PowerPoint to accompany
Technology of Machine Tools
6th Edition
Krar • Gill • Smid
CAD/CAM
Unit 79
Copyright © The McGraw-Hill Companies, Inc.
Permission required for reproduction or display.
79-2
Objectives
• Define CAD and CAM
• Explain the purposes of solid modeling
• Know the differences between
Cadworthy and Camworthy
• Describe process chaining and list the
steps in the process
• State the purposes of pocket, contour,
drill, and surface toolpaths
79-3
CAD/CAM
• Marriage of computerized forms of
drafting/design and manufacturing
– Computer graphics is CAD part
– NC is CAM part
• Covers creation of part from initial design
to finish-machines part produced on
numerically controlled machine tool
• Progressed quickly in past 10 years
• Amount of math increasingly exponential
79-4
CAD Development
• Primarily centered around
– Modeling techniques to present conventional
drawings
– Production for solid models
• Should provide means for designer to do job
faster and more accurately
• Should be closely integrated with
techniques for modeling shape and structure
of design
79-5
Systems Presently In Use
• No longer consist of only 2D or 3D
wireframe units and simple toolpaths
• Software
– enables manufacturers to produce parts faster,
more economically and more consistent quality
• Manufacturers continually revising
modeling technology, improving machining
capabilities and automated processes
79-6
Solid Modeling
• Rapidly becoming industry-modeling
standard
• Solids provide more accurate picture of
where material lies
– Wireframe data is less easy to understand
• Geometric model outlining edges
• Lines in back of object show through from front
79-7
Solid Modeling and CAD/CAM
• PC-based solid modeling make it available
to smaller machine shops
– Increases adaptability
• Gives shop capability to use data it wants
– Wireframe taken from solid
– Surfaces taken from solid
– Solid itself
• Gives shop more choices for programming
79-8
How CAD/CAM Works
"Art to Part"
• Step one: Inputting the geometry
– Creating geometry in CAD
• Imported via translators from another CAD system
– IGES, DXF, ASCII, STL, VDA, SAT, Parosol
– System imported in 2D, 3D wirefrace, 3D
surfaces or solids
– Import geometry in form of XYZ coordinates
• Points converted to splines
79-9
Cadworthy Geometry
• Created from a drafting point of view
• All details and edges of part represented
Copyright © The McGraw-Hill Companies, Inc.
Permission required for reproduction or display.
79-10
Camworthy Drawing
• Purpose strictly for CNC machine use
– Contains fewer lines – only lines needed to
create toolpath included
• Make toolpath creation easier and less confusing
• Sometimes geometry
modified to control toolpath
• Applies to 2D, wireframe,
surfaces
Copyright © The McGraw-Hill Companies, Inc.
Permission required for reproduction or display.
79-11
Camworthy Drawing
• To make camworthy drawing from
cadworthy drawing, geometry edited so all
endpoints are
connected and no
gap remains
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Permission required for reproduction or display.
79-12
Defining Where the
Cut Takes Place
• After geometry, next step is selecting order
in which geometry to be machined
– Process chaining (where cuts are to take place)
– Geometry evaluated as to appropriate toolpath
• Many different toolpath types in various
CAD/CAM softwares
79-13
How the Cut Takes Place
• Next step after toolpath assigned to
geometry
• Parameters used to identify
–
–
–
–
–
What tool to use
Size of tool
Speeds, feeds and depth of cuts (up and down)
Width of cut (side to side)
Cutter compensation
79-14
Backplotting
• Process of displaying toolpath once the
parameters have been set
• Displayed
– Showing centerlines
– Solid model with material removed or being
removed
• Onscreen visualization helps to catch errors
prior to actual cutting of part
79-15
Converting the Toolpath to
G- and M-Codes
• Next step
• Called post processing
– Converts toolpath to NC file customized for a
particular machine control
• Possible to process one toolpath through
several different post processors
– Run on several different brands of controls
79-16
Downloading Program to
Machine
• Next step in process
• Download G- and M-codes into NC
controller
– Via direct cable connection if networked
– Via floppy disk
• Usually programs too big
79-17
Setting Up the Machine
• Once loaded, part must be securely held in
holding fixture and machine set up
– Set home position on machine at same point as
program home position or origin
• Standard for location of point is with X and Y zero
positions at part's lower left corner and Z zero on
top surface
• If circular part, X and Y zero is center an Z is top
– Tip of tools or tool zero position must be set
– Set size and tool number of all tools used
79-18
Final Step: Running the Part
• After machine setup, time to press cycle start
button
– Begin machining process
• When finished machining, CAD/CAM
process completed
"art to part"
79-19
Toolpaths
• Pocket toolpath
– Purpose to remove material from cavity in stock
– Material left standing in pocket called islands
• Contour toolpath
– Purpose to cut along line/surface to form shape
• Drill toolpath
– Purpose to create holes and/or enlarge them
• Surface toolpath
– Purpose to remove material from part designed
as surface or solid
79-20
Functions
• Constant Volume Removal
– Feedrate optimization carries feedrate based on
volume of material being removed
• Can set upper and lower limits to match machine
• Optimize Entire Shop
– Feedrate optimization helps find each machine
tool's maximum efficiency zone
• Smart Cornering
– Adjusts feedrate around corners and small radii