1 - Introduction to CNC

7/31/2019 1 - Introduction to CNC

1/21

Computer Numerical ControlledMachining


2/21

Conventional

Machine

CNC Machine

Motion ControlThe Heart Of CNC


3/21

Numerical Control Programming

CNC user must be able to view the machine

tool from two distinctly different

perspectives

First as a programmer.

Secondly, when machining the component.


4/21

A programmer needs to be

comfortable with:

the machines most basic components.

the direction of the machines axes.

any additional accessory equipment. and finally be aware of what programmable

functions are included.


5/21

From the machine tool manual

you should find answers to:

What is the machines maximum RPM?

What is the spindle and drive axis motorhorsepower?

What is the maximum travel distance ofeach axis?

How many tools can the machine hold?

What is the machines rapid traverse rate?

What is the machines fastest cutting speed?


6/21

Machined Example


7/21

Axis Reference Point

Most machine tool builders make the

reference position the extreme plus side of

each axis.

Note: always make sure that all the axes are

set to zero (0,0,0) before you carry out any

operation on any machine tool.


8/21

Absolute Versus Incremental Motion

In the absolute mode, theend points for allmotions will be specifiedfrom the program zeropoint. Assign By G90

In the incremental mode,end points for motionsare specified from the

tool's current position,not from program zero.Assign by G91


9/21

+ve X table

direction

Machine

table ref.

Pt 0,0

-ve Y table

direction

Table movement from machine reference

point.


10/21

Machine

table ref.

Pt 0,0

It is more convenient to think of the tool moving

around the component, than thinking of the table

direction when writing programs.

AB

C D

To move tool from A to B table needs to movein theve X direction, from B to C the table

moves in the Y +ve direction, and to move

from C to D the table moves in the +ve

direction.


11/21

Vice position with respect to

machines set datum


12/21

Controller Reference Setting


13/21


14/21

Program Writing

What we need to know:

Where the tool starts from.

Where the tool moves to.

The tool path.

How it gets there.

When the machine needs to start and stop.

When coolant is turned on or off.

What tools are available.

How is the workpiece held.


15/21

Program Makeup

Programs are made up of commandsand commands are made up of wordsor LeterO - Program number (Used for program identification)N - Sequence number (Used for line identification)G - Preparatory function (See below)

X - X-axis designationY - Y-axis designationZ - Z-axis designationR - Radius designationF - Feedrate designationS - Spindle speed designationH - Tool length offset designationD - Tool radius offset designation

T - Tool DesignationM - Miscellaneous function

The preparatory function (G)specifies is commonly used toset modes.

Miscellaneous functions (Mwords) allow a variety ofspecial functions.


16/21

Tool Setting


17/21

Common Mistakes

Spindle not on before cutting.

Coolant not turned on during machining.

Toolpaths out of order. Eg. holes weretapped before they were drilled.

Incorrect tool installation.

Improper feed and speed entered. Start program in wrong place.


18/21

Simple Program Example 1

Start and end

50

45

8

34

29


19/21

Program start

N10 G40 G49 G90; Safe line

N20 M06 T10 ; tool change sequence

N30 G43 H10; tool length offset N40 G00 X410.0 Y-192.0 Z-340.0;

work ref. Pt.

N50 M03 S2000;turn spindle on

Typical start to NC program ie. Set the

machine parameters.


20/21

Tool path

N60 G91 G00 Z-4.0;incremental

N70 G01 Z-9.0 F100;

N80 Y45.0;

N90 X50.0;

N100 Y-45.0; N110 X-50.0;

N120 G00 Z15.0; clear workpiece


21/21

Typical end of program.

N130 MO5; stop spindle

N140 G28 X0 Y0 Z0; return to machine ref. pt.

N150 M30; end program

1 - Introduction to CNC

Documents

Transcript of 1 - Introduction to CNC