Study of anisotropy through microscopy, internal friction and electrical resistivity measurements of Ti-6Al-4V samples fabricated by selective laser melting

Purpose This paper aims to investigate the microstructural anisotropy of Ti-6Al-4V samples fabricated by selective laser melting. Design/methodology/approach Specimens are fabricated through a Renishaw AM400 selective laser melting machine. Three microstructures (as-built, 850°C annealed and 1,050°C annealed) and two building orientations, parallel (PA) and perpendicular (PE) to the building platform, are considered. Starting from in-depth microscopic observations and comprehensive electron backscattered diffraction imaging, the study addresses non-conventional techniques such as internal friction and electrical resistivity measurements to assess the anisotropy of the fabricated parts. Findings Microscope observations highlight a fine texture with columnar grains parallel to the building direction in the as-built and 850°C annealed samples. Besides, coarse grains characterized the 1,050°C annealed specimens. Internal friction measurements pointed out the presence of internal stress while storage modulus analyses appear sensitive to texture. Electrical resistivity is resulted to be dependent on grain orientation. Originality/value The work uses some novel characterization techniques to study the anisotropy and internal stresses of Ti-6Al-4V samples processed by selective laser melting. Mechanical spectroscopy results suitable in this kind of study, as it mimics the operating conditions of the material.

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Deformations and stresses prediction of cantilever structures fabricated by selective laser melting process

Rapid Prototyping Journal ◽

10.1108/rpj-10-2019-0273 ◽

2021 ◽

Vol 27 (3) ◽

pp. 453-464

Author(s):

Lan Li ◽

Tan Pan ◽

Xinchang Zhang ◽

Yitao Chen ◽

Wenyuan Cui ◽

...

Keyword(s):

Residual Stress ◽

Residual Stresses ◽

Selective Laser Melting ◽

Thermal Distortion ◽

Cantilever Beams ◽

Support Structures ◽

Laser Melting ◽

Content Type ◽

Two Samples ◽

Validation Experiments

Purpose During the powder bed fusion process, thermal distortion is one big problem owing to the thermal stress caused by the high cooling rate and temperature gradient. For the purpose of avoiding distortion caused by internal residual stresses, support structures are used in most selective laser melting (SLM) process especially for cantilever beams because they can assist the heat dissipation. Support structures can also help to hold the work piece in its place and reduce volume of the printing materials. The mitigation of high thermal gradients during the manufacturing process helps to reduce thermal distortion and thus alleviate cracking, curling, delamination and shrinkage. Therefore, this paper aims to study the displacement and residual stress evolution of SLMed parts. Design/methodology/approach The objective of this study was to examine and compare the distortion and residual stress properties of two cantilever structures, using both numerical and experimental methods. The part-scale finite element analysis modeling technique was applied to numerically analyze the overhang distortions, using the layer-by-layer model for predicting a part scale model. The validation experiments of these two samples were built in a SLM platform. Then average displacement of the four tip corners and residual stress on top surface of cantilever beams were tested to validate the model. Findings The validation experiments results of average displacement of the four tip corners and residual stress on top surface of cantilever beams were tested to validate the model. It was found that they matched well with each other. From displacement and residual stress standpoint, by introducing two different support structure, two samples with the same cantilever beam can be successfully printed. In terms of reducing wasted support materials, print time and high surface quality, sample with less support will need less post-processing and waste energy. Originality/value Numerical modeling in this work can be a very useful tool to parametrically study the feasibility of support structures of SLM parts in terms of residual stresses and deformations. It has the capability for fast prediction in the SLMed parts.

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Track evolution and surface characteristics of selective laser melting Ti6Al4V

Rapid Prototyping Journal ◽

10.1108/rpj-01-2018-0004 ◽

2018 ◽

Vol 24 (9) ◽

pp. 1554-1562 ◽

Cited By ~ 4

Author(s):

Luo Zhang ◽

Haihong Zhu ◽

Jiahe Liu ◽

Xiaoyan Zeng

Keyword(s):

Surface Morphology ◽

Selective Laser Melting ◽

Surface Characteristics ◽

Scanning Speed ◽

Bulk Sample ◽

Three Dimension ◽

Single Track ◽

Heat Accumulation ◽

Laser Melting ◽

Content Type

Purpose The purpose of this paper is to investigate the track evolution and surface characteristics of selective laser melting Ti6Al4V. Design/methodology/approach In the present paper, Ti6Al4V single-track, multi-track and bulk sample were formed at different scanning speed by selective laser melting (SLM). Then, the surface morphology, three-dimension profile and surface roughness were evaluated. The width of the single and multi-track was measured and compared. Findings The results showed that the heat accumulation played a great role on the evolution of tracks and surface characteristics from single-track to multi-track and to bulk. The surface morphology of the subsequent tracks became more regular when the single-track was irregular at the same high scanning speed. The width of last track Wn was always larger than that of the first track W1. The Ra of the top of the bulk increased with the increase of the scanning speed, this trend was as same as the Ra of the single-track, but the trend of Ra of the side was opposite. Originality/value The effect of heat accumulation on the track evolution and surface characteristics is obtained. The results can help to derive a smooth surface with a regular and continuous track in SLM.

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Structural optimization design for antenna bracket manufactured by selective laser melting

Rapid Prototyping Journal ◽

10.1108/rpj-05-2017-0084 ◽

2018 ◽

Vol 24 (3) ◽

pp. 539-547 ◽

Cited By ~ 3

Author(s):

Zefeng Xiao ◽

Yongqiang Yang ◽

Di Wang ◽

Changhui Song ◽

Yuchao Bai

Keyword(s):

Structural Optimization ◽

Modal Analysis ◽

Selective Laser Melting ◽

Optimization Model ◽

Optimization Design ◽

Analysis Data ◽

Laser Melting ◽

Design Rules ◽

Content Type ◽

Process Characteristics

Purpose This paper aims to summarize design rules based on the process characteristics of selective laser melting (SLM) and structural optimization and apply the design rules in the lightweight design of an aluminum alloy antenna bracket. The design goal is to reduce 30 per cent of the weight while maintaining the stress levels in the original part. Design/methodology/approach To reduce weight as much as possible, the titanium alloy with higher specific strength was selected during the process of optimization. The material distribution of the bracket was improved by the topology optimization design. The redesign for SLM was used to obtain an optimization model, which was more suitable for SLM. The component performance was improved by shape optimization. The modal analysis data of the structural optimization model were compared with those of the stochastic lightweight model to verify the structural optimization model. The scanning data were compared with those of the original model to verify whether the model was suitable for SLM. Findings Structural optimization design for antenna bracket realized the mass decrease of 30.43 per cent and the fundamental frequency increase of 50.18 per cent. The modal analysis data of the stochastic lightweight model and the structural optimization model indicated that the optimization performance of structural optimization method was better than that of the stochastic lightweight method. The comparison results between the scanning data of the forming part and the original data confirmed that the structural optimization design for SLM lightweight component could achieve the desired forming accuracy. Originality/value This paper summarizes geometric constraints in SLM and derives design rules of structural optimization based on the process characteristics of SLM. SLM design rules make structural optimization design more reasonable. The combination of structural optimization design and SLM can improve the performance of lightweight antenna bracket significantly.

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Selective laser melting of magnesium AZ31B alloy powder

Rapid Prototyping Journal ◽

10.1108/rpj-05-2019-0137 ◽

2019 ◽

Vol 26 (2) ◽

pp. 249-258 ◽

Cited By ~ 2

Author(s):

Andrzej Pawlak ◽

Patrycja E. Szymczyk ◽

Tomasz Kurzynowski ◽

Edward Chlebus

Keyword(s):

Mechanical Properties ◽

Selective Laser Melting ◽

Alloy Powder ◽

Az31 Alloy ◽

Optimum Process ◽

Laser Melting ◽

Content Type ◽

Fine Grained ◽

Az31b Alloy ◽

Hot Rolled

Purpose This paper aims to discuss the results of material tests conducted on specimens manufactured from AZ31 alloy powder by selective laser melting (SLM) technology. The manufactured specimens were then subjected to porosity assessment, microstructure analysis as well as to mechanical and corrosion tests. Design/methodology/approach SLM process was optimized using the design of experiments tools. Experiments aimed at selecting optimum process parameters were carried out in accordance with a five-level rotatable central composite design. Findings The porosity results showed very low values of <1 per cent, whereas mechanical properties were close to the values reported for the reference wrought AZ31 alloy in hot-rolled state. A fine-grained microstructure was observed with a large range of grain size, which enhanced the material’s mechanical properties. Corrosion characteristics of the SLM-manufactured material exceed those determined for the wrought material. Originality/value The results presented in this paper drive interest in magnesium alloys used in additive manufacturing processes. Low porosity, good mechanical properties, form of the microstructure and, most importantly, improved corrosion characteristics suggest that SLM provides great potential for the manufacture of ultralight structures, including resorbable metallic implants.

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Tool Life Performance of Injection Mould Tooling Fabricated by Selective Laser Melting for High-Volume Production

Materials ◽

10.3390/ma12233910 ◽

2019 ◽

Vol 12 (23) ◽

pp. 3910 ◽

Cited By ~ 1

Author(s):

Kashouty ◽

Rennie ◽

Ghazy

Keyword(s):

Selective Laser Melting ◽

Injection Moulding ◽

Dimensional Accuracy ◽

High Volume ◽

Operating Conditions ◽

Composition Analysis ◽

Stainless Steel 316L ◽

Laser Melting ◽

High Volume Production ◽

Volume Production

Rapid Tooling processes are developing and proving to be a reliable method to compete with subtractive techniques for tool making. This paper investigates large volume production of components produced from Selective Laser Melting (SLM) fabricated injection moulding tool inserts. To date, other researchers have focused primarily on investigating the use of additive manufacturing technology for injection moulding for low-volume component production rather than high volume production. In this study, SLM technology has been used to fabricate four Stainless Steel 316L tool inserts of a similar geometry for an after-market automotive spare part. The SLM tool inserts have been evaluated to analyse the maximum number of successful injections and quality of performance. Microstructure inspection and chemical composition analysis have been investigated. Performance tests were conducted for the four tool inserts before and after injection moulding in the context of hardness testing and dimensional accuracy. For the first reported time, 150,000 injected products were successfully produced from the four SLM tool inserts. Tool inserts performance was monitored under actual operating conditions considering high-level demands. In the scope of this research, SLM proved to be a dependable manufacturing technique for most part geometries and an effective alternative to subtractive manufacturing for high-volume injection moulding tools for the aftermarket automotive sector.

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Porosity content control of CoCrMo and titanium parts by Taguchi method applied to selective laser melting process parameter

Rapid Prototyping Journal ◽

10.1108/rpj-09-2013-0092 ◽

2016 ◽

Vol 22 (1) ◽

pp. 20-30 ◽

Cited By ~ 12

Author(s):

David Joguet ◽

Sophie Costil ◽

Hanlin Liao ◽

Yoann Danlos

Keyword(s):

Selective Laser Melting ◽

Design Methodology ◽

Melting Process ◽

Research Approach ◽

Analysis Method ◽

Laser Melting ◽

Huge Number ◽

Energy Estimation ◽

Content Type ◽

Potential Applications

Purpose – The purpose of this paper consists in the optimization and understanding of the Selective Laser Melting (SLM) manufacturing process of biomaterials, such as T40 and CoCrMo, as scaffolds. Moreover, process optimization is also challenging, with regards to the huge number of parameters and their influence on the finished product. Design/methodology/approach – The paper opted for an exploratory study using Taguchi analysis method to precisely identify the most relevant parameters and justify the energy estimation. Findings – The study showed that SLM fits perfectly with the T40 and CoCrMo part manufacturing. This method allowed to have a complete overview of all the potential applications of SLM for implant manufacturing. Originality/value – With this research approach, the results may be generalized to other material and showed a good theoretical approach.

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Metallographic evaluation of duplex stainless steel powders processed by selective laser melting

Rapid Prototyping Journal ◽

10.1108/rpj-04-2016-0053 ◽

2017 ◽

Vol 23 (6) ◽

pp. 1146-1163 ◽

Cited By ~ 10

Author(s):

Karl P. Davidson ◽

Sarat B. Singamneni

Keyword(s):

Stainless Steel ◽

Duplex Stainless Steel ◽

Selective Laser Melting ◽

A Priori ◽

Fine Tuning ◽

Structure Property ◽

Laser Melting ◽

Content Type ◽

Test Pieces ◽

Process Structure

Purpose This paper aims to establish the microstructures and the process-structure relationships in duplex stainless steel powders consolidated by selective laser melting (SLM). Design/methodology/approach A priori data on energy density levels most appropriate to consolidation of duplex stainless steel powders through SLM served as the basis to converge on the laser settings. Experimental designs with varying laser power and scan speeds and test pieces generated allowed metallographic evaluations based on optical and scanning electron microscopy and electro backscatter diffraction analyses. Findings Duplex stainless steel powders are established for processing by SLM. However, the dynamic point heat source and associated transient thermal fields affect the microstructures to be predominantly ferritic, with grains elongated in the build direction. Austenite precipitated either at the grain boundaries or as Widmanstätten laths, whereas the crystallographic orientations and the grain growth are affected around the cavities. Considerable CrN precipitation is also evidenced. Originality/value Duplex stainless steels are relatively new candidates to be brought into the additive manufacturing realm. Considering the poor machinability and other difficulties, the overarching result indicating suitability of duplex powders by SLM is of considerable value to the industry. More significantly, the metallographic evaluation and results of the current research allowed further understanding of the material consolidation aspects and pave ways for fine tuning and establishment of the process-structure-property relationships for this important process-material combination.

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Selective Laser Melting of Aluminum and Its Alloys

Materials ◽

10.3390/ma13204564 ◽

2020 ◽

Vol 13 (20) ◽

pp. 4564 ◽

Cited By ~ 1

Author(s):

Zhi Wang ◽

Raghunandan Ummethala ◽

Neera Singh ◽

Shengyang Tang ◽

Challapalli Suryanarayana ◽

...

Keyword(s):

Selective Laser Melting ◽

Processing Parameters ◽

Fatigue Properties ◽

Internal Stresses ◽

Surface Oxide Layer ◽

Alloy Development ◽

Laser Melting ◽

Powder Bed ◽

Microstructure Evaluation ◽

Melt Cooling

The laser-based powder bed fusion (LBPF) process or commonly known as selective laser melting (SLM) has made significant progress since its inception. Initially, conventional materials like 316L, Ti6Al4V, and IN-718 were fabricated using the SLM process. However, it was inevitable to explore the possible fabrication of the second most popular structural material after Fe-based alloys/steel, the Al-based alloys by SLM. Al-based alloys exhibit some inherent difficulties due to the following factors: the presence of surface oxide layer, solidification cracking during melt cooling, high reflectivity from the surface, high thermal conductivity of the metal, poor flowability of the powder, low melting temperature, etc. Researchers have overcome these difficulties to successfully fabricate the different Al-based alloys by SLM. However, there exists no review dealing with the fabrication of different Al-based alloys by SLM, their fabrication issues, microstructure, and their correlation with properties in detail. Hence, the present review attempts to introduce the SLM process followed by a detailed discussion about the processing parameters that form the core of the alloy development process. This is followed by the current research status on the processing of Al-based alloys and microstructure evaluation (including defects, internal stresses, etc.), which are dealt with on the basis of individual Al-based series. The mechanical properties of these alloys are discussed in detail followed by the other important properties like tribological properties, fatigue properties, etc. Lastly, an outlook is given at the end of this review.

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On efficiency and effectiveness of finite volume method for thermal analysis of selective laser melting

Engineering Computations ◽

10.1108/ec-03-2019-0106 ◽

2020 ◽

Vol 37 (6) ◽

pp. 2155-2175

Author(s):

Jin Wang ◽

Yi Wang ◽

Jing Shi

Keyword(s):

Thermal Analysis ◽

Finite Volume Method ◽

Selective Laser Melting ◽

Finite Volume ◽

Cost Effective ◽

Laser Melting ◽

Content Type ◽

Fast Prediction ◽

Volume Method ◽

Element Method

Purpose Selective laser melting (SLM) is a major additive manufacturing (AM) process in which laser beams are used as the heat source to melt and deposit metals in a layerwise fashion to enable the construction of components of arbitrary complexity. The purpose of this paper is to develop a framework for accurate and fast prediction of the temperature distribution during the SLM process. Design/methodology/approach A fast computation tool is proposed for thermal analysis of the SLM process. It is based on the finite volume method (FVM) and the quiet element method to allow the development of customized functionalities at the source level. The results obtained from the proposed FVM approach are compared against those obtained from the finite element method (FEM) using a well-established commercial software, in terms of accuracy and efficiency. Findings The results show that for simulating the SLM deposition of a cubic block with 81,000, 189,000 and 297,000 cells, the computation takes about 767, 3,041 and 7,054 min, respectively, with the FEM approach; while 174, 679 and 1,630 min with the FVM code. This represents a speedup of around 4.4x. Meanwhile, the average temperature difference between the two is below 6%, indicating good agreement between them. Originality/value The thermal field for the multi-track and multi-layer SLM process is for the first time computed by the FVM approach. This pioneering work on comparing FVM and FEM for SLM applications implies that a fast and simple computing tool for thermal analysis of the SLM process is within the reach, and it delivers comparable accuracy with significantly higher computational efficiency. The research results lay the foundation for a potentially cost-effective tool for investigating the fundamental microstructure evolution, and also optimizing the process parameters in the SLM process.

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Residual stress measurement techniques for Ti6Al4V parts fabricated using selective laser melting: state of the art review

Rapid Prototyping Journal ◽

10.1108/rpj-04-2019-0097 ◽

2020 ◽

Vol ahead-of-print (ahead-of-print) ◽

Author(s):

Ruben B.O. Acevedo ◽

Klaudia Kantarowska ◽

Edson Costa Santos ◽

Marcio C. Fredel

Keyword(s):

Residual Stress ◽

Selective Laser Melting ◽

Stress Measurement ◽

State Of The Art ◽

Measurement Techniques ◽

Residual Stress Measurement ◽

Hole Drilling ◽

X Ray Diffraction ◽

Laser Melting ◽

Content Type

Purpose This paper aims to generate a review of available techniques to measure Residual Stress (RS) in Ti6Al4V components made by Ti6Al4V. Design/methodology/approach State of the art; literature review in the field of Residual Stress measurement of Ti6Al4V parts made by selective laser melting (SLM). Findings Different Residual Stress measurement techniques were detailed, regarding its concept, advantages and limitations. Regarding all researched references, hole drilling (semi destructive) and X-ray diffraction (nondestructive) were the most cited techniques for Residual Stress measurement of Ti6Al4V parts made by SLM. Originality/value An extensive analysis of RS measurement techniques for Ti6Al4V parts made by SLM.

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