Over time, 3D printing has become the

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1 Basics of additive manufacturing Over time, 3D printing has become the most widely used term for a number of rapid prototyping and rapid manufacturing techniques. The techniques are called rapid because they create parts directly from digital models. They are also called additive because they make parts by depositing successive layers of material. Many of the techniques use inkjet-like printheads to deposit layers, and UV light or lasers to fuse the layers. Synonymous terms for additive techniques include additive fabrication, solid freeform fabrication, additive manufacturing, and direct digital manufacturing. Additive manufacturing is considered distinct from traditional subtractive processes such as cutting or drilling. The advantage of additive technologies is they can make objects that would otherwise be difficult if not impossible to fabricate otherwise, such as those with complex features, internal voids, and latticed structures. For the low-volume manufacturing of end-use parts, additive manufacturing can be less costly than traditional methods because it does not require tooling. The techniques are used in every industry for 3D printing everything from scale models of cars out of several materials, or building-up functional parts for motorcycles, to making life-like replicas of organs from MRI scan data so doctors can assess where to best make surgical cuts. Some metal-printing techniques even build implantable bone and hip implants. Many kinds of materials are available for 3D printing applications, each with different capabilities. Some work better to make part prototypes or surgical models, others work better to manufacture end parts or low-volume tooling. Selection depends on the requirements for form, fit, and function. Typically, each additive machine vendor supplies proprietary materials designed to function best with that machine. Some systems allow the use of material not specifically created for a machine, but these may not produce the exact features required. Additive techniques include: Stereolithography (SL/SLA) typically traces a laser beam on the surface of a vat of liquid photosensitive resin, hardening the layer. The platform on which the model sits then lowers slightly, about Multi-material 3D printers from Objet lets users combine what the company calls its Digital Materials at the same time throughout the volume of a single model. The realistic prototype of a car suspension was 3D printed in an ABSlike Digital Material in opaque shades and rubber-like tires. Presented by Sponsored by 1 OCTOBER 2012

2 metal-casting processes. Typical applications: Detailed parts and models for fit and form testing; trade show and marketing parts and models; rapid manufacturing of small detailed parts; fabrication of jigs and fixtures; and patterns for investment casting or urethane molding. Materials: acrylics; clear and rigid; ABS-like; polypropylene-like (PP); flexible or elastomeric and water-resistant. 3D Systems, Rock Hill, S.C., invented stereolithography and was the first commercial manufacturer of rapid prototyping systems. These dental copings and bridges were laser-sintered out of cobalt chrome. A 3D printed model of the ear was used to create a mold for this prosthetic ear to in., and sweeps a blade filled with resin across the part. The laser then traces out another layer. The resin s adhesive qualities cause layers to bond together. The process repeats until the prototype is complete. Supports for undercuts or overhangs are fabricated along with the object. Technicians lift the finished object from the vat and cut off the supports. SLA provides good accuracy and surface finishes and allows the printing of parts as large as complete automotive dashboards. Most SLA resins are epoxy-based and provide strong, durable, and accurate models. Prototypes made by SLA are strong enough to be machined and can be used as master patterns for injection molding, thermoforming, blow molding, and various Fused deposition modeling (FDM) is a form of thermoplastic extrusion. The technique involves plastic filament or metal wire that gets unwound from a coil to supply material to a heated extrusion nozzle, which can turn on and off the flow. The nozzle mounts to a mechanical stage that moves in both horizontal and vertical directions. The nozzle moves over the build table, depositing a thin bead of extruded plastic to form each layer. The platform is kept at a lower temperature, so the thermoplastic quickly hardens. After the platform lowers, the extrusion head deposits another layer. Supports are built along the way, fastened to the part either with a second, weaker material or a perforated junction. Materials are deposited in layers as fine as in. To prevent part warping, the build mechanism sits in a chamber that is held to a temperature just below the melting point of the plastic. The method is office-friendly and quiet. FDM is a good choice for models that must closely represent the final product in strength and durability. FDM materials include thermoplastics ABS, ABSi, polyphenylsulfone (PPSF), polycarbonate (PC), and Ultem 9085, and waxes, with different trade-offs between strength and heat-resistant properties. 2 OCTOBER 2012

3 Ultem 9085 is fire resistant, making it suitable for aerospace and aviation applications. A water-soluble material such as polyvinyl alcohol (PVA) is used to make temporary supports for overhangs or undercuts while manufacturing is in progress. The support material quickly dissolves with special mechanical agitation equipment using a heated sodium hydroxide solution. FDM is also used in prototyping scaffolds for medical tissue engineering applications. FDM machines range from fast concept modelers to slower, high-precision machines. Typical applications: detailed parts and models for fit and form testing using engineering plastics; lattice parts for higher-temperature applications; trade show and marketing parts and models; rapid manufacturing small detailed parts; fabrication of jigs and fixtures; patterns for investment casting or urethane molding. Other materials: ABS (standard and medical grade); polycarbonate (PC); polyphenylsulfone; elastomer, investment casting wax. Stratasys Inc., Eden Prairies, Minn., sells equipment based on its proprietary FDM technology; 3D Systems sells machines for consumers. Inkjet (3D printing) refers to different kind of machines that use printheads similar to those found on 2D desktop printers. One technology builds parts on a platform that sits in a bin full of powdered material. The inkjet printing head selectively deposits or prints a binder fluid to fuse the powder together in the correct areas. Unbound powder remains to support the part. The machine lowers the platform about in., adds and levels more powder, and the process repeats. When the part is complete, a technician removes it, and uses compressed air to blow off excessive powder. Finished parts can be infiltrated with wax, glue, or other sealants to improve durability and surface finish. This process is fast, and produces parts with a slightly grainy surface. Typical applications: concept models; parts for limited functional testing; color models to show FEA results; architectural and landscape models; color industrial design models, especially for consumer goods and packaging; molds for castings. Materials: starch, plaster powder. Additionally, some inkjet technologies feed melted liquid thermoplastic resin to individual jetting heads. The heads move side to side, squirting tiny droplets of the material to form a layer. The material hardens on impact. Typical applications: Models for fit and form testing; patterns for investment casting, especially for jewelry and medical devices; and patterns for urethane molding. Materials: polyester-based plastic; investment casting wax. Another 3D-printing technology uses a wide inkjet head to deposit both the photopolymer build and These small components were built using FDM. 3

4 The functional prototype of a saw handle was 3D printed to check form, fit, and function. gel-like support materials at the same time. A UV flood lamp mounted to the printhead successively cures each layer. Once the part is complete, the support material is washed away in a secondary operation. High-end machines using this technique can mix and jet more than one material at a time, letting uses build parts with many different material properties that vary through the part volume. The technique is accurate, printing layers only 16-microns thick. Typical applications: Highly detailed parts and models for fit and form testing; models for trade shows and marketing purposes; patterns for investment casting, especially jewelry and fine items; patterns for urethane and silicon rubber molding; lifelike medical models. Objet Inc., Billerica, Mass., produces what it calls its PolyJet process, based on depositing photopolymer with a wide inkjet head. The company is also the first to introduce machines that can deposit two materials simultaneously; 3D Systems produces photopolymer-based systems that use inkjet technologies. The functional front sub-frame and dashboard were printed as a single part out of glass-filled nylon using selective laser sintering (SLS). A service bureau s proprietary process was used to make the SLS part black. Laser sintering/selective laser sintering (LS/SLS) uses a laser beam which moves in the X-Y direction over the surface of a compacted thermoplastic, metal, ceramic, or glass powder to selectively fuse it. A sealed nitrogenfilled fabrication chamber is kept at a temperature just below the melting point of the plastic powder. When the layer is complete, the build tray moves up a small amount, a roller pushes more powder over everything, and the machine then prints the next layer. When the object is completed, workers remove the compacted block and brush the excess powder away. Large parts may take a several hours to cool down enough to remove from the machine. No supports are necessary because the solid powder bed surrounds any overhangs and undercuts. Because the parts are sintered, they are somewhat porous, so it may be necessary to infiltrate the object with another material to improve the part s mechanical attributes. 4

5 Compared with other additivemanufacturing methods, SLS can produce parts from a relatively wide range of commercially available powder materials. These include polymers such as nylon, (even glass-filled or with other fillers) or polystyrene, metals including steel, titanium, alloy mixtures, and composites. Depending on the material, parts can be up to 100% dense, with material properties comparable to those from conventional manufacturing methods. In many cases, for high productivity, large numbers of parts can be packed in the powder bed. SLS began as a way to build prototype parts early in the design cycle, but the method is increasingly being used in low-volume manufacturing to produce end parts. It has also become popular in the building of artistic objects and jewelry. Typical applications: slightly less detailed parts and models for fit and form testing compared to photopolymer-based methods; additive manufacturing of parts, including larger items such as air ducts; parts with snap-fits and living hinges; patterns for investment casting. Selective laser melting (SLM) is basically the same idea as SLS, but the method uses higher-powered lasers to make fully dense parts. And electron beam melting (EBM) replaces the laser with an electron beam to create fully dense parts in a variety of metals such as stainless steel. The techniques work well in medical applications such as implants. Materials: nylon, polystyrene (PS); elastomeric; steel and stainless steel alloys; bronze alloy; cobalt-chrome alloy; titanium. Arcam in Sweden, EBM machines; EOS in Novi, Mich., provides laser sintering machines; Renishaw Inc., Hoffman Estates, Ill., provides selective laser melting (SLM) systems. The process is similar to selective laser sintering, but fully melts metal or ceramic powders to directly form fully-dense parts. 5