Rapid Prototyping Operations.pptx

8/9/2019 Rapid Prototyping Operations.pptx

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Rapid-Prototyping Operations


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Introduction

In the development of a new product, there is invariably a need to produce a single example,or prototype

This is required before allocating large amounts of capital to new production facilities orassembly lines.

Capital cost is very high and production tooling takes considerable time to prepare.Consequently, a working prototype is needed for design evaluation and troubleshootingbefore a complex system is ready to be produced and marketed.

A typical product development process is outlined in Fig. 21.3 This is an if iterative process naturally occurs when

a) errors are discovered

b) more-efficient or better design solutions are learned from the study of an earliergeneration prototype. The main problem with this approach, however, is that the production prototype can be

extremely time consuming.


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Parts Made by Rapid-Prototyping

Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

(a)

(b)

(c)

Figure 20.1 Examples of parts made by rapid-prototyping processes: (a) selection ofparts from fused-deposition modeling; (b) stereolithography model of cellular phone; and(c) selection of parts form three-dimensional printing. Source : Courtesy of Stratasys, Inc.,(b) and (c) Courtesy of 3D Systems, Inc.


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The technology that speeds up the iterative product-development processconsiderably is the concept and practice of rapid prototyping (RP)

Also called

! Desktop manufacturing! Digital manufacturing! Solid free-form fabrication

Developments in rapid prototyping began in the mid-1980s. The advantages of this technologyinclude the following:

! Physical models of parts produced from CAD data files can be manufactured in a matterof hours

this allow the rapid evaluation of manufacturability and design efficiency

! With suitable materials prototypes can be used in subsequent manufacturing operationsto produce the final parts.

Sometimes called direct prototyping


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Rapid-prototyping operations can be used in some applications to produce actual tooling formanufacturing operations.

Rapid-prototyping processes can be classified into three major groups:! Subtractive!

Additive! Virtual

As the names imply, subtractive processes involve material-removal from a workpiece that islarger than the final part.

Additive processes build up a part by adding material incrementally to produce the part. Virtual processes use advanced computer-based visualization technologies.


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Characteristics of Additive Rapid-Prototyping Technologies



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Subtractive Processes

Subtractive processes increasingly use computer-based technologies., such as:

Computer-based drafting packages, which can produce three-dimensionalrepresentations of parts.

Interpretation software, which can translate the CAD file into a format usable bymanufacturing software.

Manufacturing software, which is capable of planning the operations required toproduce the desired shape.

Computer-numerical-control machinery with the capabilities necessary to produce theparts.


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Additive Processes

Additive rapid-prototyping operations build models in layers

They consist of

! Stereolithography,! Fused-deposition modelling

! Ballistic particle manufacturing! Three-dimensional printing! Selective laser sintering! Laminated object manufacturing

The main difference between the various additive processes lies In the method of

producing the individual slices, which are typically 0.1 to 0.5 mm


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Additive Processeshow they work

The first step is to obtain a CAD file description of the part

The computer then constructs slices of the three-dimensional part (Fig. 20.2b)

Each slice is analyzed separately, and a set of instructions is compiled in order tomanufacture of the part.

Following this stage, the machines generally operate unattended and provide a rough partafter a few hours. The part then is subjected to a series of manual finishing operations (suchas sanding and painting) in order to complete the rapid-prototyping process.

The finishing operations are very labour intensive and that the production time is only aportion of the time required to obtain a prototype.

In general, additive processes are much faster than subtractive processes, taking as little asa few minutes to a few hours to produce a part.


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Mechanical Properties of Selected Materials for RapidPrototyping



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ComputationalSteps in Rapid

PrototypingFigure 20.2 The computationalsteps in producing astereolithography file.

a. Three-dimensionaldescription of each part.

b. The part is divided into slices(only one in 10 is shown).

c. Support material is planned.

d. A set of tool directions isdetermined to manufactureeach slice. Also shown is theextruder path at section A-Afrom (c) for a fused-deposition-modelingoperation.


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Fused-deposition modelling

In fused-deposition modelling (FDM) process (Fig. 20.3), a gantry-robot controlled extruderhead moves in two principal directions over a table; the table can be raised and lowered asneeded.

A Thermoplastic or wax filament is extruded through the small orifice of a heated die. Theinitial layer is placed on a foam foundation by extruding the filament at a constant rate whilethe extruder head follows a predetermined path (see Fig. 20.2d).

When the first layer is completed, the table is lowered so that subsequent layers can besuperimposed

Occasionally, complicated parts are required., such as the one shown in fig. 20.4a. Theseparts require support in key locations

The layers in a FDM machine are determined by the extruder-die diameter (0.5 - 0.25 mm)


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Fused-Deposition-Modeling


Figure 20.3 (a) Schematic illustration of the fused-deposition-modeling process. (b) TheFDM 5000, a fused-deposition-modeling machine. Source : Courtesy of Stratysis, Inc.


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Support Materials and Structures in Parts


Figure 20.4 (a) A part with a protruding section which requires support material.(b) Common support structures used in rapid-prototyping machines. Source: P. F.Jacobs, Rapid Prototyping & Manufacturing: Fundamentals of Stereolithography. Society of Manufacturing Engineers, 1992.


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Stereolithography

This is a very common rapid-prototyping process that actually was developed before fused-depositionmodelling

Also known as SLA

This process (Fig. 20.5) is based on the principle of curing (hardening) a liquid photopolymer into aspecific shape

A vat containing a photopolymer can be raised or lowered

A laser generating an ultraviolet beam is focused upon a selected surface area of the photopolymer andthen moved around in the x-y plane. The beam cures that portion of the photopolymer

Note that support structures are need like FDM however these can be removed upon curing After completion the part is removed and cleaned ultrasonically in an alcohol bath after this supports are

removed.

The smallest tolerance that can he achieved in stereo lithography depends on the sharpness of the focusof the laser; typically, it is around 0.0125mm

Total cycle times in stereolithography range from a few hours to a day-without post-processing such assanding and painting.


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Stereolithography


Figure 20.5 Schematic illustration of the stereolithography process.


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Two-Button Computer Mouse


Figure 20.6 A two-button computer mouse.Source : Courtesy of 3D Systems, Inc.


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Selective laser sintering

Selective laser sintering (SLS) is a process based on the sintering of either non-metallic ormetallic powders selectively into an individual object.

Selective Laser-sintering machines are marketed 3D systems are called 3D printers

Historically has been associated with ballistic-particle manufacturing

The basic elements in this process are shown in Fig. 20.7. The bottom of the processingchamber is equipped with two cylinders:

! A powder feed cylinder, which is raised incrementally to supply powder to the part-buildcylinder through a roller mechanism.

! A part-build cylinder, which is lowered incrementally as the part is being formed


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Selective laser sintering

Principal of operation

! A thin layer of powder is first deposited in the part-build cylinder.! A Laser beam guided by a process-control computer using instructions generated by

the three-dimensional CAD program of the desired part is focused on that layer, tracingand sintering a particular cross-section into a solid mass.

! The powder in other areas remains loose, yet it supports the sintered portion.! When finished the loose particles are shaken off, and the part is recovered.! the part does not require further curing-unless it is a ceramic., which has to be fired to

develop strength.

A variety of materials can be used in this process, including polymers (such as ABS, PVC,

nylon, polyester, polystyrene, and epoxy), wax, metals, and ceramics with appropriate binders.


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Selective-Laser-Sintering


Figure 20.7 Schematic illustration of the selective-laser-sintering process.Source : After C. Deckard and P. F. McClure.


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Ballistic-particle manufacturing

In the ballistic-particle manufacturing process, a stream of a material (such as plastic,ceramic, metal, or wax) is ejected through a small orifice at a surface (target). Using an ink-Jet type mechanism

The mechanism uses a piezoelectric pump, which operates when an electric charge. Whenapplied, generates a shock wave that propels 50 m droplets at a rate of 10,000 per second.The operation is repeated in a manner similar to other processes.

! Three-dimensional printing (3DP ) is related to ballistic-particle manufacturing with theexception that (instead of depositing the prototype material) the print head deposits aninorganic-binder material.

! The parts produced through 3DP are somewhat porous and, therefore, may lackstrength.


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Three-Dimensional-Printing


Figure 20.8 Schematic illustration of the three-dimensional-printing process.Source : After E. Sachs and M. Cima.


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Three-Dimensional-Printing to Produce Metal Parts


Figure 20.9 Three-dimensional-printing using (a) part-build, (b) sinter, and (c) infiltration stepsto produce metal parts. (d) An example of a bronze-infiltrated stainless-steel part producedthrough three-dimensional printing. Source : Courtesy of ProMetal.


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Fuselage Fitting Made by Three-Dimensional-Printing


(a)

(b)

Figure 20.10 A fitting required for a helicopter fuselage. (a) CAD representation with addeddimensions. (b) Dies produced by three-dimensional printing. (c) Final forged workpiece.Source : Courtesy of ProMetal.


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Laminated-Object-Manufacturing


Figure 20.11 (a) Schematic illustration of the laminated-object-manufacturingprocess. (b) Crankshaft-part examples made by LOM. Source: (a) Courtesyof Helsis, Inc. (b) After L. Wood.


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Direct Manufacturing and Rapid Tooling

While extremely beneficial as a demonstration and visualization tool, rapid-prototypingprocesses also have been used as a manufacturing step in production. There are two basicmethodologies used:

1. Direct production of engineering metal, ceramic, and polymer components or parts byrapid prototyping.

2. Production of tooling by rapid prototyping for use in further manufacturing Operations



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Invisalign Orthodontic Aligners


(a) (b)

Figure 20.12 (a) An aligner for orthodontic use manufactured using a combination of rapidtooling and thermoforming. (b) Comparison of conventional orthodontic braces to the useof transparent aligners. Source : Courtesy of Align Technologies, Inc.


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Manufacturing of InvisalignOrthodontic Aligners


Figure 20.13 The manufacturing sequence for Invisalign orthodontic aligners. (a) Creationof a polymer impression of the patients teeth. (b) Computer modeling to produce CADrepresentations of desired tooth profiles. (c) Production of incremental models of desiredtooth movement. An aligner is produced by thermoforming a transparent plastic sheet againstthis model. Source : Courtesy of Align Technologies, Inc.

(a)

(b)

(c)


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Investment Casting Using Rapid-Prototyped Wax Parts


Figure 20.14 Manufacturing steps for investment casting that uses rapid-prototyped waxparts as blanks. This method uses a flask for the investment, but a shell method also canbe used. Source : Courtesy of 3D Systems, Inc.


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Rapid Tooling for a Rear-Wiper Motor Cover


Figure 20.15 Rapid tooling for a rear-wiper motor cover.Source : Courtesy of 3D Systems, Inc.

Rapid Prototyping Operations.pptx

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