Читать книгу 3D Printing of Foods - C. Anandharamakrishnan - Страница 37

3D printing is an additive process of developing a 3D construct from a digitalized CAD 3D design with the integration of a 3D printer with a computer. Most commonly 3D printing is used for rapid prototyping that allows testing the materials before practical implementation that has advantages like the use of lesser material resources, avoids wastage, saves energy, time, and cost (Shree et al. 2020). The higher degree of freedom of this technology allows its application to a diverse range of industrial sectors. In contrast to conventional manufacturing approaches, AM can produce goods with design personalization and mass customization. Ultimately, 3D printing could greatly limit the cost of processing with efficient utilization of resources and energy (Van Wijk and Van Wijk 2015). The basic working mechanism of a 3D printer is the printing of material in a pre‐determined design through appropriate conversion of digital CAD model into standard triangle language/ standard tessellation language (STL) (stereolithography [SLA]) file that initiates printing and controls the movement of coordinate axes. As discussed in the earlier chapters, the multi‐axis stages used in 3D printing can be of the cartesian, delta, polar, and scara configurations (Sun et al. 2018a). Among which cartesian and delta are the most used configurations in the manufacturing sector. The concept of 3D printing is the multilayer stacking of material along X, Y, and Z axes through precise control over material deposition. As a prototyping tool, the material deposition in 3D printing occurs through appropriate phase transitions and chemical reactions (Nachal et al. 2019). Based on the nature and type of heat source and the materials employed, there are several types of the AM process. These technologies are majorly used for plastics, polymers, composites, ceramics, and cement (Pradhan et al. 2021). The American Society for Testing and Materials (ASTM) framed different standards for AM and has classified processes into seven categories as follows (Liu et al. 2018c) (Figure 2.1).

 Material extrusion: A polymeric filament is melted using an electrical heat source and the melted liquid is deposited in a layered fashion using a 3D printer through an extrusion mechanism. The deposited material gets fused together upon cooling and attains the desired 3D shape (Shahrubudin et al. 2019). A filament is delivered using a Bowden mechanism for pushing the material filament through a long flexible Teflon tube to the hot end of the printing nozzle. From the nozzle tip, the melted polymer is deposited over the printing platform. Materials such as polylactic acid (PLA) and Acrylonitrile butadiene styrene (ABS) are the most commonly used polymer filaments. A temperature controlling unit is used for varying the temperature according to the melting point of the polymers used. Commercial 3D printers that are based on extrusion technology are referred to as fused deposition modelling (FDM) and fused filament fabrication (FFF). Extrusion‐based technology is comparatively cheaper than other AM processes (Vithani et al. 2019). Although the printing accuracy and precision are good, sometimes post‐polishing is required to enhance the surface smoothness of the 3D printed construct.

 Powder bed fusion: In this AM process, a heat source of either hot air or a high‐energy laser beam is employed to scan the 3D CAD design over the powder bed (Godoi et al. 2019). Due to which the powdered material gets melted and fused according to the shape and design of the 3D CAD model. After completion of the scanning process, the printed material is taken out from the loosened powder of the bed.Figure 2.1 Classification of AM technologies.

 Material jetting: Materials like wax and photo‐polymeric resins are the commonly used materials in this type of AM process. Here, the feed material is deposited in the form of a fine jet either in a continuous fashion or in a drop‐on‐demand (DoD) manner over the printing platform (Holland et al. 2019). The movement of printer arms can be operated based on the 3D model that controls the deposition of the printed layers. The melting point of the material can be precisely controlled through a temperature controller.

 Binder jetting: In the case of binder jetting, the liquid binder is sprayed over the powdered bed. Here, the binder acts as an adhesive that binds the material together. Above which the second layer of powder bed is spread over the printing platform then the liquid binder is sprayed (Sun et al. 2015). Likewise, the process is repeated continuously until the entire 3D model is printed. Commercial 3D printers such as Chef Jet and Chef Jet Pro works based on a binder jetting mechanism.

 Vat polymerization: In this process, a vat of liquid polymer‐based resin mixture is used for constructing a 3D object in a layer‐by‐layer manner. Here, a ultraviolet (UV) light source is used for curing the polymeric resin that results in the hardening of the layer of resin (Xu et al. 2020). After the formation of each layer, the platform moves the fabricated 3D object in a downward direction. Technologies such as SLA, digital light processing (DLP), and liquid crystal printers (LCD) are based on vat polymerization techniques.

 Sheet lamination: In this AM process, a laser beam acts as a knife that cuts the materials like papers, plastics, metals, and ceramics that are suitable for thermal pressing to bind thin layers together into a 3D construct (Ngo et al. 2018). Here, the movement of the laser light is controlled by a computer that moves according to the 3D CAD design. Thus, the 3D construct can be fabricated through laser as a thermal source and the unwanted portions of the material can be easily removed after the completion of the printing process.

 Direct energy deposition/laser metal deposition (LMD): This method employs a high‐energy laser source to melt the material over the processing surface. Thereafter the metal powder is injected into the melted material for the completion of the deposition process (Barro et al. 2020). The movement of the robotic arms is controlled with integration to a computer that moves according to the 2D directions that aids in the construction of a 3D object.

The above‐mentioned AM process differs based on the process of formation of the 3D construct and the way of assembling the finished structure. These AM technologies can be broadly grouped based on the type of chemical transition as controlled fusion, controlled deposition, controlled cutting with lamination, and combined technologies (Wegrzyn et al. 2012). Techniques based on controlled fusion are sintering and SLA where a heat or light source is directed to fuse the powdered materials. On the other hand, extrusion and inkjet technologies are based on the controlled deposition methods where a liquid or semi‐solid material is deposited in a controlled manner over the printing platform for the fabrication of a 3D object. Sheet lamination works based on the controlled cutting of thermal pressing materials followed by a lamination process to bind the layers together. Lamination‐based 3D printing technologies are referred to as layered object manufacturing (LOM) that are widely applied for tissue engineering for the fabrication of 3D scaffolds in the biomedical field. Sometimes, a combination of AM processes is adapted especially in bioprinting applications for the fabrication of soft scaffolds and tissues. However, not all these AM technologies are applied to the food layer manufacturing process. The 3D printing techniques that are adapted and applied for foods are discussed in the subsequent sections of this chapter.