Hybrid Additive Manufacturing Research Articles

Printing Cu on a Cold-Sprayed Cu Plate via Selective Laser Melting—Hybrid Additive Manufacturing

The development of the additive manufacturing (AM) technology proffers challenging requirements for forming accuracy and efficiency. In this paper, a hybrid additive manufacturing technology combining fusion-based selective laser melting (SLM) and solid-state cold spraying (CS) was proposed in order to enable the fast production of near-net-shape metal parts. The idea is to fabricate a bulk deposit with a rough contour first via the “fast” CS process and then add fine structures and complex features through “slow” SLM. The experimental results show that it is feasible to deposit an SLM part onto a CS part with good interfacial bonding. However, the CS parts must be subject to heat treatment to improve their cohesion strength before being sending for SLM processing. Otherwise, the high tensile residual stress generated during the SLM process will cause fractures and cracks in the CS part. After heat treatment, pure copper deposited by CS undergoes grain growth and recrystallization, resulting in improved cohesive strength and the release of the residual stress in the CS parts. The tensile test on the SLM/CS interfacial region indicates that the bonding strength increased by 38% from 45 ± 7 MPa to 62 ± 1 MPa after the CS part is subject to heat treatment, and the SLM/CS interfacial bonding strength is higher than the CS parts. This study demonstrates that the proposed hybrid AM process is feasible and promising for manufacturing free-standing SLM-CS components.

Hybrid additive manufacturing of ultra-fine high-resolution shell–core structured conductive mesh-based flexible transparent electrodes for flexible displays

ABSTRACT Metal mesh transparent electrodes present a promising alternative to Indium-Tin Oxide (ITO) due to their adjustable period and favourable trade-off between transmittance and conductivity. In this work, a template-free, non-high temperature hybrid additive manufacturing approach of the polyacrylonitrile (PAN)/Cu core–shell structure high-resolution metal mesh flexible transparent electrode (FTE) is proposed. The electric field-driven (EFD) 3D printing method was employed to print ultra-fine lines with widths as low as 1 μm. The composite-plating process combining electroless plating and electroplating has solved the structural defects of single deposition process. The prepared FTE has an excellent conductivity down to 1 Ω/sq and 89% light transmission (at 550 nm). Its exceptional mechanical properties and environmental stability make it suitable for diverse working environments. Even after undergoing 2000 bends at a radius of 3 mm, the resistance change rate remains as low as 1.4%. The resistance exhibits an approximately 8% change rate in the acid–base environment experiments conducted over 72 h. The flexible touch screen prepared with this FTE exhibits excellent writing performance in both flat and curved working scenarios. Furthermore, the significant potential of this FTE in the field of optoelectronics is effectively demonstrated through its exceptional luminescent performance in electroluminescent devices.

Microstructural Characterization of the Transition in SS316L and IN625 Bimetallic Fabricated Using Hybrid Additive Manufacturing

Microstructural Characterization of the Transition in SS316L and IN625 Bimetallic Fabricated Using Hybrid Additive Manufacturing

Resonant ultrasound spectroscopy of hybrid metal additive manufacturing

Additive manufacturing has been targeted as the next high-impact fabrication technique for parts and components. Hybrid metal additive manufacturing (AM) refers to the 3-D printed fabrication process involving secondary manufacturing processes or energy sources and multifunctional printing. Specific layers are altered within the build using additional processes (i.e., milling or peening) that are synergistic with the additive process. This combination alters the sample microstructure and can refine grains, increase dislocation density, or induce residual stresses. The effect of these hybrid layers is typically not confined within the layer alone but has a compounding effect on preceding layers. The goal is to control the changes in print parameters throughout the build to enhance component performance, but unique challenges remain for nondestructive validation of such samples. Traditional ultrasonic methods on hybrid-AM components have successfully mapped material variations with sufficient spatial resolution. However, the use of resonance ultrasound spectroscopy (RUS) for hybrid-AM is less developed. In this presentation, the use of RUS is described relative to the characterization of hybrid AM 316L stainless steel samples. The spatial organization of the hybrid samples affects the resonances relative to their mode shape. Computational models are used to quantify the impact of the hybrid processes.

Microstructure quality assessment for hybrid additive manufactured Ti6Al4V components via ultrasonics

Metal components with functionally organized microstructures for specific applications are emerging thanks to hybrid additive manufacturing (AM). The customization of these high value components accentuates the need for nondestructive methods to characterize their microstructural functional patterns. Nondestructive evaluation (NDE) methods that are economical, fast, energy efficient, and easy to integrate into routine component inspections are preferred. Most importantly, NDE methods must be sensitive to changes in the microstructure such that regions that do not satisfy the design requirements (i.e. out-of-spec regions) can be detected. In this work, ultrasonic NDE methods grounded in diffuse backscatter modeling were used to detect and quantify spatial property variations resulting from a hybrid AM process. The manufacturing process coupled directed energy deposition (DED) with milling in a cyclical manner. These methods were successfully implemented to evaluate the microstructural uniformity of Ti6Al4V samples as well as to make comparisons across an ensemble of samples manufactured with identical parameters. Out-of-spec regions were mapped with respect to the sample geometry on a layer-by-layer basis. The results of this work are expected to inform future NDE strategies for both research and practitioner contexts, and limitations are discussed.

Ultrasonic in situ measurements for hybrid metal additive manufacturing

Hybrid additive manufacturing (AM) of metals includes synergistic secondary processes such as milling or peening that impart changes to the component for improved performance. Although a valuable concept, implementation is difficult to verify due to a current lack of in situ inspection methods. In this presentation, two different strategies are described with respect to ultrasonic inspections for hybrid metal AM. Both are used for inspections during laser-based directed energy deposition with milling as the hybrid process. The first uses a transducer mounted below the build plate. This configuration allows waves to interrogate the entire sample during all additive and subtractive manufacturing steps. Experiments with Ti6Al4V show the changes in ultrasonic wave speed and attenuation that track the manufacturing temporally. The second inspection approach uses ultrasonic surface waves at the top surface of the sample. These measurements are used on samples of 316L stainless steel at the end of additive steps as well as before and after milling to quantify localized information regarding the most recent layers. Wave speed and diffuse scattering information show the variability with respect to sample geometry, build height, and process parameters. Finally, advantages and limitations of both approaches and prospects for validated parts are discussed.

Co-strengthening and deformation behaviors of hybrid additive manufactured U75V/15-5PH bimetal via optimized heat treatment

Bimetals composed of U75V pearlitic steel and 15–5 precipitation hardening (PH) steel were successfully processed by a hybrid additive manufacturing method. However, the U75V/15-5PH bimetal in the as-deposited condition showed inferior mechanical properties owing to the inhomogeneous microstructures. Herein, optimized heat treatment for the co-strengthening of U75V/15-5PH bimetal was designed by investigating the microstructural evolution and mechanical properties thoroughly. Results showed that the mechanical properties of the U75V steel region were recovered after solution treatment, reflected in the formation of lamellar pearlite. For the additive 15-5PH steel region, the formation of martensitic phase and NbC carbides contributed to the strengthening in the solution condition. Furthermore, this region was further hardened by the massive precipitation of Cu-riched precipitates induced by aging treatment. Due to the difference in yield strength of U75V/15-5PH bimetals with various locations, the deformation transfer phenomenon from U75V steel to 15-5PH stainless steel was detected during the uniaxial tensile tests. After heat-treated through the solution and aging treatment, the optimized yield strength, ultimate tensile strength, and elongation of the U75V/15-5PH bimetal achieved 878 MPa, 1201 MPa, and 11.2%, respectively. This study demonstrated experimentally that the mechanical performance of the U75V/15-5PH bimetal with various microstructures could be improved by designing a suitable solution and aging heat treatment.

Improvement of mechanical properties at cryogenic temperature of CoCrNi medium entropy alloy fabricated by hybrid additive manufacturing technology

The emergence of CoCrNi medium-entropy alloys (MEAs) holds great promise for applications in extreme service environments. However, fabricating CoCrNi MEA with an extraordinary combination of strength and ductility is urgently needed. Herein, we adopt a combination of laser direct energy deposition (L-DED) additive manufacturing and ultrasonic impact treatment (UIT) to fabricate CoCrNi additive parts. The optical microscopy results showed that the proportion of equiaxed crystals increased from 7.2% to 42.1% after UIT, while the proportion of columnar crystals with grain sizes greater than 31 μm decreased from 62.8% to 27.4%. The tensile test results at 298 and 77 K showed that the tensile strength increased by 7.0% and 27.6%, respectively, after UIT. Electron backscatter diffraction (EBSD) results indicated that the texture intensity of the XOY and XOZ planes in the additive parts decreased after UIT. The transmission Kikuchi diffraction (TKD) results showed that 29.9% of the FCC phase transformed into the HCP phase after the tensile test. Meanwhile, the volume fractions of the substructured, recrystallization, and deformation zones in the phase transformation zone and in the FCC structure were 21.2%, 58.7%, and 20.1% and 67.7%, 9.0%, and 23.3%, respectively. The enhanced transformation-induced plasticity effect contributed to the higher strength and ductility of the CoCrNi MEA treated by UIT.

Hybrid additive manufacturing of AISI H13 through interlayer machining and laser re-melting

Heat accumulation along the deposited layers in AM is an important issue that may lead to shape distortions. In this context, the present paper is aimed at analysing the feasibility of interlayer post-processing of depositions to improve interlayer bonding and process performance. Concretely, the use of interlayer machining and laser re-melting is tested and their effect on the porosity, mechanical properties and component distortion is analysed. Additionally, the results obtained after each interlayer post-processing technique were compared with an as-deposited sample to analyse the benefits of the hybrid additive manufacturing approach on the generated parts. Samples post-treated through machining showed the lowest deformation. As for the porosity, laser remelting post-processing led to best results. Hardness was also tested along the height of samples and it was observed that it increases in build direction for all the cases tested. Highest hardness values were obtained for the samples post-processed through machining.

Increased ductility of Ti-6Al-4V by interlayer milling during directed energy deposition

Additive manufacturing (AM) often results in high strength but poor ductility in titanium alloys. Hybrid AM is a solution capable of improving both ductility and strength. In this study, hybrid AM of Ti-6Al-4 V was achieved by coupling directed energy deposition with interlayer machining. The microstructure, residual stress, and microhardness were examined to explain how interlayer machining caused a 63% improvement in ductility while retaining an equivalent strength to as-printed samples. Interlayer machining introduced recurrent interruptions in printing that allowed for slow cooling-induced coarsening of acicular α laths at the machined interfaces. The coarse α laths on the selectively machined layers increased dislocation motion under tensile loads and improved bulk ductility. The results highlighted in this publication demonstrate the feasibility of hybrid AM to enhance the toughness of titanium alloys.

Microstructure and mechanical properties of 2319 aluminum alloy deposited by laser and cold metal transfer hybrid additive manufacturing

Wire and arc additively manufactured aluminum alloys are prone to porosity, leading to poor mechanical properties in samples, which hinders their broad industrial application. Laser and arc hybrid processes have garnered increasing attention for their potential to reduce porosity, stabilize the arc, and enhance deposition efficiency. This paper investigates the porosity, element distribution, microstructure evolution, and mechanical properties of 2319 aluminum alloy produced through the laser and cold metal transfer (laser-CMT) hybrid additive manufacturing process. In comparison with the as-deposited samples, the laser-CMT hybrid process decreases porosity, enhances element distribution, mitigates Cu element segregation, and results in increased θ′′ phase precipitation. Following T6 heat treatment, the ultimate tensile strength (UTS), yield strength (YS), and elongation of the x-direction specimens from the laser-CMT hybrid process are 450.0 MPa, 318.1 MPa, and 10.0%, respectively. These values are 11.27%, 7.03%, and 36.65% higher than those of the as-deposited samples. To validate the findings, a large-scale load-carrying frame for a commercial aircraft was fabricated, demonstrating the efficacy of the process. The paper also presents a detailed analysis of the strengthening mechanism. Samples deposited using the laser-CMT method exhibit reduced porosity and excellent mechanical properties, making this process promising for a wide range of applications.

Study on additive and subtractive manufacturing of high-quality surface parts enabled by picosecond laser

Low dimensional accuracy and high surface roughness induced by the inherent powder adhesion and staircase effect are the critical challenges for the application of parts fabricated by laser powder bed fusion (LPBF). In this study, an innovative hybrid additive manufacturing process by adding the ultrafast laser machining to the LPBF process was proposed. After LPBF process, the additively manufactured samples were micromachined using a picosecond laser. The effects of parameters (i.e., laser frequency, and scanning speed) of the ultrafast laser machining on the surface morphology were investigated by the single-pass ablation experiments. The impact of the scan counts on the cutting depth was analyzed by the large-area cutting experiments. Subsequently, samples with different tilt angles were fabricated by a hybrid additive manufacturing process with alternating processing of LPBF and the ultrafast laser machining. The side surface roughness (4.98 ± 0.44 µm) of the samples fabricated by hybrid additive manufacturing process was lower than that of as-built LPBF samples. The processing characteristics and the ablation morphology of the picosecond laser were investigated. The factors affecting the quality of hybrid manufacturing were systematically discussed. This work may provide a new way to manufacture parts with high dimensional accuracy and low surface roughness by LPBF.

Development of a solid-state extrusion-roll-bonding based additive manufacturing (ERB-AM) technology for aluminum alloys

To solve the poor printability issue of high-performance aluminum alloys in additive manufacturing processes, a solid-state hybrid additive manufacturing (AM) technology, combining extrusion and roll bonding operations, is proposed, in which the extruded aluminum layers are soundly bonded through the hot-rolling operation. In this feasibility and early-stage research, a lab-scale extrusion-roll-bonding prototype machine is designed and built. Aluminum alloy, AA1060, owing to its relatively low loading requirements for the prototype, is used for the proof of the concept. The extrusion-roll-bonding tests have been undertaken at different temperatures and rolling reductions to identify optimal processing parameters. The corresponding bonding quality was estimated using an optical microscope (OM). Also, miniature AM tensile samples were tested to evaluate the tensile properties of the bonding interfaces. It is of great interest to see that the AM material did not fracture at the bonding interface and its stress-strain response is similar to that of the original material. In-depth analyses on the interfacial grain and oxide distribution and their effects on the interfacial strength were undertaken using a transmission electron microscope (TEM) and scanning electron microscope (SEM)/electron backscatter diffraction (EBSD). This study demonstrates the proposed solid-state AM technique can successfully manufacture aluminum alloys at their solid states, achieving comparable mechanical properties to their wrought states. This new solid state AM technique may enable a wide range of alloys with poor printability to be used in various industries to produce safety-critical and large, structural components with simple geometry.

Hybrid additive manufacturing of ER70S6 steel and Inconel 625: A study on microstructure and mechanical properties

Hybrid Additive Manufacturing (HAM) is currently being explored because of its potential to achieve trade-off between build capacity and feature resolution. The present study aims at fabricating ER70S6-Inconel 625 (IN625) bimetallic clad using hybrid Wire Arc Additive Manufacturing (WAAM) and Laser Directed Energy Deposition (LDED) processes. Microstructure evaluation was performed at the cross section of bimetallic clad for distinct materials as well as the interface. WAAM built ER70S6 revealed equiaxed ferritic grains, whereas laser deposited IN625 region showed columnar dendrites with under developed secondary arms. However, the first layer of IN625 exhibited columnar dendrite with secondary arms due to the influence of diffused Fe from the base ER70S6 steel under the action of concentrated laser heat source, which was revealed by energy dispersive spectroscopy (EDS) maps. The measured microhardness across the cross section of the deposit showed values corresponding to inherent material system. The interface did not reveal presence of any intermetallic phases which was confirmed by hardness results and X-Ray diffraction. Shear test revealed superior bond strength between the two materials, maintaining average strength of 452 MPa. The fractography images exhibited fine dimples along with cleavages indicating mixed fracture characteristics. This additive manufacturing method explores a new dimension in multi-material fabrication which, when customized for different materials, serve critical areas in the aerospace and defence sector.

Microstructure and mechanical properties of an ultra-high strength steel fabricated by laser hybrid additive manufacturing

35CrMnSiA is a type of ultra-high-strength steel that finds extensive application in key components characterized by geometrically regular structures and complex extensions, such as structural shells. Laser hybrid additive manufacturing (LHAM) is an advanced manufacturing technology that combines the benefits of traditional manufacturing and additive manufacturing. LHAM has the potential for rapid and cost-effective production of these components. However, the formation mechanism of the microstructure in different zones of 35CrMnSiA steel fabricated by LHAM and its impact on the overall tensile performance remain unclear, thereby tremendously restricting its application. To address this issue, this study employed wrought 35CrMnSiA steel as the base material and utilized directed energy deposition (DED) to fabricate defect-free LHAM parts. The microstructure of LHAM-fabricated 35CrMnSiA steel is location-related. The laser deposition zone comprised ferrite with internal and boundary-distributed carbides, whereas the substrate zone comprised martensite. The heat-affected zone exhibited a gradient microstructure between the two. The microstructure in the deposition zone was primarily governed by solidification behavior and thermal history during the deposition process, while the heat-affected zone was mainly influenced by recrystallization. The non-uniform characteristics of the microstructure significantly influenced its mechanical properties, resulting in a “cask effect,” namely, the tensile performance of LHAM-fabricated 35CrMnSiA steel depended on the weakest laser deposition zone. The ultimate tensile strength and elongation of LHAM-fabricated 35CrMnSiA steel are 959 MP and 15.2%, respectively. This study establishes a basis for controlling the microstructure and optimizing the performance of hybrid-manufactured ultra-high-strength steel.

Gradient microstructure and strength-ductility synergy improvement of 2319 aluminum alloys by hybrid additive manufacturing

Wire-arc additive manufacturing (WAAM) technology has been considered as a suitable method for manufacturing large components of aluminum alloys due to its high deposition rate and material utilization. However, the coarse grain size, high porosity and poor mechanical properties of as-deposited aluminum alloys have limited their further development. In this study, a novel hybrid additive manufacturing (HAM) technology combining WAAM and friction stir processing (FSP) has been developed, and a gradient microstructure 2319 aluminum alloy with ultrafine grains-equiaxed grains-columnar grains was successfully fabricated. The microstructure evolution and mechanical properties also have been investigated in this study. The grain size distribution, texture analysis, and the percentage of recrystallized grains were characterized by electron backscatter diffraction (EBSD). The experimental results demonstrated that the hybrid additive manufacturing can achieve a substantial grain refinement (87.09%) and increase the dynamic recrystallization content to 62% due to alternating mechanical and thermal effects. Meanwhile, compared with WAAM specimens, the hybrid-manufactured 2319 aluminum alloy has improved yield strength (YS) by 32.22%, ultimate tensile strength (UTS) by 8.75%, and elongation (EL) by 20%. The dominant mechanism of the significant strength-ductility synergy improvement also has been revealed.

Laser‐Activated Selective Electroless Plating on 3D Structures via Additive Manufacturing for Customized Electronics

AbstractThis work proposes a facile and economical hybrid additive manufacturing (HAM)technology combining fused deposition modeling (FDM) 3D printing and laser‐activated selective electroless plating (ELP) for fabricating full functional end‐use 3D customized electronics. A functional acrylonitrile butadiene styrene (ABS) filament doped with dicopper hydroxide phosphate (Cu2(OH)PO4) catalysts is developed for FDM 3D printing. The 3D printed structure is selectively laser‐activated to generate CuI plating seeds on the ABS surface and then electrolessly plated. The poor surface finish, especially the layer lines, is an intrinsic defect of extrusion 3D printing, which not only affected the fabrication quality of the 3D substrates but also the electrical performance of the attached circuitry. Herein, a chemical polishing process based on acetone vapor is explored and characterized to significantly improve the surface quality and thereby the electrical performance of the attached copper layer. In this way, highly conductive metallic circuitry can be freeformly deposited and patterned on the 3D structure which is extremely attractive for customized 3D electronics. To show the application potential of this technology, a 3D conformal 555 timer astable oscillator circuit board and a hot‐wire flowmeter are developed as demonstrators.

Hybrid Additive Manufacturing of Forming Tools

AbstractAdditive manufacturing (AM) is widely used in the automotive industry and has been expanded to include aerospace, marine, and rail. High flexibility and the possibility of manufacturing complex parts in AM motivate the integration of additive manufacturing with classical forming technologies, which can improve tooling concepts and reduce costs. This study presents three applications of this integration. First, the possibility of successful utilization of selective laser melting for manufacturing extrusion tools with complex cooling channels and paths for thermocouples is reported, leading to significantly reduced inner die temperatures during the extrusion process. Second, sheet lamination is integrated with laser metal deposition (LMD) to manufacture deep-drawing dies. Promising results are achieved in reducing the stair step effect, which is the main challenge in sheet lamination, by LMD and following post-processing such as milling, ball burnishing, and laser polishing. The new manufacturing route shows that LMD can economically and efficiently reduce the stair step effect and omit the hardening step from the conventional manufacturing process route. Finally, LMD is used to manufacture a hot stamping punch with improved surface roughness by ball burnishing and near-surface complex cooling channels. The experimental results show that the manufactured punch has lower temperatures during hot stamping compared with the conventionally manufactured punch. This study shows the successful integration of AM processes with classical forming processes.

A Review on Multiplicity in Multi-Material Additive Manufacturing: Process, Capability, Scale, and Structure.

Additive manufacturing (AM) has experienced exponential growth over the past two decades and now stands on the cusp of a transformative paradigm shift into the realm of multi-functional component manufacturing, known as multi-material AM (MMAM). While progress in MMAM has been more gradual compared to single-material AM, significant strides have been made in exploring the scientific and technological possibilities of this emerging field. Researchers have conducted feasibility studies and investigated various processes for multi-material deposition, encompassing polymeric, metallic, and bio-materials. To facilitate further advancements, this review paper addresses the pressing need for a consolidated document on MMAM that can serve as a comprehensive guide to the state of the art. Previous reviews have tended to focus on specific processes or materials, overlooking the overall picture of MMAM. Thus, this pioneering review endeavors to synthesize the collective knowledge and provide a holistic understanding of the multiplicity of materials and multiscale processes employed in MMAM. The review commences with an analysis of the implications of multiplicity, delving into its advantages, applications, challenges, and issues. Subsequently, it offers a detailed examination of MMAM with respect to processes, materials, capabilities, scales, and structural aspects. Seven standard AM processes and hybrid AM processes are thoroughly scrutinized in the context of their adaptation for MMAM, accompanied by specific examples, merits, and demerits. The scope of the review encompasses material combinations in polymers, composites, metals-ceramics, metal alloys, and biomaterials. Furthermore, it explores MMAM's capabilities in fabricating bi-metallic structures and functionally/compositionally graded materials, providing insights into various scale and structural aspects. The review culminates by outlining future research directions in MMAM and offering an overall outlook on the vast potential of multiplicity in this field. By presenting a comprehensive and integrated perspective, this paper aims to catalyze further breakthroughs in MMAM, thus propelling the next generation of multi-functional component manufacturing to new heights by capitalizing on the unprecedented possibilities of MMAM.

Integrative modeling of hemodynamic changes and perfusion impairment in coronary microvascular disease.

Introduction: Coronary microvascular disease is one of the responsible factors for cardiac perfusion impairment. Due to diagnostic and treatment challenges, this pathology (characterized by alterations to microvasculature local hemodynamics) represents a significant yet unsolved clinical problem. Methods: Due to the poor understanding of the onset and progression of this disease, we propose a new and noninvasive strategy to quantify in-vivo hemodynamic changes occurring in the microvasculature. Specifically, we here present a conceptual workflow that combines both in-vitro and in-silico modelling for the analysis of the hemodynamic alterations in the microvasculature. Results: First, we demonstrate a hybrid additive manufacturing process to fabricate circular cross-section, biocompatible fluidic networks in polytetrafluoroethylene. We then use these microfluidic devices and computational fluid dynamics to simulate different degrees of perfusion impairment. Discussion: Ultimately, we show that the developed workflow defines a robust platform for the multiscale analysis of multifactorial events occurring in coronary microvascular disease.