INTRODUCTION

After the Second World War, there was a big spurt in the design and development of aerospace products like satellites, launch vehicles, civil and military aircraft etc. The hydraulic copying and electrical program controlled machines used at that time could not meet the manufacturing challenges posed by the complex aerospace designs. The manufacturing engineers were therefore looking for a better way of automating the machining operations. Numerical control (NC) was developed in early 50’s to meet the critical requirements of aerospace Industry. Many components used in aircraft and space vehicles are machined from solid raw materials, often involving removal of considerable stock and requiring several hundred positioning movements of the machine tool slides. Manual operation under these circumstances is not only tedious but also less efficient and unproductive. Often the part after several hours of machining is liable to be rejected due to machining errors. Digital technology developed for communication purposes became very handy for designers of control of machine tools. Since the information required to actuate and control slides was coded numerically, this technology came to be known as numerical control.

TYPES OF CNC MACHINES

Computer numerical control is applied to a variety of machines. Most of these find ready application in aircraft, automobile and general engineering industry. Some of them are listed below:

Machining Centre• Horizontal• Vertical• Universal

CNC Lathes CNC Turning Centres Turn-mill Centres CNC Milling/Drilling Machines, Plane Milling Machines Gear Hobbing Machines Gear Shaping Machines Wire Cut EDM/EDM Tube Bending Electron Beam Weldingxii. Co-ordinate Measuring Machines Grinding Machines

• Surface Grinder• Cylindrical Grinder• Centreless Grinder

Tool and Cutter Grinder CNC Boring and Jig Boring Machines PCB Drilling Machines Press Brakes

CNC Guillotines CNC Transfer Lines, SPM’s Electrochemical Milling Machines Abrasive Water Jet Cutting Machines Flow Forming Machines Roll Forming Machines Turret Punch Press

FEATURES OF CNC SYSTEMS

CONTROL SYSTEM FEATURESThese features provide information about the characteristics of the CNC system and its capabilities. Important features are given below:

1. Technology of SystemCurrently two types of architectures are being used in CNC systems

(i) Single microprocessor based systems(ii) Multi microprocessor based systems (Multiprocessor systems)

Single microprocessor architecture: In this type of system a 16, 32 or 64 bit microprocessor is used. Multiprocessor architecture: This type of the architecture is widely used in many CNC systems today. The control functions are carried out by a set of microprocessors, each doing an assigned task. This concept helps to implement various functions faster. Both hardware and software structures are modular thereby enhancing the flexibility of the system.

2. Executive ProgramThe executive program contains the intelligence needed to carry out different tasks in CNC system. The executive program is resident usually in EPROM/Bubble memory.

3. Other System FeaturesOther features of CNC system are:

(i) C R T display and alphanumeric keyboard(ii) Manual data input (M D I) and operator programming(iii) System resolution.(iv) Feed and rapid traverse rates(v) Spindle Speeds - directly programmable or through S codes(vi) Modes of operation like M D I, Single step, Auto etc.(vii) Operating controls like Jog, feedrate and spindle speed override, axis

select switch, edit, reference, dry run, test mode.

Advantages of CNC Machine tools

o Ease of part duplication

o Flexibility

o Repeatability

o Quality control through process control

o Accommodates simple to complex parts geometry

o Improved part aesthetics

o Increased productivity

o Technology costs are decreasing

o CNC machine tools are more rigid than conventional machine tools

Climb milling requires about 10 - 15 % less horsepower vs. conventional cutting, but requires a ridged machine tool with no backlash

Increased Rpm’s and feeds

GENERAL PROGRAMMING FEATURES OF CNC SYSTEMS

CNC systems can be classified into:(i) CNC Systems for machining centres(ii) CNC Systems for lathes and turning Centres(iii) CNC Systems for special applications like Grinding Machines, EDM, Electron beam welding etc.

There are many features in these CNC systems which are of general interest and some of them are discussed below:

Absolute and Incremental Programming: a plate in which 3 holes are to be drilled. The locations of the holes are indicated in the drawing of the component. For the purpose of programming, these dimensions should be specified with respect to the work piece coordinate system. The X and Y axes are to be defined first. the X and Y axes at a distance of 20 mm from the edge of the plate. The coordinates of the three hole locations should be calculated with respect to these axes.In the case of absolute coordinate system all the coordinates should be specified with respect to the workpiece datum. In the case of incremental system, the zero datum is a floating one. Every coordinate is specified with respect to the previous position.For machining the three holes the slide should be positioned under the drill spindle successively in positions 1, 2 and 3. The reference axes are marked in the figure. Thus the absolute co-ordinates to be used in the program will be:Position X Y1 40 502 40 1003 120 60

There are three ways in which the co-ordinate data are input to the machine control. They are:i. Absolute modeii. Incremental mode iii. Mixed mode

In absolute mode, all co-ordinate values are measured from a fixed datum. W is the work piece datum (X = 0, Z = 0). Points 1, 2, 3 and 4 have coordinates.

Point X Z1 0 02 20 03 20 – 404 30 – 40

In incremental mode, the co-ordinate data input for every movement is the relative distance from the previous point. For example, when the tool moves from point 3 to point 4, the X distance is +5 and Z distance is zero. Thus, the co-ordinates depend on the axis movements.The co-ordinate distances in incremental mode given below:

Point X ZT to 1 – 35 – 251 to 2 + 10 02 to 3 0 – 40

3 to 4 + 5 0

In mixed mode, the co-ordinates can be either in absolute co-ordinates or incremental co-ordinates. Absolute co-ordinates are labeled X and Z and incremental co-ordinates U and W. For the example given, the co-ordinates can also be input as:

Point Z Z1 X0 Z02 U10 Z03 X20 W – 404 U+5 W0

In lathes it is convenient to program in mixed mode whereas in the case of machining centres program segments can be either in incremental or absolute mode or the whole program can be in either one of the modes.

ii. Preparatory codes and miscellaneous codes:

A typical line of a CNC program (called block) is given below:N 0040 G01 X100.05 Y180.95 S450 M08;

Every block starts with a block number (3 or 4 digits), (N word); A block may have one or more G functions. G- functions like G01 if defined earlier and if the value is the same need not be repeated. For example, in a block if G01 is defined and if the next block also involves G01, this will be implied and need not be explicitly stated. Such G functions are called modal G functions. The block may contain the X, Y and Z co-ordinates of the target point. The feed at which the slide movement is to be executed is specified in the feed value. (e.g. F equal to 400 mm/min). If the feed is same as specified in the previous block it need not be repeated again. The spindle speed is specified by the S address. (E.g. Speed is 450 rpm). The M word represents a miscellaneous function. In this case M08 switches on the coolant motor. Thus each word has a unique alphabetic address. Hence this type of formatting the program is referred to as word address format. Other commonly used word addresses are T for tool, V for cutting speed, A for angle, etc. G-codes or G functions are mainly NC functions. These are also called preparatory functions. Some of these have been assigned standard functions and others are left to be defined by the CNC system manufacturers. Common preparatory functions in a CNC system for lathes (FANUC 0) include:(i) Interpolation functions

Positioning (G00) Linear interpolation (G01) Circular interpolation (G02, G03) Polar co-ordinate interpolation (G112, G113)

Cylindrical interpolation (G107) (ii) Thread cutting (G32, G34)(iii) Feed functions

Feed per minute (G98) Feed per revolution (G99) Dwell (G04)

(iv) Reference point Automatic reference point return (G28) 2nd, 3rd and 4th reference point (G30)

(v) Co-ordinate system setting (G50)(vi) Inch-metric conversion (G20, G21)(vii) Constant surface speed control (G96, G97)(viii) Canned cycles

Outer diameter cutting cycle (G90) Thread cutting cycle (G92) End face turning cycle (G94)

(ix) Multiple repetitive cycle Stock removal in longitudinal turning (G71) Contour parallel turning (G73) Finishing cycle (G70) Thread cutting (G76)

(x) Canned cycles Front drilling (G83) Side drilling (G87) Front tapping (G84) Front boring (G85)

(xi) Compensation function Tool Nose radius compensation (G40 - G42) Changing tool offset amount (G10)

(xii) Measurement functions Automatic tool offset (G36, G37)

M- Functions are mainly switching functions. These include spindle on/off, spindle rotation (clockwise or anticlockwise) coolant on/off, tool change, pallet change, turret indexing etc. Earlier, these functions were incorporated in the NC control itself. Nowadays, a separate programmable logic controller (PLC) interface is provided so that the machine tool designer can design his PLC program to incorporate unique control features. This allows considerable flexibility for the designer. Control of auxiliary devices like conveyors, robots, pallet loaders, bar feed systems, quick change of chuck jaw, automatic door open/close, machining completion buzzer, automatic chuck operation, chuck air blast etc. Can be easily integrated in the machine tools either by the manufacturer or by the user.iii. Interpolation

The calculation of successive increments in slide position to reach the programmable point is called interpolation. Common methods of interpolation are linear, circular and helical.

iv. Axes of movementA CNC machine tool may have several controlled axes. If simultaneous movements in 2-axes only are available, the control is called 2-axis control. The CNC lathe will have two axes i.e. X and Z. A turning centre will have three axes i.e. X, Z and C. A machining center will usually have three axes(X,Y and Z).

v. Tool offset/Tool compensation:The CNC program is written assuming that the tool traces the path (tool path) required to produce the part. The length of traverse of the slide should take into account the length of the tool. The longer the length of the tool is, the shorter will be the travel of the slide and vice versa. The CNC system therefore should calculate the displacement of the slides considering the tool length. The length of tool is measured beforehand and input into the appropriate registers of the system. This is called tool length offset. These are manually input into the memory locations corresponding to each tool position. Whenever a tool is changed, it is necessary to measure the new tool length an dinput it into the memory of the CNC machine. Tool length offset is usually measured using a tool pre-setter which can be mechanical, optical or electronic. Probes are also fitted on the machine to determine and input the tool offset automatically.In the case of machining centres the path of the slide has to be altered to take also the radius of the tool into account. This is called cutter radius compensation.Typical tool offset functions in a machining centre are:G 45 - extension of axis travel by the amount stored in the offset data memoryG 46 - Reduction by the amount stored in the offset data memoryG 47 - Double extensionG 48 - Double reductionExample: G00 G45 Z-150.0 H04;H04 is the offset stored in number “04” of offset data memory.Very often it is necessary to alter slide position in very small increments due to such factors like tool tip wear or wear of end mills etc. This is done through tool offset input.In flexible manufacturing systems and other unmanned manufacturing situations, tool offset is automatically measured using suitable devices.

vi. Tool nose radius compensation

In profile turning, or pocketing, accuracy of the work piece is affected by the tool nose radius of the tool. By incorporating a tool nose radius compensation call through an appropriate G - function, it is possible to compensate the effect of tool nose radius.G41 Tool nose radius compensation, leftG42 Tool nose radius compensation, rightG40 Tool nose radius compensation cancels

vii. Datum pointsProgramming is done with reference to the fixed points (origin of co-ordinate system of the machine) or the datum points defined by the programmer. In the latter case, the datum points can be conveniently selected to reduce computations involved in converting machining locations into X, Y, Z co-ordinates. Up to six works co-ordinate systems can be selected in many machines. These are usually stored in the appropriate registers in the memory of the control system and recalled through the NC program. In many systems G54, G55, G56, G57, G58 and G59 are reserved for specifying coordinate systems.

PROGRAMMING CODES

Programs are written using the standard word addresses given below:N Sequence number (1 to 9999)G Preparatory function: Up to 4 G functions in a block are permitted.Some systems use G codes in three digits too.XY Dimension mode in each axis, up to 3 decimal placeZIJ Arc centre offset in X, Y, Z axis + or – Axis directionKP, Q Word address codes, meaning depending on G functionB Rotation axis about Y axisF Feed rate mm/min; eg.F300.0S Spindle speed; e.g. S630T Tool function (TXX to TYY), say depending on number of tools in the magazineM Miscellaneous functionH Offset numberE Dwell functionD Cutter radius offsetL No. of repetitions of fixed cycle and sub program

G-CODES IN A CNC SYSTEM

G00 Positioning (Rapid feed)G01 Linear InterpolationG02 Circular Interpolation/helical CW

G03 Circular Interpolation/helical CCWG02.1 Circular threading CWG03.1 Circular threading, CCWG02.2 Involute interpolation, CWG03.2 Involute interpolation, CCWG02.3 Exponential function interpolation, CWG03.3 Exponential function interpolation, CCWG04 DwellG05.1 Multi-bufferG06.1 Spline interpolationG07.1 Cylindrical interpolationG09 Exact stop checkG10 Setting offset amount and work zero offset amountG10.1 PMC data settingG49 Tool length compensation cancelG45 Tool offset extensionG46 Tool offset reductionG47 Tool offset, double extensionG48 Tool offset, double reductionG50 Scaling cancelG51 ScalingG54 Selection of work co-ordinate system 1G54.1 Additional work co-ordinate systemG55 Additional work co-ordinate system 2G56 Additional work co-ordinate system 3G57 Additional work co-ordinate system 4G58 Additional work co-ordinate system 5G59 Additional work co-ordinate system 6G60 Single direction positioningG61 Exact stop check modeG62 Automatic corner override modeG63 Tapping modeG64 Continuous cutting modeG65 Call of user macroG65.3 Call of high speed machining programG66 Modal call of user macroG66.1 Macro modal call BG67 Modal call of user macro, cancelG68 Co-ordinate system rotationG69 Co-ordinate system rotation cancelG71 Metric ModeG72.1 Rotation copyG72.2 Parallel copyG73 Peck drilling cycle

G74 Reverse tapping cycleG76 Fine boring cycleG80 Fixed cycle, cancelG81 Drilling cycle, spot drillingG82 Drilling cycle, counterG83 Peck drilling cycleG84 Tapping cycleG84.2 Rigid tapping cycleG85 Boring cycleG86 Boring cycleG87 Back boring cycleG88 Boring cycleG89 Boring cycleG90 Absolute commandG91 Incremental commandG92 Setting co-ordinatesG92.1 Work co-ordinate system presetG93 Inverse time feedG94 Feed rate, mm/min modeG95 Feed rate, mm/rev. modeG98 Initial level return in fixed cycle modeG99 R level return in fixed cycle mode

M-CODES IN A CNC SYSTEM

M00 Program stopM01 Optional stopM02 End of programM03 Spindle CWM04 Spindle CCWM05 Spindle stopM06 Tool changeM07 Tap Oil onM08 Coolant onM09 Coolant/Tap Oil offM10 B-axis clampM11 B-axis unclampM12 Hydraulic power rotary table onM14 Oil hole drill coolant onM16 Heavy tool changeM17 Tap cycle confirmationM18 Tap cycle cancelM19 Spindle orientation

M20 Coolant nozzle upM21 Coolant nozzle middleM22 Coolant nozzle downM23 Detection of contact in -XM24 Detection of contact in +XM25 Detection of contact in -YM26 Detection of contact in +YM27 Tool breakage detectionM28 Automatic gap eliminationM29 M27 & M28 togetherM30 End of program and rewindM50 Air blow onM52 Tool length offset measurementM53 Tool length Offset executionM54 Tool length Offset cancelM57 Measurement along Z axisM58 Execution along Z axisM59 Cancel along Z axisM60 Measurement along +X axisM61 Measurement along -X axisM62 Execution along X axisM63 Cancel along X axisM64 Measurement along +Y axisM65 Measurement along -Y axisM66 Executing along Y axisM67 Cancel along Y axisM70 Return to zero rotary table positionM73 Y Axis mirror image offM74 Y Axis mirror image onM75 X Axis mirror image offM76 X Axis mirror image onM80 Rotary table CW rotationM81 Rotary table CCW rotationM82 Step mode tool removalM83 Step mode tool change cycleM84 Step mode tool jog operationM88 Splash guard openM89 Splash guard closeM90 Pallet changeM92 Pallet unclampM96 Pallet loading and advanceM97 Pallet loading retractM98 Call of sub programM99 End of sub program

HINTS FOR PROGRAMMING

Cutting conditionsCutting conditions should be carefully selected during program preparation since these conditions greatly influence cutting efficiency, production rate, cost and accuracy. In the case of a machining centre the following four cutting conditions are required.(i) Spindle speed (rpm): This is directly designated immediately after the letterS. For example, if a spindle speeds of 500 rpm it is designated as S500. Spindle speeds are obtained from recommended cutting speeds.(ii) Feed rate for cutting (mm/min): Feed rate is specified after the letter F. e.g.For a feed rate of 250 mm/min the program specifies F250. Feed rate is the product of feed/tooth, number of teeth of cutter and rpm of cutter. In the case of tapping the feed rate is rpm x pitch of the thread.(iii) Depth of cut: The depth of cut is determined by the position of the tool in the Z-direction.(iv) Width of cut: The width of cut is determined by the positions of the table along X and Y-axes.The cutting condition is selected either from the handbooks or from the cutting data supplied by the manufacturers of cutting tools. The rpm of the spindle is calculated from the recommended cutting speed. The cutting speed for machining carbon steel with a solid carbide cutter at a depth of cut of 4 mm, feed of 0.25 mm/tooth and tool life of 30 minutes is 183 m/min (V). If the diameter of the end mill is 18 mm (d), the spindle rpm (N) will be:N = 1000 V/ (πd)= 3237 say 3240 rpm.Tables 12.13 and 12.14 give the recommended cutting data for carbon steel and cast iron.Table 12.13 Typical Cutting Data for Carbon Steels

Feed, mm/tooth0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

Tool life, minutes45 40 35 32 30 25 20 -

a*,mm Cutting speed, m/mm2448

10

220205190177165

214200185172160

208194179167155

202188174182150

196183169158145

190178165153

-

185173160

--

-----

* Depth of CutFor cutter diameters between 12 and 25 the maximum depth of cut is 8 mm.

Table 12.14 Typical Cutting Data for Cast Iron

Feed, mm/tooth0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

Tool life, minutes

55 45 40 35 35 30 25 20a*,mm Cutting speed, m/mm

2448

10

270205230213202

246228210195185

235218201186177

225208192178169

215199183170162

205190175162155

195181167

--

187173160

--

* Depth of CutFor cutter diameters between 12 and 25 the maximum depth of cut is 8 mm.(b) Calculating spindle speed & feedrateSpindle speeds (N) and feedrate (S) may be calculated based on the cutting speed(V, m/min) and feed (F, mm/rev) according to the equation given below:N (rpm) = 1000 V/ (πd)And S = F × N; Where, d = Diameter of the cutter, mmExample:Material: Cast ironType of cut: MillingMaterial of tool: CarbideCutter diameter: 63 mmFeed: 0.2 mm/bladeNo. of teeth: 6Depth of cut: 4 mmCutting speed(From Table 12.14): 208 m/minN = 1000 × 208/ (π× 63) = (say) 1050 rpm

Calculating length of axis moveSince direction of axis movement greatly affects machining time, such dimensions should be determined after studying the characteristics of the cutter to be used. It is necessary to change the axis movement dimensions according to the conditions of tool setting dimensions, fixture details and finished condition of the work piece in the preceding machining steps.

The types of tap holders widely used are:i. Combination typeii. Expansion typeiii. Compression typeIf expansion or combination type is used, programmed feed rate could be about 15% (differs from model to model) smaller or larger than actual tap feed rate. Generally, combination type is used on machining centres. This type of holder allows the feed rate to be programmed to be equal to actual tap feed rate. Even in this case, however, the programmed feed rate may vary within about 3 to 4% smaller than actual feed rate. Air cut stroke in tapping should be at least equal to two times air cut distance in drilling. As indicated above, programmed feed rate and actual feed rate of a tap does not completely match. Therefore, if air cut stroke is small, the tap might be still engaged even after completion of tool retraction command. Machine axes

will start positioning after retraction command is executed disregarding whether the tap is still engaged or not, causing the tap and tap holder to be damaged.

PROGRAMMING A VERTICAL MACHINING CENTREFigure shows the line diagram of a vertical machining centre. The table moves in X and Y directions and the up and down movement of the spindle gives the Z axis motion.According to the right hand thumb rule notation the table movements to the left (X) and away from the column (Y) are positive. However, in programming practice, the tool is considered to move relative to the work piece and hence the directions are redefined as:Tool movement to the right + XTool movement towards the column + YThe following example illustrates the approach to programming a simple component in a vertical machining centre. The component is shown in Fig 12.45. The blank is of size300 × 200 × 50 pre-machined. There are six M10 × 1.5 tapped holes and a centre hole of 20 H7.A systematic approach to programming involves the following steps:

SETTING THE WORK PIECE ORIGINThe program coordinates are conveniently selected with reference to a work piece datum or work piece origin. The work coordinate system can be selected to suit the datum used for dimensioning the work piece. In the present example the centre of the top surface is a suitable point to be selected as origin and the X- and Y- axes directions are shown in The X and y axes are shown in the plan view and the Z- axis is shown in the elevation in the figure. The Z -axis is normal to the work surface and the positive direction means the movement of the tool away from the work surface.

It may be noted that the axis directions indicated in Fig. represent tool movements relative to the work piece. The X- and Y- axes movements are therefore opposite to those indicated in Fig.

PROCESS DESIGNThe next logical step in the programming process is the process design. In this example there are two main machining operations to be performed viz. tapping six holes and producing a tolerance hole. The threaded holes can be realized in four operations or processes.i. Centre drillingii. Core drilling (In the case of M10 × 1.5 in C.I the core diameter is 8.5 mmThis data can be obtained from standard data books.iii. Chamfering the holesiv. Machine tapping M10 × 1.5

The hole 20 H7 being a precision hole requires the following processes:i. Centre drillingii. Drill a pilot hole of 18iii. Drill a hole of 19.5 so that only a small allowance is left for the final boring or reaming operation. Leaving only a small allowance for the final finishing operation improves the accuracy of the hole.iv. Boring 20H7. Boring is preferred to reaming as boring facilities better control of dimensions in batch manufacture.In programming the machining centres a common-sense approach is to finish all operations using a tool in one go. This is because positioning of the table will take less time than tool changing. Therefore centre drilling at all the seven locations can be done as one process. Thus there are a total of 7 processes. They are listed below in Table 12.15.

Table 12.15 Processesprocess Tool Operation

1234

Centre drillφ8.5 Drillφ18 Drill

φ19.5 Drill

Centre drillingDrilling core holes for M10 tap

Pilot hole for φ20 holeSemi-finishing φ20 hole

567

φ25 Chamfering toolM10 × 1.5 Tapφ20H7 Boring

Countersinking the holeTapping

φ20H7 hole boring

SELECTION OF CUTTING CONDITIONSOnce the processes are selected the next step is to choose the cutting conditions. Then factors influencing the cutting parameters are:Work material and its hardness tool material roughing or finishing feed, depth of cut.Tables of cutting speeds and feeds are available from which one can make the appropriate selection of the cutting conditions. Spindle speeds and feed rates are coupled from these data and are then tabulated as shown in Table 12.16.

Table 12.16 Process Sheet

Process Tool pocket no.

Tool Details & Cutting Speed (m/min)

Spindle speed rpm

Feed rate mm/min.

Tool offset

N1N2N3N4N5N6N7

1234567

4mm centre Drill, 25m/min8.5 Drill, 25 m/min18 Drill, 25m/min

19.5 drill, 25/m min25 Chamfering tool, 20 m/min

M10 × 1.5 Tap, 10 m/min20H7 Boring (Carbide Tipped 75

m/min)

20009364424082543181194

100187888251477119

1234567

Note: It is not necessary to name processes as N1, N2 etc. in the serial order. Similarly tool

pocket numbers and offset numbers can be selected at the convenience of the programmer.

In machining centres feed rate is specified instead of feedo Feed rate = Feed × rpm

o Feed rate = Feed per tooth of the cutter x number of teeth x rpm

In threading feed is equal to pitch. Therefore feed rate for tapping is obtained by multiplying the pitch of the thread by the rpm of the tap.

Tool length offset values corresponding to each tool are input in the memory of the CNC system in the appropriate registers.

PROGRAMME PREPARATIONAn inspection of the component shows that the table positioning movements are for many operations are repetitive in nature and hence these movements can be coded in a sub-programme.

Sub-programme

The sub-programme is written assuming that the spindle is positioned above the reference point (work piece datum) 1. The tool is then successively positioned at locations 2, 3, 4, 5, 6 and 7.

027; (Programme Number 27. This number is used to call the sub-programme in the main programme.)

X0.0 Y50.0; (Position 2)X100.0; (Position 2)Y-50.0;X0.0;X-100.0;Y50.0;M 99; (Return to the main programme)

Main Programme

018; (Programme number 18)(Part-name)G0 G40 G80; (Rapid traverse)

(Cutter compensation cancel)(Canned cycle cancel)

G91 G28 X0 Y0 Z0; (Incremental positioning)(XYZ zero return)

/T1; (Call tool in Pocket #1 Centre Drill)/M06 (Call tool change)

(Tool #1 is now inserted in the spindle)Note: Block delete switch (/) is used here as these blocks are used only during set up. These blocks with “/” sign are again provided at the end of the programme. Hence during repeated machining the block delete switch is kept in the on position and these lines preceding / symbol are ignored.M1; (An optional stop code is introduced so that the program will

Temporarily cease execution to facilitate inspection. The program will continue if the “Start” button is pressed. Once the program is proven, the optional stop switch is shifted to “off” mode so that M1 code is ignored.)

(Centre Drilling)N1 T2; (Calling next tool i.e. 8.5 Drill)G0 G90 G54 G43 X0 Y0 Z50.0 H1 S2000 M3;

(Select work co-ordinate system (G54)Rapid positioning above location 1Tool length offset 1 activeSpindle speed 2000 rpmSpindle rotation clockwise (M03))

G98 G81 Z-8.0 R47.0 F100.0 (Canned cycle (Drilling) G81Return to Initial position (G98)Drilling depth = –5 mmRapid up to Z = 3 mmFeed rate 100 mm / min)

M98 P27; (Calling sub programme #27- Centre drilling in 7 locations)

G80 G91 G28 Z0; (Fixed cycle cancelZ axis zero return)

M6; (8.5 mm drill is now inserted in the spindle The centre drill is returned to the tool magazine)M1; Optional stop

(8.5 Drill)N2 T2 (Process #2, calling Tool #3)G0 G90 G43 X0 Y0 Z50.0 H2 S936 M3;G99 G81 Z-38.0 R47.0 F187 L0; (Rapid traverse to stop at Z=3 mm

Depth = 35 mmReturn to initial rapid level (G99)No machining to be done at this position (L0))

M98 P27;G80 G91 G28 Z0; Returned to Z home position for

Tool changeM 6;M1;(18 DIA DRILL)N3 T4;G0 G90 G43 X0 Y0 Z50.0 H3 S442 M3;G81 Z41.0 R47.0 F88;M 98 P27;

M6;M1;(19.5 DRILL)N4 T5;G0 G90 G43 X0 Y0 Z50.0 H4 S408 M3;G81 Z -38.0 R47.0 F82;G80 G91 G28 Z0;M6;M1;(CHAMFERING)N5 T6;G0 G90 G43 X0 Y0 Z50.0 H3 S442 M3;G81 Z-41.0 R47.0 F88;G80G91G28Z0;S500 H5 M3;G99G81 Z - 6.0 R47.0 F51 L0;M98 P27G80 G91 G28 Z0;M6;M1;(M10 × 1.5 TAP)G0 G90 G43 X0 Y0 Z50.0 H6 S318 M3 ;G84 Z-38.0 R40.0 F477 L0;(Note: Tapping cycle G84 involves rapid traverse, feed, reverse feed and return)M98 P27;G80 G91 G28 Z0;M6;M1;(f20 H7 BORING)N7 T1;G0 G90 G43 X0 Y0 Z50.0 H7 S1194 M3;(Note: Boring, being a critical operation is performed in two stages during initial trials. A distance of 5 mm is first machined and the operator can check whether the hole is within tolerance limits. That is why the four succeeding lines of programme starts with block delete symbol.Once the setting of the boring bar is proven to be satisfactory the block delete switch can be thrown into the “ON’ position thereby ignoring these lines during regular production run)/G81 Z-5.0 R3.0 F119;/G80 G91 G28 Z0 M5;/M1;/G0 G90 G43 X0 Y0 Z50.0 H7 M3;/G81 Z-8.0 R47.0 F119;/G80 G91 G28 Z0 M5;/M1;

/G0 G90 G43 X0 Y0 Z50.0 H7 M3;G76 Z-35.0 R47.0 P0.5 Q0.5 F119; (P, Dwell 0.5 Sec,

Q, Offset 0.5 mm)Note: G76 is precision boring operation. At the end of the boring operation the tool is withdrawn along the radial direction at the orientated stop position of the spindle. There is a dwell of 0.5 sec and the boring bar is withdrawn.G80 G91 G28 Z0;M6;M30;Note: The readers are advised to compare the G and M codes used in this program with theG and M codes of the machines available with them as there may be differences in the G-Codes and m codes from system to system.

ACE LT-25 CNC LATHE MACHINE

The LT-25 is a precision CNC turning machine well suited to machine large size components. The machine elements like ball screws, bearings, CNC systems& drives have been chosen from the best available in the world. The machine is put together by a dedicated team of skilled craftsmen under expert technical guidance.

AXESX and Z axis feature precision large diameter ball screw supported at each end by precision class ball screw support bearings. The axis assemblies are provided with safety overload clutches to protect the machine element in the event of an accident. The guide’s ways are widely spaced to ensure stability fully protected and are made of hardened are ground box way strips. The mating way is bounded with turcite for its superior wear and friction characteristics and hand scraped to perfection. Automatic matered lubrication is provided to all guide ways & ball screws.

TURRET

Robust bi-directional tool turrent offers fast and accurate indexing. Indexing time for adjacent station is 0.75 sec. Tool mounting also provides coolant to the tool point.

TAIL STOCKThe tailstock consists of a hydraulically operated quill, which moves inside the housing. The quill and the body are independently moveable .widely spaced guideways and the heavy duty design of the tailstock rigidity. Foot pedal or program activates the quill. Programmable tailstock is a standard feature.

SPINDLEThe cartridge type spindle is assembled and tasted and the controlled clean room environment. The bearing configuration gives very high stiffness to the spindle assembly in both axial and radial directions. The bearings are greases lubricated for life. A high torque spindle motor provides power for heavy stock removal.

ELECTRICAL SYSTEMThe machine uses highly reliable and internationally accepted electrical elements and sub systems. Fanuc CNC system, Fanuc high torque AC digital spindle motor with controller and Fanuc high powered axes motor with controller and offered as standard.

MACHINE FEATURES Cartridge type spindle AC spindle and axes drives High speed bi-directional tool turret Hardened and ground guide ways strips Turctile anti-slipstick liners on slide way surfaces Programmable tailstock Automatic centralised lubrication Built-in lighting system OD turning tool blocks (8 Nos) Boring bar holders (4 Nos) Facing tool holders (2 Nos) Coolant system & set of sleeves

SPECIFICATION

CAPACITYSwing over bed Swing over carriage Distance between centresMaximum turning diameterMaximum turning length

mmmmmmmmmm

54531010704201050

MAIN SPINDLE

Spindle noseBore thro spindleBar capacity*Chuck sizeFront bearing bore

mmmmmmmm

A2-880

63.5250120

TURRETNo. Of stationMaximum boring bar dia.Tool cross section

mmmm

850

25x25SPINDLE DRIVEAC motor rated power(continuous rating/ 30 min. rating)Speed range (inf. variable)Full power range

KW

RPMRPM

18.5/22

50-3000440-2630

SLIDESz-axis strokex-axis strokefeed rate (inf. variable)rapid transverse rate: z-axisx-axisthreading pitchrated torque zrated torque x

mmmm

mm/min.mm/min.mm/min.

mm (max.)mmmm

1050225

0-10,0001515322222

TAILSTOCKQuill diameterQuill strokeTaper in the quillThrust (adjustable)Tailstock base travel

mmmm

Kgfmm

100225MT5600795

WEIGHT(APPROX) Kg 6500DIMENSIONS (APPROX) mm 4350x1875x1990

CNC SYSTEM:FANUC OT FEATURES

Manual data input Simultaneously controllable 2 axes Part program storage & editing Tool nose radius compensation Self diagnostics Constant surface speed control Multiple repetitive cycles Thread cutting cycles Feed rate override Circular interpolation Direct drawing dimension programming Absolute / incremental programming

Tape punch interface (RS 232C port) Program memory 320 metres of tape-128 K Backlash compensation Background editing Inch / metric switchable