Reducción de la actividad cortical durante la SMS

Mass production of goods has been the traditional way of meeting demand in mass consumer

markets, and has its origin in the early 1900s in the Ford car production lines. Mass production lines produce units which are the same. Originally devised to meet skilled labour shortages (Day, 2011), mass production is an efficient and therefore cost-effective means of production (Boland, 2006).

Customisation refers to being able to meet the needs of an individual customer. Customisation

recognises the increasing importance of meeting the preferences and needs of the individual, and in affording the individual the power to make their own choices; the ‘final customer’ is involved ‘in the design of a product prior to manufacture’ (Boland, 2006). On a larger scale, a system of mass customisation can meet the individual needs of many customers. Paradoxically, mass customisation can also be an efficient and cost-effective means of production. For large numbers of customers, the individual needs of each are able to be met by assembling a relatively small range of component parts in a seemingly endless number of combinations (Boland, 2006), rather than by a range of mass-produced finished units that would require storage. Mass production still features in mass customisation, in the prefabrication of component parts for later assembly.

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3.2.3D printing technologies

3D printing is a digitally controlled process of building objects layer-by-layer. Objects are built from typically one only of a variety of possible materials. The successive layers of material correspond to successive cross-sections from a digital image file representing the object.

Traditionally, 3D printing has been used for the purpose of rapid prototyping, but has been developing as a manufacturing technology in its own right; in this context ‘3D printing’ is also referred to as ‘additive manufacturing’ (AM) or ‘additive layer manufacturing’ (ALM), which distinguishes it from subtractive methods whereby objects are shaped by the removal of material from a starting block, using traditional machining techniques such as cutting or grinding.

Available 3D printing technologies differ in their layering process, and in the materials to which they are applied. Examples include:

3.2.1.

Fused deposition modelling, or extrusion deposition

A coil of plastic filament or metal wire is progressively unwound and fed into an extrusion nozzle, which heats and extrudes the material and controls the flow (Wikipedia, 2014a). The nozzle can moved horizontally across a platen so that layers of material can be formed. The platen can be moved vertically to allow successive layers to be built. The material hardens immediately after extrusion, creating a self-supporting structure.

3.2.2.

Granular materials binding

Objects are built from layers of powder or granules. Within each layer, regions corresponding to the relevant cross-section of the object are selectively fused using laser sintering (for plastic, metal, ceramic and glass powders) (Wikipedia, 2014b), inkjet binding (for plaster or resins) or heated air (for granulated sugar) (The CandyFab Project, 2014). Melting, using lasers or electron beams, can be used in place of fusing to create denser and stronger materials from metal powders (Wikipedia, 2011). As each layer is finished, the printing platform is lowered

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before the next layer is deposited. Unfused powder acts as a support for the growing structure, and is later removed.

3.2.3.

Laminated object manufacturing

Sheets of paper (Mcor Technologies Ltd., 2013), plastic or metal (Wikipedia, 2011) are selectively cut to shape (following the outlines of each cross-section) and glued together. Knives or lasers are used for cutting (Wikipedia, 2011). Support during the build is provided by the un-glued material.

3.2.4.

Advantages and applications

As a manufacturing process, 3D printing offers a number of distinct advantages. Objects can be produced without the use of a pre-cast mould, because the printing process by itself is able to (re)produce accurately any shape and to handle complex geometries. Changes in object design are managed much more easily with 3D printing, and without the need to machine new moulds. 3D printing brings together the design and manufacturing processes, but at the same time, the storage and portability of design files means that objects can be produced as and when needed. In a home use setting with a desktop 3D printing unit, these features mean that printing can be a single person, one-stop operation. Alternatively, services are available which will 3D print objects to order from files sent by customers. Both situations could allow for mass customisation of a single product type to occur. For mobile phone cases, companies provide either web-based customisation software as well as a printing service (Vance, 2012), or the design files for the customer to do the printing themselves (BBC News, 2013). In industry, parts can be printed locally when needed, rather than being manufactured offshore. 3D printing can be scaled up to such an extent as to produce buildings from concrete (Day, 2011).

3D printing has been applied to a range of novel materials to create new versions of existing products which are intended to be better performing, and less time- and labour- intensive to produce than the conventional items. Examples include: bicycles built from high-strength nylon powder, which are lightweight, all-in-one structures, custom built for the rider and therefore

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requiring no adjustment (Airbus Group Inc., 2011); custom 3D-printed horseshoes offering a lightweight alternative to traditional shoes and therefore the opportunity to improve racing times (CSIRO Australia, 2013); facial prostheses printed from starch powder which are filled with silicone post printing (Wainwright, 2013). Another potential application of the technology is the printing of tissue from living cells, for the purposes of transplantation or repair. Potentially the earliest success will be with the printing of cartilage due to it lacking internal structure and vascularisation (blood supply) (Palmer and Danzico, 2011).