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The commercial or industrial applications of 3D printing or additive manufacturing are continuously increasing in diverse areas mainly in rapid prototyping. 3D printing has become part of a novel industrial growth area where simplification of assembly, waste minimization, and mass customization are important, such as aerospace, orthopedic and medical research, defense, and jewelry. There has been continuous growth or improvement in additive manufacturing, which includes the type of materials used, metamaterials, and advancements in the printers or the software. 3D printing has explored the areas where materials have been manufactured which are several times lightweight, high strength compared to traditional parts, and also resulted in a reduction in CO2 emissions. Biodegradability and sustainability are the major concern for any industry. The price of conventional thermoplastic filaments is one of the main sources of revenue and profitability for the industry. In addition to its relatively high price, some of the concerns in its wide use are the moisture resistance and VOC emissions, including iso-butanol and methyl-methacrylate (MMA) during 3D printing. These emissions cause voids in the structure which compromises the mechanical strength of the 3D-printed objects. Additives have been added with thermoplastics, such as diatoms and biodegradable materials, such as ceramics, biomaterials, graphene, carbon fibers, binders for metals, sand, and plaster to reduce the cost and VOC emissions. The cost of these additives is relatively less than the thermoplastic filaments. There has been tremendous innovative growth in the field of additive manufacturing, including solutions such as 3D-printed houses and titanium drones. The addition of additives opens the new potential applications in new arising technology, especially in robotics like behavior, mechanisms respond to user demands which are known as 4D printing where new dimension has been added to 3D printing. It is a process where a 3D-printed object transforms itself into another structure over the influence of external energy input, such as temperature, light, or other environmental stimuli. 4D printing is simply referred to as 3D printing transforming over time. 4D printing is an all-new emerging area in the field of additive manufacturing which has diverse applications in biomedical, defense, robotics, etc.
North Carolina State University, Raleigh, North Carolina, USA
Hakovirta Marko*
North Carolina State University, Raleigh, North Carolina, USA
*Address all correspondence to: mjhakovi@ncsu.edu
1. Introduction
The process of joining materials layer upon layer from 3D digital model data or Computer-Aided Design (CAD) model is known as additive manufacturing (AM) or 3D printing as per International Organization for Standardization (ISO)/American Society for Testing and Materials (ASTM) 52900:2015 standard [1]. 3D printing has a long history of development for using it in the rapid prototyping of products for manufacturing since the 1980s. This development has since then led to also accessibility to the public. These developments started when Chuck Hull of 3D System Corp. filed their patent for a stereolithographic process eventually evolving into a 3D-printing technology boom [2]. Today 3D printer is priced as low as $100 [3] and is therefore accessible to the general public. Recent advances in 3D printing include, for example, the manufacturing of biomaterials for biomedical applications, such as tissue engineering. With recent advancements in the 3D printers, the industrial printers can build as small layers as 16 μm and thus creating a major milestone for biomedical applications [4]. 3D-printing technology can be used in various forms of materials printing, including fused deposition modeling (FDM), stereolithography (SLA), selective laser melting (SLM), and electron beam melting (EBM). The most used techniques are stereolithography and fused deposition modeling [5].
The International Organization for Standardization (ISO)/American Society for Testing and Materials (ASTM) 52900:2015 has classified the additive manufacturing (AM) process into seven categories (Figure 1) [5, 6].
Figure 1.
Additive manufacturing processes.
There are several benefits to using 3D printing, such as [5, 7]:
Design to component translation.
Greater customization.
Manufacturing of complex, flexible, or lightweight components with no additional cost.
Potential of zero-waste manufacturing.
On-demand manufacturing.
Excellent scalability.
Although the 3D-printing industry is rapidly growing, there have been several economic, social, and environmental challenges that need to be addressed, such as recycling of materials, energy usage, organic compounds emission, high cost of raw materials, and standards and certifications [6]. The lack of printing material [8] and the high cost of thermoplastic polymers add to the barrier to the industrialization of 3D-printing technologies [9]. The market growth potential is considerable for 3D-printing as it is estimated that the filament market will be worth $ 6.6 billion by 2026 [10]. One concern for the advancement of 3D printing other than the high cost of raw material is the emission of volatile organic compounds (VOC), including iso-butanol and methyl-methacrylate [11]. To address the abovementioned economic and environmental concerns, there has been a new advancement in the additive manufacturing process which includes the addition of additives can such as diatoms [10] and biodegradable materials, such as ceramics, biomaterials, graphene, carbon fibers, binders for metals, sand, and plaster [12]. The cost of these additives is relatively much less than the thermoplastic filaments. In addition, there are added benefits including included in the addition of additives, such as improved moisture resistance that may slow down the process of decomposition of the filament material and may potentially open up other innovative functional possibilities, such as immobilization of chemical sensors and bacteria and virus-killing agents for novel biomedical applications.
In general, the structures fabricated with 3D printing either using single or multiple materials are intrinsically static, hence 3D printing cannot meet the demands where dynamic materials applications are needed including, for example, hygromorph biocomposites [13], adaptive wind turbines [14], active biocomposites [15], and self-folding microgrippers [16]. This addition of a new dimension to 3D printing has started a new era of printing known as 4D printing and includes novel materials compositions, additives, and chemical functionalization.
There are several challenges associated with manufacturing or scaling up of 3D printing mentioned as follows [17]:
Personal customization vs mass manufacturing: Currently AM technology is suitable for customized products, and low-volume production whereas for high-volume production, still injection molding is being industrially used because of the high-cycle time of additive manufacturing. However, there are industrial sections where high-cycle time is balanced by high demand for customized and complex geometry products, reduction in material waste, and opportunity to merge parts, such as GE fuels nozzle and customized earphones by Ownphones.
Material heterogeneity and structural consistency: For most of the industrial additive manufacturing processes, single materials are used which do not show any heterogeneousness and structural discrepancy at the interface but with the more advancement in the 3D printing, multiple materials are being used to accomplish more complex geometry of the products. Different materials have different behaviors, properties, and functionalities which leads to anisotropic mechanical properties of 3D-printed products due to the interlayer bonding deficiencies which eventually limits the variety of materials used for additive manufacturing. More research needs to be done for analyzing the uncertain behavior of multiple materials and CAD or computer software needs to be redesigned for the adoption of multiple materials in additive manufacturing.
Building scalability vs layer resolution: The two parameters scale of building parts and layer resolution are inversely proportional to each other in 3D printing which means that with the increase in the size or layer thickness of 3D-printed parts, the layer resolution decreases which results in the deprived surface quality because of layer stair-stepping effect. Typically layer resolution of 0.1 mm and layer thickness of 25 mm is used for commercial implications of 3D printing. There has been recent advancement with inkjet printing where the researchers have managed to get the layer thickness as low as 0.012 mm but at the cost of high-building time [18]. However, researchers have managed to produce products from nanoscale to macro to large scale using hybrid AM processes, coating, and post-processing subtractive machining.
Intellectual Property and AM standardization: To ensure the consistency of additive manufactured product, there is a certain need for the standardization of AM process, material, machine, and file format. ASTM has started to approve AM material standardization for several processes but there is a long way ahead for AM machine manufacturers and researchers. The open access to the downloadable file has opened a new challenge to protect the intellectual property right of researchers and commercial machine manufacturers. There is a need for planned and diverse patent filing for additive manufacturing processes which should include material, process, CAD design, machining, and post-processing modifications.
Earlier 3D printing or additive manufacturing was normally used for rapid prototyping only but in the current scenario, 3D printing has already established a large pool of diverse applications, for example, in manufacturing, sociocultural, food, and biomedical sectors. There is a wide range of applications from nano to macro to large scale for 3D printing (Figure 2).
There are several types of advancements are done recently to increase the efficiency of the additive manufacturing process, such as materials advancement, process advancement, and post-processing advancement.
4.1 Material advancements
There are several challenges associated with 3D printing, such as emission of volatile organic compounds, creation of voids, and high cost of thermoplastic polymers. To avoid all these issues, recent advancements have been done which include the use of fillers, such as carbon fibers, nanofibers, graphite, and diatomaceous earth [9, 10]. Carbon nanotube/polylactic acid composites (CNT/PLA) and multi-walled carbon nanotube/polylactic acid composites (MWCNT/PLA) with strong mechanical properties are being explored in microelectronics [19]. The smaller particles sizes are used in composites to produce stiffness and high density in the printed products, such as hydroxyapatite-reinforced polyethylene/polyamide composites (HA-PE/PA) [20]. Carbon black/polyamide 12 (CA/PA12) composites were fabricated which enhance the mechanical, thermal, and electrical properties of printed products [21]. Nanomaterial composites, such as nanosilica/polyamide, nanoclay/polyamide, and graphite nanoplatelets/polyamide composites, have also been fabricated leading to improved mechanical properties [9]. These composites can be used for multiple applications, such as biomedical applications, because of the high surface area of fillers present (Figure 3) [10].
Figure 3.
3D-printed Diatoms in the PLA matrix (original work).
Metamaterials: Metamaterials are another innovation provided by 3D printing in material science. The functional metamaterials are considered a complex machines working. For instance, there is a material developed by the Lawrence Livermore National Labs where it gets shrunk when heated up rather than expanding. USC Viterbi has created a metamaterial that can manipulate sound through the magnetic field. Metamaterial has the iron particles in its lattice structure and in the presence of a magnetic field the structure gets deformed into one which blocks the sound rather than passing them through. Similarly, researchers at Boston University have developed the metamaterial by 3d printing the plastic coil used in metamaterial which has improved the MRI scan quality and speed and also blocks 94% sound [22].
Titanium Drones: Titomic has recently used their Titomic Kinetic Fusion Process to 3D print the titanium drone by mechanically fusing the titanium powder. This innovative 3D-printing method allows to use of different materials or alloys in a single prototype and eliminated the problems associated with traditional manufacturing, such as welds (Figure 4) [22].
Figure 4.
3D-printed titanium firefighting drone [23].
4.2 Pioneering bionic 3D printing
There is an innovative advancement that mimics the living organism’s organic cellular structure and bone growth. The world’s largest 3D-printed airplane cabin component with a “bionic partition” which separates the passenger cabin from the galley has been divulged by Autodesk and Airbus. This design has made the partition very light with a 45% reduction in weight compared to traditional designs but still very strong. It has been estimated that this design would save 465,000 metric tons of CO2 emissions per year. This new bionic partition used the second-generation alloy of scandium, aluminum, and magnesium named “Scalmalloy” created by the 3D-printing expertise of Airbus subsidiary “APWorks” (Figure 5) [24].
Figure 5.
Airbus 3D printed bionic partition cabin [Source: Airbus].
Similarly, Airbus has collaborated with Materialise to produce the 3D-printed bionic spacer panel using FDM and Materialise’s post-production processes which made the panel 15% light in weight compared to traditional panels (Figure 6) [25, 26].
Stratasys has been 3D printing more Airbus cabin components for years now [27]. Airbus A350 XWB was decided to be manufactured by 3D printing (Figure 7) [28].
Figure 7.
Airbus 3D metal-printed bionic titanium bracket [Source: Airbus].
4.3 Product advancement
4.3.1 3D-Printed house
Alquist 3D has printed the first-ever 3D-printed house in the US which was assembled in 22 hours. The printer head was connected to the tube through which the traditional concrete was being pumped. Alquist 3D has teamed up with the nonprofit organization known as “Habitat for Humanity” where they will be providing homes to the people in need. Alquist 3D has claimed that the 3D-printed houses are 10–15% less in cost compared to traditional house building. It has saved the manpower also as according to Alquist 3D, only 3–4 humans were required to operate the printer [29]. This was not the first time 3D-printed houses have been built. In France, 3D-printed houses were built and Europe’s first 3D-printed house was built in 22 days which was later shortened to 3 days. In Dubai, there have been 3D-printed offices have been built. According to the Dubai government, it has saved them almost 50% of the total cost [30]. Initially, 3D printing was used only for prototyping the construction but now 3D printing has been used for constructing the whole buildings.
4.3.2 Porsche’s revolutionizing product development
Porsche has used 3D-printing technology to produce 3D-printed pistons, spare parts, and sports seats. Porsche has developed the lightweight, better thermal resistance, high-performance pistons for the twin-turbo boxer engine of the 911GT2 RS model leading to a 30-horsepower gain. This process used the laser printing or laser metal fusion process in collaboration with MAHLE & TRUMPF which uses the high-precision machine, TruPrint 3000 with a 500-Watt fiber laser and high-purity metal special aluminum alloy powder which melted to print 1200 layers ending into the desired shape (Figure 8) [31, 32].
Figure 8.
Pistons of the twin-turbo boxer engine of 911GT2 RS [Source: Porsche AG].
Porsche has been manufacturing spare parts using selective laser melting since 2018 but recently, Porsche has started manufacturing personalized bodyform full-bucket sports seats for Porsche 911 and 718. Porsche has also invested in 3D-printing specialist INTAMSYS (Figure 9).
Porsche has also produced its first complete housing for its electric drive using the additive laser fusion process which has opened the possibilities for 3D printing in the highly stressed electric sports cars sector (Figure 10) [33].
Figure 10.
Prototype for small series production [Source: Porsche AG].
4.4 Post-processing advancement
Achieving Good surface quality: As it was mentioned in section 3, there is a discrepancy with the surface quality whenever multiple materials are used because of the layer stair-stepping effect, but there have been numerous advancements done in this field to achieve the good surface quality such as mask-image-projection-based stereolithography (MIP-SL) which is a hybrid AM stereolithography process. In the MIP-SL process, Digital Micromirror Device (DMD) is used instead of a laser, unlike stereolithography. DMD is an electromechanical device that can control ~1 million small mirrors simultaneously to turn on or off a pixel at over 5kHz [18] which results in the projection of masked images on a surface area. MIP-SL process is faster than the SLA process. MIP-SL was developed to spread the liquid resin on the smooth ultrathin layer surface which basically used the meniscus equilibrium method for building the smooth up-curved surfaces [18]. There have been several approaches used to achieve the good surface quality, such as blasting, sanding, chemical finishing, which has differentiation influence on the surface quality. There is another post-processing step to achieve good surface quality is the coating method on the 3D-printed parts. For instance, there is a chemical coating XTC-3D was used because it was lost cost, easy to work on any 3D-printing surfaces (FDM, SLS, SLA) which showed that coating has filled up the gap between the layers and improved the final finished surface quality of the product [34].
Protecting Intellectual Property and AM standardization: To protect the intellectual property rights of any process, material, and file information, there has been advancement where information is either encrypted or embedded into the structure domain such as infraStructs which literally means below the structures where tags including all the information are embedded inside the digitally fabricated structure which can be read only by Terahertz (TZ) imaging system. It is not visible outside the surface and can be read only by advanced imaging systems [35]. Similarly, there is an advancement where watermarks can be extracted from the 3D prints by changing the original 3D print mesh [36, 37].
4D printing or smart printing has a unique basic characteristic that differentiates it from the static 3D-printing structures; 4D-printing materials are dynamic and able to have functionality [8]. The well-used definition describing the 4D-printing states “It is the evolution of a 3D printed structure either in shape, property, and functionality when it is exposed to external factors such as light [38], heat [39], pH [40], and water [41]”. 4D printing can be defined as the best combination of a smart material, a 3D printer, and a well-programmed automated design (Figure 11) [8].
Figure 11.
3D vs 4D printing.
There are five factors that influence the 4D printing which are the additive manufacturing process, feedstock material, stimuli, interaction mechanism, and modeling [42].
According to F. Momeni and J. Ni, there are three laws that define the shape-changing behavior of 4D-printed objects [43]. The first law states that “all the shapes changing behaviors such as curling, twisting, coiling, bending, etc. of multi-material 4D structures are due to the relative expansion between active and passive materials.”
The second law states that “there are four physical factors behind the shape changing ability of all multi-material 4D structures i.e., mass diffusion, thermal expansion, molecular transformation, and organic growth.”
The third law states that the “time-dependent shape-morphing behavior of nearly all multi-material 4D printed structures is governed by two “types” of time constants” (Table 1).
Types of materials
Examples
References
Responsive toward moisture: Hydrogels
Hydrogels respond to moisture or water and can expand up to 200% of their original volume. Sustainable materials, such as cellulose, can be used as hydrogel printing ink compatible with various types of printers
Chromophore (photosensitive) materials are inserted into smart material for which light acts as an indirect stimulus because light generates the heat which eventually changes the shape of the material.
Temperature (heating or cooling) is used as an external stimulus either to change the shape of material – shape change effect (SCE) or to transform the deformed shape into the original shape – shape memory effect (SME). SMEs can be polymers, metals, ceramics, alloys, and gels. These smart materials are used in biomedical applications such as orthodontics, physiotherapy, orthopedics, surgeries, etc.
Polyelectrolytes are used as smart material which changes their shape as the pH changes with the release or gain of protons. It has found applications in biocatalysts, valves, actuators, drug delivery, etc.
Smart materials change their shape in the presence of a magnetic field. Magnetic nanoparticles are incorporated into hydrogels which respond in the presence of a magnetic field
There are revolutionary applications associated with the 4D printing, such as biomedical applications of 4D printing in drug delivery, organ regeneration and transplantation, and tissue fabrication [44]. 4D-printed structures have great potential in soft robotics because of their capability to deform, adjust to environmental changes, and flexibility [8]. 4D-printed structures with smart materials can be used as self-evolving structures [45, 46], active origami structures [47], self-sustainable satellite manufacturing parts [8], sensors responsive toward moisture, temperature, pH, magnetic energy, etc. [8]. Despite diverse applications, 4D printing needs more research and development, especially in scaling it up. Commercializing the 4D printing is troublesome because of the high production cost, installation cost and material used and availability. Multi-materials printers could be a possible solution but need furthermore research (Figure 12).
Additive manufacturing was invented in the 1940s and it has developed a lot with innovative inventions since then. The different additive manufacturing process techniques have specific peculiarities and the disadvantage of one technique can lead to the innovation of a new technique. The development of different types of printers has enabled the AM to use different types of materials which include plastics, metals, and ceramics. New improvements in AM techniques allow the high filler loading in thermoplastic composites.
3D printing has diverse applications include for instance food, fashion, biomedical, health, aerospace, and cultural heritage preservation. 3D printing helps the consumer to customize the product as per their requirements. There are a few challenges that need to be addressed, such as emission of volatile organic compounds, creation of voids, high cost of thermoplastic polymers, and weak mechanical strength, of printed structures. To overcome these challenges composites with fillers have been fabricated such as carbon nanotube/polylactic acid composites, nanosilica/polyamide composites, and carbon black/polyamide composites which have increased the mechanical, electrical, and thermal properties of the composites.
Despite highly diverse applications of 3D printing and new advancements in 3D printing, there are still a few challenges that restrict the usage of 3D printing on a commercial scale. These include the resistance and adaptability of 3D-printed material’s properties and structures against the change in environmental factors, such as temperature, electric energy, and pH.
4D printing is basically the combination of a 3D printer, smart material, and well-designed programming that allows the 3D-printed object to change its shape, properties, and functionality with time. 4D-printed objects change or modify against environmental conditions. These materials can be responsive to heat, water, pH, electric energy, and magnetic field. 4D printing has increased the number of application areas for additive manufacturing and thus expanded to include aviation, self-sustaining material, sensors, active materials, and bioprinting.
There has been a tremendous amount of technological advancement and research on 3D and 4D printing, and its applications. New advancements have been, however, the commercialization and implementation at a larger stage are still in progress and therefore more research and development are needed. Importantly more sustainable materials need to be explored due to the environmental risks associated with some of the materials and techniques used. The potential to create solutions to some of the most challenging product development needs in various industries using 3D- and 4D-printing technologies remain high. These developments are many times related to niche products that cannot be manufactured otherwise.
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Written By
Aggarwal Salonika and Hakovirta Marko
Submitted: 07 January 2022Reviewed: 29 March 2022Published: 04 May 2022
Open access peer-reviewed chapter
