Multi-material Additive Manufacturing Research Articles

Single-vat single-cure grayscale digital light processing 3D printing of materials with large property difference and high stretchability

Multimaterial additive manufacturing has important applications in various emerging fields. However, it is very challenging due to material and printing technology limitations. Here, we present a resin design strategy that can be used for single-vat single-cure grayscale digital light processing (g-DLP) 3D printing where light intensity can locally control the conversion of monomers to form from a highly stretchable soft organogel to a stiff thermoset within in a single layer of printing. The high modulus contrast and high stretchability can be realized simultaneously in a monolithic structure at a high printing speed (z-direction height 1 mm/min). We further demonstrate that the capability can enable previously unachievable or hard-to-achieve 3D printed structures for biomimetic designs, inflatable soft robots and actuators, and soft stretchable electronics. This resin design strategy thus provides a material solution in multimaterial additive manufacture for a variety of emerging applications.

A review on additive manufacturing of SS-Ni multi-material fabrication

Additive manufacturing (AM) is an emerging technology used to fabricate complex and near net shape components with minimum tooling and material wastage. This technology has found its application in biomedical, aerospace, automobile and structural elements. Multi material additive manufacturing (MMAM) process is able to manufacture components built with a combination of different materials like metals, ceramics, and reinforced materials to achieve the desired properties at a specific location. Many multi-material combinations have been fabricated through MMAM such as Al-Fe, Al-Cu, SS-Ni, Ni-Ti, Ti-SS, diamond-W-Cu etc. The most common combination among these discussed materials are SS-Ni multi-material for its wide range of applications in gas turbine parts, energy industry, petrochemical industry, marine industry, nuclear fission reactors, aerospace structure and aerospace engines. The processing of SS-Ni multi-material using LPBF, DED and WAAM has been found to provide superior properties such as high strength at extreme temperature environment, corrosion resistance, oxidation resistance, higher toughness at low cost when compared with conventional manufacturing methods thereby, motivating the present review on SS-Ni multi-material AM. This review aims to summarize the various methods used for the fabrication of SS-Ni multi-material AM, different combination strategies and its effect on the quality of fabrication, their microstructure variations, property enhancement, challenges and applications.

Design and fabrication of multi-material broadband electromagnetic absorbers for use in cavity-backed antennas

We investigated the feasibility of designing and fabricating novel broadband radiofrequency (RF) absorbers for use in cavity-backed antennas. Fabricating the absorber involved a multi-material additive manufacturing (AM) approach that combined two polymer filaments: a low-loss dielectric filament and a lossy carbon-loaded filament. An iterative optimization algorithm was developed to deploy these filaments and create gradient distributions of material properties that minimize reflectance over a desired frequency band and a range of incident angles to achieve wideband electromagnetic absorption. The chosen material profiles were effectively realized using a spatially varying subwavelength lattice structure printed via fused filament fabrication. Experimentally, validation results demonstrated low reflectance over a wide frequency band, 10 to 40 GHz, and a range of incident angles, 0°–50°. Finally, this printed multi-material absorber was integrated within a cavity-backed spiral antenna and used to suppress backlobe radiation while maintaining an acceptable radiation pattern in the forward direction. While this study investigated cavity-backed antennas, these computational and experimental methods are potentially useful for a wide range of other applications.

Latest Developments to Manufacture Metal Matrix Composites and Functionally Graded Materials through AM: A State-of-the-Art Review.

Multi-material structure fabrication has the potential to address some critical challenges in today's industrial paradigm. While conventional manufacturing processes cannot deliver multi-material structures in a single operation, additive manufacturing (AM) has come up as an appealing alternative. In particular, laser-directed energy deposition (L-DED) is preferred for multi-material AM. The most relevant applications envisioned for multi-material L-DED are alloy design, metal matrix composites (MMC), and functionally graded materials (FGM). Nonetheless, there are still some issues that need to be faced before multi-material L-DED is ready for industrial use. Driven by this need, in this literature review, the suitability of L-DED for multi-material component fabrication is first demonstrated. Then, the main defects associated with multi-material L-DED and current opportunities and challenges in the field are reported. In view of the industrial relevance of high-performance coatings as tools to mitigate wear, emphasis is placed on the development of MMCs and FGMs. The identified challenges include-but are not limited to-tightly controlling the composition of the multi-material powder mixture injected into the melt pool; understanding the influence of the thermal history of the process on microstructural aspects, including the interactions between constituents; and studying the in-service behaviours of MMCs and FGMs with regard to their durability and failure modes.

Ultrasonic bandgaps in viscoelastic 1D-periodic media: Mechanical modeling and experimental validation

Multi-material additive manufacturing is receiving increasing attention in the field of acoustics, in particular towards the design of micro-architectured periodic media used to achieve programmable ultrasonic responses. To unravel the effect of the material properties and spatial arrangement of the printed constituents, there is an unmet need in developing wave propagation models for prediction and optimization purposes. In this study, we propose to investigate the transmission of longitudinal ultrasound waves through 1D-periodic biphasic media, whose constituent materials are viscoelastic. To this end, Bloch–Floquet analysis is applied in the frame of viscoelasticity, with the aim of disentangling the relative contributions of viscoelasticity and periodicity on ultrasound signatures, such as dispersion, attenuation, and bandgaps localization. The impact of the finite size nature of these structures is then assessed by using a modeling approach based on the transfer matrix formalism. Finally, the modeling outcomes, i.e., frequency-dependent phase velocity and attenuation, are confronted with experiments conducted on 3D-printed samples, which exhibit a 1D periodicity at length-scales of a few hundreds of micrometers. Altogether, the obtained results shed light on the modeling characteristics to be considered when predicting the complex acoustic behavior of periodic media in the ultrasonic regime.

Development of Fused Deposition Modeling of Multiple Materials (FD3M) Through Dynamic Coaxial Extrusion.

Multimaterial additive manufacturing is expanding the design space realizable with 3D printing, yet is largely constrained to sequential deposition of each individual material. The ability to coextrude two materials and change the ratio of materials while printing would enable custom-tailored polymer composites. Here, the evolution of a dynamic material coextrusion process for additive manufacturing capable of printing any ratio between and including two neat input materials is described across 3 hot-end generations and 14 implemented design iterations. The designs evolved with increased understanding of manufacturing constraints associated with the additive manufacturing of metal components with internal flow bore diameters on the order of 2 mm and typical bore length around 50 mm. The second generation overcame this issue by partitioning the design into two pieces to locate the flow channel geometry at the interface between the components so that the details could be easily printed on the components' external surfaces. The third concept generation then focused on minimizing flow channel volume to reduce the average length when transitioning between materials by 92%. The third-generation design was also used to investigate the improvements in dimensional stability during annealing of acrylonitrile butadiene styrene (ABS) made possible by coextruding ABS with a polycarbonate (PC) core. The standard deviation of part shrinkage after annealing was 7.08% for the neat ABS but reduced to 0.24% for the coextruded ABS/PC components.

Optimisation of a Multi-Material Acoustic Black Hole

Acoustic black holes (ABHs) have been proven as an effective passive vibration control measure. Typically, they are realised by introducing a geometric taper into the structure. This approach introduces thin structural sections which leaves the ABH prone to damage through fatigue. An alternative approach has been suggested in which the material properties vary within the structure, which can be realised through multi-material additive manufacturing. This allows the structure to maintain a constant thickness and this may reduce the effect of fatigue. Prior work has been performed to characterise the materials currently available that would be suitable for the ABH application. This paper investigates methods of optimising the design of the multi-material ABH, in order to minimise the reflection coefficient in a beam termination application.

Multi-Material Additive Manufacturing of High Temperature Polyetherimide (PEI)-Based Polymer Systems for Lightweight Aerospace Applications.

Rapid innovations in 3-D printing technology have created a demand for multifunctional composites. Advanced polymers like amorphous thermoplastic polyetherimide (PEI) can create robust, lightweight, and efficient structures while providing high-temperature stability. This work manufactured ULTEM, a PEI-based polymer, and carbon-fiber-infused ULTEM multi-material composites with varying layering patterns (e.g., AAABBB vs. ABABAB) using fused filament fabrication (FFF). The microstructure of fractured surfaces and polished cross-sections determined that the print quality of layers printed closer to the heated bed was higher than layers closer to the top surface, primarily due to the thermal insulating properties of the material itself. Mechanical properties of the multi-material parts were between those of the single-material parts: an ultimate tensile strength and elastic modulus of 59 MPa and 3.005 GPa, respectively. Multi-material parts from the same filaments but with different layering patterns showed different mechanical responses. Prints were of higher quality and demonstrated a higher elastic modulus (3.080 GPa) when consecutive layers were printed from the same filament (AAABBB) versus parts with printed layers of alternating filaments (ABABAB), which showed a higher ultimate strength (62.04 MPa). These results demonstrate the potential for creatively designing multi-material printed parts that may enhance mechanical properties.

Development of a Novel Tape-Casting Multi-Slurry 3D Printing Technology to Fabricate the Ceramic/Metal Part.

Printing ceramic/metal parts increases the number of applications in additive manufacturing technology, but printing different materials on the same object with different mechanical properties will increase the difficulty of printing. Multi-material additive manufacturing technology is a solution. This study develops a novel tape-casting 3D printing technology that uses bottom-up photopolymerization to fabricate the green body for low-temperature co-fired ceramics (LTCC) that consist of ceramic and copper. The composition of ceramic and copper slurries is optimized to allow printing without delamination and sintering without cracks. Unlike traditional tape-casting processing, the proposed method deposits two slurries on demand on a transparent film, scrapes it flat, then photopolymerization is induced using a liquid crystal displayer to project the layer pattern beneath the film. The experimental results show that both slurries have good bonding strength, with a weight ratio of powder to resin of 70:30, and print a U-shaped copper volume as a circuit within the LTCC green body. A three-stage sintering parameter is derived using thermogravimetric analysis to ensure good mechanical properties for the sintered part. The SEM images show that the ceramic/copper interface of the LTCC sintered part is well-bonded. The average hardness and flexural strength of the sintered ceramic are 537.1 HV and 126.61 MPa, respectively. Volume shrinkage for the LTCC slurry is 67.97%, which is comparable to the value for a copper slurry of 68.85%. The electrical resistance of the printed copper circuit is 0.175 Ω, which is slightly greater than the theoretical value, hence it has good electrical conductivity. The proposed tape-casting 3D printer is used to print an LTCC benchmark. The sintered benchmark part is validated for the application in the LTCC application.

The role of interface in joining of 316 L stainless steel and polylactic acid by additive manufacturing

Joining of dissimilar materials is of high technological interest, given the emerging multi-material additive manufacturing. Especially, joining of metals and polymers is challenging given the major differences of the melting point, thermal expansion, and shrinkage. New, easy-to-manufacture interface geometries are proposed for 316 L stainless steel produced by laser powder bed fusion and polylactic acid by fused filament fabrication. The role of roughness, interface geometry, polymer integration in the metallic interface geometry and residual stresses is investigated experimentally in tension and by finite element analysis. Appropriate heating and design of the interface geometry prove to offer an improved interface strength.

Suppression of LME cracks in Sn bronze-steel system based on multi-material additive manufacturing

The liquid metal embrittlement (LME) cracks caused by the liquid–solid compound process of Sn bronze/steel significantly deteriorate the mechanical properties of the steel layer, especially its ductility. Based on multi-material additive manufacturing, a suppression approach for LME cracks in Sn bronze-steel system was developed by introducing a cupronickel interlayer, and a Sn bronze/cupronickel/steel laminated composite with a braided-like structure was fabricated. The composite possesses a high interlaminar bonding strength, and no LME cracks were found in the steel.

Heat Treatment of Multi-Material Additively Manufactured Maraging Steel and Co-Cr-Mo Alloy

The prospect of converting an entire assembly of parts with challenging geometry to a single part with sectional variation of properties has stimulated a growing interest in multi-material Additive Manufacturing (AM). Accordingly, the present work utilized a dual-metal Laser Powder Bed Fusion (LPBF) technique to manufacture a multi-material component, consisting of Co-Cr-Mo alloy (MP1) and maraging steel (MS1) in a single manufacturing process. The research also attempted to establish a heat treatment strategy compatible with these alloys. The resulting heat treatment effects on the microstructure, texture, and microhardness were investigated. Diffusion calculation results suggested an overall diffusion depth of 120 μm in the interface after heat treatment, which can increase the resulting joint strength if intermetallic precipitation is avoided. Electron Backscatter Diffraction (EBSD) analysis of the heat-treated samples showed that both the base metal regions retained the dominant fiber textures after printing, which is the <110> || building direction (BD) fiber texture for the MP1 region and the <111> || BD and <100> || BD fiber textures for the MS1 region. Nanoindentation tests also revealed a considerably higher hardness in the MS1 region and a slight reduction of hardness in the MP1 region after heat treatment, which can be early evidence of the successful application of the heat treatment strategy to both base metals. Future work will investigate the mechanical properties of the as-printed and heat-treated samples and verify if any precipitates formed in the MS1-MP1 interface.

Development of functional gradient multi-material composites using Poly Lactic Acid and walnut shell reinforced Poly Lactic Acid filaments by fused filament fabrication technology

In construction and architectural industries, multi-material additive manufacturing is gaining more interest because of obtaining the combined material properties in a single additive process by multiple materials. The present work concentrates on developing functionally gradient multi-material composite using Poly Lactic Acid (PLA), and novel extruded walnut shell particle reinforced Poly Lactic Acid (WPLA) by Fused Filament Fabrication technology. This work followed single and multi-gradient material deposition approaches, and their mechanical, thermal, and tribological properties were compared with standard 3D printed PLA and walnut shell-reinforced PLA composite. Among the 3D printed functional graded multi-materials, the composites with single-gradient PW configuration exhibits better compressive and D shore hardness value of 63.68 MPa and 76.2 compared with the neat PLA composite. The results show that considering the tensile and flexural samples the single gradient PLA samples shows better values when compared with all other multi gradient prepared composites. The highest heat deflection temperature of 56 °C was observed on the WPLA composite and for gradient materials PW composite which is PLA (50%) and walnut shell reinforced PLA (50%) sample exhibits the maximum heat deflection temperature of 54.4 °C. Furthermore, considering the tribological and thermal properties, the multi-gradient composite of WPW configured with PLA of 40% as inner core exhibits the lowest thermal conductivity of 0.087 W/mK and a specific wear rate of 1.631 × 10−6 mm3/Nm when compared with neat PLA composite. Therefore, among the novel functional graded multi-material, the sample PW with PLA (50%) and walnut shell reinforced PLA (50%) composite will be more suitable for semi-structural applications, and the composite with WPW designation (PLA of 40% as inner core) will suit the high wear-resistant and constructional building panel material for thermal proofing applications.

Multi-material additive manufacturing of MWCNT-based conductive photocurable resin and its antimicrobial property

Multi-material additive manufacturing of MWCNT-based conductive photocurable resin and its antimicrobial property

Realisation of acoustic black holes using multi-material additive manufacturing

Acoustic black holes (ABHs) have been widely accepted as an effective passive vibration control technique, with multiple configurations investigated for different applications. However, traditional manufacturing techniques may limit the potential geometries and configurations of the ABH. For example, the required damping layer has to be applied to the surface of the ABH taper rather than being embedded throughout or within the taper. In addition, conventional subtractive manufacturing is particularly wasteful for the realisation of ABHs, which rely on the removal of material to create a tapering structure. Therefore, in this work, we investigate the use of multi-material additive manufacturing as a potential solution, which avoids waste material in the manufacturing process and is capable of realising complex geometries, such as enclosing one material inside another. An ABH taper in a beam termination application has been implemented using polymer multi-material inkjet printing. The additively manufactured ABH was modelled using finite element analysis, before being manufactured and experimentally tested to enable an investigation of the vibration attenuation capabilities of such an ABH realisation.

Multi-material additive manufacturing: effect of process parameters on flexural behavior of soft-hard sandwich beams

Purpose Understanding the effect of process parameters on interfaces and interfacial bonding between two materials during multi-material additive manufacturing (MMAM) is crucial to the fabrication of high-quality and strong multi-material structures. The purpose of this paper is to conduct an experimental and statistical study to investigate the effect of process parameters of soft and hard materials on the flexural behavior of multi-material structures fabricated via material extrusion-based MMAM. Design/methodology/approach Sandwich beam samples composed of a soft core and hard shells are fabricated via MMAM under different printing conditions. A design of experiments is conducted to investigate the effect of the print speed and nozzle temperature on the flexural behavior of soft-hard sandwich beams. Analysis of variance and logistic regression analysis are used to analyze the significance of each process parameter. The interfacial morphology of the samples after the flexural tests is characterized. Thermal distributions during the MMAM process are captured to understand the effect of process parameters on the flexural behavior based on inter-bonding formation mechanisms. Findings Experimental results show that the soft-hard sandwich beams exhibited two different failure modes, including shell failure and interfacial failure. A transition of failure modes from interfacial failure to shell failure is observed as the nozzle temperatures increase. The samples that fail because of interfacial cracking exhibit a pure adhesive failure because of weak interfacial fracture properties. The samples that fail because of shell cracking exhibit a mixed adhesive and cohesive failure. The flexural strength and modulus are affected by the nozzle temperature for the hard material and the print speeds for both hard and soft materials significantly. Originality/value This paper first investigates the effect of process parameters for soft and hard materials on the flexural behavior of additively manufactured multi-material structures. Especially, the ranges of the selected process parameters are distinct, and the effect of all possible combinations of the process parameters on the flexural behavior is characterized through a full factorial design of experiments. The experimental results and conclusions of this paper provide guidance for future research on improving the interfacial bonding and understanding the failure mechanism of multi-material structures fabricated by MMAM.

Multi-material and Multi-dimensional 3D Printing for Biomedical Materials and Devices

In recent years, Additive Manufacturing (AM) has evolved into a “multi-x” era, such as multi-part design, multi-material, multi-process, multi-mode, multi-scale, multi-dimension, and multi-function. These emerging new features of AM present both tremendous opportunities and challenges for developing and regulating new and novel biomedical materials and devices. This paper focuses on two aspects, namely multi-material and multi-dimension AM. In multi-material 3D printing, the layering step is the key. Modifying the layering method yet without changing the solidifying or bonding principles governing the AM process can enable and significantly advance multi-material 3D printing. In multi-dimensional 3D printing, typically 4D printing and 5D printing, the meaning of “D” is suggested to refer to space–time dimension rather than the number of degrees of freedom in physical space. It is proposed in this paper that an alternative dimension (or 5D) for future 3D printing processes can be that of scale. Scale here refers the different levels of resolution that are used simultaneously within a print. In such a scale dimension, continuous printing of cross-scale or varied resolution design features in a single build process without affecting the overall printing speed and time would be highly desirable. This is probably the first paper reflecting on multi-material 3D printing from the perspective of layering and on multi-dimensional 3D printing with regard to its future development.

Design and Additive Manufacture of Multi-Tapered Coaxial Baluns

In this article, a new design method is introduced for wideband transitions from an unbalanced coaxial feed to a balanced two wire port. The device expands upon the traditional tapered coaxial balun by allowing for variations of both the inner and outer conductor radii in addition to the slot width. This multi-tapered approach provides additional design freedoms useful for realizing a wide range of impedance ratios, satisfying fixed geometrical constraints, and reducing transmission losses. A multimaterial additive manufacturing (AM) approach is described for fabricating the balun’s complex 3-D geometry. Experimental validation was conducted within the Ku -band for printed back-to-back baluns and an integrated antenna feed that combined a printed connector, a multi-tapered coaxial balun, and a spiral antenna. Simulated and measured results showed good performance over the frequency band of interest.

Multi-Material Additively Manufactured Magnetoelectric Architectures with a Structure-Dependent Mechanical-to-Electrical Conversion Capability.

Multi-material additive manufacturing has become a promising trend in fabricating advanced functional architectures due to its controllable design of diverse material species and novel structures. It remains challenging to endow the multi-material components with a mechanical-to-electrical conversion capability. This study reports on multi-material selectively laser sintered magnetoelectric architectures that can convert mechanical energy to electricity in a structure-dependent manner. The principal aim is to establish a relationship between the electrical output and the printed structures by fabricating a series of porous architectures with diverse structural parameters. The findings show that the output voltage increases with the decrease of the elastic modulus and the increase of the magnetic height, which has been analyzed by numerical simulation. Owing to the mechanical-to-electrical conversion capability, a pair of multi-material printed sneakers with the functionalities of power generation and gait analysis has been prepared. The voltage output reaches as high as ≈2 V, which can lighten a light-emitting diode lamp when a user is running. The described solution in this work has offered an exploration framework for the design, fabrication, and application prospects of multi-material additively manufactured architectures.

Bifunctional Metamaterials Incorporating Unusual Geminations of Poisson's Ratio and Coefficient of Thermal Expansion.

Natural materials overwhelmingly shrink laterally under stretching and expand upon heating. Through incorporating Poisson's ratio and coefficient of thermal expansion (PR and CTE) in unusual geminations, such as positive PR and negative CTE, negative PR and positive CTE, and even zero PR and zero CTE, bifunctional metamaterials would generate attractive shape control capacity. However, reported bifunctional metamaterials are only theoretically constructed by simple skeletal ribs, and the magnitudes of the bifunctions are still in quite narrow ranges. Here, we propose a methodology for generating novel bifunctional metamaterials consisting of engineering polymers. From concept to refinement, the topology and shape optimization are integrated for programmatically designing bifunctional metamaterials in various germinations of the PR and CTE. The underlying deformation mechanisms of the obtained bifunctions are distinctly revealed. All of the designs with complex architectures and material layouts are fabricated using the multimaterial additive manufacturing, and their effective properties are experimentally characterized. Good agreements of the design, simulation, and experiments are achieved. Especially, the accessible range of the bifunction, namely, PR and CTE, is remarkably enlarged nearly 4 times. These developed approaches open an avenue to explore the bifunctional metamaterials, which are the basis of myriad mechanical- and temperature-sensitive devices, e.g., morphing structures and high-precision components of the sensors/actuators in aerospace and electronical domains.