Dr. Lotfi K. Gaafar 2002 Rapid Prototyping Dr. Lotfi K. Gaafar The American University in Cairo...
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Transcript of Dr. Lotfi K. Gaafar 2002 Rapid Prototyping Dr. Lotfi K. Gaafar The American University in Cairo...
Dr. Lotfi K. Gaafar 2002
Rapid Prototyping
Dr. Lotfi K. GaafarThe American University in CairoDepartment of Mechanical [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
Redesign
Pass
Reject
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
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
Prototyping- Why?
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
Such Technology is known by different terms, such as : Desktop Manufacturing Rapid Prototyping Tool-less Manufacturing 3-D printing Free form Fabrication (F3)
Sophistication of Prototyping Technology
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 objectsThe more complex the build object, the more sophistication in the technology.
Dr. Lotfi K. Gaafar 2002
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
Sophistication of Prototyping Technology
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 SinteringSelective Laser Sintering
Dr. Lotfi K. Gaafar 2002
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.
Rapid prototyping Processes- SLS
Dr. Lotfi K. Gaafar 2002
Rapid prototyping Processes- SL
Stereolithography 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
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
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
Rapid prototyping Processes- SL
Dr. Lotfi K. Gaafar 2002
Rapid prototyping Processes- LOM
Laminated Object ManufacturingLaminated Object Manufacturing
Dr. Lotfi K. Gaafar 2002
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
Rapid prototyping Processes- LOM
Dr. Lotfi K. Gaafar 2002
Rapid prototyping Processes- FDM
Fused Deposition ModelingFused Deposition Modeling
Dr. Lotfi K. Gaafar 2002
Rapid prototyping Processes- FDM
Dr. Lotfi K. Gaafar 2002
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.
Rapid prototyping Processes- FDM
Dr. Lotfi K. Gaafar 2002
• 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.
Rapid prototyping Processes
Dr. Lotfi K. Gaafar 2002
Rapid Prototyping Products