Effect of surface state and material on surface quality enhancement by Dual Laser Powder Bed Fusion

Parts produced by Laser Powder Bed Fusion typically exhibit a limited surface quality often requiring systematic post-processing. The KU Leuven AM team recently developed a Dual Laser Powder Bed Fusion strategy to improve the quality of inclined up-facing surfaces during building. It consists of two steps: (1) a pulsed laser induces shock waves to remove powder from inclined surfaces, followed by (2) in-situ laser remelting of the newly exposed surfaces. The first part of this paper covers the powder removal efficiency using shock waves depending on the used material. A design of experiments was performed for horizontal samples of tool steels, titanium and aluminium alloys. The second part deals with the effect of the initial surface state on the powder removal efficiency for inclined surfaces (SaR,LT60=16.2 µm, SaR,LT120=24.0 µm). Finally, the third part demonstrates the surface quality improvement, resulting in a reduction of Ra up to 61% for 15° inclinations.Mechanical Engineerin

HIGH SPEED VIDEO IMAGING OF OVERHANG SURFACES IN BEAM SHAPED LASER POWDER BED FUSION OF 316L STAINLESS STEEL

Beam shaping has seen rising interest in the AM industry and research field because of the increased level of control over the spatial distribution of the thermal input during Laser Powder Bed Fusion, allowing for faster build rates. This report investigates if the more uniform heat input offers benefits to the scanning of unsupported overhanging structures. In-situ high speed video imaging is combined with post process surface characterization to derive a relation between the scan parameters and quality of the overhang surface. The best results were achieved at low energy densities, but no clear advantage of top-hat shaped laser spots over the standard Gaussian beams is observed.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

Understanding elastic anisotropy in diamond based lattice structures produced by laser powder bed fusion: Effect of manufacturing deviations

Laser powder bed fusion (L-PBF) allows the production of metal lattice cellular structures with tailored mechanical properties. In order to generate the specific structural behavior it is of utmost importance to understand the response of the unit cells when different load conditions are considered. In this article the mechanical response of diamond based cellular structures has been investigated focusing on the impact of geometrical inaccuracy generated by the manufacturing process on the elastic anisotropy of the mentioned unit cell. The μ-CT analysis of the structures shows that the manufacturing deviations occur in certain orientations that depend highly on the building direction and proximity to nodes. The measured imperfection types were implemented in a finite element model in order to predict their single and combined effects in the elastic directional response. The results indicate that the L-PBF process can induce a significant change of elastic anisotropy in the diamond unit cells, including a substantial variation of the optimal orientation for minimal compliance. Methods are presented to calculate this anisotropy such that it can be taken into account when designing and using such lattice structures in real-life applications with multi-axial load condition

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

Emergence of 3D Printed Dosage Forms: Opportunities and Challenges

The recent introduction of the first FDA approved 3D-printed drug has fuelled interest in 3D printing technology, which is set to revolutionize healthcare. Since its initial use, this rapid prototyping (RP) technology has evolved to such as extent that it is currently being used in a wide range of applications including in tissue engineering, dentistry, construction, automotive and aerospace. However, in the pharmaceutical industry this technology is still in its infancy and its potential yet to be fully explored. This paper presents various 3D printing technologies such as stereolithographic, powder based, selective laser sintering, fused deposition modelling and semi-solid extrusion 3D printing. It also provides a comprehensive review of previous attempts at using 3D printing technologies on the manufacturing dosage forms with a particular focus on oral tablets. Their advantages particularly with adaptability in the pharmaceutical field have been highlighted, including design flexibility and control and manufacture which enables the preparation of dosage forms with complex designs and geometries, multiple actives and tailored release profiles. An insight into the technical challenges facing the different 3D printing technologies such as the formulation and processing parameters is provided. Light is also shed on the different regulatory challenges that need to be overcome for 3D printing to fulfil its real potential in the pharmaceutical industry

The KU Leuven student electric car project: From theory to practice

© 2014, FISITA. All rights reserved. The main purpose of this work is to indicate how engineering students can be educated in a project-based framework in order to develop important competences such as working in team, practical problem solving, decision making and bridging the gap between theory and practice. These skills are crucial for all engineering students and project-based education in an effective way for student to learn these competences.status: publishe

Fused Filament Fabrication on the Moon

Additive manufacturing (AM) techniques possess the capabilities to rapidly produce complex and customised parts, typically in low-volume and with reduced material us- age and preparation tools . These attributes magnify their indispensability when the availability of materials and equipment is limited. It can be such a case for off-Earth manufacturing, e.g. in manned lunar explorations. This article presents a preliminary discussion on the possibility of performing fused filament fabrication (FFF) on the Moon from the perspective of heat transfer in printed parts. It makes use of experimen- tal data and simulations to quantify the significance of each heat transfer mechanism taking place during printing. The quantification then enables us to investigate how the lunar environment affects the cooling in the printed parts. Finally, FFF on the Moon is predicted to be feasible. Yet, apparent differences in the process window and types of applications are pointed out as compared with the counterpart printing activities on the Earth. The full paper may be found in a special issue of the TMS publication JOM, March 2022.Mechanical Engineerin

Thermography based in-process monitoring of Fused Filament Fabrication of polymeric parts

© 2019 CIRP Temperature management is crucial in Fused Filament Fabrication (FFF). This paper presents an infrared based set-up able to record spatial and temporal variations during printing of an FFF part, with a field of view of (21.7 × 14.9)mm 2 and at spatial resolution of 30.2 μm. The system is experimentally verified and the captured temperature profiles are compared to numerical data, obtained via an own-developed FFF numerical model. This work is a first step towards a combined experimental-numerical approach for in-process monitoring of FFF, with implications for filament developers, machine builders and (end-)users, ultimately demanding high quality (certified)parts.status: publishe

Laser Sintering of PA12/PA4,6 Polymer Composites

This work investigates the laser sintering (LS) processing of polyamide-12/polyamide-4,6 composites and the performance of resulting parts. The coalescence and consolidation of the PA12/PA4,6 powder mixture are characterized. This demonstrates that at the LS processing window for PA12 (grade PA2200), the powder mixture exhibits bimodal melting behavior. In this behavior PA2200 melts during LS processing but PA4,6 remains solid. After laser sintering of the materials, the microstructure and the mechanical properties of the resulting parts are characterized. This illustrates that the PA2200 coalesces well and PA4,6 remains as a secondary phase during the LS processing. Further developments to improve the powder size and morphology in order to obtain better relative density of the parts are necessary. The investigated processing approach opens up new perspectives for LS of advanced engineering thermoplastics.Mechanical Engineerin