Advantages And Disadvantages Of CNC

CNC Computer Numerical Control machines are widely used in manufacturing industry. Traditional machines such as vertical millers, center lathes, shaping machines, routers etc.... operated by a trained engineer have, in many cases, been replaced by computer control machines

Advantages

1. CNC machines can be used continuously 24 hours a day, 365 days a year and only need to be switched off for occasional maintenance.
2. CNC machines are programmed with a design which can then be manufactured hundreds or even thousands of times. Each manufactured product will be exactly the same.
3. Less skilled/trained people can operate CNCs unlike manual lathes / milling machines etc.. which need skilled engineers.
4. CNC machines can be updated by improving the software used to drive the machines.
5. Training in the use of CNCs is available through the use of ‘virtual software’. This is software that allows the operator to practice using the CNC machine on the screen of a computer. The software is similar to a computer game.
6. CNC machines can be programmed by advanced design software such as Pro/DESKTOP^®, enabling the manufacture of products that cannot be made by manual machines, even those used by skilled designers / engineers.
7. Modern design software allows the designer to simulate the manufacture of his/her idea. There is no need to make a prototype or a model. This saves time and money.
8. One person can supervise many CNC machines as once they are programmed they can usually be left to work by themselves. Sometimes only the cutting tools need replacing occasionally.
9. A skilled engineer can make the same component many times. However, if each component is carefully studied, each one will vary slightly. A CNC machine will manufacture each component as an exact match.

Disadvantages

1. CNC machines are more expensive than manually operated machines, although costs are slowly coming down.
2. The CNC machine operator only needs basic training and skills, enough to supervise several machines. In years gone by, engineers needed years of training to operate centre lathes, milling machines and other manually operated machines. This means many of the old skills are been lost.
3. Less workers are required to operate CNC machines compared to manually operated machines. Investment in CNC machines can lead to unemployment.
4. Many countries no longer teach pupils / students how to use manually operated lathes / milling machines etc... Pupils / students no longer develop the detailed skills required by engineers of the past. These include mathematical and engineering skills.

CNC G Code

G-Codes Simple Definition

G00     Rapid traverse
G01     Linear interpolation with feedrate
G02     Circular interpolation (clockwise)
G03     Circular interpolation (counter clockwise)
G2/G3   Helical interpolation
G04     Dwell time in milliseconds
G05     Spline definition
G06     Spline interpolation
G07     Tangential circular interpolation / Helix interpolation / Polygon interpolation /             Feedrate interpolation
G08     Ramping function at block transition / Look ahead "off"
G09     No ramping function at block transition / Look ahead "on"
G10     Stop dynamic block preprocessing
G11     Stop interpolation during block preprocessing
G12     Circular interpolation (cw) with radius
G13     Circular interpolation (ccw) with radius
G14     Polar coordinate programming, absolute
G15     Polar coordinate programming, relative
G16     Definition of the pole point of the polar coordinate system
G17     Selection of the X, Y plane
G18     Selection of the Z, X plane
G19     Selection of the Y, Z plane
G20     Selection of a freely definable plane
G21     Parallel axes "on"
G22     Parallel axes "off"
G24     Safe zone programming; lower limit values
G25     Safe zone programming; upper limit values
G26     Safe zone programming "off"
G27     Safe zone programming "on"
G33     Thread cutting with constant pitch
G34     Thread cutting with dynamic pitch
G35     Oscillation configuration
G38     Mirror imaging "on"
G39     Mirror imaging "off"
G40     Path compensations "off"
G41     Path compensation left of the work piece contour
G42     Path compensation right of the work piece contour
G43     Path compensation left of the work piece contour with altered approach
G44     Path compensation right of the work piece contour with altered approach
G50     Scaling
G51     Part rotation; programming in degrees
G52     Part rotation; programming in radians
G53     Zero offset off
G54     Zero offset #1
G55     Zero offset #2
G56     Zero offset #3
G57     Zero offset #4
G58     Zero offset #5
G59     Zero offset #6
G63     Feed / spindle override not active
G66     Feed / spindle override active
G70     Inch format active
G71     Metric format active
G72     Interpolation with precision stop "off"
G73     Interpolation with precision stop "on"
G74     Move to home position
G75     Curvature function activation
G76     Curvature acceleration limit
G78     Normalcy function "on" (rotational axis orientation)
G79     Normalcy function "off"

G80 - G89 for milling applications:
G80     Canned cycle "off"
G81     Drilling to final depth canned cycle
G82     Spot facing with dwell time canned cycle
G83     Deep hole drilling canned cycle
G84     Tapping or Thread cutting with balanced chuck canned cycle
G85     Reaming canned cycle
G86     Boring canned cycle
G87     Reaming with measuring stop canned cycle
G88     Boring with spindle stop canned cycle
G89     Boring with intermediate stop canned cycle

G81 - G88 for cylindrical grinding applications:

G81     Reciprocation without plunge
G82     Incremental face grinding
G83     Incremental plunge grinding
G84     Multi-pass face grinding
G85     Multi-pass diameter grinding
G86     Shoulder grinding
G87     Shoulder grinding with face plunge
G88     Shoulder grinding with diameter plunge
G90     Absolute programming
G91     Incremental programming
G92     Position preset
G93     Constant tool circumference velocity "on" (grinding wheel)
G94     Feed in mm / min (or inch / min)
G95     Feed per revolution (mm / rev or inch / rev)
G96     Constant cutting speed "on"
G97     Constant cutting speed "off"
G98     Positioning axis signal to PLC
G99     Axis offset
G100   Polar transformation "off"
G101   Polar transformation "on"
G102   Cylinder barrel transformation "on"; cartesian coordinate system
G103   Cylinder barrel transformation "on," with real-time-radius compensation         (RRC)
G104   Cylinder barrel transformation with center line migration (CLM) and RRC
G105   Polar transformation "on" with polar axis selections
G106   Cylinder barrel transformation "on" polar-/cylinder-coordinates
G107   Cylinder barrel transformation "on" polar-/cylinder-coordinates with RRC
G108   Cylinder barrel transformation polar-/cylinder-coordinates with CLM and         RRC
G109   Axis transformation programming of the tool depth
G110   Power control axis selection/channel 1
G111   Power control pre-selection V1, F1, T1/channel 1 (Voltage, Frequency, Time)
G112   Power control pre-selection V2, F2, T2/channel 1
G113   Power control pre-selection V3, F3, T3/channel 1
G114   Power control pre-selection T4/channel 1
G115   Power control pre-selection T5/channel 1
G116   Power control pre-selection T6/pulsing output
G117   Power control pre-selection T7/pulsing output
G120   Axis transformation; orientation changing of the linear interpolation rotary     axis
G121   Axis transformation; orientation change in a plane
G125   Electronic gear box; plain teeth
G126   Electronic gear box; helical gearing, axial
G127   Electronic gear box; helical gearing, tangential
G128   Electronic gear box; helical gearing, diagonal
G130   Axis transformation; programming of the type of the orientation change
G131   Axis transformation; programming of the type of the orientation change
G132   Axis transformation; programming of the type of the orientation change
G133   Zero lag thread cutting "on"
G134   Zero lag thread cutting "off"
G140   Axis transformation; orientation designation work piece fixed coordinates
G141   Axis transformation; orientation designation active coordinates
G160   ART activation
G161   ART learning function for velocity factors "on"
G162   ART learning function deactivation
G163   ART learning function for acceleration factors
G164   ART learning function for acceleration changing
G165   Command filter "on"
G166   Command filter "off"
G170   Digital measuring signals; block transfer with hard stop
G171   Digital measuring signals; block transfer without hard stop
G172   Digital measuring signals; block transfer with smooth stop
G175   SERCOS-identification number "write"
G176   SERCOS-identification number "read"
G180   Axis transformation "off"
G181   Axis transformation "on" with not rotated coordinate system
G182   Axis transformation "on" with rotated / displaced coordinate system
G183   Axis transformation; definition of the coordinate system
G184   Axis transformation; programming tool dimensions
G186   Look ahead; corner acceleration; circle tolerance
G188   Activation of the positioning axes
G190   Diameter programming deactivation
G191   Diameter programming "on" and display of the contact point
G192   Diameter programming; only display contact point diameter
G193   Diameter programming; only display contact point actual axes center point
G200   Corner smoothing "off"
G201   Corner smoothing "on" with defined radius
G202   Corner smoothing "on" with defined corner tolerance
G203   Corner smoothing with defined radius up to maximum tolerance
G210   Power control axis selection/Channel 2
G211   Power control pre-selection V1, F1, T1/Channel 2
G212   Power control pre-selection V2, F2, T2/Channel 2
G213   Power control pre-selection V3, F3, T3/Channel 2
G214   Power control pre-selection T4/Channel 2
G215   Power control pre-selection T5/Channel 2
G216   Power control pre-selection T6/pulsing output/Channel 2
G217   Power control pre-selection T7/pulsing output/Channel 2
G220   Angled wheel transformation "off"
G221   Angled wheel transformation "on"
G222   Angled wheel transformation "on" but angled wheel moves before others
G223   Angled wheel transformation "on" but angled wheel moves after others
G265   Distance regulation – axis selection
G270   Turning finishing cycle
G271   Stock removal in turning
G272   Stock removal in facing
G274   Peck finishing cycle
G275   Outer diameter / internal diameter turning cycle
G276   Multiple pass threading cycle
G310   Power control axes selection /channel 3
G311   Power control pre-selection V1, F1, T1/channel 3
G312   Power control pre-selection V2, F2, T2/channel 3
G313   Power control pre-selection V3, F3, T3/channel 3
G314   Power control pre-selection T4/channel 3
G315   Power control pre-selection T5/channel 3

G316   Power control pre-selection T6/pulsing output/Channel 3
G317   Power control pre-selection T7/pulsing output/Channel 3

Note that some of the above G-codes are not standard. Specific control features, such as laser power control, enable those optional codes.