2. ME8691 Computer Aided Design and
Manufacturing
UNIT I INTRODUCTION
Product cycle- Design process- sequential and concurrent engineering- Computer
aided design – CAD system architecture- Computer graphics – co-ordinate
systems- 2D and 3D transformations- homogeneous coordinates - Line drawing -
Clipping- viewing transformation-Brief introduction to CAD and CAM –
Manufacturing Planning, Manufacturing control- Introduction to CAD/CAM –
CAD/CAM concepts ––Types of production - Manufacturing models and Metrics –
Mathematical models of Production Performance
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4. UNIT IV
FUNDAMENTAL OF CNC AND PART PROGRAMING
Introduction to NC systems and CNC - Machine axis and Co-ordinate
system- CNC machine tools- Principle of operation CNC-
Construction features including structure- Drives and CNC
controllers- 2D and 3D machining on CNC- Introduction of Part
Programming, types - Detailed Manual part programming on Lathe &
Milling machines using G codes and M codes- Cutting Cycles,
Loops, Sub program and Macros- Introduction of CAM package.
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10. Processing equipment
The third basic component of an NC system is the processing
equipment that performs the actual productive work (e.g.,
machining).
It accomplishes the processing steps to transform the starting
workpiece into a completed part.
Its operation is directed by the MCU, which in turn is driven by
instructions contained in the part program.
In the most common example of NC, machining, the processing
equipment consists of the worktable, spindle, motors and control
units to drive them.
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12. Advantages of NC
Non-productive time is reduced.
Greater accuracy and repeatability.
Lower scrap rates.
Inspection requirements are reduced.
More complex part geometries are possible.
Engineering changes can be accommodated more gracefully.
Simpler fixtures.
Shorter manufacturing lead times.
Reduced parts inventory.
Less floor space.
Operator skill requirements are reduced.
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13. Disadvantages of NC
Higher investment cost.
Higher maintenance effort.
Part programming.
Higher utilization of NC equipment.
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28. Subroutine:
Subroutine is also called as subprograms.
When a similar machining operation is to be performed repeatedly then the general programming method
will not be used because,
It is very lengthy.
It is tedious.
It is more time consuming.
It consumes more space in the computer memory.
In such case, subroutine method is used. It is a time saving technique.
It is an independent program similar to general program and stored in the computer memory under
separate program number.
It can be called anywhere in the main program and for any number of times.
To call the subroutine in the main program, the miscellaneous code M98 is used. The instruction block for
subroutine can be written as follows: N10 M98 P50 L1;
where,
M98 indicates a call to subroutine,
P50 indicates the program number (here 50),
L1 indicates to call subroutine only one time.
After execution of subroutine return back to the main program and continue it.
To end the subroutine and return back to the main program M99 code is used.
It is important to note that, the main program is written in absolute programming mode (G90) and
subroutine is written in incremental programming mode (G91). Hence, use code G91 at the start of
subroutine and G90 before use of M99.
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29. Canned cycle
Canned cycle is also called as multiple-repetitive cycle.
It is a set of instructions stored in the computer memory which is used perform a
fixed sequence of operation.
It is commonly used for repetitive operation where material is to be cut number of
passes.
The main advantage of canned cycle is that, it reduces length of the program hence
memory space and the complexity of the program.
In this cycle, the final position is mentioned in the instruction block and the cutter
path is automatically plotted by the controller itself.
Canned cycle can be called and cancelled by using G-codes (preparatory codes).
According to the shape of workpiece various G-codes are used for canned cycle.
For example: G74 for slot or rectangular pocket milling and G77 for circular
pocket milling
Canned cycle can be cancelled by using G80 code.
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31. Loops
Loop in CNC programming usually refers to a command or a series of commands.
In the realm of CNC programming, loops are executed on a repeated basis for a
specified number of times.
In simple words, a looping command in CNC usually portrays the controller two
things- where to loop back from and where to loop back to.
What is Do Loops?
In most programming languages, a do loop is a control flow statement. The main
objective of executing a do loop command is to run code blocks at least once.
Another main aim of executing a do loop command is not to over depend on a given
Boolean condition at the end of each block. In the realm of CNC programming, a do
loop refers to a set of operations which would be repeated over a number of equal
steps.
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32. Macros
Macro programming is a method using variable data in a special subprogram (now
called a macro), with actual values defined in the main program. This method
provides a single ‘master’ program that can be used many times with different
numerical values. A typical example is a bolt circle, where only a few values change.
The main purpose of a macro program is to save programming time.
A macro program looks like a regular CNC program, but includes many other
features. A macro program is structured as a subprogram - it is stored under its own
program number (O-), and it is usually called by the main program, using the G65
preparatory command. In a simple form, macro features can be used in the main
program, without the macro call.
Macros are defined in a similar way as subprograms, but they are called or invoked
by the G65 command.
The G65 macro command accepts variable definitions, called arguments. Arguments
are actual program values required for a particular macro only. They are passed to the
macro. Variable data in the macro is then replaced with the supplied arguments.
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