Multi-material Additive Manufacturing Process Research Articles

Iterative printing of bulk metal and polymer for additive manufacturing of multi-layer electronic circuits

In pursuing advancing additive manufacturing (AM) techniques for 3D objects, this study combines AM techniques for bulk metal and polymer on a single platform for one-stop printing of multilayer 3D electronic circuits with two novel aspects. The first innovation involves the embedded integration of electronic circuits by printing low-resistance electrical traces from bulk metal into polymer channels. Cross-section grinding results reveal (92 ± 5)% occupancy of electrically conductive traces in polymer channels despite the different thermal properties of the two materials. The second aspect encompasses the possibility of printing vertical bulk metal vias up to 10 mm in height with the potential for expansion, interconnecting electrically conductive traces embedded in different layers of the 3D object. The work provides comprehensive 3D printing design guidelines for successfully integrating fully embedded electrically conductive traces and the interconnecting vertical bulk metal vias. A smooth and continuous workflow is also introduced, enabling a single-run print of functional multilayer embedded 3D electronics. The design rules and the workflow facilitate the iterative printing of two distinct materials, each defined by unique printing temperatures and techniques. Observations indicate that conductive traces using molten metal microdroplets show a 12-fold reduction in resistance compared to nanoparticle ink-based methods, meaning this technique greatly complements multi-material additive manufacturing (MM-AM). The work presents insights into the behavior of molten metal microdroplets on a polymer substrate when printed through the MM-AM process. It explores their characteristics in two scenarios: When they are deposited side-by-side to form conductive traces and when they are deposited out-of-plane to create vertical bulk metal vias. The innovative application of MM-AM to produce multilayer embedded 3D electronics with bulk metal and polymer demonstrates significant potential for realizing the fabrication of free-form 3D electronics.

Factors affecting interface bonding in multi-material additive manufacturing

Additive manufacturing or 3D printing is the process of depositing material layer-by-layer to create 3-dimensional products. When creating 3D-printed products from two or more materials, multi-material additive manufacturing processes are used which eliminate the need for assembly operations. Fused filament fabrication multi-material additive manufacturing permits the production of a single printed item employing multiple materials in fused filament fabrication. This work studied the factors affecting fused filament fabrication multi-material additive manufacturing, by reviewing existing works, designing part(s), conducting design of experiments, and carrying out parts’ performance test. An E3D multi-material filament 3D printer was utilised throughout this study. The chosen polymer combination was polycarbonate (PC) and poly(methyl methacrylate) (PMMA), whilst the design and testing of the multi-material parts was limited to lap-shear testing. Results showed that the interface bonding of the PMMA/PC (PMMA printed first and followed by PC) specimens was stronger than the one of the PC/PMMA specimens. Furthermore, to investigate the effect of the contact or overlapping area on the interface bonding strength, PMMA/PC specimens with varying dimensions were designed, printed, and tested. When the contact area was reduced, a strong interface bonding between the PMMA and PC layers was still maintained.

Three-dimension dithering and its effect on the interfacial strength of multi-material and emulated multi-material additive manufacturing processes

Multi-Material Additive Manufacturing (MMAM) offers the potential for superior functional parts by varying properties throughout a structure. Previous work has shown that the interface region of such MMAM parts has great importance on their overall strength. Most of these studies have focused on rigid–compliant interfaces within parts manufactured via material jetting (MJT). This work focuses, initially, on the creation of different interfacial geometries within functionally graded tensile bars by extending two dimensional dithering algorithms from the realm of image processing into the third dimension. It tests these dithered patterns, along with Schwarz P and Gyroid structures, across rigid–complaint MJT interfaces before further exploring the previously unaddressed question of how these different geometries affect interfacial strength across rigid–rigid interfaces for both UV cured materials, via MJT, and thermoplastic materials, via a new prototype electophotographic toner-based AM system. Within the MJT parts, the samples often failed inside the large regions of the more compliant material rather than at the interface itself. In addition, the interfacial length is shown to have more effect on the mechanical properties compared to interface pattern. However, the thermoplastic samples consistently failed within the interface region. The toughness of these thermoplastic parts increased with an increase in the connected surface area in the tensile direction between the largest regions of each of the two materials, with three dimensional random dithering over a 20 mm gradient length exhibiting the toughest interface overall (40.8% increase in the work at break when compared to a control sample with no special interfacial geometry). This work, therefore, provides a new emphasis to explore, within the context of the design of thermoplastic multi-material interfaces, geometries that increase this connected surface area.

Vision-Based Quality Assurance of Composites Printed by Extrusion-Based 3D-Printers

Additive manufacturing (AM) has been emerging as a promising production approach due to its expanded design freedoms and cost-effective batch size. Yet, its commercial acceptance is hindered by technical challenges in terms of quality assurance and defects of printed parts. Conventionally, this results in failed parts, waste of time, labor, and material. Though there have been successful attempts for process monitoring and quality assurance for single-material additive manufacturing processes, limited work has been reported for multi-material printing applications. This paper proposes a vision-based method for characterizing the material deposition accuracy of multi-material printing. More specifically, layer-wise images of a printed part are acquired, segmented, and compared with its equivalent digital reference, and position accuracy is measured by pixel differences, which provides a feasible solution for evaluating the overall performance of the multi-material AM process. An exploratory image acquiring setup using an offline camera is presented to experimentally validate the feasibility of the proposed workflow. The study concludes that detecting material deposition errors for two contrasting materials offers promising feasibility by using image processing methods and using the histogram of the image can quantify the degree of inaccuracy. This research provides a preliminary base for further research in the direction of integrating image acquisition systems with the printer, automating the image processing stage and extending the image histogram reading techniques for higher precision.

Tunable soft–stiff hybridized fiber-reinforced thermoplastic composites using controllable multimaterial additive manufacturing technology

As a revolutionary manufacturing technology, material extrusion exhibits great potential for fabricating thermoplastic composites. However, the application of controllable multiple-thermoplastic materials for producing a tunable soft–stiff hybridized fiber-reinforced thermoplastic composite (CCFRTP-TSSH) based on material extrusion has yet to be extensively studied. Thus, this study proposes a controllable multimaterial additive manufacturing process for integrating continuous carbon fibers (CCF) as reinforcement for the thermoplastic structures. Structural reinforcement and tunable soft–stiff hybridization were achieved by adopting thermoplastic polyurethane (TPU) and polylactic acid (PLA) as the soft and stiff materials, respectively. Additionally, the mechanical properties of the CCFRTP-TSSH specimens were systematically investigated and discussed based on various process parameters, such as nozzle temperature, layer thickness, and supporting resin volume ratio (SRVR). The experimental results revealed that the layer thickness had a significant influence on the tensile properties, followed by the SRVR and nozzle temperature, wherein the highest tensile strength obtained was 90.89 MPa. Moreover, the bending strength depends on both the layer thickness and loading direction, with the largest bending strength of 65.96 MPa. Furthermore, the influence of SRVR on various fusion interfaces, e.g., PLA/ TPU, PLA/CCF, and PLA/PLA, was analyzed using scanning electron microscopy, including the influence of process parameters on the wall thickness of the stiff and soft resins, to realize an enhanced tunable soft–stiff hybridization. Ultimately, several distinct components, including a thin-walled hollow cylinder, round table, and a socket for a limb prosthetic, were fabricated to demonstrate the feasibility and accuracy of the proposed method. Therefore, this study presents a novel approach for the integrated manufacturing of soft–stiff hybridized composites, particularly in the field of wearable devices.

The Examination of Restrained Joints Created in the Process of Multi-Material FFF Additive Manufacturing Technology.

The paper is focused on the examination of the internal quality of joints created in a multi-material additive manufacturing process. The main part of the work focuses on experimental production and non-destructive testing of restrained joints of modified PLA (polylactic acid) and ABS (Acrylonitrile butadiene styrene) three-dimensional (3D)-printed on RepRap 3D device that works on the “open source” principle. The article presents the outcomes of a non-destructive materials test in the form of the data from the Laser Amplified Ultrasonography, microscopic observations of the joints area and tensile tests of the specially designed samples. The samples with designed joints were additively manufactured of two materials: Specially blended PLA (Market name—PLA Tough) and conventionally made ABS. The tests are mainly focused on the determination of the quality of material connection in the joints area. Based on the results obtained, the samples made of two materials were compared in the end to establish which produced material joint is stronger and have a lower amount of defects.

Inline additively manufactured functionally graded multi-materials: microstructural and mechanical characterization of 316L parts with H13 layers

In the current work, a functionally graded multi-material consisting of stainless steel 316L and hot work tool steel H13 has been fabricated by additive manufacturing (AM). Due to the modification of the recoating apparatus, a lean, multi-material AM process can be achieved via inline selective laser melting. The generated functionally graded specimens are characterized by an equiaxed grain growth at the interfaces of the steel layers, which results in excellent bonding of both constituents. Concerning the mechanical properties, tensile tests confirm that failure occurs within the material layer exhibiting the lower tensile strength. Further, this work analyzes microstructural developments in the melt pools which can predominately be described by the Marangoni effect.

Assessment of Embedded Conjugated Polymer Sensor Arrays for Potential Load Transmission Measurement in Orthopaedic Implants.

Load transfer through orthopaedic joint implants is poorly understood. The longer-term outcomes of these implants are just starting to be studied, making it imperative to monitor contact loads across the entire joint implant interface to elucidate the force transmission and distribution mechanisms exhibited by these implants in service. This study proposes and demonstrates the design, implementation, and characterization of a 3D-printed smart polymer sensor array using conductive polyaniline (PANI) structures embedded within a polymeric parent phase. The piezoresistive characteristics of PANI were investigated to characterize the sensing behaviour inherent to these embedded pressure sensor arrays, including the experimental determination of the stable response of PANI to continuous loading, stability throughout the course of loading and unloading cycles, and finally sensor repeatability and linearity in response to incremental loading cycles. This specially developed multi-material additive manufacturing process for PANI is shown be an attractive approach for the fabrication of implant components having embedded smart-polymer sensors, which could ultimately be employed for the measurement and analysis of joint loads in orthopaedic implants for in vitro testing.

Design framework for multifunctional additive manufacturing: Coupled optimization strategy for structures with embedded functional systems

The driver for this research is the development of multi-material additive manufacturing processes that provide the potential for multi-functional parts to be manufactured in a single operation. In order to exploit the potential benefits of this emergent technology, new design, analysis and optimization methods are needed. This paper presents a method that enables in the optimization of a multifunctional part by coupling both the system and structural design aspects. This is achieved by incorporating the effects of a system, comprised of a number of connected functional components, on the structural response of a part within a structural topology optimization procedure. The potential of the proposed method is demonstrated by performing a coupled optimization on a cantilever plate with integrated components and circuitry. The results demonstrate that the method is capable of designing an optimized multifunctional part in which both the structural and system requirements are considered.

Development of a multi-material additive manufacturing process for electronic devices

In order to increase the versatility of additive manufacturing multimaterial processes, a hybrid system has been developed, which is capable of combining 3D printing technology by DLP (Digital Light Processing) with a two-dimensional Drop-on-Demand Inkjet printing system.Through DLP technology based on digital micromirror devices (DMDs) it is possible to build up 3D geometries layer-by-layer using polymerization of photosensitive resins. Concurrently, while the construction process is performed, the InkJet printing system is used to deposit tiny drops of conductive inks on the substrate generated, which will thus constitute an electric circuit embedded within the three dimensional structure.On the other hand, photosensitive resins have been filled with Low Temperature Co-firing Ceramic (LTCC) particles, in order to modify the basis properties of the part by using sinterizable slurries. Finally the challenges in the sintering process for achieving functional parts are discussed and a few prototypes have been built in order to validate this technology.

Potential for Multi-functional Additive Manufacturing Using Pulsed Photonic Sintering

This paper proposes the integration of pulsed photonic sintering into multi-material additive manufacturing processes in order to produce multifunctional components that would be nearly impossible to produce any other way. Pulsed photonic curing uses high power Xenon flash lamps to thermally fuse printed nanomaterials such as conductive metal inks. To determine the feasibility of the proposed integration, three different polymer additive manufacturing materials were exposed to typical flash curing conditions using a Novacentrix Pulseforge 3300 system. FTIR analysis revealed virtually no change in the polymer substrates, thus indicating that the curing energy did not damage the polymer. Next, copper traces were printed on the same substrate, dried, and photonically cured to establish the feasibility of thermally fusing copper metal on the polymer additive manufacturing substrates. Although drying defects were observed, electrical resistivity values ranging from 0.081 to 0.103Ω/sq. indicated that high temperature and easily oxidized metals can be successfully printed and cured on several commonly used polymer additive manufacturing materials. These results indicate that pulsed photonic curing holds tremendous promise as an enabling technology for next generation multi- material additive manufacturing processes.

3D soft lithography: A fabrication process for thermocurable polymers

In this work, a novel fabrication process for thermocurable polymers that allows the fabrication of three-dimensional internal and external features is introduced. It is hard for other manufacturing processes to build thermocurable polymer parts with complex internal features. The proposed method allows the polymer to be cured at a given temperature rather than needing to continuously cure the polymer, which allows greater control over its properties. This process uses multimaterial additive manufacturing processes to build a 3D mold with support and uses solvents to remove the support as well as to dissolve the mold after curing of the polymer. This process was implemented using a commercial FDM machine to fabricate three PDMS parts that would be difficult or impossible to manufacture with other manufacturing processes. Results validate the feasibility of the proposed process and show that the resolution of the part corresponds to that of the machine used to fabricate the mold.