Defence university collage

Department of Production engineering

Manufacturing systeM engineering Course of Modern Manufacturing System PE 6412

Term Paper

Title: Rapid prototyping for agility in manufacturing (SLS and MDF)

Prepared By: Diribssa Tadesse

Instructor: Prof. Ramaprasad.H

Abstract Prototyping or model making is one of the important steps to finalize a product design. It

helps in conceptualization of a design. Rapid prototyping (RP) is used to save time and cut

costs at every stage of the product development process. Prototypes can now be produced in a

matter of hours that have typically taken weeks or even months to make.

The purpose of this paper is to present a conceptual model of integration of CAD/CAM with

Rapid PrototypingTechnology (RPT) for infusing agility in traditional manufacturing

environment. With increased competition from the global economy, manufacturers face the

challenge of delivering new customized products more quickly than before to meet customer

demands. A delayed development or delivery is nothing but business failure. In this paper

rapid prototyping technique is discussed in detail and its significance in the agile

manufacturing is highlighted.

Agility requires the capability to survive and prosper in a competitive environment of

continuous and unpredictable change by reacting quickly and effectively to changing

markets, driven by customer-designed products and services. There is a demand for tooling

with complex geometry to be produced quickly at low cost. This paper provides an overview

of RP technology in brief and emphasizes on their ability to shorten the product design and

development process. Classification of RP processes and details of few important processes is

given. An attempt has been made to include some important factors to be considered before

starting part deposition for proper utilization of potentials of RP processes.

Introduction

Prototyping or model making is one of the important steps to finalize a product design. It

helps in conceptualization of a design. Before the start of full production a prototype is

usually fabricated and tested. Manual prototyping by a skilled craftsman has been an ageold

practice for many centuries. Second phase of prototyping started around mid-1970s,

when a soft prototype modeled by 3D curves and surfaces could be stressed in virtual

environment, simulated and tested with exact material and other properties. Third and the

latest trend of prototyping, i.e., Rapid Prototyping (RP) by layer-by-layer material

deposition, started during early 1980s with the enormous growth in Computer Aided

Design and Manufacturing (CAD/CAM) technologies when almost unambiguous solid

models with knitted information of edges and surfaces could define a product and also

manufacture it by CNC machining.

In the design and development of new products, making sufficient quantity of

prototypes for assessment requires tools (Juster 1994). The important issue is to produce

them quickly and cheaply. Otherwise the development cost can be expensive and fail to get

the prototype to the market as soon as possible. So far, traditional methods for production

of tooling either for prototype or large-scale batch rely on CNC and EDM machining.

LITERATURE REVIEW

BASIC PRINCIPLE OF RAPID PROTOTYPING PROCESSES

RP process belong to the generative (or additive) production processes unlike subtractive

or forming processes such as lathing, milling, grinding or coining etc. in which form is

shaped by material removal or plastic deformation. In all commercial RP processes, the

part is fabricated by deposition of layers contoured in a (x-y) plane two dimensionally. The

third dimension (z) results from single layers being stacked up on top of each other, but not

as a continuous z-coordinate. Therefore, the prototypes are very exact on the x-y plane

but have stair-stepping effect in z-direction. If model is deposited with very fine layers,

i.e., smaller z-stepping, model looks like original. RP can be classified into two

fundamental process steps namely generation of mathematical layer information and

generation of physical layer model.

WHAT IS RAPID PROTOTYPING TECHNOLOGY (RPT)?

The term rapid prototyping (RPT) refers to a class of technologies that can automatically

construct physical models from Computer-Aided Design (CAD) data. These "three

dimensional printers" allow designers to quickly create tangible prototypes of their designs,

rather than just two-dimensional pictures. Such models have numerous uses. They make

excellent visual aids for communicating ideas with co-workers or customers. In addition,

prototypes can be used for design testing. Designers have always utilized prototypes; RPT

allows them to be made faster and less expensively. In addition to prototypes, RP techniques

can also be used to make tooling (referred to as rapid tooling) and even production-quality

parts (Rapid manufacturing). For small production runs and complicated objects, rapid

prototyping is often the best manufacturing process available.

RAPID PROTOTYPING PROCESSES

The professional literature in RP contains different ways of classifying RP processes.

However, one representation based on German standard of production processes classifies

RP processes according to state of aggregation of their original material.

Here, few important RP processes namely Stereolithography (SL), Selective Laser

Sintering (SLS), Fused Deposition Modeling (FDM) and Laminated Object Manufacturing

(LOM) are described.

Rapid Prototyping achievements

• Reduction in prototyping times (from weeks to days)

• Reduction in prototyping costs (from thuousands to hundreds $)

• Increase of the possible design iterations (from 2-3 to 8-9)

• Increase of possible form, fit, function tests

Shorter design cycle

Reduced Time-to-Market.

Useful Conditions for rapid prototyping(RP)

• Single unique item or small number of copies needed

• Shape of object is in computer form

• Shape is too complex to be economically generated using conventional methods

Advantages of RP

CAD data files can be manufactured in hours.

Tool for visualization and concept verification.

Prototype used in subsequent manufacturing operations to obtain final part

Tooling for manufacturing operations can be produced

Cost reduction is up to 50%.

Processing time reduction up to 75%.

High design fiexibility to enable short term component Modifications

Prototyping can increase creativity through quicker user feedback.

Encourages active participation among users and producers.

Early visibility of the prototype gives users an idea of what the final system looks

like, and mainly decreases delivery time.

Disadvantages of Rapid Prototyping

Not suitable for large work pieces.

Often lack flexibility.

Project management is difficult.

Possibility of causing system to be left unfinished.

Rapid Prototyping Technologies

• Six basic commercial technologies:

StereoLithography (SL)

Laminated Object Manufacturing (LOM)

Selective Laser Sintering (SLS)

Fused Deposition Modeling (FDM)

Solid Ground Curing (SGC)

Inkjet technologies (3D Plotting, MJM, 3DP..)

Fig1 Examples of pars made by RP processes.

1. Stereolithography (SL)

3D Systems, Valencia, CA

patent 1986, beginning of RP

photopolymerization using UV laser

accuracy 0.025 mm

epoxies, acrylates

Fig 2a Stereolithography process.

Fig2b Stereo lithography process.

2. Laminated Object Manufacturing LOM

Cubic Technologies, Carson, CA (former Helisys)

patent 1985

cross-sectional cutouts fused together

accuracy 0.076 mm

paper, plastic

Fig 3 Laminated Object Manufacturing LOM process

Fig 4 LOM process

Laminated implies laying down of layers which are adhesively bonded to one another

Uses layer of paper or plastic sheets with heat activated glue on one side of the

product parts

Excess material to be removed manually

Simplified by preparing the laser to burn perforations in cross-sectional pattern

LOM uses sheets as thin as 0.05mm

Compressed paper has appearance and strength of soft wood, and often mistaken for

elaborate wood carvings.

3. Solid-Base Curing (SBC)

Cubital, Troy, MI (Failed 2000)

patent 1991

photopolymerization using UV light passing through a mask

accuracy 0.510 mm

Photopolymers

• Also called Solid ground curing

• Entire slices of part are manufactured at one time

• So large throughput is achieved

• Most expensive & time consuming

• The entire process is shown

4. Inkjet technologies(3D Plotting, MJM, 3DP)

a) 3D Plotting

Solidscape Inc., Marrimack, NH

Inkjet technology

Dual heads deposit part material (thermoplastic) and support material (wax)

Accuracy 0.025 mm (layers 0.013 mm)

Thermoplastic (build) Wax, fatty esters (support)

3D Plotting applications:

Spare pare production like gear, roller bearings, machine parts etc

b) Multi-jet Modelling (MJM)

•Accelerated Tech., 3D Systems, Solidimension Ltd

Inkjet technology

Multiple heads deposit support material and part material cured immediately by UV

light

Accuracy 0.020 mm

Photopolymers

c) 3D Printing(3DP)

Z Corporation, Burlington, MA

Printing head deposits binder solution onbuild powder

Accuracy 0.076 mm

Waxes, acrylates, epoxies

Schematic illustration of the three-dimensional-printing process. Source:

After E. Sachs and M. Cima.

3-D Printing process

• Print head deposits an inorganic binder material

• Binder directed onto a layer of ceramic metal powder

• A piston supporting the powder bed is lower incrementally with each step a layer is

deposited and unified by binder

• Commonly used materials – Aluminum oxide, silicon carbide, silica and zirconium.

• Common part produced by 3-D printing is a ceramic casting shall

• Curing around 150 C – 300 F Firing – 1000 C – 1500 C

5. Selective Laser Sintering (SLS)

3D Systems, Valencia, CA (former DTM)

patent 1989, Carl Deckard’s master thesis

fusing polymeric powders with CO2 laser

accuracy 0.040 mm

polycarbonate, nylon, wax, glass-filled nylon, powder coated metals or ceramics

a)

b)

Fig5. SLS process

• SLS based on sintering of nonmetallic powders onto a selective individual objects

• Basic elements in this process are bottom of processing chambers equipped with two

(2) cylinders

• Powder feed cylinder which is raised incrementally to supply powder to part-build

cylinder through a roller mechanism

• Part-build cylinder which is lowered incrementally to where the sintered part is

formed.

• Set of the proper computer files and the initiation of the production processes

• Machine operate unattended and provide rough part after few hours

• Finishing operations as sanding and painting

• Labor intensive & production time varies from few minutes to few hours

• Layer of powder is first deposited on part build cylinders

• A laser beam controlled by instruction from 3-D file is focused on that layer tracing &

sintering a particular cross-section into a solid mass & dust is taken off.

• Another layer of powder is now deposited this cycle is repeated again and dust is

shaken off.

One of the new approaches is to use Selective Laser Sintering (SLS) for production of

tooling directly from a computer aided drawing (CAD). SLS is one of the many rapid

prototyping technologies that are based on a layer manufacturing approach. It was

developed for polymers initially and has been extended to metals. The processing sequence

in SLS involves many steps as follows: A three-dimensional CAD solid model of the part

is represented by a series of triangles and stored as an STL file. The STL file is then

divided into many layers. A CO2 laser beam scans the cross-section of the object and fuses

the wax and phenolic resin coated metal powders together and to the underlying layer.

After the first layer is built, another fresh layer of powder is added.

In Selective Laser Sintering (SLS) process, fine polymeric powder like polystyrene,

polycarbonate or polyamide etc. (20 to 100 micrometer diameter) is spread on the substrate

using a roller. Before starting CO2 laser scanning for sintering of a slice the temperature of

the entire bed is raised just below its melting point by infrared heating in order to minimize

thermal distortion (curling) and facilitate fusion to the previous layer. The laser is

modulated in such away that only those grains, which are in direct contact with the beam,

are affected (Pham and Demov, 2001). Once laser scanning cures a slice, bed is lowered

and powder feed chamber is raised so that a covering of powder can be spread evenly over

the build area by counter rotating roller.

6. Fused Deposition Modeling (FDM)

Stratasys, Eden Prarie, MN

patent 1992

robotically guided fiber extrusion

accuracy 0.127 mm

casting and machinable waxes, polyolefin, ABS, PC

• A gantry robot controlled extruder head moves in two principle directions over a table

• Table can be raised or lowered as needed

• Thermo plastic or wax filament is extruded through the small orifice of heated die

• Initial layer placed on a foam foundation with a constant rate

• Extruder head follows a predetermined path from the file

• After first layer the table is lowered and subsequent layers are formed

In Fused Deposition Modeling (FDM) process a movable (x-y movement) nozzle on to a

substrate deposits thread of molten polymeric material. The build material is heated

slightly above (approximately 0.5 C) its melting temperature so that it solidifies within a

very short time (approximately 0.1 s) after extrusion and cold-welds to the previous layer

as shown in figure 8. Various important factors need to be considered and are steady

nozzle and material extrusion rates, addition of support structures for overhanging features

and speed of the nozzle head, which affects the slice thickness. More recent FDM systems

include two nozzles, one for part material and other for support material. The support

material is relatively of poor quality and can be broken easily once the complete part is

deposited and is removed from substrate. In more recent FDM technology, water-soluble

support structure material is used. Support structure can be deposited with lesser density as

compared to part density by providing air gaps between two consecutive roads.

Fig8. Selective Laser Sintering System

Fig. Fused Deposition Modeling Process (after Pham and Demov, 2001

Fused Deposition Modeling (FDM) is the rapid prototyping technology that forms three-

dimensional objects from CAD generated solid or surface models. A temperature-controlled head

extrudes ABS plastic wire layer by layer and as a result, the designed object emerges as a fully

functional three-dimensional part.

Why use rapid prototyping? Rapid prototyping (RP) is used to save time and cut costs at

every stage of the product development process. Prototypes can now be produced in a matter of

hours that have typically taken weeks or even months to make.

“With rapid prototyping, companies are now able to verify and change designs with much less

investment in time and money”, “And if Idaho manufacturers utilize this technology, it should

improve their capability to bring products into the marketplace in a more timely manner and at a

more competitive price.”

“WaterWorks uses a water-based solution to simply wash away the supports right down the drain.

Your model is left smooth and clean – no nicks or scratches – and the fine details remain intact.

You’ll find that the convenience of this special feature lets your designers, engineers and

manufacturers get down to business, instead of spending their time removing supports from

newly created prototypes.”

FDM Features:

• Competitive with other RP technologies

• Strong and durable model

• APS plastic (with color choices) and Elastomer material choices

• Water proof, paintable

• Maximum size- 10” x 10” x 16”

Rapid prototype models can be used as design evolution, manufacturing tools (assemblies,

test fixtures, visual aids), sales tools (internal and external), estimating tools (prototype parts

included in drawings) and master patterns for composite molds.

The time it takes to develop a concept from its initial phase to its introduction to the

marketplace can be critical. Manufacturers are always looking for ways to shorten this process.

With the assistance of computer-assisted design tools, such as CAD, manufacturers have taken

significant steps toward utilizing these tools to design and develop new products.

“Traditionally, Engineers have created three-dimensional models and prototypes by using

conventional methods of fabrication, such as machine tooling. Long turnaround times result in

delays in getting products to market. Rapid prototyping (RP) was developed to automate new

product development and to shorten the development cycle significantly.”- Stratasys Inc.

For more information on Rapid Prototyping, contact Steve Hatten at 426-2182 or

shatten@boisestate.edu.

Applications of Rapid prototyping (RP)

• Production of individual parts

• Production of tooling by Rapid Prototyping (Rapid Tooling)

Benefits to Rapid prototyping (RP) Technologies

Visualization, verification, iteration, and design optimization

Communication tool for simultaneous engineering

Form-fit-function tests

Marketing studies of consumer preferences

Metal prototypes fabricated from polymer parts

Tooling fabricated from polymer parts

Conclusions

Rapid prototyping (RP) is used to save time and cut costs at every stage of the product

development process. Prototypes can now be produced in a matter of hours that have typically

taken weeks or even months to make. “With rapid prototyping, companies are now able to verify

and change designs with much less investment in time and money”,

• Rapid prototyping is a new tool, which used appropriately ...

– allows the manufacturing enterprise to run smoother

– increases throughput and product quality

• New uses and applications are discovered everyday

• Future areas include new materials directly deposited (metals, ceramics)

In general Rapid Prototyping decreases development time by allowing corrections to a

product to be made early in the process. By giving engineering, manufacturing, marketing

and purchasing a look at the product early in the design process, mistakes can be corrected

and changes can be made while they are still inexpensive. Rapid Prototyping improves

product development by enabling better communication in a concurrent engineering

environment. In the given paper the proposed conceptual model of CAD/CAM and RPT

integration can yield valuable and interesting developments for achieving agility and thereby

acquire global competitiveness.

REFERENCES

1. Internet

2. Chua, C.K., Leong, K.F. (2000) Rapid Prototyping: Principles and Applications in

Manufacturing, World Scientific.

3. Gebhardt, A., (2003) Rapid Prototyping, Hanser Gardner Publications, Inc., Cincinnati.

4. Pandey, P.M., Reddy N.V., Dhande, S.G. (2003a) Slicing Procedures in Layered

Manufacturing: A Review, Rapid Prototyping Journal, 9(5), pp. 274-288.

5. Pandey, P.M., Reddy, N.V., Dhande, S.G. (2003b) Real Time Adaptive Slicing for

Fused Deposition Modelling, International Journal of Machine Tools and Manufacture,

43(1), pp 61-71.