1. 1. What is Rapid Prototyping
The term "rapid prototyping" is a relatively new expression for the generation of three-dimensional models manufactured without the need for machining or tooling.
Production of models by machining has a number of limitations:
- Material removed during forming is difficult to reclaim.
- Machining, in the form of drilling, turning, milling, spark erosion etc., is limited by the shapes it can produce.
- In the event of design change conventional tooling such as patterns, core boxes, dies, jigs etc., become expensive to alter and, in many cases, may require complete re-manufacture.
Rapid prototyping differs by:
- Adding material layer by layer until the desired shape is achieved, immediately reducing or avoiding the loss of material.
- Cutting out the conventional draftsperson, patternmaker and in some situations even the moulder, the system goes a long way towards reducing time taken and cost and improving accuracy.
Rapid Prototyping: Traditional manufacturing:
additive material subtractive material

2. 1.1 Characteristics of RP
A technology that produces models and prototype parts from 3D CAD model data, CT and MRI scan data, and model data created from 3D object digitizing systems
RP systems join together liquid, powder and sheet materials to form parts
MRI – Magnetic Resonance Imaging
Layer by layer, RP machines fabricate plastic, wood, ceramic and metal objects
RP also known as Solid Freeform Fabrication (SFF)
or Layer Manufacturing (LM)

3. 1.2 Basic process of RP Three stages: pre-processing, building, and
post processing
CAD Model
Surface/Solid
Model
Pre Process
RP Process
Post Process
Generate
.STL file
Build
Prototype
Remove
Supports
Build Supports
if needed
Clean Surface
There are basically three stages of building physical models based on the CAD data, namely the pre-processing, building and the post processing.
The pre-processing stage is to generate the RP machine controlling codes based on the CAD output data. The CAD model is converted to STL format for the pre-processing. There are four steps in this process, they are the verification, orientation, support generation & editing and finally the Slicing and converging steps.
in CAD
Post Cure if needed
Part Completed
Slicing
in RP
systems

4. 1.3 Benefits of RP Improved product quality
RP enable more design iterations in a given time
Shorten time to market & reduced development cost
THE COST OF CHANGE
PHASE COST
Conceptual modeling $10
Detail design $100
Prototype/test $1,000
Manufacturing $10,000
Product release $100,000
Source: Wohlers Associates
3D visualization of product designs
Esure that customers have a clear understanding
“A picture is worth a thousand words; a model is worth a thousand pictures.”
Prototypes with the characteristics of finished products allow detailed evaluation and analysis to help avoid costly design iterations. Additional, physical prototypes can be used as masters and patterns for a wide range.
The cost of changing the basic design of a product increases rapidly as the design advances through the development cycle.
With rapid prototyping (RP) systems, companies can produce functional parts in days instead of weeks or months. In recent years, RP has had a dramatic effect on reducing the time needed to move the design from the digital and paper phase of development, to prototyping and testing. Many companies have reported the development of complete prototypes without a single engineering drawing.
RP enables more design iterations in a given time thus facilitating better quality in design.
Hands-on prototypes ensure that customers have a clear understanding of new and innovative concepts.

5. 2. Common types of RP The first RP system was introduced in 1988
Common types of RP technologies now:
- StereoLithography (SL)
- Fused Deposition Modeling (FDM)
- Selective Laser Sintering (SLS)
- Laminated Object Manufacturing (LOM)
- 3D Printing (3DP)

6. 2.1 Stereo-Lithography (SL)
1. The elevator lowered by 1 layer deep;
2. The Blade sweep across the vat, apply an even layer of resin on top of the part;
3. As the laser beam strikes the resin surface, the liquid resin is hardened to a solid plastic;
4. Loop through the three steps to cure a new layer.
Laser
Scanning
Mirror
Liquid Resin
Supports
Cured resin
to form model
Elevator & Platform
Re-coating
Blade
The laser draw each slice of the part similar to zigzag milling of a CNC. It is a hatching process of X and Y.

7. Stereo-Lithography Apparatus (SLA)
Representative:
from 3D Systems, Inc.
Materials:
photocurable resins
Adv. & Disadvantages:
 Good dimensional accuracy
 Good surface finish
 Narrow range of materials
 Relatively high cost
 Post curing
Application areas:
- Prototypes for concept models;
- Form-fit for assembly tests and process planning;
- Models for investment casting, replacement of the wax pattern;
- Patterns for metal spraying, epoxy molding and other soft tooling
A variety of resin is available for SLA, each with its own advantage and weakness.
Resin used in SLA process are mixture of photo-initiator and monomer mixture in liquid state, external energy source will trigger the chain reaction of polymerization. The external energy can be in the form of heat or light wave, and the shrinkage of the resin varies according to the form of energy supplied.
The resin are stored in an environment with tight temperature control. For example, the chamber of SLA are maintained at 28°C ± 1°C.
Typical SLA resins only react to a narrow bandwidth of UV ray, as different model of SLA machine use different laser, resin is generally not interchangeable.
Advantages:
- Unattended building process - The system is very stable. Once started the process is fully automatic and can be unattended until the process is completed.
- Good dimensional accuracy - The process is able to maintain the dimensional accuracy of the built parts to within +/-0.1mm.
- Good surface finish - Glass-like finishing can be obtained on the top surfaces of the part although stairs can be found on the side walls and curve surfaces between build layers.
- The process is of high resolution and capable to build parts with rather complex details.
- 3D Systems Inc. have developed a software called "Quickcast" for building parts with hollow interior which can be used directly as wax pattern for investment casting.
- It is the most widely used process in the RP field.
Disadvantages:
- Curling and warping - The resin absorb water as time goes by resulting curling and warping especially in the relatively thin areas.
- Relatively high cost (US$ K) - However, it is anticipated that the cost will be coming down shortly.
- Narrow range of materials - The material available is only photo sensitive resin of which the physical property, in most of the cases, cannot be used for durability and thermal testing.
- Post curing - The parts in most cases have not been fully cured by the laser inside the vat. A post curing process is normally required.
- High running and maintenance cost - The cost of the resin and the laser gun are very expensive. Furthermore, the optical sensor requires periodical fine tuning in order to maintain its optimal operating condition which will be considerable expensive.

8. 2.2 Fused Deposition Modeling (FDM)
Support
Part
Heated extrusion
head
Model & Support Filaments
Elevator & Platform
1. Extrusion head and elevator move to start position;
2. The head extrude layer of support;
3. The head extrude layer of model;
4. Loop through the three steps to build the next layer.
In the FDM Hardware, the FDM head moves in two horizontal axes across a foundation and deposits a layer of material for each slice. The material filament is pulled into the FDM head by the drive wheels.
Thermoplastic modeling material in the form of filament, feeds into the temperature-controlled FDM extrusion head, where it is heated to a semi-liquid state. The head extrudes and deposits the material in thin layers onto a foam or acrylic sheet base. The head directs the material into place with precision. The material solidifies, laminating to the preceding layer.

9. Fused Deposition Modeling (FDM)
Representative:
from Stratasys Inc.
Materials:
thermoplastic material such as wax, ABS plastic & elastomer
Adv. & Disadvantages:
 clean, simple, easy to operate
 A good variety of material
 Mid range performance/cost
 Relative low accuracy
 Poor strength in vertical direction
- Slow for building a mass part
Application areas:
- Conceptual modeling;
- Fit, form and functional test;
- Pattern for investment casting;
- The MABS (methy methacrylate ABS) material is particularly suitable for medical applications.
The FDM is capable of using a variety of inert, nontoxic materials such as wax, ABS plastic and elastomer. Each material comes wound on a spool in the form of a filament approximately 0.07" in diameter, so it is both easy to load and easy to store.
The materials may be stored at normal room temperature. Humidity must be eliminated when using ABS plastics. Exposing the filament material to temperatures outside normal office temperatures may cause the filament to fracture. It is recommended to store ABS plastic spools in dry boxes. These materials also can be stored inside two plastic bags. Enclosed a bag of desiccant with the spool. Place the plastic bags in a closed cabinet or sealed environment. This is to protect them from dust and moisture. Handle the spools of material with care. Sudden
or abrupt impacts to material spools may cause the filament to fracture.
Advantages:
- True desktop manufacturing system that can be run in office environment. There is no worry of exposure to toxic fume and chemicals.
- The process is clean, simple, easy to operate and produces no waste
- Fast building for bottle like structure or hollow parts
- Material is supplied in spool form which is easy to handle and can be changed in minute
- Materials used are very cost effective, typical parts cost under US$20
- A good variety of material is available including colorable ABS and Medical ABS, investment casting wax and elastomer
- Mid range performance/cost RP system
Disadvantages:
- Accuracy is relatively low and is difficult to build parts with complicated details
- Poor strength in vertical direction
- Slow for building a mass part

10. 2.3 Selective Laser Sintering (SLS)
1. Piston of the part built chamber lower by one layer;
2. Piston of powder cartridges raise up;
3. Roller spread powder evenly over the built surface;
4. Laser beam scan over the top of the part, melting the powder and fuse it to the previous layer;
5. Loop through the four steps to build the next layer.
Laser
Scanning
Mirror
Roller
Piston
Part
Support
Powder
cartridges
Build
Chamber
CAD files are transferred to the system, where they are sliced and drawn, one cross-section at a time, by applying the laser beam to a thin layer of powder. The laser beam fuses the powder particles to form a solid mass that matches the CAD design. As each layer is drawn, the prototypes take shape within the system.
The environment of the process chamber is tightly controlled. The temperature within the chamber is regulated at a level slightly lower than the melting point of the material being used.
The chamber is also filled with nitrogen to prohibit the oxidation of the materials at the elevated temperature. At the beginning of the process, a thin layer of powder is deposited onto the part building cylinder within the process chamber. A heat generated CO2 laser traces the cross section of the object, elevates the temperature of the powder to the melting point, and fuses the powder particles to form a layer of solid mass.
A new layer of powder is deposited on the top of the fused layer and the previous process is repeated with each layer fusing to the layer underneath.
After Processing, the part is removed from the process chamber and the powder falls away. SLS parts may then be require some post-processing, such as sanding, depending upon the application. Compared to other processes, however, this post processing is minimal.

11. Selective Laser Sintering (SLS)
 Representative:
from DTM Corporation
 Materials:
powder material such as nylon, wax, polycarbonate, metal, ceramic, elastomer, etc.
Adv. & Disadvantages:
 Large variety of material available
 Produced in short time
 No additional support required
 No post curing required
 Heat up powder & cool down part
 Smoothness of surface restricted
 Expensive running cost
 Toxic gases generated
 Application areas:
- Visual representation;
- durable enough for most functional tests;
- Pattern for making soft tooling, casting;
- Direct manufacture of metal mould;
- Small batch production run.
The material available for SLS are:
Nylon for prototypes
Polycarbonate
Wax for investment casting
CastForm PS. Polystyrene powder for investment casting
Advantages:
- Capable of producing the toughest part compared with other process
- Large variety of material can be used, including most engineering plastic, wax, metal, ceramic, etc.
- Parts can be produced in short time, normally at a rate of up to 1 inch per hour
- No post curing of parts is required
- During the building process, the part is fully supported by the powder and no additional support is required.
Parts can be built on top of others
Disadvantages:
- The powder material requires to heat up to the temperature below the melting point before the building process which takes about 2 hours. After building the parts, it also takes 5 to 10 hours to cool down before removing the parts from the powder cylinder.
- The smoothness of the surface is restricted to the size of the powder particles and the laser spot resulting that the surface of the part is always porous. Smooth surface can only be obtained by post processing.
- The process chamber requires continuous supply of nitrogen to provide a safe environment for the sintering process to be taken place resulting expensive running cost of the process.
- Toxic gases will be generated from the process which leads to an environmental issue.
- Process using different material require different license.

12. 2.4 Laminated Object Manufacturing (LOM)
1. The sheet material is stretched from the supply roller to the take-up roller;
2. The heated laminated roller passes over the sheet bonding it to the previous layer;
3. Laser cuts the profile of that layer and hatching the excess material for later removal;
4. Loop through the three steps to form a new layer.
The sheet material (paper with a thermo-setting resin glue on its under side) is stretched from a supply roller across a platform to a take-up roller on the other side. A heated roller passes over the paper bonding it to the platform or previous layer. A laser, focused to penetrate through one thickness of paper cuts the profile of that layer. The excess paper around and inside the model is etched into small squares to facilitate its removal. Meanwhile, this surplus material provides support for the developing model during the build process. The process of gluing and cutting continuous layer by layer until the model is complete.

13. Laminated Object Manufacturing (LOM)
 Representative:
from Helisys
 Materials:
sheet material such as paper, plastic, ceramic, composite etc.
Adv. & Disadvantages:
 A relatively high speed process
 No post curing required
 No support structure required
 Simple to use
 The most commonly used material is only paper
 Must be post processed immediately
 Restricted to build complex parts
 Fire hazard occasionally happened
 Application areas:
- Visual representation;
- Concept modeling;
- Pattern for sand casting;
Advantages:
- It is a relatively high speed process as the laser is only required to trace the contour and no need to scan the entire cross section. The more volume of material within the part, the more greater is the speed gain.
- Parts can be used immediately after the process and no post curing is required.
- No support structure is required as the part is supported by its own material.
- Simple to use and no environmental concern
Disadvantages:
- Although there is some choice of materials including paper, plastic, ceramic and composite, the most commonly used material is only paper. Others are still under development.
- The built parts absorb moisture quickly resulting that the built parts must be post processed immediately and impregnating with epoxy that is specially designed for LOM technology, such as LOMPOXY.
- Inherent deficiency in building fin-shape parts, in other words the process is restricted to build complex parts.
- Since it is very difficult, if not impossible, to remove the waste materials from inside, the process is incapable of building reentrant shapes.
- Fire hazard is occasionally happened when the working chamber becomes too hot.
Because of the wooden-like characteristic of the built parts and the large machine working envelop, this process is most suitable for building pattern for sand casting.

14. 2.5 3D Printing (3DP) less costly and less capable
Companies install them in offices
near their CAD systems for concept
modeling.
less costly and less capable
variation of RP technology

15. 3. Application cases of RP
Common applications of the RP technology:
Design
concept models
Marketing
models for tenders, customer feedback, presentations and brochures
Test & Analysis
functional testing;
strong models for wind
tunnel and stress analysis
Tooling
masters and patterns for a broad range of manufacturing processes
Medicine
artificial limbs, tools and instruments

16. 4. Rapid Tooling Making (RTM)
INDIRECT RPM: Pattern created by RP used to fabricate tool
- RP-fabricated part as master in making silicon-rubber mold (subsequently used as production mold)
- RP patterns to make sand molds for sand casting
- Fabrication of patterns of low-melting pt. materials for Investment casting
DIRECT RPM: RP used to make the tool itself
- 3D printing to create die geometry in metallic powders (followed by sintering & infiltration)
Soft tooling:
When companies need quantities of five to 50 parts for review, testing, and customer samples, prototype tooling is an attractive alternative. Using patterns produced from RP systems, companies can produce soft tooling in as few as three to ten days. An example is silicone rubber molds and vacuum casting. This limits the user to casting urethane materials, but the accuracy and detail is impressive.
Its application is mainly to produce plastics or metal prototypes in small batch by the gravity casting method. The casting materials normally used are PU, polyester, epoxy, tin-lead alloy (200 °C), pewter (230 °C) and zinc alloy (400 °C).
The batch size is from several pieces to over hundreds. Multiple moulds, sometimes, are required depend on the complexity of the parts. In fact, the ease of producing multiple moulds is one of the advantage of this technology.
Intermediate:
Rapid tooling (RT) for larger quantities in production materials can take twice as long, but this is still much shorter than the 12 to 16 weeks that many companies wait. As many as 20 different organizations are developing RT solutions and some show a lot of promise. Still, none of them can yet produce molds that match the qualities of those produced using conventional and high-speed machine tools.
1. Metal filled Epoxy Tooling – the indirect approach
Mould that is made of plastics is built from casting some special grade epoxy resins directly onto the RP master model. This mould making method does not require high precision machine tools as with conventional metal mould production. This technology of direct transferal from the master model allows large reduction in mould production costs and time.
In the past, plastics materials are not suitable for injection mould due to the lack of strength and the high shrinkage during curing. Many problems arise such as damage during mould making and moulding process. However, a special grade epoxy resin is developed for better strength and stiffness. Epoxy resin is a thermoset plastic that can be cast to shape before cured. This special grade epoxy resin is aluminum powder filled for strength, stiffness and thermal conductivity improvement.
The mould made by the this process is only suitable for injection moulding of plastics parts. Common plastics materials like ABS, POM, etc. can be produced from this mould in small batch size up to 3,000 pieces.
2. Powdered Metal Tooling – the direct approach
- Low Cost & Fast Tooling - The mould produced from the MRM process can mould the parts as good as the steel mould. However, the cost is only one third of the steel mould and the mould making time can be reduced from months to a few days.
- Fine Details and Thin Wall Design - Very fine details can be copied and thin wall parts can be produced due to the high injection pressure.
- For Plastics Parts Only.

17. 4. Rapid Tooling Making (RTM)
low volume (from tens to hundreds)
- Soft Tooling
Intermediate (from hundreds to thousands)
- Metal filled Epoxy
Tooling
- Powdered Metal
Soft tooling:
When companies need quantities of five to 50 parts for review, testing, and customer samples, prototype tooling is an attractive alternative. Using patterns produced from RP systems, companies can produce soft tooling in as few as three to ten days. An example is silicone rubber molds and vacuum casting. This limits the user to casting urethane materials, but the accuracy and detail is impressive.
Its application is mainly to produce plastics or metal prototypes in small batch by the gravity casting method. The casting materials normally used are PU, polyester, epoxy, tin-lead alloy (200 °C), pewter (230 °C) and zinc alloy (400 °C).
The batch size is from several pieces to over hundreds. Multiple moulds, sometimes, are required depend on the complexity of the parts. In fact, the ease of producing multiple moulds is one of the advantage of this technology.
Intermediate:
Rapid tooling (RT) for larger quantities in production materials can take twice as long, but this is still much shorter than the 12 to 16 weeks that many companies wait. As many as 20 different organizations are developing RT solutions and some show a lot of promise. Still, none of them can yet produce molds that match the qualities of those produced using conventional and high-speed machine tools.
1. Metal filled Epoxy Tooling – the indirect approach
Mould that is made of plastics is built from casting some special grade epoxy resins directly onto the RP master model. This mould making method does not require high precision machine tools as with conventional metal mould production. This technology of direct transferal from the master model allows large reduction in mould production costs and time.
In the past, plastics materials are not suitable for injection mould due to the lack of strength and the high shrinkage during curing. Many problems arise such as damage during mould making and moulding process. However, a special grade epoxy resin is developed for better strength and stiffness. Epoxy resin is a thermoset plastic that can be cast to shape before cured. This special grade epoxy resin is aluminum powder filled for strength, stiffness and thermal conductivity improvement.
The mould made by the this process is only suitable for injection moulding of plastics parts. Common plastics materials like ABS, POM, etc. can be produced from this mould in small batch size up to 3,000 pieces.
2. Powdered Metal Tooling – the direct approach
- Low Cost & Fast Tooling - The mould produced from the MRM process can mould the parts as good as the steel mould. However, the cost is only one third of the steel mould and the mould making time can be reduced from months to a few days.
- Fine Details and Thin Wall Design - Very fine details can be copied and thin wall parts can be produced due to the high injection pressure.
- For Plastics Parts Only.
Aluminum-filled epoxy mold, SL master, and molded thermoplastic parts