Automation & CNC Machining

Automation /Numerically Controlled Machine Tools


Automatic machines are generally used to minimise the need for manual effort.   The benefits are reduced operating costs, reduced operator errors, increased reliability, minimum work reduction due to human fatigue, illness and labour disputes.. Automatic Machines generally possess the following characteristics.

  1. They operate with minimum human involvement
  2. They include feedback to indicate process /machining deviations from the required task
  3. They make the required corrections with minimum human involvement

The following terms apply to modern automatic machines...

  • Feedback ..The measure of the actual result of the operation compared to the desired result providing a feedback generated error
  • Output.. The actual work produced.. This could be the product machined, the movement of the vehicle or item conveyed
  • Input..The data, instructions, command specifying the operations to produce the required output
  • Sensors..The additional instrumentation required to allow the feedback to be generated
  • Actuators /Drives..The additional drive systems required to provide the necessary machine movements
  • Control Center..The system used to process the input data and feedback systems and provide the necessary controls to the drive systems. The control center also includes for human interfacing
Automatic Material Handling

The transportation of materials around the floor of a workshop can be automated using AGV's (Automatically guided Vehicles) these are generally battery powered vehicles which are controlled using wires embedded into the floor or by taking using laser beams or using inertial systems. Material handling into and out of the machine tool can be accomplished using proprietory robotic arms or gantry systems for heavier items.  The control systems for the handling equipment must be integrated with the machine tool control system

NC Controlled Machine Tools

Numerical Control (N/C) is the term given to the programming control system for automatically operated machine tools and other manufacturing units..  Most modern machine tools
can include N/C systems.  DNC is the term used for Direct numerical control when a central computer system controls a number of machine tool work stations..  CNC is the term for computer numerical control which is local control of a machine tool be a built in computer. N/C programmes are coded instructions written in a standard language which is interpreted by the Machine Control Unit (MCU) which converts the instructions into electric signals which control the AC, DC or servo drives or the hydraulic or pneumatic valves feeding the fluid actuators on the machine tools. Typical Applications for Computer Numerical Control.

Machine tools Including.

  • Milling Machines /Machining Centres
  • Centre Lathes and Turning Centres
  • Drilling Machines

  • Precision Grinding Machines
  • EDM - Spark Erosion Machines
  • Die Sinking Machines

Sheet Metal Machines Including

  • Turret Punching Machines
  • Riveting Machines
  • Forming Machines

Fabrication Machines Including

  • Flame Cutting Machines
  • Welding Machines
  • Tube Bending Machines

Automatic Inspection Machine for tracing contours.

Co-ordinate System

NC systems as used by, milling machines and lathes ,are generally based on the cartesian co-ordinate system.  The Z axis being the machine tool spindle. The programming movement of a CNC machine can be described in four ways.

  1. Point-to-point..The tool is moved from point to point on the workpiece. The movements between the points are controlled by the machine to take the shortest possible route. This system would be used for drilling and punching
  2. Linear Path system..The system is still moved from point to point- the programmer can however set the rate of traverse between the points.  This system may be used for milling a straight slot.
  3. Parallel Path system..The system is still moved from point to point- The path between the points is always parallel to an axis..This option is used for simple turning and milling operations
  4. Continuous Path control..This allows complex contours to be machined with tool movements in 3 axes simultaneously. This allows complex shapes only limited by the Machine tool and cutting tool geometries
Control Feedback

The CNC controls fall into two general types Open Loop Control and Closed Loop Control.  The open loop control option includes for stepping motor drives with no feedback other than the internal system on the drive which provides for accurate descrete step movements.  The closed loop system is based on feedback generally with high powered servo drives.  The second option provides more reliable accuracy for long production cycles....

CNC programming Notes

Character..  This is a number letter or symbol which is recognised by the controller Word..a group of characters which defines a complete item of information.. There are two types of words as follows. Dimensional words..  These are words directly interpreted as dimensions.  They begin with X, Y, Z (referring to dimensions parallel to the relevant axes) and I, J, K (referring to arcs of circles).Management words..These are words not related to dimensions. Examples of management words are provided below;

  1. N4 ..Sequence number N followed by up to 4 digits identifying the sequence step
  2. G2 ..Preparation function G followed by up to 2 digits (G0- G99)
  3. F4 ..Feed rate command : The character F followed by up to 4 digits
  4. S4 ..Spindle speed command:the character S followed by up to 4 digits
  5. T2 ..Tool identifier : The character T followed by up to 2 digits
  6. M2 ..Miscellaneous command : M followed by up to 2 digits (G0- G99)

Format:  Different Controls systems use different formats, the relevant manual normally explains the format.  A block of data consists of a complete line of instruction words for the controller.
Word (or Letter) Address Format: The most currently most widely used format is the word (address) format. Each word commences witha letter called an address. Each word is identified within the block by its letter and not by its position.    Thus in each block only instructions which change have to be included.

CNC coding

Block Numbers (N)
Each block is preceded with the block number e.g. N5, N10, N15 etc the numbers are in steps of 5 to allow insertions of late code..
Preparatory functions (G) Note: the G numbers below are for illustrative purposes only. There are actually a number of different G number tables e.g Fanuc 0MB, 0TC,3M, 5M, 5T, 6M,6T,10M, 10T, Haas Lathe, Haas Mill, Mazak M32,Okuma OSP500 lathe et.etc Many of these can be obtained from the CNC reference links below:

G00Rapid Positioning-Point to Point
G01Positioning at controlled feedrate normal dimensions
G02Circular Interpolation-Normal Dimensions
G03Circular Interpolation CCW -Normal Dimensions
G04Dwell for programmed interval
G05Hold: Cancelled by operator
G06Reserved for future use
G07Reserved for future use
G08Programmed Slide accelaration
G09Programmed Slide accelaration
G10Linear Interpolation -Short dimensions
G11Linear Interpolation -Long dimensions
G123D Interpolation
G13-16Axis Selection
G17XY Plane Selection
G18ZX Plane Selection
G19YZ Plane Selection
G20Circular Interpolation CW:Long dimensions
G21Circular Interpolation CW:Short dimensions
G22Coupled Motion: Positive
G23Coupled Motion: Negative
G25-29Available for individual use
G30Circular Interpolation CCW:Long dimensions
G31Circular Interpolation CCW:Short dimensions
G32Reserved for future Standardisation
G33Thread Cutting: constant lead
G34Thread Cutting: increasing lead
G35-39Thread Cutting: reducing lead
G40Cutter compensation:Cancel
G41Cutter compensation:left
G42Cutter compensation:right
G43Cutter compensation:positive
G44Cutter compensation:negative
G45Cutter compensation:+/+
G46Cutter compensation:+/-
G47Cutter compensation:- / -
G48Cutter compensation:- / +
G49Cutter compensation:0 /+
G50Cutter compensation:0 / -
G51Cutter compensation:+ / 0
G52Cutter compensation:- / 0
G53Linear Shift: Cancel
G54Linear Shift: X
G55Linear Shift: Y
G56Linear Shift: Z
G57Linear Shift: XY
G58Linear Shift: XZ
G59Linear Shift: YZ
G60Positioning : exact 1
G61Positioning : exact 2
G64Change of rate
G65Reserved for future
G66Reserved for future
G67Reserved for future
G68Reserved for future
G69Reserved for future
G70Turning-Canned Finishing Cycle
G71Turning-Canned Roughing Cycle
G72Turning-Canned Facing Cycle
G73Reserved for future
G74Turning-Canned Peck Drilling Cycle
G75Turning-Canned Grooving Cycle
G76Turning-Canned Threading Cycle
G77Reserved for future
G78Reserved for future
G79Reserved for future
G80Cancel Canned Cycle.-Milling
G81Canned Drilling Cycle.-Milling
G82Canned C'bore Cycle.-Milling
G83Canned Deep Hole Drilling Cycle.-Milling
G84-89Fixed cycles
G90Absolute Positioning.-Milling-
G91Incremental Positioning.-Milling-
G92Repositioning or re-setting the origin point.-Milling-
G93Reserved for future
G94Reserved for future
G90-99Reserved for future
G95Reserved for future
G96Reserved for future
G98Turning-Linear Feedrate Per Time
G98Milling-Cancel G92 position set.(Part Reference Zero)
G99Turning-Feedrate Per Revolution

Dimensional Words

A CNC control will instruct the machine to move the desired tool to
a position parallel to the identified axis to the position indicated
by the dimension words e.g X10.0 Y-20.0. If there is no sign it shall be assumed to be
positive. To drill a hole 50mm deep at a set position the line of code would read (say)
N20 G01 X30.0, Y60.0, Z -50.0.

Feed Rate

There are a number of methods of indicating the feed rate.. i.e.

F45 may indicate 45mm/min..

F0.3 may indicate 0.3mm/rev..

F10 may indicate a feed rate number for a rate
predetermined by the machine tool maker..

Tool Number

The different tools used for machining a part will be allocated a different number. The tool number
will identify the tool offset parameters and the tool loading position amongst other information.

Miscellaneous functions

A number of miscellaneous functions are available for various housekeeping operations..

M00Program Stop
M01Optional Stop
M02End Program
M03Spindle CW
M04Spindle CCW
M05Spindle off
M06Tool Change
M07Mist coolant on
M08Flood Coolant on
M09Coolant off
M30End of Tape

Data Input

One method of inputting the information into CNC machines is via Manual Date Input
MDI. This can be from a keyboard or via a learning mode..

The technology for stored data input has evolved from punched tape to magnetic tape to floppy
disc. Program information can be input via a PC using the G & M codes as indicated above or direct for
CAD CAM software..

Links Providing information on Automation in machine tools
  1. Gudel - Gantry based handling systems..Module gantry handling systems - Downloadable design information
  2. Training Materials For CNC..Various products can be obtain for training /application of CNC
  3. CAD\CAM\CNC GLOSSARY..A comprehensive list of the relevant terms
  4. Promot systems..Brochure of Automation companies equipment
  5. Wikipedia -Numerical control notes..Lots of Useful Info