Manufacturing Technology - CNC Machining and other CNC Applications

8/9/2019 Manufacturing Technology - CNC Machining and other CNC Applications

1/46

CNC Machining and otherCNC Applications


2/46

Lesson Outcomes

By the end of this lesson, students should be able to:• Understand the concept of Computer NumericalControl System and its applications

• Understand the fundamental components of anCNC system

• Understand aspects of CNC motion control

• Understand aspects of CNC codes• Understand the advantages and disadvantages of

CNC control systems


3/46

What is Computer Numerical

Control (CNC)?

– (Definition:) A form of programmableautomation in which the mechanical actions ofa machine tool or other equipment are

controlled by a program. – Program of instructions (numbers, letters

symbols) used to control a process

– Main advantage: Flexibility (easy to change program of instructions for different parts)


4/46

1. Machine tool applications to control the

relative motion between cutting tool andworkpiece.

Examples: – CNC Lathe

– CNC Milling

– CNC Machining Ctr – CNC Turning Center

– CNC Wire-cut

– CNC EDM

– CNC Grinder

– CNC Laser-cut – CNC Water-jet

– CNC Punch & Blanking

– CNC Drilling & Boring

Applications of CNC Control

Technology


5/46

Applications of CNC Control

2. Non-Machine Tool Applications

Examples:-Assembly

(CNC used to control assembly machines)

-Drafting

(Once a CAD drawing is completed, CNC is used tocontrol a plotter to generate an engineering drawing)

-Robotics(CNC is used to control the motors that move robotic arms)

-Quality Control and Inspection

(eg CNC CMM)


6/46

Components of an CNC System

1. Program of instructions or part program2. Machine control unit

3. Processing equipment


7/46


8/46


1. Program of instructions:The detailed step by step commands that

direct the actions or movements of the

machine

Program – written manually & key-in or viaCAD/CAM


9/46


2. Machine Control Unit (MCU):Microcomputer and control hardware thatread and interprets the program of instructions

and converts it into signals to the processingequipment.

Diskette / RS232C/ CPU/CRT/HDD/RAM buffer/CPU – convert CNC program intoelectronic pulses to drive various motors


10/46


3. Processing equipment:The part of the CNC System that performs theuseful work

Examples are:

• Worktable, spindle and motors in a machine tool

• Motors and linkages in a robotic system

• This machine tool/ production process designed togive high level of repeatability and precision

CNC M ti C t l


11/46

CNC Motion Control

Systems

Three aspects of CNC Motion ControlSystems:

1. Point-to-point

2. Interpolation methods (Continuous Path

Control)

3. Absolute vs. Incremental positioning


12/46

NC Motion Control Systems1. Point to point system:

• Tool movement is arbitrary as long as the finaldestination is reached

• A tool may move through a number of different points before reaching the final destination.

• Examples: drilling and spot welding operations

• Processing action is performed after location isreached


13/46

NC Motion Control Systems

2. Interpolation methods (Continuous path controlsystem)

• Some shapes such as circles and ellipses arecontinuous.

• NC control system, however, is digital.

• Therefore, a circle or ellipse must be divided

into straight segments to approximate the curve.• This leads to a very large number of points

• Interpolation methods calculate the intermediate

points and generate a smooth continuous points


14/46

NC Motion Control Systems2. Interpolation methods (Continuous path control

system:• The path followed by the tool is continuouslycontrolled to get the desired geometrical feature

• Movement of worktable by continuously andsimultaneously controlling two or more axes.

• Provides control of the tool path.

• Processing action is performed duringmovement.

• Allow for generation of 2D and 3D contours


15/46

CNC Motion Control Systems2. Absolute vs. Incremental Positioning

Absolute positioning:

Positions are defined with respect to the origin

of coordinate system

Incremental positioning:

Positions are defined relative to the previouslocation


16/46

CNC Co-ordinate System


17/46

Floating zero point system

• This feature allows the user to place asecondary coordinate system anywhere on

the machine table.

• This makes it easy to develop the part

program & machine the workpiece


18/46

CNC Codes• CNC Code (forms the

program of instructions)

• Types of CNC Code:

– Sequence/block number (NCode)

– Preparatory Codes (GCodes)

– Miscellaneous Codes (M

Codes) – Feed and Speed Codes

– Tools Codes

Source: MTAB


19/46

CNC Codes

Sequence/Blocknumber (N

Codes)

– Describes the

block of codes in

a program

Source: MTAB


20/46

CNC Codes

Preparatory Codes (G Codes)

Relevant G Codes:G00G00

G01G01G02G02

G03G03

G20G20

G21G21

G28G28

G90G90G91G91

G92G92G94G94

Source: MTAB


21/46

CNC CodesPreparatory Codes (G Codes)

G00 Rapid Traverse of fast Traverse

• A G00 causes the tool to move to the specified position at maximum speed.

(for non-cutting movements)

• Example: G00 X20 Y30 Z1

Here the tool is moved to X 20mm, Y 30mm, and

Z 1mm (for metric system)


22/46

CNC Codes

Preparatory Codes (G Codes)

G01 Linear Interpolation• A G01 causes linear motion to the given

position.

• Example: G01 X20 Y30 F45

Here the tool is moved to X 20mm, Y 30mm


23/46


G02 Clockwise Circular Interpolation

• Arcs can be specified by either radius or by centre.

• Example: G02 X30 Y20 R15

In this example the tool is moved to X 30mm and Y20mm. The arc has a radius of 15mm.

• “I” and “J” specifies the arc centre relative to the arcstart. If the value-+ is 0 then it need not be specified.

Example: G02 X30 Y20 I15 J0


24/46


G03 Counter-Clockwise Circular Interpolation

• G03 causes counter-clockwise circular motion• Similar to G02


25/46


G20 Imperial Units

• All future instruction parameters will be takenas imperial values.


26/46


G21 Metric Units

• All Future instruction parameters will be takenas metric values.


27/46


G28 Automatic Zero Return

• Send spindle to home position• Usually used for tool change or setting up for a

new programMilling: Lathe:

N020 G91 G28 Z0N020 G91 G28 Z0

N030 G28 X0 Y0N030 G28 X0 Y0N020 G28 U0 W0N020 G28 U0 W0


28/46


G40 Cancel cutter compensation

• G41 and G42 are used to locate the tool oneither left or right side of the profile

• G40 is used to cancel this tool compensation


29/46


G90 Absolute Movement

• All future movements will be absolute untiloverridden by a G91 instruction

Example: G90G01 X30 Y0

The new position becomes X30 Y0


30/46


G91 Incremental Movement

• All future movements will be incremental until

overridden by a G90 instruction.

• Example: G90

G01 X15G91

G01 X2The position becomes X17


31/46


G92 Programming of the coordinate system

• Defines a coordinate system

• Example: G00 X30.0 Y40.0

G92 X0.0 Y0.0Converts the position that was X30 Y40 to X0

Y0


32/46

CNC Codes

Miscellaneous Codes (M Codes)

Relevant M Codes:

M03M03

M05M05M06M06


33/46

CNC CodesMiscellaneous Codes (M Codes)

Relevant M Codes:

M03 Start Spindle

• An M03 instruction starts forward spindle motion.• Example: M03 S2200

• The spindle should be switched on before anymovement below the component surface.


34/46


Relevant M Codes:

M05 Stop Spindle• An M05 instruction stops spindle rotation.

• M05 is issued before a tool change, and at theend of a program.


35/46


Relevant M Codes:

• M06 Change Tool

• The M06 instruction causes the a change to adifferent tool. The tool changing operation should bedone in the home position only.

• Example: M06 T1Changes to the tool in turret 1


36/46


Relevant M Codes:

M30 End of Program• Rewind program and reset memory


37/46

CNC CodesFeed and Speed Codes

• Feed code (F code) – Specifies the tool motion feed rate

– Unit can be in mm/min, in/min, mm/rev or in/rev

Example: F50

• Speed code (S code)

– Specifies the rate of tool revolution – Unit is in RPM

Example: S1200


38/46

CNC CodesTool code (T code)

• Refers to a location on tool turretExample: M06 T1

CNC Machine tools:


39/46

Program of Instructions example (Milling)

G00 Rapid Traverse of fast TraverseG00 Rapid Traverse of fast Traverse

G01 Linear InterpolationG01 Linear Interpolation

G02 Clockwise Circular InterpolationG02 Clockwise Circular InterpolationG03 Counter G03 Counter --Clockwise CircularClockwise Circular

InterpolationInterpolation

G20 Imperial UnitsG20 Imperial Units

G21 Metric UnitsG21 Metric Units

G28 Automatic Zero ReturnG28 Automatic Zero Return

G40 Cancel cutterG40 Cancel cutter

compensationcompensation

G71 Rough out profile byG71 Rough out profile by

turningturning

G70 Finishing CycleG70 Finishing Cycle

G90 Absolute MovementG90 Absolute Movement

G91 Incremental MovementG91 Incremental Movement

G92 Programming of theG92 Programming of the

coordinate s stemcoordinate s stem

G94 Feed rate in mm/minG94 Feed rate in mm/min

in/min (G98 performs thein/min (G98 performs the

function in the CNC lathefunction in the CNC lathe

G95 Feed rate in mm/revG95 Feed rate in mm/revin/revin/rev

M03 Start SpindleM03 Start Spindle

M05 Stop SpindleM05 Stop Spindle

M06 Change ToolM06 Change Tool

M30 End of ProgramM30 End of Program

F Feed code (FF Feed code (F

code)code)

S Speed codeS Speed code

(S code)(S code)

T Tool code (TT Tool code (T

code)code)



40/46


Source: MTAB

G00 Rapid Traverse of fast TraverseG00 Rapid Traverse of fast Traverse



41/46

Source: MTAB

AC

DEF

B


G02 Clockwise Circular InterpolationG02 Clockwise Circular Interpolation

G03 Counter G03 Counter --Clockwise CircularClockwise Circular





G40 Cancel cutter compensationG40 Cancel cutter compensation

G71 Rough out profile by turningG71 Rough out profile by turning



G91 Incremental MovementG91 Incremental MovementG92 Programming of the coordinate systemG92 Programming of the coordinate system

G94 Feed rate in mm/min or in/min (G98G94 Feed rate in mm/min or in/min (G98

performs the same function in the CNCperforms the same function in the CNC

lathe)lathe)

G95 Feed rate in mm/rev or in/revG95 Feed rate in mm/rev or in/rev





F Feed code (F code)F Feed code (F code)

S Speed code (S code)S Speed code (S code)

T Tool code (T code)T Tool code (T code)


42/46

CNC Program of Instructions example (Lathe)

Z1

Source: MTAB

CNC Codes:


43/46

Summary of relevant codes

G00 Rapid Traverse of fast TraverseG00 Rapid Traverse of fast TraverseG01 Linear InterpolationG01 Linear Interpolation

G02 Clockwise Circular InterpolationG02 Clockwise Circular Interpolation

G03 Counter G03 Counter

--Clockwise CircularClockwise Circular





G40 Cancel cutter compensationG40 Cancel cutter compensation

G71 Rough out profile by turningG71 Rough out profile by turning



G91 Incremental MovementG91 Incremental Movement

G92 Programming of the coordinate systemG92 Programming of the coordinate system

G94 Feed rate in mm/min orG94 Feed rate in mm/min orin/min (G98 performs the samein/min (G98 performs the same

function in the CNC lathe)function in the CNC lathe)

G95 Feed rate in mm/rev orG95 Feed rate in mm/rev or

in/revin/rev





F Feed code (F code)F Feed code (F code)

S Speed code (S code)S Speed code (S code)

T Tool code (T code)T Tool code (T code)


44/46

Advantages of CNC Control systems

1. Reduce nonproductive time

2. Greater accuracy and repeatability

3. More complex part geometeries are

possible4. Lesser operator skill-level is required

5. Easy to make engineering changes(flexible).

6. Less floor space requirement

Disadvantages of CNC


45/46

Control Systems

1. Higher cost of initial investment

2. Higher maintenance cost

3. Requires part programming (conventional

machining does not require any

programming)


46/46

Summary• CNC is a form of programmable automation

• The three components of an CNC system are the program of instructions, MCU, and the processing equipment

• Three aspects of CNC motion control are Point-to-point vs. Continuous Path Control,Interpolation methods and Absolute vs.Incremental positioning

• Alphanumeric CNC codes (G&M) codes areused for tool motion control and miscellaneous

parts

Manufacturing Technology - CNC Machining and other CNC Applications

Documents