RAPID PROTOTYPING

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RAPID PROTOTYPING

• The engineering department designs, produces and
  tests the first model of a new product. These
  first models are called PROTOTYPES.
• A prototype is a fully functional full sized
  model of the product. Prototypes are made with
  the actual materials and working components that
  will be used in the production. With the
  prototype, engineers run tests to make sure the
  product works as it was designed. A number of
  factors are checked. These include ease of
  manufacturing, durability, ergonomics, function
  and operation.
• Todays new engineering include virtual
  manufacturing systems, rapid prototyping etc.
  More flexible for changes in design and more
  responsive for the customer needs.

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• Rapid prototyping refers to a broad set of
  engineering topics that are intended to be item
  one of a new design. For many products, it is
  necessary to produce a physical item so that fit,
  accessibility and other interrelated product
  aspect can be determined. Rapid prototyping is
  the process that allows the first off to be
  produce more quickly and inexpensively. Altough
  rapid prototyping normally refers to the
  fabrication of a physical product, it also can
  refer to creation of software. The processes that
  are normally used in physical rapid prototyping
  include layered deposition of material. These
  layered methods processes have been referred to a
  3-D copying because the layers of the materials
  are deposited in 2-D form and then built up to
  make a 3-D object.

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• Benefits
• 1) Reduced lead times to produce prototype
  components.
• 2) Improved ability to visualize the part
  geometry due to its physical existence.
• 3) Earlier detection and reduction of design
  errors.
• 4) Increased capability to compute manufacturing
  properties of components and assemblies.

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• Classification of rapid prototyping
• 1) Subtractive Material removal from a work
  piece larger than the final part.
• 2) AdditiveBuild up a part by adding material
  incrementally (See next slide)
• 3) VirtualComputer based visualization
  technologies.
• Work part
• Almost all materials can be manufactured through
  rapid prototyping operation, but polymers are the
  work piece material most commonly used today,
  because it is less expensive.

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• Techniques of additive rapid prototyping
• Stereolithograpy The Stereolithography (SLA)
  process converts a design into a solid object by
  building up thin layers of material. It was the
  first of the rapid prototyping technologies to be
  developed in 1988. A 3-dimensional CAD model of
  the desired part is sliced, in software, in to a
  series of adjacent 2D slices. This data is used
  to control a laser beam that draws each slice of
  the model, in turn, onto the surface of a tank of
  sensitive resin. Where the laser beam strikes,
  the resin is instantaneously cured to a solid.
• The model is built on to a
  platform within the resin tank. At the start of
  the process the platform is positioned just below
  the surface of the resin. The first layer of the
  model, the base, is drawn by the laser to form a
  solid layer, typically 0.1 mm thick.
• The platform then descends
  in the bath to allow new liquid resin to cover
  the cured layer and the next model slice is
  constructed above it. In this way the whole of
  the model is built from the base up. The process
  is illustrated in the next page.

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• 2) Selective Laser Sintering (SLS) The most
  advanced laser fusion technique is the commercial
  selective laser sintering
• (SLS). In this process the feed stock is a
  thin layer of ceramic coated with a thermoplastic
  binder. A laser beam scans the surface defining
  the regions to sinter, fusing the polymer and
  bonding the particles. The remainder of the
  layer remains as a loose powder.
  The layer is lowered and a further loose powder
  layer is applied. The laser is then used to
  process the next layer, bonding it to the first
  layer. The procedure is repeated
  until the green state component is produced. This
  can then be processed through traditional
  processes once the binder has been burnt out. It
  is believed that any material that can be
  densified by traditional sintering techniques can
  be processed by
• SLS, for example Al2O3, SiC and Zr
  composites.

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• 3) Fused Deposition Model(FDM)
• A heated nozzle applies layer by layer of
  the melted material on the already solidified
  material like a hot-melt gun. The wire-shaped
  material runs from a coil into an extruder where
  a thermoplastic or a precision casting wax is
  melted into a thin thread. The layer thickness
  depends on the size of the nozzle opening, which
  may range between 0.25 x03mm and 1.25 x03mm. This
  method offers advantages based on its high speed
  and, nevertheless, good production tolerances.
  There are no cooling or hardening times. A
  disadvantage is that this system cannot produce
  acute angles or sharp edges. The hot thread must
  be processed quickly after the process has
  started because the temperature setting at the
  nozzle is difficult to regulate and the material
  otherwise burns and the model would be scrap.

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• 4) Solid Base Curing or Solid Ground Curing Most
  expensive type of rapid prototyping technique.
  Basic approach consists of the following steps.
• 1) Once a slice is created by the software, a
  mask of the slice is printed on the glass sheet.
• 2) While mask is prepared, a thin layer of
  polymer is laid sown on the work surface.
• 3) Photomask is placed over the work surface,
  and an ultraviolet light is projected through the
  mask, wherever the mask is clear, the light
  shines through to hardened the surface.
• 4) The left over material, still liquid, is
  vacuumed.
• 5) Water soluble liquid wax is spread accross
  the work area, filling cavities, the wax hardens
  quickly.
• 6) Milling operation is applied to correct
  flatness and thickness.

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• 7) Process repeated.
• Benefits High production rate, support is water
  soluble and can be removed immediately or used to
  support in shipping, no finishing required.
• Advantages
• Multiple parts can be positioned within
  the entire working envelop resulting high
  throughput
• No support structure is required as the
  wax support the structure in all directions
• Each layer is fully cured resulting that
  the dimension is very stable with no shrinkage
  effect after the process and requires no
  post-curing process
• Capable to build even the most
  complicated parts without much difficulty
• Build session can be interrupted and
  erroneous layer can be erased

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• Disadvantages
• The process is rather
  complicate which required skilled people to look
  after and unattended operation is not possible
• The resin consumption is
  disregard of the size of the cross section of the
  parts but only depended on the number of layers
  resulting that it is too expensive for parts with
  small cross sectional area
• High equipment cost (over
  US500,000) made it not easily to be justified

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• 5) Ballistic Particle Manufacturing A stream of
  material is ejected through a small nose at a
  target. The ink jet head is guided by a 3-axis
  robot with a rate of 50-?m droplets at 10.000 per
  second.

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• 6) Laminated Object Manufacturing(LOM) Uses
  layers of paper or plastic sheets with a heat
  activated glue on one side to produce parts. The
  desired shapes are burned into the sheet with a
  laser and the parts are build layer by layer. LOM
  uses 0.05 mm (0.002 in) sheets. It is the
  cheapest method, refered to as desk top rapid
  prototyping machine. It has limited work space.
• CAD data goes into the LOM System's process
  controller and a cross-sectional slice is created
  by the LOM software. The CO² laser cuts the
  cross-sectional outline in the top layer and then
  cross-hatches the excess material for
  later removal. A new layer is bonded to the
  previously cut layer and a new cross section is
  created and cut as before. Once all layers have
  been laminated and cut, excess material is
  removed to expose the finished model.

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• Advantages
• It is a relatively high speed process as the
  laser is only required to trace the contour and
  no need to scan the entire cross section. The
  more volume of material within the part, the more
  greater is the speed gain.
• Parts can be used immediately after the process
  and no post curing is required.
• No support structure is required as the part is
  supported by its own material.
• Simple to use and no environmental concern

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• Disadvantages
• Although there is some choice of materials
  including paper, plastic, ceramic and composite,
  the most commonly used material is only paper.
  Others are still under development.
• The built parts absorb moisture quickly resulting
  that the built parts must be post processed
  immediately and impregnating with epoxy
  that is specially designed for LOM technology,
  such as LOMPOXY
• Inherent deficiency in building fin-shape parts,
  in other words the process is restricted to build
• complex parts
• Since it is very difficult, if not impossible, to
  remove the waste materials from inside, the
  process is incapable of building reentrant shapes
  
• Fire hazard is occasionally happened when the
  working chamber becomes too hot

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• Applications
• 1) Direct production of the desired parts,
  altough it is not economical for large
  quantities.
• 2) Production of tooling (MOLDs), but surface
  quality is not very good, tool life is short.