Multi-material Additive Manufacturing Research Articles

Simultaneously improving fabrication accuracy and interfacial bonding strength of multi-material projection stereolithography by multi-step exposure

ABSTRACT Multi-material additive manufacturing (MMAM) takes full advantage of the ability to arbitrarily place materials of additive manufacturing technology, enabling immense design freedom and functional print capabilities. Among MMAM technologies, projection stereolithography (PSL) exhibits a great balance of high resolution and fast printing speed. However, fabrication accuracy of multi-material PSL is hindered by large overcure used to strengthen interfacial bonding weakened by chemical affinity and material-exchange process. We present a novel multi-step exposure method for multi-material PSL process to overcome this shortcoming. Firstly, the whole layer is moderately exposed producing overcure of single-material PSL level to generate geometries. Then weakened interfaces are strengthened individually with additional steps of exposure. The multi-step exposure is integrated into the already efficient materials printing order of multi-material PSL process. Curing depth and overcure of photocurable resins are modeled and characterized. Exposure required to achieve sufficient interfacial bonding of single-material interfaces built through material-exchange process and multi-material interfaces with altering materials printing order is determined with tensile tests. Microfluidic channels are used to compare fabrication accuracy of traditional single-step exposure and our multi-step exposure method. This method can be widely applied in multi-material PSL to improve fabrication accuracy in a variety of applications including microfluidic devices.

Active-mixing printhead for on-the-fly composition adjustment of multi component materials in Direct Ink Writing

Multi-Material Additive Manufacturing (MMAM) enables the grading of material properties and the integration of functions within printed parts. While most MMAM methods are limited to process single-component or pre-mixed multi-component materials, the in-process mixing and extrusion of multi-component materials enables innovative material properties and use cases. When processing liquid multi-component materials, the individual component streams need to be homogenized in-process, but the required volume in conventional passive mixing hinders rapid transitions in material composition. In this paper, a two component printhead is presented which combines an active mixing approach with a continuous composition adjustment for a third additive. The approach to control the mixing composition is to influence the hydrodynamic equilibrium of individual material streams before merging them near the point of extrusion. The printhead’s functionality is verified in terms of mixing homogeneity and transition speed between material compositions.

Bioinspired Soft-Hard Interfaces Fabricated by Multi-material Additive Manufacturing: A Fracture Mechanics Investigation using Essential Work of Fracture

This study employs the Essential Work of Fracture (EWF) concept to evaluate the interfacial fracture toughness of bioinspired interfaces between soft-hard polymer phases. The experimental framework utilizes a model material system with Polylactic Acid (PLA) as the hard phase and Thermoplastic Polyurethane (TPU) as the soft phase. Employing the Fused Filament Fabrication (FFF) technique, bioinspired sutural interfaces are created, characterized by interpenetrating soft and hard protrusions. The modulation of a critical parameter in the FFF process enables the variation of interpenetration length of protrusions at the interface, thereby achieving a spectrum of interfacial strength and toughness. The determination of essential work of fracture from double edge notch tension samples, with varied ligament sizes, allows for the specific EWF measurement. This specific EWF is found to align with the initiation value of plane strain interfacial fracture toughness obtained through the Double Cantilever Beam (DCB) test. Therefore, the proposed approach asserts the elimination of the need for complex interfacial fracture tests, such as DCB. A noteworthy discovery is the establishment of a correlation between specific plastic energy dissipation and protrusion length. This correlation suggests an increased plastic dissipation with longer protrusions within the investigated bioinspired interface. Due to this heightened plastic energy dissipation, the shape of the interfacial nominal stress-displacement curves demonstrates substantial dependence on interface morphology, shifting from a triangular shape to a trapezoidal shape as protrusion length increases. These findings offer valuable insights into the mechanics of bioinspired interfaces, presenting a more efficient and nuanced approach to characterizing their fracture properties.

Development of Hot-Wire Laser Additive Manufacturing for Dissimilar Materials of Stainless Steel/Aluminum Alloys

The formation of brittle intermetallic compounds (IMCs) at the interface between dissimilar materials causes considerable problems. In this study, a multi-material additive manufacturing technique that employs a diode laser and the hot-wire method was developed for stainless steel/aluminum alloys. An Al-Mg aluminum alloy filler wire (JIS 5183-WY) was fed on an austenitic stainless-steel plate (JIS SUS304) while varying the laser power and process speed and using paste-type flux and flux-cored wire. The effects of laser power and process speed on phenomena during manufacturing and IMC formation were investigated. Finally, the wall-type multilayer specimens were fabricated under optimized conditions. The suppression of IMC formation to a thickness of less than 2 μm was achieved in the specimens, along with a high interfacial strength of over 120 MPa on average.

Numerical Simulation of the Evaporation Behavior of Fe-Mn Heterogeneous Powder in Selective Laser Melting Process.

Multi-material additive manufacturing using heterogeneous powders as raw materials is one of the important development directions of metal additive manufacturing technology. The evaporation behavior of heterogeneous powders in the selective laser melting (SLM) process has a significant influence on the accuracy of chemical composition control and the quality of the final product. In this paper, the fusion process of Fe20Mn (80 wt.% Fe and 20 wt.% Mn) heterogeneous powder, Fe and Mn elemental powders, and Fe20Mn pre-alloyed powder is numerically simulated using FLOW-3D® software and partially validated through SLM experimental results. The morphology and the characteristics of the flow field and temperature field in the melt pool for four kinds of powder materials are analyzed. The influence of the elemental evaporation behavior of different powders on the mass loss of the Mn element is discussed. The results show that the excessive accumulation of heat increases the maximum temperature of the melt pool, thus increasing mass loss. The Fe20Mn heterogeneous powder has a wider heat-affected zone and a higher peak value of temperature, nearly 400 K higher than that of the Fe20Mn pre-alloyed powders, which exhibits an intensive evaporation behavior. The mass loss of the Mn element obtained from the SLM experiment for Fe20Mn heterogeneous powders forming parts is more than the Fe20Mn pre-alloyed powders' forming parts for different laser powers, up to 17 wt.% at P = 120 W. This tendency is consistent with the numerical analysis of the effect of evaporation behavior of Fe-Mn heterogeneous powder during the SLM process. This study provides the necessary theoretical reference and process guidance for realizing the precise control of the SLM composition of a heterogeneous powder in multi-material additive manufacturing caused by evaporation behavior.

Flexural strength of the sandwich-structured parts made of polylactic-acid and thermoplastic-polyurethane fabricated by using extrusion-based multi-material additive manufacturing

Flexural strength of the sandwich-structured parts made of polylactic-acid and thermoplastic-polyurethane fabricated by using extrusion-based multi-material additive manufacturing

Factors affecting interface bonding in multi-material additive manufacturing

Factors affecting interface bonding in multi-material additive manufacturing

Design of dissimilar material joint for defect-free multi-material additive manufacturing via laser-directed energy deposition

Additive manufacturing technology has advanced beyond creating optimized features, from strengthening materials to make them lightweight to fabricating multi-material combinations that offer functionalities beyond the capabilities of individual materials. In this study, a lamination method for laser-directed energy deposition (LDED) is developed to achieve dense multi-material features, and a design that combines different and dissimilar materials is developed. To evaluate these novel developments, two materials—AISI 316L stainless steel and Inconel 625—are introduced. Tensile specimens, fabricated via multi-material additive manufacturing using LDED, are subjected to tensile tests that are recorded on video for digital image correlation. After the tests, fracture surface analyses of the fractured specimens are performed via scanning electron microscopy, and optical monitoring analyses are performed on the specimens that are not subjected to the tensile tests. The results indicate that the specimens demonstrate varied mechanical properties due to the influence of lamination direction and order, which affect the formation of critical cracks and pores.

Advancements in multi-material additive manufacturing of advanced ceramics: A review of strategies, techniques and equipment

Ceramics possess notable attributes including excellent wear resistance, exceptional high-temperature strength, superior hardness, and outstanding biocompatibility, rendering them indispensable for the fabrication of key industrial components. Additive manufacturing presents significant benefits such as precise fabrication, design flexibility, and the ability for mass customization. This technology facilitates the creation of intricate structural or functional ceramic components with complex geometries, effectively addressing issues that are inadequately managed by conventional methods, such as the inherent brittleness of ceramics and challenges associated with ceramic machining. As advancements in aerospace, special industry, and biomedical sectors progress, the performance limitations of uniform ceramic materials and structures have emerged as a bottleneck constraining the broadening of their application range. There is a pressing need to transition from single-material ceramic additive manufacturing to multi-material printing. This paper highlights and compares various notable advancements in typical single-material ceramic additive manufacturing. In addition, it delves into the present status of multi-material ceramic additive continuous forming and the development of associated equipment, focusing on different forming mechanisms. Finally, the paper concludes by identifying the primary challenges and research priorities in multi-material ceramic additive manufacturing, and suggests potential directions for future development.

The impact of interfacial characteristics on the interfacial properties of 316 L/CuSn10 multi-material manufactured by laser powder bed fusion

Multi-material additive manufacturing (MMAM) enables the simultaneous creation of multi-material components in a single process, accomplishing customized different performances in specific regions of the same components. In particular, the copper-steel multi-material structure can provide considerable strength and high thermal conductivity, thus playing a crucial role in electronic components, heat exchangers and injection molds. However, few studies have explored the relationship between the microstructure and properties of the copper-steel fusion zone. Therefore, this study aims to reveal the heterogeneous evolution of the microstructure in the copper/steel fusion zone and its impact on the interfacial properties of 316 L/CuSn10 multi-material structure fabricated by laser powder bed fusion (L-PBF). We characterized the multi-layer specimens using laser confocal microscopy and SEM to obtain the macroscopic and microscopic microstructure, liquid metal embrittlement (LME) microcrack characteristics and precipitation evolution of the copper-steel fusion zone. The generation of liquid phase separation (LPS) was explored based on block specimens, and the textural characteristics of the fusion zone were analyzed using EBSD. As a result, because of multiple element precipitation and the high thermal conductivity of copper alloy, abrupt grain size changes occur in the fusion zone, affecting the fusion zone's corrosion resistance and nano-hardness. In tensile tests analyzing the anisotropy, the results show that LME microcracks have little impact on the interfacial bonding properties of the copper-steel bimetallic structure, among which the ultimate tensile strength of the specimens formed at 30° to the substrate reached a maximum of 562.9 MPa. These findings add substantially to our understanding of the relationship between the microstructure and properties of copper-steel bimetallic interface, and provide a theoretical reference for additive manufacturing copper-steel multi-material components.

Microscopic evaluation of polymer–polymer interfaces in multi-material additive manufacturing

Microscopic evaluation of polymer–polymer interfaces in multi-material additive manufacturing

Effect of Core Material Thickness on the Shore Hardness of the Sandwich-Structured Multi-Material 3D-Printed Parts

Fused Filament Fabrication (FFF) continues to experience improvements in terms of its flexibility and functionality, therefore it attracts public attention to use this technology. Multi-Material Additive Manufacturing (MMAM) is an approach in the FFF technology that allows the manufacturing of 3D-printed products composed of two or more materials in a single printing process. MMAM enables the user to apply various configurations to obtain a 3D-printed material with adjustable properties. This study aims to determine the effect of core material on the Shore hardness of the FFF printed parts with the MMAM approach. There were two types of materials combined with the MMAM approach in this work, namely polylactic-acid (PLA) and thermoplastic elastomer (TPE). The Shore hardness test was conducted according to the ASTM D2240-15 standard. The results showed that the thickness of the core material inserted into the printed material had a significant effect on the hardness value of printed multi-material parts. In addition, the hardness value was highly dependent on the modulus of elasticity of the material. Therefore, the hardness value changed following the proportion of the printed material.

Path planning of complicated hierarchical thin-wall structures using multi-material additive manufacturing technology

Multilayer thin-wall structures have demonstrated significant application potential in wearable devices, pressure vessels, and aerospace industries, with additive manufacturing (AM) poised to further unlock their capabilities. Although path planning, a crucial aspect of AM, has been extensively studied for homogeneous structures, research on path planning for heterogeneous structures remains limited. This study introduces a novel path planning algorithm, termed CPCNHTS, for generating continuous paths in complex non-rotating bodies with hierarchical thin-walled structures. CPCNHTS encompasses adaptive slicing, path offset, and robotic postprocessing techniques. The adaptive slicing method is employed to enhance the slicing model’s accuracy through volume error control. Moreover, the path offset method is designed to derive the printing path using a parallel curve of the inner contour. Identification of the inner contour is based on the curvatures and areas of single and double contours, respectively. The robotic postprocessing method is employed to convert the printing path into executable codes for multimaterial additive equipment. As a compelling application of the CPCNHTS algorithm, a limb prosthetic socket was successfully fabricated, highlighting the remarkable potential of this approach within the wearable devices domain.

Investigating enhanced interfacial adhesion in multi-material filament 3D printing: a comparative study of t and Mickey Mouse geometries

AbstractIn this study, a novel design to enhance interfacial adhesion in multi-material components produced through filament 3D printing techniques is presented. Multi-material additive manufacturing often faces challenges related to poor chemical affinity between polymers and physical discontinuities between component sub-parts. To address these issues, an interface geometry that leverages both diffusion and mechanical adhesion mechanisms to facilitate interlocking is proposed. The performance of the widely used T-shaped geometry, as per existing literature, with a newly introduced Mickey Mouse lobate modified shape is compared. Additionally, the linear butt interface, which relies solely on chemical diffusion is investigated. For the study, Polylactic Acid and Polyethylene Terephthalate as the material pairs was selected. The findings underscore the significant impact of interface geometry on the mechanical properties of multi-material components. Using the ultimate tensile strength of the standard ISO 527-2 specimen as a reference, a butt interface results in a residual strength of 60% for homogeneous materials, but only 10% for heterogeneous materials. The adverse impact of the heterogeneous materials configuration was alleviated by the interfaces, leading to an enhancement of 7% and 58% for the Mickey Mouse and T geometries, respectively. While the Mickey Mouse geometry effectively reduces stress concentrations, it falls short of achieving the desired improvement in multi-material adhesion between parts. This outcome suggests the necessity of further research, particularly towards optimizing the proposed geometry for enhanced performance.

Research Trends in the Directed Energy Deposition Method of Heterogeneous Materials

Metal Additive Manufacturing (AM) or 3D printing garners attention for economically producing components with superior strength, durability, and corrosion resistance. The microstructure, influenced by factors like heat input, scanning speed, and layer thickness, shapes metal materials intricately in 3D printing.Unlike traditional manufacturing with separate fabrication and post-processing, Multi Materials AM (MM-AM) streamlines the construction of composite structures in a single step using a single machine. Although initial MM-AM, especially inpolymer 3D printing, was simpler, the shift to metal-based MM-AM presents challenges. The distinctive bonding style in MM-AM facilitates robust connections between different metals, minimizing stress concentration and simplifying the joining of diverse metals. Challenges like intermetallic compound formation, residual stress, and material-specific issues leading to cracks persist. Ongoing research focuses on metallurgy, process optimization,and computational simulation to overcome these hurdles. This review delves into current research trends in multi-material AM, identifying pathways for technological advancements. It discusses the application of Directed Energy Deposition (DED)in stacking austenitic and ferritic metals for nuclear power plant cooling system piping's gradient-form safe-ends. The study emphasizes advanced manufacturing techniques for developing functionally graded materials and dissimilar metal joints, highlighting the transformative potential of additive manufacturing across industries.

Investigation of the bonding behavior between thermosets and thermoplastic elastomers in multi-material additive manufacturing

Multi-material additive manufacturing (AM) pushes the boundaries of modern processing by creating parts with synergetic material-related effects and superior properties. A promising technology is represented by the so-called fusion jetting (FJ) process which simultaneously combines thermosets and thermoplastics into multi-material AM parts. However, the bonding behavior between thermoset-reinforced and non-reinforced regions proved to be a challenge within FJ processing which is investigated in the context of this study. Based on shear testing, significant impact factors and improving process strategies regarding interlaminar bonding are highlighted. A viable shear specimen design is derived for material combinations with strong dissimilarity of the individual material elasticities. For this investigation, acrylate-based photopolymers are combined with thermoplastic polyurethanes (TPU). Based on the shear testing results, a minimized layer height of 100 μm is identified to achieve maximum mechanical bonding. Further, increased laser powers between 15 and 17 W positively impact the bonding strength between photopolymer-reinforced and non-reinforced regions due to the increase of the volumetric energy density and promotion of interlocking effects with embedded TPU particles. Additionally, an increase in bonding strength is achieved through specific tailoring of the laser power within selected layers. The results showed that decreased laser powers promote interlocking effects by infiltration of the photopolymer in already melted subjacent regions. All in all, this investigation not only contributes to the advancement of FJ processing but successfully sketches a transferable strategy for the characterization and improvement of interlaminar bonding in various AM technologies targeting hard/soft structures.

Interlaminar Adhesion Study of Fused Filament Fabrication (FFF)-Printed Soft and Rigid Bilayer Structure with Composites

Multi-material Additive manufacturing (AM) has opened new opportunities for the creation of multifunctional structures that enables value-added structural product designs. Among the multi-material AM techniques, multi-nozzle fused filament fabrication which is a type of material extrusion technique is found to be the more popular choice for multi-material polymer fabrication. One major challenge of multi-material additive manufacturing of polymers is the poor mechanical strength at the interface of the dissimilar materials such as polylactic acid (PLA) and thermoplastic polyurethane (TPU) due to the lack of chemical affinity. Therefore, understanding the mechanical strength at the interface of these dissimilar materials becomes an important topic as it allows product designers to do necessary tweak to the design to compensate for the weaker link in the structural design. In this work, we investigated the tensile strength and the shear strength of different combinations of PLA and TPU and their respective nanocomposites, as well as the fatigue analysis of the bi-layer structures made of these dissimilar materials in a 3-point bending test configuration. Generally, when functional fillers or particles are added to the polymer in composites, they tend to adversely affect the interlaminar adhesion property and fatigue life of the soft-rigid bilayer structure. It was found, that the interlaminar tensile strength and the interlaminar shear strength can reduce as high as 44% and 78%, respectively, compared to the baseline samples with no fillers.

Multi-material additive manufacturing via fused deposition modeling 3D printing: A systematic review on the material feeding mechanism

The rapid advancements in fused deposition modeling (FDM) 3D printing methods have unlocked new opportunities in multi-material additive manufacturing (AM). This technique offers a viable solution for creating high-performance, multi-functional graded materials, parts, and tooling. Despite the extensive efforts invested in exploring the potential of the FDM-type multi-material additive approach, there is a noticeable lack of discussion specifically centered around the material feeding mechanism of this extrusion-based 3D printing method. This work provides a systematic review on the current studies related to the multi-material FDM 3D printing. It is found that the interlayer adhesion quality of different feedstock materials is a first and foremost feature in determining the strength of the entire print. To this end, we particularly focus on analyzing the feeding system of multiple materials and the strategy for material alternation. From our analytical evaluations, it is noticed that the single-nozzle/multi-feed and multi-nozzle/multi-feed FDM printers present unique pros. and cons., respectively. Inspired by multi-material applications of direct ink writing extrusion-based 3D printing, we also suggest to choose a suitable method based on the material rheology and thermal properties of the constituent materials. This can be a chance to gain further benefits from the multi-material AM.

Development of fiber-reinforced polylactic acid filaments using untreated/silane-treated trichosanthes cucumerina fibers for additive manufacturing

Multi-material additive manufacturing is gaining importance due to the enhancement of properties by utilizing different materials in a single additive process, especially in 3D printing. The prime motive is the need for eco-friendly materials, with the waste-to-wealth concept being the current global trend. Trichosanthes Cucumerina stem fiber, which is obtained from the discarded stem of Trichosanthes Cucumerina plant, is used in this work; the treatment of the Trichosanthes Cucumerina fibers was done using silane. Six filaments were developed with varying untreated/silane-treated Trichosanthes Cucumerina contents (3, 6, and 9%) compared with pure PLA filaments for 3D printing. Developed filaments were assessed for ultimate tensile strength, diameter variation, differential scanning calorimetry, water absorption, morphological and surface roughness. The test results elucidated that the 6% silane-treated Trichosanthes Cucumerina fiber-reinforced/PLA filament had the highest tensile strength of 63.5 MPa with better fiber distribution. The 3% silane-treated Trichosanthes Cucumerina fiber-reinforced/PLA filament had the least diameter deviation of 0.0015 mm. Based on the test data, the 6% silane-treated Trichosanthes Cucumerina fiber-reinforced/PLA filament can be utilized to prepare biodegradable components.

Wideband Broadside-Coupled Line Baluns Enabled by Multimaterial Additive Manufacturing

Wideband Broadside-Coupled Line Baluns Enabled by Multimaterial Additive Manufacturing