RAPID PROTOTYPING

Authors: M.SarasChandra (14MMF0011)

PawarShashikantShivaji (14MMF0038)

Abstract:

Rapid Prototyping technologies have emerged for quickly creating 3D products directly fromcomputer-aided design systems. These technologies significantlyimprove the present prototyping practices in industry.This paper reviews the main technologies and applications of RP. We discuss different stages in rapid prototyping, different types of manufacturing techniques, their applications and Problems.

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Introduction:

To substantially shorten the time for developing patterns,moulds, and prototypes, some manufacturing enterpriseshave started to use rapid prototyping methodsfor complex patterns making and component prototyping. Nowadays technology is evolving rapidly. Product manufacturing industry is facing important task of a) reduction of product development time and b) improvement on flexibility for manufacturing small batch size products.

Rapid prototyping is the technique of physically modelling the design using specialized technology. RP systems produce models and prototype parts from model data likefrom a 3D-Digitizing system. In this, we use additiveapproach to building shapes. RP Machines fabricate plastic, wood, ceramic and metal powders using thin, horizontal cross-sections of computer model. Some industries are using this tool to produce final parts also.

Stages of RP:

Although several rapid prototyping techniques exist, all employ the same five-step process:

Creation Of CAD model of design

Conversion into STL format

Slicing of STL file into thin cross Sectional layers

Layer by layer construction

Cleaning and Finishing the model

Creation of CAD model:

The object to be build is modelled using Computer-Aided Design (CAD) software. Solid modellers, such as Pro-E, CATIA, SolidWorks can be used. This process is identical for all of the RP build techniques

Conversion of CAD model to STL format:

A standard format has been adopted known as STL (Stereolithography) is an industry standard for rapid prototyping

Slicing of STL file into layers:

In the third step, a pre-processing program is used to prepare the STL file for construction. The STL model is sliced into a number of layers from 0.01mm to 0.7mm thick

Layer by layer construction:

In the fourth step, the actual construction is done. Layers can be produced by different methods. One of these techniques can be used to produce the part.

Cleaning and Finishing:

In this step, the prototype is taken out of the machine and supports are detached. Prototype may require minor cleaning and surface treatment which will improve appearance and durability

Rapid Prototyping Methods:

1)Liquid Phase Methods:

a)Stereo lithography

b)Solid ground curing

c)Droplet deposition Manufacturing

2)Solid Phase Methods:

a)Laminated Object Manufacturing

b)Fused Deposition Modelling

3)Powder Based Methods:

a)Selective Laser Sintering

b)3-D Printing

1. Liquid Phase Methods:

(I) Stereo lithography:

Principle:When liquid photo sensitive polymers like epoxy, acrylate resin are exposed to Ultra Violet light they getsolidified.

Process: In this process a platform is situated in Liquid Epoxy or Acetyl Resin. When UV lights falls on the liquid layer, the part that to be constructed gets solidified and remaining part stays liquid. An elevator is provided to lower the platform to form successive layers. In this way process is repeated to get the final model. After the model is taken out, the excess liquid is removed and part is placed in UV oven for complete curing.

(II) Solid ground curing:

Principle: It is similar to stereo-lithographic technique except curing of entire layer is done at a time.

Process: A photo mask is created on a glass plate. Next a thin layer of liquid photo polymer is distributed over the surface of the work platform. The mask is provided on the surface and exposed by high power UV light. The portions of the unprotected layers by mask are solidified. Shaded areas remain in liquid state. Mask is removed and subsequent process again by layer to layer. The new layers are filled with hot wax and when the wax has solidified, the polymer-wax surface is milled to form a flat layer of specified thickness, ready to receive the next layer of polymer.

(III) Droplet deposition Manufacturing:

Principle: These systems operate by melting the starting material and shooting small droplets onto a previously formed layer. The liquid droplets cold weld to the surface to form a new layer.

Process: The deposition of droplets in each layer controlled by a moving x-y spray nozzle workhead whose path based on a cross section of CAD geometric model has been sliced into layers.After each layer has been applied, the platform supporting the part is lowered to layer thickness and ready for next layer.

2. Solid Phase Methods:

i) Laminated object Manufacturing:

Principle: The layers of the adhesive coated sheet material are bonded together to make a prototype.

Process: A solid model is produced by stacking layers of sheet stock that are cut to an outline corresponding to the cross-sectional shape of the CAD model that has been sliced to layers. Laser beam is used to cut the outline of layers. After each layer is prepared and cut out, platform is lowered and new layer formed by fresh material.

ii) Fused Deposition Modelling:

Principle: Thermo plastic or wax filament is heated and deposited using extrusion workhead.

Process: The workhead is controlled in x-y plane during each layer and then moves up by a distance equal to one layer in z-direction. The part is fabricated from the base up, using a layer by layer procedure similar to other RP systems.

3. Powder Based Methods:

i) Selective Laser Sintering:

Principle: A laser beam is used to sinter heat-fusible powders in areas corresponding to the CAD geometric model one layer at a time to build the solid part.

Process: Here a platform is placed just below the surface with heat-fusible powder. After fusing the first layer by beamplatform is lowered by height of layer and powder applied again. It is repeated until the model created.

ii) 3D-Printing:

Principle: It builds the part layer by layer using an ink jet printer with an adhesive bonding material onto successive layers of powders. The binder holds the powder together to form the solid part, while the unbounded powders remain loose to be removed later.

Process: The part is built on a platform whose level is controlled by a piston. A layer of powder is spread over the existing part. An ink jet head moves across the surface and ejects the droplets of binder on those parts. When printing of layer is complete piston lowers the platform to the next layer.

Applications of Rapid Prototyping:

Engineering

Architecture

Medical

Arts and Archaeology

Entertainment

Advantages:

  1. Production of parts easy and quicker
  2. Material saving
  3. Product Testing is quick
  4. Reduction in material cost
  5. Quick design modification possible

Disadvantages:

  1. It doesn’t replicate the real thing
  2. Part accuracy
  3. Limited variety of materials
  4. Mechanical performance of prototype

References:

  1. Mikell p. Groover. “Fundamentals of modern manufacturing 4th edition”pp-786-799
  2. SeropeKalpakjian, Stephen Schmid (2009) “ Manufacturing, Engineering and Technology SI 6th Edition”

pp-525-551

  1. Xue Yan and P Gu ‘A review of Rapid Prototyping technologies and systems’ Elsevier,Computer-AidedDesign, Vol.28, No.4, pp307-318, 1996
  2. SolidConcepts.com(SLA)

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