scan pattern) throughout the full build process. However, the part’s geometry has a large influence on the stability of the process and therefore the quality of some features like for instance thin walls, sharp corners, down facing layers (layers above powder), is often poor. This problem can be overcome by using knowledge of the geometry a priori. This paper presents a methodology to detect critical features in the model of the part, based on the slicing data. In this way these critical features can then be processed with optimized parameters. As a proof of concept this a priori parameter adaptation methodology is applied on production overhang.status: publishe

EDM technology and strategy development for the manufacturing of complex parts in SiSiC

Silicon carbide (SiC) is an extremely hard and difficult-to-shape engineering ceramic material used extensively in industry because of its superior mechanical properties, wear and corrosion resistance even at elevated temperature. Conventional ceramic processing and structuring techniques such as injection molding and grinding are costly and difficult to obtain flawless complex shaped components. By infiltrating free Si into the SiC, the electrical conductivity of the matrix is largely improved. Thus it can be machined by electrical discharge machining (EDM). In this paper, a die-sinking EDM technology for manufacturing components in a commercial available silicon infiltrated silicon carbide (SiSiC) is developed. The influences of the major operating EDM parameters (discharge current ie, open gap voltage ui, discharge duration te and pulse interval to) of the iso energetic generator on the machining performances like Material Removal Rate (MRR), Tool Wear Ratio (TWR) and surface roughness (Ra) are examined. Relaxation pulses which have lower energy input are also considered to improve the surface quality. Furthermore, the topography and surface integrity of the material after the EDM process are analysed to determine the corresponding material removal mechanism. With the developed machining strategy, a sample piece with designed features such as ribs, a deep cavity and chamfers are manufactured to examine the machining performances. © 2009 Elsevier B.V. All rights reserved.status: publishe

Optimisation of Scan Strategies in Selective Laser Melting of Aluminium Parts With Downfacing Areas

Selective Laser Melting (SLM) is an additive manufacturing technique in which metal products are manufactured in a layer-by-layer manner. One of the main advantages of SLM in the large geometrical design freedom. Because of the layered build, parts with inner cavities can be produced. However, complex structures, such as downfacing areas, influence the process behavior significantly. The downfacing areas can be either horizontal or inclined structures. The first part of this work describes the process parameter optimization for noncomplex, upfacing structures to obtain relative densities above 99%. In the second part of this research, parameters are optimized for downfacing areas, both horizontal and inclined. The experimental results are compared to simulations of a thermal model, which calculates the melt pool dimensions based on the material properties (such as thermal conductivity) and process parameters (such as laser power and scan speed). The simulations show a great similarity between the thermal model and the actual process.status: publishe

Online Quality Control of Selective Laser Melting

Selective Laser Melting (SLM) is an Additive Manufacturing technique which allows producing three-dimensional metallic parts from powder material, using a layer-by-layer fashion. Typical applications of this technology are parts with high geometrical complexity or internal features such as biomedical implants or casting molds with conformal cooling channels. In order to break through in industries with very high quality standards (such as aerospace industries), an important issue to be addressed is quality monitoring and control during the actual building process. Online quality control can significantly increase the robustness of the process by enabling to check the quality of the building process in the earliest possible stage, such that eventually corrective actions can be taken during the process. This is in contrast with on-line and a posteriori quality control which does not allow taking corrective measures if the quality of the part does not meet the desired quality standard. The development of a framework for online quality control of Selective Laser Melting is the subject of this paper. The framework consists of two complementary systems: A system for visual inspection of powder deposition and a system for online and real-time monitoring of the melt pool. A combination of these two systems enables to guarantee the quality of SLM parts with high confidence.status: publishe

Production of AlSi10Mg parts with downfacing areas by Selective Laser Melting

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Online Quality Control of Selective Laser Melting

Selective Laser Melting (SLM) is an Additive Manufacturing technique which allows producing three-dimensional metallic parts from powder material, using a layer-by-layer fashion. Typical applications of this technology are parts with high geometrical complexity or internal features such as biomedical implants or casting molds with conformal cooling channels. In order to break through in industries with very high quality standards (such as aerospace industries), an important issue to be addressed is quality monitoring and control during the actual building process. Online quality control can significantly increase the robustness of the process by enabling to check the quality of the building process in the earliest possible stage, such that eventually corrective actions can be taken during the process. This is in contrast with on-line and a posteriori quality control which does not allow taking corrective measures if the quality of the part does not meet the desired quality standard. The development of a framework for online quality control of Selective Laser Melting is the subject of this paper. The framework consists of two complementary systems: a system for visual inspection of powder deposition and a system for online and real-time monitoring of the melt pool. A combination of these two systems enables to guarantee the quality of SLM parts with high confidence.Mechanical Engineerin

Melt Pool System Identification and Feedback Control for Selective Laser Melting

Observation of the melt pool, formed during a normal Selective Laser Melting (SLM) build process, shows a non-uniform melt pool intensity distribution throughout one layer and scan track. The associated variation of the melt pool intensity can cause unwanted defects (e.g. pores). The change in melt pool intensity and possible defects cannot only be observed within one layer but will propagate itself throughout all the layers. To counteract the change in melt pool characteristics, a system identification was performed on the melt pool intensity, during several layers, in function of the laser power. The system identification provides a mathematical model of the melt pool intensity that was used for the development of a feedback controller. The benefit of the feedback controller was simulated.status: publishe