Numerical ControlNumerical Control

It might be said that numerical control is control It might be said that numerical control is control by by

numbers.numbers.

Numerical control uses any of the basic machine Numerical control uses any of the basic machine tools. tools.

In a broad sense, numerical control converts In a broad sense, numerical control converts numerical values into physical values, such as numerical values into physical values, such as

quantities and dimensions.quantities and dimensions.

Electronics plays an important part in Electronics plays an important part in

numerical control. numerical control.

Electronic circuits have been designed to Electronic circuits have been designed to "remember" a number. "remember" a number.

They have been designed to turn a switch on They have been designed to turn a switch on and /or off when a particular number is and /or off when a particular number is reached.reached.

This means that if a control unit can be This means that if a control unit can be designed to measure and "remember" designed to measure and "remember" numbers, the unit then has the ability to run a numbers, the unit then has the ability to run a machine.machine.

BASIC COMPONENTS OF AN N/C SYSTEMBASIC COMPONENTS OF AN N/C SYSTEM

1. 1. The control unitThe control unit, , which interprets the coded which interprets the coded instructions (the tape) and directs the machine instructions (the tape) and directs the machine through the operations.through the operations.

2. 2. The tapeThe tape, , which is punched full of holes, with which is punched full of holes, with each hole providing an electronic pulse. This tape each hole providing an electronic pulse. This tape holds the coded instructions. holds the coded instructions.

3. 3. The motorThe motor, , which supplies the power to move which supplies the power to move the tool or table of the machine.the tool or table of the machine.

4. 4. The electronic The electronic feedback devicefeedback device (transducer), (transducer), which tells how much movement has taken place.which tells how much movement has taken place.

Vertical Milling Machine Equipped with N/C Vertical Milling Machine Equipped with N/C controlcontrol

MOOG N/CMOOG N/C

HOW NUMERICAL CONTROL HOW NUMERICAL CONTROL WORKSWORKS

As the prepared tape passes through the As the prepared tape passes through the tape reader head, silicon photo diodes tape reader head, silicon photo diodes sense light as it passes through holes in the sense light as it passes through holes in the tape. tape.

This causes signals to be sent to the This causes signals to be sent to the electronic control. electronic control.

The number and location of the holes in The number and location of the holes in each row across the tape conform to a each row across the tape conform to a code.code.

The code is interpreted by the control The code is interpreted by the control unit. This unit stores all information until unit. This unit stores all information until a complete block of information is a complete block of information is obtained.obtained.

The control then causes the motors to The control then causes the motors to make the required number of steps.make the required number of steps.

During the tool cycle, the next tape During the tool cycle, the next tape block will be read and stored. block will be read and stored.

TYPES OF NUMERICAL TYPES OF NUMERICAL CONTROLCONTROL

There are actually two forms of There are actually two forms of numerical control:numerical control:

1. Discrete positioning. This is 1. Discrete positioning. This is commonly known as point-to-point.commonly known as point-to-point.

2. Continuous path, or contouring 2. Continuous path, or contouring

TapTapee

PREPARATORY FUNCTIONPREPARATORY FUNCTION 4 peck drill;4 peck drill;

Table moves to selected location. Peck drill Table moves to selected location. Peck drill cycle initiated upon arrival at location. cycle initiated upon arrival at location. Cycle time set by timer on console.Cycle time set by timer on console.

5 DRILL5 DRILL::Table moves to selected location. Spindle Table moves to selected location. Spindle moves down rapidly to preset feed point, moves down rapidly to preset feed point, proceeds at set feed rate to final depth and proceeds at set feed rate to final depth and retracts rapidly.retracts rapidly.

6 MILL:6 MILL:Spindle moves down rapidly to set feed Spindle moves down rapidly to set feed point, proceeds at set feed rate to final point, proceeds at set feed rate to final depth and then at set mill feed rate to depth and then at set mill feed rate to selected location.selected location.

7 BORE:7 BORE:Table moves to selected location. Spin dle moves down Table moves to selected location. Spin dle moves down rapidly to preset feed point, proceeds through work at set rapidly to preset feed point, proceeds through work at set feed rate. When final depth is reached, spin dle retracts feed rate. When final depth is reached, spin dle retracts from work at set feed rate to feed point and then retracts from work at set feed rate to feed point and then retracts rapidly.rapidly.

8 TAP:8 TAP:Table moves to preset location. Spindle moves down Table moves to preset location. Spindle moves down rapidly to preset feed point. Tap feeds into work at rate rapidly to preset feed point. Tap feeds into work at rate determined by lead screw. When final depth is reached, determined by lead screw. When final depth is reached, the spindle reverses itself and retracts from hole to feed the spindle reverses itself and retracts from hole to feed point. The spindle then rapidly retracts.point. The spindle then rapidly retracts.

9 READ Z BLOCK.9 READ Z BLOCK.This preparatory function does not initiate any motion of This preparatory function does not initiate any motion of the table or spindle. It supplies feed point and final depth the table or spindle. It supplies feed point and final depth information into the machine. This depth information is information into the machine. This depth information is then used in the next op eration of the machine. This then used in the next op eration of the machine. This information will be read while machine is positioning for information will be read while machine is positioning for next operation.next operation.

MISCELLANEOUS FUNCTIONSMISCELLANEOUS FUNCTIONS

00 PROGRAM STOP:00 PROGRAM STOP:Program is interrupted by placing the system in its manual Program is interrupted by placing the system in its manual mode of operation after completion of all commands in the mode of operation after completion of all commands in the block. Coolant flow and spindle feed are interrupted after the block. Coolant flow and spindle feed are interrupted after the spindle has been fully retracted from the workpiece. It is spindle has been fully retracted from the workpiece. It is necessary for the operator to push a button in order to necessary for the operator to push a button in order to continue with the remainder of the program. continue with the remainder of the program.

02 END OF program:02 END OF program:The function signifies the completion of the workpiece. After The function signifies the completion of the workpiece. After completion of all commands in the block, the system is re set completion of all commands in the block, the system is re set to its manual mode. Coolant flow and spindle feed are to its manual mode. Coolant flow and spindle feed are stopped after the spindle has been fully retracted from the stopped after the spindle has been fully retracted from the workpiece.workpiece.

06 TOOL CHANGE06 TOOL CHANGEThis is a command to execute the change of tool(s) manually, not to This is a command to execute the change of tool(s) manually, not to include tool selection. After completion of all commands in the block, the include tool selection. After completion of all commands in the block, the system is placed in its manual mode of operation. Coolant flow and system is placed in its manual mode of operation. Coolant flow and spindle feed are interrupted after the spindle has been fully retracted from spindle feed are interrupted after the spindle has been fully retracted from the workpiece.the workpiece.

07 COOLANT ON 07 COOLANT ON : This is a command to turn on flood coolant. : This is a command to turn on flood coolant.

08 COOLANT ON 08 COOLANT ON : This is a command to turn on mist coolant: This is a command to turn on mist coolant

09 COOLANT OFF09 COOLANT OFF: This is a command to shut off all coolant.: This is a command to shut off all coolant.

80 NO CHANGE IN MISCELLANEOUS FUNCTION80 NO CHANGE IN MISCELLANEOUS FUNCTION:: All miscellaneous functions remain in previously commanded operation. All miscellaneous functions remain in previously commanded operation. This applies to all miscellaneous functions with the exception of PROGRAM This applies to all miscellaneous functions with the exception of PROGRAM STOP, 02, and TOOL CHANGE, 06, which merely interrupt the sequence of STOP, 02, and TOOL CHANGE, 06, which merely interrupt the sequence of automatic operations.automatic operations.

MEASURING BASIS FOR N/C CONTROL MEASURING BASIS FOR N/C CONTROL SYSTEMSSYSTEMS

The Cartesian The Cartesian (rectangular) (rectangular) coordinate system is coordinate system is the basis for the basis for measuring N/C measuring N/C machine tools. machine tools.

In this system, all In this system, all point positions are point positions are described in terms of described in terms of distances from the distances from the origin .These are called origin .These are called the X, Y, and Z axes. the X, Y, and Z axes.

The Cartesian Coordinate SystemThe Cartesian Coordinate System The Cartesian Coordinate System The Cartesian Coordinate System A.A. Quadrants (4)Quadrants (4)

1.1. 1st quadrant (+,+)1st quadrant (+,+) 2.2. 2nd quadrant (-,+)2nd quadrant (-,+) 3.3. 3rd quadrant (-,-)3rd quadrant (-,-) 4.4. 4th quadrant (+,-)4th quadrant (+,-)

B.B. Origin (0,0)Origin (0,0)

C.C. Moog N/C Vise Location #1 Zero OffsetsMoog N/C Vise Location #1 Zero Offsets 1.1. zero offsets are always (2, -2) zero offsets are always (2, -2) 2.2. Moog N/C is always programmed in 4th Moog N/C is always programmed in 4th

quadrantquadrant 3. Machine control does not recognize negative 3. Machine control does not recognize negative

numbers so Y values are always programmed asnumbers so Y values are always programmed as positive even though in the 4th quadrant they are positive even though in the 4th quadrant they are negative.negative.

4. The tape coding values for the zero offset are 4. The tape coding values for the zero offset are X = 02000, Y = 02000X = 02000, Y = 02000

Vise LocationVise Location

Coordinate/Conventional DimensioningCoordinate/Conventional Dimensioning

DimensioningDimensioning

Program SheetProgram Sheet

Work piece CoordinatesWork piece Coordinates

Tooling Tooling SheetSheet

TapeTape

Components of a Typical BlockComponents of a Typical Block C.C. Components of a Typical Block Components of a Typical Block

1.1. track numbers (1-8)track numbers (1-8) 2.2. row numbers (1-20)row numbers (1-20) 3.3. track values (1,2,4, and 8)track values (1,2,4, and 8) 4. coded row data4. coded row data

a.a. block number - rows 1-3block number - rows 1-3 b.b. preparatory function - row 4preparatory function - row 4 c.c. X dimension - rows 5-9X dimension - rows 5-9 d.d. Y dimension - rows 10-14Y dimension - rows 10-14 e.e. reserved row (not used) - row 15reserved row (not used) - row 15 f. f. tool number - rows 16-17tool number - rows 16-17 g.g. miscellaneous function - rows 18-miscellaneous function - rows 18-

1919 h.h. end of block (EOB) - row 20end of block (EOB) - row 20

Coded Numeric DataCoded Numeric Data

D.D. Coded Numeric DataCoded Numeric Data 00 no track punchedno track punched

11 track 1 punchedtrack 1 punched22 track 2 punchedtrack 2 punched33 tracks 1 & 2 punchedtracks 1 & 2 punched44 track 3 punchedtrack 3 punched55 tracks 1 & 3 punchedtracks 1 & 3 punched66 tracks 2 & 3 punchedtracks 2 & 3 punched77 tracks 1, 2, & 3 punchedtracks 1, 2, & 3 punched88 track 4 punchedtrack 4 punched99 tracks 1 & 4 punchedtracks 1 & 4 punched

EOBEOB track 8 only punchedtrack 8 only punched

The Fixed Decimal SystemThe Fixed Decimal System The Fixed Decimal SystemThe Fixed Decimal System A.A. OptionsOptions

1. Full floating decimals (many N/Cs, all CNCs)1. Full floating decimals (many N/Cs, all CNCs)

2. Fixed decimals (many N/Cs including ours2. Fixed decimals (many N/Cs including ours)) B. Programming Implications:B. Programming Implications: All X and Y coordinate information assumes theAll X and Y coordinate information assumes the fixed decimal point is two digits from the left of afixed decimal point is two digits from the left of a five digit dimension and a decimal point is neverfive digit dimension and a decimal point is never used.used. Absolute vs Incremental ProgrammingAbsolute vs Incremental Programming A. AbsoluteA. Absolute: all dimensions are derived from their: all dimensions are derived from their respective distances from the machine tool's respective distances from the machine tool's origin.origin. B. IncrementalB. Incremental: subsequent dimensions derive their : subsequent dimensions derive their

valuevalue based on their distance from the previous based on their distance from the previous

dimension.dimension.

Part Dimensioning for N/CPart Dimensioning for N/C

A.A. Dimensioning Convention Dimensioning Convention NomenclatureNomenclature

1.1. baseline dimensioningbaseline dimensioning

2.2. absolute dimensioningabsolute dimensioning

3.3. datum line dimensioningdatum line dimensioning

4.4. coordinate dimensioningcoordinate dimensioning B.B. Eliminates "Tolerance Stack"Eliminates "Tolerance Stack" C.C. Facilitates ProgrammingFacilitates Programming D.D. Facilitates InspectionFacilitates Inspection

Simple Point-To-Point Drilling ProgramSimple Point-To-Point Drilling Program A. Conversion of Conventional Drawing to A. Conversion of Conventional Drawing to

CoordinateCoordinate Dimensioned Drawing Dimensioned Drawing 1. zero offsets: X = 02000, y = 020001. zero offsets: X = 02000, y = 02000

2. X and Y dimensions given from datums2. X and Y dimensions given from datums 3. sequence of operations provides for most 3. sequence of operations provides for most economical tool movemeneconomical tool movemen

C.C. Programming Sheet Programming Sheet 1.1. review data in headingreview data in heading 2.2. review data for block rows review data for block rows

(N,G,X,Y,T,M)(N,G,X,Y,T,M)

D.D. Tooling SheetTooling Sheet 1.1. data in headingdata in heading 2.2. operation descriptionoperation description 3.3. spindle feed and RPMspindle feed and RPM 4.4. X and Y axis feedX and Y axis feed 5.5. tool descriptiontool description

Tool Presetting Tool Presetting A.A. PurposesPurposes 1. Quick and efficient replacement of broken or 1. Quick and efficient replacement of broken or

dull toolsdull tools 2. close tolerances on depth dimensions2. close tolerances on depth dimensions

(interchangeability of tools during the production (interchangeability of tools during the production cycle mandates exact uniformity of length for a cycle mandates exact uniformity of length for a given type and size of tool; this is crucial for N/Cgiven type and size of tool; this is crucial for N/C production and flexible automation (FMS/FMC))production and flexible automation (FMS/FMC))

Variance in Tool LengthVariance in Tool Length

1. Fresh drills from the manufacturer 1. Fresh drills from the manufacturer come in varying lengths.come in varying lengths.

2. Milling cutters, counterbores, spot drills, 2. Milling cutters, counterbores, spot drills, countersinks, reamers, etc., display the countersinks, reamers, etc., display the same characteristicsame characteristic

3. Routine sharpening amplifies 3. Routine sharpening amplifies discrepancies in lengthdiscrepancies in length

Setting Tool LengthsSetting Tool Lengths

A.A. ProcedureProcedure Tools are loaded into their respective tool holders Tools are loaded into their respective tool holders

and clamped such that their preset length and clamped such that their preset length corresponds to that of the tool setting drawing corresponds to that of the tool setting drawing within a tolerance of + or - .001" (+ or - .02mm). within a tolerance of + or - .001" (+ or - .02mm).

This typically requires special fixtures such as This typically requires special fixtures such as vernier height gages, high-precision dial indicators vernier height gages, high-precision dial indicators ..

For the purposes of standardization , the preset For the purposes of standardization , the preset length for all drills destined for use on the Moog length for all drills destined for use on the Moog N/C will be N/C will be 5.125". 5.125".

Collets held cutters and very small drills will Collets held cutters and very small drills will necessarily have a much shorter preset length.necessarily have a much shorter preset length.

N/C Exercise #2N/C Exercise #2IntroductionIntroduction

This numerical control program is designed to systematically drill holes in a part for This numerical control program is designed to systematically drill holes in a part for production. A Bridgeport N/C machine will use a drill cycle geometry code to first production. A Bridgeport N/C machine will use a drill cycle geometry code to first center drill the holes then return to the same location to drill the trough holes then center drill the holes then return to the same location to drill the trough holes then once more counter boring the same holes. For this process we will use a point-to-once more counter boring the same holes. For this process we will use a point-to-point method. Reading further |pjti will be informed of the sequence of operations, point method. Reading further |pjti will be informed of the sequence of operations, thethe

tools used and the references used.tools used and the references used.

Sequence of OperationsSequence of Operations Included is a tooling sheet which states the tools needed and what order they are Included is a tooling sheet which states the tools needed and what order they are

used. For this operation a center drill will/be used to eliminate the tendency for the used. For this operation a center drill will/be used to eliminate the tendency for the drill bit to walk on the parts surface. The machine continues through the all the hole drill bit to walk on the parts surface. The machine continues through the all the hole locations with each tool to eliminate excessive tool changes. Once the center drill is locations with each tool to eliminate excessive tool changes. Once the center drill is done the tool is changed to the drill bit to/systematically drill the through holes. Once done the tool is changed to the drill bit to/systematically drill the through holes. Once the drill has created all the through holes needed the tool is changed to the counter the drill has created all the through holes needed the tool is changed to the counter bore. Once the holes are counter bored the machining process is done. The tool life is bore. Once the holes are counter bored the machining process is done. The tool life is optimized using calculation of speeds and feeds with numbers from optimized using calculation of speeds and feeds with numbers from The Machinery's The Machinery's Handbook*.Handbook*. These numbers are based on a forty five minute tool life for drilling These numbers are based on a forty five minute tool life for drilling operations.operations.

Tooling UsedTooling Used The order of tooling has been set and should be numbered accordingly. There will be The order of tooling has been set and should be numbered accordingly. There will be

three tools used in this exercise and also three turret stop settings. The first tool three tools used in this exercise and also three turret stop settings. The first tool listed is the number three center drill and is numbered 01. The second is the 1/8 listed is the number three center drill and is numbered 01. The second is the 1/8 diameter drill bit and is numbered 02. The third tool is the one quarter inch counter diameter drill bit and is numbered 02. The third tool is the one quarter inch counter bore and is numbered 03. The tools have there own respective turret stop settings. bore and is numbered 03. The tools have there own respective turret stop settings. No tooling material was specified nor a manufacturer so specifications for the tools No tooling material was specified nor a manufacturer so specifications for the tools would be speculation. I used tools made of high speed steel and used stock made of would be speculation. I used tools made of high speed steel and used stock made of 4130 steel with a Brinell hardness of 200. Following is the RPM and feed rate 4130 steel with a Brinell hardness of 200. Following is the RPM and feed rate calculations:calculations:

Cutting speed(CS)Cutting speed(CS)

The most important considerations for any type of The most important considerations for any type of machining process are cutting speed, feed and machining process are cutting speed, feed and coolants.coolants.

Cutting speed(CS): Means the cutting distance in Cutting speed(CS): Means the cutting distance in one minute. CS is normally based on surface feed one minute. CS is normally based on surface feed per minute (SFPM).per minute (SFPM).

Machine ‘s spindle speed is given in (rpm), so cutting Machine ‘s spindle speed is given in (rpm), so cutting speed should be changed to rpm.speed should be changed to rpm.

RPM = 12 * CS/RPM = 12 * CS/ π π * d * d

FEEDFEED

Feed: Cutting tool should be fed into the work-Feed: Cutting tool should be fed into the work-piece; the bigger the drill, the slower the drill piece; the bigger the drill, the slower the drill should be fed into the work-piece.should be fed into the work-piece.

Feed is calculated in inches/rev.Feed is calculated in inches/rev.

IPR= cpt (in/min) * # teethIPR= cpt (in/min) * # teeth

IPM = RPM * IPRIPM = RPM * IPR