Dr. Lotfi K. Gaafar 2002 Rapid Prototyping Dr. Lotfi K. Gaafar The American University in Cairo Department of Mechanical Engineering [email protected]

Dr. Lotfi K. Gaafar 2002

Rapid Prototyping

Dr. Lotfi K. GaafarThe American University in CairoDepartment of Mechanical [email protected](202) 797-5355


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.


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.


Rapid Prototyping Technique

• Process Flow

3D Solid modeling

Data preparation

Part Building

Redesign

Pass

Reject


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 ….


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


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?


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


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



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.


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



Rapid Prototyping Processes

SLS --- Selective Laser Sintering

SLA --- Stereolithography

LOM --- Laminated Object Manufacturing

FDM --- Fused Deposition Modeling

Others


Rapid prototyping Processes- SLS

Selective Laser SinteringSelective Laser Sintering


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


Rapid prototyping Processes- SL

Stereolithography Stereolithography


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.


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


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


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


Rapid prototyping Processes- LOM

Laminated Object ManufacturingLaminated Object Manufacturing


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


Rapid prototyping Processes- FDM

Fused Deposition ModelingFused Deposition Modeling




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.



• 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


Rapid Prototyping Products

Documents

Dr. Lotfi K. Gaafar 2002 Rapid Prototyping Dr. Lotfi K. Gaafar The American University in Cairo Department of Mechanical Engineering [email protected]