1 CNC Milling Machine Mohd Zaid Bin Akop 25 March 2008.

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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 MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

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1. INTRODUCTIONFAKULTI KEJURUTERAAN MEKANIKAL

UNIVERSITI TEKNIKAL MALAYSIA MELAKA

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 they possess. 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 part or fixture in relation to zero reference point on machine table.

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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, flat surfaces and pockets.

a. pocketingb. 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, including eye 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 tools

4. 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 closed while in automatic operation. Do not disable or override any of the safety features that were put there to protect you.

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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 to common 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 commandY Optional Y-axis motion commandZ 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 part change. 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 minuteX Optional X-axis motion commandY Optional Y-axis motion commandZ Optional Z-axis motion commandR Radius of the circleC 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 current program 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 the programmed 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 changeG90 – Absolute Position CommandsG54 – Select work coordinate systemM03 – Turn spindle on in the forward directionG43 – Tool length compensation + (Add)M08 – Coolant onM09 – Coolant offG53 – Non-modal machine coordinate selectionM30 – Program endH- Tool length offset selection

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G02 CW / G03 CCW Circular Interpolation Motion

F Feedrate in inches (mm) per minuteI Optional distance along X axis to center of circleJ Optional distance along Y axis to center of circleK Optional distance along Z axis to center of circleR Optional radius of circleX Optional X-axis motion commandY Optional Y-axis motion commandZ Optional Z-axis motion command

These G codes are used to specify circular motion. Two axes are necessary 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 end point 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 R address 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 addressThe R-value defines the distance from the starting point to the

center of 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 millisecondsG04 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 10 seconds.

G09 Exact Stop

The G09 code is used to specify a controlled axes stop. It only affects the 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 to the 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 subtracted from 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 minuteL Number of holes to drill if G91 (Incremental Mode) is usedR Position of the R plane (position above the part)X X-axis motion commandY Y-axis motion commandZ 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 M06G00 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)X2.0X3.0 Y-3.0X4.0 Y-5.625X5.250 Y-1.375G80 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 minuteL Number of holes if G91 (Incremental Mode) is usedP The dwell time at the bottom of the holeR Position of the R plane (position above the part)X X-axis location of holeY Y-axis location of holeZ 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

F Feedrate in inches (or mm) per minuteI Size of first cutting depthJ Amount to reduce cutting depth each passK Minimum depth of cutL Number of holes if G91 (Incremental Mode) is usedP Pause at end of last peck, in seconds (Dwell)Q Cut depth, always incrementalR Position of the R plane (position above the part)X X-axis location of holeY Y-axis location of holeZ Position of the Z-axis at the bottom of hole

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 DescriptionT2 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-2.875X4.188 Y-3.313X5.0 Y-4.0G80 G00 Z1.0 M09 (Canned cycle cancel)G28 (Return to machine zero)M30 (program end)

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G84 Tapping Canned Cycle

F Feedrate in inches (or mm) per minuteL Number of holes if G91 (Incremental Mode) is usedR Position of the R plane (Position above the part)X X-axis location of holeY Y-axis location of holeZ Position of the Z-axis at the bottom of hole

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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-2.875X4.188 Y-3.313X5.0 Y-4.0G80 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 usedR Position of the R plane (position above the part)X X-axis location of holesY Y-axis location of holesZ 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. IncrementalIncremental coordinates are referenced from the previous

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

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G150 General Purpose Pocket Milling

D Cutter size selectionF FeedrateI 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 shapeQ Incremental Z-axis cut depth per pass (must be a positive

value)R R plane positionS Optional spindle speedX X position of starting holeY Y position of starting holeZ 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. The finishing 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 multiple passes 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 StopM01 works the same as M00, except the Optional Stop feature

must be on.

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M02 Program EndThe 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 CommandsM03 turns spindle on in the forward directionM04 turns spindle on in the reverse directionM05 Stops the spindleSpindle 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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M08 Coolant On / M09 Coolant OffThe M08 code will turn on the optional coolant supply and an

M09 code will turn it off.

M30 Program End and RewindThe 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 the program. M30 cancels tool length offsets.

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3. CAD/CAM SOFTWAREFAKULTI KEJURUTERAAN MEKANIKAL


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 a workpiece 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 Systèmes, 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 1The 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 2The 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 3The 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 4The final product of the CAD/CAM process is the NC code. The

NC code 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 ½ 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!

1 CNC Milling Machine Mohd Zaid Bin Akop 25 March 2008.

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Transcript of 1 CNC Milling Machine Mohd Zaid Bin Akop 25 March 2008.