Metal 3D Printing Research Articles

Static and Fatigue Load Bearing Investigation on Porous Structure Titanium Additively Manufactured Anterior Cervical Cages.

This study investigates the static and fatigue behavior of porous and conventional anterior cervical cages. Porous structure titanium anterior cervical cages were manufactured using direct selective laser sintering technique. Four different types of cervical cages were designed and manufactured, among which three designs consist of porous structure (type 1, type 2, and type 3) and manufactured using metal 3D printing. Remaining one design (type 4) was manufactured using conventional machining and did not consist any porous structure. All types of manufactured cages were tested in compression under static and fatigue loading conditions as per ASTM F2077 standard. Static and fatigue subsidence testing was performed using ASTM F2267 standard. Static compression testing results of type 1 and type 4 cages reported higher yield load when compared to the type 2 and type 3 cages. Static subsidence testing results reported almost 11% less subsidence rate for additively manufactured cages than the conventional cages. Fatigue subsidence testing results showed that type 2 and type 3 cages can withstood approximately 21% higher number of cycles before subsidence as compare to the type 1 and type 4 cages. During fatigue testing, all the cages design survived 5 million cycles at the 3000 N loading. For 6000 N and 8000 N, loading rate type 2 and type 3 cages showed lower fatigue life when compared to other cages design. Since fatigue life of type 2 and type 3 cage designs were reported lower than other cages design, it is concluded that the performance of the additively manufactured porous cages can be significantly varied based upon the cage design features.

Mechanical testing and microstructural analysis of wire arc additively manufactured steels

Wire arc additive manufacturing (WAAM) is a metal 3D printing method that allows the cost-effective and efficient production of large-scale elements, and has thus gained great interest from architects and structural engineers. Integration of this novel technology into the construction industry, however, requires the development of a clear understanding of the mechanical behaviour of WAAM materials. To this end, a comprehensive experimental study into the mechanical properties and microstructure of WAAM plates made of normal- and high-strength steels has been undertaken and is reported herein. A total of 137 as-built and machined tensile coupons were tested, extracted in various directions relative to the print layer orientation from WAAM plates of two nominal thicknesses, built using different deposition strategies. The influence of the geometric undulations inherent to the WAAM process and deposition strategy on the resulting mechanical properties was investigated. Microstructural characterisation was also performed by means of optical microscopy (OM) and electron backscatter diffraction (EBSD). The WAAM normal-strength steel plates exhibited a principally ferritic-pearlitic microstructure, while the WAAM high-strength steel plates displayed a mixed microstructure featuring ferrite, bainite and martensite. The EBSD analysis revealed a weak crystallographic texture, which explained the observed mechanical properties being almost isotropic. No significant differences in tensile properties were observed with the different deposition strategies, except for some variation in ductility. The geometric undulations of the as-built coupons resulted in some reduction in effective mechanical properties and a degree of anisotropy. Overall, the examined WAAM material exhibited consistent mechanical properties, a Young’s modulus comparable to conventionally-produced steel plates, marginally lower strength, reflecting the slower cooling conditions than is customary, and good ductility.

A general fruit acid chelation route for eco-friendly and ambient 3D printing of metals

Recent advances in metal additive manufacturing (AM) have provided new opportunities for prompt designs of prototypes and facile personalization of products befitting the fourth industrial revolution. In this regard, its feasibility of becoming a green technology, which is not an inherent aspect of AM, is gaining more interests. A particular interest in adapting and understanding of eco-friendly ingredients can set its important groundworks. Here, we demonstrate a water-based solid-phase binding agent suitable for binder jetting 3D printing of metals. Sodium salts of common fruit acid chelators form stable metal-chelate bridges between metal particles, enabling elaborate 3D printing of metals with improved strengths. Even further reductions in the porosity between the metal particles are possible through post-treatments. A compatibility of this chelation chemistry with variety of metals is also demonstrated. The proposed mechanism for metal 3D printing can open up new avenues for consumer-level personalized 3D printing of metals.

New Level of high-resolution Computed Tomography with a 450kV Meso Focus x-ray Source

Computed Tomography (CT) production applications of modern components are increasingly faced with the challenge of achieving a very high resolution even with high densities and a comparatively large material thickness. These components in the aerospace, automotive and electronics industries often consist of 3D-printed metals such as iron, copper, nickel or alloys with resolution requirements rising higher than 10 lp/mm (50 μm). With Computed Tomography and the new MesoFocus x-ray source at 450 kV, YXLON uses the innovative Comet technology, which is made for industrial applications where resolution and penetration of dense material-objects matter. CT with the MesoFocus sources eliminates the tradeoff everyone has to make today between sealed tube solutions and open microfocus tubes – sealed tubes are robust and stable and made for production environments, but offer only limited resolution, while open microfocus tubes offer high resolution, but are not made for production environments and 24/7 operation. YXLON’s new CT solutions allow hassle-free operation, while they bring lab resolution to the production floor. The excellent stability of the sealed MesoFocus x-ray source enables long exposure times that are an enormous advantage for CT applications and are a perfect fit for inspection in aerospace, automotive and electronics industries. The excellent resolution down to 30 μm makes the CT solution the key enabler for advanced manufacturing technologies such as additive manufacturing. We will present CT results for 3D-printed iron and copper parts as well as for finest mechanics surrounded by gold with sub40μm resolution. Duplex wire IQI and ASTM E1695 results prove the image chain resolution.

Evaluation of metal additive manufacturing for high-field modular-stellarator radial plates and conductors

The utilization of metal additively manufactured radial plates and conductors for high-field modular-stellarator coils is assessed, particularly, for resistive coils having turns of variable cross-section (additively manufactured aluminium or copper turns). This concept of radial plates might also be applicable to superconducting wire and resistive conductors of constant cross-section.Modular coils and their winding packs for (high-field) stellarators require high precision, durability under high internal Lorentz forces and thermal stresses, stiffness and strength, in rather contorted components. Radial plates have been utilized in tokamaks (i.e. ITER) and are proposed for tokamak and stellarator reactors (i.e. FFHR), particularly when the high Lorentz forces may compromise the mechanical integrity of the insulation and winding pack. Radial plates for tokamaks have been produced by milling steel plate, and welding different segments if the size requires it. However, the contorted shape of stellarator modular coils makes the manufacturing of radial plates more challenging. This suggests the possible use of additive manufacturing, which is particularly appropriate for short series of geometrically complex parts.In relation to those matters, this work investigates whether metal additive manufacturing of contorted radial plates and metallic conductor turns (windings, to be introduced in the radial plates) of variable cross-section and proper insulation, may be satisfactory for small or middle size high-field stellarators. The emphasis is placed on the accuracy, mechanical properties and cost of those parts. The feasibility, advantages and weakness of the additive manufacturing process and the assembling procedure are tested and studied. With the present commercial metal 3D printers, metal additively manufactured radial plates will require final milling to achieve enough accuracy. Coil casings appear feasible without final milling, and windings of variable cross-section, produced from brazing modified flexible copper wire, are promising.

Intensity Modulated High Dose Rate (HDR) Brachytherapy Using Patient Specific 3D Metal Printed Applicators: Proof of Concept.

PurposeIn high-dose-rate (HDR) brachytherapy, an anisotropic dose distribution may be desirable for achieving a higher therapeutic index, particularly when the anatomy imposes challenges. Several methods to deliver intensity-modulated brachytherapy (IMBT) have been proposed in the literature, however practical implementation is lacking due to issues of increased delivery times and complicated delivery mechanisms. This study presents the novel approach of designing a patient-specific inner shape of an applicator with 3D metal printing for IMBT using an inverse plan optimization model.MethodsThe 3D printed patient-specific HDR applicator has an external shape that resembles the conventional brachytherapy applicator. However, at each dwell position of the HDR source, the shielding walls in the interior are divided into six equiangular sections with varying thicknesses. We developed a mathematical model to simultaneously optimize the shielding thicknesses and dwell times according to the patient’s anatomical information to achieve the best possible target coverage. The model, which is a bi-convex optimization problem, is solved using alternating minimization. Finally, the applicator design parameters were input into 3D modeling software and saved in a 3D printable file. The applicator has been tested with both a digital phantom and a simulated clinical cervical cancer patient.ResultsThe proposed approach showed substantial improvements in the target coverage over the conventional method. For the phantom case, 99.18% of the target was covered by the prescribed dose using the proposed method, compared to only 58.32% coverage achieved by the conventional method. For the clinical case, the proposed method increased the coverage of the target from 56.21% to 99.92%. In each case, both methods satisfied the treatment constraints for neighboring OARs.ConclusionThe study simulates the concept of the IMBT with inverse planning using the 3D printed applicator design. The non-isotropic dose map can be produced with optimized shielding patterns and tailored to individual patient’s anatomy, to plan a more conformal plan.

Fundamental Experiments of Pulsed GMA Additive Manufacturing

Metal 3D printing based on laser sintering is important in various industrial fields. However, its limitations are being revealed due to the need for expensive machines and metal powder. Meanwhile, wire arc additive manufacturing (WAAM) is rapidly arising as an alternative technology thanks to its relatively economic cost. Despite the boom of WAAM, its advantages are not that clear, because the majority of the research to date has been based on relatively expensive facilities, of which the cold metal transfer (CMT) machine is representative. In this study, the WAAM process is being improved with general pulsed GMA to lower the barrier of high cost and facilitate the adoption of the WAAM process in actual manufacturing industries. All process parameters, such as current, voltage, welding speed, and CTWD were examined to figure out a proper synergic line for WAAM. As a result, a high sulfur proportion wire and proper process parameters could be suggested. Finally, the proposed synergic line successfully produced a steel wall consisting of 10 layers with a thickness of 7.2 mm and a height of 22.4 mm, which can serve as an example of WAAM with pulsed GMA.

The atrophic edentulous alveolus. A preliminary study on a new generation of subperiosteal implants.

The aim of this cohort case series is to present a new subperiosteal implant device that uses CAD-CAM technologies together with 3D metal printing capabilities to produce direct bone-anchored dental prosthetic solutions for the management of atrophic edentulous alveolus and jaws. The clinical experience of 21 subperiosteal devices implanted over a 4-year period is presented. The results of this study showed 14 of the 21 cases were successful (66.7%), while 7 cases had complications including exposure of the metal frame (5 cases), mobility of the device (1 case) and 1 case failed for reasons unrelated to the device. Four of the 7 cases were successfully salvaged resulting in an overall success rate of 85.7% (18 /21 cases). This study supports the use of fully customized subperiosteal jaw implants as a simple and reliable alternative for dental rehabilitation of atrophic edentulous cases which would otherwise require bone grafts for conventional fixed dental implant solutions. With more research, the clinical potential for this device is significant as it not only avoids the need for complex and lengthy reconstructive jaw surgery but also allows for the placement of immediate prosthetic teeth at the time of implantation.

Clinical and Radiographic Outcomes of Novel 3D-Printed Highly Porous Knee Cone Design.

Metaphyseal bone defects seen at revision total knee replacement (TKA) have traditionally been treated with bone graft or cement. Recently, metal augments have surfaced as viable alternatives to conventional methods previously used in these patients. Newer 3D-printed metal cones offer better biological fixation as a means of improving construct stability. This study aimed to determine clinical and radiographic outcomes of the novel 3D-printed titanium cone augments for femoral and tibial metaphyseal bone defects. A retrospective review was undertaken of 72 patients who underwent revision TKA with metaphyseal cones (Stryker) and stemmed implants from 2015-2017. Knee Injury and Osteoarthritis Outcome Scores (KOOS Jr) and VR/SF-12 scores were recorded. Knee Society radiographic scores were calculated at latest follow up to evaluate for radiolucency and biological fixation. Loosening noted on radiographs and reoperation for any reason were the endpoints to determine survivorship. A total of 68 patients with 78 cones (58 tibial, 20 femoral) met inclusion criteria. Mean follow up was 3.4 years (range 2-5.4 years). The average KOOS Jr score increased from 38 preoperatively to 66 at two years. The average VR/SF-12 PH score increased from 33 preoperatively to 37 at two years. The average VR/SF-12 MH score increased from 46 preoperatively to 54 at two years. Twelve percent of tibial implants and 10% of femoral implants with cones were found to have lucency in at least one radiographic zone. Overall survivorship at latest follow up was 93% with two patients requiring revision for infection, two revised following mechanical complications, and one patient who underwent polyethylene exchange after experiencing mechanical complications. When considering only aseptic loosening, survivorship was 100%. This 3D-printed titanium femoral and tibial cone augment system showed excellent survivorship, biological fixation, clinical outcomes, and radiographic outcomes in the setting of TKA. Further studies are needed for assessment of long-term survivorship.

Role of metal 3D printing to increase quality and resource-efficiency in the construction sector

Demand for the construction of new structures is increasing all over the world. Since the construction sector dominates the global carbon footprint, new construction methods are needed with reduced embodied carbon and high resource efficiency to realize a sustainable future. In this direction, Metal Additive Manufacturing, also known as metal 3D printing, can be an opportunity. Many studies are underway to answer open questions about the metal 3D printing processes and products for high-tech industries. The construction sector must join the metal 3D printing research more actively to enrich the knowledge and experience on this technology, and correctly adapt the process parameters suitable to the construction sector requirements. This paper states the opinion of a research group composed of academics and practitioners from Europe, the US, Japan, and South Africa on how metal 3D printing can be a complementary tool/technology to conventional manufacturing to increase productivity rates, and reduce the costs and CO 2 emissions in the construction industry.

The effects of a 3D-printed magnesium-/strontium-doped calcium silicate scaffold on regulation of bone regeneration via dual-stimulation of the AKT and WNT signaling pathways

Numerous studies have demonstrated that calcium silicate (CS) can be doped with various trace metal elements such as strontium (Sr) or magnesium (Mg). These studies have confirmed that such modifications promote bone regeneration. However, the development and emergence of 3D printing have further made it possible to fabricate bone grafts with precise structural designs using multi-bioceramics so as to better suit specific clinical requirements. We fabricated scaffolds using Mg-doped CS as the outer layer with Sr-doped CS in the center. In addition, PCL was used to improve printability of the scaffolds. This enhanced Mg and Sr architecture prevented premature degradation of the scaffolds during immersion while enabling the release of ions in a sustained manner in order to achieve the desired therapeutic goals. Even the capabilities of stem cells were shown to be enhanced when cultured on these scaffolds. Furthermore, the hybrid scaffolds were found to up-regulate the expression of bone-related proteins such as factors leading to differentiation-inducing pathways, including PI3K/Akt, Wnt, and TRPM7. The in vivo performance of the proposed scaffolds was assessed using micro-CT. The histological results revealed that the hybrid scaffolds were able to further enhance bone regeneration as compared to uni-bioceramics. By combining 3D printing, multi-ceramics, and trace metal elements, a novel hybrid scaffold could be fabricated with ease and specifically suited to future bone tissue engineering applications.

Multiphysics simulation of microscale copper printing by confined electrodeposition using a nozzle array

3D printing of metals at the microscale and nanoscale is crucial to produce high-density interconnects and intricate structures in electronic devices. Conventional melting and sintering processes are not suitable for these scales due to a reliance on individual metal particles in the size range of tens of micrometers. Confined electrodeposition (CED) is an established alternative to conventional metal 3D printing processes in which an electrolyte is used to selectively induce deposition of the metal on the printing surface. However, commercialization and efficiency of this process have been limited due to a reliance on sub-micrometer nozzles to achieve desirable deposition rates and single nozzle to achieve uniformity of printed structures. Here, we address these challenges by computationally analyzing an array of microscale nozzles. We tailor the convection within the electrolyte to alter both deposition rate and geometric uniformity of the printed structures. The results show that for large nozzles the evaporation alone is not sufficient to obtain high deposition rates, yet an external pressure can be used to increase deposition and alter uniformity (thickness) of printed structures. Our results can be used to design and analyze new experiments toward parallel multi-nozzle deposition using CED toward high-throughput metal printing.

AM for aerospace repair

GE Aviation's facility in Singapore is reportedly the first to offer metal 3D printing for engine component repair. This article discusses the benefits of using the process.

3D printing in the field

Metal 3D printing is not the most mobile of technologies. However, the Australian Army and additive manufacturing (AM) company SPEE3D have found a way to manufacture metal armored vehicle parts in the field in just this way.

First 3D Printed IH-Type Linac Structure—Proof-of-Concept for Additive Manufacturing of Linac RF Cavities

Additive manufacturing (AM or “3D printing”) has become a powerful tool for the rapid prototyping and manufacturing of complex part geometries. Especially interesting for the world of particle accelerators is the process of the 3D printing of stainless steel (and copper) parts. We present a first prototype of a 433 MHz IH-type linac cavity with an internal drift tube structure manufactured by metal 3D printing. The prototype cavity has been constructed to act as a proof-of-concept for the technology. In this paper we present the concept of the cavity as well as first results of vacuum testing and materials testing.

Online monitoring of 3D printing of steel via optical emission spectroscopy

Abstract Additive manufacturing by laser metal deposition (LMD) requires continuous online monitoring to ensure quality of printed parts. Optical emission spectroscopy (OES) is proposed for the online detection of printing defects by monitoring minute variations in the temperature of a printed spot during laser scan. A two-lens optical system is attached to a moving laser head and focused on a molten pool created on a substrate during LMD. The light emitted by the pool is collected by an ultraviolet–visible (UV–vis) spectrometer and processed. Two metrics are used to monitor variations in the surface temperature: the spectrally integrated emission intensity and correlation coefficient. The variations in the temperature are introduced by artificial defects, shallow grooves, and holes of various widths and diameters carved on a substrate surface. The metrics show sufficient sensitivity for revealing the surface defects, except for the smallest holes with an under-millimeter diameter. Additionally, numeric simulations are carried out for the detection of emission in the UV–vis and near-infrared (NIR) spectral ranges at various surface temperatures. It is concluded that both the metrics perform better in the NIR range. In general, this work demonstrates that spectrally resolved OES suits well for monitoring surface defects during 3D metal printing.

Effective magnetic susceptibility of 3D-printed porous metal scaffolds.

3D-printed porous metal scaffolds are a promising emerging technology in orthopedic implant design. Compared to solid metal implants, porous metal implants have lower magnetic susceptibility values, which have a direct impact on imaging time and image quality. The purpose of this study is to determine the relationship between porosity and effective susceptibility through quantitative estimates informed by comparing coregistered scanned and simulated field maps. Five porous scaffold cylinders were designed and 3D-printed in titanium alloy (Ti-6Al-4V) with nominal porosities ranging from 60% to 90% using a cellular sheet-based gyroid design. The effective susceptibility of each cylinder was estimated by comparing acquired B0 field maps against simulations of a solid cylinder of varying assigned magnetic susceptibility, where the orientation and volume of interest of the simulations was informed by a custom alignment phantom. Magnitude images and field maps showed obvious decreases in artifact size and field inhomogeneity with increasing porosity. The effective susceptibility was found to be linearly correlated with porosity (R2 =0.9993). The extrapolated 100% porous (no metal) magnetic susceptibility was -9.9ppm, closely matching the expected value of pure water (-9ppm), indicating a reliable estimation of susceptibility. Effective susceptibility of porous metal scaffolds is linearly correlated with porosity. Highly porous implants have sufficiently low effective susceptibilities to be more amenable to routine imaging with MRI.

Nonlinear Acoustic Technique for Monitoring Porosity in Additively Manufactured Parts

Abstract Ultrasonic wave based techniques are widely used for damage detection and for quantitative and qualitative characterization of materials. In this study, ultrasonic waves are used for probing the response of additively manufactured 316L stainless steel samples as their porosity changes. The additively manufactured stainless steel specimens were fabricated using a laser powder bed fusion (LPBF) metal 3D printer. Four different levels of porosity were obtained by suitably controlling the LPBF process parameters. For generating ultrasonic waves, lead zirconate titanate (PZT) transducers were used. The signals were generated and propagated through the specimens in a transmission mode setup. Both linear and nonlinear analyses were used during the signal processing of the recorded signals for damage characterization. Linear ultrasonic parameters such as the time-of-flight (related to wave velocity) and signal amplitude (related to wave attenuation) were recorded. The nonlinear ultrasonic parameter, Sideband Peak Count—Index (SPC-I), was obtained by a newly developed nonlinear analysis technique. The experimental results obtained for the specimens were analyzed and compared for both linear and nonlinear ultrasonic analyses. Finally, the effectiveness of the SPC-I technique in monitoring porosity levels in additively manufactured specimens is discussed.

A review on various approaches of 3D printing of Ti-Alloy

The demand for 3D metal components with complex shape and high quality with timely delivery is the focus for the development of additive manufacturing known as 3D printing. 3D metal printing is becoming very popular day by day among manufacturing industries, young engineers and “startups” due to the flexibility of realization of ideas. 3D metal printing is growing into a revolutionary technology in today’s world due to application in various industries such as aerospace, biomedical and automotive sectors etc. Fabrication and development of net-shape metallic components of complex geometric shape is the key strength of 3D metal printing where layer-by-layer metal powder is deposited from a 3D printer through computer-aided design. Powder metallurgy is the traditional method to fabricate titanium alloy whereas laser additive manufacturing is the emerging technology now-a-days. The advantage of 3D metal printing of titanium-based components is light in weight, cost effective approach and reduces material loss. The growth of last ten-year’s data shows the emerging trends of 3D printing as future disruptive technology with application in every field of life such as food, cloths, machines, building, biomedical implants and even human body parts. This paper overviews on various approaches to 3D printing of Titanium alloy (Ti-6Al-4V) on recent development with fabrication method, limitations and application and finally summarizes the findings. It is evident from the observations that the 3D printed titanium alloys produced through laser melting yields higher strength and yield point compared to conventional methods. Finally, further research in 3D metal printing has been presented.

On the Development of Metal 3D Printed Bandpass Filter With Wide Stopband Based on Deformed Elliptical Cavity Resonator With an Additional Plate

This paper presents a newly developed metal 3D printed waveguide bandpass filter based on a modified deformed elliptical cavity resonator with an additional plate. The modified resonator has excellent design freedom allowing semi-independent control of centre frequency, bandwidth, and transmission zeros. Furthermore, transmission zeros can be placed close and far from the passband to improve frequency selectivity and stopband’s width and rejection, respectively. Theory of the resonator, filter design with an example, and simulated and experimental results with extensive discussion are given. As proof of concept, a 5-pole <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ku</i> -band wideband filter was designed and manufactured using Selective Laser Melting, a metal 3D printing technique. Even though the prototypes were tested as-built, i.e. without any surface post-processing, the simulated and measured results have good agreement and consistency between all four printed prototypes. Moreover, the prototypes were manufactured in one piece, significantly improving measured results compared to the previous two-piece prototypes.