lecture cad cam

7/29/2019 Lecture Cad Cam

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Manufacturing Department

Mechanical Engineering

University Technology Malaysia

Manufacturing Process

SKMM2713

Monday -2013/05/20 AIE/NR


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CAD: Computer Aided Design

CAM: Computer Aided Manufacturing

CNC: Computer Numerical Control


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:It is the technology concerned with the

use of computers to perform designand manufacturing functions.

CAD/CAM ( Computer Aided Designand Computer Aided Manufacturing)


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:it can be defined as the use of computersystems to perform certain functions in thedesign process.

CAD


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CAM: is the use of computer systems toplan, manage and control the operations

of manufacturing plant through eitherdirect or indirect computer interface withthe plants production resources

Computer aided Manufacturing(CAM)


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From CAM definition, the application of

CAM falls into two broad categories:1. Computer monitoring and control .

Computer ProcessProcessdata

Control signals

Computer ProcessProcess data


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2. Manufacturing support application .

Control signalsComputer Mfg

operations

Process data


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1) Improve productivity.

2) Lead time reduction.

3) Reduce engineering personal requirements.

4) Improve accuracy of product.

Benefits of CAM:


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5) Reduce training time for routine drafting.

CONT

6) Fewer errors in NC part programming.

7) Provide the potential of using more existing

parts and tooling.

8) Waste can be kept to a minimum.


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1) Process planning and scheduling.

2) Programming for numerical control and

Industrial robots.3) Design of dies and molds for casting.

4) Die for metal working operations.

5) Design of tooling and fixtures and EDMelectrodes.

6) Quality control and inspection.

7) Plant layout.

Some typical applications of CAD/CAM


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Computer Numerical control (CNC)


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History of CNC

1949US Air Force asks MIT to develop a "numericallycontrolled" machine.

1952Prototype NC machine demonstrated (punched tape input)

1980-CNC machines (computer used to link directly to controller)

1990-DNC: external computer drip feeds control programmer tomachine tool controller


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DEFINITIONIn CNC (Computer Numerical Control), theinstructions are stored as a program in amicro-computer attached to the machine.The computer will also handle much of thecontrol logic of the machine, making it moreadaptable than earlier hard-wired

controllers.


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Conventional vs. CNC machine


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Conventional vs. CNC machine


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Difference between Conventional M/C& CNC M/C

Item Conventional

machine

CNC

machine

1. Movement Acme screw Ball screw

2. Feed manual motor

3.measurement manual Linear scale


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CNC APPLICATIONS

- Machining

2.5D / 3D

Turning ~ Lathes, Turning Centre

Milling ~ Machining Centres2-Forming

2D

Plasma and Laser CuttingBlanking, nibbling and punching

3D

Rapid Prototyping


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SAMPLE CNC MACHINES

CNC TURNING CNC MILLING


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SAMPLE CNC MACHINES

CNC LASER CUTTING CNC PLASMA CUTTING


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CNC PRESS CNC RAPID PROTOTYPING

SAMPLE CNC MACHINES


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Advantages of CNC1) Easier to program.2) Easy storage of existing programs.

3) Easy to change a program.

4) Avoids human errors.

5) NC machines are safer to operate.

6)Complex geometry is produced as cheaply as simple

ones.

7) Usually generates closer tolerances than manual

machines .


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DRAWBACKS of CNC1) High capital cost )Machine tools cost $30,000 -

$1,500,000 ).

2) Retraining and recruitment of staff .

3) New support facilities .

4) High maintenance requirements.

5) Not cost-effective for low-level production onsimple parts.

6)Maintennce personnel must have both mechanical

and electronics expertise .


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CNC SYSTEM ELEMENTSA typical CNC system consists of the following six

elements

1) Part program

2) Program input device

3) Machine control unit

4) Drive system

5) Machine tool

6) Feedback system


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STANDARD MILLING MACHINE COORDINATESYSTEM


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STANDARD LATHE COORDINATE SYSTEM


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RIGHT HAND RULE

Vertical Machine Horizontal Machine


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Zero and reference points on CNC


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Zero Point of machine on a CNC lathe


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Machine Zero Point and Work part zeropoint on CNC milling machine


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Additional Axis of Movement

(A) FOURTH AXIS ROTARY MOTION : Rotate about axis X.

(B) FIFTH AXIS ROTARY MOTION: Rotate about axis Y.

(C )AUXILIARY EXTERNAL ROTARY AXIS :Rotate about axis Z.


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Programming Systems

Two types of programming modes, theincremental system and the absolute system,are used for CNC.


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What is the value in X and Y for each hole in absolute and

incremental positing .

CNC Positioning systems


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Point-to-Point Positioning

CNC Positioning systems

Point-to-point positioning is used when it is

necessary to accurately locate the spindle,

or the workpiece, perform such operations

as drilling, reaming, boring, tapping.


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Point-to-Point Positioning


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Continuous Path (Contouring)

Contouring, or continuous path machining,involves work such as that produced on a lathe

or milling machine, where the cutting tool is incontact with the workpiece as it travels fromone programmed point to the next.


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Continuous Path (Contouring)


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G-codes (preparatory functions):

Most G-codes set the machine in a modewhich stays in effect until it is changed orcancelled by another G-code. Thesecommands are called modal.


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G00 Rapid TransverseG01 Linear InterpolationG02 Circular Interpolation,CWG03 Circular Interpolation,

CCW

G17 XY PlaneG18 XZ PlaneG19 YZ PlaneG20/G70 Inch unitsG21/G71 Metric UnitsG40 Cutter compensation

cancelG41 Cutter compensation leftG42 Cutter compensationright

G43 Tool lengthcompensation (plus)

G44 Tool lengthcompensation (minus)

G49 Tool length

compensation cancelG80 Cancel canned cycles

G81 Drilling cycle

G82 Counter boring cycle

G83 Deep hole drilling

cycleG90 Absolute positioning

G91 Incrementalpositioning

Modal G-Code List


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CIRCULAR PLANE SELECTION


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G17 XY CIRCULAR PLANE SELECTION


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G18 XZ CIRCULAR PLANE SELECTION


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G19 YZ CIRCULAR PLANE SELECTION


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CUTTER COMPENSATION

G41 Cutter Compensation Left

That is the tool is moved to the left of theprogrammed path to compensate for theradius of the tool

G42 Cutter Compensation Right

That is the tool is moved to the right of theprogrammed path to compensate for thesize of the tool.

NOTE :G40 Cancel Cutter Comp G41 and G42


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TOOL LENGTH COMPENSATIONG43 Tool Length Compensation + (plus)This code selects tool length compensation in a positive direction.That is; the tool length offsets are added to the commanded axispositions.


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:are used to either turn ON or OFF different

functions which control certain machine tool

operations

M or miscellaneous codes :


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M00 Program stopM01 Optional program stopM02 Program endM03 Spindle on clockwiseM04 Spindle on counterclockwiseM05 Spindle stopM06 Tool change

M08 Coolant onM09 Coolant offM10 Clamps onM11 Clamps off

M30 Program stop, reset to start

M Codes


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X,Y, and Z Codes

X, Y, and Z codes are used to specify thecoordinate axis.

Number following the code defines thecoordinate at the end of the move relativeto an incremental or absolute referencepoint.


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I,J, and K Codes

I, J, and K codes are used to specify thecoordinate axis when defining the centerof a circle.

Number following the code defines therespective coordinate for the center of the

circle.


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F,S, and T Codes

F-code: used to specify the feed rate

S-code: used to specify the spindle speed

T-code: used to specify the tool

identification number associated with thetool to be used in subsequent operations.


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CNC Programming:


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The first step in producing a CNC program is to take the information from the print

and produce a program manuscript


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1) Manual

Write code directly

2)Computer-assisted

Draw cutter path

3) CAD/CAM

Draw the part Cutter path is generated


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INFORMATION NEEDED by a CNC1) Preparatory Information: units, incremental or absolut

positioning

2) Coordinates: X,Y,Z, RX,RY,RZ

3) Machining Parameters: Feed rate and spindle speed

4) Coolant Control: On/Off, Flood, Mist

5) Tool Control: Tool and tool parameters

6) Cycle Functions: Type of action required

7) Miscellaneous Control: Spindle on/off, direction of rotationstops for part movement

This information is conveyed to the machine through a set

of instructions arranged in a desired sequence Program.

OC O


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BLOCK FORMAT

Sample Block :N135 G01 X1.0 Y1.0 Z0.125 F5

Restrictions on CNC blocks.Each may contain only one tool move.

Each may contain any number of non-tool move G-codes.Each may contain only one feedrate.Each may contain only one specified tool or spindle speed.The block numbers should be sequential.

Both the program start flag and the program number must beindependent of all other commands (on separate lines).The data within a block should follow the sequence shown in

the above sample block.


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Block of Information

CNC information is generally programmed in blocks offive words


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Three Main parts of a CNC program

N5 G90 G21 (Absolute units, metric)

N10 M06 T2 (Stop for tool change, usetool # 2)

N15 M03 S1200 (Turn the spindle on CW to1200 rpm)

Part 1- Program Petup


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General formula for calculating the cutting parameters


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G90 G01 X110 Y75.0 F20;

To move tool at point B write block as :


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RAPID POSITION COMMAND

G00 RAPID POSITIONING MOTION*X Positioning X axis motion*Y Positioning Y axis motion*Z Positioning Z axis motion

*A Positioning A axis motion


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LINEAR INTERPOLATION COMMAND

G01 LINEAR INTERPOLATIONMOTION*X Linear X-axis motion*Y Linear Y-axis motion

*Z Linear Z-axis motion*A Linear A-axis motion*F Feed rate in inches (mm)per minute


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G02 CW CIRCULAR INTERPOLATION MOTION &G03 CCW CIRCULAR INTERPOLATION MOTION*X Circular end point X-axis motion

*Y Circular end point Y-axis motion*Z Circular end point Z-axis motion*A Circular end point A-axis motion*I X-axis Distance from start point to arc center (If R is not used)*J Y-axis Distance from start point to arc center (If R is not used)

*K Z-axis Distance from start point to arc center (If R is not used)*R Radius of the arc to be machined (If I, J, K are not used)*F Feed rate in inches (or mm) per minute

CIRCULAR INTERPOLATION COMMANDS


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EXAMPLE

G02 CCW CIRCULAR INTERPOLATION

G02 CW CIRCULAR INTERPOLATION USING "I", &"J"


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FOR THE X & Y AXIS


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G02 CW CIRCULAR MOTION USING "R"


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G03 CCW CIRCULAR INTERPOLATION

EXAMPLE

G03 CCW CIRCULAR INTERPOLATION USING "I", &"J"


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G03 CCW CIRCULAR INTERPOLATION USING I , & JFOR THE X & Y AXIS

EXAMPLE : Cutter Compensation


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EXAMPLE : Cutter Compensation(G41/G42/G40)


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N5 G90 G21 (Absolute units, metric)

N10 M06 T2 (Stop for tool change, usetool # 2)

N15 M03 S1200 (Turn the spindle on CW to1200 rpm)

Part 1- Program Petup


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N20 G00 X1 Y1 (Rapid to X1,Y1 from origin

point)N25 Z0.125 (Rapid down to Z0.125)N30 G01 Z-0.125 F100 (Feed down to Z-0.125 at

100 mm/min)N35 G01 X2 Y2 (Feed diagonally to X2,Y2)N40 G00 Z1 (Rapid up to Z1)N45 X0 Y0 (Rapid to X0,Y0)

Part 2- Chip Removal


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N50 M05 (Turn the spindle off)

N55 M00 (Program stop)

Part 3- System Shutdown

EXAMPLE OPERATION on CNC


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EXAMPLE OPERATION on CNCMILLING MACHINE


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First pass : conventional mill toa depth of 0.125 around edgeprofile. Tool 1 is a inch dia.end mill.

%

:1002N5 G90 G20N10 M06 T1N15 M03 S1200N20 G00 X0.125 Y0.125N30 Z0.125

N35 G01 Z-0.125 F5N40 X3.875N45 Y4.125N50 X0.125N55 Y0.125


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Second pass:conventional mill to a

depth of 0.25 aroundedge profile.

N35 Z-0.250N40 X3.875

N45 Y4.125

N50 X0.125

N55 Y0.125

N60 Z0.125

Third pass:


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Third pass:conventional mill to adepth of 0.125

around pocket profile.

N65 G00 X1.25 Y1.0

N70 G01 Z-0.125 F5N75 X1.75

N80 Y2.5

N85 X1.25

N90 Y1.0N95 Z0.125

Fourth pass: climb


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Fourth pass: climbmill to a depth of

0.125 acrossremaining material.

N100 Y2.125

N105 X2.625

N110 Z0.125

N115 G00 X-5 Y-5 Z5

N120 M05

N125 M30


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Exercises

1-Write CNC blocks for paths as shownbelow.

2)Write CNC program for machining w/p as dawning


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