The Manufacturing Technology of the Future: 3D Printing

Three-dimensional printer technology is the process of printing any three-dimensional object designed in a virtual environment in solid form. Although its first application was carried out in 1984 by Chuck Hull of 3D Systems, it has only been used by many companies in recent years within the framework of changing production technologies. Particularly with the use of open-source three-dimensional printers, known as the Rep-rap project which started in 2006, the cost of this technology has decreased considerably. Thanks to this project, many ordinary users have been able to produce objects they designed with three-dimensional printers. At the same time, three-dimensional printer technology is directing people not toward mass production but rather toward customized production. Three-dimensional printers are particularly used in the medical sector, in the preparation of molds where cells can adhere for biological tissue and artificial organ production, in chemical compound or drug production, in designing protein molecules with diverse functions in biochemistry, in nanotechnology and in producing parts in the biomedical sector. Three-dimensional printers can perform production using different technology methods. To list these technologies, selective laser sintering, layered production technology and stereolithography are among the most commonly used three-dimensional printer technologies. Layered production technology is generally used in three-dimensional printers worldwide. The working principle is based on the method of producing a thermoplastic material by stacking it layer by layer. Thermoplastic polymers such as acrylonitrile-butadiene-styrene (ABS) or poly(lactic acid) (PLA) are generally used as filament of 3 or 1.75 mm, passing through a metal head heated to 250–300°C, where they reach a thickness below 1 mm and transition to a glassy phase that adheres to the area where they are stacked. The thermoplastic material stacked in layers on the plate in the molten phase creates the three-dimensional object.

1. Three-Dimensional (3D) Production Technology

Three-dimensional production, desktop manufacturing or in English "Additive Manufacturing," is generally translated into Turkish as "Layered Production." In this technology known as rapid prototyping, a three-dimensional computer design is transformed into a real object. The file extension of the three-dimensional digital model is converted to STL (Standard Tessellation Language) format and sent to the 3D printer. The 3D printer builds layer by layer to create the real object. Three-dimensional printer technology (3D Printing) or additive manufacturing technology (Additive Manufacturing) is the production of three-dimensional solid objects utilizing three-dimensional digital data. This process, unlike traditional machining operations, is a technology aimed at adding material rather than removing it.[1] Three-dimensional production technology uses many different materials and can largely eliminate raw material requirements suitable for mold and part geometry. For example, in parts produced by the machining method, a raw material (semi-finished product) that encompasses the external geometry of the part must be used, and unwanted voids are removed from this semi-finished material. This operation can take hours or even days, and the scrap rate is also quite high. In additive manufacturing or three-dimensional production technologies, this process is both quite short and the scrap rates are close to zero. Additionally, stages such as fixture and tool design required in machining processes are eliminated. The advantage of three-dimensional production or additive manufacturing technologies over processes such as precision casting that enable easy production of shapes with complex geometry is again mold design and mold production. This technology, which predominantly uses plastic materials such as ABS and PLA in model or prototype manufacturing, has in the ten years we have been behind added two other main material groups, ceramic and metal, to its portfolio with quite rapid development. Today, three main material groups—metal, plastic and ceramic—can be produced with this technology.

1.1 What is a Three-Dimensional Printer?

Three-dimensional printers are machines that convert a digital three-dimensional file (three-dimensional CAD drawing) into a three-dimensional solid object. To create a three-dimensional object, the digital file is converted into cross-sections in thinly sliced layers. During the printing phase, the three-dimensional printer creates the final object by stacking thin layers on top of each other (Figure 1.1).

Figure 1.1: Cartesian-type three-dimensional printer

With a three-dimensional printer, a three-dimensional drawing designed on a computer can be quickly and cost-effectively converted into a real object. This technology can produce geometries that are impossible to achieve with traditional manufacturing methods. Today, three-dimensional printers used for both prototyping and production purposes have entered architecture, construction, industrial design, automotive, aviation, space, defense, engineering, dentistry, medical, biotechnology (artificial tissue), fashion, footwear, jewelry, accessories, education, food and many other fields.

Table 1.1 Three-dimensional production methods and materials used

1.2 Purpose of Three-Dimensional Printers

3D printers have effective roles in many different areas. The most important of these will be discussed. Visual control of the product can be performed and possible form errors can be observed. In this way, geometry-based errors that could occur before the product moves to mass production are prevented. Possible errors are corrected in the CAD environment to obtain suitable geometry. A prototype product is created again with a 3D printer and visually checked for any problems. The fitting details of products containing multiple materials can be checked for their compatibility. The functionality of mechanisms can be tested. A multi-part assembly can be manufactured and run in a single operation. In other words, through the 3D printer, any product can be manufactured in assembled form and the manufactured assembled part can work together as a matched set. What is important here is the surface quality and fitting tolerances of the assembled part. Because fitting tolerances and surface roughness in 3D printers have not yet reached the quality that can be obtained through machining. In situations requiring very high precision, its use is not particularly recommended. It is possible to manufacture various assembled parts in assembled form such as bolts-nuts, bearings, threaded shafts, non-standard machine elements, and clips. Rapid prototype models can be used as master models in mold production. Rapid prototype models can be used for precision casting. By this method, the exact same product that will be produced with the mold is manufactured through the 3D printer, and the correctness of the dimensions of the mold being prepared or already prepared can be verified. Perhaps the most effective application is use in the medical and dental sector. Through 3D printer devices, implants and prosthetics that previously could only be manufactured after very lengthy processes can now be easily produced in a short time. For this procedure, the implant or prosthetic to be manufactured is first scanned with a 3D scanner to obtain its actual appearance. Necessary adjustments are made using a CAD program in the computer environment to make it suitable for 3D manufacturing. The product is then manufactured through the printer. One of the greatest advantages of this method is that it allows many identical products to be manufactured simultaneously. Finally, thanks to open-source projects, 3D printers that have now begun to be used in homes allow ordinary parts to be manufactured at low cost and enable hobby and entertainment use.

1.3 Modeling in Three-Dimensional Printers

The starting point of three-dimensional printer technology is a solid model designed on a computer. To manufacture with three-dimensional printers, a three-dimensional model is first required. This modeling process is generally called computer-aided design or CAD in foreign literature. Today, CAD programs are quite accessible and there are even many free 3D modeling programs available. Examples include Sketchup, Autodesk 123d and TinkerCAD.[2,3]

1.4 Slicing in Three-Dimensional Printers

The second phase of three-dimensional printing is slicing. The model designed with CAD software or three-dimensionally scanned is generally converted to STL, OBJ or AMF format to prepare for the slicing process. STL format is a model format consisting of polygons. This information must be converted into machine language that can be understood by 3D Printers, namely G-Code. G-code is a set of codes that define how machine axes should move at each moment. Nearly 90% of the code is based on axial movement. The slicing process is the most critical phase of 3D production (Figure 1.2). At this stage, all parameters that determine the properties of the product to be produced are also determined. Below you can see an example G-code: [4] Figure 1.2: a) Three-dimensional solid modeling, b) Slicing of the modeled shape in the slicing program, c) Print produced in a three-dimensional printer

1.5 Three-Dimensional Printer Technologies

We call the industrialized form of the rapid prototyping and three-dimensional printing method technology Layered Manufacturing (Additive Manufacturing). Layered production occurs through the conversion of a three-dimensional CAD model into a model with triangular mesh surface (STL), slicing into layers with special software, and then producing the product layer by layer starting from the bottom using a 3D printer. There are multiple technologies classified into different classes according to production techniques. According to the F2792-12a Layered Production Technology Terminology Standard prepared by the ASTM (American Society for Testing and Materials) committee on the subject, seven different classes are defined according to production techniques. These layered manufacturing technology classes are: binder jetting, directed energy deposition, material extrusion, material jetting, powder bed fusion, sheet lamination and vat photopolymerization. The most important of the layered production technologies is FDM (Fused Deposition Modeling) technology that produces with the material extrusion technique and means fused deposition modeling. It is estimated that approximately 70% of the three-dimensional printers used worldwide use FDM technology (Figure 1.3). [5]

Figure 1.3 Layered production technology classes in three-dimensional printers

1.6 Development of Layered Production Technologies

The rapid prototyping industry, which began in 1987 with the layer-by-layer curing of ultraviolet light-sensitive polymers with a laser, has transformed into an industry worth approximately USD 2 billion after 35 years, with more than 40 different system manufacturers primarily from the USA, Japan, China and Germany and over 50,000 system installations worldwide. Given that the number of CAD system users has increased from 150,000 to over 5 million in the last 10 years, it is a fact that 50,000 system installations are quite small. However, the fact that more than half of these system installations have occurred in the last 5 years is an important indicator of how much faster this sector will grow in the coming days. Since these systems are not used only for Rapid Prototyping purposes as in their early years and are also used for direct part manufacturing in some places, the terminology has evolved and is now referred to as Layered Production Technologies - LPT (Additive Manufacturing Technologies). [6]

1.7 Layered Production Technology Classes in Three-Dimensional Printers

It is estimated that approximately 70% of the 3D printers used worldwide use FDM (Material Extrusion Stacking) technology. In common use, SLS (powder bed fusion) ranks second. Although not as widely used as the first two, polyjet and SLA (Vat Photopolymerization) technologies can also be counted among common uses. On the other hand, powder binder jetting, LENS (Directed Energy Deposition), and LOM (Sheet Lamination) technologies are also different three-dimensional printing technologies.

1.7.1 Binder Jetting

A molding process in which an adhesive (binder) material is sprayed onto selected portions of powdered raw material to bind them together, creating the structure. In the 3D printer process, plastic, metal, ceramic or any other powder can be used as the printing raw material (Figure 1.4). An adhesive is sprayed from a multi-nozzle head to bind the powders together. A roller spreads a new layer of powder. After printing is complete, the powder surrounding the part, which also served as support material, is cleaned (with a vacuum cleaner and/or brush). Depending on the material used and the application, different additional processes such as infiltration and sintering can also be performed. [7]

Figure 1.4 3D printers using binder jetting technology

1.7.2 Electron Beam Melting (LENS) Technology

LENS technology is a process that completely melts dense metal powders with a powerful electron beam and builds layer by layer. Each layer is melted according to the geometry defined by a CAD model. In this technology, a high-power electron beam is used that generates the energy required for high melting capacity and high efficiency. Electrons are emitted from a filament heated to over 2,500 °C. When electrons strike the powder, kinetic energy is converted to heat. This heat melts the metal powder. Electrons are accelerated toward the anode at half the speed of light. The electron beam is controlled with extreme precision and speed by electromagnetic coils that provide precise beam control. After melting is complete, the table descends vertically and a new layer of metal powder is spread. These operations continue until the model is complete. EBM technology, which produces parts with better material properties than casting and forging and with stresses relieved, is performed in vacuum and high temperature. The vacuum system provides 10-5 mbar or better pressure throughout production. In this method, metal (cobalt chromium and titanium alloys) and ceramic materials can be used. With high strength, low density and superior corrosion resistance, titanium and its alloys are used in surgery and medicine, aviation, automotive, chemical plants, energy production, sports and other major industries. Parts produced by this method can be used directly (Figure 1.5). [8]

Figure 1.5: Schematic image of LENS technology

1.7.3 Fused Deposition Modeling (FDM) Technology

The technology, the acronym for Fused Deposition Modelling, has a Turkish translation of "Fused Deposition Modeling." Through a temperature-controlled nozzle, thermoplastic material is layered onto the production table layer by layer. When the model is complete, support structures can be easily removed by hand and in a water-chemical mixture. Today, the most popular method is FDM (Fused Deposition Modelling) or material deposition stacking technology. FDM technology is a technique developed by Scott Crump in the late 1980s. It was commercialized by Stratasys company in 1990. This method uses heat-moldable thermoplastic polymer materials (PLA, ABS). The thermoplastic material used in FDM technique is in filament (wire) form. Generally, wire thicknesses of 3 mm or 1.75 mm are used. During 3D printing, the wire-form material is passed through a 0.4 mm diameter nozzle to melt and is produced by stacking through axial movement. The object is formed as a result of stacking layers on top of each other. The melting method of the material is extrusion (Figure 1.6). [9]

Figure 1.6: FDM's Lamination Stacking Mechanism 1: Nozzle where molten material arrives, 2: Stacking of molten material, 3: Controllable movement table.

Process Steps:

a. BDT file is transferred to the machine using the IGES neutral format, b. File is brought to NURBS-based StrataSlice software, c. Adjustments can be made here or desired surface fit is provided, d. Slicing is selected at desired layer thicknesses, e. Output NC codes (a format containing coordinates of specific points) are obtained, f. 3D Models system creates the part. In the Fused Deposition Modeling (FDM) process, three-dimensional objects are produced directly from three-dimensional CAD data. Through a temperature-controlled head, thermoplastic material is layered onto the machine production table layer by layer. The FDM process begins with importing an STL model file into the system software. This model is positioned and mathematically sliced into layers with thicknesses varying between 0.13 mm and 0.35 mm. Support structures are created for required areas according to the part's position and geometry. After this preview and after extracting the paths the head will follow, data is sent to the FDM machine and the three-dimensional structure is created by stacking molten material. Assoc. Prof. Dr. Mehmet Atilla Taşdelen / Faculty of Engineering Polymer Engineering Department / Yalova University Naci Uysal / Senior Polymer Engineer Faculty of Engineering Polymer Engineering Department / Yalova University Serhat Oran / Doctoral Student / Faculty of Engineering Polymer Engineering Department / Yalova University Onur Turp / Polymer Engineer Faculty of Engineering Polymer Engineering Department / Yalova University

References 1. http://www.3byazici.com/p/3d-printer-teknolojileri- 3d-yazclar-ile.html 2. L.B. David, J.B.J. Joseph, C.L. Ming and W.R. David, "A brief history of additive manufacturing and the 2009 roadmap for additive manufacturing: looking back and looking ahead", US-TURKEY Workshop On Rapid Technologies, September 24, 5-1, (2009). 3. http://www.priyoid.com 4. TÜBİTAK Science and Technology Magazine, Year 46, Issue 561, December 2012 5. http://www.3byazici.com 6. www.prototip.org 7. www.infotron.com.tr 8. (Dumlupınar University Institute of Science and Technology Magazine, Issue 31, August 2013) 9. www.additively.com