BASICS OF CAD (FOR MOLD
DESIGN)
Computer-Aided Design (CAD) is a computer-aided technique for
improving the efficiency of design engineering and manufacturing
activities. The term CAD was originally
used to mean computer-aided design and is still sometimes used in this sense in
that it is the use of computer in conceptual design/engineering design part of
the process and includes analysis and simulation rather than drafting. The term CAD has also nevertheless been used
to mean computer-aided drafting. Some
CAD applications in the Design Engineering are as listed
(1) Preparation of
quotations
(2) Conceptual design
(3) Styling
(4) Finite-element
analysis
(5) Simulation
(6) Engineering designs
(7) Detailed design
(8) Part listing
(9) Quality assurance
COMPUTER-AIDED DESIGN
With the help of computer technology, the designer has the
capability of managing the enormous number of design, material, and process
applications available when designing with plastics. IN the past, the designer more often than not
had to limit the material, process, and design choices to those that were
familiar. However, the computer now
provides a means of developing a number of design concepts, quickly evaluating
them against established functional and performance criteria in a wide range of
materials and processes, and making the necessary design modifications.
The approach provides finished drawings and specifications that can
be furnished with increased accuracy and confidence, usually in less time than
before. In addition, the computer
provides many other advantages. IF one
dimension is changed that effects many others, all the dimensions will be
changed automatically by the computer a the same time the initial change is
made.
It is of course possible that entering the initial three-dimensional
geometry for various design concepts into a computer can be more time consuming
than developing concept sketches with conventional long-hand methods. However, subsequent revisions and analyses of
that geometry can be performed many times faster on computer than manually.
BENEFITS OF CAD:
(1) Direct cost saving
(2) Direct time saving
(3) Improvement in
product quality
(4) Increase in volume
of business
Benefits of using can be explained taking case in which, by manual
techniques, design and drafting of a part takes two people 15 days each or
total of 30 man-days.
As a direct cost saving, for example, terminate the employment of
one of the people, thus making a saving in salary costs (this is a fairly
unusual solution, since it implies stagnation of the company’s business, and
most companies look to CAD/CAM to promote growth);
As a direct time saving, for example by only spending 15 days on
design and drafting of this part, the overall design engineering cycle time
will be reduced. Hopefully, the part can be therefore be produced and
sold earlier than would have been possible without CAD/CAM. Since both people are retained by the
company, the 15 days “saved” can be used
to design another part, which can also be produced and sold earlier than would
otherwise have been possible.
As an improvement in product quality: continue to spend 30 days on
design and drafting of the part, but investigate more than design alternatives
and carry out more through checks of the design;
As an increase of volume of business: spending the required 15 days
on the part, but spending the 15 days “saved” on preparation a proposal and
quotation to compete for a tender that would otherwise have been ignored.
INTRODUCTION TO
AUTOCAD:
The AUTOCAD design package is a general purpose Computer Aided
Design/drafting application software for the computers. CAD applications are tremendously powerful
tools. The speed and ease with which a
drawing can be prepared and modified using a computer offers a phenomenal
advantage over “hand” preparation.
There is virtually no limit to kinds of the drawings you can prepare
using AUTOCAD. IF a drawing can be
created by hand, it can be generated by AUTOCAD.
The application for which AUTOCAD is being used today.
* Work flow charts and
organizational diagrams.
* Proposals and
presentations.
* Graphs of all kinds.
* Drawings
for electronic, chemical, civil, mechanical, automotive, and aerospace
engineering applications.
* Plots
and other representations of mathematical and scientific functions.
* technical
illustrations and assembly diagrams.
* Company
logos.
AUTOCAD remembers the locations,
sizes, and colors of the objects you draw,
maintaining them in a database for
subsequent retrieval, analysis and manipulations.
No technical knowledge is required
to use AUTOCAD effectively; practice and a
thorough understanding of its
features are key to proficiency.
THE AUTOCAD DRAWING :
An AUTOCAD drawing is a file that
describes a graphic image. AUTOCAD uses
this
description to produce the image on
the screen or the plotter paper.
CREATING THE DRAWINGS:
The following concepts and terms
introduce the main elements of an AUTOCAD
drawing.
(1) WORLD CO-ORDINATE SYSTEM:
AUTOCAD uses a
fixed cartesian co-ordinte system, to locate point in your drawings. A point is expressed as an (x,y,z)
co-ordinate pair. the origin is where
the values of x and y,z are zero. We’ll
call this system the world co-ordinate system.
(2) USER
CO-ORDINATE SYSTEM:
The world
co-ordinate system is fixed and cannot be altered in AUTOCAD. However, you can define an arbitrary
coordinate system, called user co-ordinate system (UCS), within this UCS.
(3) CO-ORDINATE
SYSTEM ICON:
To help your
bearings among different co-ordinate systems in drawings, you can refer to the
co-ordinate system icon.
(4) RIGHT
HAND RULE :
AUTOCAD uses the
right hand rule, to define all coordinate system.
(5) DRAWINGS
UNITS & SCALING :
The distance
between two co-ordinate is measured in drawing units.
(6) DRAWING
LIMITS AND EXTENTS :
AUTOCAD assumes
that you are drawing in a rectangular area.
The drawing limits are the borders of this rectangle, expressed in X,Y
drawing co-ordinates. You can select
whatever limits make sense for your drawing.
(7) DRAWING
ENTITIES :
Much of the
“drawing” you do with AUTOCAD consists of positioning entities at co-ordinate
locations. An entity is predefined
element that you place in a drawing by means of a single command. Lines, arcs, and circles use entities you
will use frequently.
(8) COLOURS
AND LINETYPES :
You can assign and
a linetypes to each entity. the colour
is a number from 1 to 255 that selects the actual colour in which items are
drawn on the graphics monitor. A lintype
is a specific sequence of alternating line segments and spaces using these
properties, you can draw attention to important details in your drawing,
highlight recent changes, or depict the relationships among entities.
(9) LAYERS
:
You can assign
portions of your drawing to different layers, and you can define as many layers
as you like. The layering concept is
similar to the transparent overlap used in many drafting applications. Layering allows you to view and plot related
aspects of a drawing separately or in any combination.
(10) DRAWING
INSERTION :
You can treat an
existing AUTOCAD drawing (stored on disk) as a block and merge it into the
drawing that you are currently creating.
(11) FREE
HAND SKETCHING :
AUTOCAD has a
facility for sketching. You can draw
short, connected lines freehand with a pointing device allowing you to trace
map, or add your signature to a drawing.
VIEWING THE DRAWING
AUTOCAD offers
many ways for you to view your drawing in progress and after it is completed.
(i) Zooming
and Panning.
(ii) Display
Extents.
(iii) Plan view and 3D views.
(iv) Viewports.
(v) Resolution.
(vi) Editing
the drawing.
PRODUCT DESIGN MAKING IN AUTO CAD (example)
In the next part we will see about the commands which are mainly used for making mould design and product design...
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