CNC_Milling.ppt

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CNC Milling Machine

Mohd Zaid Bin Akop25 March 2008


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CONTENTS

1. Introduction

2. CNC Milling Program

CNC Codes

Coordinates

3. CAD/CAM software

FAKULTI KEJURUTERAAN MEKANIKAL

UNIVERSITI TEKNIKAL MALAYSIA MELAKA


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1. INTRODUCTIONFAKULTI KEJURUTERAAN MEKANIKAL


CNC Milling Machine

Computer Numerical Control (CNC) Milling is the most common

form of CNC.

CNC mills can perform the functions of drilling and often turning.

CNC Mills are classified according to

the number of axes that theypossess. Axes are labeled as

x and y for horizontal movement,

and z for vertical movement


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Roles in CNC Machine Production

Design Engineer

Determines part specifications

Designs and makes sketch of part. May work directly with

computer aided design and drafting system (CAD) to create

sketch. Designs and makes sketch of work-holding fixture if needed.

Drafter

Makes engineering drawing of part. May also use CAD system

to produce final drawing.

Makes engineering drawing of fixture if needed.

N/C Programmer

Studies engineering drawing to determine best sequence of

machining operations; identifies position points needed for

programming. Determines location of art or fixture in relation to zero


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Determines coordinate dimension for position points.

Determines tool selection, cutting speeds and feed rate. Write program manuscript.

Typist

Typist program manuscript on computer terminal

Stores program on disc or tape Verifies program

N/C Machine Operator

Insert N/C tape in MCU(machine control unit) tape reader or

enters N/C program into MCU memory.

Mounts fixture and workpiece on machine

Installs tools in toolchanger or manually changes tools.

Adjust feeds, speed, tool-depth stop and coolant on machines

where these are not automatically controlled.

Removes machined work piece from machine.


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The Basic Machining Operations

1. Milling is a process of using a rotating tool to remove material along

a contour or line.

2. Milling has traditionally been used to create flat surfaces and

straight edges on prismatic work pieces (three dimensional shapes

that look more like cubes than cylinders.3. Creating curved contours on a conventional milling machine is an

especially difficult task that requires a great amount of skill and

specialized tooling.

4. CNC machine tools have made curved contours much easier to

create.

5. The most common milling operation are as following


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End milling and face milling are the two basic categories of milling that

can be used to create common features such as contours, flatsurfaces and pockets.

a. pocketing

b. contouringc. facing

d. side milling


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CNC Safety

Machining and CNC machining all have inherent dangers with

rapidly moving machinery, sharp edges and hot flying chip.

However, we can minimize many of these dangers by giving some

thought to our actions and following the safety rules.

1. Same precautions as with conventional machine tools, includingeye protection and standard setup procedures and operation.

2. Do not let others distract you from your work. Your concentration is

critical when setting-up and operating machine tools.

3. CNC machine tools move automatically. They are extremely fast

and powerful; therefore, special precautions should be taken when

working around CNC machine tools4. You should never attempt to operate a CNC machine tool that you

do not fully understand. Instead, you should ask you instructor

whenever you are not sure of any procedure or function.


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5. You should never work inside CNC machine tool when some one

else is touching the controls. Might accidentally start the machine &cause serious injury.

6. Special care should be used when using rapid traverse on CNC

machine tool, including allowing an adequate distance above the

work piece and not using rapid traverse below the surface of the

part.7. Part programs should be tested by first using a computer simulation

on PC, simulating on the control and then try running above the

w/piece at a reduced rate & in single block mode.

8. Most programming errors can be caught by simply proof reading

your code. should print a hard copy of your code and spend a few

minutes checking for critical safety issues including proper speeds

and feeds, proper tool location when using rapid traverse and the

correct tool offsets.

9. You should never leave CNC machine tool unattended. Tools can

fail rapidly and cause damage or injury if not stopped immediately

10. CNC machine tools should only be operated with the doors


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2. CNC MILLING PROGRAMFAKULTI KEJURUTERAAN MEKANIKAL


Codes for Positioning and Milling

Modern CNC machine tools can be programmed to perform machining

operations with a language G code & M codes. It simple

instructions that the programmer will write to make the machine

behave in a certain way. There are dozens of G-codes and M-codes

used to perform everything from complex machining operations tocommon tool changes. However, just a few codes, if learned, will

get most of the work done. The others are just enhancements to

make programming more powerful and provide advanced machine

functions.

G00 Rapid Motion Positioning

X Optional X-axis motion command

Y Optional Y-axis motion command

Z Optional Z-axis motion command


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Rapid traverse is used for quickly positioning the tool in preparation for

making a cut/moving the tool to a safe location for tool and partchange. G00 can be used any place where the tool is not directly in

contact with the w/piece and where you wish to save time. Rapid

traverse is never used to perform a cut the velocity is far too fast

and is not constant.


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G01 Linear Interpolation Motion

F Feedrate in inches (mm) per minute

X Optional X-axis motion command



R Radius of the circle

C Distance from center of intersection where the chamfer begins

This G code moves the axes at a commanded feed rate. It is primarily

used to cut the workpiece. A G01 feed can be a single axis move or

a combination of the axes. The rate of axes movement is controlled

by feed rate (F) value. The feed rate value (F) can be on the currentprogram line, or a previous line (the control will always use to most

recent F value until another F value is commanded) .

G01 is a modal command, which means that it will stay in affect until

canceled by a rapid command such as G00 or a circular motion

command like G02 or G03


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Once a G01 is started all programmed axes will move and reach the

destination at the same time. If an axis is not capable of theprogrammed feed rate the control will not proceed with the G01

command and an alarm (max feed rate exceeded) will be

generated.


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M6 Tool change

G90 Absolute Position Commands

G54 Select work coordinate system

M03 Turn spindle on in the forward direction

G43 Tool length compensation + (Add)

M08 Coolant on

M09 Coolant off

G53 Non-modal machine coordinate selection

M30 Program endH- Tool length offset selection


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G02 CW / G03 CCW Circular Interpolation Motion

F Feedrate in inches (mm) per minute

I Optional distance along X axis to center of circle

J Optional distance along Y axis to center of circle

K Optional distance along Z axis to center of circle

R Optional radius of circleX Optional X-axis motion command



These G codes are used to specify circular motion. Two axes arenecessary to complete circular motion and the correct plane, G17-

19, must be used. There are two methods of commanding a G02 or

G03, the first is using the I, J, K addresses and the second is using

the R address.


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Using I, J, K addresses

I, J and K address are used to locate the arc center in relation to the

start point. In other words, the I, J, K addresses are the distances

from the starting point to the center of the circle. Only the I, J or K

specific to the selected plane are allowed (G17 uses IJ, G18 uses

IK and G19 uses JK). The X, Y, and Z commands specify the endpoint of the arc. If the X, Y, or Z location for the selected plane is not

specified, the endpoint of the arc is the same as the starting point

for that axis.

To cut a full circle the I, J, K addresses must be used; using an Raddress will not work. To cut a full circle, do not specify an ending

point (X, Y and Z); program I, J or K to define the center of the

circle. For example: G02 I3.0 J4.0 (Assumes G17; XY plane)


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An arc that does not end at a quadrant may require the precise

use of trigonometry.

G02 X .7071 Y.7071 I1.0 J0.0


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An circular arc that does not start or end at a quadrant

G02 X .7071 Y.7071 I .7071 J-0.7071


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Using the R address

The R-value defines the distance from the starting point to the centerof the circle. Use a positive R-value for radius of 180 or less, and a

negative R-value for radius more than 180.


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Example for G02 and G03 using R for normal radius


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G04 Dwell

P The dwell time in seconds or milliseconds

G04 is used to cause a delay or dwell in the program. The block

containing G04 will delay for the time specified by the P code. For

example G04 P10.0. This will delay the program for 10 seconds.

Note the use of the decimal point G04 P10. is a dwell of 10seconds.

G09 Exact Stop

The G09 code is used to specify a controlled axes stop. It only affectsthe block in which it is commanded; it is on-modal, it does not affect

the following blocks. Machine moves will decelerate to the

programmed point before another command is processed.


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G20 Select Inches / G21 Select Metric

The G codes G20 (inch) and G21 (mm) codes are used to ensure that

the inch/metric selection is set correctly for the program.

G28 Return to Machine Zero Thru Optional G29 Reference Point

The G28 code is used to return all axes to machine zero, unless an

axis (or axes) is specified, in which case only that axis (or axes) is

returned to machine zero. G28 cancels tool length

offsets for the following lines of code.


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G40 Cutter Comp Cancel

G40 will cancel G41 or G42 cutter compensation.

G41 2D Cutter Compensation Left / G42 2D Cutter Comp. Right

G41 will select cutter compensation left; that is, the tool is moved tothe left of the programmed path to compensate for the size of the

tool. A D address must be programmed to select the correct tool

radius or diameter offset. If the value in the selected offset is

negative, cutter compensation will operate as though G42 (Cutter

Comp Right.) was specified.The right or left side of the programmed path is determined by looking

at the tool as it moves away from you. If the tool needs to be on the

left of the programmed path as it moves away from you, Use G41. If

it needs to be on the right of the programmed path as it moves

away from you, use G42.


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G43 Tool Length Compensation + (Add) / G44 Tool Length Comp -

(Subtract)

A G43 code selects tool length compensation in the positive direction;

the tool length in the offsets page is added to the commanded axis

position. A G44 code selects tool length compensation in the

negative direction; the tool length in the offsets page is subtractedfrom the commanded axis position. A non-zero H address must be

entered to select the correct entry from the offsets page.

G49 - G43/G44/G143 Cancel (Group 08)

G49 -This G code cancels tool length compensation.(G43,G44,G143)

Programming note: An H0, G28, M30, and Reset will also cancel tool

length compensation.(G28-Return to m/c zero, M30 program end)


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G81 Drill Canned Cycle

F Feedrate in inches (or mm) per minute

L Number of holes to drill if G91 (Incremental Mode) is used

R Position of the R plane (position above the part)

X X-axis motion command

Y Y-axis motion command

Z Position of the Z-axis at the bottom of hole


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Program Example (G81-Drilled canned cycle)

The following is a program to drill through an aluminum plate:

T1 M06

G00 G90 G54 X1.125 Y-1.875 S4500 M03 (G90-absolute position,

G54-Select work coordinate system)

G43 H01 Z0.1 (G43 tool length compensation)

G81 G99 Z-0.35 R0.1 F27. (G99-canned cycle R plane return)X2.0

X3.0 Y-3.0

X4.0 Y-5.625

X5.250 Y-1.375

G80 G00 Z1.0 (Canned cycle cancel)G28 (Return to machine zero)

M30 (program end)


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G82 Spot Drill Canned Cycle

F Feed rate in inches (or mm) per minute

L Number of holes if G91 (Incremental Mode) is usedP The dwell time at the bottom of the hole


X X-axis location of hole

Y Y-axis location of hole

Z Position of bottom of holeProgramming Note: G82 is similar to G81 except that you have the

option to program a dwell (P)


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G83 Normal Peck Drilling Canned Cycle


I Size of first cutting depth

J Amount to reduce cutting depth each pass

K Minimum depth of cut

L Number of holes if G91 (Incremental Mode) is used

P Pause at end of last peck, in seconds (Dwell)

Q Cut depth, always incremental





If I, J, and K are specified, the first pass will cut in by the amount of I,

each succeeding cut will be reduced by amount J, and the minimum

cutting depth is K.


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If P is specified, the tool will pause at the bottom of the hole for that

amount of time. The following example will peck several times and

dwell for 1.5 seconds:

G83 Z-0.62 F15. R0.1 Q0.175 P1.5.

The same dwell time will apply to all subsequent blocks that do not

specify a dwell time.

Program Example Description

T2 M06 (Tool #2 is a 0.3125)G90 G54 G00 X0.565 Y-1.875 S2500 M03(G90-absolute position,

G54-Select work coordinate system)

G43 H02 Z0.1 M08 (G43 tool length compensation)

G83 Z-0.720 Q0.175 R0.1 F15.

X1.115 Y-2.750X3.365 Y-2.875

X4.188 Y-3.313

X5.0 Y-4.0

G80 G00 Z1.0 M09 (Canned cycle cancel)

G28 (Return to machine zero)M30 (program end)



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G84 Tapping Canned Cycle


L Number of holes if G91 (Incremental Mode) is used

R Position of the R plane (Position above the part)






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Program example

T3 M06 ( Tool #3 is a 3/8)

G90 G54 G00 X0.565 Y-1.875 S900 M3 (G90-absolute position, G54-

Select work coordinate system)

G43 H03 Z0.2 M08 (G43 tool length compensation)

G84 Z-0.600 R0.2 F56.25 (G84 Tapping Canned Cycle )

X1.115 Y-2.750X3.365 Y-2.875

X4.188 Y-3.313

X5.0 Y-4.0

G80 G00 Z1.0 M09 (Canned cycle cancel)

G28 Y0 Z0 (G28-Return to machine zero)M30 (program end)



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G85 Boring Canned Cycle

F Feedrate in inches (or mm) per minuteL Number of holes if G91 (Incremental Mode) is used


X X-axis location of holes

Y Y-axis location of holes

Z Position of the Z-axis at the bottom of hole.



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G90 Absolute Position Commands

All coordinates were given relative to a fixed point called the origin.

G91 Incremental Position Commands

These G codes change the way the axis commands are interpreted.

Axes commands following a G90 will move the axes to the machine

coordinate. Axes commands following a G91 will move the axis that

distance from the current point.



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Absolute VS. Incremental

Incremental coordinates are referenced from the previous point as

thought the previous point has become a new origin. The referencepoint is essentially moving with every new coordinate.



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G150 General Purpose Pocket Milling

D Cutter size selectionF Feedrate

I X-axis cut increment (must be a positive value)

J Y-axis cut increment (must be a positive value)

K Finishing cut allowance (must be a positive value)

L Optional repetition countP Subroutine number defining outside of shape

Q Incremental Z-axis cut depth per pass (must be a positive value)

R R plane position

S Optional spindle speed

X X position of starting holeY Y position of starting hole

Z Final depth of the pocket



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If I is used, the pocket is cut from a series of strokes in the X-axis. If J

is used, the pocket is cut from a series of strokes in the Y-axis. Thefinishing pass is width K. There is no finishing pass in the Z depth.

The R value should be specified even if it is zero (R0); or the last

value specified for R will be used.



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Multiple passes over the area can be selected to control the depth of

the cut. At least one pass is made over the pocket and multiplepasses are made after feeding down by amount Q until the Z depth

is reached. If an L count is specified, the entire block is repeated

and an incremental X or Y (G91) will reposition the pocket.

The subroutine must define a closed area by a series of G01, G02, or

G03 motions in X and Y.Example : Square pocket



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M Code Introduction

M-Codes are non axes moving commands for the machine. The format

for an M code is the letter M followed by two numbers, for

example M03. Only one M code may be programmed per line of

code. All M codes take effect at the end of the block.

M00 Stop ProgramThe M00 code is used to stop a program. It stops the axes, spindle,

turns off the coolant (including Through Spindle Coolant). The next

block (block after the M00) will be highlighted when viewed in the

program editor. Pressing Cycle Start will continue program

operation from the highlighted block.

M01 Optional Program Stop

M01 works the same as M00, except the Optional Stop feature must

be on.



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2. CNC MILLING PROGRAMUNIVERSITI TEKNIKAL MALAYSIA MELAKA

M02 Program End

The M02 code is used to end a program. Note that the most common

way of ending a program is with an M30.

M03 / M04 / M05 Spindle Commands

M03 turns spindle on in the forward direction

M04 turns spindle on in the reverse directionM05 Stops the spindle

Spindle speed is controlled with an S address code, for example,

S5000 will command a spindle speed of 5000RPM.

M06 Tool ChangeThe M06 code is used to change tools, for example M06 T12 this will

put tool 12 into the spindle. If the spindle is running, the spindle and

coolant will be stopped by the M06 command.



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2. CNC MILLING PROGRAMUNIVERSITI TEKNIKAL MALAYSIA MELAKA

M08 Coolant On / M09 Coolant Off

The M08 code will turn on the optional coolant supply and an M09

code will turn it off.

M30 Program End and Rewind

The M30 code is used to stop a program. It stops the spindle and turns

off the coolant and the program cursor will return to the start of theprogram. M30 cancels tool length offsets.



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3. CAD/CAM SOFTWAREUNIVERSITI TEKNIKAL MALAYSIA MELAKA

What is CAD/CAM software?

-Many toolpaths are too difficult and expensive to program manually.

For these situations, we need the help of a computer to write an NC

part program.

-The fundamental concept of CAD/CAM is that we can use a

Computer-Aided Drafting (CAD) system to draw the geometry of aworkpiece on a computer.

-Once the geometry is completed, then we can use a Computer-Aided

Manufacturing (CAM) system to generate an NC toolpath based on

the CAD geometry.

-Some of the CAM software providers are UGS Corp, Dassault Systmes,PTC, Hitachi Zosen, Delcam, Planit-Edgecam, Tebis, TopSolid, CNC

(Mastercam), SolidCAM, DP Technology's ESPRIT, OneCNC, Sescoi,

SurfCAM, BobCAD, and GibbsCAM

-The progression from a CAD drawing all the way to the working NC

code is illustrated as follows:



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Step 1

The geometry is defined in a CAD drawing. This workpiece contains a

pocket to be machined. It might take several hours to manually

write the code for this pocket. However, we can use a CAM

program to create the NC code in a matter of minutes.



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Step 2

The model is next imported into the CAM module. We can then select

the proper geometry and define the style of toolpath to create,

which in this case is a pocket. We must also tell the CAM system

which tool to use, the type of material, feed and depth of cut

information.



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Step 3

The CAM model is then verified to ensure that the toolpaths are

correct.

If any mistake are found, it is simple to make changes at this point.

Step 4

The final product of the CAD/CAM process is the NC code. The NCcode is produced by post-processing the model to create NC code

that is customized to accommodate the particular variety of CNC

control.



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FINAL TEST


Final Test : 20% of final marks

Duration: 1 hours

Date: 3 April 2008

Time: 8.30 10.00 pm

Location: BK5 & BK6 (Bangunan

Akademik, Cubic)




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THE END


Good Luck!

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