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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
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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 companys 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;
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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.
SYSTEM REQUIREMENTS CAD
To run CAD on Windows NT or Windows 95, the following minimum software and
hardware are required:
Windows NT 3.51/4.0 or Windows 95
IT is recommended that you install and run CAD on an operating system in the samelanguage as your CAD software or on an English version of one of the supported
operating systems.
Intel 486 or Pentium processor or compatible
32 MB of RAM-Windows NT
50 MB of hard disk space
64 MB of additional RAM for each concurrent session
2.5 MB of free disk space during installation only (this space is used for temporary
files that are removed when installation is complete)
Windows NT 3.51 only: Service Pack 4 or 5 if you install Internet Utilities with the
custom or full installation method
NOTE : An additional 8 MB to 15 MB of space may be required for files installed
in the system folder. This doesnt need to be on the same drive as the program folder
where you load Auto CAD.
CD-ROM drive
640 x 480 VGA video display (!024 x 768 recommended)
Windows-supported display adapter
Mouse or other pointing device
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for international single-users and student locked version only: IBM-compatible
parallel port and hardware lock.
For a more detailed listing of system requirements, see the Installation Guide for each
specified CAD software.
INTRODUCTION TO AUTOCAD:
The AUTOCAD design package is a general purpose Computer Aided Design/drafting
application software for the computers. CAD applications are tremendosly 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.
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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. Apoint is expressed as an (x,y,z) co-ordinate pair. the origin is where the values of x and
y,z are zero. Well 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 :
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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 aspecific 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.
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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.
UTILITY COMMANDS USED IN THE MOLD DESIGN BY USING CAD
The following is an alphabetical list of commands used in development of the standard
mold base and design of molds.
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S.No. COMMAND DESCRIPTION REMARKS
1.
2.
3.
4.
5.
6.
7.
ARC
AREA
ARRAY
ATTDEF
ATTEDIT
AXIS
BLOCK
Draws an arc of any size.
The default method is by
specifying two ends points
and a point along the arc,
but several other methods
are available.
Computes the area of a
polygon, polyline, or circle.
Makes multiple copies of
selected objects in a
rectangular or circular plan.
Creates an Attribute
definition entity for textual
information to be associated
with a Block Definition.
Permits editing of
Attributes.
Displays a ruler line on
the graphics monitor.
Forms a compound object
from a group of entitles.
This command is effectively
used in the product
development.
Used in the calculation of core
and cavity development and
clamp-force factors.
Polar circular array and
rectangular array is used in
core and cavity layout plan.
Preparation of database for
standard mold parts.
Used in preparation of
database.
Gives on-line element
locations.
Development of database for
mold parts e.g. guide pillar,
screws, guide bush, locating
ring etc.
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8.
9.
10.
11.
12.
13.
14.
CHAMFER
CHPROP
CIRCLE
COLOR
COPY
DELAY
DIM
Creates a chamfer at the
intersection of two lines.
Modifies properties of
selection objects.
draws a circle of any size.
The default method is by
centre point and radius, but
other methods are available.
Establishes the color for
subsequently drawn objects.
Draws a copy of selected
objects.
Delays execution of the next
command for and for a
specified time. Used with
command scripts.
Invokes dimensioning mode,
permitting many dimension
notations to be added to a
drawing.
Used in detailed designs and
drafting.
Used in the editing during the
mold drafting to alter the part
positioning.
To differentiate the important
parts like core and cavity in
the assembly different colours
may be used.
Used in cavity and runner
layout design for multi-
impression molds.
Used in dimensioning of the
mold parts.
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15.
16.
17.
18.
19.
20.
21.
22.
DIM 1
DIST
DIVIDE
DOUGHNUT or
DONUT
DTEXT
DVIEW
ELEV
ELLIPSE
Allows one dimension
notation to be added to a
drawing then returns to
normal command mode.
Finds distance between two
points.
Places markers along a
selected object, dividing itinto a specified number of
equal parts.
Draws rings with specified
inside and outside
diameters.
Draws text items
dynamically.
Defines parallel or visual
perspective views
dynamically.
Sets elevation and extrusion
thickness for subsequently
drawn entities. Used in 3D
visualizations.
Used in dimensioning of the
mold parts.
Used to check the exact
position of cavity and runner
positions.
Used to divide core and cavity
into required number of parts
for the analysis purpose.
Used to highlight the
impression or molding.
Preparation of title blocks, bill
of materials.
To view the core and cavity
assembly in different angles.
Modifying thickness of mold
core and mold plates.
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23.
24.
25.
26.
27.
28.
END
ERASE
FILL
FILLET
GRID
HATCH
Draws ellipses using any of
several specifications.
Exits the drawing editor
after saving the updated
drawing.
Erases entities from the
drawing
Controls whether solids,Traces, and wide Polylines
are automatically filled on
the screen and the plot
output.
Constructs an arc of
specified radius between
two lines, arcs, or circles.
Displays a grid of dots, at
desired spacing, on the
screen.
Perform crosshatching and
pattern filling.
Used for editing the existing
drawings.
Cavity development.
Detailed drawing works.
This feature helps to get a
sense of the sizes of drawing
entities and this relationship.
The grid is not considered part
of the drawing, it is for visual
reference only and is never
plotted.
Hatching generates line
entities for the chosen pattern
and adds them to the drawing.
Since a pattern may contain
many lines, CAD normally
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29.
30.
31.
32.
33.
34.
HELP or ?
HIDS
LAYER
LIMITS
LINE
LINETYPE
Displays a list of valid
commands and data entry
options or obtains help for a
specific command.
Regenerates a 3D
visualization with hiddenlines removed.
Creates names drawing
layers and assigns color and
linetype properties to those
layers.
Changes the drawing
boundaries and controls
checking of those
boundaries.
Draws a straight lines of any
length.
Defines linetypes
(sequences of alternating
line segments and spaces),
loads them from libraries,
groups there lines into an
internally generated block.
Displays a list of valid
commands and data entry
options or obtains help for a
specific command.
Regenerated a 3D
visualization with hidden
lines removed.
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35.
36.
37.
38.
39.
40.
41.
42.
LIST
LTSCALE
MEASURE
MIRROR
MOVE
MULTIPLE
ORTHO
PLAN
and sets the linetype for
Subsequently drawn objects.
Lists database information
for selected objects.
Sets scale factor to be
applied to all linetypes
within drawing.
Places markers at specifiedintervals along a selected
object.
Reflects designed entities
about a user specified axis.
Moves designated entities to
another location.
Causes the next command to
repeat until canceled.
Constrains drawing so that
only lines aligned with the
grid can be entered.
Puts the display in PLAN
view (V POINT 0, 0, 1)
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43.
44.
45.
46.
47.
48.
49.
50.
PLOT
POLYGON
QUIT
SAVE
SCALE
SHAPE
SKETCH
SOLID
relative to either the current
UCS, a specified UCS, or
the World Coordinate
System.
Plots a drawing on a pen
plotter.
Draws regular polygons
with the specified number of
side.
Exists the Drawing Editor
and returns to AUTOCADS
Main Menu, discarding any
changes to the drawing.
Updates the current drawing
file without exiting the
Drawing Editor.
Alters the size of existing
objects.
Draws pre-defined shapes.
Permits free-hand sketching.
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51.
52.
53.
54.
55.
56.
57.
STATUS
STRETCH
STYLE
TEXT
TIME
UNITS
VIEWPORTS
OR VPORTS
Draws filled in polygons
Displays drawing statistics
& modes.
Allows you to move a
portion of a drawing while
retaining connections to
other parts of the drawing.
Creates named text styles,with user selected
combinations of font,
mirroring, obliquing, and
horizontal scaling.
Draws text characters of any
size, with selected styles.
Displays drawing creation
and update times, and
permits control of an
elapsed timer.
Selects coordinate and
angled display formats and
precision.
Divide AUTOCADS
graphics display into
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58.
59.
60.
61.
VPOINT
3D FACE
3D MESH
3DPOLY
multiple viewports, each of
which may contain a
different view of the current
drawing.
Selects the viewpoint for a
3D visualization.
Draws three-dimensional
plane sections.
Defines a three dimensional
polygon mesh by specifying
its size (in terms of M and
N) and the location of each
vertex in the mesh.
Creates a three-dimensional
polyline.
DIMENSIONING COMMANDS
COMMAND DESCRIPTION
ALIGNED
ANGULAR
BASELINE
Generates a linear dimension with the dimension line parallel to the
specified extension line origin points. This permits you to align the
dimensioning notation with the object.
Generates an arc to show the angle between two nonparallel lines.
Continues a linear dimension from the baseline (first extension line)
of the previous dimension.
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CENTRE
CONTINUE
DIAMETER
EXIT
HOMETEXT
HORIZONTAL
LEADER
NEWTEXT
RADIUS
REDRAW
RPTATED
STATUS
Draws a Circle/Arc centre mark or centre lines.
Continues a linear dimension from the second extension line of the
previous dimension. In effect, this breaks one long dimension into
shorter segments that add up to the total measurement.
Dimensions the diameter of a circle or arc.
Returns to the normal Drawing Editor command mode.
Restores the text of an associative Dimensions.
Generates a linear dimension with a horizontal dimension line.
Draws a line or sequence of lines (similar to the normal LINE
command) for controlled placement of dimension text. Useful mostly
for radius and diameter dimensioning.
Changes the text of existing associative Dimensions.
Dimensions the radius of a circle or arc, with an optional centre mark
or centre lines.
Redraws the entire display, erasing any marker blips that were
present (just like the normal REDRAW command).
Generates a linear dimension with the dimension line drawn at a
specified angle.
Displays all dimensioning variables and their current values.
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STYLE
UNDO
UPDATE
VERTICAL
Switches to a new text style.
Erases the annotations produced by the most recent dimensioning
command.
Updates existing associative Dimension entities to use the current
settings of the dimension variables, the current UNITS settings.
Generates a linear dimension with a vertical dimension line.
OBJECT SELECTION :
OBJECT
SELECTION
OPTION
MEANING
POINT
MULTIPLE
Selects one object that crosses the small pick box. If no
object crosses the pick box and Auto mode has been selected,
this designated point is taken as the first corner of a Crossing or
window box.
allows selection of multiple objects using a single search of the
drawing. the search is not performed until you give a null
response to the select objects prompt.
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LAST
WINDOW
CROSSING
BOX
AUTO
PREVIOUS
ADD
REMOVE
UNDO
SINGLE
selects the most recently drawn object that is currently visible.
Selects all objects that lie entirely within a window.
Selects all objects that lie within or cross a window.
Prompts for two points. If the second point is to the right of the
first point, selects all objects inside box (like Window).
Otherwise, selects all objects within or crossing the box (like
crossing).
Accepts a point, which can select an object using the smallpick box. If the point you pick is in an empty area, it is taken
as the first corner of a Box (see above).
Selects the previous selection set.
Establishes add mode to add following objects to the
selection-set.
Sets remove mode to remove following objects from the
selection-set.
Undo (remove objects last added).
Sets single selection mode. As soon as one object or one
group of objects via Window/Crossing box) is selected, the
selection-set is considered complete and the editing command
uses it without further user interaction.
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