me 60305 lecture 1
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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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Introduction to CAD/CAM/CAE (continued)
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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Introduction to CAD/CAM/CAE (continued)
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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Introduction to CAD/CAM/CAE (continued)
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.
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Introduction to CAD/CAM/CAE (continued)
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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Introduction to CAD/CAM/CAE (continued)
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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Introduction to CAD/CAM/CAE (continued)
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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Introduction to CAD/CAM/CAE (continued)
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.
Introduction to CAD/CAM/CAE (continued)
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Introduction to CAD/CAM/CAE (continued)
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.
Introduction to CAD/CAM/CAE (continued)
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Introduction to CAD/CAM/CAE (continued)
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.
Introduction to CAD/CAM/CAE (continued)
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Introduction to CAD/CAM/CAE (continued)
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.
Introduction to CAD/CAM/CAE (continued)
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Introduction to CAD/CAM/CAE (continued)
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.
Introduction to CAD/CAM/CAE (continued)
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Introduction to CAD/CAM/CAE (continued)
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.
Introduction to CAD/CAM/CAE (continued)
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Introduction to CAD/CAM/CAE (continued)
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.
Introduction to CAD/CAM/CAE (continued)
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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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Introduction to CAD/CAM/CAE (continued)
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.
Introduction to CAD/CAM/CAE (continued)
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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.
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Introduction to CAD/CAM/CAE (continued)
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.
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Introduction to CAD/CAM/CAE (continued)
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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Introduction to CAD/CAM/CAE (continued)
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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Introduction to CAD/CAM/CAE (continued)
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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Introduction to CAD/CAM/CAE (continued)
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.
Introduction to CAD/CAM/CAE (continued)
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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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Introduction to CAD/CAM/CAE (continued)
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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Introduction to CAD/CAM/CAE (continued)
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.
Introduction to CAD/CAM/CAE (continued)
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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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