the raw material into finished products. Manufacturing processes are classified as the additive process, subtractive process, formative process, and joining process (Bandyopadhyay and Heer 2018). As the name implies additive process involves the formation of an object by the addition of the material in a layered manner one above the other. On the other hand, the removal of the material by sculpturing an object out of the solid raw material is referred to as a subtractive process. In the formative process, the finished products are formed out of molten raw material as in the case of casting and forging. The latter is the joining process that combines the pieces of raw material either temporarily or permanently through fastening or welding. All the above processes other than additive manufacturing (AM) are grouped as traditional processing methods that involve a top‐down approach (Tofail et al. 2018). In contrast, AM represents a bottom‐up approach and is termed as a rapid prototyping (RP) layer‐based technique that involves the direct fabrication of physical objects from raw material (Figure 1.1) (Hon 2007). The International Organization for Standardization (ISO)/ American Society for Testing and Materials (ASTM) defined AM as the process of creating a 3D object out of a computer‐designed 3D model through deposition and fusion of material in a layerbylayer manner (Jiang et al. 2019). Several other terms that were used synonymously in place of RP and AM are free‐form fabrication, ingress manufacturing, layered manufacturing, and digital manufacturing. 3D printing is one such technique of AM that allows for layer‐by‐layer construction of 3D objects with minimal processing and less wastage of raw materials (McClements 2017).
Figure 1.1 Schematic representation of subtractive and additive manufacturing.
The ISO/(ASTM) 52900:2015 standard had classified AM processes into seven different categories based on its working mechanism as material extrusion (ME), binder jetting (BJ), material jetting (MJ), powder bed fusion (PBF), sheet lamination (SL), directed energy deposition (DED), and vat photopolymerization (VP) (Tofail et al. 2018). Among these 3D printing techniques, extrusion‐based 3D printing is the most commonly used technique because of its simplicity and low cost (Jiang et al. 2019). Before food printing, 3D printing technology has widely applied for printing polymers (plastics, resins, and photopolymers), ceramics, metals, biomaterials, etc., with the assistance of external (thermal or mechanical) energy. The feed supply of these materials can be either in liquid or solid material in the form of powders/sheets/filaments. The process involves the deposition of feed materials in their fluidic state and gets fused and bonded together through appropriate chemical interactions. Raw materials such as polymers can be easily melted and bonded together due to their low melting point and glass transition temperatures while metals and ceramics require higher temperatures that employ an external heat source either laser or electron beams for post‐deposition (Ligon et al. 2017). Each of the AM technologies has its advantages and limitations and the specific printing technique can be selected based on its applicability and end‐use requirements. With the present scenario, 3D printing is expected to reach a peak of inflation in the coming years and is predicted to receive the main focus during 2019 and 2024 (Jayaprakash et al. 2019). This chapter covers the digital advancements of printing technology and printers, potential advantage, and applications of 3D food printing over the traditional food processing techniques.
1.2 Digital Manufacturing: From Rapid Prototyping to Rapid Manufacturing
Digital manufacturing involves the direct fabrication of objects without setting pre‐tools or workpiece requirements. Although the terms RP and AM are used synonymously, there was a distinct difference among them. RP refers to the process associated with the development of a prototype model, i.e. here the model processing is restricted till the pre‐production step that could not be used as functional working objects. Thus, the progressive transformation of RP leads to the AM processes that involve the actual production of functional workpieces from prototype models. Thus, AM allows RP to evolve into rapid manufacturing (RM) with more flexibility, work freedom, and exploitation of applications in developing a layered physical object. 3D printing was found to have vast potential applications of prototyping in several industrial sectors such as pharmaceuticals, automotive, space engineering, civil constructions, art, aviation, archaeology, cosmetics, and fashion industries (Rahman et al. 2018). Nevertheless, the most attractive application of 3D printing in food manufacturing is designing foods in a customized manner that leads to the development of the food fabrication process commonly referred to as food 3D printing. 3D printing of foods has a quite huge market potential as it aids in the mass customization, personalized diets, and sustainability practices than the traditional food manufacturing technologies (Derossi et al. 2019). Thus, 3D printing of foods referred to as food layer manufacturing (FLM) involves the sequential process of fabricating three‐dimensional edible constructs in a layer‐by‐layer manner with the capability of binding the adjacent layers through phase transitions or by chemical reactions (Nachal et al. 2019). A typical 3D printing process follows a series of well‐defined steps (Figure 1.2). First, it starts with scanning of real‐time objects or the creation of a 3D model using computer‐aided design (CAD) software. The shape and surface characteristics are stored in a unique STL file format that is native to 3D printing technology. Later the digital representation of the stored 3D object is transformed to the sliced information using a slicing software that translates the 3D model into computer‐generated codes (G and M codes). Based on which the movement arms and motors of 3D printers are controlled (Bechtold 2016). Thus, the whole printing process is controlled digitally using computers with minimal human interactions.
Figure 1.2 Workflow of 3D printing process.
1.3 Milestones in 3D Printing Technology
Although 3D printing received a wide attention in recent years, the technology dated back to several decades. Printing technology that uses two laser beams to fabricate the 3D objects was patented by Wyn Swainson of Denmark in the 1970s (Bechtold 2016). Later in the 1980s, another patent on 3D printing was filed by Dr. Hideo Kodama of Japan. However, this patent got rejected as the deadline for filing was passed out. After that, the next patent was awarded to Charles Chuck Hull in 1986 for his efforts in developing a stereolithography (SLA) apparatus (Beltagui et al. 2020). Hull co‐founded 3D Systems, one of the leading companies in the 3D industry. Later the company introduces the first commercialized 3D printer based on SLA in 1988. Further, they have developed a new file format that was specific to 3D printing technology named STL that was understandable to 3D printers which aid in the printing of 3D objects. While in 1988 DTM Inc., developed the first 3D printer based on selective laser sintering (SLS) technique (Saptarshi and Zhou 2019). Another 3D printing technology named fused deposition modelling (FDM) which was the most commonly adopted 3D printing technique was developed by Scott and Lisa Crump in the 1980s. They received a patent on this FDM technology and co‐founded Stratasys, another major player among the 3D industries (Su and Al’Aref 2018).
During the 1990s with the advancements of technology researchers of Stanford and Mellon proposed several other 3D techniques applied for micro‐level casting and spraying of materials. In 1993, MIT filed a patent on inkjet technology that employs liquid‐based ink for the construction of 3D objects commonly used in inkjet printers (Prasad and Smyth 2016). Later this technique was transferred and licensed to Z corporation for the development and marketing of 3D printers. Apart from materials manufacturing at the industrial level, 3D printing allows to produce consumer end products. In 2005, the RepRap project (3D printing open‐source project) was started by Adrian Bowyer at the University of Bath for the development of 3D printers at a low cost that could be affordable to