Selective Laser Sintering

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Selective Laser Sintering

• By
• Rohan Malkar (132090008)
• Swapnil Pawar(132090006)

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Definition of Rapid prototyping

• Rapid Prototyping (RP) can be defined as a group
  of techniques used to quickly fabricate a scale
  model of a part or assembly using
  three-dimensional computer aided design (CAD)
  data.

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Why Rapid Prototyping

• The reasons of Rapid Prototyping are  
• To increase effective communication.
• To decrease development time.
• To decrease costly mistakes.
• To minimize sustaining engineering changes.
• To extend product lifetime by adding necessary
  features and eliminating redundant features early
  in the design. 

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Rapid Prototyping

• Goal is to fabricate 3-D models quickly and
  automatically directly from CAD models.
• Current RP system are based on Layered
  Manufacturing Technology.
• In this method solid model ( triangle polyhedral
  form ) is decomposed into cross sectional layer
  representation.
• The RP software prepares tool path to physically
  built these layers automatically to form the
  object in the machine.

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RP process chain showing fundamental process steps
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• Depending upon the form of the raw materials used
  RP systems are classified as follows

RP Systems
Solid
Liquid
Powder
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Selective Laser Sintering

• Selective laser sintering was originally
  developed by University of Texas at Austin.
• Commercialised by DTM Corporation USA. DTMS SLS
  is presently owned by 3D systems.
• It is a solid based RP process.
• It is the first process to emerge at the
  commercial scale to make metallic parts and
  tools.
• Selective Laser Sintering (SLS) uses a laser to
  sinter powder based materials together,
  layer-by-layer, to form a solid model.

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• A SLS system has three major components

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• Schematic of SLS apparatus

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Methodology
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Step 1
Step 2
Step 4
Step 3
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Step 5
Metal Powder SLS Machine ( Courtesy EOS )
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Working of SLS

• It is an additive RP techniques.
• Layer of powder is first deposited on part build
  cylinders.
• The laser ( CO2 ) traces a two-dimensional cross
  section of the part.
• During laser exposure, the powder temperature
  rises above the glass transition point after
  which adjacent particles flow together. This
  process is called sintering. 
• Platform descends down by an amount equal to the
  thickness.
• The roller pushes the material on the built
  platform and the process is repeated again an
  again.

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• Following video will clearly depict the working
  of the sls process.

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Materials used for SLS.

• Metallic and non metallic powders are used
  typically of the size 50µm.
• Commonly used materials
• Plastics
• Waxes (Investment wax casting)
• Low melting temperature metal alloys.
• Polymer coated metals.
• Ceramics (Green preforms).
• Nylon ( Duraform, Glass-Filled Nylon (Duraform
  GF), Flame Retardant Nylon and Durable Nylon.)

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SLS Products
Engine Manifold
Valve
Medical implant
Electronic Packaging
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Complexity!!! Not a ProblemIn SLS
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Strengths of SLS

• Any material that can be converted into powder
  having low melting temperature (350 to 500) can
  be used to make parts in this process.
• No support structure required.
• Parts obtained are tough.
• No post curing required.
• No tooling cost incurred.
• No wastage of material.
• Functional metal and ceramic parts can be
  obtained directly.

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Weakness of SLS

• Surface finish is improper.
• Parts are porous in nature.
• Continuous monitoring of the building operation
  is required.
• Large amount of time is required to heat up
  material chamber before building part.
• Uniform cooling is difficult to maintain in order
  to avoid warpage.
• Parts obtained are brittle.

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• Steriolithoraphy (SLA)

• Selective Lasser Sintering (SLS)

• Limited to photosensitive resins making it
  brittle.
• Good surface finish
• Accuracy is very high.
• Less prone to residual stresses.
• SLA suffers from trapped volume problem (cups in
  the structure which hold hot fluid cause
  inaccuracies)

• Polymers can be used for sintering thereby
  approximating thermoplastics.
• Surface finish operation as required since part
  is powdery.
• Accuracy is one of the biggest disadvantage of
  this process.
• Higher residual stresses due to longer curing.
• SLS does not have this problem.

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• SLA

• SLS

• SLA products are difficult to machine due to
  their brittle nature.
• SLS and SLA objects can be made of the same size.
• SLA is rarely preferred ( Quick cast is the
  one process in which investment casting is
  preferred developed by 3D systems using SLA.)

• SLS product are made from thermoplastic material
  which can be easily machined.
• SLS and SLA objects can be made of the same size.
• SLS is mostly used in investment casting also
  sometimes to prepare master patterns.

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Areas employing SLS

• Aerospace.
• Automotive.
• Organ replacement.
• Haemotology.
• Surgical Tools.
• Medical Instruments.