Transcript Manufacturing Processes

Rapid Prototyping
Dr. Lotfi K. Gaafar
The American University in Cairo
Department of Mechanical Engineering
[email protected]
(202) 797-5355
Dr. Lotfi K. Gaafar 2002
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.
Dr. Lotfi K. Gaafar 2002
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.
Dr. Lotfi K. Gaafar 2002
Rapid Prototyping Technique
• Process Flow
3D Solid
modeling
Data
preparation
Part Building
Pass
Reject
Redesign
Dr. Lotfi K. Gaafar 2002
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 ….
Dr. Lotfi K. Gaafar 2002
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 today’s industry
 Rapid production (concurrent activities)
 JIT concept (0 Inventory)
 Rapid tooling / no tooling -- trend in
technology
Dr. Lotfi K. Gaafar 2002
Prototyping- Why?
Design verification
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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
Dr. Lotfi K. Gaafar 2002
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
Dr. Lotfi K. Gaafar 2002
Sophistication of Prototyping Technology
Such Technology is known by different terms, such as :
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Desktop Manufacturing
Rapid Prototyping
Tool-less Manufacturing
3-D printing
Free form Fabrication (F3)
Dr. Lotfi K. Gaafar 2002
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.
Dr. Lotfi K. Gaafar 2002
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
Dr. Lotfi K. Gaafar 2002
Rapid Prototyping Processes
 SLS --- Selective Laser Sintering
 SLA --- Stereolithography
 LOM --- Laminated Object Manufacturing
 FDM --- Fused Deposition Modeling
 Others
Dr. Lotfi K. Gaafar 2002
Rapid prototyping Processes- SLS
Selective Laser Sintering
Dr. Lotfi K. Gaafar 2002
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.
Dr. Lotfi K. Gaafar 2002
Rapid prototyping Processes- SL
Stereolithography
Dr. Lotfi K. Gaafar 2002
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.
Dr. Lotfi K. Gaafar 2002
Desirable features of SL resin
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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
Dr. Lotfi K. Gaafar 2002
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
Dr. Lotfi K. Gaafar 2002
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
Dr. Lotfi K. Gaafar 2002
Rapid prototyping Processes- LOM
Laminated Object Manufacturing
Dr. Lotfi K. Gaafar 2002
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
Dr. Lotfi K. Gaafar 2002
Rapid prototyping Processes- FDM
Fused Deposition Modeling
Dr. Lotfi K. Gaafar 2002
Rapid prototyping Processes- FDM
Dr. Lotfi K. Gaafar 2002
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.
Dr. Lotfi K. Gaafar 2002
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.
Dr. Lotfi K. Gaafar 2002
Rapid Prototyping Products
Dr. Lotfi K. Gaafar 2002