Conventional Manufacturing Techniques Research Articles

A Review of 3D Polymeric Scaffolds for Bone Tissue Engineering: Principles, Fabrication Techniques, Immunomodulatory Roles, and Challenges.

Over the last few years, biopolymers have attracted great interest in tissue engineering and regenerative medicine due to the great diversity of their chemical, mechanical, and physical properties for the fabrication of 3D scaffolds. This review is devoted to recent advances in synthetic and natural polymeric 3D scaffolds for bone tissue engineering (BTE) and regenerative therapies. The review comprehensively discusses the implications of biological macromolecules, structure, and composition of polymeric scaffolds used in BTE. Various approaches to fabricating 3D BTE scaffolds are discussed, including solvent casting and particle leaching, freeze-drying, thermally induced phase separation, gas foaming, electrospinning, and sol-gel techniques. Rapid prototyping technologies such as stereolithography, fused deposition modeling, selective laser sintering, and 3D bioprinting are also covered. The immunomodulatory roles of polymeric scaffolds utilized for BTE applications are discussed. In addition, the features and challenges of 3D polymer scaffolds fabricated using advanced additive manufacturing technologies (rapid prototyping) are addressed and compared to conventional subtractive manufacturing techniques. Finally, the challenges of applying scaffold-based BTE treatments in practice are discussed in-depth.

Heterogeneous deformation behavior of hybrid manufactured TC11 titanium alloy via directed energy deposition

Hybrid manufacturing technique by combining of the conventional manufacturing techniques with the additive manufacturing technique has an attractive potential to fabricate the large and complex components. In this study, hybrid manufactured TC11 titanium part was produced by depositing TC11 alloy on a rolled TC11 plate via directed energy deposition (DED) process. Microstructure, microhardness and tensile properties of hybrid manufactured TC11 samples were examined. The deformation behavior of the hybrid manufactured TC11 samples was also investigated using in-situ tensile test and digital image correlation (DIC). The results demonstrate that the hybrid manufactured TC11 sample can be divided into three zones: the laser deposition zone (LDZ), the heat affected zone (HAZ) and the rolled substrate zone (SZ). The gradient microstructure is formed in the HAZ along the deposition direction due to the different thermal conditions. A special bimodal microstructure consisting of coarse primary α (αp) phase platelet and ultrafine lamellar α phase has been generated in the upper HAZ. The texture of α phase shows the highest intensity in the easily-activated orientation in the LDZ with larger Schmid factor leading to fracture when loading along the deposition direction. The small grains size with super fine αs in the HAZ results in the highest strength and microhardness.

Low-frequency transducer with a periodic displacement amplification structure based on 3D printing

The main structure of an underwater acoustic transducer is metallic, and it is fabricated using conventional mechanical manufacturing techniques. Therefore, it cannot adopt complex geometries. Three-dimensional (3D) printing technology solves this problem owing to its ability to manufacture mechanical parts of arbitrary geometry such as closed cavity structures, which can be used to fabricate transducers with complex designs. Therefore, a transducer with periodic displacement amplification structure was proposed. The periodic shell structure of the transducer had a periodic arrangement with a flextensional structure as the basic unit. The structural parameters of the transducer can be adjusted while maintaining the displacement amplification performance. This enabled transducer design according to requirements such as volume constraints for applications in small target platforms. The transducer was manufactured using 3D printing owing to the complexity of the structure. A finite element model of the transducer was established by combining the periodic shell structure with a fixed-size driving vibrator. The dimensions of the transducer were optimized using the finite element method to maintain a higher transmitting voltage response level at a low frequency. Finally, a fabricated and tested prototype with a transmitting response level of 122 dB and resonance frequency of 2400 Hz was obtained. The experimental results demonstrated that the transducer can be used as a low-frequency underwater acoustic source with potential application prospects.

Additive or Conventional Manufacturing as spare parts manufacturing technology: the impact of qualification tests

Additive manufacturing (AM) has recently emerged as a potential breakthrough technology in the world of spare parts management. Thanks to its characteristics, it can enable the production of spare parts with very low production lead time, with considerable impacts in terms of inventory levels. Some researchers have recently focused on the topic, trying to understand whether it is convenient to produce spare parts in AM or in Conventional Manufacturing (CM) techniques. However, all these works neglect a crucial aspect. Spare parts, before being utilized, need to be qualified from certified entities. The qualification requirements vary depending on the criticality of the spare parts, but they are all associated with non-negligible costs, which however have been completely neglected so far. In this work, to overcome this gap we develop a mathematical model that can support managers and practitioners in choosing the most convenient manufacturing technology (i.e. AM or CM) considering for the first time the qualification costs. The model proposed has been applied to a real case study to demonstrate its applicability.

Research Progress on Powder Injection Molding in Malaysia-A Review

In this era, parts complexity, dimensional accuracy, and cost-effectiveness are one of thebasic requirements of the modern industry. Most of the conventional manufacturingtechniques have failed to fulfill the industry’s needs. Powder injection molding (PIM) startedin the early 70s, which is a combination of powder metallurgy and plastic injection moldingthat fulfills the gaps in conventional manufacturing techniques. In Malaysia, PIM wasintroduced by SIRIM Sdn Bhd Malaysia in late 2000. The latter few universities startedworking on PIM. Among all universities, the Advanced Functional Materials Research(AFM) group at Universiti Teknologi PETRONAS (UTP) started to work in 2008 under thedirection of Prof. F. Ahmad and was decided to target various industries and their latestrequirements. The work completed during the past 11 years has been published in varioushigh-quality international journals, secure intellectual property (IP), i.e., trademarks, patents,a pre-commercialization grant from the government, one commercialization agreement, andsigned a technology licensing agreement. They also worked on carbon Nanotube reinforcedcopper nanocomposite for thermal management and secured two patents. This project wascommercialized for heat sink materials for LED Lights. The group is also working oncontrolling the orientation of fibers in the metal matrix to enhance thermal conductivity.Moreover, grafting graphene on metal oxide for its potential use as a radiation shieldingmaterial is one of the noble works. Currently, the group is working on the fabrication of softmagnetic material with enhanced permeability for potential use in hearing Aids, electricmotors, and several other applications. Besides, bio-medical parts like a dental screw, biomedical material of 316L SS reinforced by nano Titanium and additive manufacturing byusing ultra-fused BASF 316L SS parts made through FDM represent the scope of works inPIM.

Carbon-Based Piezoresistive Polymer Nanocomposites by Extrusion Additive Manufacturing: Process, Material Design, and Current Progress.

Advancement in additive manufacturing (AM) allows the production of nanocomposites with complex and custom geometries not typically allowable with conventional manufacturing techniques. The benefits of AM have led to recent interest in producing multifunctional materials capable of being printed with current AM technologies. In this article, piezoresistive composites realized by AM and the matrices and fillers utilized to make such devices are introduced and discussed. Carbon-based nanoparticles (Carbon Nanotubes, Graphene/Graphite, and Carbon Black) are often the filler choice of most researchers and are heavily discussed throughout this review in combination with extrusion AM methods. Piezoresistive applications such as physiological and wearable sensors, structural health monitoring, and soft robotics are presented with an emphasis on material and AM selection to meet the demands of such applications.

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.

Ultraviolet-assisted direct-write printing strategy towards polyorganosiloxane-based aerogels with freeform geometry and outstanding thermal insulation performance

Developing aerogels with a tailored geometric feature is of prime importance for enlarging their functional effects in application scenarios. However, conventional manufacturing techniques have remained challenging in the on-demand shaping of aerogels due to their costly and time-consuming fabrication process and poor designability of casting molds. Herein, an ultraviolet-assisted direct-write printing strategy has been proposed for fabricating polyorganosiloxane-based aerogels with tunable molecular triple-crosslinks consisting of hydrogen bonds, hydrocarbon chains, and polysiloxanes. The implementation of direct-write printing depends on the close synergy of consecutive ink deposition and instantaneous photopolymerization, appearing as a considerable characteristic of solidification-while-printing, which is conducive to constructing spatially freeform geometries with high structural complexity and shape fidelity. The resultant 3D-printed polyorganosiloxane-based aerogels exhibit outstanding nanoporous performances, such as low density (0.14 g·cm−3), high surface area (484 m2·g−1), superhydrophobicity (water contact angle, 150°), high specific modulus (27.9 kN·m·kg−1), and low thermal conductivity (37.48 mW·m−1·K−1), which are ideal materials for shape-dominated thermal insulation applications. This work would provide an alternative printing strategy to fabricate nanoporous materials with arbitrary architectures for wider applications.

Improving fatigue performance of additively manufactured Ti-6Al-4V using sulfur-based self-terminating etching processes

The adoption of Additively Manufactured (AM) Ti-6Al-4V (Ti64) is continually increasing in the industry due to its benefits over the conventional manufacturing techniques. However, AM Ti64 parts are prone to poor surface finish, which significantly affects their fatigue performance. Therefore, AM Ti64 parts need post-processing to enhance surface finish and fatigue performance. Prior work with a sulfur-based self-terminating etching process for AM Ti64 demonstrated support removal and surface roughness reduction. To further this work, this manuscript details the impact of this sulfur-based post-processing technique on the mechanical properties and the fatigue life of AM Ti64 by characterizing the surface roughness, microstructural evolution, and fracture surfaces. This post-processing technique decreased the surface roughness parameter - Sv by 55 % from 84 ± 11 µm to 38 ± 19 µm and increased the average fatigue life by 340 % from about 7000 cycles to 30,000 cycles.

Ultrasonic-Assisted Electrochemical Milling of SLM-Printed Hastelloy X Based on Analysis of Material Passivation Characteristics

Hastelloy X (HX) is widely used in the aerospace field for its excellent corrosion resistance and high-temperature mechanical properties that can be fabricated into complex structures directly by the selective laser melting (SLM) technique. However, SLM-printed (SLM-ed) HX with high strength and hardness is challenging to process using conventional manufacturing techniques and may result in machining flaws that don’t fulfill engineering standards. Therefore, an ultrasonic-assisted electrochemical milling (UAECM) method using a tube electrode is proposed to fabricate high aspect ratio structures on SLM-ed HX with high-quality. Firstly, the passivation characteristics of SLM-ed HX before and after solid solution treatment (SST) were investigated using polarization curves and electrochemical impedance spectroscopy (EIS). Secondly, the electrochemical milling process and the electrode gap flow field were simulated. Then, the effect of processing parameters such as ultrasonic amplitude, electrical parameters, and mechanical parameters on the groove width and stability was investigated by the orthogonal and single factor experiments. Finally, the cavity and bump structures were machined by layered milling with an average groove width of 960 ± 15 μm, a groove depth of 4.4 mm, an aspect ratio of 4.5, and surface roughness of 1.524 μm and 1.622 μm, respectively, demonstrating the adaptability and machining accuracy of the UAECM method.

Lithography-based additive manufacturing of porosity graded alumina

• In recent years, alumina ceramics exhibiting gradient in porosity, i.e., porosity graded alumina ceramics (PGACs), with a controlled amount of both open/closed or macro/micro pores is of high interest for several applications such as thick barrier coating, cores for precision casting, biocompatible implants, membranes/filters, and fabrication of functionally graded metals through infiltration. • Lithography-based Ceramic Manufacturing (LCM) offers high quality and near-net manufacturing of complex ceramic components with high resolution. • Two-vat system in the newly developed multi-material LCM printer setup enables not only assigning one material to any desired layer but also use of different materials in each layer by assigning the respective materials to selected pixels of the layer image. • This article introduces methodologies for the fabrication of porosity gradient alumina with continuous and discrete porosity transitions zones by combining sacrificial templating and LCM. With the developments in manufacturing technologies, interest on porosity graded alumina ceramics has increased for applications such as thick barrier coating, cores for precision casting and biocompatible implants. Lithography-based Ceramic Manufacturing (LCM) offers high quality and near-net manufacturing of complex ceramic components with high resolution. Multi-material LCM printing setup can overcome the main problems of conventional manufacturing techniques for fabrication of porosity graded alumina with desired microstructure and gradient architecture (i.e., gradient direction, fraction, type). Two-vat system in the newly developed multi-material LCM printer setup enables not only assigning one material to any desired layer but also use of different materials in each layer by assigning the respective materials to selected pixels of the layer image. This article introduces methodologies for the fabrication of porosity graded alumina ceramics (PGACs) with continuous and discrete porosity transitions zones by combining sacrificial templating and LCM. It is illustrated how the properties of the slurry and the desired gradient architecture play an important role for the selection of suitable method.

Recent Advances on Composition-Microstructure-Properties Relationships of Precipitation Hardening Stainless Steel.

Precipitation hardening stainless steels have attracted extensive interest due to their distinguished mechanical properties. However, it is necessary to further uncover the internal quantitative relationship from the traditional standpoint based on the statistical perspective. In this review, we summarize the latest research progress on the relationships among the composition, microstructure, and properties of precipitation hardened stainless steels. First, the influence of general chemical composition and its fluctuation on the microstructure and properties of PHSS are elaborated. Then, the microstructure and properties under a typical heat treatment regime are discussed, including the precipitation of B2-NiAl particles, Cu-rich clusters, Ni3Ti precipitates, and other co-existing precipitates in PHSS and the hierarchical microstructural features are presented. Next, the microstructure and properties after the selective laser melting fabricating process which act as an emerging technology compared to conventional manufacturing techniques are also enlightened. Thereafter, the development of multi-scale simulation and machine learning (ML) in material design is illustrated with typical examples and the great concerns in PHSS research are presented, with a focus on the precipitation techniques, effect of composition, and microstructure. Finally, promising directions for future precipitation hardening stainless steel development combined with multi-scale simulation and ML methods are prospected, offering extensive insight into the innovation of novel precipitation hardening stainless steels.

Changes in Mechanical Properties Due to Heat Treatment on Additive Manufactured Ti-6Al-4V

Laser-based additive manufacturing (AM) of Ti-6Al-4V has become increasingly important for use in components of transportation devices. The most significant advantage over conventional steel structures is the reduction in specific weight. Complex geometries can be produced with the layer-by-layer manufacturing process and the personalised, unique part production can be faster and produced with the lower costs and less material waste than the conventional manufacturing techniques. Between the manufacturing process of an additively manufactured part and its use, the post-processing is an essential factor related to the strength properties or porosity of the finished product. The heat treatment is a possibility to change the final part properties.

Functionalized Cellulose Nanocrystals as Active Reinforcements for Light-Actuated 3D-Printed Structures.

Conventional manufacturing techniques allow the production of photoresponsive cellulose nanocrystals (CNC)-based composites that can reversibly modify their optical, mechanical, or chemical properties upon light irradiation. However, such materials are often limited to 2D films or simple shapes and do not benefit from spatial tailoring of mechanical properties resulting from CNC alignment. Herein, we propose the direct ink writing (DIW) of 3D complex structures that combine CNC reinforcement effects with photoinduced responses. After grafting azobenzene photochromes onto the CNC surfaces, up to 15 wt % of modified nanoparticles can be introduced into a polyurethane acrylate matrix. The influence of CNC on rheological properties allows DIW of self-standing 3D structures presenting local shear-induced alignment of the active reinforcements. The printed composites, with longitudinal elastic modulus of 30 MPa, react to visible-light irradiation with 30-50% reversible softening and present a shape memory behavior. The phototunable energy absorption of 3D complex structures is demonstrated by harnessing both geometrical and photoresponsive effects, enabling dynamic mechanical responses to environmental stimuli. Functionalized CNC in 3D printable inks have the potential to allow the rapid prototyping of several devices with tailored mechanical properties, suitable for applications requiring dynamic responses to environmental changes.

Design and Manufacturing of a Low Cost 3 Axis CNC Router Machine

Computer numerical controlled machines (CNC) are playing a huge role in the Industry today. It is capable of producing complex parts in large volumes along with keeping high level of accuracy. This paper presents a simple design of a 3 axis CNC routing Machine. The machine is driven by stepper motors utilizing lead screws and guides manufactured in a local workshop using conventional manufacturing techniques. The machine is controlled by Mach-3 open source software connected to the machine via parallel port and a breakout board which is connected directly to stepper motors. The hand calculation for the design of the lead screws and the sizing of the motor were carried out. The 3D model was built using Computer aided design software. After the fabrication experimental tests were conducted to measure the performance and the accuracy of the CNC.

An additively manufactured γ-based high Nb-TiAl composite via coherent interface regulation

Novel γ-based TiAl alloys are a promising alternative to conventional dual-phase TiAl alloys, which suffer from microstructural degradation and solid-state phase transformations at high temperatures. However, monolithic intermetallic γ phases exhibit poor plasticity, and they are incompatible with conventional manufacturing techniques. In this study, a microstructural modification was used to enable the preparation of a single-phase matrix from an Nb-rich TiAl metal matrix composite using additive manufacturing (AM) techniques. Micro/nano-precipitates of Ti5Si3 and Ti2AlN were produced by adding Si3N4 precursors to the pre-alloy powder, which reacted with the γ-TiAl matrix during the AM process. Thus, strong interfacial cohesion was achieved. The Ti5Si3 and Ti2AlN precipitates refined the grains in the metal and Ti5Si3 strengthened the grain boundaries. The enhanced interfacial cohesion and unique distribution of precipitates suppressed intergranular cracks during AM and increased the plasticity of the alloy.

A comprehensive review on applications of 3D printing in natural fibers polymer composites for biomedical applications

Over the past few decades, three-dimensional (3D) printing technologies have surpassed the conventional manufacturing techniques due to their wide applications and advantages. The applications of 3D printing in biomedical field is ever increasing due to improvement in accuracy and surface quality of products. The development of biomedical implants through patient specific data and rapid tooling techniques has revolutionized the research activities. Now-a-days, the metal printers have capability to directly create metal implants using biocompatible metallic alloys. This paper focuses on the potential applications of 3D printing in biomedical fields with specific emphasis on tissue engineering and bio-printing of organs using bio-inks. This paper also reviews various biocompatible and biodegradable materials used in recent in-vivo and in-vitro studies. It has been deduced from the study that use of natural fibers in polymers resulted in improved mechanical strength of products. Also, the implementation of additive manufacturing technologies for production of composites would lead to production of customized product.

Microstructural analysis as a requirement for sinter-based additive manufacturing of highly conductive copper

Abstract To further improve the range of battery-powered electric vehicles, new concepts in power electronics are required. The use of so-called “wide-bandgap” semiconductor materials, such as SiC, could meet the need for even more powerful power electronics, but this also increases the demands on the thermal management of the components. Complex copper cooler structures adapted to the temperature field could be a suitable way to meet these increasing requirements for heat dissipation. However, conventional manufacturing techniques such as forging, casting and milling are reaching their limits for the production of complex Cu structures, and new processes such as additive manufacturing are coming into focus. Additive manufacturing processes such as selective laser melting (SLM) place high demands on the laser system for highly-conductive copper (Cu) [1]. This means that less established sinter-based processes such as binder jetting (BJ) or fused filament fabrication (FFF) are also suitable for the production of complex Cu structures. In sinter-based methods, the sintering process and the microstructure, which is strongly influenced by it, is crucial for achieving good physical properties of the component [2]. In this work, methods are presented that allow for a quantitative and qualitative evaluation of the sintering process of copper at the microstructure level in order to derive optimized process parameters that enable higher sintering densities and thus greater conductivities. The influence of residual porosity and impurities on conductivity was investigated and allows for a specific prediction of the expected conductivity of sintered Cu structures.

Additive Manufacturing of Viscoelastic Polyacrylamide Substrates for Mechanosensing Studies.

Polymerized polyacrylamide (PAA) substrates are linearly elastic hydrogels that are widely used in mechanosensing studies due to their biocompatibility, wide range of functionalization capability, and tunable mechanical properties. However, such cellular response on purely elastic substrates, which do not mimic the viscoelastic living tissues, may not be physiologically relevant. Because the cellular response on 2D viscoelastic PAA substrates remains largely unknown, we used stereolithography (SLA)-based additive manufacturing technique to create viscoelastic PAA substrates with tunable mechanical properties that allow us to identify physiologically relevant cellular behaviors. Three PAA substrates of different complex moduli were fabricated by SLA. By embedding fluorescent markers during the additive manufacturing of the substrates, we show a homogeneous and uniform composition throughout, which conventional manufacturing techniques cannot produce. Rheological investigation of the additively manufactured PAA substrates shows a viscoelastic behavior with a 5–10% loss moduli compared to their elastic moduli, mimicking the living tissues. To understand the cell mechanosensing on the dissipative PAA substrates, single live cells were seeded on PAA substrates to establish the basic relationships between cell traction, cytoskeletal prestress, and cell spreading. With the increasing substrate moduli, we observed a concomitant increase in cellular traction and prestress, but not cell spreading, suggesting that cell spreading can be decoupled from traction and intracellular prestress in physiologically relevant environments. Together, additively manufactured PAA substrates fill the void of lacking real tissue like viscoelastic materials that can be used in a variety of mechanosensing studies with superior reproducibility.

High resolution-optical tomography for in-process layerwise monitoring of a laser-powder bed fusion technology

With the implementation of Laser Powder Bed Fusion technologies for industrial production, the need for in-process monitoring has emerged to ensure stable conditions and the process to succeed. Indeed, despite significant technological advances, the rejected parts are still too high if compared to the more conventional manufacturing techniques. Several defects are known to affect the process, more likely when complex geometries are fabricated. Among these, the production of inclined thin walls without support structures is still critical and, in most cases, geometric distortions are observed on the overhanging surfaces. In order to overcome the above mentioned problems and improve the quality of these critical structures, an high resolution monitoring system based on Optical Tomography (OT) was proposed, called High Resolution-Optical Tomography (HR-OT). It uses a very high-resolution sensor, operating in the visible spectrum of light, on a large area of the surface layers comprising the entire printing platform. This very recent technique, typically applied for the detection of volumetric defects, such as porosity or lack of fusion, was successfully applied, in this paper, for the detection of geometric distortions, allowing to avoid onerous pre-processing phases in the image processing workflow. Specific geometric indexes were selected as monitoring outputs and were used for the construction of appropriate control charts in order to carry out statistical process monitoring. Finally, an off-line 3D reconstruction, by means of digital close range photogrammetry, was used to verify the effectiveness of the proposed monitoring solution when applied for in-process detection of geometric distortions.