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CAD for ManufacturingCourse coverage:

Introduction to CAD/CAM/CAE for manufacturing. Introduction to geometric modelling. Basic modelling and representation of lines, curves,

surfaces and solids. Constructive Solids Geometry. Surface modelling techniques.Solids Modelling. Boundary Representation. Spatial enumerative techniques. Objectrepresentation.

Object validation. Constraints and feature modelling. Feature based data representation.

Object visualization. Texturing. Ray tracing and related algorithms.

Assembly modelling. Feature based analysis. Disassembly analysis. Manufacturinganalysis.

Dimensioning, Tolerance and fits representation and analysis. Product manufacturingplanning. Design Structure matrix. Data extraction for product design analysis.

Elements of primary processes CAD modelling Casting, Rapid prototyping etc.

Tools for automated generation of cutter path from CAD representation in secondary

processes. Rapid Prototyping and machine data generation from CAD models. Elementsand data structures for standards based data exchanges IGES, STEP, STP etc. Web-based product visualization and collaboration. Web based manufacturing planning.

Lecture material available on Course Homepagehttp://www.facweb.iitkgp.ernet.in/~sankhadeb/ME60305.html

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Introduction to CAD/CAM/CAE

In order to survive worlds competition, todays industries must introduce new products with

better quality, at lower cost and with shorter lead time for delivery.

Accordingly they have used the computers huge memory capacity, fast processing speed,

and user friendly interactive graphics capabilities to automate and integrate otherwise

cumbersome and separate engineering or production tasks, thus reducing the time and

cost of product development and production.

Computer-Aided Design (CAD), Computer-Aided Manufacturing (CAM) and Computer-

Aided Engineering (CAE) are the technologies used for this purpose during the product

cycle.

The typical product cycle is shown in Figure in the next slide.

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Introduction to CAD/CAM/CAE (continued)

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As indicated in Figure, the product cycle is composed of two main processes: the

design process and the manufacturing process.

The design process starts from customers demands that are identified by the

markettingpersonnel and ends with a complete description of the product,

usually in the form of a drawing.

The manufacturing process starts from the design specifications and ends with

shipping of the actual products.

The activities involved in the design process can be classified largely as two

types: synthesis and analysis.

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As illustrated in Figure, the initial design activities (such as identification of design need, formulation

of design specifications, feasibility study with collecting relevant design information, and designconceptualization) are part of the synthesis subprocess.

That is the result of the synthesis subprocess is a conceptual design of the prospective product in

the form of a sketch or a layout drawing that shows the relationships among the various components

as well as any surrounding constraints.

The major financial commitment needed to realize the product idea are made and the functionality of

the product is determined during this phase of the cycle.

Most of the information generated and handled in the synthesis subprocess is qualitative and

consequently is hard to capture in a computer system.

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Once the conceptual design has been developed, the analysis subprocessbegins with analysis and

optimization of the design.

An analysis model is derived first because the analysis subprocess is applied to the model rather than the

design itself.

The analysis model is obtained by removing from the design unnecessary details, reducing dimensions

and recognizing and employing symmetry.

Dimensional reduction, for example, implies that a thin sheet of material is represented by an equivalent

surface with a thickness attribute or that a long slender region is represented by a line having cross-

sectional properties.

Bodies with symmetries in their geometry and loading are usuallyanalyzed by considering a portion of the

model.

I t d ti t CAD/CAM/CAE ( ti d)

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Once a design has been completed, after optimization or some tradeoff decisions, the design

evaluation phase begins.

Prototypes may be built for this purpose.

Prototypes can be built in a laboratory or a computer to test the design.

Computer prototypes are less expensive and faster to generate.

Nowadays new technologies like rapid prototyping are becoming popular for constructing prototypes.

The rapid prototyping process fabricates the object by starting at the base and building each layer on

top of the preceding layer to approximate the solid shape.

As layer thickness decreases, accuracy increases.

There are variety of layer-building processes used in rapid prototyping.

Stereolithographyuses a photosensitive liquid polymer that cures (solidifies) when subjected to intense

light. Curing is accomplished using a moving laser beam whose path at each layer is controlled by the

CAD model.


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If the design evaluation of the prototype indicates that the design is unsatisfactory, the

process described is repeated with a new design.

When the outcome of the design evaluation is satisfactory, the design documentation is

prepared.

This includes preparation of drawings, reports, and bill of materials.

Conventionally, blueprints are made from the drawings and passedon to manufacturing.


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As illustrated in Figure, the manufacturing process begins with process planning, using the drawings from

the design process, and it ends with the actual products.

Process planning is a function that establishes which processes and the proper parameters for the

processes are to be used.

It also selects the machines that will perform the processes.

The outcome of process planning is a production plan, materials order and machine programming.

Once process planning has been completed,

the actual product is produced and inspected

against quality requirements.

Parts that pass the quality control inspection

are assembled, functionally tested,

packaged, labeled, and shipped to the

customers.


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Let us discuss how the computer or CAD, CAM and CAE technologies, are employed in

the cycle.

The analysis subprocessof the design process is the area where computer finds

application.

There are many available software packages for stress analysis, interference checking,

and kinematicanalysis, etc. These software packages are classified as CAE.

However, an analysis model must be derived first from the conceptual design by

eliminating unnecessary details from the design or by reducing its dimensions.

The proper level of abstraction differs, depending on the type of analysis and the desired

accuracy of the solution.

It is a common practice to create the abstract shape of the design by using a computer-

aided drafting system or a geometric modeling system or sometimes by using the built-in

capabilities of the analysis packages.


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Analysis packages usually require the structure of interest to be represented by an

aggregation of interconnected meshes that divide the problem into manageable chunks forthe computer.

This activity of generating meshes is called finite element modeling. It also includes the

activity of specifying the boundary conditions and external loads.

The design is further optimized by implementing various optimization procedures with the

help of computer.

The design evaluation phase can be also facilitated by the use of computer.

If a prototype is needed for design evaluation, it can be constructed by using software

packages that automatically generates the program that drives rapid prototyping machines.


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Alternatively a virtual prototype of the design known as digital mockup can be also

prepared.

It is based on virtual reality technology, and involves the use of the CAD geometric model

to construct a digital mock-up of the product.

It enables the designer and the others to obtain the sensation of the real physical product

without actually building the physical prototype.

Virtual prototyping has been used in automotive industry to evaluate new car style designs.

Other applications include checking the feasibility of assembly operations.


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The final phase of the design process is design documentation. In this phase, computer-

aided drafting is a powerful tool.

CAD systems can be used as automated drafting machines to prepare highly accurate

engineering drawings quickly.

CAD systems increase the productivity in the drafting function by about five fold over

manual preparation of drawings.

The file handling capability of computer drafting systems also allows systematic storage

and retrieval of documents.


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Computer technologies are also used in manufacturing process andcan be classified

as Computer-Aided Manufacturing (CAM) e.g. production planning, ordering

materials, NC programming, quality control and so on.

For example, computer-aided process planning (CAPP) software to aid the process

planning activity is one type of CAM software.

There are software packages that can generate the numerically controlled (NC)

programs that drive NC machines.

In addition, also belonging to CAM are the software packages to program the robot

motion to assemble components or deliver them to the various manufacturing

activities, or to program a coordinate measuring machine (CMM) to inspect the

product.


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Computer-Aided Design (CAD) is the technology concerned with the use of computer

systems to assist in the creation, modification, analysis, and optimization of a design.

CAD tools can vary from geometric tools for manipulating shapes, tolerance analysis, mass

property calculation, finite element modeling and visualization of the analysis results,

optimization, to name a few.

The most basic role of CAD is to define the geometry of design. Computer-aided drafting

and geometric modeling are typically used for this purpose.

The geometry created by these systems can be used as a basis for performing other

functions in CAE and CAM.


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Computer-Aided Manufacturing (CAM) is the technology concerned with the use of

computer systems to plan, manage and control manufacturing operations through either

direct or indirect computer interface with the plants production resources.

Some CAM applications for manufacturing planning areComputer-Aided Process

Planning, Computer-assisted NC part programming, computerized machinabilitydata

systems, development of work standards, cost estimating, production and inventory

planning, computer-aided line balancing, and so on.

Some CAM applications for manufacturing control areprocess monitoring and control,

quality control, shop floor control, inventory control, and just-in-time systems, and so on.


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( )

Computer-Aided Manufacturing (CAM) is the technology concerned with the use of

computer systems to plan, manage and control manufacturing operations through eitherdirect or indirect computer interface with the plants production resources.

Manufacturing planning

CAM applications for manufacturing planning are those in which the computer is used

indirectly to support the production function.

The computer is used offline to provide information for the effective planning and

management of production activities.

Some important applications of CAM in this category are:

CAPP, Computer-assisted NC part programming, computerized machinabilitydata

systems, development of work standards, cost estimating, production and inventory

planning, computer-aided line balancing and so on.

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Computer-Aided Process Planning (CAPP)

Process planning is concerned with the preparation of route sheets that list the

sequence of operations and work centres required to produce the product and its

components.

Computer-Aided Process Planning (CAPP) systems are available today to prepare

these route sheets.

Computer-assisted NC part programming

For complex part geometries, computer-assisted part programming represents a much

more efficient method of generating the control instructions for the machine tool than the

manual part programming.


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( )

Computerized machinability data systems

One of the problems in operating a machine tool is determining the speeds and feeds.

Computer programs have been written to recommend the appropriate cutting conditions to use for

different materials.

The calculations are based on data obtained either in the factory or lab that relate tool life to

cutting conditions.

Development of work standards

Establishing the time standards by direct time study can be a tedious and time consuming task.

There are several commercial packages for setting work standards.

These computer programs use standard time data that have been developed for basic workelements that comprise any manual task.

By summing the times for individual elements required to performa new job, the program

calculates the standard time for the job.

I d i CAD/CAM/CAE ( i d)

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Cost estimating

The task of estimating the cost of a new product has been simplified in most industries by

computerizing several of the key steps required to prepare the estimate.

The computer is programmed to apply the appropriate labor and overhead rates to the sequence

of planned operations for the components of new products.

The program then sums the individual component costs from the engineering bill of materials to

determine the overall product cost.

Production and inventory planning

The computer has found widespread use in many of the functions in production and inventory

planning.

These functions include: maintenance of inventory records, automatic reordering of stock items

when inventory is depleted, production scheduling, maintaining current priorities for the different

production orders, materials requirement planning, and capacity planning.

I d i CAD/CAM/CAE ( i d)

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Production and inventory planning (continued)

The production schedule is a specific plan of the quantities to be produced of individual

models within each product line.

The Materials Requirement Planning (MRP) is a planning techniqueusually

implemented by computer that translates the production schedule of end products into a

detailed schedule for the raw materials and parts used in those end products.

Capacity planning is concerned with determining the labor and equipment resources

needed to achieve the production schedule.

Computer-aided l ine balancing

Finding the best allocation of work elements among stations on an assembly line is a

large and difficult problem if the line is of significant size.

Computer programs have been developed to assist in the solution of this problem.


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Manufacturing control

The second category of CAM applications is concerned with developing computer

systems to implement the manufacturing control function.

It is concerned with managing and controlling the physical operations in the factory.

These management and control areas include:

process monitoring and control, quality control, shop floor control, inventory control, andjust-in-time systems.


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Process monitoring and control

Process monitoring and control is concerned with observing and regulating the

production equipment and manufacturing processes in the plant.

The applications of computer process control in automated production systems include

transfer lines, assembly systems, CNC, robotics, material handling, and flexible

manufacturing systems.

Quality control

It includes a variety of approaches to ensure the highest quality levels in the

manufactured product.

Shop floor control

It refers to production management techniques for collecting data from factory

operations and using the data to help control production and inventory in the factory.


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Inventory control

It is concerned with maintaining the most appropriate levels of inventory in the face of

two opposing objectives: minimizing the inventory and storage costs of holding inventory

and maximizing service to the customers.

Just-in-time production systems

The term just-in-time refers to a production system that is organized to deliver exactly

the right number of each component to downstream work stations in the manufacturing

sequence just at the time when that component is needed.

It applies to not only production operations but to supplier delivery operations as well.


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Computer-Aided Engineering (CAE) is a technology concerned with the use of computer

systems to analyze CAD geometry, allowing the designer to simulate and study how the

product will behave so that the design can be refined and optimized.

CAE tools are available for a wide range of analyses e.g. kinematics analyses, mass

properties analysis, Interference checking, tolerance analysis, finite element analysis and

so on.

For example, kinematic analysis can be used to study the operation of mechanicallinkages to analyze their motions.

Typically it consists of specifying the motion of one or more driving members of the linkage

and the resulting motions of other links are determined by the analysis package.

Dynamic analysis extends the kinematicanalysis by including the effects of mass of each

linkage member and the resulting acceleration forces as well as any externally appliedforces.


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Mass properties analysis involves computation of volume, surface area, weight, centre

of gravity, etc.

It is especially applicable in mechanical design.

Inerference checking examines the 2-D geometric models to identify interferences

between components.

It is useful for analyzing mechanical assemblies.

Software forTolerance analysis is used for various functions like

To assess how the tolerance affects the products function and operating performance

To determine how the tolerance affects the ease or difficulty of assembling the product

To assess how the variations in the component dimensions affect the overall size of the

assembly


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Another widely used method of computer analysis in engineering is finite element

analysis (FEA) used to determine stress, deformation, heat transfer, magnetic field

distribution, fluid flow and other problem.

It is a numerical analysis technique for determining the approximate solutions to

physical problems described by differential equations that are very difficult or

impossible to solve.

In FEA, the physical object is modeled by an assemblage of discrete interconnected

nodes (finite elements) and the variable of interest in each node is expressed by

simple mathematical equations.

By solving the equations for each node, the distribution of values of the variable

throughout the physical object is determined.


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FEA model to analyze the temperature of a cutt ing tool


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A proper level of abstract model is required by the finite element method instead of the design

geometry itself. The abstract model is obtained by eliminating the unnecessary details from the design geometry

or by reducing the dimensions of the design geometry.

For example, a 3D object having thin thickness may become a 2D shell model when it is converted

to an analysis model.

It is necessary to generate the abstract model either automatically or interactively in order to use a

finite element method. Once the abstract model has been developed, the finite elements are

generated to yield the analysis model.

The software tools that enable the construction of the abstract model and generation of the finite

elements are called pre-processors.

After performing an analysis on each element, the computer assembles the results and displays it

visually e.g. areas of high stress may be shown in red. The software tools for this visualization are

called post-processors.


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Thus CAD, CAM, and CAE are concerned with automating specific functions of the product cycle

and making them more efficient. Because they were developed separately, they have not fully realized the potential of integrating

the design and manufacturing activities of the product cycle.

To solve this problem, a technology called computer integrated manufacturing (CIM) has been

introduced.

CIM is aimed at integrating the separate islands of automation together into a smoothly running

efficient system.

CIM is concerned with using the computer database as a way to run an entire enterprise more

efficiently, having an impact on accounting, scheduling, shipping and other management functions

in addition to the engineering design and production functions of concern to CAD/CAM/CAE.

CIM is often said to be more of a business philosophy than a computer system.

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Me 60305 Lecture 1