Promising Manufacturing Technology Research Articles

The enhanced ZrO2 produced by DLP via a reliable plasticizer and its dental application

Digital light processing (DLP) is considered as one of the most promising additive manufacturing technologies to process ceramics. However, the potential defects produced in the debinding and sintering process extremely restrict ceramic application. In this work, a plasticizer which effectively inhibits defects of the green body in debinding process was investigated. The effects of plasticizer (Polyethylene glycol 200) on the rheological behavior and curing property of the slurry were discussed. In addition, the debinding process and the mechanical of zirconia parts with different PEG200 contents were studied. Adding 20 vol% PEG200 could efficiently suppress the defects in debinding process, and the flexural strength increased from 302 ± 15 to 1210 ± 25 MPa of the ZrO2 ceramic sintered at 1600 °C. The superior biocompatibility and mechanical property reveal that the DLP zirconia has a promising application prospect of biology dental ceramic prostheses.

Simultaneous fabrication of multiple tablets within seconds using tomographic volumetric 3D printing

3D printing is driving a shift in patient care away from a generalised model and towards personalised treatments. To complement fast-paced clinical environments, 3D printing technologies must provide sufficiently high throughputs for them to be feasibly implemented. Volumetric printing is an emerging 3D printing technology that affords such speeds, being capable of producing entire objects within seconds. In this study, for the first time, rotatory volumetric printing was used to simultaneously produce two torus- or cylinder-shaped paracetamol-loaded Printlets (3D printed tablets). Six resin formulations comprising paracetamol as the model drug, poly(ethylene glycol) diacrylate (PEGDA) 575 or 700 as photoreactive monomers, water and PEG 300 as non-reactive diluents, and lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) as the photoinitiator were investigated. Two printlets were successfully printed in 12 to 32 s and exhibited sustained drug release profiles. These results support the use of rotary volumetric printing for efficient and effective manufacturing of various personalised medicines at the same time. With the speed and precision it affords, rotatory volumetric printing has the potential to become one of the most promising alternative manufacturing technologies in the pharmaceutical industry.

Finite element simulation of residual stress distribution during selective laser melting of Mg-Y-Sm-Zn-Zr alloy

Selective laser melting (SLM) has been confirmed as a promising additive manufacturing technology for the formation of lightweight structural parts of magnesium alloy. However, it is noteworthy that residual stress is easily generated during the SLM process of magnesium alloy, and it will induce cracks to reduce the compactness of formed parts. In this study, a three-dimensional (3D) nonlinear transient thermodynamic coupled finite element model (FEM) was built to analyze the effects of the scanning strategy on the thermal stress evolution and residual stress distribution during the SLM process of Mg-Y-Sm-Zn-Zr alloy. Moreover, six groups of simulation tests were performed based on three different scanning strategies (i.e., successive scanning, island scanning, and orthogonal scanning). The stress values of equal scale specimens produced with the same process parameters were examined to verify the simulation results. The equivalent residual stress was the largest under the use of the successive scanning strategy, as indicated by the results. Using the island scanning, the stress distribution in the island was similar to that of successive scanning, whereas there was a high-stress island close to the interface. Besides, the average S11 and S22 residual stresses were 4.90% and 36.13% lower than that of the successive scanning, respectively. Orthogonal scanning was confirmed as the most effective scanning strategy to reduce residual stress. To be specific, the average S11 and S22 residual stresses were 25.19% and 43.12% lower than that of successive scanning when using the intralayer orthogonal scanning. The simulation and experimental verification results indicated that the maximum equivalent residual stress is the lowest (229 MPa), and the stress distribution was most uniform when orthogonal scanning was performed between 4 × 4 island.

FATIGUE AND FRACTURE BEHAVIOR OF ALSILOMG MANUFACTURED BY SELECTIVE LASER MELTING: A REVIEW

Selective laser melting (SLM) is one of the most promising metal additive manufacturing technologies. SLMed Al-Si alloys have been widely used in the rail transport, aerospace, and automotive industries. Recently, the fatigue and fracture properties of SLMed Al-Si alloys have attracted considerable attention due to their application in critical load-bearing structures. This review aims to better understand the recent progress on the fatigue and fracture investigations of SLMed Al-Si alloys, especially AlSi10Mg, with emphasis on the effect of defects, heterogeneous microstructure, residual stress, and post-treatment methods. In addition, fatigue and fracture modeling methods are discussed. Finally, the challenges and future research opportunities are prospected.

Refined W-3.5Nb alloy fabricated by electron beam melting via doped carbon

Electron beam melting (EBM) is a promising powder bed fusion additive manufacturing (AM) technology for the preparation of complex refractory components due to the significant advantages of vacuum environment and high level in energy utilization, scanning speed and temperature in the build chamber. However, the fabrication of crack-free and refined W-based alloy remains a challenge. This study aims to address this problem by introducing 0.7 wt% carbon in EBM W-3.5Nb alloy. Results revealed that the as built W-3.5Nb alloy had a typical columnar structure with obvious solidification cracks along the grain boundary. Doping 0.7 wt% carbon generated refined microstructure, which was composed of the initial dendrite of tungsten and the eutectic phase in the dendrites gap. Due to the low distribution coefficient of carbon, the nucleation at the bottom of the molten pool was caused by constitutional supercooling in the front of liquid solidification in a single molten pool, and velocity of the solidification front was reduced by carbon concentration leading increased thermal supercooling. Supercooling (thermal supercooling together with constitutional supercooling) refined the microstructure of W-3.5Nb alloy effectively. Meanwhile, due to the formation of eutectic phase with low melting point, the fluidity of liquid phase at the terminal solidification was improved and the solidification cracks along the grain boundary were reduced. The carbon addition also played a significant role in alloy strengthening. The microhardness of the alloy increased from 382 HV to 696 HV, and the compressive strength increased from 962.89 MPa to 1892.56 MPa. These findings offer a new perspective on the AM fabrication of high-quality W-based alloys.

Energy benchmark for evaluating the energy efficiency of selective laser melting processes

Although additive manufacturing (AM) is a promising advanced manufacturing technology, it consumes much more electricity energy than conventional manufacturing techniques during the production phase. This is a barrier to promoting the use of AM technology across manufacturing industries. Energy consumption (EC) of AM has been a subject of academic studies, especially the EC modelling of AM. However, the energy-saving methods to reduce the EC of AM are limited and insufficient. The energy benchmark has been recognised as an effective analytical methodology and management tool to improve energy efficiency. Nonetheless, research about energy benchmarks for the AM is lacking. Selective laser melting (SLM) is one of the most promising and widely used AM processes. As such, SLM is selected as a representative AM process for energy reduction. Because most additively manufactured parts have new designs without historical energy data, we develop an energy benchmark for the SLM using the prediction model. Besides, we design a dynamic rating system to be consistent with the SLM's energy-saving potentials, which can effectively evaluate the energy efficiency of each loading scheme of the parts. The case study shows that 18.99 % of EC of SLM for a turbine rotor is reduced by using the proposed energy benchmark methodology. A trade-off between energy efficiency and production tardiness is discussed.

Effect of sintering temperature and sintering additives on the properties of alumina ceramics fabricated by binder jetting

Binder jetting (BJ), a promising additive manufacturing technology for fabricating ceramic components, is currently limited by drawbacks such as high sintering temperature, low density, and poor mechanical performance. In this study, Ca(OH)2–MgO–SiO2 was introduced as a sintering additive for improving the properties of Al2O3 ceramics during the BJ process. The effect of the sintering additive content and sintering temperature on the relative density, microstructure, and mechanical properties of the fabricated Al2O3 ceramics was analyzed by scanning electron microscopy, X-ray diffraction, and universal testing. The results show that during the sintering process, sintering additives react with Al2O3 to form a liquid ceramic phase, which contributes to the reduced porosity of the green body and the increased relative density and mechanical strength of the final ceramic parts. The shrinkage along the Z-axis reaches to 37%, the relative density achieves its highest value of 83.3%, and the compressive strength also reaches to the maximum of 58.7 MPa when 30% content of sintering additives and sintering temperature of 1500 °C are used, which is better than that in previous studies. It suggests that adding sintering additives provides a feasible method to fabricate Al2O3 ceramics with agreeable performance via the BJ process.

Methods of Additive Manufacturing for Dental Co-Cr Alloys: Systematic Review

Additive manufacturing is a popular method of producing items directly from digital models through a layer-by-layer material build-up process. To evaluate the Current State of Knowledge on Dental Co-Cr Alloy Additive Manufacturing Techniques. Innovative additive printing technologies have made it possible to produce intricate dental components customized for each patient. This study investigated the manufacturing method (build orientation and process parameters), post-processing techniques, and metallic powders utilized in dental applications (stress relieving, surface finishing). The databases PubMed, Science Direct, Mendeley, and Google Scholar were used to carry out an electronic search. A manual search of pertinent article citations was also carried out; inclination angle, stress relieving, heat treatment, cobalt-chromium, selective laser melting, selective laser sintering, and powder bed fusion, dentistry were some of the keywords utilized. Although this publication tries to contain the most recent study from the previous eleven years (2010–2021), and to explain the materials powders and metal used in dental applications. A cutting-edge technique called additive manufacturing uses a layer-by-layer approach to material build-up to produce things directly from digital models. It is missing a tool, a manufacturing process that produces fully thick metallic components quickly and with good precision. Qualities of additive aspects of production such component design flexibility, part complexity, light- weighting, component consolidation, and functional design are generating specific interest in the additive fabrication of metal for use in automotive, marine, oil & gas, and aerospace industries during powder bed fusion, each layer of the powder bed is only partially fused employing a laser or electron beam as an energy source, the recent and most promising additive manufacturing technologies utilized to produce intricate, low-volume, tiny metallic parts. By using computer-aided design (CAD) technology, recent developments in digital dentistry have changed dental offices and dental laboratories, by utilizing 3D printing because precise metal framework fitting and technique faster.

In situ monitoring of beam current in electron beam directed energy deposition based on adsorbed electrons

Electron beam directed energy deposition (EB-DED) is a promising and efficient additive manufacturing technology, but the vacuum environment challenges the in situ parameters monitoring. In this paper, an in situ beam current monitoring method is developed based on the absorbed electrons. A series of experiments show that there is a linear relationship between the absorbed electron current and the impinging beam current. However, this relationship only holds when the beam power density is relatively low. When the power density is high, the absorbed electron current will be lower than the theoretical value determined by the linear relationship. This is mainly due to the massive generation and ionization of metal vapor. The critical power density depends on the melting point of the material. Nonetheless, the deviation of the absorbed electron current at high power density can roughly determine the relative position between the focal spot and the workpiece surface. In addition, the slope of the linear relationship is material-dependent, so this method can also distinguish different materials.

Identification of continuous twin-screw melt granulation mechanisms for different screw configurations, process settings and formulation

Twin-screw melt granulation (TSMG) is a promising continuous manufacturing technology for the processing of high drug load formulations and to formulate heat- and moisture-sensitive active pharmaceutical ingredients (APIs). This study evaluates the influence of process parameters for TSMG, mainly focusing on the effect of the screw configuration combined with screw speed, throughput and barrel temperature, to elucidate the melt granulation mechanisms. For the kneading zone, the stagger angle was varied between 30°, 60° and 90°, and investigated for both the forward and the reversed direction. In addition to the process parameters, the influence of the formulation differing in their API-binder miscibility was evaluated. As responses, the granule (size, friability and porosity) and process properties such as torque were evaluated, indicating that the screw configuration is the most influential factor. Nucleation, consolidation and breakage are the granulation mechanisms for the forward and the neutral configuration, while consolidation and densification with shear elongation are identified for the reversed configuration. The formulations differ mainly in the forward and neutral configuration since the immiscible formulation shows a bimodal granule size distribution with a larger fraction of fines and weaker granules is obtained. For the reversed configuration, similar granulation mechanisms are seen for both formulations.

Tracking and quantifying spatter characteristics in a laser directed energy deposition process using Kalman filter

Laser-based directed energy deposition (L-DED) has emerged as one of the most promising additive manufacturing (AM) technologies in the past decade. This is particularly due to its ability to print functionally graded materials and achieve a higher deposition rate compared to its counterparts. For L-DED, the flow dynamics of the powder particles and laser-material interactions are the chief determinants of the build quality. In particular, we are interested in the characterization of spatter, which is the ejection of the molten material from the deposition zone that includes the melt pool and the area where the laser interacts with the incident powder particles. Spatters are detrimental to the overall build quality as they can increase porosity and lead to irregular surface morphology. While recent studies have investigated the spatter formation, very little attention has been given to its quantitative in situ characterization. To this end, we develop a high-speed imaging capability integrated with an L-DED process to record the trajectory of the spatter particles as they eject out from the deposition zone. We use a Kalman filter to track the trajectory of the individual spatter particles in real-time. By using the trajectory information and apriori knowledge of the material properties, we estimate the percentage of the material lost as spatter. Our results indicate that at a laser power of 300 W and a feed rate of 7.41 mm/sec, only an estimated 11% of the powder material (released from the nozzles) interacts with the laser beam. Out of this, approximately 12% of the material is ejected out as spatter. This shows that a significant portion of the material is wasted during the L-DED process.

Heterogeneous structures in a Ni-based superalloy with tailoring mechanical properties produced by a twin laser powder bed fusion system

Powder bed fusion using a laser beam (PBF-LB) is a promising additive manufacturing (AM) technology, used to produce components with complex geometry and design freedom. The parts are built in a layer-by-layer fashion during PBF-LB, and changing the processing parameters within different layers can lead to the modification of microstructures and finally a great impact on the mechanical properties. Thus, PBF-LB provides the possibility for the customization of material properties by changing the microstructures of layers using different processing parameters. In this investigation, a twin PBF-LB system, i.e., with a low-power laser beam and a high-power laser beam in a machine, is used to produce fine and coarse microstructures using the Inconel 718 (IN718) alloy, respectively. The fine and coarse microstructures are alternately printed to form different heterogeneous structures. Correspondingly, different mechanical properties are achieved. The microstructures are analyzed using optical microscope (OM), scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and numerical calculation. The defects generated by these 2 laser beams are simultaneously discussed. This study facilitates the tailoring of alloy properties using the PBF-LB technology to meet the users’ needs of multiple service conditions.

Evolution of Melt Pool and Porosity During Laser Powder Bed Fusion of Ti6Al4V Alloy: Numerical Modelling and Experimental Validation

Laser powder bed fusion (L-PBF) is one of the most promising additive manufacturing technologies for metals. In this work, the discrete element method (DEM) was used to reproduce a powder bed of particles distributed in a random way to be as close as possible to reality. Single and multiple scan tracks simulations were performed for Ti6Al4V alloy using a commercial CFD software, FLOW-3D AM®. The output from the numerical simulations was elaborated to obtain shape and size of melt pools, morphology of scan track surfaces and porosity content. In particular, a specific model was used in order to predict air entrainment in the melt pool and, therefore, to estimate gas porosity content, as an innovative approach to predict such defects. Results from simulations were compared with experimental data from Ti6Al4V samples produced by L-PBF in terms of melt pools size and morphology, as well as density. The good agreement between calculated and experimental results indicates that simulation of L-PBF can represent a powerful tool not only for the optimization of process parameters, but also for the prediction of porosity level.

3D PRINTING TECHNOLOGY: A CUSTOMIZED ADVANCED DRUG DELIVERY

Three dimensional (3D) printing has emerged as one of the most promising additive manufacturing technology for producing 3D objects, with applications ranging from engineering prototyping to medications and cell-laden medical models. 3D printing techniques involve the deposition of materials such as thermoplastic polymers or hydrogel in sequential layers one on top of another to produce 3D object, regardless of the type, or underlying theory. The rapid rise in the number of published articles and patents in recent years indicates 3D printing’s current momentum in developing various drug delivery systems for pharmaceutical applications. While 3D printing techniques have a promising future, they must overcome a number of challenges before they can be used in commercial-scale production. The current ways of modifying drug delivery while making 3D printed dosage forms with different drug release patterns and properties are discussed in this review. These achievements are related to the delivery and development of patient-specific medicines. Major benefits of each type of 3D printing application, which are discussed; however, a critical review will show the limitations and constraints associated with 3D printing. Future research could focus on developing and adapting the techniques to suit with a wider range of materials. More emphasis on developing cost-effective printing technologies and compatible materials with these printers is needed to broaden the range of applications for 3D printed products.

Optimal droplet transfer mode maintenance for wire + arc additive manufacturing (WAAM) based on deep learning

In the last decade, wire + arc additive manufacturing (WAAM), which is one of the most promising metal additive manufacturing technologies, has been attracting high interest from both academia and industry. WAAM systems are increasingly employed in the industry and academia, but there are still several challenges and barriers to process stability control. The process stability is highly dependent on how the molten feed wire is added into the melt pool, which is known as the droplet transfer mode. To ensure a stable WAAM deposition process, it is essential to maintain the transfer mode in a suitable stable status. Without an effective transfer mode control method, the operators need to determine and control the transfer mode based on their experience using manual adjustment, which is difficult to achieve in a long period of production process. In this paper, a deep learning-based technology was proposed for the control of the droplet transfer mode based on the data collected from the WAAM process. A long short term memory neural network was applied as the core transfer mode classification model. A time-series data, arc voltage, was collected and statistical and frequency features were extracted, which included 11 relevant features, as the inputs of the classification model. Then, the distance between the melted wire and the melt pool was adjusted based on the determined transfer mode to keep a suitable stability of the process. A case study was used to evaluate the proposed approach and to show its merit. The proposed approach was compared to three commonly used machine learning algorithms, k-nearest neighbours, support vector machine, and decision tree. The proposed method obtained the highest accuracy in determining the transfer mode, which was over 91%. The performance of the proposed approach was also evaluated by the single-pass and oscillated wall building. The proposed deep learning based approach improved the process stability in real-time, which resulted in better deposition qualities, in terms of geometry size and processing cleanliness compared to without control. Furthermore, this data-driven method could be applied to other WAAM processes and materials.

Selective Laser Melting of Ti6Al4V: Effects of Heat Accumulation Phenomena due to Building Orientation

Titanium alloy Ti6Al4V is one of the most utilized alloys in the field of additive manufacturing due to the excellent combination of mechanical properties, density and good corrosion behavior. These characteristics make the use of this material particularly attractive for additively manufacturing components with complex geometry in sectors such as aeronautics and biomedical. Selective Laser Melting (SLM), by which a component is fabricated by selectively melting of stacked layers of powder using a laser beam, is the one of most promising additive manufacturing technologies for Ti6Al4V alloy. Although this technique offers numerous advantages, it has some critical issues related to the high thermal gradients, associated with the process, promoting the formation of a metastable martensitic microstructure resulting in high tensile strength but poor ductility of the produced parts. The formation of microstructural defects such as balling and porosity can occur together with the presence of residual stresses that may significantly affect the mechanical characteristics of the component. Specific process parameters and geometries can determine heat accumulation phenomena that result in a progressive decrease in thermal gradients between layers. These heat accumulation phenomena are influenced by the number of layers deposited, but also by the building orientation that, for a given geometry, determines a variation of the deposited surface for each layer.

Multi-axis direct metal deposition process with effective regrouping strategy

Direct metal deposition (DMD) process has been regarded as a promising additive manufacturing technology. But this process is hard to fabricate structures with overhang features in a support-free manner because the machine equipped with a 3-axis platform could only fabricate structures in 2.5 dimensions instead of 3 dimensions. Therefore, the multi-axis DMD process has been developed to fabricate complicated metal structures without support combined with the motion of the platform. Decomposition operation of the input 3D model to generate several sub-volumes and the following regrouping operation of the sub-volumes are two key procedures in the multi-axis printing process. We adopt the decomposition strategy to obtain the horizontal deposition bases on the previous depth after rotation operations of the platform. However, the traditional regrouping strategy may result in excessively accumulated temperature fields at the connecting regions, especially for some hard-to-print materials like nickel-titanium alloy (NiTi). To solve these problems, the multi-axis DMD process with an improved regrouping strategy is developed in this paper. A novel sequence planning algorithm is proposed by minimizing the cost function to avoid excessively accumulated temperature fields. The cost function is directly related to the moving distance during the regrouping of sub-volumes at connecting regions. Numerical simulations with different interval time values are conducted to determine the cost function. Experiments are conducted to validate the effectiveness of our proposed multi-axis DMD algorithms. Three groups of “Y shape” samples are fabricated using different strategies for comparison and then various characterizations are carried out. Results show that compared with traditional decomposition and regrouping strategies, the samples fabricated with our proposed algorithms could obtain the pore-free morphology, higher microhardness value, and more homogeneous and fine microstructures. Therefore, our proposed strategies in this paper can significantly improve the characterization and microhardness of the fabricated structures during the multi-axis DMD process.

Additive Manufacturing of Solid Products for Oral Drug Delivery Using Binder Jetting Three-Dimensional Printing

Binder jetting (BJ) three-dimensional (3D) printing is becoming an established additive manufacturing technology for manufacturing of solid products for oral drug delivery. Similar to traditional solutions based on compaction of powder mixture, successful processing of BJ products requires control of bulk powder properties. In contrast to traditional compaction-based process, BJ 3D printing allows for flexible modifications on microstructure, material composition and dose in the printed pharmaceutical products. Currently, systematic strategies for selecting excipients and optimizing the printing process have not been fully established. To address this challenge, a summary of the published work and selected patent literature around BJ 3D printing to fabricate pharmaceutical solid products for oral administration purposes is presented. First, an overview of characteristics of printed products as a part of the product design and a description of the commonly used excipients and active pharmaceutical ingredients is given. The critical powder and ink properties, as well as physical geometries and inner structures of a final product, are discussed in term of the mechanisms that determine the formation of a printed solid product and finally the quality of this product. This review is also summarizing the technical features of printers, printheads, and the critical considerations for post-processing procedures. BJ 3D printing is one of the most promising additive manufacturing technologies for mass customization of pharmaceutical products.

From impact to solidification in drop-on-demand metal additive manufacturing using MetalJet

Drop-on-demand metal jetting is a promising additive manufacturing (AM) technology that is gaining interest due to its capability to directly print complex single and multi-material components at high resolutions. It also has key advantages over other metal AM techniques, such as avoiding powder handling and extensive post-processing. In this method, parts are built via spatially controlled deposition of individual molten droplets onto a substrate. Therefore, the success of the process entirely depends on the behaviour of these single droplets from deposition to solidification including their interactions with the substrate, which is scarcely investigated to date. To fill this research gap, the in-house MetalJet platform was used to investigate the spreading and solidification of metallic micro-droplets at low Weber numbers. This was undertaken onto various substrates using a range of jetting and substrate temperatures through an integrated experimental, analytical, and computational approach. This study reports that increasing the substrate temperature enhanced the diffusion between the droplet and substrate, hence improving the bonding. Moreover, ripples forming on a droplet’s periphery during solidification disappeared at elevated substrate temperatures, resulting in improved inter-droplet bonding. Furthermore, the significant role of the substrate wettability and thermal properties, which control the droplet’s dynamics and solidification behaviour, respectively, is elucidated. This highlights the importance of substrate material selection using this technology. The results presented in this article underpin the optimal process conditions under which the 3D structures produced with this technology can exhibit reliable integrity and consistency. This represents a step forward in the direct metal printing of high resolution functional multi-material components.

Microstructures and mechanical properties of crack-free 316L stainless steel and Inconel 625 joint by using Laser Engineered Net Shaping

The additively manufactured (AM) joint of 316L stainless steel (SS316L) and Inconel 625 (IN625) with flexible structural adjustability and good joint strength are pivotal components for aerospace and shipbuilding fields. As a promising metal additive manufacturing technology, Laser Engineered Net Shaping (LENS) technology brings possibilities for the combination of dissimilar metals. In this study, a gradient SS316L/IN625 joint with a composition ranging from 100% SS316L to 100% IN625 alloy was successfully prepared using LENS. The compositions, microstructures of each layer, and the interfaces between every two layers of the SS316L/IN625 joint were investigated. The results showed that the microstructure and elements were uniformly distributed along the deposition direction. No second phase or crack was detected in each layer or interface was observed in the SS316L/IN625 joint. The microhardness increased from 198 to 265 HV with increasing the content of IN625. The SS316L/IN625 joint showed a tensile strength of 672 MPa and a yield strength of 486 MPa.