Electron Beam Melting Machine Research Articles

The Effect of Post-Processing on the Mechanical Behavior of Ti6Al4V Manufactured by Electron Beam Powder Bed Fusion for General Aviation Primary Structural Applications

In this work a mechanical characterization of Ti6Al4V processed by electron beam powder bed fusion additive manufacturing was carried out to investigate the viability of this technology for the manufacturing of flyable parts for general aviation aircraft. Tests were performed on different manufacturing conditions in order to investigate the effect of post processing as machining on the mechanical behavior. The study provides useful information to airframe designers and manufacturing specialists that work with this technology. The investigation confirms the low process variability and provides data to be used in the design loop of general aviation primary structural elements. The test results show a high level of repeatability indicating that the process is well controlled and reliable enough to match the airworthiness requirements. In addition, the so-called “as-built specimens”, i.e., specimens produced by the electron beam melting machine without any major post-processing, have lower mechanical performances than specimens subjected to a machining phase after the electron beam melting process. Specific primary structural elements will be designed and flight cleared, resulting from the findings presented herein.

Pilot investigation of surface-tilt and gas amplification induced contrast during electronic imaging for potential in-situ electron beam melting monitoring

Electron Beam Melting (EBM) is a powder bed fusion (metal additive manufacturing) technique employed by many industrial sectors. In-situ EBM monitoring for quality assurance purposes has been a popular research area, and the potential of electronic imaging has been investigated recently. The imaging conditions inside an EBM machine are different from that of a typical scanning electron microscope. These differences are thought to affect image quality, and investigations should be carried out to understand the potential challenges of carrying out electronic imaging inside an EBM machine. This study addresses two of these challenges: (1) surface-tilt image contrast due to large-area imaging, and (2) gas amplification of the feedback electron signal due to the presence of chamber gas. This knowledge gap was tackled by the following approach: (1) estimating both the feedback electron yield and gas amplification of electron signal during electronic imaging; (2) simulating the surface-tilt image contrast during large-area imaging; and (3) presenting an electronic imaging experiment conducted at room temperature to investigate the influence of surface-tilt and gas amplification on image contrast. Experimental results indicate that when conducting electronic imaging in a typical EBM machine, the total feedback electron yield is of the order of 20%; the surface-tilt image contrast is insignificant over the EBM machine processing area; and the influence of gas amplification creates observable, non-uniform signal variation when imaging was conducted over a plain stainless steel plate. This article serves as a pilot study, laying the scientific foundation for subsequent investigations into another challenge under real EBM condition, i.e. the influence of metallisation during melt-pool electronic imaging.

Quality by Design for industry translation: Three‐dimensional risk assessment failure mode, effects, and criticality analysis for additively manufactured patient‐specific implants

AbstractThe complexity of patient‐specific implants combined with the current limited expertise in reliability engineering and manufacturability in the additive manufacturing (AM) sector is posing a number of quality performance challenges. Worldwide medical device regulatory bodies are facing increasing pressure to devise adequate standards to ensure long‐term patient safety and product performance. The implementation of the Quality by Design (QbD) system to titanium 3D‐printed bone implants offers a proven system to ensure that products are designed and manufactured correctly from the beginning without errors. This article reports on the development of a failure mode, effects, and criticality analysis (FMECA) coupled with a 3D risk assessment approach. This integrated approach is based on a questionnaire performed with three industry firms and three university research groups with significant experience and expertise in medical device product development and/or research in this field. Research outcomes include a FMECA form containing 137 failure modes with AM materials, AM machine general, fabrication, electron beam melting machine, finishing, and design being as the most sensitive process areas in terms of product quality. We subsequently propose corresponding preventive and corrective strategies for risk mitigation. The approach forms part of the QbD system being developed by the authors specifically for additive manufactured titanium patient‐specific implants.

Material characterisation using electronic imaging for Electron Beam Melting process monitoring

In-situ process monitoring in Electron Beam Melting (EBM) is critical in certifying build quality, by identifying contamination from the feedstock and condensate spallation from within the build area. The chamber condition in an EBM machine is different from a typical electron microscope. Therefore this study explores in-situ EBM material characterisation with a custom electronic imaging prototype. Typical contamination elements found in a popular EBM material (Ti-6Al-4V) were electronically imaged at room temperature. Material contrast is observed in the electronic images generated by the prototype. This trial is thought to serve as a baseline study for future EBM monitoring system development.

In-situ areal inspection of powder bed for electron beam fusion system based on fringe projection profilometry

Additive manufacturing (AM) techniques provide significant advantages over conventional subtractive manufacturing techniques in terms of the wide range of part geometry that can be obtained. Powder delivery is a process that occurs thousands of times during the AM build process, consequently assessment of delivery quality would be advantageous in the process in order to provide feedback for process control. This paper presents an in-situ quantitative inspection technique for assessing the whole of the powder bed post raking, by using fringe projection profilometry. In order to increase accuracy and traceability of the inspection technique, an accepted fringe projection method, is enhanced using a novel surface fitting algorithm employed to reduce the influence of phase error and random noise during calibration. A simulation was conducted to verify the accuracy of the proposed system calibration. The proposed in-situ inspection technique has been applied in an Electron Beam Powder Bed Fusion (PBF-EB) machine, also known as Electron Beam Melting (EBM). Some examples of melting edge swelling and excessive powder delivery due to rake damage during a real part build are used to demonstrate the system capability on the actual EBM machine. A build process with presented fringe projection system is reported in this paper. Experimental results demonstrate that powder defects can be efficiently inspected and the results used as feedback information in a build process.

Benchmarking spatial resolution in electronic imaging for potential in-situ Electron Beam Melting monitoring

Electron Beam Melting (EBM) is an increasingly used Additive Manufacturing (AM) technique employed by many industrial sectors, including the medical device and aerospace industries. In-situ EBM monitoring for quality assurance purposes has been a popular research area. Electronic imaging has recently been investigated as one of the in-situ EBM data collection methods, alongside thermal / optical imaging techniques. So far, the disseminations focus on the design of an electronic imaging system and the ability to generate electronic images in-situ, experiments are yet to be carried out to benchmark one of the most important features of any imaging systems – spatial resolution. This article addresses this knowledge gap by: (1) proposing an indicator for the estimation of spatial resolution which includes the Backscattered Electrons (BSE) information depth, (2) estimating the achievable spatial resolution when electronic imaging is carried out inside an Arcam A1 EBM machine, and (3) presenting an experimental method to conduct a knife edge test with the EBM machine. Analyses of experimental results indicated that the spatial resolution was of the order of 0.3 to 0.4 mm when electronic imaging was carried out at room temperature. It is believed that by disseminating an analysis and experimental method to estimate and quantify spatial resolution, this study has contributed to the on-going quality assessment research in the field of in-situ monitoring of the EBM process.

Microstructure and Mechanical Properties of Welded Additively Manufactured Stainless Steels SS316L

Microstructure and mechanical properties of additively manufactured SS316L has been investigated. The samples produced by selective electron beam melting machine were then subjected to gas tungsten arc welding. Various examinations were performed including metallography and microscopy, hardness testing, and tensile testing coupled with digital image correlation software. Strain distribution was clearly evident on the samples during tensile testing with necking taking place at the heat affected zone on both sides of the weldments. From tensile testing, it was clear that the ductility and strengths of the samples were equal to those of conventionally produced samples such as rolled sheet. Hardness testing indicated the uniform distribution across the base metal and the weldments. Scanning electron microscopy identified the presence of Cr and Mo-rich precipitates on the grain boundaries, while the fracture surface was entirely covered with dimples (microvoid coalescence) indicating a ductile fracture mode.

Pilot investigation of feedback electronic image generation in electron beam melting and its potential for in-process monitoring

Electron Beam Melting (EBM) is an additive manufacturing technique increasingly used by many industrial sectors, including the medical and aerospace industries. The application of this technology is, however, challenged by the lack of process monitoring and control systems to monitor process repeatability and component quality reproducibility. Various monitoring systems, mainly involving thermal and optical cameras, have been employed in previous attempts to study the quality of the EBM process. However, these systems have limitations, which include: (1) images generated unavoidably include monitoring-irrelevant regions beyond the processing area and (2) images are subject to keystone distortion. In this paper, a digital electronic imaging system prototype is described for the Arcam A1 EBM machine. This paper aims to: (1) disseminate the prototype design, (2) demonstrate the prototype ability to overcome limitations of the existing thermal and optical imaging systems, (3) showcase the potential for the prototype to serve as an alternative EBM monitoring technique, and (4) serve as a pilot study for future in-process EBM monitoring research with electronic imaging. Digital electronic images were generated by detecting both secondary electrons and backscattered electrons originating from interactions between the machine electron beam and the processing area using specially designed hardware. Prototype capability experiments at room temperature and approximately 320°C were conducted with digital images being generated and analysed from a Ti-6-Al-4V (as demonstrator material) test build. Results suggest that this prototype has significant potential to be used for in-process monitoring of EBM in many manufacturing sectors.

Cranioplasty Enhanced by Three-Dimensional Printing: Custom-Made Three-Dimensional-Printed Titanium Implants for Skull Defects.

The authors studied to demonstrate the efficacy of custom-made three-dimensional (3D)-printed titanium implants for reconstructing skull defects. From 2013 to 2015, 21 patients (8-62 years old, mean = 28.6-year old; 11 females and 10 males) with skull defects were treated. Total disease duration ranged from 6 to 168 months (mean = 33.6 months). The size of skull defects ranged from 84 × 104 to 154 × 193 mm. Custom-made implants were manufactured by Medyssey Co, Ltd (Jecheon, South Korea) using 3D computed tomography data, Mimics software, and an electron beam melting machine. The team reviewed several different designs and simulated surgery using a 3D skull model. During the operation, the implant was fit to the defect without dead space. Operation times ranged from 85 to 180 minutes (mean = 115.7 minutes). Operative sites healed without any complications except for 1 patient who had red swelling with exudation at the skin defect, which was a skin infection and defect at the center of the scalp flap reoccurring since the initial head injury. This patient underwent reoperation for skin defect revision and replacement of the implant. Twenty-one patients were followed for 6 to 24 months (mean = 14.1 months). The patients were satisfied and had no recurrent wound problems. Head computed tomography after operation showed good fixation of titanium implants and satisfactory skull-shape symmetry. For the reconstruction of skull defects, the use of autologous bone grafts has been the treatment of choice. However, bone use depends on availability, defect size, and donor morbidity. As 3D printing techniques are further advanced, it is becoming possible to manufacture custom-made 3D titanium implants for skull reconstruction.

Macroscopic simulation and experimental measurement of melt pool characteristics in selective electron beam melting of Ti-6Al-4V

Selective electron beam melting of Ti-6Al-4V is a promising additive manufacturing process to produce complex parts layer-by-layer additively. The quality and dimensional accuracy of the produced parts depend on various process parameters and their interactions. In the present contribution, the lifetime, width and depth of the pools of molten powder material are analyzed for different beam powers, scan speeds and line energies in experiments and simulations. In the experiments, thin-walled structures are built with an ARCAM AB A2 selective electron beam melting machine and for the simulations a thermal finite element simulation tool is used, which is developed by the authors to simulate the temperature distribution in the selective electron beam melting process. The experimental and numerical results are compared and a good agreement is observed. The lifetime of the melt pool increases linearly with the line energy, whereby the melt pool dimensions show a nonlinear relation with the line energy.

Effect of processing parameters of electron beam melting machine on properties of Ti-6Al-4V parts

Purpose This paper aims to study the effect of processing parameters of an electron beam melting (EBM) machine on the surface roughness, critical pitting temperature and density of Ti-6Al-4V parts produced from the EBM machine. Design/methodology/approach In this study, statistically designed experiments were used to manufacture Ti-6Al-4V samples in the EBM machine under different process parameters of beam current, beam speed and offset focus. Surface roughness was measured for as-built samples using a 3D profilometer. Then, a potentiostatic test was conducted under 2.40 V vs saturated calomel electrode to determine the critical pitting temperature (CPT) in 3.5 per cent mass NaCl solution for the samples of different processing parameters. Next, density was measured for these samples. Finally, model equations were established to relate EBM’s process parameters to measured properties of surface roughness, CPT and density. Findings Results showed that offset focus had the main influence on surface roughness more than the beam current and the beam speed. Changing processing parameters did not affect corrosion behavior of EBM Ti-6Al-4V as CPT did not vary widely, although a slight effect on CPT values obtained from the beam current and the beam speed. Density was greatly affected by the offset focus more than the other parameters. It can be concluded that uniform and precise measurements of roughness and density are not achievable through this machine; only a range of these properties can be attained. Originality/value EBM machine produces 3D parts in a layer-based building process under high temperature and vacuum atmosphere. Due to the manufacturing technique and conditions, the resulting object has irregularities on the exterior surface and voids that are formed within the part, both of which affect samples’ properties like surface roughness, CPT and density. This study established model equations that can relate parts’ properties to processing parameters so that parts of specific properties are obtained to fit the application they are used for. For each property, ANOVA fits vs linear energy were also obtained.

Corrosion evaluation of Ti-6Al-4V parts produced with electron beam melting machine

Purpose This paper aims to evaluate the corrosion behavior of Ti-6Al-4V parts produced with electron beam melting (EBM) machine and compare it with wrought Ti-6Al-4V alloy. Design/methodology/approach Potentiodynamic and potentiostatic tests were applied on EBM Ti-6Al-4V in 3.5 per cent mass NaCl solution to determine the pitting potential and critical pitting temperature (CPT). A relation between pitting potential and temperature was established for EBM Ti-6Al-4V alloy by conducting potentiodynamic testing under different temperatures. CPT was also measured for EBM Ti-6Al-4V alloy in 3.5 per cent mass NaCl solution at a standard potential of 800 mV vs saturated calomel electrode (SCE). The same tests were performed on wrought Ti-6Al-4V for comparison purposes. Moreover, CPT for EBM Ti-6Al-4V alloy was measured in 3.5 per cent mass NaCl solution of different pH of 2.0, 5.7 and 10.0 to examine the effect of aggressive conditions on the pitting corrosion of EBM alloy. Findings Potentiodynamic test resulted in a relatively high pitting potential of EBM alloy, which was close to the pitting potential of wrought alloy even at higher temperatures. In addition, EBM samples did not pit when potentiostatic test was performed at 800 mV vs SCE, even at high and low values of pH. Originality/value EBM Ti-6Al-4V alloy has been increasingly playing an important role in aerospace, automobile and industrial fields. The technique and conditions of manufacturing form voids and increase roughness of the exterior surface of EBM objects, which might increase the tendency to initiate pitting corrosion within its holes and surface folds. This article shows that, despite surface variations and porosity in EBM Ti-6Al-4V alloy, the material maintained its corrosion resistance. It was found that the corrosion behavior of EBM alloy was close to that of the conventionally made wrought Ti-6Al-4V alloy.

Building new entities from existing titanium part by electron beam melting: microstructures and mechanical properties

Electron beam melting (EBM) has been recognized as an emerging additive manufacturing technology, which allows the production of fully dense parts from various metals. The technique builds parts using an electron beam to melt metal powder, layer by layer, in a powder bed. Thus, complex parts, including internal structures, can be made directly from 3D CAD models without special fixtures and cutting tools. Much research is conducted to study the microstructure and mechanical properties of EBM-built parts or to investigate the effects of EBM process parameters on the quality of parts. However, using EBM for building new features on an existing part has received little attention from the research community. Due to its performance, EBM seems able to transform an end-of-life (EoL) part/existing part into a new part without returning to the level of raw material. The aim of this study is to validate such principle. In this paper, an EBM machine was used to produce new Ti-6Al-4V features on a Ti-6Al-4V plate, which was considered as a useful core retrieved from an EoL product. The built samples, including EBM-built features and Ti-6Al-4V plate, were investigated in terms of their microstructure and mechanical properties. The results showed that EBM technique allows new features with a suitable microstructure and controlled mechanical properties to be built on an existing part. Moreover, the EBM-built features have a strong bond with the existing part leading to the same mechanical characteristics as original part. These demonstrate that the EBM technology has a promising potential for producing new parts from EoL parts/existing parts.

Skull Reconstruction with Custom Made Three-Dimensional Titanium Implant.

BackgroundSource material used to fill calvarial defects includes autologous bones and synthetic alternatives. While autologous bone is preferable to synthetic material, autologous reconstruction is not always feasible due to defect size, unacceptable donor-site morbidity, and other issues. Today, advanced three-dimensional (3D) printing techniques allow for fabrication of titanium implants customized to the exact need of individual patients with calvarial defects. In this report, we present three cases of calvarial reconstructions using 3D-printed porous titanium implants.MethodsFrom 2013 through 2014, three calvarial defects were repaired using custommade 3D porous titanium implants. The defects were due either to traumatic subdural hematoma or to meningioma and were located in parieto-occipital, fronto-temporo-parietal, and parieto-temporal areas. The implants were prepared using individual 3D computed tomography (CT) data, Mimics software, and an electron beam melting machine. For each patient, several designs of the implant were evaluated against 3D-printed skull models. All three cases had a custom-made 3D porous titanium implant laid on the defect and rigid fixation was done with 8 mm screws.ResultsThe custom-made 3D implants fit each patient's skull defect precisely without any dead space. The operative site healed without any specific complications. Postoperative CTs revealed the implants to be in correct position.ConclusionAn autologous graft is not a feasible option in the reconstruction of large calvarial defects. Ideally, synthetic materials for calvarial reconstruction should be easily applicable, durable, and strong. In these aspects, a 3D titanium implant can be an optimal source material in calvarial reconstruction.

The Manufacture of Custom Made 3D Titanium Implant for Skull Reconstruction

Nowadays, with advanced 3D printing techniques, the custom-made implant can be manufactured for the patient. Especially in skull reconstruction, it is difficult to design the implant due to complicated geometry. In large defect, an autograft is inappropriate to cover the defect due to donor morbidity. We present the process of manufacturing the 3D custom-made implant for skull reconstruction. There was one patient with skull defect repaired using custom-made 3D titanium implant in the plastic and reconstructive surgery department. The patient had defect of the left parieto-temporal area after craniectomy due to traumatic subdural hematoma. Custom-made 3D titanium implants were manufactured by Medyssey Co., Ltd. using 3D CT data, Mimics software and an EBM (Electron Beam Melting) machine. The engineer and surgeon reviewed several different designs and simulated a mock surgery on 3D skull model. During the operation, the custom-made implant was fit to the defect properly without dead space. The operative site healed without any specific complications. In skull reconstruction, autograft has been the treatment of choice. However, it is not always available and depends on the size of defect and donor morbidity. As 3D printing technique has been advanced, it is useful to manufacture custom-made implant for skull reconstruction.

Production of customized hip stem prostheses – a comparison between conventional machining and electron beam melting (EBM)

PurposeThe purpose of this paper is to study the use of the additive manufacturing (AM) method, electron beam melting (EBM), for manufacturing of customized hip stems. The aim is to investigate EBM's feasibility and commercial potential in comparison with conventional machining, and to map out advantages and drawbacks of using EBM in this application. One part of the study concerns the influence on the fatigue properties of the material, when using the raw surface directly from the EBM machine, in parts of the implant.Design/methodology/approachThe research is based on a case study of manufacturing a batch of seven individually adapted hip stems. The stems were manufactured both with conventional machining and with EBM technology and the methods were compared according to the costs of materials, time for file preparation and manufacturing. In order to enhance bone ingrowths in the medial part of the stem, the raw surface from EBM manufacturing is used in that area and initial fatigue studies were performed, to get indications on how this surface influences the fatigue properties.FindingsThe cost reduction due to using EBM in this study was 35 per cent. Fatigue tests comparing milled test bars with raw surfaced bars indicate a reduction of the fatigue limit by using the coarse surface.Originality/valueThe paper presents a detailed comparison of EBM and conventional machining, not seen in earlier research. The fatigue tests of raw EBM‐surfaces are interesting since the raw surface has shown to enhance bone ingrowths and therefore is suitable to use in some medical applications.

Fabrication and compressive properties of Ti6Al4V implant with honeycomb‐like structure for biomedical applications

PurposeThe purpose of this paper is to verify the feasibility and evaluate the compressive properties of Ti6Al4V implants with controlled porosity via electron beam melting process. This process might be a promising method to fabricate orthopedic implants with suitable pore architecture and matched mechanical properties.Design/methodology/approachTi6Al4V implants with controlled porosity are produced using an electron beam melting machine. A scanning electron microscope is utilized to examine the macro‐pore structures of the Ti6Al4V implants. The compressive test is performed to investigate the mechanical properties of the porous implants.FindingsThe fabricated samples show a fully interconnected open‐pore network. The compressive yield strength of the Ti6Al4V implants with the porosity of around 51 percent is higher than that of human cortical bone. The Young's modulus of the implants is similar to that of cortical bone.Research limitations/implicationsThe surface of samples produced by electron beam melting process is covered with loosely spherical metal particles. Polishing and ultrasonic cleaning have to be used to remove the loose remnants.Originality/valueThis paper presents the potential application in the fabrication of orthopedic or dental implants using electron beam melting process.

Applications of structural optimization in direct metal fabrication

PurposeOptimization techniques can be used to design geometrically complex components with a wide variety of optimization criteria. However, such components have been very difficult and costly to produce. Layered fabrication technologies such as electron beam melting (EBM) open up new possibilities though. This paper seeks to investigate the integration of structural optimization and direct metal fabrication process.Design/methodology/approachMesh structures were designed, and optimization problems were defined to improve structural performance. Finite element analysis code in conjunction with nonlinear optimization routines were used in MATLAB. Element data were extracted from an STL‐file, and output structures from the optimization routine were manufactured using an EBM machine. Original and optimized structures were tested and compared.FindingsThere were discrepancies between the performance of the theoretical structures and the physical EBM structures due to the layered fabrication approach. A scaling factor was developed to account for the effect of layering on the material properties.Practical implicationsStructural optimization can be used to improve the performance of a design, and direct fabrication technologies can be used to realise these structures. However, designers must realize that fabricated structures are not identical to idealized CAD structures, hence material properties much be adjusted accordingly.Originality/valueIntegration of structural optimization and direct metal fabrication was reported in the paper. It shows the process from design through manufacturing with integrated analysis.