Perspective Chapter: Multi-Material in 3D Printing for Engineering Applications

*Rajkumar Velu, R. Sathishkumar and A. Saiyathibrahim*

## **Abstract**

3D Printing or Additive Manufacturing is one of a novel method in manufacturing of materials with increased accuracy of manufacturing in terms of complexity in parts, design of aerospace and defense parts, light-weighting, etc., This manufacturing method involves layer-by-layer printing or deposition of materials or metals into the perfectly aligned especially in corners, edges and in most complex designs. The design process mostly involved software so that production cost could be estimated in the design stage itself. Additive Manufacturing is one of the most promising approach for small and low-volume productions. The filament used for the process is prominent to the designer, along with the various printing processes. Recent modern printing techniques involve multiple nozzles, whereas designers can use multiple materials on single printing. The use of multi-material in a single part enables the manufacturer to rapidly produce products which have specific applications. This chapter discusses about various multi-material with different mechanical properties that can be used for structural applications through different printing technologies on various precious applications. This technology is quickly adopted by even small-scale industries in recent times.

**Keywords:** multi-material, 3D Printing, filament, fusion, functionally gradient materials

## **1. Introduction**

Recent advances in 3D printing allow industrialists and researchers to create a whole new foundation for future manufacturing. This new foundation gives multi-material in 3D printing which allows various properties of materials which can be printed that can lead to excellent productivity with very good application like aerospace, bio-applications, spacecraft materials, electronic components, etc., Polymers, ceramics, metals, and biomaterials have all been utilized in several AM techniques to create multi-material structures. In which multi-material within a single component we can achieve properties like hardness, corrosion resistance, tensile and compressive properties needed areas of the product can be achieved and also eliminate the need for complex manufacturing and expensive tooling. These new processes and printing of multi-material can be incorporated in a single part, eliminating the need for multi-part modeling. Multiple material printing can provide increased characteristics, including controlled material anisotropy, that can be

#### *Advanced Additive Manufacturing*

essential for functional systems such as those needing surface alignment while still having a high load capacity. Much more progress is required in this sector due to its binding difficulties and usage of printing methods this chapter highlights us to 3D printed metal-metal, metal ceramic, polymer-based, functionally graded material usage, and its application in the structural field is thoroughly discussed.

## **2. Need for multi-material in structural applications**

In recent advancements for specific application-oriented functional needs, there is a growing need for excellent tooling techniques and manufacturing techniques utilized for specific purposes. In order to achieve the particular application, tooling and testing requires more time and multiple tooling which cannot be enabled for the various process while we select new advanced machining techniques. Thus, the new technique 3D printing has given us a wide range of selection of materials or machining techniques that can be resolved. In addition, very specific applications like spacecraft, aerospace, automobile structures, biomechanics, electronic components need a wide range of materials to be machined or incorporated into a single material which eliminates the number of components to be manufactured. Especially in biomechanical application various tissues, muscles, blood vessels, bones are incorporated into a single replacement for various operating and tearing of muscles needed by the surgeon and in electronic components, various chips and motherboards need a separate manufacturing or placing of various sensors to be placed this multi-material printing reach us to a new way of printing single incorporated boards and robotic structures are enabled. For continuous electronics manufacturing, Stereolithography and Direct Ink Write were combined, while for embedded electronics manufacture, Fused filament fabrication and Direct Ink Write were mixed. Products like embedded electronics, sensors, soft robotics, and customized pharmaceutical products might be made more readily for medical or space applications that are not possible with those other traditional production processes. That is why there is a growing need for multi-material 3D printing.

## **3. Selection of multi-material for 3D printing applications**

In the near future, the potential of multi-material 3D printing will be a revolutionary moment in rapid production, customized design, and structural applications. Multi-material 3D printing is compatible with functionally graded materials which has a single structural form, also it has the potential to be used in structural applications to benefit from hybridized/combined material characteristics. Multimaterial printing creates quick and durable structures that incorporate the features and functions of all of the hybrid materials which are shown in **Figure 1** [1].

Multi-material 3D printing can be used to build innovative smart 4D structures with specified contour/attributes/operations. Established AM processes, such as FDM, can be enhanced to Hybrid Deposition Manufacturing (HDM) with integrated components to manufacture more sophisticated, interconnected multi-material components than previous approaches [2]. It has been observed that build configuration, manufacturing parameters, and related factors can have a significant impact on the relationship between multilateral interfaces all through 3D printing, thus they should have been adjusted to provide superior thermal, mechanical and surface characteristics [3]. The selection of materials for end-use for performing multi-material 3D printing operation is based on the availability of materials and its machinability, material properties, technique used for printing, processing time and rate of material *Perspective Chapter: Multi-Material in 3D Printing for Engineering Applications DOI: http://dx.doi.org/10.5772/intechopen.102564*

**Figure 1.**

*Overview of some manufacturing and enhancement possibilities for multi-material additive manufacturing.*

loss, reengineering and reparability of material, environmental conditions and cost, and the applicational areas such as biomechanics, bioengineering, robotic and space.

#### **3.1 Based on availability of materials and machinability**

Availability of the materials for the wide range of applications are the potential thing while selecting a multi material. These are the materials that are easily available and used for general applications that can be printed even on all types of printers like PET – polyethylene terephthalate, PA – polyamide TPU –thermoplastic polyurethane, PC – polycarbonate, HIPS – high impact polystyrene among many others. Investigations on the multi-material parts/components manufactured by 3D printing has been increased significantly in the recent past. Using this multi-material 3D printing, it is possible to generate good quality components through tailoring different layers of different materials up to the desired thickness. This uniqueness made this process stand out when comparing conventional manufacturing methods. Hence, materials used in multi-material 3D printing has to be decided in the design stage itself mainly based on the desired applications. A variety of polymers, ceramics, metals, and biomaterials are available to design and fabricate multi-material components through 3D printing. Some of the investigations conducted are presented here for a better understanding of the availability of materials for multi-material 3D printing [4–6].

Polymer composites filled with carbon or glass fibers wood particles (PLA matrix) sandstone (co-polyester matrix), magnetic (PLA matrix with iron particles), electric conductive (PLA matrix with carbon-based fillers); Photopolymer on the basis of flexible, rigid, and support material widely available one that can be easily machinable in Inkjet printers and Fused Deposition Modeling techniques used for hinge application.

3D printing of silicone elastomers combined with nanosilica (NS) is one type of next-generation advanced structure possessing improved performance and low cost

#### *Advanced Additive Manufacturing*

to fabrication. Such multi-material components are made using Direct Ink Writing (DIW) process and are finding their applications in medical devices, flexible electronics, and soft robotics. Silicones are low viscosity materials which are requiring a long curing time during 3D printing processes but their attractive elasticity makes them suitable in the abovementioned areas. To overcome these printability issues, nanosilica is incorporated nowadays with elastomers as a rheology modifier and this addition does not reduce any elasticity of elastomers. The Food and Drug Administration (FDA) is classified this NS is a biocompatible material and hence it is successfully used to manufacture parts for human implants nowadays [7].

Polyethylene glycol (PEG) is an attractive hydrogel with good compatibility to chemical modifications and is used mainly in tissue engineering scaffolds [8]. PEGX – Gelatin multi-material components synthesized by bioink methods are possessing self-supporting layer-by-layer printing quality with robustness (**Figure 2**). PEG can be used with biopolymers to manufacture 3D printed layouts with tailored properties. Also, it is possible to create PEG-polymer and PEG- PEG crosslinked multi-material structures using bioink methods [9].

Recent advancements in human implants especially bone replacement focused on developing a new multi-material which has good compressive strength. Propylene fumarate dimethacrylate (PFDMA) is a macromer that has low viscosity and possesses the required qualities to form High Internal Phase Emulsions (HIPE). This PFDMA polyHIPE has good properties such as biodegradable and cytocompatibility. Lack of compressive properties have been addressed frequently while printing 3D structures during bioink printing processes. To overcome this limitation, a thermoplastic polyester shell is nowadays incorporated to form an outer layer surrounding the trabecular bone scaffold. **Figure 3** shows the PFDMA polyHIPE – polyester shell (PCL) layer by layer printing multi-material 3D printed scaffold for use in human implants [10].

Surprisingly, conductive thermoplastic elastomer filaments have also been developed for multi-material Fused Deposition Modelling (FDM) to produce complicated structures by using more than one polymeric filament. Lately, multi-material 3D functional prototypes were produced with recycled thermoplastics such as High Impact Polystyrene (HIPS), Acrylonitrile Butadiene Styrene (ABS), and Polylactic Acid (PLA) using FDM. HIPS has high impact resistance and good machinability and hence can be useful for structural parts. A very important property of PLA is its excellent biodegradability which promotes them to biomedical applications. As a familiar thermoplastic, ABS contains good thermal and heat resistance hence can be suitable for civil structures. Combining all these properties in different ratios, it is possible to form 3D multi-material structures in FDM. Multi-material layered

#### **Figure 2.**

*3D bioprinting PEGX-Gelatin (a) extrusion through 200 μm tip, (b) four printed layers, 15 × 15 mm and (c) 20 layers porous hexagon shape ≈5 mm thick [9].*

*Perspective Chapter: Multi-Material in 3D Printing for Engineering Applications DOI: http://dx.doi.org/10.5772/intechopen.102564*

**Figure 3.**

*3D printing process of (a) thermoplastic polyester outer shells and HIPE emulsion ink inner material, and (b) integration between the emulsion ink and thermoplastic (PCL) shell.*

ABS/PLA/HIPS flexible functional prototypes synthesized using FDM are shown in **Figure 4** which are finding their desired interests in soft electronics and robotics [1] .

It may be noted that multi-material 3D printing of multiple thermoplastic polymers is possible for operational devices and can enhance their mechanical characteristics. In the recent past, many investigations are going on the development of more unique combinations of materials for structural entities in 3D printing processes.

#### **3.2 Based on material properties**

Mechanical performance of multi-material additively produced components is often superior to that of single-material printing. The development of voids across succeeding layers of printed components might impact their mechanical characteristics due to a reduction in interfacial adhesion within printed layers. Another typical issue of multi-material AM is the difference in mechanical behavior between horizontal tension or compression and vertical tension or compression. Robust 3D printing methods, such as micro-additive stacking, are required to ensure layer consistency and enhance surface quality to the specifications required for their respective purposes.

**Figure 4.** *Multi-material layered ABS/PLA/HIPS flexible functional prototypes.*

3D printed polyamide-based composites filled and laminated with continuous and short carbon fibers have very good synergistic reinforcement on the mechanical properties. Thermal, morphological, and mechanical tests for the printing drives were performed initially in order to determine the characteristics of the printing elements that provide good continuous carbon fiber strength. Carbon Fiber bundles soaked with polycarbonate solution have been created during the embedding procedure. Inseminated carbon bundles were inserted in 3D printed Polycarbonate to boost mechanical strength that may be utilized in building health monitoring constituents with markedly better material characteristics. ABS – acrylonitrile butadiene styrene, PLA polylactic acid, and PVA – Polyvinyl alcohol, each one with different purposes and performance characteristics, excellent mechanical properties, less smell while printing, used for varying support structures, and can be easily removed without damaging the structure [11].

Furthermore, by leveraging AM's design flexibility, the computational optimization-based design technique may be extended to multiple design scales for diverse characteristic composites, potentially improving the functionality of developed composite materials structures.

Novel multi-material bilayer absorbing composites comprised of graphene, Li0.35Zn0.3Fe2.35O4, polymethyl methacrylate (GFP) as the corresponding layer and graphene, carbonyl iron powder, polymethyl methacrylate (GIP) as the absorption layer (**Figures 5** and **6**) were created using multi-material digital light processing (DLP) 3D printing method, wherein graphene has been used as a conductive, highly resistant, transparent material and hardness [12].

The successive coating of all-inorganic viscoelastic TE inks comprising Bi*x*Sb2-*x*Te3 particles and customized utilizing <sup>2</sup><sup>−</sup> *Sb Te* 2 <sup>4</sup> chalcogenidometallate binders resulted in the multi-material 3D printing of composition-segmented BiSbTe materials.

By modifying the composition of Bi*x*Sb2-*x*Te3 particles, the peak ZTs of the 3D-printed substances were controlled to switch from ambient temperature to 250° C. Fabricated ideally constructed Thermo Electric Generators (TEG) comprised of the 3D-printed, composition-segmented tri-block Bi0.55Sb1.45Te3/Bi0.5Sb1.5Te3/ Bi0.35Sb1.65Te3 TE leg, as shown in **Figure 7**, which then expands the peak ZTs and fulfills complete compliance throughout the whole temperature scale, achieving record-high efficiency in multi-material 3D printing of composition-segmented BiSbTe materials by sequential deposition of all-inorganic viscoelastic TE inks comprising Bi*x*Sb2-*x*Te3 particles customized with <sup>2</sup><sup>−</sup> *Sb Te* 2 <sup>4</sup> chalcogenidometallate binders. By modifying the composition of Bi*x*Sb2-*x*Te3 particles, the apex *ZT*s of the 3D-printed materials were controlled to switch from ambient temperature to 250° C.

#### **Figure 5.**

*A framework of process structure properties performance in polymeric composites via AM.*

*Perspective Chapter: Multi-Material in 3D Printing for Engineering Applications DOI: http://dx.doi.org/10.5772/intechopen.102564*

#### **Figure 6.**

*(a) Schematic diagram of the design principle of the bilayer absorber; (b) schematic diagram of the DLP 3D printing process of the GFP þ GIP bilayer absorber and a photograph of the GFP þ GIP bilayer absorber. (A color version of this figure can be viewed online.) [12].*

#### **Figure 7.**

*Scheme of a sequential 3D printing of multi-segmented TE materials. Green (Top), orange (Middle), and blue (Bottom) colored patterns correspond to each block in the compositionally segmented TE legs by multimaterial 3D printing using TE inks containing Bi0.55Sb1.45Te3, Bi0.5Sb1.5Te3, and Bi0.35Sb1.65Te3 particles, respectively.*

The optimized TEG with the 3D-printed, composition segment enhances the apex *ZT*<sup>s</sup> and fulfills complete compatibility over the whole temperature spectrum, attaining a record-high efficiency for electrical and conductive multi-material systems.

Functional gradient digital composites may also be created and manufactured using 3D printing multi-material, which can increase the effectiveness of the manufactured structural design [13], for instance, have envisioned a digital laminate composite optimization method. The suggested digital design flow can keep updating both the macroscale shape of the constructed laminate configuration and the alignment of short reinforced fibers within the topography at the same time. Aside from short-fiber reinforced composites, AM can also be used to digitally design and construct functional gradient continuous fiber-reinforced laminates. Numerous design strategies have been introduced to regulate the alignment and volume fraction of AM manufactured continuous fiber composites. Their findings demonstrate that the optimal functional gradient laminate outperforms standard CFRP laminates with homogeneous orientation angles and fiber densities in terms of stiffness and strength [14].

## **3.3 Based on various techniques of printing**

In the initial stages printing of material is limited to the extrusion properties and growing printing techniques thus it has been extended to multi-material with very good machinability structures. PVA – polyvinyl alcohol, ABS – acrylonitrile butadiene styrene, and PLA – polylactic acid was the primary alternatives in the early phases, each having its own set of applications and functional properties. Whilst ABS is recognized for its mechanical qualities, PLA is noted for its printing ease and lack of a strong plastic odor or fumes. PVA, on the other hand, has mostly been utilized to print support structures when the item includes suspending portions. Powder fusion, extrusion, and liquid polymerization all rely on powder, liquid-solid transitions, or solid-liquid-solid transitions [15].

Various methods can be utilized in each sector. Powder fusion is used in processes such as selective laser melting (SLM), selective laser sintering (SLS), and electron beam melting (EBM). Material extrusion is the basis for fused deposition modeling (FDM) (fusion then solidification of the material). **Figures 8** and **9** depict the different 3D printing processes that are now available. Finally, stereolithography is based on a liquid's polymerization (liquid-solid transition).

## *3.3.1 Vat Photopolymerization*

The three primary vat polymerization techniques are digital light synthesis (DLS), digital light processing (DLP), and stereolithography (SL). Although the vat photopolymerization method does not always enable multi-material applications, due to its numerous benefits such as surface quality, dimension precision, and the ability to print on a wide range of materials, vat photopolymerization has indeed been modified to enable multi-material printing [16].

**Figure 8.**

*Multi-material 3D printing of structural from various powerful engineering techniques.*

*Perspective Chapter: Multi-Material in 3D Printing for Engineering Applications DOI: http://dx.doi.org/10.5772/intechopen.102564*

**Figure 9.**

*The illusion of various additive manufacturing techniques.*

## *3.3.2 Stereolithography*

In a vat photopolymerization, SL employs a photopolymer liquid as the source material. By lowering the construction platform into the vat and curing it with a UV laser, liquid plastic is converted layer by layer into a 3D item [13, 17, 18]. Advantage of this stereolithography can build large parts with very good accuracy and surface finish but Works with photopolymers which are not stable over time and do not have well defined mechanical properties which has casting patterns,

**Figure 10.** *Differences of DLP and SLA schematic.*

Prototypes, jewelry, and medical applications. **Figure 10** depicts the stereolithography process with DLP.

## *3.3.3 Digital light processing (DLP)*

DLP technology is very similar to SL but uses a different light source and makes use of a liquid crystal display panel. In this two or more digital micromirroring devices are used for delivering multi ink materials for multi-material applications, thus **Figure 11** depicts the Digital Light Processing technique [20, 21]. A tiny microfluidic chip had also been employed for multiple material supply and interchange, allowing for direct printing of multicellular cell-laden microstructures. Both blue light (470 nm) and green light (530 nm) are used for radical curing, but only blue light is used for cationic curing. Printing of multi-material 3D structures with specified and spatially defined mechanical and chemical characteristics may be efficiently accomplished by selectively projecting pictures with two wavelengths of light [19]. This has the benefit of higher print performance relative to SLA, outstanding laying precision, low-cost printing but the insecurity of the consumable material, high cost of materials with applications in prototypes, casting, patterns, jewelry, dentistry, and medical area.

## *3.3.4 Extrusion*

It may be divided into two major subgroups based on the temperature necessary or appropriate for extrusion: fused filament fabrication (FFF) or fused deposition modeling (FDM) for extrusion of melted thermoplastic polymers and direct ink writing (DIW) for extrusion without melting.

## *3.3.5 Fused Filament Fabrication*

A nozzle is used to extrude a plastic filament that has been melted. Layer-bylayer, objects are constructed and it can construct completely functioning components out of common polymers [16, 22–24], however anisotropy in the z-direction (vertical direction) and a step-structure on the surface are characteristics of printed components, as seen in **Figure 12**. The applications that can be printed

**Figure 11.** *Illustrations of the positions of the glass plate used in each step of multi-material fabrication [19].* *Perspective Chapter: Multi-Material in 3D Printing for Engineering Applications DOI: http://dx.doi.org/10.5772/intechopen.102564*

**Figure 12.** *Fused Filament Fabrication schematic.*

include prototypes, support components (jigs, fixtures), and small series items. Furthermore, multi-material printing capabilities for FDM is required to build sacrificial support structures for printing components with overhang characteristics. Multi-material FDM, like multi-material DIW technology, is accomplished by utilizing several extrusion heads with independently controllable nozzle temperature, printing speed, and resolution. This bi-extruder features an intermixing with thick blades that create passive mixing of two melted filaments. The mixing also allowed for the printing of functionally graded materials as well as the improvement of interfacial bonding strength between two distinct materials by increasing the mechanical interlocking of the materials at the interface. Printing with a carbon nanotube (CNT)-coated filament and microwave heating after printing has been demonstrated to improve interfacial bonding, but they have not been used to connect diverse materials. BS + carbon fiber, ABS + Fe/Cu, PCL + TCP, PLA + carbon fiber are some of the multi-material that can be printed using FFF or Fusion Deposition Modeling.

### *3.3.6 Direct ink writing (DIW)*

Material in the form of a semi-liquid or paste can be extruded via a nozzle and utilized to print the cross-sections of a sliced 3D model in this method. The material mixer also enables the printing of a mixture of different materials, as seen in **Figure 13**. Furthermore, by precisely controlling material flow via specific pressure lines, a mixing ratio may be adjusted to the required concentration, enabling 3D printing of functionally graded materials with customized properties (e.g., mechanical, chemical). This has the benefit of highest resolution for an extrusion system Ideal for research settings and medical (bone) applications, but with limited part geometry, the system is expensive. Small build volume applications include solid monolithic components, scaffolds, physiologically compatible tissue implants, customized composite materials and ceramics [20, 25–27].

## *3.3.7 Binder jetting*

Inkjet printing heads spray a liquid-like bonding agent onto the powder's surface. The item is built up layer by layer by connecting the particles together, as seen in **Figure 14**. Binder jetting is best suited for big printing and the production of low-cost metal components. Binder jetting takes place at ambient temperature,

**Figure 13.**

*(a) The scheme shows a multi-phase additive manufacturing system that combines DIW components (1) with FDM modules (2) heated platform (3) and with gear-boxes (b) Schematic showing the processes involved in a dynamic photomask-assisted DIW multi-material system. The DIW-printed structure is placed under the dynamic photomask which consists of a projector with a set of light patterns [25].*

**Figure 14.** *Schematic of Binder Jet Printing.*

which avoids warping and curling issues. Powder size, layer thickness during binding, part orientation in bed, heater power, roller speed, curing temperature, curing duration, sintering time, sintering temperature, and sintering environment are examples of these. To investigate the impact of each of these factors and their interactions, a massive experimental design with hundreds of samples and testing would be required [28–30]. BJ enjoys the benefits of A relatively quick and inexpensive technique, with a wide range of material types and the ability to produce full-color parts, however parts produced straight from the machine have restricted mechanical characteristics and applications such as prototypes, casting patterns, molds, and cores.

### *3.3.8 Material jetting—Multijet modeling (MJ)*

Inkjet printing head jets molten wax onto a printing bed. Once the material is cooled and solidified, it allows to fabricate layers on top of each other shown in **Figure 15**. This method has the benefit of obtaining very high precision and surface qualities, but it only works with wax-like materials for prototypes, casting, and patterns.

*Perspective Chapter: Multi-Material in 3D Printing for Engineering Applications DOI: http://dx.doi.org/10.5772/intechopen.102564*

**Figure 15.** *Schematic of Material jetting.*

## *3.3.9 Polyjet modeling*

Unlike multijet, the printing head jets liquid photopolymers onto a printing bed. The material is quickly cured and cemented by UV light, allowing layers to be built on top of one other. Different materials may be jetted together to create multimaterial and multi-color things, but it works with UV-active photopolymers, that are not long-lasting.

## *3.3.10 Powder bed fusion*

Powder bed fusion (PBF) [31–33] is an AM technique that operates on the same fundamental concept as milling in that components are produced by adding material rather than removing it through traditional forming processes. The PBF method starts with the development of a 3D CAD model that is numerically sliced into many distinct layers. Because the heat source is generally an energy beam, a heat source scan path is generated for each layer, which specifies both the boundary contour and some sort of fill sequence, commonly a raster pattern. The benefits of power bed fusion include reduced material waste and expense (superior buy-to-fly ratio), Improved manufacturing development timelines, fast prototyping and low-volume production Capable of producing functionally graded components, Parts that are fully customized on a batch-by-batch basis, removing set designs, when compared to other additive manufacturing methods, it has a high resolution. The unmelted powder may be recycled effectively.

## *3.3.11 Laser sintering (LS)*

SLS and LS have certain commonalities. A laser is used to selectively melt a tiny layer of plastic powder. The components are built up layer by layer in the powder bed. This may make parts in standard plastics with good mechanical characteristics, a continuously expanding list of materials available, but products do not have the same qualities as their injection-molded counterparts possessing application of prototypes, support parts, small series parts.

## *3.3.12 Selective laser sintering (SLS)*

Selective laser sintering (SLS) is an additive manufacturing (AM) technique that utilizes a laser as the power source to sinter powdered material (typically nylon or polyamide), intending the laser automatically at points in space described by a 3D

#### *Advanced Additive Manufacturing*

model, binding the material together so that creates the solid structure as seen in **Figure 16**. It is comparable to selective laser melting; the two are instantiations of the same principle but differ in technical specifics [34–46]. SLS is a newer technology that has mostly been utilized for fast prototyping and low-volume manufacturing of component parts. As the commercialization of additive manufacturing technology progresses, the number of production positions grows. Polymers such as polyamides (PA), polystyrenes (PS), thermoplastic elastomers (TPE), and polyaryletherketones (PAEK). Polyamides have been the most widely utilized SLS materials because of their excellent sintering tendency as a semi-crystalline thermoplastic, leading to components with desired mechanical characteristics. Polycarbonate (PC) is a material of great interest for SLS owing to its excellent toughness, thermal stability, and flame resistance; nevertheless, such amorphous polymers are difficult to produce.

## *3.3.13 Electron beam melting*

The EBM method makes use of a high-power electron beam to produce the energy required for high melting capacity and productivity. The hot process produces components with minimal residual stress, while the vacuum guarantees a clean and regulated atmosphere. By scanning the concentrated electron beam to selectively melt certain powder regions, the EBM system constructs structures from the bottom up. It takes data from a 3D CAD model and applies successive layers of powdered material. The technique is repeated until the final layer of the component is constructed. It takes place in a vacuum, making it an excellent method for fabricating structures made of reactive materials which cannot be released into the atmosphere.

In material extrusion systems, dual or multi-extruder printing heads are commonly utilized to print multi-material components at the same time. It is standard practice, for instance, to utilize one extruder to print dissolvable endorses that may be readily detached from the main printed structure, or to print in two colors or two materials that will be included in the finished print. Conversely, dual and multi-extrusion printers generally have a few constraints: the existence of an extra extruder (second or more) reduces the printing area that would have been accessible with a single extruder; the possibilities of oozing and stringing increase. A dual-extruder had been utilized to print components out of PLA, ABS, and high

**Figure 16.** *Schematic of Selective Laser Sintering.*

impact polystyrene and the findings demonstrate that mechanically interlocked extrudates significantly minimize adhesion failures inside as well as between filaments, as seen in **Table 1**.

## **3.4 Based on less processing time and material losses**

The 3D printing technology was used to create a huge nozzle 40 inches in diameter and 38 inches tall, with integrated cooling channels for space applications. This nozzle had been created in approximately 30 days, as opposed to nearly a year using standard welding processes. The next image, **Figure 17**, clearly indicates the reduced processing time of additive manufacturing has indeed been given with less machinability.

When compared to other 3D printing technologies, digital light processing (DLP)-based 3D printing is a low-cost, high-speed, and high-resolution 3D printing technology that is derived on a localized photopolymerization process stimulated by the projection of digitally masked UV patterns on to the liquid surface, allowing us to achieve near-zero material loss. Because the printing process begins in a


#### **Table 1.** *Summary of each printing method.*

#### **Figure 17.**

*Process comparison of conventional manufacturing processes versus AM for creating multi-layered structures.*

liquid environment, this approach avoids the need for any support elements in the production of porous or hollow structures, pneumatically actuated soft robots, and other structures and devices having trusses or cavities. Projection microstereolithography, which generated micron-scale printing resolution, continuous liquid interface production, which enabled 100 times faster printing, and large area projection microstereolithography, which manufactured 3D features with feature sizes ranging from nanometers to centimeters, are among the remarkable innovations in this technology. In an effort to minimize fabrication time, topdown exposing DLP with several resin containers were used, however, the use of cleaning solutions to eliminate uncured resin proved detrimental to features finer than 300 m. It also was discovered that regulating the liquid levels in the numerous containers was challenging, and the process was still rather sluggish in the manufacture of complicated multi-material components.

## **3.5 Based on biomechanics and bioengineering products**

Alginate-gelatin, collagen, chitosan, cellulose, titanium alloys, synthetic polymers (e.g., polycaprolactone [PCL], ABS, PLA, PA, polydimethylsiloxane [PDMS], polyether ether ketone [PEEK]) are the most commonly utilized alloys in 3D printing techniques. Composite materials can be readily photographed and are less corrosive than metal alloys. The use of laser cladding in additive manufacturing to combine Ti and Mo (15%) powder. The microstructure and hardness for changing Mo content were studied by constructing compositionally graded structures, and it has been found that the greatest hardness of 450 HV [47–49].

The HA/Ti6Al4V (Hydroxyapatite/Titanium alloy) composite powder, as well as bind, has high biocompatibility, allowing it to merge with bone and enhance osteointegration and bonding strength throughout time just after the initial stage of implantation [50–56]. To make the braided carbon/PEEK composite compressive bone plates, a micro-braiding manufacturing process was used to achieve high and uniform implantation of the matrix into reinforcing fibers. Three different braiding angles were used to examine the four-point bending characteristics of composite bone plates [57–61]. Despite the fact that the bending characteristics of braided carbon/PEEK composites indicated good potential for bone plate usage. For the

*Perspective Chapter: Multi-Material in 3D Printing for Engineering Applications DOI: http://dx.doi.org/10.5772/intechopen.102564*

treatment of fractured bones, a composite braided cast with a Kevlar/Cold cure composite had also proven to be both practical and promising (**Figure 18**).

Braided casts have indeed been studied as a possible alternative for compression bone plates. ABS plastic, which has great impact resistance and hardness, has been selected for the polygonal tablet of nacre-like composite, whereas softer plastic Poly Lactic Acid (PLA) and Thermoplastic Polyurethane (TPU) rubber-like materials are chosen for the adhesive and cohesive layer.

Defense graded Aluminum (AA5083-H116) platelets are glued together via thin vinylester adhesive layers. Cohesive and sticky layers assist to attenuate and absorb the energy given by the shock wave, reducing plastic degradation to the composite tablets. Bioactive composites composed of 85% poly(-caprolactone) (PCL) and 15% nanometric hydroxyapatite (HA) derived from biogenic sources have been 3D printed using an extrusion-based technique to create porous scaffolds appropriate for bone regeneration.

**Figure 18.** *Procedural steps for Biological 3D Printing from STL files.*

PCL/bio-HA scaffolds have better mechanical characteristics and bioactivity. Biocompatible composites of 80 wt% polyvinyl alcohol (PVA)-(20 wt%) polyvinylpyrrolidone (PVP) blend with various concentrations of bioactive nanohydroxyapatite, Ca10(PO4)6(HO)2 (HAP) [80PVA-20PVP-xHAP] offered to continue to support cues for the increase in cell viability and biocompatibility with antibacterial.

PA12/ceramic (PA12/ZrO2/HAP) composites have been discovered to function well with the FDM method, allowing the fabrication of medical implants with satisfactory mechanical capabilities for non-load bearing purposes [62]. The hybrid bio-ceramic filled PA12 composite feedstock filament for craniofacial reconstruction via FDM framework, in which the fixed 15 % loading of zirconia (ZrO2) and also various weight fractions (30, 35, 40 wt%, etc.) of beta-tricalcium phosphate (β-TCP) have always been compounded with PA12 to custom tailor the printability of the PA12 composites.

A multi-material 3D printer is used to create an in vitro drug-testing device for heart tissue. Six distinct materials were utilized to create this complicated gadget, each with its own function: (1) dilate dextran as a release layer for the cantilever, (2) dilute thermoplastic polyurethane (TPU) as the cantilever, (3) carbon black and TPU mixture as a strain gauge wire, (4) shear-thinning soft PDMS (polydimethylsiloxane) as a feature to guide tissue orientation, (5) shear-thinning mixture of gold and polyamide as electrical contact pads, (6) shear-thinning PDMS and insulation. This work exemplifies how 3D printing various materials can provide multifunctional devices that can inspire the construction of complex tissues that will improve the area of tissue engineering.

PDMS (Polydimethylsiloxane) lines with 4 wt% CF reinforced PDMS composite provide high biocompatibility strength [63]. Furthermore, due to the remarkable strength and biological properties of PEEK and its CHAp composite, 3D-printed PEEK offers numerous biomedical uses, and its biological macromolecular behavior leads to health sustainability. Organic solvents and extremely high temperatures are not always used in multi-material bioprinting.

#### **3.6 Based on robotic and space applications**

Rapid manufacturing of soft robotic systems, such as combustion-powered jumpers, multilegged robots, and stiffness-tunable actuators, is a significant benefit of 3D printing for robotics. Recently, shape-memory alloy and motor tendons actuated 3D printed soft crawling robots have also been created and demonstrated a substantial advantage in the easy and rapid manufacturing that significantly requires multi-material application. In which sensors, tubes, pipelines, metals, caps, motility models, and so on are combined into a single multi-material part, where 3D printing offers significant advantages.

Fabrication of a low-profile antenna for spatial applications with an integrating artificial magnetic conducting (AMC) ground plane. This system has two deposition heads, with one print head dispensed Polycarbonate (PC) that used a filament extrusion technique to print all dielectric components while the second head dispensed silver conducting parts using a micro-dispensing technology. A silver palladium paste (ESL 9694-SA) has been used as a conductive material in soft robotics wearables because it displays good adhesion, great solderability, and high conductivity. There is a necessity for viscosity reduction so that multi-material resin or ink-like structure 20% ethanol has been added as a solvent, and mixing well for 20 minutes in printing provides flexible and stretchable enough even for wearables.

To create an innovative caterpillar-inspired pneumatically-driven soft crawling robot that can then be directly 3D printed without the need for a complex assembly process. This allows us to lessen the number of parts from a pneumatic bellow-type

## *Perspective Chapter: Multi-Material in 3D Printing for Engineering Applications DOI: http://dx.doi.org/10.5772/intechopen.102564*

body, 12 anisotropic frictional feet, as well as two end caps into a single part while also putting additional feature synergy locomotion. Translucent photopolymer (Agilus 30 Clr) is utilized as the principal material, and to increase the viscosity of the substance, low-yield polymer Journal Pre-proof 7 (SUP706B) is employed as that of the backup material with good mobility.

**Figure 19** illustrates the functionally gradient material which can be utilized for smooth hand grippers, roller wheels, and chairs that are used for robotic applications. To construct multi-material components and FGMs with complete 3D flexibility, we require voxel-level spatial control over component placement. Several existing AM methods on the market seem to be capable of this level of compositional control, although they are largely targeted toward prototype or one-off component production.

Rapid Analysis and Manufacturing Propulsion Technology (RAMPT) will assist in the development of methods to 3D print metal rocket engine components utilizing blasted powder-directed energy deposition. The upgraded system provides academics, researchers, and manufacturers, ranging from machine and metal injection molding (MIM) shops to high-volume manufacturers. Binder jetting uses a digital file to inkjet a binder into a bed of powder particles, resulting in a variety of binding solid parts being created one layer at a time. When printing metals, the finished item must be sintered to fuse the particles all together in a solid object with varying material properties.

## **3.7 Based on recycling and remanufacturing**

Very few studies on the recycling and remanufacturing of multi-material have been undertaken. Fiber-reinforced thermoplastic composites are a popular multi-material that may be recycled and remanufactured completely. A closedloop material recycling scheme for carbon fiber and matrix had been employed

#### **Figure 19.**

*(A) Polymer-polymer FGMs could simplify the construction of flexible joints connecting rigid elements for soft robotics, combine supple viscoelastic materials with stiff engineering polymers for applications like airless tires, and bring furniture design using multi-material.*

for continuous FRTPs, long FRTPs, short FRTPs, and ultimately powder reinforced plastics has been presented and experimentally shown in **Figures 20** and **21**. A notion of direct structural recycling of thermoplastic composites was also proposed, in which big composite goods may be broken into small-size structural parts that can be directly utilized to make smaller composite products. The recycling of FRTP is well illustrated in the figure below. Nonetheless, completely recovering continuous fiber and matrix remains a problem for the development and use of fiber-reinforced thermoplastic composites. Development of novel and improved recyclable composite materials, as well as manufacturing processes, is required for future development in order to fulfill end-use characteristics and recyclability at the same time. Due to the ordered distribution of continuous carbon fiber tows, 3D printing of continuous carbon fiber reinforced thermoplastic composites (CFRTPCs) provides both high mechanical performance and the potential of entirely recycling and even remanufacturing. Given that the recycled carbon fiber filaments already included a few thermoplastics, the filament feed rate was decreased significantly from 100 mm/min to 80 mm/min to maintain a fiber composition comparable to the initially printed samples. Several measures were used to test the performance of 3D printed CFR PLA composites. The universal testing equipment was used to evaluate flexural and interlaminar shear strength. Furthermore, after the carbon fiber had been recycled into an impregnated filament and used again in the remanufacturing process, there has been no discernible improvement in tensile strength and modulus, most likely due to the unidirectional nature of the produced composites, wherein the tensile force was sustained primarily by the carbon fiber rather than interfaces. The modulus of

#### **Figure 20.**

*Scheme of recycling and remanufacturing of 3D printed CFRTPCs (a), and key elements for each step: (b) hot air gun system, (c) remolding nozzle, (d) recycled impregnated filament, and (e) remanufacturing process.*

*Perspective Chapter: Multi-Material in 3D Printing for Engineering Applications DOI: http://dx.doi.org/10.5772/intechopen.102564*

**Figure 21.**

*Impact strength of pure PLA, originally printed and re-manufactured composites specimens, inserted pictures are standard specimens (a), broken specimen from the original printing.*

remanufactured composite specimens was somewhat reduced. This opens up the prospect of creating a "green" composite for the future via 3D printing without the need for carbon fibers. Aside from mechanical performance, economic and environmental concerns might be addressed. Moreover, whenever high-performance natural fibers like flax are utilized in the 3D printing process, true green composites will be generated in the future. This unique idea addresses all elements of minimizing the environmental effect of composites, including lowering the cost of the expensive raw material-carbon fiber, employing renewable resources, fully recycling composites to a higher level, and remanufacturing with greater performance [19].

#### **3.8 Significance of multi-material over other the recently available material**

Multi-material printing is becoming more popular in the medical field for a variety of applications. Wearables with multi-material capabilities are being developed to detect cancer at an early stage. It will be useful in identifying malignancies that are typically not discovered at an early stage, such as mesothelioma. This cancer is caused mostly by asbestos inhalation, and the early symptoms are mild enough to have been disregarded. Early diagnosis of cancer using multi-material enabled wearables combined with Artificial Information that can help patients live longer lives. Their lower life span, which might offer some risks, can be readily addressed by multi-material devices such as sensors and transmitters integrated with multimaterial medical implants. Numerous design ideas of multi-material printing may be answered in the software itself through decreasing according to the demands of the patients particular and applications. Furthermore, this application has the benefit of creating two or more material advantages in a single part above typical high strength or accessible materials. This technique lowers the pain associated with any existing traditional methods or materials.

## **4. Conclusion and future research**

Multi-material Additive Manufacturing provides a variety of material properties in a single component while also allowing us to tool several components into a single component. Multi-functional 3D components have the potential to revolutionize several industries, including biomedical engineering, soft robotics, electronics, spatial, and aerospace applications. Despite significant advances in MMAM over the last few years, there are many other outstanding problems to be encountered, such as low production throughput, poor scalability and surface finish, limited material selection, high cross-contamination, and low interfacial bonding among different materials. In addition to this as well, a fundamental scientific knowledge of materials science, particularly MMAM, FGM, kinetics, and mechanics, is required to promote and improve MMAM research. As the processing complexities of MMAM rise rapidly because of the diversity of materials involved, the creation of new manufacturing products and new advancements in advanced manufacturing must be addressed. Advances in MMAM and its numerous new searches in the advanced study will lead us to varied combinations of new materials over existing material models. We can affect the manufacturing sector with new breakthroughs in the developing 3D printing technology by gaining a better knowledge of diverse material understanding and binding forces, as well as conquering rigorous printing time reduction with very excellent processing time.

## **Author details**

Rajkumar Velu1 \*, R. Sathishkumar2 and A. Saiyathibrahim3

1 Additive Manufacturing Research Laboratory, Indian Institute of Technology Jammu, Jammu and Kashmir, India

2 C.A.R.E Engineering College, Tiruchirappalli, India

3 Karpagam Institute of Technology, Coimbatore, India

\*Address all correspondence to: rajkumar7.v@gmail.com; rajkumar.v@iitjammu.ac.in

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Perspective Chapter: Multi-Material in 3D Printing for Engineering Applications DOI: http://dx.doi.org/10.5772/intechopen.102564*

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## **Chapter 7**
