Additive Manufacturing (AM)
Additive manufacturing is the official industry standard term (ASTM F2792) for all applications of the technology. It is defined as the process of joining materials to make objects from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing methodologies. Synonyms are additive fabrication, additive processes, additive techniques, additive layer manufacturing, layer manufacturing, and freeform fabrication.The primary applications of additive fabrication are design/modeling, fit and function prototyping, and direct part production. Around the world, AM is changing the way organizations design and manufacture products. When used correctly, it can save impressive amounts of time and money. Companies maintain that AM has helped trim weeks, even months, of design, prototyping, and manufacturing time, while avoiding costly errors and enhancing product quality.
How Does it Work 
The clue to the basics of additive manufacturing; rather than producing an end result by taking material away, it adds to it instead. Traditional manufacturing methods involve a material being carved or shaped into the desired product by parts of it being removed in a variety of ways. Additive manufacturing is the pole opposite; structures are made by the addition of thousands of minuscule layers which combine to create the product. The process involves the use of a computer and special CAD software which can relay messages to the printer so it “prints” in the desired shape. Suitable for use with a range of different materials, the cartridge is loaded with the relevant substance and this is “printed” into the shape, one wafer-thin layer at a time. These layers are repeatedly printed on top of each other, being fused together during the process until the shape is complete.
The term AM encompasses many technologies including subsets like 3D Printing, Rapid Prototyping (RP), Direct Digital Manufacturing (DDM), layered manufacturing and additive fabrication. AM application is limitless. Early use of AM in the form of Rapid Prototyping focused on pre-production visualization models. More recently, AM is being used to fabricate end-use products in aircraft, dental restorations, medical implants, automobiles, and even fashion products. While the adding of layer-upon-layer approach is simple, there are many applications of AM technology with degrees of sophistication to meet diverse needs including: + a visualization tool in design + a means to create highly customized products for consumers and professionals alike + as industrial tooling + to produce small lots of production parts + one day….production of human organs
- Modeling: 3D printable models may be created with a computer-aided design (CAD) package, via a 3D scanner, or by a plain digital camera and photogrammetry software. 3D printed models created with CAD result in reduced errors and can be corrected before printing, allowing verification in the design of the object before it is printed. The manual modeling process of preparing geometric data for 3D computer graphics is similar to plastic arts such as sculpting. 3D scanning is a process of collecting digital data on the shape and appearance of a real object, creating a digital model based on it.
- Printing: Before printing a 3D model from an STL file, it must first be examined for errors. Most CAD applications produce errors in output STL files: holes, faces normals, self-intersections, noise shells or manifold errors. A step in the STL generation known as "repair" fixes such problems in the original model. Generally STLs that have been produced from a model obtained through 3D scanning often have more of these errors. This is due to how 3D scanning works-as it is often by point to point acquisition, reconstruction will include errors in most cases. Once completed, the STL file needs to be processed by a piece of software called a "slicer," which converts the model into a series of thin layers and produces a G-code file containing instructions tailored to a specific type of 3D printer (FDM printers). This G-code file can then be printed with 3D printing client software (which loads the G-code, and uses it to instruct the 3D printer during the 3D printing process). Printer resolution describes layer thickness and X-Y resolution in dots per inch (dpi) or micrometers (µm). Typical layer thickness is around 100 µm (250 DPI), although some machines can print layers as thin as 16 µm (1,600 DPI). X-Y resolution is comparable to that of laser printers. The particles (3D dots) are around 50 to 100 µm (510 to 250 DPI) in diameter. Construction of a model with contemporary methods can take anywhere from several hours to several days, depending on the method used and the size and complexity of the model. Additive systems can typically reduce this time to a few hours, although it varies widely depending on the type of machine used and the size and number of models being produced simultaneously. Traditional techniques like injection moulding can be less expensive for manufacturing polymer products in high quantities, but additive manufacturing can be faster, more flexible and less expensive when producing relatively small quantities of parts. 3D printers give designers and concept development teams the ability to produce parts and concept models using a desktop size printer. Seemingly paradoxic, more complex objects can be cheaper for 3D printing production than less complex objects.
- Finishing: Though the printer-produced resolution is sufficient for many applications, printing a slightly oversized version of the desired object in standard resolution and then removing material with a higher-resolution subtractive process can achieve greater precision. Some printable polymers such as ABS, allow the surface finish to be smoothed and improved using chemical vapor processes based on acetone or similar solvents. Some additive manufacturing techniques are capable of using multiple materials in the course of constructing parts. These techniques are able to print in multiple colors and color combinations simultaneously, and would not necessarily require painting. Some printing techniques require internal supports to be built for overhanging features during construction. These supports must be mechanically removed or dissolved upon completion of the print. All of the commercialized metal 3D printers involve cutting the metal component off the metal substrate after deposition. A new process for the GMAW 3D printing allows for substrate surface modifications to remove aluminum or steel.
Categories of AM
In 2010, the American Society for Testing and Materials (ASTM) group “ASTM F42 – Additive Manufacturing”, formulated a set of standards that classify the range of Additive Manufacturing processes into 7 categories (Standard Terminology for Additive Manufacturing Technologies, 2012).
- VAT Photopolymerisation: Vat polymerisation uses a vat of liquid photopolymer resin, out of which the model is constructed layer by layer. Find out more here.
- Material Jetting: Material jetting creates objects in a similar method to a two dimensional ink jet printer. Material is jetted onto a build platform using either a continuous or Drop on Demand (DOD) approach.
- Binder Jetting: The binder jetting process uses two materials; a powder based material and a binder. The binder is usually in liquid form and the build material in powder form. A print head moves horizontally along the x and y axes of the machine and deposits alternating layers of the build material and the binding material.
- Material Extrusion: Fuse deposition modelling (FDM) is a common material extrusion process and is trademarked by the company Stratasys. Material is drawn through a nozzle, where it is heated and is then deposited layer by layer. The nozzle can move horizontally and a platform moves up and down vertically after each new layer is deposited.
- Powder Bed Fusion: The Powder Bed Fusion process includes the following commonly used printing techniques: Direct metal laser sintering (DMLS), Electron beam melting (EBM), Selective heat sintering (SHS), Selective laser melting (SLM) and Selective laser sintering (SLS).
- Sheet Lamination: Sheet lamination processes include ultrasonic additive manufacturing (UAM) and laminated object manufacturing (LOM). The Ultrasonic Additive Manufacturing process uses sheets or ribbons of metal, which are bound together using ultrasonic welding.
- Directed Energy Deposition: Directed Energy Deposition (DED) covers a range of terminology: ‘Laser engineered net shaping, directed light fabrication, direct metal deposition, 3D laser cladding’ It is a more complex printing process commonly used to repair or add additional material to existing components.
Additive Manufacturing Technologies The figure below gives an overview of most widely used 3D printing technologies
source: 3D Hubs
Pros and Cons of Additive Manufacturing
Additive manufacturing is not always the right choice: It has distinct advantages and disadvantages. It’s up to each company and engineer to decide if additive manufacturing is the best process for their projects.
- Complexity is free: It actually costs less to print a complex part instead of a simple cube of the same size. The more complex (or, the less solid the object is), the faster and cheaper it can be made through additive manufacturing.
- Variety is free: If a part needs to be changed, the change can simply be made on the original CAD file, and the new product can be printed right away.
- No assembly required: Moving parts such as hinges and bicycle chains can be printed in metal directly into the product, which can significantly reduce the part numbers.
- Little lead time: Engineers can create a prototype with a 3-D printer immediately after finishing the part’s stereo lithography (STL) file. As soon as the part has printed, engineers may then begin testing its properties instead of waiting weeks or months for a prototype or part to come in.
- Little-skill manufacturing: While complicated parts with specific parameters and high-tech applications ought to be left to the professionals, even children in elementary school have created their own figures using 3-D printing processes.
- Few constraints: Anything you can dream up and design in the CAD software, you can create with additive manufacturing.
- Less waste: Because only the material that is needed is used, there is very little (if any) material wasted.
Infinite shades of materials: Engineers can program parts to have specific colors in their CAD files, and printers can use materials of any color to print them.
- Slow build rates: Many printers lay down material at a speed of one to five cubic inches per hour. Depending on the part needed, other manufacturing processes may be significantly faster.
- High production costs: Sometimes, parts can be made faster using techniques other than additive manufacturing, so the extra time can lead to higher costs. Additionally, high-quality additive manufacturing machines can cost anywhere from $300,000 to $1.5 million, and materials can cost $100 to $150 per pound.
- Considerable effort in application design and setting process parameters: Extensive knowledge of material design and the additive manufacturing machine itself is required to make quality parts.
- Requires post-processing: The surface finish and dimensional accuracy may be lower quality than other manufacturing methods.
- Discontinuous production process: Parts can only be printed one at a time, preventing economics of scale.
- Limited component size/small build volume: In most cases, polymer products are about 1 cubic yard in size, while metal parts may only be one cubic foot. While larger machines are available, they will come at a cost.
- Poor mechanical properties: Layering and multiple interfaces can cause defects in the product.
The Rising Importance of AM
Further proof of the rising importance of additive manufacturing is America Makes. America Makes is a public-private venture established by the United States Government to act as the national accelerator for additive manufacturing and 3D printing. Member organizations (of America Makes) from industry, academia, government and non-government agencies to work in collaboration to increase America’s global manufacturing competitiveness by innovating and accelerating Additive Manufacturing. Other countries have similar initiatives including Belgium, China, England, Germany, Japan, and Singapore.
- Definition - What is Additive Manufacturing (AM)? Wohlers Assoc.
- How Does Additive Manufactuting Work? SPI Lasers
- Applications of Additive Manufacturing (AM)? AM
- The General Principles Additive Manufacturing (AM) Wikipedia
- The 7 Categories of Additive Manufacturing University
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