Rapid Prototyping

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Rapid Prototyping
Dr. Lotfi K. Gaafar The American University in
Cairo Department of Mechanical Engineering gaafar_at_
aucegypt.edu [phone]
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Introduction

• Rapid Prototyping (RP) techniques are methods
  that allow designers to produce physical
  prototypes quickly.
• It consists of various manufacturing processes by
  which a solid physical model of part is made
  directly from 3D CAD model data without any
  special tooling.
• The first commercial rapid prototyping process
  was brought on the market in 1987.
• Nowadays, more than 30 different processes (not
  all commercialized) with high accuracy and a
  large choice of materials exist.
• These processes are classified in different ways
  by materials used, by energy used, by lighting of
  photopolymers, or by typical application range.

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The Rapid Prototyping Technique

• In the Rapid Prototyping process the 3D CAD data
  is sliced into thin cross sectional planes by a
  computer.
• The cross sections are sent from the computer to
  the rapid prototyping machine which build the
  part layer by layer.
• The first layer geometry is defined by the shape
  of the first cross sectional plane generated by
  the computer.
• It is bonded to a starting base and additional
  layers are bonded on the top of the first shaped
  according to their respective cross sectional
  planes.
• This process is repeated until the prototype is
  complete.

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Rapid Prototyping Technique

• Process Flow

3D Solid modeling
Data preparation
Part Building
Pass
Reject
Redesign
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Prototyping- What is it ?

• . Physical Model of the product
• . Degrees of Prototyping
• . Full Complete scale Model - functional model
• . Scaled Model - functional/ simulated
  material
• . Geometrical configuration
• . Partial .

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Prototyping- Why?

• Visualization
• Design Change (iterations)
• Free Form Prototyping (complex object
  fabrication/ visualization)
• Testing Fit/ Packaging
• Cost, Time, and resource estimation
• Process Planning
• First to Market -- Critical for todays
  industry
• Rapid production (concurrent activities)
• JIT concept (0 Inventory)
• Rapid tooling / no tooling -- trend in
  technology

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Prototyping- Why?

• Design verification
• Design for manufacturability
• Design for assembly
• Design for maintainability
• Design for reliability
• Design for Quality
• Design Parameters (Tolerances/ allowances)
• Concurrent Engineering
• Tooling
• . Reverse Engineering
• . Die fabrication
• . Tool Path generation
• Limited Production

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Classification of Prototyping Technology

• Subtractive Processes (Material Removal)
• Ex Milling, turning, grinding,-- machining
  centers .., when used for prototype production
• Degree of automation vary
• Additive (Material Build-up)
• Ex Stereolithography
• Degree of sophistication vary
• Formative (Sculpture)
• Ex Forging, Casting, ..
• When used for Prototyping, it is usually manual

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Sophistication of Prototyping Technology

• Such Technology is known by different terms, such
  as
• Desktop Manufacturing
• Rapid Prototyping
• Tool-less Manufacturing
• 3-D printing
• Free form Fabrication (F3)

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Sophistication of Prototyping Technology

• Fabrication process
• The process must take a material in some
  shapeless form, and turn out solid objects with
  definite shape
• Degree of Automation
• High degree of automation. Since Prototyping is
  a stage in a cycle, it is expected that the
  technology will enable automated chaining to
  the before and after links in the cycle.
• Ability to build complex objects
• The more complex the build object, the more
  sophistication in the technology.

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Sophistication of Prototyping Technology

• Tooling (no Tooling) Less tools is better
• One shot operations No assembly of parts,
  ..etc.
• Time The less time the better it is
• The closeness to serve the purpose of the
  prototype Accurate representation of the design
• Flexible Modifications, addition of parameters,
  scaling
• Equipment size, weight, maintenance..etc
• Economical Both equipment and operating costs
• Clean, safe operation
• User friendly

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Rapid Prototyping Processes

• SLS --- Selective Laser Sintering
• SLA --- Stereolithography
• LOM --- Laminated Object Manufacturing
• FDM --- Fused Deposition Modeling
• Others

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Rapid prototyping Processes- SLS
Selective Laser Sintering
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Rapid prototyping Processes- SLS

• Application Range
• Visual Representation models
• Functional and tough prototypes
• cast metal parts
• Advantages
• Flexibility of materials used
• PVC, Nylon, Sand for building sand casting cores,
  metal and investment casting wax.
• No need to create a structure to support the part
• Parts do not require any post curing except when
  ceramic is used.
• Disadvantages
• During solidification, additional powder may be
  hardened at the border line.
• The roughness is most visible when parts contain
  sloping (stepped) surfaces.

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Rapid prototyping Processes- SL

• Stereolithography

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Rapid Prototyping Resin

• Basic Polymer Chemistry
• SL Resin It is a liquid photocurable resin
• Characteristics
• Fully 100 reactive component
• Energy efficient requiring 50 to 100 times less
  energy than thermally cured coatings
• Polymerization It is the process of linking
  small molecules (monomers) into larger molecules
  (polymers) comprised of many monomer units.
• As polymerization occurs (chemical reaction) many
  properties changes, shear strength increase,
  density increased as resin changes from liquid to
  solid (shrinkage)
• Polymerization occurs in SL through the exposure
  of liquid resin to laser. The layer thickness to
  be polymerized is given by the amount of liquid
  which has been recoated onto the part, and any
  excess laser radiation that penetrates this layer
  acts to slightly increase the curing of the
  previous layers.
• The important properties for selecting the resin
  has to do with posture shrinkage and the
  resulting posture distortions.

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Desirable features of SL resin

• Improved Impact resistance (less brittleness)
• Greater Flexibility
• Improved photospeed
• Increased Strength
• Better overall part accuracy
• Electrical conductivity
• High temperature resistance
• Solvent resistance or vice versa

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Some measures to reduce distortions

• Use high exposure and slow scan speed such that
  polymerization is essentially complete under the
  laser spot.
• Use resin with a faster rate of polymerization
• Decrease laser power to decrease scan speed for a
  given exposure.
• Use low-shrinkage resin
• Increase layer thickness to increase the strength

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Rapid prototyping Processes- SL

• Application Range
• Parts used for functional tests
• Manufacturing of medical models
• Form fit functions for assembly tests
• Advantages
• Possibility of manufacturing parts which are
  impossible to be produced conventionally in a
  single process
• Can be fully atomized and no supervision is
  required.
• High Resolution
• No geometric limitations
• Disadvantages
• Necessity to have a support structure
• Require labor for post processing and cleaning

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Rapid prototyping Processes- LOM
Laminated Object Manufacturing
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Rapid prototyping Processes- LOM

• Application Range
• Visual Representation models
• Large Bulky models as sand casting patterns
• Advantages
• Variety of organic and inorganic materials can be
  used
• Paper, plastic, ceramic, composite
• Process is faster than other processes
• No internal stress and undesirable deformations
• LOM can deal with discontinuities, where objects
  are not closed completely
• Disadvantages
• The stability of the object is bonded by the
  strength of the glued layers.
• Parts with thin walls in the z direction can not
  be made using LOM
• Hollow parts can not be built using LOM

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Rapid prototyping Processes- FDM
Fused Deposition Modeling
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Rapid prototyping Processes- FDM
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Rapid prototyping Processes- FDM

• Application Range
• Conceptual modeling
• Fit, form applications and models for further
  manufacturing procedures
• Investment casting and injection molding
• Advantages
• Quick and cheap generation of models
• There is no worry of exposure to toxic chemicals,
  lasers or a liquid chemical bath.
• Disadvantages
• Restricted accuracy due to the shape of material
  used, wire is 1.27 mm diameter.

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Rapid prototyping Processes

• Other Processes
• Ballistic Particle Manufacturing (BPM)
• This process uses a 3D solid model data to direct
  streams of material at a target.
• 3D Printing
• It creates parts by layered printing process. The
  layers are produced by adding a layer of powder
  to the top of a piston and cylinder containing a
  powder bed and the part is being fabricated.
• Model Maker
• It uses ink jet printer technology with 2 heads.
  One deposits building material, and the other
  deposits supporting wax.

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Rapid Prototyping Products