CNC Machines

CNC Machines

What is a CNC Machine?

1955 - US Air Force define a need to develop a machine tool capable of machining complex and close tolerance aircraft parts.

1959 - MIT is the contractor and builds the machine for the project. MIT announces Automatic Programmed Tools (APT) programming language

1960 - Direct Numerical Control (DNC). This eliminates paper tape and allows programmers to send files directly to machine tools

1980s - CNC machine is introduced. Unix and PC based systems

1997 - PC- Windows operating system is attached to cnc

History

Turning CentersMilling CentersVertical Machining CentersHorizontal Machining CentersDrilling MachinesEDM MachinesLaser-Cutting Machines

TYPES OF CNC MACHINE

TURNING CENTERS

MILLING CENTERS

VMC Machine

Vertical Machining Centers (VMCs)Spindle in a vertical orientation.

VMCs are high-precision

Used for tight-tolerance

HMC Machine

Horizontal Machining Centers (HMCs)Spindle in a horizontal orientation.

Horizontal orientation encourages chips to fall away.

HMCs are high-precision

Used for tight-tolerance

Controlled by G and M codes.These are number values and co-ordinates.Each number or code is assigned to a particular operation.Typed in manually to CAD by machine operators.G & M codes are automatically generated by the computer software.

How CNC Works

Common Format of a Block

O - Program number N - Sequence number 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

Programming Key Letters

G00 Rapid TransverseG01 Linear InterpolationG02 Circular Interpolation, CWG03 Circular Interpolation, CCWG20/G70 Inch unitsG8 Cancel canned cyclesG81 Drilling cycleG82 Counter boring cycleG83 Deep hole drilling cycleG90 Absolute positioningG91 Incremental positioning

Table of Important G codes

M00 Program stopM01 Optional program stopM02 Program endM03 Spindle on clockwiseM04 Spindle on counterclockwiseM05 Spindle stopM06 Tool changeM08 Coolant onM09 Coolant offM10 Clamps onM11 Clamps offM30 Program stop, reset to start

Table of Important M codes

Operator Panel

Build by Machine

Automobile Part

AerospaceCNC machine manufactures this items

Diamond & Jewellery Ind.Textile MachineryDie & Mould Manufactures

Tools of Machine

Tools of MachinePosess hardness and strength at high temperatures

Able to withstand when heat is generate

Angle of the cutting face

Flute width, number of flutes, teeth, and margin size

Lubricating during cutting process

Cooling the workpiece at high cutting speeds

Improving tool life,

Improving surface finish

Flushing away chips from the cutting zone

Corrosion protection of the machined surface CUTTING FLUIDS / COOLANT

STRAIGHT OILS -Non-emulsifiable and are used in machining operations in an undiluted form they are composed of a petroleum oil , lubricants such as fats, vegetable oils ( BEST LUBRICATION )

SOLUBLE OILS -Contain no petroleum or mineral oil , composed of alkaline inorganic and organic compounds ( BEST COOLING )

SEMISYNTHETIC FLUIDS- Emulsion when mixed with water ( LEAST EXPENSIVE )

SYNTHETIC FLUIDS-Combination of synthetic and soluble oil fluids ( COST AND HEAT TRANSFER PERFORMANCE )

TYPE OF CUTTING FLUIDS

High Accuracy e.g. Aircraft partsProduction rate is very highComplex surfaces need to be machined Flexibility in job change , automatic tool settingsMore safe , higher productivity , better qualityLess paper work , faster prototype production

Advantages

Costly setup

Skilled operators

Computers , Programming knowledge required

Maintenance is very difficultDisadvantages

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