NC Systems

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NC System NC / CNC: ‘The automatic operation of machine tool by a series of coded instructions’   Numerical Control (NC) was the term first coined for the manufacturing processes Term Computer Numerical Control (CNC) was adopted with introduction of computers in the manufacturing environment in 1970’s Both terms are still used and should be taken to mean the same CAD/CAM  tanveer ahmed

Transcript of NC Systems

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NC System

NC / CNC:

‘The  automatic operation of machine tool by a series of codedinstructions’  

Numerical Control (NC) was the term first coined for the

manufacturing processes

Term Computer Numerical Control (CNC) was adopted with

introduction of computers in the manufacturing environment in1970’s 

Both terms are still used and should be taken

to mean the same

CAD/CAM  tanveer ahmed

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NC System

CNC Machine:

Conventionally, an operator decides and adjusts variousmachines parameters like feed, depth of cut and more depending

on the type of job and controls the movements by hand

In a CNC Machine, functions and movements are controlled by

motors using computer programs

In CNC machine, the Machine Control Unit (MCU) decides cuttingspeed, feed, depth of cut, tool selection, coolant on / off and tool

 paths

The MCU issues commands in the form of numeric data to motors

that position slides and tool accordingly

CAD/CAM  tanveer ahmed

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NC System

CNC Machine:

Numerical Control (NC) developed out of the need to meet therequirements of high production rates, uniformity & consistent

 part quality

Programmed instructions are converted into output signals

which in turn control machine operations such as spindle speeds,

tool selection, tool movement and cutting fluid flow

CAD/CAM  tanveer ahmed

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NC System

CNC Machine:

CNC machining begins with a part program which is a sequentialinstructions or coded commands that direct the specific machine

 functions

The part program may be generated manually or more

commonly generated by computer aided part programming

systems

CAD/CAM  tanveer ahmed

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NC System

Machining Strategy:

The sequence of operations Fixturing & orientation

Selection of speeds and feeds

Type of tool and the tool configuration

Mathematical and geometrical calculations

Inspection

“The nature of subsequent code generation is

determined by the programing method ”  

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NC System

Manual Programming:

 An individual manually write all the sequential program ofinstructions in the form of a series of codes (i.e. G-codes)

according to the particular format required

This code is then inputted into the NC machine tool via the MCU

either directly or indirectly

CAD/CAM  tanveer ahmed

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NC System

Manual Programming:

 Advantages:

• No software required

• Suitable for simple jobs like point-to-point (PTP) applications

Disadvantages:

• Labour intensive

• Skilled programmer required• Error prone

• Different code formats may be required for different machines

• Unsuitable for large jobs in low production volumes

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NC System

Computer Assisted Programming:

The program is prepared in English-like language (i.e. APT

[Automatically Programmed Tool])

The program can automatically define some parameters (e.g.

cutter offset)

The software then translates this into the language format

accepted by the NC machine tool•  Advantages:

o Less skilled process

• Disadvantages:

o Labour input still requiredo Programming language still requires a degree of learning

CAD/CAM  tanveer ahmed

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NC System

Computer Assisted Programming: 

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MACHINE UNIT

NUMERICAL

CONTROLLER

NUMERICALDATA

(NC CODE)

MANUFACTURING

OPERATOR

PROCESSED

PART

Drive Control

Video Clip 

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NC System

Milling Machine:

Milling Machine is used for

cutting mostly prismatic parts

The work-piece is stationary

and the cutting tool is rotating

The most typical type is

Vertical Milling Machine

CAD/CAM  tanveer ahmed

Conventional

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NC System

CNC Milling Machine: 

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NC System

Lathe Machine:

Lathe Machine is used for turning operations

The work-piece rotates and the cutting tool is stationary

CAD/CAM  tanveer ahmed

Conventional

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NC System

CNC Lathe Machine: 

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NC System

NC/CNC Advantages:

The first major advantage offered by all forms of NC machine

tools is improved Automation

• Higher labor efficiency

•  Accurate costing and production planning

• Lower skill level

The second major benefit of NC technology is Quality Standards• High machining accuracy and repeatability

• Lower intervention = fewer mistakes

• Lower inspection costs due to predictable quality

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NC System

NC/CNC Advantages:

The third Major benefit offered by most forms of NC machine

tools is Flexibility

• Programs are electronically stored

• Shorter Lead times/Shorter setup time

• Fast changeover

CAD/CAM  tanveer ahmed

Video Clip 

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NC System

NC/CNC Disadvantages:

High investment costs

Machine operation 24 hrs / day-shift work

Less labour - redundancies

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NC System

Coordinate System: 

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 Absolute Coordinate System Incremental Coordinate System

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NC System

Programming: 

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“Programming is the process of creating a set of

commands such, as cutter movement, feed-rate and

spindle speed in order for the machine to perform

some operations”  

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NC System

Programming Flow: 

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Workpiece Drawing

Select machine, fixture,

cutter & holder

Process planning (rough & finish)

Machining conditions

Generate tool path

and program

Transfer of program

Machining

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NC System

Programming Key Letters:

O - Program number (Used for program identification)

N - Sequence number (Used for line identification)

G - Preparatory function

 X - X axis designation

Y - Y axis designation

 Z - Z axis designation R - Radius designation

F – Feed rate designation

S - Spindle speed designation

H - Tool length offset designation

D - Tool radius offset designation

T - Tool Designation

M - Miscellaneous function

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NC System

Programming Exercise (Cylindrical Part): 

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Raw Material

Finished Part

       2       5

70  

       2

       2 .       5

       1

       7 .       5

20  

30  

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NC System

Programming Exercise - 2:

a. Move from P1 to P2 without machining using absolute

dimensional positioning

b. Move from P1 to P2 without machining using incremental

dimensional positioning

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NC System

Tool / Part Movement: 

CAD/CAM  tanveer ahmed

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NC System

Homogeneous Transformations:

Transformation Matrix:

CAD/CAM  tanveer ahmed

Rotation Translation

Homogeneous

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NC System

Homogeneous Transformations:

3 – Dimensional Coordinate Frame:

CAD/CAM  tanveer ahmed

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NC System

Homogeneous Transformations:

Right Handed Coordinate System:

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C S

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NC System

Homogeneous Transformations:

Direction of Positive Rotation:

CAD/CAM  tanveer ahmed

NC S

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NC System

Homogeneous Transformations:

Direction of Positive Rotation:

CAD/CAM  tanveer ahmed

The right hand rule to determine the direction of positive angles. Point your right

thumb along the positive direction of the axis you wish to rotate around. Curl your

 fingers. The direction that your fingers curl is the direction of positive rotation

NC S

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NC System

Homogeneous Transformations:

Transforming points between frames:

CAD/CAM  tanveer ahmed

NC S

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NC System

Homogeneous Transformations:

Transforming points between frames:

• If the coordinate frames j and k only differ by a translation

and to get from k coordinates to j coordinates you translate (a,

b, c) along k’s x, y, and z axes, then T K   J   , the matrix that takes

a point in j coordinates to a point in k coordinates is

CAD/CAM  tanveer ahmed

NC S

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NC System

Homogeneous Transformations:

Transforming points between frames:

CAD/CAM  tanveer ahmed

NC S t

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NC System

Homogeneous Transformations:

Transforming points between frames:

CAD/CAM  tanveer ahmed

Tm c = 

NC S t

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NC System

Homogeneous Transformations:

Rotation Matrices:

CAD/CAM  tanveer ahmed

NC S t

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NC System

Homogeneous Transformations:

Moving Coordinate System:

• When we use “moving axes”  we list the moves that we did from

start to end, compute the individual matrices for each part

and then multiply them together. For example, in this situation

our sequence of equations is:

“ Rot x(-90) * Rot z(-90) * Trans(0,0,5)”  

CAD/CAM  tanveer ahmed

NC S t

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NC System

Homogeneous Transformations:

Fixed Coordinate System:

• When we using “fixed   axes”   computation, (i.e. each new

rotation is relative to the end coordinate frame), we write the

equations from end to start:

“ Trans (0,5,0) * Rot y (-90) * Rot x(-90 )”  

CAD/CAM  tanveer ahmed

NC S t

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NC System

Homogeneous Transformations: 

CAD/CAM  tanveer ahmed

NC S t

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NC System

Homogeneous Transformations: 

CAD/CAM  tanveer ahmed

NC S t

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NC System

Homogeneous Transformations: 

CAD/CAM  tanveer ahmed

1 0 0 0

[ Ba I Sl ]= 0 1 0 Y

0 0 1 0,146

0 0 0 1

0 0 1 0,153 + Z

[ Sl I T ]= 0 1 0 0

-1 0 0 0,05

0 0 0 1

0 0 1 0,153 + Z

[ Bl I T ]= 0 1 0 Y

-1 0 0 0,196

0 0 0 1

NC System

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NC System

Homogeneous Transformations: 

CAD/CAM  tanveer ahmed

-1 0 0 0,64

[ Ba I PS ]= 0 1 0 0

0 0 -1 0

0 0 0 1

0 0 -1 0,25

[ PS I Pa ]= 0 1 0 0

1 0 0 -0,279

0 0 0 1

0 0 1 0,39

[ Ba I Pa ]= 0 1 0 0

-1 0 0 0,279

0 0 0 1

1 0 0 0,083

[ Pa I Ho ]= 0 1 0 0,15+0,25 n

0 0 1 -0,150 0 0 1

NC System

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NC System

Homogeneous Transformations: 

CAD/CAM  tanveer ahmed

0 0 1 0,24

[ Ba I Ho ]= 0 1 0 0,15+0,25 n

-1 0 0 0,196

0 0 0 1

0 0 1 0,153 + Z

[ Bl I T ]= 0 1 0 Y

-1 0 0 0,196

0 0 0 1

NC System

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NC System

CAD/CAM  tanveer ahmed

Homogeneous Transformations:• HTM Exercise:

 

y2 

x2 

z2 = z3 = Z’2

x3 

y3 = y4

z4 = zt

x4 

xt 

yt 

X’2= x1 = x2 Y’2 

y1=y0 = y’1 

z1 

z0 

x0 

Z’1 

X’1 

NC System

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NC System

Homogeneous Transformations:• HTM Exercise:

 

y2 

x2 

z2 = z3 = Z’2

x3 

y3 = y4

z4 = zt

x4 

xt 

yt 

X’2= x1 = x2Y’2 

y1=y0 = y’1

z1 

z0 

x0 

Z’1 

X’1 

NC System

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NC System

1 0 0 0

[2 I 3] = 0 1 0 0

0 0 1 Z

0 0 0 1

1 0 0 0

[3 I 4] = 0 1 0 Y

0 0 1 0

0 0 0 1

c  -s  0 0

[ 4I t] = s  c  0 0

0 0 1 L

0 0 0 1

c  -s  0  0 

[ 2I t] =  s  c  0   Y 

0  0  1  Z + L 

0  0  0  1 

NC System

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NC System

1 0 0 0

[2 I 2'] = 0 1 0 0

0 0 1 c

0 0 0 1

1 0 0 X

[2' I 1] = 0 1 0 0

0 0 1 0

0 0 0 1

1 0 0 0

[ 1I 1'] = 0 1 0 b

0 0 1 0

0 0 0 1

cB 0 sB 0

[ 1'I 0] = 0 1 0 0

-sB 0 cB 0

0 0 0 1

NC System

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NC System

cB 0 sB X

[ 2I 0] = 0 1 0 b

-sB 0 cB c

0 0 0 1