What is 3D printing? Working Principle / Types / Applications

The concept of 3D printing was outlined by David E.H. Jones in 1974. However, methods and materials for making models were not developed until the early 1980s. The term "3D printing" encompasses numerous processes and methods that offer a wide range of possibilities for producing parts and products from various materials. These processes have evolved considerably in recent years and can now play a crucial role in many applications. This overview article aims to explain the different types and processes of 3D printing, how they work, and what their uses and advantages are in the current market. Let's start with the most important question. What is 3D printing? 3D printing, also known as additive manufacturing, is the process of creating a physical object from a 3D digital model or CAD model. It involves various computer techniques in which material is joined or solidified to create a real object. Typically, material (such as powder particles or fluid molecules fused together) is added layer by layer on a millimeter scale. This is why 3D printing is also called an additive manufacturing process.

In the 1990s, 3D printing technologies were called rapid prototyping. They were only suitable for making aesthetic or functional prototypes. We have come a long way since then. Today's 3D printing technology is advanced enough to create complex structures and geometries that would otherwise be impossible to create by hand. The accuracy, range of materials, and repeatability of 3D printing has increased to the point where we can create almost anything from simple prototypes to complex end products such as eco-friendly buildings, aircraft parts, medical instruments, and even artificial organs using layers of human cells. How exactly does this work? All 3D printing methods are based on the same principle: A 3D printer takes a digital model (as input) and turns it into a physical three-dimensional object, adding material layer by layer. This method differs from traditional manufacturing processes such as injection molding and CNC machining, which use different cutting tools to build the desired structure from a solid block. 3D printing, however, requires no cutting tools: the objects are made directly on an embedded platform.

The process starts with a 3D digital model (object design). The software (specific to the printer) slices the 3D model into thin 2D layers. It then converts them into a set of machine language instructions for the printer to execute. Depending on the type of printer and the size of the object, printing takes several hours. The printed object often requires post-processing (such as sanding, applying varnish, paint, or other types of common finishing touches) to achieve an optimal surface finish, which requires additional time and manual labor. Different types of 3D printers use different technologies that treat different materials differently. Perhaps the most basic limitation of 3D printing, in terms of materials and applications, is that there is no one-size-fits-all solution. Types/Processes of 3D printing According to the ISO / ASTM 52900 standard, all 3D printing processes can be divided into seven groups. Each has its own pros and cons associated with it, which usually include aspects such as cost, speed, material properties and geometric limitations.
1. Photopolymerization VAT

The Vat photopolymerization-based D-printer has a container filled with photopolymer resin that is hardened with an ultraviolet light source to create an object. The three most common forms of vat polymerization are: 1A) Stereolithography (SLA): Invented in 1984, SLA uses an ultraviolet laser to crosslink chemical monomers and oligomers to form polymers that make up the body of a three-dimensional solid. Although the process is fast and can build almost any structure, it can be expensive. 1b) Digital Light Processing (DLP): This uses conventional light sources such as arc lamps (instead of lasers). Each layer of the object is projected onto a bath of liquid resin, which is then cured layer by layer as the lifting platform is lifted or lowered. 1c) Continuous Liquid Interface Production (CLIP): It is similar to stereolithography, but continuous and up to 100 times faster. CLIP can produce rubbery and flexible objects with smooth sides that cannot be created by other methods.
2. Material extrusion

In this process, a filament of solid thermoplastic material is pushed through a heated nozzle that melts the material and deposits it on a construction platform along a predetermined path. This material eventually cools and hardens to form a three-dimensional object. The most commonly used methods in this process are: 2a) Fusion Modeling (FDM): it uses a continuous filament of a thermoplastic material such as nylon, thermoplastic polyurethane or polylactic acid. 2b) Robocasting: Robotic machining involves extruding a paste-like material from a small nozzle while the nozzle moves across a construction platform. This process differs from FDM in that no drying or solidification of the material is required after extrusion to maintain its shape.
3. Sheet Lamination - combining sheet materials

Some printers use paper and plastic as a construction material to reduce the cost of printing. In this method, several layers of adhesive plastic, paper, or metal laminates are sequentially joined together and cut to the desired shape with a laser cutter or knife. The resolution of the layer can be determined by the source material. It is usually one to several sheets of copy paper. The process can be used to make large parts, but the dimensional accuracy of the final product will be much lower than that of stereolithography.
4. Directional energy deposition

The directed energy deposition method is widely used in high-tech metallurgy and in rapid production. The printing device contains a nozzle that is attached to a multi-axis robot arm. The nozzle applies metallic energy to an assembly platform, which is then fused by a laser, plasma, or electron beam to form a solid object. This type of 3D printing supports a variety of metals, functionally classified materials and composites, including aluminum, stainless steel and titanium. Not only can it design completely new metal parts, but it can also attach the material(s) to existing parts, allowing for hybrid manufacturing.
5. Material Jetting

Inkjet printing works similarly to inkjet paper printers. In this process, light-sensitive material is applied in droplets through a small-diameter nozzle and then cured with ultraviolet light, creating the part in layers. The materials used in this technique are thermosetting photopolymers (acrylics). Multicomponent printing and a wide range of materials (including rubber-like and transparent materials) are also available. Because inkjet printing of 3D printing materials can create parts with high dimensional accuracy with a smooth surface, it is an attractive option for making both visual prototypes and commercial tools.
6. Inkjet Binding

Two materials are used for binder jetting: a powder base and a liquid binder. The powder is distributed in even layers in a construction chamber, and the binder is applied through jet nozzles that "glue" the powder particles together to create the desired object. Wax or thermoset polymer is often mixed with the binder powder to increase its strength. After 3D printing is complete, the remaining powder is collected and used to print another structure. Because this technique is very similar to inkjet printing, it is also called injection 3D printing. It is mainly used to print elastomer parts, overhangs and colored prototypes.
7. Powder layer fusion

Powder fusion is a subset of additive manufacturing in which a heat source (such as a thermal imaging head or laser) is used to combine material into a powder form to create physical objects. The five most common forms of this technology are: 7a) Selective Laser Sintering (SLS): a laser is used as an energy source to sinter a powdered material such as polyamide or nylon. Here the term sintering refers to the process of compacting and forming a solid mass of material by applying pressure or heat without melting it to the point of liquefaction. 7b) Selective Laser Melting (SLM): Unlike SLS, this method is designed to completely melt and fuse metal powders together. It can create fully dense materials (layer by layer) that have mechanical characteristics similar to those of traditional fabricated metals. It is one of the rapidly evolving processes that is being implemented in both industry and research. 7c) Electron Beam Melting (EBM): In this process, raw materials (wire or metal powder) are placed in a vacuum and fused together using an electron beam. Although EBM can only be used with conductive materials, it has a superior assembly rate due to its higher energy density. 7d) Selective Heat Sintering (SHS): This uses a thermal print head to apply heat to layers of thermoplastic powder. Once the layer is finished, the powder layer is moved down and a new layer of material is added, which is then sintered to form the next cross section of the model. This method is best suited for making low-cost prototypes and parts for functional testing. 7e) Direct Metal Laser Sintering (DMLS): This is similar to SLS, but uses the power of metal instead. The remaining power becomes the auxiliary structure of the object and can be reused for the next 3D printing. DMLS parts are mainly made from powdered materials such as titanium, stainless steel, aluminum and a few niche alloys. It is an ideal process for custom medical parts, oil and gas components, and durable functional prototypes. Applications 3D printing has evolved considerably in the last decade. Because it can be used to quickly produce complex designs at a lower cost, it has become an indispensable tool in industries ranging from commercial manufacturing and medicine to architecture and custom design. Many additive manufacturing technologies can be used for food production. Today's 3D printers come preloaded with recipes on the built-in computer, and also allow users to create their food remotely on computers and smartphones. Food printed on a 3D printer can be altered in texture, color, shape, taste and nutrition. The technology has also proven effective in pharmaceutical formulations. The first drug made by 3D Printing was released in 2015. That same year, the FDA approved the first 3D-printed tablet.

In 2014, SpaceX delivered the first 3D printer to the International Space Station. It is currently being used by astronauts to print useful tools such as an end wrench. Technology companies are now integrating additive manufacturing with cloud computing to enable decentralized and geographically independent distributed production. Some companies are offering online-3D printing services (via a website) to both private and commercial customers. The Future of 3D Printing The big dream of 3D printing is "a factory in everyone's home." It may sound strange, but there's no denying that owning a machine that can instantly produce infinitely customizable things is exciting. According to GrandViewResearch, the global 3D printing market was valued at $11.58 billion in 2019 and is expected to reach more than $33 billion by 2027 (at a 14% annual growth rate). Factors expected to drive market growth include aggressive R&D and growing demand for prototyping applications from a variety of industries, particularly automotive, aerospace, defense and medical.


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