Producing Crack-Free, High Density M2 HSS Parts by Selective Laser Melting: Pre-Heating the Baseplate

Cracks and delamination, resulting from residual stresses are a barrier in the world of Additive Manufacturing and Selective Laser Melting (SLM) that prohibits the use of many metals in this field. By preheating the baseplate, thermal gradients are lowered and stresses can be reduced. In this work, some initial tests were performed with M2 Tool Steel. Results show that pre-heating enables the production of dense M2 parts. The influence of pre-heating on density and mechanical and physical properties is investigated. The paper shows many promising results for the production of SLM parts in materials that are very sensitive to crack formation and delamination. When using a pre-heating of 200°C, crack-free parts were produced with a relative density of 99.8%.Mechanical Engineerin

TOWARDS THE LIMITS IN COPPER LATTICE PRODUCTION VIA FIBER LASER POWDER BED FUSION

Additive manufacturing of copper, by means of Laser Powder Bed Fusion (LPBF), paves the way for innovation in thermal systems and heat transfer devices. Recent simulations have shown that by interchanging typical fin designs with more complex structures, an overall improvement in pressure drop and weight can be obtained while offering the same thermal performance. Here, small-scale lattice structures are especially of interest for AM as they form a reliable, periodic infill. However, until now, their study has been mainly theoretical. To analyze these structures in more detail, an in-house built LPBF machine at KU Leuven has been successfully used to manufacture pure copper parts. Measurements showed a conductivity exceeding 100%IACS, which is the result of low contamination and low porosity in the as-built material. In this work, the parameter optimization for thin-walled lattices is discussed, the limitations in terms of minimal feature size are described and physical mechanisms behind these limitations are uncovered.Mechanical Engineerin

Automated motion analysis of bony joint structures from dynamic computer tomography images: A multi-atlas approach

Dynamic computer tomography (CT) is an emerging modality to analyze in-vivo joint kinematics at the bone level, but it requires manual bone segmentation and, in some instances, landmark identification. The objective of this study is to present an automated workflow for the assessment of three-dimensional in vivo joint kinematics from dynamic musculoskeletal CT images. The proposed method relies on a multi-atlas, multi-label segmentation and landmark propagation framework to extract bony structures and detect anatomical landmarks on the CT dataset. The segmented structures serve as regions of interest for the subsequent motion estimation across the dynamic sequence. The landmarks are propagated across the dynamic sequence for the construction of bone embedded reference frames from which kinematic parameters are estimated. We applied our workflow on dynamic CT images obtained from 15 healthy subjects on two different joints: thumb base (n = 5) and knee (n = 10). The proposed method resulted in segmentation accuracies of 0.90 ± 0.01 for the thumb dataset and 0.94 ± 0.02 for the knee as measured by the Dice score coefficient. In terms of motion estimation, mean differences in cardan angles between the automated algorithm and manual segmentation, and landmark identification performed by an expert were below 1◦. Intraclass correlation (ICC) between cardan angles from the algorithm and results from expert manual landmarks ranged from 0.72 to 0.99 for all joints across all axes. The proposed automated method resulted in reproducible and reliable measurements, enabling the assessment of joint kinematics using 4DCT in clinical routine

Preclinical validation of the advection diffusion flow estimation method using computational patient specific coronary tree phantoms

Coronary computed tomography angiography (CCTA) does not allow the quantification of reduced blood flow due to coronary artery disease (CAD). In response, numerical methods based on the CCTA image have been developed to compute coronary blood flow and assess the impact of disease. However to compute blood flow in the coronary arteries, numerical methods require specification of boundary conditions that are difficult to estimate accurately in a patient-specific manner. We describe herein a new noninvasive flow estimation method, called Advection Diffusion Flow Estimation (ADFE), to compute coronary artery flow from CCTA to use as boundary conditions for numerical models of coronary blood flow. ADFE uses image contrast variation along the tree-like structure to estimate flow in each vessel. For validating this method we used patient specific software phantoms on which the transport of contrast was simulated. This controlled validation setting enables a direct comparison between estimated flow and actual flow and a detailed investigation of factors affecting accuracy. A total of 10 CCTA image data sets were processed to extract all necessary information for simulating contrast transport. A spectral element method solver was used for computing the ground truth simulations with high accuracy. On this data set, the ADFE method showed a high correlation coefficient of 0.998 between estimated flow and the ground truth flow together with an average relative error of only 1 % . Comparing the ADFE method with the best method currently available (TAFE) for image-based blood flow estimation, which showed a correlation coefficient of 0.752 and average error of 20 % , it can be concluded that the ADFE method has the potential to significantly improve the quantification of coronary artery blood flow derived from contrast gradients in CCTA images. </p

PROCESS AND MATERIAL OPTIMISATIONS FOR INTEGRATION OF CHOPPED GLASS FIBRES IN LASER SINTERED POLYMER PARTS

Additively manufactured polymer composites gain popularity in a variety of industries such as aerospace, biomedical and automotive. Laser sintering (LS) is a well-known AM process that typically uses polyamide which can serve as matrix material. Hence LS has the potential to produce reinforced polymers that can meet demanding requirements. In previous research, issues with powder flowability and poor fibre dispersion led to limited increase of mechanical properties. To overcome this, a novel fibre deposition system was recently developed and optimised at KU Leuven to successfully produce fibre reinforced LS samples with random inter- and intralayer fibre orientations. A limited but promising influence of deposited glass fibres on produced LS parts was noted after mechanical testing. In this work, the influence of different (heat) treatments on glass fibres used during LS will be discussed as well as the resulting differences in the fibre/matrix behaviour as analysed through hot stage microscopy.Mechanical Engineerin

Occupational Radiation Protection in Interventional Radiology: A Joint Guideline of the Cardiovascular and Interventional Radiology Society of Europe and the Society of Interventional Radiology

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Homogenizing the Melt Pool Intensity Distribution in the SLM Process through System Identification and Feedback Control

The common scanning strategies in Selective Laser Melting lead to an inhomogeneous melt pool intensity distribution throughout the different layers and scan tracks. This results in various defects such as porosity at the edges, residual stresses, or even excessive warping and delamination. In this research, this issue is resolved by the implementation of an on-line and real-time PID feedback controller. The PID feedback controller will alter the laser power based upon the melt pool intensity resulting in a homogeneous intensity distribution throughout the different scan tracks and layers. 2D intensity maps can be generated from the on-line monitoring system during the production of a benchmark part and will serve as validation for the PID feedback controller.Mechanical Engineerin

The Influence of a Dynamically Optimized Galvano Based Laser Scanner on the Total Scan Time of SLM Parts

Most commercially available Selective Laser Melting (SLM) machines use galvano based laser scanner deflection systems. This paper describes the influence of the dynamical optimization of such galvano based laser scanner on the total scan time. The system identification of a galvano laser scanner was performed in combination with the development and implementation of an optimal ‘Input Shaper’. Tests were performed on lattice structured SLM parts. The process time was hereby compared, with and without the use of the optimal ‘Input Shaper’. Significant scan time reduction was observed when using the optimal ‘Input Shaper’.Mechanical Engineerin