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
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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 in1970s

    Both terms are still used and should be taken

    to mean the same

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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

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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

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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

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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

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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

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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

    http://localhost/var/www/apps/conversion/tmp/scratch_3/CNC%20Machining.VOBhttp://localhost/var/www/apps/conversion/tmp/scratch_3/CNC%20Machining.VOBhttp://localhost/var/www/apps/conversion/tmp/scratch_3/CNC%20Machining.VOB
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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

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    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

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    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

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    Video Clip

    http://localhost/var/www/apps/conversion/tmp/scratch_3/CNC%20Machining%20Demo%20Workpiece%20At%20AMB%20Fair%202008.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/CNC%20Machining%20Demo%20Workpiece%20At%20AMB%20Fair%202008.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/CNC%20Machining%20Demo%20Workpiece%20At%20AMB%20Fair%202008.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/CNC%20Machining%20Demo%20Workpiece%20At%20AMB%20Fair%202008.mp4
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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

    25

    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:

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    NC System

    Homogeneous Transformations:

    Transformation Matrix:

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    Rotation Translation

    Homogeneous

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    NC System

    Homogeneous Transformations:

    3 Dimensional Coordinate Frame:

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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:

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    NC S

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    NC System

    Homogeneous Transformations:

    Direction of Positive Rotation:

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    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:

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    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 ksx, y, and z axes, then TKJ , the matrix that takes

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

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    NC S

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    NC System

    Homogeneous Transformations:

    Transforming points between frames:

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    NC S t

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    NC System

    Homogeneous Transformations:

    Transforming points between frames:

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    Tmc =

    NC S t

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    NC System

    Homogeneous Transformations:

    Rotation Matrices:

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    NC S t

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    NC System

    Homogeneous Transformations:

    Moving Coordinate System:

    When we use movingaxeswe 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)

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    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)

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    NC S t

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    NC System

    Homogeneous Transformations:

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    NC S t

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    NC System

    Homogeneous Transformations:

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    NC S t

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    NC System

    Homogeneous Transformations:

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    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:

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    -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:

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    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

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    Homogeneous Transformations: HTM Exercise:

    y2

    x2

    z2= z3 = Z2

    x3

    y3= y4

    z4 = zt

    x4

    xtyt

    X2=x1 = x2Y2

    y1=y0= y1

    z1

    z0

    x0

    Z1

    X1

    NC System

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    NC System

    Homogeneous Transformations: HTM Exercise:

    y2

    x2

    z2= z3 = Z2

    x3

    y3= y4

    z4 = zt

    x4

    xtyt

    X2=x1 = x2Y2

    y1=y0= y1

    z1

    z0

    x0

    Z1

    X1

    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