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Densification of pure copper by selective laser melting process
摘要： Pure copper is utilized as a material for products with complicated shape and high thermal conductivity such as heat exchangers. However, it is difficult to fabricate pure copper parts with high density by the selective laser melting (SLM) process. One of the reasons is considered to be its high thermal conductivity by which the heat in the melt pool rapidly diffuses away. Additionally, the lower rate of energy absorption of fiber laser power for pure copper makes the size of melt pool smaller. In this research, the optimum fabrication condition of high-purity 99.9% copper fabricated by SLM process was investigated by evaluating the density and microstructure. As a result, it was found that the optimum condition of laser power and scan speed are 800~900W and 300 mm/s, respectively, and the optimum energy density is around 1000 J/mm3, which is much higher than that of other materials due to high reflectivity and high thermal conductivity of pure copper. And also, it was found that the hatch pitch is important factor to achieve the densification of the as-built specimen and the optimum hatch pitch was 0.01 mm. The high density parts were successfully fabricated by the optimum fabrication condition. The maximum density of the as-built specimen was 96.6 % and was much higher than that of the as-built part already reported.
关键词： Microstructure,Copper,Density,Process parameter,Additive manufacturing
更新于2025-09-23 15:19:57
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Fatigue properties and damage mechanisms of components manufactured by laser additive welding of H13 on S355 steel
摘要： Laser additive manufacturing is an advanced, very perspective technology with potentially wide industrial applications, one of them being an improvement of durability of forms and dies. The aim is to improve surface properties like wear resistance using special layers of powder sintered or remelted by laser beam. Other possible applications are repairs of worn dies or shape changes. At present, dies are manufactured by machining with following bulk heat treatment, which is an expensive process. Another problem is to find suppliers with big size furnaces and limited capacity often results in long time dates and terms. Concerning repairs of dies, they are usually performed manually, using arc or plasma welding with numerous difficulties and disadvantages in comparison with promising and advanced laser overlaying. The paper contains results of a comprehensive evaluation of several types of hard overlayed powder of H13 tool steel on a S355 structural steel using laser beam. Properties like macro- and microstructure, mechanical properties like hardness and its course in the layers, high-cycle fatigue resistance in bending and fatigue damage mechanisms were investigated with the emphasis on fatigue crack initiation process evaluated using scanning electron microscopy. The results indicated that surface additive laser welded layers of a high quality can be reached. On the other hand, some drop of fatigue resistance and endurance limit was observed, affected by surface defects – small welding imperfections
关键词： Laser additive manufacturing,H13 and S355 steels,fatigue
更新于2025-09-23 15:19:57
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Laser-Assisted Machining of Ti-6Al-4V Fabricated by DED Additive Manufacturing
摘要： Recently, the commercialization of hybrid machine tools that combine directed energy deposition (DED) additive manufacturing (AM) technology and subtractive manufacturing (SM) has rapidly progressed. This technology trend has been developed to meet the market demand for processing quality (precision) and productivity, and to produce products such as lightweight parts, and complex and special functional parts, as well as to facilitate mold production and part repair. Compared to SM technology, metal AM technology has limitations in terms of surface quality and shape accuracy. Therefore, post-processing is necessary for the AM output. Laser-assisted machining (LAM) is an innovative hybrid technique in which surface quality and productivity can be improved by enhancing the machinability of difficult-to-cut materials. LAM studies have mainly been performed on titanium alloys, nickel based alloys and ceramic materials. However, except for ceramics, no high-strength material studies have been conducted to analyze the LAM process machining characteristics of workpieces fabricated by AM process. Therefore, in this study, LAM is applied to post-processing of output fabricated by AM of Ti-6Al-4V. DED device was developed using metal powder feeder and a laser. The Ti-6Al-4V workpieces were successfully fabricated through many tests. The cutting depth for LAM was selected through thermal analysis for LAM of the fabricated workpiece. Compared to the case of traditional machining without preheating, machining characteristics in LAM experiments were analyzed and property testing was performed.
关键词： Machining characteristics,Additive manufacturing,Directed energy deposition,Ti-6Al-4V,Laser-assisted machining
更新于2025-09-23 15:19:57
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Generation of graded porous structures by control of process parameters in the selective laser melting of a fixed ratio salt-metal feedstock
摘要： The demonstration of salt dissolution incorporated within laser powder-bed fusion fabrication processes has allowed the creation of complex porous structures without the need for sophisticated design algorithms. This serves to simplify the process, for porous structure creation in powder-bed fabrication techniques, creating a new opportunity for the realisation of optimised structures. A new methodology is presented here in which modulation of the energy density while using a single feedstock material enables three-dimensional control of porosity, ranging from 20 % to 49 %. Through structured experimentation, the response of the material to varying the process parameters in selective laser melting is evaluated and nested structures of distinct densities and morphologies are created. Correlation of the process parameters with modulus and ultimate compressive stress are established. A simple-assembly algorithm was used to generate complex parts consisting of locally assigned porosities having characteristic properties.
关键词： Selective laser melting,Graded materials,Mechanical performance,Controlled-porosity,Additive manufacturing,Cellular structures,Porous
更新于2025-09-23 15:19:57
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Laser surface re-melting of additive manufactured samples with a line focused beam
摘要： The laser polishing mechanism is based on the fusion of a micro layer of material due to the action of the high temperature laser beam. Laser polishing, also known as laser surface remelting, involves melting a thin layer of the substrate, with surface tension causing the material to flow from peaks to valleys. In laser polishing, the material is not removed; rather it is relocated as a molten pool. The laser beam with sufficient energy density is first allowed to quickly fuse a layer on the substrate surface of microscopic thickness. Accordingly, the peaks of the asperities on the substrate surface are fused. Owing to the fluidity of this molten metal, it easily flows into the adjacent valleys of the asperities on the surface. The same molten layer is then allowed to re-solidify so that solidified layer remains adhered to the substrate surface. This, in turn, diminishes the peaks and valleys of the asperities, which ultimately results in a smoother surface. Since surface roughness is one major limitation of additive manufacturing components, so this article makes an attempt to address the roughness of such components. The capability of laser polishing (or laser surface remelting) in reducing surface roughness is explored for various beam power and scan speed. The better set of parameters for this purpose are presented. A final surface roughness in the range of 1.0–1.1 lm is obtained for three different set of parameters. 85% reduction in surface roughness due to laser polishing is also observed.
关键词： Cylindrical lens,Laser polishing,Surface roughness,Additive manufacturing,Laser surface remelting
更新于2025-09-23 15:19:57
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A comparative study of microstructure and hydrogen embrittlement of selective laser melted and wrought 17a??4??PH stainless steel
摘要： In this study, the microstructure and hydrogen embrittlement of 17–4 PH stainless steel produced by Selective Laser Melting (SLM) were investigated. The microstructure of SLM-ed 17–4 PH stainless steel was found to be fully ferritic, in contrast to the wrought martensitic steel. This finding was correlated to the high cooling and heating rates of the SLM process that suppressed the austenite formation and retained the delta ferrite to room temperature. The SLM-ed steel shows grains elongated in the building direction and its grain size is higher than the prior austenitic grain size of the wrought steel. The two steels present nanoscale copper precipitation after ageing 4 h at 580°C. The yield strength of the SLM-ed steel was found lower by only 10% with respect to the wrought steel. The hydrogen embrittlement was evaluated by performing slow strain rate tensile tests under cathodic charging after ageing 4 h at 580°C. It was found that SLM-ed 17–4 PH steel was more susceptible to hydrogen embrittlement compared to its wrought counterpart. This was attributed to the difference in microstructures, more specifically grain size. The crack initiation and propagation was much easier in the ferritic SLM-ed steel than in the martensitic wrought steel because of the higher grain size. The fracture in both steels was due to a significant subcritical crack growth followed by fast overload fracture of the remaining ligament. The fracture surface of the wrought steel showed a brittle intergranular fracture mode close to the surface and a ductile mode at the center. The brittle intergranular fracture mode was associated with the slow subcritical crack growth, while the ductile mode was due to the final fast overload fracture. On the other hand, in the SLM-ed steel, both the subcritical crack growth and the final fast overload fracture were obtained by transgranular cleavage. This shows that under hydrogen the martensitic wrought steel is prone to brittle intergranular fracture in contrast to the ferritic SLM-ed steel which is subject to brittle transgranular cleavage. The same tendency is obtained under air when notched specimens are used. This propensity of the martensitic steel to fracture along prior austenite grain boundaries can be interpreted in terms of the easiest fracture path.
关键词： Cleavage,Subcritical crack growth,Martensitic stainless steels,Selective laser melting,Additive manufacturing,Hydrogen cracking,Hydrogen embrittlement,Intergranular
更新于2025-09-23 15:19:57
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Selective Laser Melting: Materials and Applications
摘要： Additive manufacturing (AM) is one of the emerging manufacturing techniques of immense engineering and scientific importance and is regarded as the technique of the future. AM can fabricate any kind of material, including metals, polymers, ceramics, composites, etc. Selective laser melting (SLM), also known as the laser-based powder bed fusion process (LPBF), is the most widely used AM techniques that can fabricate a wide variety of materials, including Al-based, Fe-based, Ti-based, Co-based, Cu-based and Ni-based alloys, etc. Similar to any AM processes, the SLM/LPBF process also offers several advantages, like added functionality, near-net-shape fabrication with minimal or no post-processing, shorter lead-time, offer intricacy for free, etc. The SLM process has its applications in the aerospace, automobile, oil refinery, marine, construction, food and jewelry industries, etc. However, there exist some shortcomings in the SLM field, which are (a) SLM-based alloy development, (b) the premature failure of materials, even though improved properties are observed, (c) process innovation and development, (d) structure-property correlation and (e) numerical simulations, etc.
关键词： Selective Laser Melting,Materials,Additive Manufacturing,Properties,Applications,Microstructure
更新于2025-09-23 15:19:57
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Biomimetic design and laser additive manufacturinga??A perfect symbiosis?
摘要： Biomimetics as well as additive manufacturing have prominently produced novel design approaches for parts and products independently from each other. The combination of both has resulted in numerous innovative part designs that were unseen before. However remarkable the marketing impact of individual 3D printed biomimetic parts has been, a widespread industrial application is missing to date. This publication, therefore, takes a closer look at how biomimetic design in additive manufacturing is currently pursued and evaluates the different design approaches based on their suitability for industrial application. The assessment reveals that algorithms and thesaurus tools should be preferred in an industrial biomimetic design process. From the various additive manufacturing methods, laser additive manufacturing today is a dominating industrial application when it comes to metal parts. Thus, several case studies of biomimetic designs produced with laser additive manufacturing are presented. On the basis of the selected examples, the added value through biomimetic design is discussed and reviewed critically, raising the question of when a biomimetic design approach is promising compared to conventional design approaches. Based on the review of current use cases and the potentials that the combination of biomimetics and additive manufacturing offer, recommended fields of research are concluded. Finally, the road to industry for biomimetic additive manufacturing design is outlined, taking into account the findings on existing biomimetic design methodologies and tools.
关键词： laser additive manufacturing,biomimetic design,3D printing
更新于2025-09-23 15:19:57
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A deep learning-based model for defect detection in laser-powder bed fusion using in-situ thermographic monitoring
摘要： Additive manufacturing of metal components with laser-powder bed fusion is a very complex process, since powder has to be melted and cooled in each layer to produce a part. Many parameters influence the printing process; however, defects resulting from suboptimal parameter settings are usually detected after the process. To detect these defects during the printing, different process monitoring techniques such as melt pool monitoring or off-axis infrared monitoring have been proposed. In this work, we used a combination of thermographic off-axis imaging as data source and deep learning-based neural network architectures, to detect printing defects. For the network training, a k-fold cross validation and a hold-out cross validation were used. With these techniques, defects such as delamination and splatter can be recognized with an accuracy of 96.80%. In addition, the model was evaluated with computing class activation heatmaps. The architecture is very small and has low computing costs, which means that it is suitable to operate in real time even on less powerful hardware.
关键词： Additive manufacturing,Convolutional neural networks,Machine learning,Quality assurance
更新于2025-09-23 15:19:57
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Calibration of galvanometric scan heads for additive manufacturing with machine assembly defects consideration
摘要： The calibration of additive manufacturing machines using scanning heads in processes such as Laser Powder Bed Fusion (LPBF) and vat photopolymerization is an iterative and time-consuming process often based on limited physical models. Indeed, the relationship between the laser spot position in the work plane and the actuators position (galvanometers) is achieved by interpolating correction tables experimentally determined. In this paper, representative geometrical models of the real system are established in order to reduce the time required to obtain the final correction tables. For this purpose, a geometrical model is developed with assembly defects consideration. This model is used in a process of defects identification to obtain a virtual machine representative of the real system and thus directly generates the final correction tables. The geometrical model thereby developed is used to quantify the impact of assembly defects on the laser spot position, to compensate them and to reduce the calibration time of an additive manufacturing machine.
关键词： Assembly defects,Additive manufacturing,Geometrical model,Virtual machine,Calibration
更新于2025-09-19 17:15:36