Additive Manufacturing

Additive manufacturing was first introduced in the 1980’s and was defined by the American Society of Testing Materials as “ The process of joining materials to make objects from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing methodologies; Synonyms: 3D printing, additive fabrication, additive process, additive techniques, additive layer manufacturing, layer manufacturing, and freeform fabrication.”

Additive manufacturing also known as Rapid prototyping allows for quick prototyping, and complex geometries that would typically take special tooling if developed by traditional machining methods. Additive manufacturing is typically designed and developed from Computer Aided Design software’s which are then transformed into one of the recognizable Additive manufacturing files type

Additive manufacturing differs from other machining techniques due to the fact that most other techniques are subtractive forms of manufacturing, subtractive manufacturing is a process that removes material from a solid work piece, examples of subtractive manufacturing machines would be:

Mills
Lathes
Laser Cutter
Water Jet
Grinders and Sanders
The advantages of additive manufacturing versus conventional manufacturing techniques are shorter lead times of prototypes and outsourced parts, less material consumed and wasted, cheaper prototyping and small production part cost.

The term 3D printing covers a variety of processes in which material is joined or solidified under computer control to create a three-dimensional object,[1] with material being added together (such as liquid molecules or powder grains being fused together), typically layer by layer. In the 1990s, 3D printing techniques were considered suitable only for the production of functional or aesthetical prototypes and a more appropriate term was rapid prototyping. Today, the precision, repeatability and material range have increased to the point that some 3D printing processes are considered viable as an industrial production technology, whereby the term additive manufacturingcan be used synonymously with 3D printing. One of the key advantages of 3D printing is the ability to produce very complex shapes or geometries, and a prerequisite for producing any 3D printed part is a digital 3D model or a CAD file. There are many different branded 3D printing processes, that can be grouped into seven categories:[2]

The most commonly used 3D Printing process is a material extrusion technique called fused deposition modeling (FDM).[3] Metal Powder bed fusion has been gaining prominence lately during the immense applications of metal parts in the 3D printing industry. In 3D Printing, a three-dimensional object is built from a computer-aided design (CAD) model, usually by successively adding material layer by layer, unlike the conventional machining process, where material is removed from a stock item, or the casting and forging processes which date to antiquity.[4][5]

The term “3D printing” originally referred to a process that deposits a binder material onto a powder bed with inkjet printer heads layer by layer. More recently, the term is being used in popular vernacular to encompass a wider variety of additive manufacturing techniques. United States and global technical standards use the official term additive manufacturing for this broader sense.

Terminology

The umbrella term additive manufacturing (AM) gained popularity in the 2000s,[6] inspired by the theme of material being added together (in any of various ways). In contrast, the term subtractive manufacturing appeared as a retronym for the large family of machining processes with material removal as their common theme. The term 3D printing still referred only to the polymer technologies in most minds, and the term AM was more likely to be used in metalworking and end use part production contexts than among polymer, ink-jet, or stereo lithography enthusiasts.

By early 2010s, the terms 3D printing and additive manufacturing evolved senses in which they were alternate umbrella terms for additive technologies, one being used in popular language by consumer-maker communities and the media, and the other used more formally by industrial end-use part producers, machine manufacturers, and global technical standards organizations. Until recently, the term 3D printing has been associated with machines low in price or in capability.[7] 3D printing and additive manufacturing reflect that the technologies share the theme of material addition or joining throughout a 3D work envelope under automated control. Peter Zelinski, the editor-in-chief of Additive Manufacturing magazine, pointed out in 2017 that the terms are still often synonymous in casual usage[8] but some manufacturing industry experts are trying to make a distinction whereby Additive Manufacturing comprises 3D printing plus other technologies or other aspects of a manufacturing process.[8]

Other terms that have been used as synonyms or hypernyms have included desktop manufacturingrapid manufacturing (as the logical production-level successor to rapid prototyping), and on-demand manufacturing (which echoes on-demand printing in the 2D sense of printing). Such application of the adjectives rapid and on-demand to the noun manufacturing was novel in the 2000s reveals the prevailing mental model of the long industrial era in which almost all production manufacturing involved long lead times for laborious tooling development. Today, the term subtractive has not replaced the term machining, instead complementing it when a term that covers any removal method is needed. Agile tooling is the use of modular means to design tooling that is produced by additive manufacturing or 3D printing methods to enable quick prototyping and responses to tooling and fixture needs. Agile tooling uses a cost effective and high quality method to quickly respond to customer and market needs, and it can be used in hydro-formingstampinginjection molding and other manufacturing processes.

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.[31] 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.

CAD models can be saved in the stereolithography file format (STL), a de facto CAD file format for additive manufacturing that stores data based on triangulations of the surface of CAD models. STL is not tailored for additive manufacturing because it generates large file sizes of topology optimized parts and lattice structures due to the large number of surfaces involved. A newer CAD file format, the Additive Manufacturing File format (AMF) was introduced in 2011 to solve this problem. It stores information using curved triangulations.[32]

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,[33][34] of the following types:

  1. holes;
  2. faces normals;
  3. self-intersections;
  4. noise shells;
  5. manifold errors.[35]

A step in the STL generation known as “repair” fixes such problems in the original model.[36][37] Generally STLs that have been produced from a model obtained through 3D scanning often have more of these errors.[38] This is due to how 3D scanning works-as it is often by point to point acquisition, 3D reconstruction will include errors in most cases.[39]

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).[citation needed] 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).[40] 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.[citation needed] For that printer resolution, specifying a mesh resolution of 0.01–0.03 mm and a chord length ≤ 0.016 mm generate an optimal STL output file for a given model input file.[41] Specifying higher resolution results in larger files without increase in print quality.

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.[42]

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.[43]

Finishing

Though the printer-produced resolution is sufficient for many applications, greater accuracy can be achieved by printing a slightly oversized version of the desired object in standard resolution and then removing material using a higher-resolution subtractive process.[44]

The layered structure of all Additive Manufacturing processes leads inevitably to a strain-stepping effect on part surfaces which are curved or tilted in respect to the building platform. The effects strongly depend on the orientation of a part surface inside the building process.[45]

Some printable polymers such as ABS, allow the surface finish to be smoothed and improved using chemical vapor processes[46] 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[47] or steel.[48]

Multi-material printing

Multi-material printing allows objects to be composed of complex and heterogeneous arrangements of materials. It requires a material being directly specified for each voxel inside the object volume. The process is fraught with difficulties, due to the isolated and monolithic algorithms. There are many different ways to solve these problems, such as building a Spec2Fab translator.[49] Or use microstructures to Control Elasticity in 3D Printing.[50] There is also a solution about how to print a Multi-material 3d painting :Deep Multispectral Painting Reproduction via Multi-Layer, Custom-Ink Printing.[51]

Multi-material 3D printing is a fundamental element for development of future technology.[52] It has been already applied to variable industries. Other than common applications in small manufacturing industries, to produce toys, shoes, furniture, phone cases, instruments or even artworks.[53] With the BAAM (Big Area Additive Manufacturing) machine,[54]large products such as 3D printed houses or cars are quite feasible. It has also been widely used in high-tech industries. Researchers are devoting to producing high-temperature tools with BAAM for aerospace applications.

In medical industry, a concept of 3D printed pills and vaccines has been recently brought up.[55] With this new concept, multiple medications are capable of being united together, which accordingly will decrease many risks. With more and more applications of multi-material 3D printing, the costs of daily life and high technology development will become irreversibly lower.

Metallographic materials of 3D printing is also being researched.[56] By classifying each material, CIMP-3D can systematically perform 3D printing with multi materials.[57]

Applications

In the current scenario, 3D printing or Additive Manufacturing has been used in manufacturing, medical, industry and sociocultural sectors which facilitate 3D printing or Additive Manufacturing to become successful commercial technology.[87] More recently, 3D printing has also been used in the humanitarian and development sector to produce a range of medical items, prosthetics, spares and repairs.[88] The earliest application of additive manufacturing was on the toolroom end of the manufacturing spectrum. For example, rapid prototyping was one of the earliest additive variants, and its mission was to reduce the lead time and cost of developing prototypes of new parts and devices, which was earlier only done with subtractive toolroom methods such as CNC milling, turning, and precision grinding.[89] In the 2010s, additive manufacturing entered production to a much greater extent.

Impact

Additive manufacturing, starting with today’s infancy period, requires manufacturing firms to be flexible, ever-improving users of all available technologies to remain competitive. Advocates of additive manufacturing also predict that this arc of technological development will counter globalization, as end users will do much of their own manufacturing rather than engage in trade to buy products from other people and corporations.[9] The real integration of the newer additive technologies into commercial production, however, is more a matter of complementing traditional subtractive methods rather than displacing them entirely.[185]

The futurologist Jeremy Rifkin[186] claimed that 3D printing signals the beginning of a third industrial revolution,[187] succeeding the production line assembly that dominated manufacturing starting in the late 19th century.

See also

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