Reflecation paper

- Module 5 - Direct Digital Prototyping

and Manufacturing

Digital manufacturing is the ability to describe every aspect of the

product development process digitally using tools that include:

• digital design,

• Computer-Aided Design (CAD),

• Office documents,

• Product Life cycle Management (PLM) systems,

• Analysis software,

• Simulation,

• Computer-Aided Manufacturing (CAM) software, etc.

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- Module 5 – Cont.

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A Computer-Integrated Manufacturing system can use a common database to drive

various processes in the product prototyping stages.

.Communication with customers to define

-product need,

-product design,

-purchasing of raw materials.

- Module 5 – Cont.

Will define:

• What is a solid model ?

• Why is a solid model needed in digital manufacturing ?

• What is a CSG model? What is a B-rep model ?

• How is a curved surface represented in a solid model ?

• What is B-spline? What is NURBS ?

• How to represent a curved surface in a B-spline or NURBS ?

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❑ Solid Models And Prototype Representation

- Module 5 – Cont.

• The language of digital manufacturing and assembly is geometry. Digital manufacturing starts with being able to draw an idea into a

computer.

• Other modeling methods include wire frame models, which can be

ambiguous about solid volume

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A wireframe model of a block with a hole.

- Module 5 – Cont.

➢ Solid Modeling

• Solid modeling is the best way for CAD/CAM integration and

applications since it can define solid parts well.

• Boundary representation (B-rep) represents a solid object by

boundary surfaces which are then filled to represent a solid.

• Because B-rep includes such topological information, a solid is

represented as a closed space in 3D space.

• The boundary of a solid separates the points inside from points

outside the solid.

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- Module 5 – Cont.

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A B-rep solid model representation of the block with a hole example.

- Module 5 – Cont.

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• In CSG (Constructive Solid Geometry) representation, an object is specified with

reference to a library of simple primitives, such as

blocks, cylinders, prisms, pyramids, spheres, cones, etc.

A library of commonly used primitives for CSG representation

- Module 5 – Cont.

• Solid modeling software could be used to model solid parts and

model assemblies of parts.

• The immediate usage of a solid model is to calculate mass

properties of parts and assemblies and reflects the ‘‘bill of

materials’’ required to build the product.

• The understanding of data representation of a solid model is very

important in CAD/CAM integration activities.

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➢CAD Data Representation

- Module 5 – Cont.

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• It is not possible to use an infinite number of points, but two points

should be able to represent a line.

• Therefore, the two point coordinate data, A and B, are

stored in the database to represent the line.

where t is a variable.

In other words, in addition to the database, one will also need to have an

algorithm to represent geometry, and the equation here is the algorithm.

- Module 5 – Cont.

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• Parametric surface patches are joined together side-by-side to form a more

complicated shape as shown in Figure

Multiple parametric surface patches are used to represent a free-form surface.

- Module 5 – Cont.

As the curves and surfaces are formed by multiple patches, there are

several levels of continuity:

- C0 curve continuity: means simply connected, or when two curve

segments join together at an endpoint.

- C1 curve continuity: can be recognized when two curve segments

join together at an endpoint and the directions of the two

segments’ tangent vectors, or the first derivative, are equal at the

join point.

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- Module 5 – Cont.

A quadratic curve can be in the form of

A cubic curve can be in the form of

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- C2 curve continuity is commonly referred to as geometric

continuity that can be visually recognized as something ‘‘very

smooth,’’ or when two curve segments join together at an

endpoint, and the two segments’ first and second derivatives are

equal at the join point.

- Module 5 – Cont.

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-Both curves can be defined from a series of known points. -The curves could pass through the points. -The cubic curve can also be expressed as

- Module 5 – Cont.

Plot the original curve and approximation curve in the XY plane as

shown in Figure

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➢ Error Analysis

Error between the approximation and actual ellipse curves.

- Module 5 – Cont.

Will define:

• What is reverse engineering ?

• Why is reverse engineering needed ?

• How does reverse engineering work ?

• What is the procedure for reverse engineering ?

• What are the tools for reverse engineering ?

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❑ Reverse Engineering For Digital Representation

- Module 5 – Cont.

• In general, reverse engineering is defined as the process of discovering the technological principles of a device, object, or

system through analysis of its structure, function, and operation.

• It often involves taking something apart and analyzing its workings

in detail,

• usually with the intention to construct a new device or program

that does the same thing without actually copying anything from

the original.

• Reverse engineering can also be defined as the development of a

complete Technical Data Package (TDP) for an existing

component or subassembly.

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- Module 5 – Cont.

• Reverse engineering is commonly applied to the general process

of recreating existing 3D geometry in the computer.

• This 3D geometry could be the shape of a real, manufactured

object, like a car, or it could be some type of organic shape, like a

plant or a human body.

• Although many manufactured objects are now defined digitally

using some type of 3D modeling software, in many instances, the

part may not be able to obtain the existing geometry digitally.

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➢ Reverse Engineering And Product Prototyping

- Module 5 – Cont.

• CAD models are often unavailable or unusable for parts which must be duplicated or modified when:

1. CAD was not used in the original design,

2. There is inadequate documentation on the original design,

3. The original CAD model is not sufficient to support modification

or manufacturing using modern methods,

4. the original supplier is unable or unwilling to provide additional

parts, or

5. there have been shop floor changes to the original design.

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- Module 5 – Cont.

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• The CMM is an accurate measuring device used to verify

dimensions to ensure part quality.

• The sequence for programming a CMM with a probe includes

several steps.

• Traditional CMMs typically have better accuracy, but

can be limited in the size and complexity of the object to

be scanned.

• Portable CMMs are generally less accurate, but they

are portable, with less limitation on the size of an object.

- Module 5 – Cont.

Geometry is usually represented in terms of surface points or

collections of parametric surface patches to describe positional

information.

There are up to two steps in the process of reverse engineering:

• Digitizing the parts.

• Building CAD models.

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➢ Reverse Engineering Process

- Module 5 – Cont.

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Points were selected row-by-row to create a

surface.

Solid model created in a CAD system.

- Module 5 – Cont.

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• Complex shapes are often divided into zones.

The nozzle can be broken into three segments: end conical section, center conical

section, and end cylindrical section.

- Module 5 – Cont.

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❑ Prototyping And Manufacturing Using CNC Machining

• In the competitive industry, productivity is achieved by guiding a

product from concept to market quickly and inexpensively.

• Advanced CNC machining technology can aid this process by

automating the fabrication of a prototype part from a 3D CAD model.

• While conventional prototyping technologies may take weeks or

even months, CNC machining prototyping can be a quicker, more

cost-effective means of building prototypes.

- Module 5 – Cont.

The codes used to drive a CNC machine are called G- and M-codes.

• G-codes are the preliminary functions.

code consists of the letter G followed by two digits that correspond

to specifying a control mode of operation.

Preparatory functions include:

. the x-, y-, and z-axis movements,

. thread cutting, radius compensation, canned cycles, circular interpolations, inch or metric measurement system, dimensional input

formats, tool feed rates, tool spindle revolutions, etc.

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➢ Machine Codes For Process Control

- Module 5 – Cont.

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- Module 5 – Cont.

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• M-codes are the miscellaneous functions.

. Many M-codes are defined by the CNC machine manufacturer for their

machines’ unique operating characteristics

. control options like

program stop, end of program,

spindle rotation direction,

tool changes, coolant 1 and 2 off/on,

clamp and unclamp, and

return to program start.

- Module 5 – Cont.

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- Module 5 – Cont.

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• Integrating CAD with CAM provides the link between software

systems that helps streamline the transfer of files between the

following important functions:

(1) design modeling,

(2) manufacturing modeling,

(3) NC programming.

• A postprocessor translates actions taken in the CAM software into

machine code.

• The CAM programs often output CL data files that consist of

generic tool path and critical operations of the CNC machine.

• CL-data format is designed so that it is machine independent.

- Module 5 – Cont.

• Many CAM software packages have the ability to simulate the

motion of the cutter paths and the material removed by the paths.

• These software packages are invaluable in locating problems that

may not be apparent until the program is run on the machine.

➢ Developing A Successful Postprocessor

• If a machine is not listed as a standard configuration in the CAD

software, more effort may be needed to output the proper codes

for CNC machining.

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➢ Using CAD/CAM For Digital Manufacturing

- Module 5 – Cont.

Front view of the machine spindle and axis.

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- Module 5 – Cont.

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❑ Fully Automated Digital Prototyping And Manufacturing

• What would it take to provide a fully automatic digital prototyping

and manufacturing system ?

• What is CAPP ? What level of part complexity can be handled by

current CAPP software ?

• What is feature-based design ? Why is it important in digital

prototyping and manufacturing ?

• Is it true that feature-based design will only be suitable for some

simple solid models ?

- Module 5 – Cont.

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➢ Process Planning And Digital Fabrication

• The planning begins with engineering drawings, specifications, parts or

material lists, and a forecast of demand.

Results of planning:

• Routings that specify operations, operation sequences, work centers,

standards, tooling, and fixtures.

• Process plans that typically provide more detailed, step-by-step work

instructions including dimensions related to individual operations, machining

parameters, setup instructions, and quality assurance checkpoints.

• Fabrication and assembly drawings to support manufacture.

- Module 5 – Cont.

➢ Feature-Based Design And Fabrication

➢ User-assisted Feature-based Design

➢ Basic System Components

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