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Additive manufacturing techniques such as laser powder bed fusion (LPBF) enable production of components with highly complex geometries. However, their as-built surface quality and geometrical precision remain insufficient for high-end applications, requiring further post-processing. Unlike horizontal surfaces, inclined up-facing surfaces cannot be improved by in-situ remelting, as they remain covered with powder. In this research a dual laser setup replaces the traditional single-laser layout. Surface enhancement is achieved in two steps: a nanosecond pulsed laser is used to remove powder from selected areas via laser-induced shock waves (LISW), so that these surfaces can be remelted with a continuous wave laser. This work presents an investigation of in-situ remelting (laser polishing) of inclined surfaces in their as-built orientation, after powder removal by brushing or using LISW. Particular focus is given on the effect of process parameters (laser power, scanning speed, number of scans) on the surface and subsurface quality and dimensional accuracy. As a result, this in-situ processing leads to a comparable surface texture on horizontal and inclined surfaces, without introducing any major subsurface defects. ispartof: Journal Of Materials Processing Technology vol:298 status: Published online more...

Fabrication of fully dense and highly conductive copper alloy parts via laser-based additive manufacturing (L-AM) is challenging due to the high optical reflectivity and high thermal conductivity. To overcome this, the use of optically absorptive surface-modified copper powders is being evaluated in the laser powder bed fusion (LPBF) process. Although the surface-modified powders exhibit high optical absorption at room temperature, not all of them allow the fabrication of fully dense parts at a laser power below 500 W. Accordingly, this article proposes the use of optically absorptive carburized CuCr1 powder for the consistent fabrication of copper parts. Moreover, a densification mechanism of parts is discussed to explain the distinct LPBF processing behavior of different surface-modified powders, such as carburized CuCr1 and carbon mixed CuCr1 powders, albeit having similar room temperature optical absorption. This investigation clearly outlines the advantage of a firmly bonded modified layer present on the surface of the carburized CuCr1 powder over a loosely attached carbon nanoparticle layer present in the carbon-mixed CuCr1 powder. Apart from the successful fabrication of CuCr1 parts, fabricated parts are subjected to two different post-heat treatments, and it is shown that the final properties can be customized by applying tailored post-heat treatments. ispartof: Materials & Design vol:198 status: published more...

Laser powder bed fusion (L-PBF) is one of the most promising additive manufacturing (AM) methods which provides an exceptional opportunity to improve the existing designs and move toward fabricating fine features and complex geometries with higher efficiencies. Considering the layer-wise nature of this technique, the possibility of fabricating fine features is tied to the ability to deposit thin powder layers in this process. Since the powder layer thickness is directly dictated by the powder particle size, finer powders are required to further enhance the ability of the L-PBF technique in manufacturing fine features and intricate geometries. Accordingly, this study aims at investigating the processability of fine AlSi10Mg powder (D50 = 9 µm) by using the L-PBF process. The densification level, surface quality and dimensional accuracy of the final parts are investigated in a wide range of process parameters and are compared to those manufactured by the commonly used AlSi10Mg powder (referred to as coarse powder with D50 = 40 µm). The underlying reasons behind the different processability of fine and coarse powders are explored from the density, surface quality, microhardness and dimensional accuracy viewpoints through analyzing the flowability, bed packing density and optical absorption of powders. Moreover, the process-microstructure-microhardness relationship is assessed in detail for both fine and coarse powders. This study reinforces the idea that the utilization of fine powders in the range used in this study for L-PBF processing is rather challenging. ispartof: Additive Manufacturing vol:37 status: Published online more...

After laser powder bed fusion (LPBF) of an ultra-strong in situ TiC whisker reinforced β-Ti composite, this paper investigates the evolution of microstructure and mechanical properties in response to heat treatment at different temperatures. Using in depth nano-SEM and TEM analyses, it is shown that ageing at 400 °C rounds the whiskers, annihilates the strain fields and grows Mo segregated nano-cells, but without improving the ductility. In contrast, ageing at 600 °C enables the transformation of metastable β to a lamellar β + α, leading to a dual phase matrix embedding TiC particles. This is in such a manner that extra ageing at 600 °C coalesces the nano-lamellar α + β microstructure to form a coarser micro-lamellar α + β matrix. This microstructure achieves 66 % of the compressive deformation of Cp-Ti, and over 1400 MPa compressive strength after 1 h of ageing at 600 °C. Despite this success under compression, hard and stiff TiC particles may still cause large spherical fractured voids, severely limiting the plastic deformation under tension. After laser powder bed fusion (LPBF) of an ultra-strong in situ TiC whisker reinforced β-Ti composite, this paper investigates the evolution of microstructure and mechanical properties in response to heat treatment at different temperatures. Using in depth nano-SEM and TEM analyses, it is shown that ageing at 400 °C rounds the whiskers, annihilates the strain fields and grows Mo segregated nano-cells, but without improving the ductility. In contrast, ageing at 600 °C enables the transformation of metastable β to a lamellar β + α, leading to a dual phase matrix embedding TiC particles. This is in such a manner that extra ageing at 600 °C coalesces the nano-lamellar α + β microstructure to form a coarser micro-lamellar α + β matrix. This microstructure achieves 66 % of the compressive deformation of Cp-Ti, and over 1400 MPa compressive strength after 1 h of ageing at 600 °C. Despite this success under compression, hard and stiff TiC particles may still cause large spherical fractured voids, severely limiting the plastic deformation under tension. ispartof: Additive Manufacturing vol:36 status: published more...

Surface topography measurements are vital in industrial quality control. Linear roughness measurements are among the most preferred methods, being quick to perform and easy to interpret. The ISO 16610 standard series prescribes filters that can be used for most cases, but has limitations for restricted measurement lengths. This is because the standard filter type is a Gaussian filter, which like most instances of kernel convolution filters has no output near the edges of the profile, effectively shortening the length of the filtered output profile as compared to the input. In some cases, this leads to a lack of representative data after filtration. Especially in fields such as Additive Manufacturing (AM) this becomes a problem, due to the high “roughness to measurable data length”-ratio that characterizes complex AM parts. This paper describes a method that allows to overcome this limitation:•A method for circular padding of short measured tracks is described and validated.•A flexible profile data post-processing tool was developed in MATLAB to grant users more control over the data analysis. Results obtained from roughness profiles long enough for normal ISO procedures are shown to not change significantly when circularly padded. When only a shorter section of the data is available, where the standard protocol would not be able to compute a filtered profile and related parameters anymore, the circular padding method is shown to lead to results that are in good agreement with the ISO standard procedures., Graphical abstract Image, graphical abstract more...

© 2019 Elsevier Ltd Selective laser melting (SLM) was used to fabricate tungsten heavy alloy (WHA) with a nominal composition of W-7Ni-3Fe (wt%). Depending on the processing parameters (laser power, scanning speed, preheating, etc.), three different bonding mechanisms were observed, i.e., liquid phase sintering, partial melting and complete melting. The difference in applied energy density also reflected in a variation of the final composition, amount of W dendrites in γ-phase and the W grain contiguity. High density materials (>95%TD) were produced under optimal processing conditions. The effect of the as-built microstructure and post-process heat-treatment on the properties of WHA processed by SLM was evaluated. In the as-built condition, the WHA exhibited an UTS of 871 ± 30 MPa with a brittle fracture behaviour regardless of the applied processing parameters. With a suitable post-process heat-treatment, a material with a more optimal microstructure was obtained, with properties comparable to those of WHAs produced by conventional powder metallurgy (UTS of 850 ± 21 MPa with an elongation of 10.2 ± 1.0%). ispartof: International Journal of Refractory Metals and Hard Materials vol:82 pages:23-30 status: Published online more...

In this study, fully dense commercially pure titanium (CP Ti) parts were successfully fabricated by selective laser melting (SLM) using the same optimal laser energy density Ep¯ but with two different laser powers: high laser power EH ~250 W and low laser power EL ~50 W. It was found that at the same Ep¯ different laser powers led to different phase formation, microstructure, texture and mechanical properties of the selective laser melting fabricated (SLMed) CP Ti. A weak-textured CP Ti with isotropic mechanical properties was achieved using EH while a strong-textured CP Ti with anisotropic mechanical properties was obtained using EL. The underlying mechanism was attributed to the formation of α' phase in the CP Ti as a result of the higher cooling rates at EH. The formation of α' phase also contributed to the observed high ultimate compressive strength ~1.1 GPa and high compressive strain ≥50% in the SLMed weak-textured CP Ti at EH. This study provides important insights into the role of laser energy in the SLM fabrication of CP Ti with tailorable crystallographic texture and thus mechanical properties. Keywords: Commercially pure titanium, Selective laser melting, Martensitic phase transformation, Crystallographic texture, Mechanical properties more...

Additive Manufacturing (AM) allows to produce improved, custom made, patient specific and complex shaped medical implants. Both mechanical and biological aspects as well as type of implant and patient specific requirements determine the shape of the implant and the material it will be made of. The current chapter reviews the metals and metallic alloys that can be successfully processed by powder bed fusion AM technologies, focusing on the interrelationship between their chemistry and microstructure, on one hand, and their biological and mechanical behavior, respectively, on the other hand. more...

© 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license Base plate preheating is one of the recent enhancing tools added to the process of Selective Laser Melting (SLM). This tool aims at a reduction of thermal stresses in SLM parts, achieved by decreasing the thermal gradients during SLM processing. In the current study, base plate preheating up to a temperature of 400°C is applied during SLM of 4 different materials, including aluminum 7075 alloy, nickel alloy Hastelloy X, H13 tool steel and CoCr. General trends, as well as material specific effects are discussed regarding part density, crack formation, internal stresses, microstructure and mechanical properties. These show how base plate preheating can induce different influences according to each particular material category. ispartof: pages:5-11 ispartof: Procedia CIRP vol:74 pages:5-11 ispartof: 10th CIRP Conference on Photonic Technologies (LANE) location:Furth, GERMANY date:3 Sep - 6 Sep 2018 status: published more...

© 2015 Elsevier Ltd. All rights reserved. With the increasing use of laser sintering for the production of end-use parts, there is considerable interest in developing new and improved polymer materials for this technique. Due to the complexity of the process, however, materials are subject to very specific requirements in order to be easy processable. To gain a better understanding of these material requirements, this study investigates the currently most widely used material family: polyamides. Four commercial polyamide sintering grades, including two polyamide-12 grades, one polyamide-11 and one polyamide-6 grade, are characterized, using a new screening approach that encompasses all material properties essential for laser sintering. These include powder characteristics, melt flow, and solidification behavior of the polymer. The study reveals several particular characteristics of polyamides that explain the current popularity of this material family for laser sintering, and may be used as a guideline for finding new materials for the process. publisher: Elsevier articletitle: Characterization of polyamide powders for determination of laser sintering processability journaltitle: European Polymer Journal articlelink: http://dx.doi.org/10.1016/j.eurpolymj.2015.12.014 content_type: article copyright: Copyright © 2015 Elsevier Ltd. All rights reserved. ispartof: European Polymer Journal vol:75 pages:163-174 status: published more...

Octahedron-shaped porous scaffolds made from shape memory nickel–titanium (NiTi) were manufactured with different solid volume fractions using selective laser melting (SLM). Various SLM parameters were selected to affect the mechanical behaviour and shape memory response. It was shown that high laser power with high scanning speed (HP) parameters reduced the martensitic transformation temperatures as compared to low laser power low scanning speed (LP) parameters, resulting in an increased pseudoelastic behaviour (due to presence of austenite at room temperature). HP parameters, however, led to a larger geometrical mismatch with the original design and a higher solid volume fraction. The compression behaviours were also analysed and exhibited in correlation with the volume fractions. publisher: Elsevier articletitle: Influence of SLM on shape memory and compression behaviour of NiTi scaffolds journaltitle: CIRP Annals - Manufacturing Technology articlelink: http://dx.doi.org/10.1016/j.cirp.2015.04.039 content_type: article copyright: Copyright © 2015 CIRP. Published by Elsevier Ltd. All rights reserved. ispartof: CIRP ANNALS-MANUFACTURING TECHNOLOGY vol:64 issue:1 pages:209-212 status: published more...

The number of industrial applications of Computed Tomography (CT) is large and rapidly increasing. After a brief market overview, the paper gives a survey of state of the art and upcoming CT technologies, covering types of CT systems, scanning capabilities, and technological advances. The paper contains a survey of application examples from the manufacturing industry as well as from other industries, e.g., electrical and electronic devices, inhomogeneous materials, and from the food industry. Challenges as well as major national and international coordinated activities in the field of industrial CT are also presented. more...

Publisher Summary NURBS stands for Non-Uniform Rational B-Splines, the popular mathematical tool used for computer-aided geometric design (CAGD) of free-form curves and surfaces. The geometrical shape of NURBS curves and surfaces is mainly controlled by their control points and the corresponding weights. This chapter concerns the identification of NURBS curves and surfaces from discrete points measured on coordinate measuring machines (CMMs), laser scanners or other digitizing equipments. The complete process is divided into two steps. The weights of the control points are first identified with singular value decomposition (SVD) or symmetric eigen value decomposition (SEVD) techniques through a linear homogeneous system. The control points are then solved with linear least squares fitting techniques. Both interpolation (exact) and fitting (approximate) solutions are studied. The emphasis of the present chapter is on SVD and SEVD applications during the first step for the identification of the weights. more...

Physical and chemical machining (also called non-traditional machining) has revolutionised the manufacturing practice during the second part of the twentiest century. Not only did PC they also opened the way to machine new hard material. The biggest revolution may have been introduced in the last few years, by the introduction of P&C machining processes that are able to produce parts by adding or growing material to the required product shape. more...

The proposed self-calibration method, like other methods, uses a ball plate for the error identification, but unlike other methods the ball plate needs not to be calibrated, i.e. the distances between the different balls on the plate need not to be known accurately. After the measurement of the ball plate in different positions in the measuring volume, the systematic geometrical errors in the geometric error model of the measuring machine can be computed. This geometrical error model is used by the software error correction to correct on-line every single measurement of the measuring machine. This results in a higher accuracy for the measuring machine. The self-calibration method has been carried out on a CNC 3D-CMM and the resulting software error correction has been evaluated using stepgauge measurements. The evaluation results show that the systematic geometrical errors are largely reduced. more...