Additive Manufacturing Processes

ADDITIVE MANUFACTURING  Definition and Principles of Additive manufacturing Additive manufacturing (AM) refers to the technologies that create objects through sequential layering. Additive manufacturing (AM) is an agreed terminology by the technical committee within ASTM International to replac...

ADDITIVE MANUFACTURING  Definition and Principles of Additive manufacturing Additive manufacturing (AM) refers to the technologies that create objects through sequential layering. Additive manufacturing (AM) is an agreed terminology by the technical committee within ASTM International to replace the term rapid prototyping (RP) which has been used in a variety of industries to describe a process for rapidly creating a system or part representation before final release or commercialization. The basic principle of additive manufacturing is that a model, initially generated using a three-dimensional Computer Aided Design (3D CAD) system, can be fabricated directly without the need for process planning. Although this is not in reality as simple as it first sounds, AM technology certainly significantly simplifies the process of producing complex 3D objects directly from CAD data. The key to how AM works is that parts are made by adding material in layers; each layer is a thin cross-section of the part derived from the original CAD data. Obviously in the physical world, each layer must have a finite thickness to it and so the resulting part will be an approximation of the original data. Additive Manufacturing Processes Material extrusion is an additive manufacturing technique in which thermoplastic material is pushed through a heated extrusion nozzle and deposited layer by layer to build an object. Fused filament fabrication (FFF), also referred to as fused deposition modeling (FDM), is the most commonly used additive material extrusion process. The completed part is removed from the print bed and support materials are cleaned. Freshly printed FFF parts have visible layer lines, so post-processing is done to produce a smooth surface finish. Industrial-grade materials such as ABS and PLA are commonly used for FFF due to their high heat resistance and excellent strength-to-weight ratio. Sheet lamination, also called laminated object manufacturing (LOM), is a rapid prototyping process in which sheets of material are joined together to create an object. It is commonly used for building durable 3D objects with complex geometries. Ultrasonic additive manufacturing (UAM) is a type of sheet lamination process that uses principles of ultrasonic welding to produce metal parts. It uses CAD data to ultrasonically bind layers of metal sheets to metal substrate surfaces. A bonding adhesive is used to join paper sheets, whereas moderate force and high-frequency vibratory energy are required to create metal parts. Binder jetting, also known as drop-on-power printing, is a 3D printing process that creates solid objects using a 3D CAD file. It works with a variety of materials, including ceramics, composites, sand, and plastics. In binder jetting, the process uses a modified version of the inkjet printing process, therefore not requiring a heat source to bind the materials. Material jetting is a full-color additive manufacturing technique in which droplets of thermoplastic are selectively deposited using drop on demand (DOD) technology, similar to how an inkjet printer dispenses individual ink drops only when needed. In material jetting, the print head is not heated to bind the material. Instead, an ultraviolet (UV) light source is used to cure the liquid resin. Directed energy deposition (DED) is an additive manufacturing process that uses a heat source, such as a laser or electron beam, to melt metal powder or wire. Parts are created by melting material and placing it where it is needed. It is commonly used to repair or add additional features to existing parts. Powder bed fusion (PBF) is an additive manufacturing technology that uses a heat source, such as an electron or laser beam, to melt and join material powder to create three-dimensional objects. This technique can be used to create both plastic and metal parts. There are four types of powder bed fusion processes depending on the source of heat used. Direct metal laser sintering (DMLS), selective laser sintering (SLS), and selective laser melting (SLM) use laser fusion, electron beam melting (EBM) uses electronic beam fusion, multijet fusion uses agent and energy fusion, and selective heat sintering (SHS) uses thermal fusion. Vat photopolymerization is an additive manufacturing process that uses a vat, or container, filled with photosensitive liquid resin and a light source to create solid objects. The build platform then lowers by one layer height and more resin flows over the top of the print bed. A sweeper blade moves over the previous layer to ensure that a thin coat of liquid resin is spread out evenly on the surface. This process is repeated layer-by-layer until the part is finished. The printed part is then removed from the resin and from the build platform. It is then submerged in a chemical bath that washes away excess resin and cured in a UV oven to increase its stability and strength. At this point, any support materials are removed from the printed part. Digital Light Synthesis™ is the newest innovation in additive manufacturing that uses Carbon’s CLIP™ (continuous liquid interface production) technology to produce functional parts with exceptional surface finish and mechanical properties. 3D Printing 3D Printing Concepts and Theories 3D Printing is a method of manufacturing known as ‘Additive manufacturing’, due to the fact that instead of removing material to create a part, the process adds material in successive patterns to create the desired shape. 3D Printing uses software that slices the 3D model into layers (0.01mm thick or less in most cases). Each layer is then traced onto the build plate by the printer, once the pattern is completed, the build plate is lowered and the next layer is added on top of the previous one.  Layer by layer production allows for much greater flexibility and creativity in the design process. No longer do designers have to design for manufacture, but instead they can create a part that is lighter and stronger by means of better design. Parts can be completely re-designed so that they are stronger in the areas that they need to be and lighter overall. There is no problem with creating one part at a time, and changing the design each time it is produced. Parts can be created within hours.  Expensive hardware and expensive materials. This leads to expensive parts, thus making it hard if you were to compete with mass production. It requires a CAD designer to create what the customer has in mind, and can be expensive if the part is very intricate. 3D Printing Technologies FDM works on an "additive" principle by laying down material in layers. A plastic filament or metal wire is unwound from a coil and supplies material to an extrusion nozzle which can turn the flow on and off. The nozzle is heated to melt the material and can be moved in both horizontal and vertical directions by a numerically controlled mechanism, directly controlled by a computer-aided manufacturing (CAM) software package. Stereolithography is an additive manufacturing process which employs a vat of liquid ultraviolet curable photopolymer "resin" and an ultraviolet laser to build parts' layers one at a time. For each layer, the laser beam traces a cross-section of the part pattern on the surface of the liquid resin. Exposure to the ultraviolet laser light cures and solidifies the pattern traced on the resin and joins it to the layer below. Selective laser sintering is an additive manufacturing technique that uses a high power laser (for example, a carbon dioxide laser) to fuse small particles of plastic, metal (direct metal laser sintering), ceramic, or glass powders into a mass that has a desired three-dimensional shape. DLP (Digital Light Processing) is a 3D printing technology used to rapidly produce photopolymer parts. It’s very similar to SLA with one significant difference -- where SLA machines use a laser that traces a layer, a DLP machine uses a projected light source to cure the entire layer at once. The part is formed layer by layer. DLP printing can be used to print extremely intricate resin design items like toys, jewelry molds, dental molds, figurines and other items with fine details. Electron Beam Melting (EBM) is a 3D manufacturing process in which a powdered metal is melted by a high- energy beam of electrons. An electron beam produces a stream of electrons that is guided by a magnetic field, melting layer upon layer of powdered metal to create an object matching the precise specifications defined by a CAD model. Production takes place in a vacuum chamber to guard against oxidation that can compromise highly reactive materials. Types of 3D Printers Technology: Fused deposition modeling (FDM) Materials: Thermoplastics (e.g. PLA, ABS), eutectic metals, edible materials Technology: Direct metal laser sintering (DMLS), Electron beam melting (EBM), Selective heat sintering (SHS), Selective laser sintering (SLS), Powder bed and inkjet head 3d printing, Plaster-based 3D printing (PP) Materials: Almost any metal alloy, thermoplastic powder, metal powders, ceramic powders, plaster Technology: Laminated object manufacturing (LOM) Materials: Paper, metal foil, plastic film Technology: Stereolithography (SLA), Digital Light Processing (DLP) Materials: Paper, metal foil, plastic film, photopolymer, liquid resin Types of 3D Printing Materials Plastic products are generally made with FDM printers, in which thermoplastic filaments are melted and molded into shape, layer by layer. The types of plastic used in this process are usually made from one of the following materials: Polylactic Acid Polyastic acid (PLA): One of the eco- friendliest options for 3D printers, polyastic acid is sourced from natural products like sugar cane and corn starch and is therefore biodegradable. Available in soft and hard forms, plastics made from polyastic acid are expected to dominate the 3D printing industry in the coming years. Hard PLA is the stronger and therefore more ideal material for a broader range of products. Acrylonitrile butadiene styrene (ABS): Valued for its strength and safety, ABS is a popular option for home-based 3D printers. Alternately referred to as “LEGO plastic,” the material consists of pasta-like filaments that give ABS its firmness and flexibility. ABS is available in various colors that make the material suitable for products like stickers and toys. Increasingly popular among craftspeople, ABC is also used to make jewelry and vases. Polyvinyl Alcohol Plastic (PVA): Used in low-end home printers, PVA is a suitable plastic for support materials of the dissolvable variety. Though not suitable for products that require high strength, PVA can be a low-cost option for temporary-use items. Polycarbonate (PC): Less frequently used than the aforementioned plastic types, polycarbonate only works in 3D printers that feature nozzle designs and that operate at high temperatures. Among other things, polycarbonate is used to make low- cost plastic fasteners and molding trays. Today’s more state-of-the-art 3D printers use powdered materials to construct products. Inside the printer, the powder is melted and distributed in layers until the desired thickness, texture and patterns are made. The powders can come from various sources and materials, but the most common are: Polyamide (Nylon): With its strength and flexibility, polyamide allows for high levels of detail on a 3D-printed product. The material is especially suited for joining pieces and interlocking parts in a 3D- printed model. Polyamide is used to print everything from fasteners and handles to toy cars and figures. Nylon 66 Alumide: Comprised of a mix of polyamide and gray aluminum, alumide powder makes for some of the strongest 3D-printed models. Recognized by its grainy and sandy appearance, the powder is reliable for industrial models and prototypes. One of the more limiting and therefore less-used materials in 3D printing is resin. Compared to other 3D-applicable materials, resin offers limited flexibility and strength. Made of liquid polymer, resin reaches its end state with exposure to UV light. Resin is generally found in black, white and transparent varieties, but certain printed items have also been produced in orange, red, blue and green. High-detail resins: Generally used for small models that require intricate detail. For example, four- inch figurines with complex wardrobe and facial details are often printed with this grade of resin. Paintable resin: Sometimes used in smooth-surface 3D prints, resins in this class are noted for their aesthetic appeal. Figurines with rendered facial details, such as fairies, are often made of paintable resin. Transparent resin: This is the strongest class of resin and therefore the most suitable for a range of 3D-printed products. Often used for models that must be smother to the touch and transparent in appearance. The second-most-popular material in the industry of 3D printing is metal, which is used through a process known as direct metal laser sintering or DMLS. This technique has already been embraced by manufacturers of air-travel equipment who have used metal 3D printing to speed up and simplify the construction of component parts. The range of metals that are applicable to the DMLS technique is just as diverse as the various 3D printer plastic types: Stainless-steel: Ideal for printing out utensils, cookware and other items that could ultimately come into contact with water. Bronze: Can be used to make vases and other fixtures. Gold: Ideal for printed rings, earrings, bracelets and necklaces. Nickel: Suitable for the printing of coins. Aluminum: Ideal for thin metal objects. Titanium: The preferred choice for strong, solid fixtures. Composites such as carbon fiber are used in 3D printers as a top-coat over plastic materials. The purpose is to make the plastic stronger. The combination of carbon fiber over plastic has been used in the 3D printing industry as a fast, convenient alternative to metal. In the future, 3D carbon fiber printing is expected to replace the much slower process of carbon-fiber layup. Graphene has become a popular choice for 3D printing because of its strength and conductivity. The material is ideal for device parts that need to be flexible, such as touchscreens. Graphene is also used for solar panels and building parts. Proponents of the graphene option claim it is one of the most flexible of 3D-applicable materials. As a common material in medical implants, nitinol is valued in the 3D printing world for its super-elasticity. Made from a mixture of nickel and titanium, nitinol can bend to considerable degrees without breaking. Even if folded in half, the material can be restored to its original shape. As such, nitinol is one of the strongest materials with flexible qualities. For the production of medical products, nitinol allows printers to accomplish things that would otherwise be impossible. Designs can be printed on paper with 3D technology to achieve a far more realistic prototype than a flat illustration. When a design is presented for approval, the 3D- printed model allows the presenter to convey the essence of the design with greater detail and accuracy. This makes the presentation far more compelling, as it gives a more vivid sense of the engineering realities should the design be taken to fruition.