Computer Numerical Controlled Machines

CNC Machines

History of Control1.Steam engines: String – Connecting rod+

flywheel2.Copying machines: Master + stylus + lever3.Automatic lathes: Cams + Mechanisms4.Transfer machines: Collection of machines +

automatic material handling (for one job)5.NC and CNC

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CNC MachinesHistory of NC:• 1952: The first NC conventional milling machine (at

Massachusetts Institute of Technology).• 1957: Air craft manufacturers installed a milling machine as

the beginning of NC technology.• Drilling machines, jig borers, lathers • NC machining and turning centers appeared • 1960’s: Smaller electronic components such as transistors,

resistors, and diodes have increased the reliability, reduced size and cost of NC machine tools.

• 1965: Integrated circuits in 1965’s led to a further reduction of the size and cost of the control units and provided the basis for the use of minicomputers in (CNC) and (DNC) machining.

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CNC MachinesNumerical control (NC):The term used to describe the control of machine

movements and various other functions by instructions expressed as a series of numbers and initiate via electronic control system.

Computer numerical control (CNC):The term used when the control system includes a

computer.

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CNC Machines

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CNC Machines

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CNC Machines

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CNC MachinesAdvantages of NC:• Greater flexibility: through tape/program changes

can be made rapidly, and design changes to parts can be made rapidly through minor changes to the part program.

• Elimination of templates, models, jigs, and fixtures: The NC control tape takes over the job of locating the cutting tools.

• Easier setups: By using more simple work holding and locating devices, the operator does not have to set table limit stops or dogs or depend on the feed screw dials when setting up for machining.

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CNC Machines• Reduced machining time: Machining with NC

provides the use of a wider range of speeds and feeds than conventional machine tools. Optimum selection of feed rates and cutting speeds is ensured. The NC equipment can also move from one cutting operation to the next faster than the operator which, significantly, reduces the total machining time.

• Greater accuracy and uniformity: No human errors are possible and machining the same part is performed in the same way through the stored tape/program. Hence, scrape and rework are greatly reduced or completely eliminated by using NC.

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CNC Machines• Greater safety: The operator is not as closely

involved with the actual machining operations as in case of the conventional machine tools.

• Conversion to the metric system:, NC system can be converted to accept either inch or metric inputs.

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CNC MachinesDisadvantages of NC:• NC follows programmed instruction that may lead to

machine destruction if they are not properly prepared

• NC cannot add any extra machining capability to the machine tool.

• NC machines costs 5 to 10 times than conventional machines of the same working capacity.

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CNC Machines• The skill required to operate an NC is usually high.

(Part programmers, tool setters, punch operators, and maintenance staff that are more educated and well trained than conventional machine operators)

• Special training for personnel for the software and hardware is very important.

• NC requires high investments in terms of wages of highly skilled personnel and expensive spare parts.

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CNC Machines

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PTP - NC

CNC Machines

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Straight-Cut NC

CNC Machines

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Contouring/NC

CNC Machines

16Example of NC motions

CNC Machines

17Example of NC motions

CNC Machines

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CNC Machines

1. CNC drilling machines2. CNC milling machines3. CNC turning machines4. CNC machining centers5. CNC turning centers

CNC Machines

19CNC drilling

CNC Machines

20CNC milling

CNC Machines

21CNC turning

CNC Machines

22CNC machining center

CNC Machines

23CNC turning center