RAPID PROTOTYPIN

GPRESENTED BY,

E.CHELLADURAI

B.E MECHANICAL

(2013-2017)

INTRODUCTION

• Rapid prototyping technologies are able to produce physical model in a layer by layer manner directly from their CAD models without any tools, dies and fixtures and also with little human intervention.

• RP is capable to fabricate parts quickly with too complex shape easily as compared to traditional manufacturing technology.

• RP helps in earlier detection and reduction of design errors.

STEPS IN RAPID PROTOTYPING

Create a CAD model of the design

Convert the CAD model to STL format (stereo lithography)

Slice the STL file into thin cross-sectional layers

Construct the model one layer atop another

Clean and finish the model

CAD Model Creation:• First, the object to be built is modeled using a

Computer-Aided Design (CAD) software package or coordinate measuring machine or laser scanner.

• Solid modelers, such as Pro/ENGINEER, tend to represent 3-D objects more accurately than wire-frame modelers such as AutoCAD, and will therefore yield better results.

• This process is identical for all of the RP build techniques.

Conversion to STL Format:

• To establish consistency, the STL (stereo lithography, the first RP technique) format has been adopted as the standard of the rapid prototyping industry and acts as the interface b/w CAD software and machines.

• The second step, therefore, is to convert the CAD file into STL format. This format represents a three-dimensional surface as an assembly of planar triangular facets.

• STL files use planar elements, they cannot represent curved surfaces exactly. Increasing the number of triangles improves the approximation.

Slice the STL File: • In the third step, a pre-processing program

prepares the STL file to be built. • The pre-processing software slices the STL model

into a number of layers from 0.01 mm to 0.7 mm thick, depending on the build technique.

• The program may also generate an auxiliary structure to support the model during the build. Supports are useful for delicate features such as overhangs, internal cavities, and thin-walled sections.

Layer by Layer Construction:• The fourth step is the actual construction of the

part. • RP machines build one layer at a time from

polymers, paper, or powdered metal. • Most machines are fairly autonomous, needing

little human intervention.

Clean and Finish: • The final step is post-processing. This involves

removing the prototype from the machine and detaching any supports.

• Some photosensitive materials need to be fully cured before use

• Prototypes may also require minor cleaning and surface treatment.

• Sanding, sealing, and/or painting the model will improve its appearance and durability.

FUNDAMENTALS OF RAPID PROTOTYPING

The Rapid Prototyping Wheel depicting the 4 major aspects of RP

• INPUT• METHOD• MATERIAL• APPLICATION

Input refers to the electronic information required to describe the physical object with 3D data.

There are two possible starting points – a computer model or a physical model.

The computer model created by a CAD system can be either a surface model or a solid model

On the other hand, 3D data from the physical model is not at all straightforward.

It requires data acquisition through a method known as reverse engineering.

In reverse engineering, a wide range of equipment digitizer, to capture data points of the physical model and “reconstruct” it in CAD system.

INPUT

METHOD While they are currently more than 20

vendors for RP systems, the method employed by each vendor can be generally classified into the following categories:• photo-curing, • cutting and gluing/joining, • melting and solidifying/fusing and

joining/binding. Photo-curing can be further divided into categories of • single laser beam, • double laser beams and • masked lamp

MATERIAL The initial state of material can come in either

• solid, liquid or powder state. In solid state, it can come in various forms such

• a pallets, wire or laminates. The current range materials include

• paper, nylon, wax, resins, metals and ceramics. APPLICATIONS

Applications can be grouped into:• Design• Engineering, Analysis and

Planning• Tooling and Manufacturing

A wide range of industries can benefit from RP and these include, but are not limited to, • aerospace, • automotive, • biomedical, consumer, • electrical and electronics products.

ADVANTAGES• Almost any shape or geometric feature can be produced.• Reduction in time and cost (could range 50 –90%. Wohler)• Errors and flaws can be detected at an early stage.• RP/RM can be used in different industries and fields of life

(medicine, art and architecture, marketing..)• Discussions with the customer can start at an early stage.• Assemblies can be made directly in one go.• Material waste is reduced.• No tooling is necessary.• The designers and the machinery can be in separate places.•  

DISADVANTAGES

• The price of machinery and materials.• The surface is usually rougher than machined

surfaces.• Some materials are brittle.• The strength of RP-parts are weaker in z-

direction than in other.

TYPES OF RP─────────────────────────────────────────────────────────────────────────────────────

LIQUID-BASED• Liquid-based RP systems have the initial form of its

material in liquid state. • Through a process commonly known as curing, the

liquid is converted into the solid state. SOLID-BASED• Except for powder, solid-based RP systems are

meant to encompass all forms of material in the solid state.

• In this context, the solid form can include the shape in the form of a wire, a roll, laminates and pallets.

POWDER-BASED• In a strict sense, powder is by-and-large in the solid

state. • However, it is intentionally created as a category

outside the solid-based RP systems to mean powder in grain-like form.

STEREOLITHOGRAPHY APPARATUS(SLA)

• Stereo lithography is the most widely used RP-technology. It can produce highly

• Accurate and detailed polymer parts. SLA was the first RP-process, introduced in 1988 by 3D Systems Inc.

Principle SLA uses a low-power, highly focused UV laser to produce a three dimensional object in a vat of liquid photosensitive polymer.

Process• This is based on selective polymerization of a

photosensitive resin using ultraviolet light.• In this system, an ultraviolet laser beam is focused

on the top layer of photo sensitive resin contained in a vat.

• The beam is positions and moved in horizontal X and Y directions to polymerize the resin within the boundary a particular cross-section.• The cured layer of polymer is lowered by a platform attached to it, so that a fresh layer of liquid resin covers the cured layer.Working

A vat containing a mechanism whereby a platform can be lowered and raised is filled with a photocurable liquid-acrylate polymer.

The liquid is a mixture of acrylic monomers, oligomers (polymer intermediates), and a photoinitiator ( a compound that undergoes a reaction upon absorbing light).

At its highest position (depth a), a shallow layer of liquid exists above the platform.

A laser generating an ultraviolet (UV) beam is focused upon a selected surface area of the photopolymer and then moved around in the x-y plane.

The beam cures that portion of the photopolymer and thereby produces a solid body.

 

The platform is then lowered sufficiently to cover the cured polymer with another layer of liquid polymer, and the sequence is repeated.

The process is repeated until level b is reached. Thus far, we have generated a cylindrical part with a constant wall thickness. Note that the platform is now lowered by a vertical distance ab.

At level b, the x-y movements of the beam define a wider geometry, so we now have a flange-shaped portion that is being produced over the previously formed part.

After the proper thickness of the liquid has been cured, the process is repeated, producing another cylindrical section between levels b and c.

Note that the surrounding liquid polymer is still fluid (because it has not been exposed to the ultraviolet beam) and that the part has been produced from the bottom up in individual ‘slices’. The unused portion of the liquid polymer can be used again to make another part or another prototype.  

   

Abbreviation: SLA

Material type: Liquid(Photopolymer) Materials: Thermoplastics(Elastom

ers)Min layer thickness: 0.02 mmSurface finish: SmoothBuild speed: AverageApplications: Form/fit testing,

Functional testing, Very detailed parts, Presentation models, Snap fits..

ADVANTAGES DISADVANTAGES

Achieving accuracy in industries

Capable of high detail and thin walls

Good surface finish High part complexity

Requires post-curing. Some war page,

shrinkage and curl due to phase change.

Limited materials (Photo polymers).

Support structures always needed. Removal of support structures can be difficult.

FUSED DEPOSITION MODELLING (FDM)

• (FDM) is a solid-based rapid prototyping method that extrudes material, layer-by-layer, to build a model.

• It was developed by StratasysPrinciple A plastic or wax material is extruded through a nozzle that traces the part´s cross sectional geometry layer by layer

Process• The FDM technique relies on melting and selectively

depositing a thin filament of thermoplastic polymer in a cross-hatching fashion to form each layer of the part.

• The material is in the form of a wire supplied in sealed spools which is mounted on the machine and the wire is threaded through the FDM head.

• The head is moved in the horizontal X and Y directions for producing each layer through zigzag movements.

• The supporting table moves in the vertical direction and is lowered after the completion of each layer.

Working• In FDM process, a gantry robot-controlled

extruder head moves in two principal directions over a table, which can be raised and lowered as needed.

• A thermoplastic filament is extruded through the small orifice of a heated die.

• The initial layer is placed on a foam foundation by extruding the filament at a constant rate while the extruder head follows a predetermined path.

 

 • When the first layer is completed, the table is

lowered so that subsequent layers can be superimposed.

• In some parts, the filament is required to support the slice where no material exists beneath to support it.

• The solution is to extrude a support material separately from the modelling material. The use of such support structures allows all of the layers to be supported by the material directly beneath them.

• The support material is produced with a less dense filament spacing on a layer, so it is weaker than the model material and can be broken off easily after the part is completed.

• The layers in an FDM model are determined by the extrusion-die diameter, which typically ranges from 0.050 to 0.12mm. This thickness represents the best achievable in the vertical direction.

• In the x-y plane, dimensional accuracy can be as fine as 0.025mm

 

Abbreviation: FDM

Material type: Solid(Filaments)Materials: ABS, Polycarbonate,

Poly phenyl sulfonite ;Elastomers

Min layer thickness: 0.15mmSurface finish: RoughBuild speed: SlowApplications: Form/fit testing,

Functional testing, Small detailed parts, Presentation models.

ADVANTAGES DISADVANTAGES Durable parts can be made Minimal wastage Easy handling, material changeover and support removal. No post curing. Office environment friendly. Low end, economical machines. Easy material changeover and support removal. Variety of materials

Longer to build Low accuracy compared to SLA Not good for small features, details and thin walls. Surface finish is rough. Support design / integration / removal is difficult. Weak Z-axis. Slow on large / dense parts. Supports required on some materials / geometries.

LAMINATED OBJECT MANUFACTURING (LOM)• As the name implies the process

laminates thin sheets of film (paper or plastic) .

• The laser has only to cut/scan the periphery of each layer

Principle The build material is placed on a platform and a heated roller bonds it to the previous layer and the sheet is cut to required profile by laser and glued to previous sheet.

Process• The main components of the system are a feed

mechanism that advances a sheet over a build platform, a heater roller to apply pressure to bond to the layer below, and a laser to cut the outline of the part in each sheet layer.

• After each cut is completed, the platform lowers by a depth equal to the sheet thickness (0.05 –0.5 mm). • The laser cuts the outline and the process is repeated until the part is completed.• After a layer is cut, the extra material remains in place to support the part.

Working Lamination implies a laying down of layers that are

bonded adhesively to one another. The simples and least expensive versions of LOM

involve using control software and vinyl cutters to produce the prototype.

Vinyl cutters are simple CNC machines that cut shapes from vinyl or paper sheets.

Each sheet then has a number of layers and registration holes, which allow proper alignment and placement onto a build fixture.

 

LOM systems are highly economical and are popular in schools and universities because of the hands-on demonstration of additive manufacturing and production of parts by layers.

LOM systems can be elaborate; the more advanced systems use layers of paper or plastic with a heat-activated glue on one side to produce parts.

The desired shapes are burned into the sheet with a laser, and the parts are built layer by layer.

On some systems, the excess material must be removed manually once the part is completed. Removal is simplified by programming the laser to burn perforations in crisscrossed patterns.

The resulting grid lines make the part appear as if it had been constructed from gridded paper (with squares printed on it, similar to graph paper).

   

Abbreviation: LOM

Material type: Solid(Sheets)Materials: Thermoplasticssuchas

PVC; Paper; Composites(Ferrousmetals; Non-ferrousmetals; Ceramics)

Min layer thickness: 0.05mmSurface finish: RoughBuild speed: FastApplications: Form/fit testing,

Less detailed parts, Rapid tooling patterns…

ADVANTAGES DISADVANTAGES

Wide range of materials

Fast Build time High accuracy durability High part complexity

Requires post-curing. Overheated roller

may damage sheet Limited materials

(Photo polymers). Support structures

always needed.

SELECTIVE LASER SINTERING (SLS)

• SLS is a process based on the sintering of non metallic or (less commonly) metallic powders selectively into an individual object.

• SLS was patented in 1989.Principle It uses a moving laser beam to trace and selectively sinter powdered polymer and/or metal composite materials.

Process• In this process a high power laser beam selectively melts and

fuses powdered material spread on a layer.• The powder is metered in precise amounts and is spread by a

counter-rotating roller on the table.

• A laser beam is used to fuse the powder within the section boundary through a cross-hatching motion.

• The table is lowered through a distance corresponding to the layer thickness (usually 0.01 mm) before the roller spreads the next layer of powder on the previously built layer.

• The unsintered powder serves as the support for overhanging portions, if any in the subsequent layers.Working First, a thin layer of powder is deposited in the part-

build cylinder Then, a laser beam guided by a process-control

computer using instructions generated by the 3D CAD program of the desired part is focused on that layer, tracing and sintering a particular cross-section into a solid mass.

The powder in other areas remains loose, yet it supports the sintering portion.

 

Another layer of powder is then deposited; this cycle is repeated again and again until the entire 3D part has been produced.

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.

It is most common to use polymers because of the smaller and less expensive, and less complicated lasers are required for sintering.

With ceramics and metals, it is common to sinter only a polymer binder that has been blended with the ceramic or metal powders.

The resultant part can be carefully sintered is a furnace and infiltrated with another metal if desired.

Abbreviation: SLS

Material type: Powder(Polymer)

Materials: Thermoplastics: Nylon, Polyamide and Polystyrene; Elastomers; Composites

Min layer thickness: 0.10mmSurface finish: AverageBuild speed: FastApplications: Form/fit testing,

Functional testing, Less detailed parts, Parts with snap-fits& living hinges, High heat applications..

ADVANTAGES DISADVANTAGES

No need of support structures

No post curing required Variety and Flexibility of

materials The main advantage is

that the fabricated prototypes are porous (typically 60% of the density of moulded parts), thus impairing their strength and surface finish.

Fast build times.

Rough surface finish. Additional powder may

get hardened while solidification along border line

Mechanical properties below those achieved in injection mouldings process for same material.

Many build variables, complex operation.

Material changeover difficult compared to FDM & SLA.

STEREOLITHOGRAPHY APPARATUS(SLA)

• Three Dimensional Printing (3DP) technology was developed at the MIT and licensed to several corporations.

• It was Produced by Z Corporation, USA.Principle An ink-jet printing head deposits a liquid adhesive that binds the starch powder material.

Process• Spread a layer of powder• Print the cross section of the part• Spread another layer of powder• Parts are printed with no supports to remove

• Post processed by cleaning the excess powder, air blow , gluing and sanding.

• Paint coated by sprayers or brushers to get finished productWorking In 3D printing (3DP) process, a print head deposits

an inorganic binder material onto a layer of polymer, ceramic, or metallic powder.

A piston supporting the powder bed is lowered incrementally, and with each step, a layer is deposited and then fused by the binder.

3DP allows considerable flexibility in the materials and binders used.

Furthermore, since multiple binders print heads can be incorporated into a machine, it is possible to produce full-color prototypes by having different-color binders.

The effect is a 3D analog to printing photographs using three ink colors on an ink-jet printer.

The effect is a 3D analog to printing photographs using three ink colors on an ink-jet printer.

A common part produced by 3DP from ceramic powder is a ceramic-casting shell, in which an aluminium-oxide or aluminium silica powder is fused with a silica binder.

The moulds have to be post processed in two steps: (1) Curing at around 150ºC and (2) Firing at 1000º to 1500ºC. The parts produced through the 3DP process are

somewhat porous and therefore may lack strength. 3DP of metal powders can also be combined with

sintering and metal filtration to produce fully dense parts, using the sequence.

The part is produced as before directing the binder onto powders. However, the build sequence is then followed by sintering to burn off the binder and partially fuse the metal powders, just as in powder injection moulding.  

Common metals used in 3DP are stainless steels, aluminium, and titanium.

Infiltrating materials typically are copper and bronze, which provide good heat-transfer capabilities as well as wear resistance

Abbreviation: 3DP

Material type: PowderMaterials: Ferrousmetalssuchas

Stainlesssteel; Non-ferrousmetalssuchas Bronze; Elastomers; Composites; Ceramics

Min layer thickness: 0,05mmSurface finish: RoughBuild speed: VeryFastApplications: Concept models, Limited

functional testing, Architectural& landscape models, Consumer goods& packaging

ADVANTAGES DISADVANTAGES

High speed Versatile - used for

automotive, aerospace, footwear, packaging , etc

Simple to operate - straightforward

Can recycle Enable complex

colour scheme No wastage of

material

Requires post-curing. Limited functional

parts models are weak Limited materials -

starch & plaster-based only.

poor surface finish need post-processing

RAPID TOOLING

• The term Rapid Tooling (RT) is typically used to describe a process which either uses a Rapid Prototyping (RP) model as a pattern to create a mould quickly or uses the Rapid Prototyping process directly to fabricate a tool for a limited volume of prototypes.

Conventional Tooling vs Rapid Tooling:

Tooling time is much shorter than for a conventional tool. Typically, time to first articles is below one-fifth that of conventional tooling.

Tooling cost is much less than for a conventional tool. Cost can be below five percent of conventional tooling cost.

Tool life is considerably less than for a conventional tool.

Tolerances are wider than for a conventional tool.

RT is distinguished from conventional tooling in that,

o Minimize cost

o Increase productivity

o Increase dimensional accuracy

o Decrease tool time

Need for RT

Advantages of RTo Quantity : large no of parts to be machined

o Design : fabrication of complex partso Material : for machining difficult materialso Speed : to increase the speed of machining

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