Recent advances in additive manufacturing (AM) have attracted significant industrial interest. Initially, AM was mainly associated with the fabrication of prototypes, but the AM advances together ...with the broadening range of available materials, especially for producing metallic parts, have broaden the application areas and now the technology can be used for manufacturing functional parts, too. Especially, the AM technologies enable the creation of complex and topologically optimised geometries with internal cavities that were impossible to produce with traditional manufacturing processes. However, the tight geometrical tolerances along with the strict surface integrity requirements in aerospace, biomedical and automotive industries are not achievable in most cases with standalone AM technologies. Therefore, AM parts need extensive post-processing to ensure that their surface and dimensional requirements together with their respective mechanical properties are met. In this context, it is not surprising that the integration of AM with post-processing technologies into single and multi set-up processing solutions, commonly referred to as hybrid AM, has emerged as a very attractive proposition for industry while attracting a significant R&D interest. This paper reviews the current research and technology advances associated with the hybrid AM solutions. The special focus is on hybrid AM solutions that combine the capabilities of laser-based AM for processing powders with the necessary post-process technologies for producing metal parts with required accuracy, surface integrity and material properties. Commercially available hybrid AM systems that integrate laser-based AM with post-processing technologies are also reviewed together with their key application areas. Finally, the main challenges and open issues in broadening the industrial use of hybrid AM solutions are discussed.
A key advantage of additive manufacturing (AM) is that it allows the fabrication of lattice structures for customized biomedical implants with high performance. This paper presents the use of ...statistical approaches in design optimization of additively manufactured titanium lattice structures for biomedical implants. Design of experiments using response surface and analysis of variance was carried out to study the effect design parameters on the properties of the AM lattice structures such as ultimate compression strength, specific compressive strength, elastic modulus, and porosity. In addition, the lattice dimensions were optimized to fabricate a diamond cellular structure with properties that match human bones. The study found that the length of a diamond-shaped unit cell strut is the most significant design parameter. In particular, the porosity of the unit cell increases as the strut length increases, while it had a significant reverse effect on the specific compressive strength, elastic modulus, and ultimate compression strength. On the other hand, increasing the orientation angle was found to reduce both the specific compressive strength and modulus of elasticity of the lattice structure. An optimized lattice structure with strut diameter of 0.84 mm, length of 3.29 mm, and orientation angle of 47° was shown to have specific compressive strength, elastic modulus, ultimate compression strength, and porosity of 37.8 kN m/kg, 1 GPa, 49.5 MPa, and 85.7%, respectively. A cellular structure with the obtained properties could be effectively applied for trabecular bone replacement surgeries.
The next-generation medical implants require locally customised biomechanical behaviour to echo the properties of hard tissues, making additive manufacturing (AM) an ideal route due to its superior ...manufacturing flexibility. AM of titanium alloys with designed porosity is the mainstream for artificial implants, which, however, hardly balance the strength-modulus combination. Here a martensitic TiNi biomaterial with low modulus and asymmetric mechanical behaviour that mimics human bones is explored. TiNi functionally graded lattice structure (FGLS) is bio-inspired by bone architecture and processed by AM. Bio-inspired FGLS shows much higher strength and ductility than the uniform lattice despite having an equivalent structural porosity. Post-process heat-treatments alter the microstructure and result in a multi-scale hierarchically strengthened behaviour in FGLS, offering one of the highest specific strengths (about 70 kN m/kg) among porous biometals, while keeping a low specific modulus and reasonable ductility. Besides, the deformation behaviour of FGLS is in-situ monitored, which, together with microscopic observations, reveal a multi-scale failure mechanism. The bio-inspired FGLS shows better biomechanical compatibility than the uniform lattice, including density, tension/compression asymmetry, modulus, and strength. The findings highlight the ability of AM in tailoring a modulus-strength-ductility trade-off through bio-inspired multi-scale hierarchical structure design.
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•Mechanically asymmetric martensitic TiNi echoes bone mechanical behaviour.•Bio-inspired functionally graded lattices can mimic natural bone properties.•Graded lattice achieves an ultrahigh specific strength among porous biometals.•A multi-scale hierarchical microstructure created unique properties.
Additive manufacturing (AM) technologies are currently employed for the manufacturing of completely functional parts and have gained the attention of high-technology industries such as the aerospace, ...automotive, and biomedical fields. This is mainly due to their advantages in terms of low material waste and high productivity, particularly owing to the flexibility in the geometries that can be generated. In the tooling industry, specifically the manufacturing of dies and molds, AM technologies enable the generation of complex shapes, internal cooling channels, the repair of damaged dies and molds, and an improved performance of dies and molds employing multiple AM materials. In the present paper, a review of AM processes and materials applied in the tooling industry for the generation of dies and molds is addressed. AM technologies used for tooling applications and the characteristics of the materials employed in this industry are first presented. In addition, the most relevant state-of-the-art approaches are analyzed with respect to the process parameters and microstructural and mechanical properties in the processing of high-performance tooling materials used in AM processes. Concretely, studies on the AM of ferrous (maraging steels and H13 steel alloy) and non-ferrous (stellite alloys and WC alloys) tooling alloys are also analyzed.
Ceramic materials are increasingly used in micro-electro-mechanical systems (MEMS) as they offer many advantages such as high-temperature resistance, high wear resistance, low density, and favourable ...mechanical and chemical properties at elevated temperature. However, with the emerging of additive manufacturing, the use of ceramics for functional and structural MEMS raises new opportunities and challenges. This paper provides an extensive review of the manufacturing processes used for ceramic-based MEMS, including additive and conventional manufacturing technologies. The review covers the micro-fabrication techniques of ceramics with the focus on their operating principles, main features, and processed materials. Challenges that need to be addressed in applying additive technologies in MEMS include ceramic printing on wafers, post-processing at the micro-level, resolution, and quality control. The paper also sheds light on the new possibilities of ceramic additive micro-fabrication and their potential applications, which indicates a promising future.
Functionally graded materials (FGMs) and functionally graded structures (FGSs) are special types of advanced composites with peculiar features and advantages. This article reviews the design criteria ...of functionally graded additive manufacturing (FGAM), which is capable of fabricating gradient components with versatile functional properties. Conventional geometrical‐based design concepts have limited potential for FGAM and multi‐scale design concepts (from geometrical patterning to microstructural design) are needed to develop gradient components with specific graded properties at different locations. FGMs and FGSs are of great interest to a larger range of industrial sectors and applications including aerospace, automotive, biomedical implants, optoelectronic devices, energy absorbing structures, geological models, and heat exchangers. This review presents an overview of various fabrication ideas and suggestions for future research in terms of design and creation of FGMs and FGSs, benefiting a wide variety of scientific fields.
Multi‐scale functionally graded additive manufacturing (FGAM) design is reviewed and the state‐of‐the‐art of FGAM technologies and multifunctionalities and potential applications in biomedical implants, optoelectronic devices, energy absorbing structures, geological models, and heat exchangers is summarized. An overview of various fabrication suggestions for future research in terms of design and creation of FGM/FGS is also presented, benefiting a wide variety of scientific fields.
The rolling process of rebar steel production is one of the well established manufacturing processes; however, it should be subjected to revision and redesign for productivity enhancement and power ...reduction throughout the slit rolling process. In this work, slitting passes are extensively reviewed and modified for the attainment of better rolling stability and reduction in power consumption. The study has been applied for grade B400B-R Egyptian rebar steel, which is equivalent to steel grade ASTM A615M, Grade 40. Traditionally, the rolled strip in the rolling pass is edged before implementing a slitting pass using grooved rolls; this produces a single barreled strip. This single barrel form causes instability in the next slitting stand on the pressing by the slitting roll knife. Multiple industrial trials are attempted to achieve the deformation of the edging stand using a grooveless roll. As a result, a double barreled slab is produced. In parallel, finite element simulations of the edging pass are performed using grooved and grooveless rolls, and similar slab geometry with single and double barreled form are produced. In addition, further finite element simulations of the slitting stand are execute using idealized single barreled strips. The power calculated by the FE simulations of the single barreled strip is (245 kW), which is in acceptable agreement with the experimental observations in the industrial process (216 kW). This result validates the FE modeling parameters such as material model and boundary conditions. The FE modeling is extended to the slit rolling stand of a double barreled strip, which was previously produced by the grooveless edging rolls. It is found that the power consumption is (165 kW) 12% lower than the power consumed (185 kW) for slitting the single barreled strip.
•A canister-free hot isostatic pressing was introduced for porous structures.•CF-HIPed samples of particle size (5–50)μm had porosities of 1.4%–25.4%.•Decreasing the powder size resulted in an ...improvement of mechanical properties of the CF-HIPed samples.•Porous structures with mechanical properties similar to human bones were produced.
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Porous biomedical implants are known for their improved osseointegration due to the ingrowth of bone tissues, combined with a lower elastic modulus to solid implants, resulting in a reduced likelihood for stress shielding and implant loosening. In this work, the control of the porosity content in capsule-free powder hot isostatic pressing (CF-HIPing) of 316L stainless steel was investigated. The proposed approach utilises cold isostatic pressing (CIPing) to form green compacts using rubber moulds, followed by CF-HIPing under suitable conditions. Porosity control was attained via the selection of the powder particle size used in creating the green compacts. The microstructural and mechanical properties development of the CF-HIPed structures was studied using optical and scanning electron microscopy, micro-computer tomography, hardness, and compression testing. The occurrence of powder necking was visualised using electron backscattered diffraction. The results showed a significant increase in the pore fraction of the samples by increasing the particle size of the powder. However, increasing the particle size was also associated with a drop in the elastic modulus, compressive strength, ductility, and hardness of the final structures. Nonetheless, porous structures with elastic modulus between 17 and 30GPa were successfully produced using a powder particle size range of 32–50μm, matching the elastic modulus of human bones.
Laser-based Direct Energy Deposition (L-DED) is one of the most commonly employed metal additive manufacturing technologies. In L-DED, a laser beam is employed as a heat source to melt the metal ...powder that is deposited on a substrate layer by layer for the generation of a desired component. The powder is commonly fed through a nozzle into the molten pool by means of a carrier gas and therefore, a nozzle design that ensures optimal deposition of the material is of critical importance. Additionally, its design also affects the powder and gas flows that arise in the nozzle and during the deposition. This, in turn will affect the characteristics of the generated clad and the performance of the whole deposition. Therefore, an optimization of deposition nozzle geometry can be as important as the controlling of deposition process parameters in order to obtain best component qualities. In this context, the present review work is aimed at analysing the different nozzle designs employed in powder-based L-DED processes and the influence of different geometrical features and configurations on the resulting powder and gas flows. Concretely, the main characteristics of each design, their advantages and their possible shortcomings are analysed in detail. Additionally, a review of most relevant numerical models employed during the development of new and optimised nozzle designs are also addressed.
Origami structures have attracted attention in biomedical applications due to their ability to develop surgical tools that can be expanded from a minimal volume to a larger and functional device. On ...the other hand, four-dimensional (4D) printing is an emerging technology, which involves 3D printing of smart materials that can respond to external stimuli such as heat. This short communication introduces the proof of concept of merging origami and 4D printing technologies to develop minimally invasive delivery of functional biomedical scaffolds with high shape recovery. The shape-memory effect (SME) of the PLA filament and the origami designs were also assessed in terms of deformability and recovery rate. The results showed that herringbone tessellation origami structure combined with internal natural cancellous bone core satisfies the design requirement of foldable scaffolds. The substantial and consistent SME of the 4D printed herringbone tessellation origami, which exhibited 96% recovery compared to 61% for PLA filament, was the most significant discovery of this paper. The experiments demonstrated how the use of 4D printing in situ with origami structures could achieve reliable and repeatable results, therefore conclusively proving how 4D printing of origami structures can be applied to biomedical scaffolds.
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