Cnc Automation

7/30/2019 Cnc Automation

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1. Automation of the manufacturing system2. Automation of manufacturing support systems

Automation of the manufacturing system operates in the factory on the physicalproduct.

They perform operations such as processing, assembly, inspection or material

handling. Automated machine toolsTransfer lines performing series of machining operationManufacturing systems using robots for processing/assembly.Automatic material handling and storageAutomatic inspection system for quality control

It is classified into the following three types


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Fixed Automation

Sequence of processing (or assembly) operations is fixed by the equipment configuration

Ex: Feeding of rotating spindle

Typical features:

Suited to high production quantities

High initial investment for custom-engineered equipment

High production rates

Relatively inflexible in accommodating product variety

The economic justification for fixed automation is found in products that are produced in very

Large quantities and at high production rate.

Application: Machining transfer, automated assembly machines.Programmable Automation

The production equipment is designed with the Capability to change the sequence ofoperations through re-programming to accommodate different product configurations. Theoperation sequence is controlled by a program, which is a set of instructions coded so thatthey can be read and interpreted by the system. It can also be modified or new programs can

be prepared to produce new products.Typical features:

High investment in programmable equipmentLower production rates than fixed automationFlexibility to deal with variations and changes in product configurationMost suitable for batch production

Physical setup and part program must be changed between jobs (batches)Ex: NC Machines, Industrial Robots, PLC(Programmable logic controller)


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Flexible Automation

Extension of programmable automation.

System is capable of changing over from one job to the next with little lost time between

jobs.

It is a case of soft variety, so that the amount of changeover required between styles isminimal. Typical features:

High investment for custom-engineered system

Continuous production of variable mixes of products

Medium production rates

Flexibility to deal with product design variations

Programmable

Automation

Flexible

Automation

Fixed

Automation

Variety

Quantity1 100 10,000 1,000,000


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Automation of manufacturing support systems

Business functions sales and marketing, order entry, cost accounting,customer billing

Product design - research and development,design engineering, prototype shopManufacturing planning- process planning,production planning, MRP, capacity planningManufacturing control

shop floor control, inventory control, quality control

(INFORMATION PROCESSING CYCLE)

CIM(Computer Integrated Manufacturing): pervasive use of computer systems todesign the products, plan the production, control the operation, and performbusiness function

Automation of manufacturing support systems isaimed at reducing the amount of manual andclerical efforts in product design, manufacturingplanning and control, and business function of thefirm.

CAD: Computer Aided Design: use of computer systems to support product designCAM: Computer Aided Manufacturing: use of computer systems to support

manufacturingCIM= CAD+ CAM+ Business functions related to manufacturing


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Reasons for Automating

1. To increase labor productivity

2. To reduce labor cost

3. To mitigate the effects of labor shortages

4. To reduce or remove routine manual and clerical tasks

5. To improve worker safety6. To improve product quality

7. To reduce manufacturing lead time

8. To accomplish what cannot be done manually

9. To avoid the high cost of not automating


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A numerical control, or NC, system controls many machine functions and movements which

were traditionally performed by skilled machinists.

Numerical control developed out of the need to meet the requirements of high production

rates, uniformity and consistent part quality.

Programmed instructions are converted into output signals which in turn control machine

operations such as spindle speeds, tool selection, tool movement, and cutting fluid flow.

It is easier to write new program than to make major alternation of the processing equipment.Hence, capability to change the program makes NC suitable for small and medium production.

Machine tool application: Turning, Milling, drilling, boring

Non-Machine tool application: Assembling, Inspection, Material Handling, Drafting, polishing

Numerical Control (NC) refers to the method of controlling the manufacturing operation by

means of directly inserted coded alpha numerical instructions into the machine tool.

It is a form of programmable automation.

Basic components of NC, system


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1. Program of instructions /part programDetailed step by step commands that direct the actions of the processingequipment.Command may be referred to positioning of cutting tool/machine spindle

w.r.t. work table Or selection of spindle speed, feed rate, cutting tool andother functions.The program is coded on a suitable medium like 1 inch wide punched tape(earlier), Magnetic Tapes, diskettes, and electronic transfer of part programsfrom a computer.

2. Machine Control Unit(MCU) Consist of electronic and controlled hardware that read and interpret

the program of instructions And convert it into mechanical action of themachine tools and other processing equipments.

Type of readers depend on the storage media for the part program.

Punched tape reader, magnetic Tape reader, floppy disk drive. Includes control system software, calculation algorithm, and translation

software to convert NC part program to suitable format.3. Processing Equipment

It performs the useful work. Its operation is directed by MCU. It consist of work table, spindle, motor and controls needed to drive them


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Types of NC systems1. Traditional numerical control (NC);

2. Computer numerical control (CNC);

3. Distributed numerical control (DNC).

Traditional numerical control machines have hardwired control, whereby control isaccomplished through the use of punched paper (or plastic) tapes or cards. Tapes tendto wear, and become dirty, thus causing misreading. Many other problems arise fromthe use of NC tapes, for example the need to manual reload the NC tapes for each newpart and the lack of program editing abilities, which increases the lead time.

CNC refers to a system that has a local computer to store all required numerical data.Use of CNC allowed the use of other storage media, magnetic tapes and hard disks. Theadvantages of CNC systems are not limited to the possibility to store and execute anumber of large programs (especially if a three or more dimensional machining ofcomplex shapes is considered), to allow editing of programs, to execute cycles ofmachining commands, Etc.

The development of CNC over many years, along with the development of local areanetworking, has evolved in the modern concept of DNC. Distributed numerical controlis similar to CNC, except a remote computer is used to control a number of machines.An off-site mainframe host computer holds programs for all parts to be produced in theDNC facility. Programs are downloaded from the mainframe computer, and then thelocal controller feeds instructions to the hardwired NC machine. The recent

developments use a central computer which communicates with local CNC computers(also called Direct Numerical Control)


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NC CO ORDINATE SYSTEM

A standard axis system must be defined by which the positioning of the work headrelative to the Work part can be specified.1. Flat and Prismatic work part: drilling and punching of flat sheet metals to

distinguish +ve from - ve Right Hand Rule is used.

2. Rotational parts: Associated with NC lathes and turning centers. The path of thecutting tool relative to the rotating work piece is defined in the X-Z plane where theX axis is the radial location and Z axis is parallel to the axis of the part.

The part programmer must decide where the origin of the coordinate axis systemshould be Located based on programming convenience. Ex: Corner of the part or center(Symmetrical w/p). It is called as Targetpoint.

FIXED ZERO VERSUS FLOATING POINT ZERONC machines have either of two methods for specifying the zero point. The firstpossiblity is for the machines to have fixed zero. In this case the origin is always locatedat the same position is for the machine table. Usually that position is the southwestcorner of the table and all the tool locations will be defined by positive x and ycoordinates.

The second and more common feature on modern NC machines allows the machineoperator to set the zero point at any position on the machine table. This feature is calledfloating point zero. The part programmer is the one who decides where the zero pointshould be located. The decision is based on part programming convenience. Forexample the workpart may be symmetrical and the zero point should be established atthe center of symmetry. The operator must move the cutting tool under manualcontrol to the target point .


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Motion control

1. Point-to-point systems:

Some machine tools for example drilling, boring

and tapping machines etc, require the cutter and

the work piece to be placed at a certain fixed

relative positions, without regard for the speed &path taken to get to that location at which they

must remain while the cutter does its work. These

machines are known as point-to-point machines

2. Continuous path systems

In this system, relative positions of the work piece

and the tool is continuously controlled. It involves

motion of work piece with respect to the cutter

while cutting operation is taking place as in milling,

turning, routing machines etc.

Contouring machines can also be used as point-to-

point machines, but it will be uneconomical.

When tool is moved parallel to only one of the

major axes: Straight cut NC

When simultaneous control of two or more axes is

done in machining operation: Contouring


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Absolute and Incremental Positioning:

An absolute NC system is one in which all position coordinates are referred to one fixed origin

called the zero point. The zero point may be defined at any suitable point within the limits of the

machine tool table and can be redefined from time to time. Any particular definition of the zero

point remains valid till another definition is made.

In an incremental system the movements in each Part program block are expressed as thedisplacements along each coordinate axes with reference to the final position achieved at the

end of executing the previous program block.

INTERPOLATIONS:

Interpolation consists in the calculation of the coordinated movement of several axes using the

programmed parameters, in order to obtain a resulting trajectory, which can be of various types,

such as: - Straight line, Circular, Helicoidal

The interpolation module computes instant by instant position commands for the servo module,

which in turn, drives the motors. There are two types of interpolators, namely:

- Process interpolator (for continuous axes)

- Point-to-point interpolator (for point-to-point axes)

The various interpolations are:

1. Linear Interpolation

2. Circular Interpolation

3. Helical Interpolation

4. Parabolic and Cubic interpolation.


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NC Part ProgrammingIt consists of planning and documenting the sequence of processing steps to beperformed on an NC machine.Part program: A computer program to specify

- Which tool should be loaded on the machine spindle;- What are the cutting conditions (speed, feed, coolant ON/OFF etc)- The start point and end point of a motion segment- how to move the tool with respect to the machine.- application of cutting fluids.

A Binary digit is a bit. Represented by presence or absence of holeCombination of bits Character (0 to 9, A to Z) Combination of charactersWord Combination of words Block.

A Block is one complete NC instruction.

Manual part programmingComputer assisted part programmingPart programming with APTPart programming using CAD/CAM


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NC Words (Codes)N Code - Sequence Number : identifying program blocksG Code - Control Functions/ Preparatory functions: set up the mode in which the restof the operation is to be executed

D Code- Dimension words, specify the coordinate positions of the programmed path.X and Z specify the absolute coordinates, and U and W specify the incremental coordinatesF Code - Feed RateS Code - Spindle SpeedT Code - Tool SelectionM Code - Miscellaneous functions

G Codes

G00 Positioning (not cutting)

G01 Linear interpolation

G02 Clockwise circular interpolation

G03 Counterclockwise circular interpolation

G20 Inch data inputG21 Metric data input

G54 Workpart coordinate preset

G80 Canned cycle cancel

G81-89 Canned cycles

G90 Absolute programming

G91 Incremental programming

M Codes

M00 Program stop

M02 Program end

M03 Start spindle CW

M04 Start spindle CCW

M05 Stop spindleM06 Execute tool change

M07 Turn coolant on

M25 Open chuck

M26 Close chuck

M30 Stop Machine


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Sequence and format of words:

N3 G2 X+1.4 Y+1.4 Z+1.4 I1.4 J1.4 K1.4 F3.2 S4 T4 M2

sequence no

preparatory function

destination coordinates dist to center of circle

feed rate spindle speed

tool

miscellaneous functionO0013

N0010 T0404N0020 G57 G00 X26.00 Z0.0 S500 M04N0030 G01 X-0.20 F100N0040 G00 Z2.0N0050 X50.0 Z50.0N0060 T0404N0070 G57 G00 X25.00 Z2.0 S500 M04N0080 G01 X22.5 Z-70.0 F100N0090 G00 X26.0 Z2.0 S500N0100 G84 X17.5 Z-20.0 D0=200 D2=200 D3=650N0110 G00 Z2.0

N0120 X50.0 Z50.0 T00N0130 M30


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O0013

Program identification numberN0010 T0404

N0010 Sequence number

T0404 Select tool number 404N0020 G57 G00 X26.0 Z0.0 S500 M04

G57 PS0

G00 Rapid movement (no cutting)

X26.0 Xlocation (as a diameter; 13 form

zero)Z0.0 Zlocation

S500 Spindle speed is 500 rpm

M04 Rotate spindle counterclockwiseN0030 G01 X-0.20 F100

G01 Linear interpolation (cutting)

X-0.20 Move only in x direction until youpass the center by 0.1 mm (facing)

F100 Set feed rate to 100 mm/min.

N0040 G00 Z2.0

G00 Move rapidly away from work piece (no

cutting) Z2.0 the movement is 2 mm awayfrom the face.


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N0070 G57 G00 X25.00 Z2.0 S500 M04

G57 PS0

G00 Rapid movement (no cutting)

X25.0 Xlocation (as a diameter; 12.5 form

zero) Z2.0 Zlocation

S500 Spindle speed is 500 rpm

M04 Rotate spindle counterclockwise

N0080 G01 X22.5 Z-70.0 F100

G01 Linear interpolation (cutting)

Z-70 Move only in z direction (external

turning)F100 Set feed rate to 100 mm/min.N0090 G00 X26.0 Z2.0 S500

G00 Move rapidly away from workpiece (no

cutting) to location x= 26.0 (13.0 from zero)

and z = 2.0.

N0100 G84 X17.5 Z-20.0 D0=200 D2=200 D3=650

G84 Turning cycle for machining the step

X17.5 final diameter Z-20 length of step is 20

mm D0=200 Finish allowance in X direction

(0.2 mm)D2=200 Finish allowance in Z

direction (0.2 mm)D3=650 De th of cut in each ass 0.65 mm


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N0110 G00 Z2.0

G00 Move rapidly away from workpiece (no

cutting) Z2.0 the movement is 2 mm away

from the face.

N0120 X50.0 Z50.0 T00

X50.0 Z50.0 Move to the tool changing

location

T00 cancel tool selection

N0130 M30

M30 Program End

Cnc Automation

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