Reflecation paper

- Module 6 - Rapid Prototyping Processes

. Highly intense competition pushes manufacturing companies within different industries to apply world-class manufacturing practices.

. These practices require more investment in new technological knowledge

. Many of the processes involved in the -design,

-test,

-manufacture,

-material resources

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- Module 6 - Cont.

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. Rapid prototyping (RP) is a free form manufacturing process that

allows users to fabricate a real physical part directly from a CAD

(computer-aided design) model.

. The CAD model is sliced into many layers by any number of software

packages.

. Prepare the part for whichever layered manufacturing machine is to

be used. The part is then built layer by-layer.

. This process allows us to quickly build geometrically complex parts.

. RP technologies can greatly reduce cycle time.

- Module 6 - Cont.

➢ WHAT IS RAPID PROTOTYPING ?

The role of prototypes in today’s industries includes but is not limited to

the following:

• Experimentation and learning

• Testing and proofing

• Communication and interaction

• Synthesis and integration

• Scheduling and decision making

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- Module 6 - Cont.

Prototypes enable the product development team to:

- Think,

- plan,

- experiment,

- learn the processes while designing the product.

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- Module 6 - Cont.

1. Communications

2. Receiving input from toolmakers and suppliers

3. Tooling applications

4. Verify CAD data

5. Styling and ergonomics studies

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➢RP Applications

- Module 6 - Cont.

➢ ALTERNATIVES OF RAPID PROTOTYPING ?

• A subtractive operation.

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starts with a single block of

solid material, and material

is removed until the desired

shape is obtained.

- Module 6 - Cont.

• An additive fabricator.

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An additive fabricator is a process where a material is manipulated so that

successive portions of it are combined to form the desired object.

- Module 6 - Cont.

• An formative fabricator.

In a formative fabricator,

mechanical force or restrictive

force is applied on a material

so it can be formed into

a desired shape.

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- Module 6 - Cont.

• Although most of the current RP processes are additive fabricators, it does not limit the RP processes to just additive fabricators.

• A CNC machining process is generally not considered to be an

RP technology for the following reasons:

(1) it still requires skillful human intervention to help plan the

operations.

(2) custom fixturing and special tooling are often required; and

(3) machining has inherent geometric limitations.

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- Module 6 - Cont.

• The advantages of using a CNC process for RP include:

1- Almost no limit on materials,

2- Excellent dimensional control,

3- Good surface finish.

• The major limitation is the possible accessibility of machine tools.

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- Module 6 - Cont.

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The Figure shows the development time comparison between a traditional CNC

milling process vs. an RP process when developing a typical product.

- Module 6 - Cont.

➢ PRODUCING FUNCTIONAL PARTS

1. Indirect method

• Use RP to make molding and die casting for volume production.

• This process creates an RP model as a pattern.

• Uses the RP pattern to make a durable pattern.

• Uses the durable pattern for volume production.

• Indirectly used to fabricate metals or parts with other materials.

• The only drawback is during transition, some accuracy may be lost.

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- Module 6 - Cont.

• Direct method

• The direct fabrication or Direct Metal Deposition (DMD) or laser

metal deposition (LMD) uses CAD to drive the process.

• Uses a laser to fuse materials together.

• Among RP processes, the laser-based deposition process is a

technique, which can produce fully functional parts directly from a

CAD system and eliminate the need for intermediate steps.

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- Module 6 - Cont.

❑ RAPID PROTOTYPING PROCEDURE

Expectations:

• How can a CAD solid model be used to drive a stereolithography

machine ?

• How can a rapid prototyping process translate the STL file into

signals that perform the motion necessary for manufacturing ?

• What is the significant importance of slicing the geometry into

triangles rather than rectangles or circles ?

• What are the major differences between creating a prototype on a

rapid prototype machine and creating one on a CNC machine ?

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- Module 6 - Cont.

• The recent improvements of RP technologies can be closely linked

with the developments of computer technologies.

• The declining costs of computer technologies and advancements in

many computer-related areas including CAD, CAM, and CNC

machining tools and approaches have completely changed today’s

factory functions.

• The existence of RP systems would not have been possible unless

these computer technologies evolved with reduction in costs.

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- Module 6 - Cont.

➢ WHY IS RP PROCESS FASTER ?

• RP is faster because it takes virtually no human effort to run the

machine.

• After the virtual model has been made, only a few simple buttons

need to be pushed to begin the rapid prototyping.

• Process become limited by tools available or space needed for the

tools.

• Since the model is built in layers, almost all structures can be built

without a problem.

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- Module 6 - Cont.

➢ A TYPICAL RAPID PROTOTYPING PROCESS

It includes the following steps:

1. Construct the CAD model

2. Convert the CAD model to STL format

3. Check and fix STL file

4. Generate support structures if needed

5. Slice the STL file to form layers

6. Produce physical model

7. Remove support structures

8. Post-process the physical model

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The data flow of the basic RP process.

- Module 6 - Cont.

• The RP input can be described as the electronic information

required to specify the physical object with 3D data.

• There are two possible starting models:

. A computer model:

is created from a CAD system can be either a surface model or

a solid model.

. A physical model:

can be obtained by digitizing or scanning the geometry of

a physical part.

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- Module 6 - Cont.

➢ WHY STL FILES ?

• The STL files translate the part geometry from a CAD system to the

RP machine.

• Universal file format that every system needs to be able to produce

so that an RP machine can process what a part looks like for slicing.

• Slicing a part is easier compared to other methods.

• Triangulation, as shown in the Figure, is breaking the model into

these discrete pieces to make a practical file size without sacrificing

too much accuracy. 20Dr. Munther Hermez

- Module 6 - Cont.

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An example of a CAD model. An example of an STL triangulation model.

- Module 6 - Cont.

➢ CONVERTING STL FILE FROM VARIOUS CAD FILES

Methods used for generating an STL file in various CAD files:

(1) Making STL files from SolidWorks.

(2) Making STL files from Pro/Engineer.

(3) Making STL files from Unigraphics.

(4) Making STL files from NX-12.

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- Module 6 - Cont.

• When generating the STL files, triangular surfaces are used to

express the real surfaces of the part.

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The tolerance between a circle and an octagon representation of the circle.

- Module 6 - Cont.

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Two ways of STL approximation:

Upper figure (chord height control): maximum acceptable distance between the

model line and the original curve.

Lower figure (angle control): maximum acceptable angle between the model line

and the tangent of the original curve.

- Module 6 - Cont.

➢ CONTROLLING PART ACCURACY IN STL FORMAT

Using Pro/Engineer as an example, there are two options, angle control and

chord height, to be specified when making an STL file.

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Pro/Engineer model used to make STL files.

- Module 6 - Cont.

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• When generating an STL file, the errors will often need to be

corrected before further processing.

• All surfaces in an STL data file should construct one or more

nonmanifold entities according to Euler’s rule for legal solids:

F - E + V = 2B

Where:

F : number of faces.

E : number of edges.

V : number of vertices.

B : number of separate solid bodies.

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- Module 6 - Cont.

➢ SLICING THE STL FILE

• Generally, the user can specify the Z-thickness of the slice.

• Typical thickness is 0.006 in.

• The main error associated with this is the staircase error.

• After the STL part is properly oriented and positioned, the user then

slices the part into layers.

• It automatically generates the support structure, as most RP

software does.

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The cone is sliced into fine layers.

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- Module 6 - Cont.

➢ BUILDING AN RP PART

• Once the STL file is sliced and transferred into an RP machine, the

build process is fully automated.

• The method of support material removal can vary from process to

process.

• For example, some processes will require support breakaway or

grinding operation to remove the support material.

• Figure shows the finished part.

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Part (bottle opener) is completed.

- Module 6 - Cont.

❑ LIQUID-BASED RP PROCESSES

• The objective of this section is to help understand the concept of

liquid-based rapid prototyping processes, such as processes:

-Stereolithography Apparatus (SLA)

-Solid ground curing (SGC).

• Liquid-based rapid prototyping has its initial materials in liquid state.

• Limitation is on the type of materials that can be solidified.

• The heat source, such as a UV laser, is chosen to control the curing

in a tiny spot to gain good part accuracy.

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- Module 6 - Cont.

➢ STEREOLITHOGRAPHY PROCESS

• The Stereolithography Apparatus (SLA) process is the first

commercialized Rapid Prototyping process.

• Stereolithography uses a photo curable resin that can be classified as

an epoxy.

• The stereolithography process converts 3D computer image data into

a series of very thin cross-sections.

• The object will be sliced into hundreds or thousands of layers.

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An illustration of the SLA process.

- Module 6 - Cont.

• A laser beam then traces a single layer onto the surface of a vat of liquid polymer as shown in Figure.

• The ultraviolet light causes the polymer to harden precisely at the

point where the light hits the surface.

• The model is built upon a platform situated just below the surface in a

vat of liquid epoxy or acrylate resin.

• A low-power highly focused UV laser traces out the first layer.

• The UV laser is controlled by a galvanometer scanner to generate

X–Y motion. 35Dr. Munther Hermez

- Module 6 - Cont.

Stereolithography process step-by-step:

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- Module 6 - Cont.

(a) a layer of resin to be solidified on a platform.

(b) UV laser selectively traced out the first layer.

(c) second layer with laser tracing from the left.

(d, e) repeat to build the rest of the layers.

(f ) the final part after the support structures are removed.

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- Module 6 - Cont.

• It has the capacity to build a volume of 1500 x 705 x 500 mm3.

• The uniqueness of this process is its resolution and accuracy.

• The process is able to maintain the dimensional accuracy of the built

parts to within ±0.1mm.

• It has become a much used technology in so many industries,

aerospace, automotive, consumer electronics, toys, industrial

equipment, medical equipment, surgical applications, and dental

applications.

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- Module 6 - Cont.

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An SLA model of a dashboard part. (Courtesy of 3D Systems.)

- Module 6 - Cont.

➢ Process Limitation

• The major advantage of RP processes is that any geometrical

shape can be made with virtually no limitation.

• most RP processes, liquid processes also have process limitations.

• parts with enclosed and hollow structures are problems as the liquid

may be trapped inside the enclosed body during building.

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- Module 6 - Cont.

➢ MASK-BASED PROCESS

• The primary material used for this process is resin and the

secondary material used is wax.

• It works on a principle similar to the previous stereolithography

process, but in this case, a whole layer is produced at a time.

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The schematics of mask-based process prototyping a coffee cup.

- Module 6 - Cont.

➢ INJECT-BASED LIQUID PROCESS

• One representative inject-based liquid process is PolyJet, a hybrid of

material jetting or printing and stereolithography.

• the process by Objet Geometries uses printing technology to deposit

supports and build material combined with photo or UV curable

materials.

• it is capable of producing results similar to those from

stereolithography processes.

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- Module 6 - Cont.

➢ RAPID FREEZE PROTOTYPING PROCESS

• A cold source is used to freeze the liquid point by point and thus

transfer liquid into a solid part.

• This process builds a 3D ice part from a CAD model by depositing

and rapidly freezing water in a layer-by-layer manner.

• low-cost and environmentally benign process as it uses water and

inexpensive equipment to build the part.

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- Module 6 - Cont.

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Schematic of the rapid freeze prototyping (RFP) process.

- Module 6 - Cont.

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➢ SOLID-BASED RP PROCESSES

➢EXTRUSION-BASED PROCESS

➢CONTOUR-CUTTING PROCESS

➢ULTRASONIC CONSOLIDATION PROCESS

- Module 6 - Cont.

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➢ POWDER-BASED RP PROCESSES

. What are the various types of powder-based RP processes ?

. What are the differences between the various powder-based RP

processes ?

. What are the advantages and disadvantages of each of the powder-

based RP processes ?

. How to choose among the RP processes ?

. What are the material choices in solid-based processes ?

. How do various RP technologies use powder to build a part ?

. How difficult would it be to maintain the thickness and porosity of the

deposited layer ?

- Module 6 - Cont.

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. When a mold is needed for a small batch, for smooth, hard surface,

which rapid prototyping process should be used ?

. When a part needs multiple colors, which rapid prototyping process

should be used ?

. When a part has convoluted internal spaces, for easy support

removal, which rapid prototyping process should be used ?

. How to compare powder-based processes with liquid-based

processes ?

. How does electron beam sintering compare to laser sintering ?

- Module 6 - Cont.

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A schematics diagram of a laser sintering process.

- Module 6 - Cont.

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➢ 3-D INJECT PRINTING PROCESS

Direct shell production casting.

- Module 6 - Cont.

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➢ DIRECT LASER DEPOSITION

The schematics of the DLD process.

- Module 6 - Cont.

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➢ ELECTRON BEAM MELTING PROCESS

➢ HYBRID MATERIAL DEPOSITION AND REMOVAL

PROCESSES

- Module 6 - Cont.

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➢ FUTURE RP PROCESSES

• Reasonably inexpensive:

• More varieties of materials:

• More accurate:

• Much larger parts:

• Much smaller parts:

• Rapid manufacturing:

• Extensive medical applications:

• Repair and reuse:

• Functionally gradient materials:

➢