CHAPTER 19

Rapid Prototyping Operations

Rapid prototyping

• Introduction

• Subtractive processes

• Additive process

• Virtual Prototyping

• Applications

Rapid prototyping

• Technology which considerably speeds the iterative product development process

Fig: a) Examples of parts made by rapid prototyping b) Stereolithography model of cellular phone

Advantages

• 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

Classification of Rapid Prototyping

• Rapid prototyping is classified to 3-major groups

Subtractive ( Removal of material )

Additive ( Adding of material )

Virtual ( Advanced computer base visualization)

Subtractive Process

• Subtractive process use computer based Prototype technology to speed the process

• Essential Technologies for subtractive prototyping :

• Computer – based drafting packages ( 3-D representation of parts)

• Interpretation software (Translation of cad file to manufacturing software)

• Manufacturing Software (Planning Machining operations)

• Computer-Numerical Control Machinery

Additive Process

• Build parts in layer by layer (slice by slice as stacking a loaf of bread)

Fig: The computational steps in producing a stereolithography file a) Three dimensional description of part b)The part is divides into slices (only one in 10 is shown) c)support material is planned d)A set of tool directions is determined to manufacture each slice. Shown is the extruder path at section A-A from c) For a fused-deposition-modeling operation

Require elaborate software

1 : Obtain cad file

2 : Computer then constructs slices of a 3-dimensional part

3 : slice analyzed and compiled to provide the rapid prototyping machine

4 : setup of the proper unattended and provide rough part after few hours

5 : Finishing operations and sanding and painting

6:labor intensive and production time varies from few minutes to few hours

Additive Process

Fused Deposition Modeling

• 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 Fig : (a)Fused-deposition-modeling process.

(b)The FDM 5000, a fused-decomposition-modeling-machine.

Fused Deposition Modeling

Fig: a)A part with protruding section which requires support material b) Common support structures used in rapid-prototyping machines

Stereolithiography

• Works based on the principle of curing liquid photomer into specific shape

• A vat which can be lowered and raised filled with photocurable liquid acrylate polymer

• Laser generating U-V beam is focused in x-y directions

• The beam cures the portion of photo polymer and produces a solid body

• This process is repeated till the level b is reached as shown in the figure

• Now the plat form is lowered by distance ab

• Then another portion of the cylinder is shaped till the portion is reached

Fig :Stereolithiography Process

Selective laser sintering (SLS) :

Fig: The selective laser sintering process

Selective laser sintering

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

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

Selective laser sintering

• 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

Selective laser sintering

Solid Base curing :

• 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

Fig:The solid based curing process

• Ballistic particle manufacturing

• Stream of material , such as plastic ,ceramic, metal or wax ejected through small orifice at a surface

• Mechanism similar to inkjet mechanism ( piezo-electric pump)

• Operation repeats similar to other process to form a part with layers of wax deposited on top of each other

• Ink jet heat guided by three-axis robot

Ballistic Particle Manufacturing

3-D Printing process

Similar to ballistic particle manufacturingSimilar to ballistic particle manufacturing

Fig:Three dimensional 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

3-D Printing process

Laminated object manufacturing (LOM )

• 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.

Laminated Object Material (LOM)

Fig : (a) Laminated object-manufacturing process (b)Crankshaft-part example made by LOM

Virtual prototyping

• Virtual prototyping (modeling and simulation of all aspects of a prototype, i.e. mechanical design, kinematics, dynamics, and controls accompanied by a realistic visualization).

• Realizing the best design in the shortest lead-time of complex products/processes

• Allows the exotic, unconventional designs be prototyped, rapidly and cost-effectively

Applications of Rapid Prototyping

• Production of individual parts• Production of tooling by Rapid Prototyping (Rapid Tooling)

Fig: Manufacturing steps for investment casting that uses rapid prototyped wax parts as blanks.

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 mold quickly or uses the Rapid Prototyping process directly to fabricate a tool for a limited volume of prototypes .

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

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

c) Tool life is considerably less than for a conventional tool.

d) Tolerances are wider than for a conventional tool.

Rapid Tooling

Fig: Manufacturing steps in sand casting that causes that uses rapid-prototyped patterns

Rapid Tooling

Fig: Manufacturing steps in sand casting that causes that uses rapid-prototyped patterns

THE END