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[ACM Press the 1st Annual ACM Symposium - Cambridge, Massachusetts (2017.06.12-2017.06.13)] Proceedings of the 1st Annual ACM Symposium on Computational Fabrication - SCF '17 - Shape optimization of fabricated transparent layer for pixel density uniformalization in non-planar rear projection
摘要： When an image is projected onto a non-planer surface, the resolution is not spatially uniform because projectors are normally designed to display an image with spatially uniform pixel density on a flat surface. We propose to insert a transparent layer between a projector and a non-planar surface and optimize its shape to make the projection pixel density spatially uniform, which can be controlled by non-uniformly refracting a projection light through the transparent layer. We use a multi-material 3D printer to fabricate the transparent layer combined with a non-planar surface. From the result of a projection experiment with the surface, we validate our proposed method.
关键词： multi-material 3D printer,rear projection
更新于2025-09-23 15:23:52
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Case Study of Empirical Beam Hardening Correction Methods for Dimensional X-ray Computed Tomography Using a Dedicated Multi-material Reference Standard
摘要： This paper presents a case study of two selected beam hardening correction methods and their effects on dimensional measurements of multi-material objects. The methods under test are empirical cupping correction (ECC) and empirical dual energy calibration (EDEC). These methods were originally developed for medical applications and their potential for the reduction of artefacts is typically only analysed based on grey value images. For testing and benchmarking of the mentioned methods for dimensional metrology, a dedicated multi-material reference standard—a multi-material hole cube—is used. This reference standard was originally developed for acceptance testing of CT systems. This paper shows a second application of this standard. The reference standard has been calibrated by tactile measurements to assess centre–centre distance errors as well as patch-based bidirectional length measurement errors on beam hardening corrected data and on uncorrected data. For the application of the method also to industrial multi-material scenarios, slight modifications of the ECC method are proposed. Practical aspects of both the ECC and the EDEC approaches as well as measurement results are analysed and discussed in detail. ECC was able to significantly improve dimensional measurements and was especially able to reduce extreme errors occurring in particular in multi-material scenarios by a factor of more than 4. EDEC, the dual-energy approach, reduced grey value inhomogeneities caused by artefacts even more. Its performance for dimensional measurements was however a little worse than ECC. EDEC data resulted in a slightly larger total range of residual measurement errors, mainly due to an elevated noise level.
关键词： Beam hardening correction,Industrial computed tomography,Multi-material measurements,Material influence,Dimensional metrology
更新于2025-09-23 15:22:29
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Selective laser melting 316L/CuSn10 multi-materials: Processing optimization, interfacial characterization and mechanical property
摘要： Adopting selective laser melting (SLM), a typical technology of additive manufacturing (AM), to form multi-material metallic composites is a challenging and promising field. In this study, SLM 316L/CuSn10 multi-material composites was an innovative attempt to develop functional and structural materials with excellent properties of steel and copper alloys. Dense 316L/CuSn10 specimens with no interfacial macrocracks were successfully fabricated. Results showed that the Vickers microhardness gradually decreased from 329.5±12.5 HV in 316L region to 172.8HV±7.4 in CuSn10 region. The ultimate tensile strength and flexural strength of 316L/CuSn10 sample was 210 MPa, which was higher than the steel/copper alloys fabricated by other methods. It indicated an ideal interfacial bonding condition of 316L/CuSn10 multi-material, which was benefited from sufficient agitation of the molten pools and elements diffusion in the term of continuous distribution of elements and the enrichment of the heterogeneous alloy phases. Also, the grain refinement by re-melting and recrystallization upgraded the bonding performance at the interface. Finally, the 316L/CuSn10 lattice structure was formed by SLM, hinting at the prospects for industrial applications of steel/copper multi-material by SLM in future.
关键词： Selective laser melting (SLM),Mechanical properties,Interface,316L/CuSn10,Multi-material,Microstructure
更新于2025-09-23 15:21:01
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Multi-physics modelling of molten pool development and track formation in multi-track, multi-layer and multi-material selective laser melting
摘要： Selective laser melting (SLM) is a promising powder-based additive manufacturing technology due to its capability to fabricate metallic components with complex geometries. While most previous investigations focus on printing with a single material, recent industry-orientated studies indicate the need for multi-material SLM in several high-value manufacturing sectors including medical devices, aerospace and automotive industries. However, understanding the underlying physics in multi-material SLM remains challenging due to the di?culties of experimental observation. In this paper, an integrated modelling framework for multi-track, multi-layer and multi-material SLM is developed to advance the in-depth understanding of this process. The main novelty is in modelling the molten pool evolvement and track morphology of multiple materials deposited on the same and across different layers. Discrete element method (DEM) is employed to reproduce the powder deposition process of multiple materials in different deposition patterns, with particle size distribution imported from a particle size analyser. Various phenomena including balling effect, keyhole depression, and lack of fusion between layers are investigated with different laser energy inputs. As a result of the different thermal properties, several process parameters including energy density and hatch spacing are optimised for different powder materials to obtain a continuous track pro?le and improved scanning e?ciency. The interface between two layers of different materials is visualised by simulation; it was found that the phase migration at the interface is related to the convection ?ow inside the molten pool, which contributes to the mixing of the two materials and elemental diffusion. This study signi?cantly contributes to the challenging area of multi-material additive manufacturing by providing a greater in-depth understanding of the SLM process from multi-material powder deposition to laser interaction with powders across multiple scanning tracks and different building layers than can be achieved by experimentation alone.
关键词： Additive manufacturing,Discrete element method (DEM),Computational ?uid dynamics (CFD),Heat transfer,Multi-material,Selective laser melting (SLM)
更新于2025-09-23 15:19:57
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Additive Manufacturing of Three-dimensional Metal-glass Functionally Gradient Material Components by Laser Powder Bed Fusion with In situ Powder Mixing
摘要： Existing commercial three-dimensional (3D) printing systems based on powder bed fusion approach can normally only print a single material in each component. In this paper, functionally gradient materials (FGM) with composition variation from a copper alloy to a soda-lime glass were manufactured using a proprietary nozzle-based multi-material selective laser melting (MMSLM) system. An in situ powder mixing system was designed to mix both metal and glass powders at selective ratios and the mixed powders were dispensed with an ultrasonic vibration powder feeding system with multiple nozzles. From the cross section analysis of the gradient structures, glass proportion increased gradually from the metallic matrix composite (MMC), transition phase to ceramic matrix composite (CMC). The pure copper alloy joined the MMC part and the pure glass phase penetrated into the CMC part during laser processing, which anchored the glass phase, as the main mechanism of combining pure metal and pure glass by FGM in 3D printed parts. From results of indentation, tensile and shear tests on the gradient material samples, it showed that mechanical properties of the FGM gradually changed from ductility (metal side) to brittle (glass side). The weakest part of the FGM structure occurred at the interface between transition phase and the CMC, which was also the interface between the ductile and brittle phases.
关键词： copper-glass,Powder Bed Fusion,horizontal gradient structure,multi-material selective laser melting,functionally gradient materials
更新于2025-09-19 17:13:59
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Laser metal deposition of copper on diverse metals using green laser sources
摘要： Green laser sources are advantageous in the processing of copper due to the increase of absorptivity compared with more commonly available infrared lasers. Laser metal deposition of copper with a green laser onto various substrate metals namely copper, aluminium, steel and titanium alloy was carried out and observed through high-speed imaging. The effects of process parameters such as laser power, cladding speed and powder feed rate, and material attributes such as absorptivity, surface conditions and thermal conductivity are tied together to explain the size and geometry of the melt pool as well as the fraction of the power used for melting material. The copper substrate has the smallest melt pool with a high angle, followed by aluminium, steel and titanium alloy. The incorporation times for powder grains in the melt pools vary based on the substrate materials. Its dependency on material properties, including surface tension forces, melting temperatures and material density, is discussed. Oxide skins present on melt pools can affect powder incorporation, most significantly on the aluminium substrate. The lower limits of the fraction of power irradiated on the surface used purely for melting were calculated to be 0.73%, 2.94%, 5.95% and 9.78% for the copper, aluminium, steel and titanium alloy substrates, respectively, showing a strong dependence on thermal conductivity of the substrate material. For a copper wall built, the fraction was 2.66%, much higher than a single clad on a copper substrate, due to reduced workpiece heating. The results of this paper can be transferred to other metals with low absorptivity such as gold.
关键词： Multi-material,DED,High-speed imaging,LMD,Copper,Green 515-nm laser,Laser metal deposition,Powder grain incorporation,Additive manufacturing,Directed energy deposition,Absorptivity
更新于2025-09-19 17:13:59
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Influence mechanism of process parameters on the interfacial characterization of selective laser melting 316L/CuSn10
摘要： Bimetallic structures can combine the performance of dissimilar metal materials to meet the multifunctional requirement in industrial solutions. In this paper, steel-bronze bimetallic structures were fabricated via self-developed multi-material selective laser melting (SLM) equipment. In order to investigate the influence of laser power, scanning speed, and hatching space on the interfacial characterization, three factors and five levels of orthogonal experiments were performed on twenty layers of CuSn10 tin bronze after forming the 316L stainless steel. Optical microscope (OM), large depth field microscope, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), tensile properties, electron backscattering diffraction (EBSD) and nanoindentation were used to characterize these bimetallic structures to validate the impact from process parameters. The large depth field microscope revealed protrusions at the steel/bronze interface, and its height increased and then decreased with increasing volumetric energy input. Besides, the generation of interfacial defects is related to the interfacial process parameters, and it is found that the types of defects are mainly classified as holes and cracks. Insufficient energy will cause cracks in the horizontal direction and then lead to bonding failure. Conversely, higher energy input will generate microcracks in the vertical direction. The defects near the interfacial region are the main factors affecting the ultimate strength of the bonding strength. As a result, the steel-bronze bimetallic structure displays optimal joint ultimate strength of 459.54±3.08 MPa with elongation of 5.23±0.65%, and minimum joint ultimate strength of 199.02±0.56 MPa with elongation of 1.70±0.22%. Their fracture morphology also exhibited gully-like and fan-shaped features, respectively. Additionally, the EBSD results show that there are fine grain regions appeared in the interfacial region, which helps increase the average nano-hardness of the interfacial region. This study provides a reference for the influence of process parameters on the interfacial characterization and mechanical properties of steel-bronze bimetallic parts prepared by selective laser melting.
关键词： Interfacial characterization,Mechanical properties,Selective laser melting,Bimetallic structure,Multi-material
更新于2025-09-19 17:13:59
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[IEEE 2018 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC) - Sydney, Australia (2018.11.10-2018.11.17)] 2018 IEEE Nuclear Science Symposium and Medical Imaging Conference Proceedings (NSS/MIC) - PET-enabled Dual-energy CT: A Proof-of-Concept Simulation Study
摘要： Standard dual-energy CT uses two different x-ray energies to obtain energy-dependent tissue attenuation information to allow quantitative material decomposition. Combined use of dual-energy CT and PET may provide a more comprehensive characterization of disease states in cancer and many other integration of dual-energy CT with PET diseases. However, is not trivial, either requiring costly hardware upgrade or increasing radiation dose. This paper proposes a novel dual-energy CT imaging method that is enabled by the already-available PET data on PET/CT. Instead of using a second x-ray CT scan with a different energy, this method exploits time-of-flight PET image reconstruction to obtain a 511 keV gamma-ray attenuation image from PET emission data and combines the high-energy gamma-ray CT image with the low-energy x-ray CT of PET/CT to provide a pair of dual-energy CT images. We conducted a computer simulation to test the concept for material decomposition using air, soft tissue, fat and calcium. The simulations results indicate that this PET-enabled dual-energy CT method is promising for quantitative material decomposition, though future work is needed for noise supression. The proposed method can be readily implemented on time-of-flight PET/CT scanners to enable simultaneous PET and dual-energy CT for multiparametric imaging.
关键词： Time-of-flight PET,multi-material decomposition,image reconstruction,dual-energy CT
更新于2025-09-16 10:30:52
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[IEEE 2019 IEEE 32nd International Conference on Micro Electro Mechanical Systems (MEMS) - Seoul, Korea (South) (2019.1.27-2019.1.31)] 2019 IEEE 32nd International Conference on Micro Electro Mechanical Systems (MEMS) - Rapid Multi-Material Direct Laser Writing
摘要： The additive manufacturing or “three-dimensional (3D) printing” technology direct laser writing (DLW) offers a level of geometric versatility at submicron scales that yields substantial benefits for fields including photonics, meta-materials, and 3D cell biology. A key limitation of DLW, however, stems from the difficulties in 3D printing micro/nanoscale structures with more than a single material. Specifically, producing multi-material components requires laborious and time-intensive protocols for manual substrate/material processing and alignment to maintain structural continuity among distinct photomaterials. To overcome these challenges, here we introduce a “rapid multi-material DLW (RMM-DLW)” strategy that enables 3D nanostructured features comprised of multiple, fully integrated photomaterials to be additively manufactured with unprecedented speed and accuracy. This approach leverages an impermanent elastomeric bonding technique to achieve temporary microchannels through which distinct photomaterials can be serially loaded, photopolymerized, and developed; the elastomer can be removed thereafter. Preliminary RMM-DLW results revealed a 74% reduction in fabrication time, with a multi-material alignment accuracy of 0.14±0.17 μm (?X) and 0.20±0.15 μm (?Y) – an improvement of up to one order of magnitude over conventional multi-material DLW. In combination, these results suggest a promising pathway to achieve fundamentally new classes of multi-material, and in turn, multi-functional 3D nanostructured systems.
关键词： additive manufacturing,direct laser writing,microfluidics,multi-material,3D printing
更新于2025-09-12 10:27:22
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Multi-material modelling for selective laser melting
摘要： Selective Laser Melting (SLM) is a powder-bed Additive Manufacturing (AM) process which uses a laser beam to fully melt the powders layer upon layer to build a 3D part. While most studies are conducted on SLM using single material, the application of multi-materials using this technology can offer more advantages than the conventional manufacturing methods. Complex multi-materials parts can be built which conventional manufacturing methods are unable to due to their restriction in design of freedom. However, the SLM process has its own limitations in producing multi-material parts. Since SLM uses a powder bed to build parts, the use of different powder materials in the powder bed will result in contamination of the unused powder, rendering unnecessary wastages. Therefore, using modelling techniques to attain the optimized parameters before conducting the actual experiment to verify its validity will aid in reducing wastages, leading to cost saving. To study the effects of the interface of different materials during the laser scanning, a model was simulated to observe the melting process. An open-source LAMMPS (Large-scale Atomic Molecular Massively Parallel Simulator) software uses Molecular Dynamics (MD) to simulate the melting process. The materials used for the simulations are iron (FE) and aluminum (Al). The modelling is extended to multiple layers to allow the observation of the bonding between layers.
关键词： Multi-material modelling,Additive Manufacturing,Selective Laser Melting
更新于2025-09-12 10:27:22