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Introduction to NC/CNC

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Definitions of NC/CNC

• Numerical Control (NC) is the term used to

describe the control of machine movements

and various other functions by instructions

expressed as a series of numbers and initiated

via an electronic control system.

Consequently, Computer Numerical Control

(CNC) is the term used when the electroniccontrol system is influenced by a computer. [1]

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Definitions of NC/CNC cont.

• Numerical Control (NC) is the operation of a machine tool by a

series of coded instructions consisting of numbers, letters of 

the alphabet and symbols that the machine control unit

(MCU) can understand. These instructions are converted into

electrical pulses of current that the machine’s motors and

controls follow to carry out machining operations on a

workpiece. The numbers, letters and symbols are coded

instructions that refer to specific distances, positions,

functions or motions which the machine tool can understandas it machines the workpiece. [2]

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Definitions of NC/CNC cont.

• Computer Numerical Control is the control of 

a machine tool using numbers and letters. It is

a system in which programmed numerical

values are directly inserted and stored on

some form of input medium and automatically

read and decode to cause a corresponding

movement in the machine which it iscontrolling.[4]

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Definitions of NC/CNC cont.

• CNC is the process of manufacturing

machined parts using a computerizedcontroller to command motors which

drive each machine axis

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Effect of NC/CNC in

Manufacturing

• NC and CNC have changed the manufacturing industry more

specifically the metalworking industry.[2]

• Machines that are combined with NC or CNC can produce and

fabricate parts with an accuracy that is nearly impossible to

achieve by human operators. [2]

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Effect of NC/CNC in

Manufacturing cont.

• Furthermore, these parts can be replicated

many times over given that the NC or CNC

controls and commands allow it.[2]

• The operating commands that control the

machine tool are executed automatically with

amazing speed, accuracy, efficiency and

repeatability. [2]

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Effect of NC/CNC in

Manufacturing cont.

Reasons for using CNC/NC [3]:

• Increase production throughput

•

Improve the quality and accuracy of manufactured parts

• Stabilize manufacturing costs

•

Manufacture complex or otherwise impossible jobs – 2D and 3D contours

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Getting to Know the CNC

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CNC Manufacturing Process

Machine Tool Control

SlideMovement

SpindleRotation

ToolingWork

HoldingSupporting

Function

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CNC Manufacturing Process cont.

Spindle Rotation

- Control of machine spindles are driven directly

or indirectly by electric motors.

- The speed of the spindle is often infinitely

variable and will automatically changes as

cutting is taking place to maintain a

programmed surface speed.

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CNC Manufacturing Process cont.

Tooling

- may incorporate turrets or magazines which

hold a number of cutting tools.

- The machine controller can be programmed to

cause indexing of the turret or magazine to

present a new cutting tool to the work or to

facilitate tool removal and replacement where

automatic tool-changing devices are involved.

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CNC Manufacturing Process cont.

Work holding

- can be fairly conventional: vices, chucks,

collets and fixtures are all used.

- The NC can extend to loading the workpiece

by the use of robots and securely clamping it

by activating hydraulic or pneumatic clamping

systems.

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CNC Manufacturing Process cont.

Supporting functions

- supplementary functions that are done during

machining which might be vital to the success

of the operation.

- Tool monitoring might also fall under this

category.

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Machining Process

• Roughing

•

Semi Roughing

• Semi Finishing

• Finishing

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History of NC/CNC

• 1947 Developed a control system that

directed a spindle to many points in

succession

• 1951 Added computer to Parson’s system 

• 1952 Cincinnati Milicron Hydro-Tel Vertical

Spindle Milling Machine

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History of NC/CNC cont.

• 1954 NC was announced in public

•

1957 First production NC machines weredelivered and installed

•

1960 NC machine tool commonly available

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Advantages of NC/CNC

• Flexibility of operation is improved, as is the

ability to produce complex shapes with good

dimensional accuracy, repeatability, reduced

scrap loss, and high production rates,productivity and product quality

• Tooling costs are reduced, since templates and

other fixtures are not required.

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Advantages of NC/CNC cont.

• Machine adjustments are easy to make with

microcomputers and digital readouts

• Simplified inspection. Once the first piece has

passed inspection, minimal inspection is

required on subsequent parts

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Advantages of NC/CNC cont.

• Faster prototype production is possible.

•

Required operator skill is less than that for aqualified machinist, and the operator has

more time to attend to other tasks in the work

area.

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Limitations of NC/CNC

• Relatively high initial cost of the equipment.

•

The need and cost for programming andcomputer time.

•

Special maintenance with trained personnel.

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Limitations of NC/CNC cont.

• High preventative maintenance since

breakdowns is costly.

• Tools on NC machines do not cut metal any

faster than conventional machines

• NC does not eliminate the need for expensive

tools.

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Limitations of NC/CNC cont.

• NC will not totally eliminate errors. Operators

can still fail to push the correct buttons, make

incorrect alignments and fail to locate parts

properly in a fixture.

• Physical limitations

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Thank You