manufacturing technology (me461) lecture2
TRANSCRIPT
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ME-461, Manufacturing
Technology
Instructor: Shantanu Bhattacharya
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Computer aided design
A large no. of factors are responsible for the success
of any engineering organization.
Engineering design of products and processes is one
of the most critical factors for success. Understanding of the design process and the
computer aided design tool CAD is required to realize
a producible product design.
Computer graphics play an important role in the
product development process by generating
presenting and manipulating geometric models.
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Product design process Contemporary design is a highly sophisticated process and it requires the involvement of not
only design engineers but also personnel from the departments of manufacturing, finance,
marketing, and so on.
The primary input to any design process is the recognition of the fact that a need for aproduct or service exists.
The basic steps involved in the design process are (a) Problem identification (b)Preliminary
ideas (c) Refinement process (d) Analysis process (e) Decision process (f) Implementation.
(1)Problem Identification: The key to designing a
successful product lies in properly identifying the need
and the attributes of that need to which the product is
being developed.
Therefore the problem identification process should
involve the collection of field data; conducting field
surveys and experiments; use of intuition, judgment,
and personal observation and physical
measurements.For example: Consider the problem of developing a
line of high quality notebook sized computers that will
eventually beat the competition. There is a need to
identify the characteristics of the product that will be
successful in a highly competitive market.
For example the design product should be light in weight, highly portable, self contained, and sized to fit in abriefcase, have a standard keyboard layout feel, and have a compatible operating system, among many other
features.
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Product Design Steps
(2) Preliminary Ideas:Once the problem domain has been identified, the
second phase is to generate as many ideas as possible. Brainstormingsessions should be used to generate solutions to the present problem that
may revolutionize present methods. For example: in case of notebook
sized computers, consider the possibility of technological choices in very
large scale integrated (VLSI) circuits; materials choices and design
complexities for price competitiveness; and choices for making theproduct reliable, testable and producible.
(3) Refinement Process: During the refinement process, several good ideas
are pursued, using scale drawings to determine their merits in terms of
space requirements, critical measurements, dimensions of structural
members, and interactions of surfaces and planes.(4) Analysis Process: The analysis phase is concerned with the evaluation of
best designs from the point of view of a number of criteria such as cost,
functional requirements, and marketability. Other engineering tools such
as finite element methods and assembly analysis tools should be used to
evaluate alternative designs from the functionality point of view.
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Product Design Steps
(5) Decision Process: Most often a product is ultimately manufactured using a
single design. Therefore there has to be a decision phase of the design
process wherein a design that has all desirable characteristics is selected
with the following attributes:
(a)Manufacturable at minimum cost.
(b)Design with all desirable quality built-in.
(c) Design that can be quickly manufactured to make the product avialable to
the customers faster.
(6) Implementation process: This step is essentially a detailed design phase.
The detailed specifications of materials, dimensions, tolerances, and
surface roughness should be provided. The idea is to make the drawings to
be used directly for developing process plan so that the product can be
manufactured.
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A brief history of CAD
Automotive and aerospace industries have been at the
forefront of development of CAD technology.
Its origin however can be traced back to Ivan Sutherlands
thesis in 1963 describing a system called sketch pad.
The system known as sketch pad is now known as interactive
graphics and was developed under the SAGE (semi automatic
ground environment) project.
It helped change the radar information into computer
integrated pictures and allowed the flexibility of choosing the
information by pointing a light pen at the desired location on
the cathode ray tube display.
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CAD/CAM systems A wide variety of CAD/CAM systems are currently avialable.
Essentially a CAD system comprises of three major components:
Hardware, which includes computer and input/output devices, application
software, and the operating system software.
The operating systems software act as the interface between the
hardware and the CAD application software system.
The classification scheme we use in thissection is based on hardware of the system.
More specifically, we classify systems by the
host computer that drives the system.
Generally, CAD/CAM systems are classifiedinto four types:
1. Mainframe Based systems
2. Minicomputer based systems
3. Workstation based systems
4. Microcomputer based systems
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Mainframe based system When large engineering projects are involved mainframe based systems are
preferred. The organization of such systems are shown below.
Two major computer system environments
in such a system are the user environment
and the system environment.
The user environment includes workstations
and peripherals such as printers andplotters.
The number of workstations is limited by the
capacity of the host computer so as to
permit a system desired system response
time.
The main segments of a workstation areinput and output devices.
Input devices include cursor control devices
for graphic input and a keyboard containing
programmed function keys for text input.
The light pen, joystick, mouse, stylus on a
digital tablet are commonly used forcontrolling the cursor.
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Input output devices
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Introduction to Geometric Transformation
Computer graphics plays an important role inthe product development process by
generating, presenting, and manipulating
geometric models of objects.
During the product development process, for
proper understanding of designs, it is
necessary not only to generate geometric
models of objects but also to perform such
manipulations on these objects as rotation,
translation and scaling.
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Introduction to Geometric transformation
Essentially, computer graphics is concerned with generating,
presenting and manipulating models of an object and itsdifferent views using computer hardware, software and
graphic devices.
Usually the numerical data generated by a computer at very
high speeds is hard to interpret unless one represents thedata in graphic format and it is even better if the graphic can
be manipulated to be viewed from different sides, enlarged or
reduced in size.
Geometric transformation is one of the basic techniques thatis used to accomplish these graphic functions involving scale
change, translation to another location or rotating it by a
certain angle to get a better view of it.
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Geometric Transformation
Two dimensional transformation:
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2-D transformation
Example : In the figure above, suppose the initial coordinates of vertices A,B,C are
(1,3), (4,5), and (5,3.5), respectively. Determine the coordinates of new vertices A, B
and C after translating the triangle by a distance D= [7, -2]T(where T represents
transpose). Verify that the lengths of the edges of the triangle are unchanged.
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2-D transformation
2 D f i
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2-D transformation Scaling
Example: From the figure on the right, show that
the length of the edge AB is equal to three times
that of AB after scaling the object uniformly by
factor 3.
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2-D transformationRotation:
Rotation in 2D space is defined as moving
any point (x,y) of an object to a new position
by rotating it through a given angle about
some reference point. Positive angles are
measured counterclockwise from x to y. The
mathematical expression for the rotating
transformation is not as obvious as the
formulas for translation and scaling
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2-D transformation (Rotation)
Example: Determine the new position of
object A placed on a round holding tableafter the table has been rotated by 35 deg.
Solution:
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Homogeneous transformation
Although the 2D and 3D transformationspresented in the previous sections have
obvious geometric meaning it is not efficient
or economical to implement them on a
computer.
This is because translation involves the
addition of matrices whereas scaling and
rotation involves multiplication.
It is however possible to implement a scheme
involving only multiplication which would
simplify the transformation process.
H T f ti
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Homogeneous Transformation