PT MANUAL / B-TECH / MECHANICAL / KUK

EXPERIMENT NO - 1

AIM: TO MACHINE A JOB “DRILLING AND BORING” IN P.T. LAB INVOLVING FACING, OUTSIDE TURNING, DRILLING AND BORING OPERATION ON LATHE MACHINE.

TOOL AND EQUIPMENT: LATHE, THREE JAW CHUCK, H.S.S. FACING AND TURNING TOOL 12X12MM, CENTRE DRILL, TWIST DRILL 5.0 MM, 15 & 20 MM, BORING BAR, BORING TOOL, VERNIER CALIPER.

MATERIAL REQD.: MILD STEEL ROUND Φ40 X 35 MM.

PROCEDURE:

1.SELECT SUITABLE RPM TURNING USING FORMULA CUTTING SPEED ΠDN/1000 WHERE DIA IS IN MM.

2. USE MAX. DEPTH OF CUT 0.5MM, FEED 0.2-0.3MM/REV.

3. HOLD THE WORK PIECE IN THREE JAW CHUCK FACING ON ONE SIDE AND TURN DIA. 38.0MM ABOVE 20.0MM.

4. CHANGE THE WORK PIECE DIRECTION START FACING AND MAINTAINED 30.0MM LENGTH. TURN Φ38.0MM REMAINING DIA.

5. HOLD DRILL CHUCK IN TAILSTOCK AND CENTERING THE WORK PIECE. THEN Φ5.0MM, 15.0 AND 20.0MM. DRILL USE ON WORK PIECE.

6. HOLD BORING BAR IN TOOL POST AND SET IT ACC. TO WORK PIECE.

7. BORE Φ 25.0MM COMPLETE AS PER DRAWING.

EXPERIMENT NO - 2

AIM: TO MACHINE A JOB “MULTI SLOTS” IN P.T LAB INVOLVING PLAIN SURFACE, SIDE SURFACE, “V” SLOT MAKING AND “KEYWAY SLOT” MAKING OPERATION ON SHAPER.

TOOL AND EQUIPMENT: SHAPER, MACHINE VICE, H.S.S. TOOL 12X12.0MM, STEEL RULE, OUTSIDE CALIPER, INSIDE CALIPER, VERNIER CALIPER.

MATERIAL REQD: MILD STEEL SQUARE 48X48.0MM.

PROCEDURE –

1. SELECT SUITABLE NO. OF STROKE OF RAM FORMULA CUTTING SPEED LXNX5/3X 1/1000.

2. USE MAX. DEPTH OF CUT 1.0MM.

3. HOLD THE WORK PIECE IN MACHINE VICE; SET THE LENGTH OF STROKE AND POSITION OF STROKE SHAPER’S RAM.

4. RECTANGULAR PACKING USE FOR WORK PIECE SETTING.

5. START PLAIN FACE AND CHANGE DIRECTION OF WORK PIECE WITH HELP OF TRY SQUARE MAINTAINED SQUARE AT 45.0MM.

6. MARKING OF WORK PIECE 10.0MM ON ONE SIDE AND 10.0MM ON OTHER SIDE ON SAME DIRECTION AND BOTH THE 2^ND DIRECTION ALSO AND “V” OPERATION COMPLETE.

7. THEN 3^RD SIDE MAKE KEYWAY SLOT WITH “V” SHAPE AND PARTING OR SIDE TOOL.

8. INSPECT THE WORK PIECE AS PER DRAWING.

EXPERIMENT NO - 3

AIM: TO MACHINE A JOB “EXTERNAL THREADING” IN P.T. LAB INVOLVING FACING, OUTSIDE TURNING, CHAMFERING AND GROOVING AND THREAD MAKING OPERATION ON LATHE MACHINE.

TOOL AND EQUIPMENT: LATHE, THREE JAW CHUCK, H.S.S. FACING AND TURNING TOOL 12X12MM, THREADING TOOL, VERNIER CALIPER.

MATERIAL REQD.: MILD STEEL ROUND Φ25 X 94 MM. LENGTH.

PROCEDURE:

1. SELECT SUITABLE RPM TURNING USING FORMULA CUTTING SPEED ΠDN/1000 WHERE DIA IS IN MM.

2. USE MAX. DEPTH OF CUT 0.5MM, FEED 0.2-0.3MM/REV.

3. HOLD THE WORK PIECE IN THREE JAW CHUCK FACING ON ONE SIDE.

4. CHANGE THE WORK PIECE DIRECTION START FACING AND COMPLETE 90.0MM LENGTH.

5. THEN HOLD WORK PIECE ABOUT 22.0MM IN CHUCK.

6. TOOL POSITION 90⁰ TO WORKPIECE AXIS AND START PLAIN TURNING MAKE Φ22X60MM TO ONE SIDE.

7. CHAMFER ON WORK PIECE 5X45⁰ ON THE SIDE.

8. CHANGE GROOVING TOOL AND MAKE GROOVE Φ18X10MM WIDTH AFTER 50MM LENGTH TO THE SIDE.

9. HOLD THREADING TOOL WITH THE HELP OF HALF NUT AND CHART ON LATHE M/C MAKE AND COMPLETE EXTERNAL THREAD 16 T.P.I. ON THE SIDE.

10. INSPECT THE WORK PIECE AS PER DRAWING

EXPERIMENT NO - 4

AIM: - TO MAKE SPUR GEAR ON MILLING MACHINE

EQUIPMENT: - MILLING MACHINE, LATHE MACHINE, DRILLING MACHINE, VERNIER CALIPER, 22 M DRILL BIT, SINGLE POINT CUTTING TOOL, INDEXING HEAD, FORM CUTTER

MATERIAL: - MILD STEEL (50MM $ X 25)

THEORY: - IN CUTTING GEAR ON MILLING MACHINE AND FORM CUTTERS ARE USED, IN WHICH PROFILE OF THE CUTTING TEETH CONFORM TO THE TOOTH PROFILE REQUIRED ON THE GEAR, EVERY GEAR CUTTER IS SPECIFIED BY DIAMETER PITCH, CUTTER NUMBER PRESSURE ANGLE AND THE DIAMETER OF CUTTING BORE.

DIAMETER OF THE GEAR BLANK = PITCH CIRCLE DIAMETER + 2(ADDENDUM)

D = PITCH CIRCLE DIAMETER

P = PITCH OF THE GEAR TEETH

N = NO. OF TEETH

M = MODULE

TYPE = INVOLUTE TEETH= D+2/P {ADDENDUM = 1/P} = N/P + 2/P {D = N/P} = (N+2)/P

= NO. OF TEETH TO BE CUT + 2

P

DIAMETRICAL PITCH P = NO OF TEETH TO BE CUT + 2

DIAMETER OF GEAR BLANK

GEAR BLANK DIAMETER = N/P +• 2/P

= MN + 2M {1/P = (N+2)

M = DIAMETER OF GEAR BLANK

NO. OF TEETH TO BE CUT + 2

FROM THE ABOVE RELATIONS TO DIAMETRIC PITCH (P) OF THE CUTTER CAN BE FOUND OUT

EXPERIMENT NO - 5

AIM: - TO PRACTICE OF SLAB MILLING ON MILLING MACHINE

EQUIPMENT: - HORIZONTAL MILLING MACHINE, ARBOR SIZE-25MM

TOOLS: - SLAB MILLING CUTTER, WORK CLAMPS.

MATERIAL: - MILD STEEL (40MMX40MMX50MM)

THEORY: - IN SLAB MILLING ALSO CALLED PERIPHERAL MILLING; THE AXIS OF CUTTER ROTATION IS PARALLEL TO THE WORK PIECE SURFACE TO BE MACHINED. THE CUTTER, GENERALLY MADE OF HIGH SPEED STEEL, HAS A NUMBER OF TEETH ALONG ITS CIRCUMFERENCE, EACH TOOTH ACTING LIKE A SINGLE POINT CUTTING TOOL CALLED A PLAIN MILL.

CUTTERS FOR SLAB MILLING MAY HAVE STRAIGHT OR HELICAL TEETH RESULTING IN, RESPECTIVELY, ORTHOGONAL OR OBLIQUE CUTTING ACTION. THE HELICAL TEETH ON THE CUTTER ARE PREFERRED OVER STRAIGHT TEETH BECAUSE THE LOAD ON THE TOOTH IS LOWER, RESULTING IN A SMOOTHER OPERATION AND REDUCING TOOTH FORCES AND CHATTER.

PROCEDURE: -

1. SET THE MACHINE FOR MILLING OPERATION.

2. FIX THE CUTTER ON THE ARBOR.

3. CLAMP THE WORK PIECE ON MILLING MACHINE TABLE.

4. SET THE CUTTER TO TAKE A DEPTH OF 2MM

5. RUN THE MACHINE FOR OPERATION AND FEED THE CUTTER OVER THE ENTIRE LENGTH OF THE WORK.

6. CHECK FOR THE FINISH OF THE WORK PIECE.

RESULT: - WE OBTAIN THE REQUIRED FINISHED WORK AFTER MEASURING DIMENSIONS

CUTTER

ARBOR

EXPERIMENT NO - 6

AIM: - TO CUT GEAR TEETH ON MILLING MACHINE USING DIVIDING HEAD.

EQUIPMENT: - MILLING MACHINE, LATHE MACHINE, DRILLING MACHINE, VERNIER CALIPER, 22 M DRILL BIT, SINGLE POINT CUTTING TOOL, INDEXING HEAD, FORM CUTTER

MATERIAL: - MILD STEEL (50MM $ X 25)

THEORY: - IN CUTTING GEAR ON MILLING MACHINE AND FORM CUTTERS ARE USED, IN WHICH PROFILE OF THE CUTTING TEETH CONFORM TO THE TOOTH PROFILE REQUIRED ON THE GEAR, EVERY GEAR CUTTER IS SPECIFIED BY DIAMETER PITCH, CUTTER NUMBER PRESSURE ANGLE AND THE DIAMETER OF CUTTING BORE.

DIAMETER OF THE GEAR BLANK = PITCH CIRCLE DIAMETER + 2(ADDENDUM)

D = PITCH CIRCLE DIAMETER

P = PITCH OF THE GEAR TEETH

N = NO. OF TEETH

M = MODULE

TYPE = INVOLUTE TEETH= D+2/P {ADDENDUM = 1/P} = N/P + 2/P {D = N/P} = (N+2)/P

= NO. OF TEETH TO BE CUT + 2

P

DIAMETRICAL PITCH P = NO OF TEETH TO BE CUT + 2

DIAMETER OF GEAR BLANK

GEAR BLANK DIAMETER = N/P +• 2/P

= MN + 2M {1/P = (N+2)

M = DIAMETER OF GEAR BLANK

NO. OF TEETH TO BE CUT + 2

DIVIDING HEAD

THESE HEADS HELPS IN CHANGING THE ANGULAR POSITION OF THE WORK PIECE IN RELATION TO THE CUTTER. WITH THEIR USE IT IS POSSIBLE TO DIVIDE THE PERIPHERY OF THE WORKPIECE INTO ANY NUMBER OF EQUAL PARTS. THESE HEADS ARE GENERALLY OF THE FOLLOWING TYPES:

PLAIN DIVIDING HEAD

UNIVERSAL DIVIDING HEAD

OPTICAL DIVIDING HEAD

OUT OF THESE THE OPTICAL IS THE MOST PRECISE ONE AND USED FOR VERY PRECISE INDEXING WORK OR FRO CHECKING THE ACCURACY OF THE OTHER TYPES OF DIVIDING HEADS.

PLAIN DIVIDING HEAD: - THESE INDEXING HEAD ARE OF TWO TYPES. THE FIRST TYPE CARRIES THE INDEXING PLATE DIRECTLY MOUNTED ON ITS SPINDLE AND HAS NO USE OF WORM AND WORM WHEEL. IT IS THE SIMPLEST TYPE AND USED IN DIRECT INDEXING. THE INDEXING PLATE CARRIES 12 OR 24 EQUISPACED SLOTS ON ITS PERIPHERY.

ANOTHER USEFUL FORM OF THE PLAIN DIVIDING HEAD IS THE ONE USED IN SIMPLE INDEXING. IT CONSISTS OF A CAST BODY, CARRYING THE SPINDLE. ON THE FRONT END OF THE SPINDLE ARE MOUNTED THE CARRIER ARID THE CENTER. ON ITS REAR SIDE THE MOUNTED THE INDEX PLATE, WHICH IS HAVING DIFFERENT HOLE CIRCLES ON ITS FACE AND TEETH ON ITS PERIPHERY. THE PLATE GETS MOVEMENT THROUGH A WO"^RN CY ROTATING THE HANDLE. THE PLATE HAVING 3 CIRCLES OF 16, 42 AND 60 OR 24, 30 AND 36 ' JIES ARE PROVIDED ON THESE HEADS.

UNIVERSAL DIVIDING HEAD: - UNIVERSAL DIVIDING HEAD IS USED FOR MOSTLY ALL THE OPERATION OF MILLING MACHINE. THE UNIVERSAL DIVIDING HEAD PERFORMS THE FOLLOWING OPERATION: -

1. IT SETS THE WORKPIECE IN A DESIRED POSITION IN RELATION TO THE MACHINE TABLE.

2. AFTER EACH CUT, IT ROTATES THE JOB THROUGH A DESIRED ANGLE AND, THUS, INDEXES THEPERIPHERY OF THE WORK.

3. IT PROVIDES A CONTINUOUS ROTARY MOTION TO THE JOB DURING MILLING MACHINE OF HELICAL GROOVES.

WORKING: - DIVIDING HEAD IS TO PROVIDE SUPPORT TO THE WORK PIECE, HOLD IT IN POSITION AND ROTATES IT THROUGH A DESIRED ANGLE AFTER EACH CUT IS OVER. THE INDEX CRANK IS ROTATED TO PROVIDE ROTARY MOTION TO THE JOB AND THE INDEX PLATE ENABLES THIS ROTATION TO TAKE PLACE ALWAYS TO THE DESIRED ANGLE. WHEN THE

CRANK ROTATES; THE WORM WHEEL ROTATES WHICH IN TURN ROTATES THE WORM WHEEL. SINCE THE WHEEL IS MOUNTED DIRECTLY ON THE SPINDLE THE LATTER ROTATES ALONG WITH THE FORMER.

INDEXING METHODS: - THE FOLLOWING INDEXING METHODS ARE COMMONLY USED: -

1. DIRECT INDEXING

2. PLAIN INDEXING OR SIMPLE INDEXING

3. COMPOUND INDEXING

4. DIFFERENTIAL INDEXING

5. ANGULAR INDEXING

OUT OF THESE THE DIRECT INDEXING IS THE SIMPLEST ONE, BUT WE COMMONLY USE THE PLAIN INDEXING PLAIN INDEXING: - THIS METHOD OF INDEXING IS USED WHEN THE DIRECT INDEXING METHOD CANNOT BE EMPLOYED FOR OBTAINING THE REQUIRED NUMBER OF DIVISIONS ON THE WORK. FOR THIS INDEXING METHOD UNIVERSAL INDEXING HEAD CAN BE USED. THIS METHOD OF INDEXING INVOLVES THE USE OF CRANK, WORM, WORM WHEEL AND INDEX PLATE. WORM CARRIES 40 TEETH AND WORM IS SINGLE START. THE WORM WHEEL IS DIRECTLY MOUNTED ON THE SPINDLE. SINCE THE WORM HAS SINGLE START THREAD AND THE WORM WHEEL 40 TEETH, WITH ONE TURN OF THE CRANK THE WORM WHEEL WILL ROTATES THROUGH ONE PITCH DISTANCE, I.E. EQUAL TO 1/40 OF A REVOLUTION. SIMILARLY 2 TURNS OF THE CRANK WILL MAKE THE WORK TO ROTATE THROUGH 1\20 AND A 3 TURN THROUGH 3/40 OF A REVOLUTION. THUS THE CRANK WILL HAVE TO ROTATE THROUGH 40 TURNS IN ORDER TO ROTATE THE WORK THROUGH ONE COMPLETE TURN. FOR N DIVISIONS ON THE WORK PIECE, THE CRANK WILL MAKE 40/N TURNS. SUPPOSE THAT THE WORK HAS TO BE DIVIDED INTO 23 EQUAL DIVISIONS THEN THE CORRESPONDING CRANK MOVEMENT WILL BE GIVEN BY: -

CRANK MOVEMENT = 40 / 23 = 1

EXPERIMENT NO - 7

AIM: TO STUDY CONSTRUCTIONS DETAIL & WORKING OF CNC LATHE.

THEORY:

COMPUTER NUMERICAL CONTROL (CNC)

CNC MAY BE DEFINED AS AN NC SYSTEM IN WHICH A DEDICATED STORED PROGRAM COMPUTER IS USED TO PERFORM STORE OR ALL OF THE BASIC NC FUNCTIONS IN ACCORDANCE WITH CONTROL PROGRAMS STORED IN THE READ-WRITE MEMORY OF THE COMPUTER. CNC IS ALSO CALLED SOFT-WIRED NC. IN CONTRAST, IN THE HARD-WIRED CONTROLS, THE LOGIC FUNCTIONS ARE WIRED TOGETHER IN A FIXED, PRE-ENGINEERED ARRANGEMENT. CNC IS QUITE DIFFERENT THAN DIRECT NUMERICAL CONTROL (DNC). COMPUTERS SUPPORT­ING DNC ARE USED TO DISSEMINATE MANUFACTURING DATA TO, AND COLLECT PRODUCT INFORMATION FROM, SEVERAL MACHINE CONTROLLERS. CNC GENERALLY SUPPORTS ONLY ONE MACHINE. THE MICROPROCESSOR OF CNC IS ACCORDINGLY IN CLOSE PROXIMITY OF THE MACHINE BUT THE COMPUTER OF DNC IS REMOTE FROM THE MACHINE TOOLS.

36.17.1. ELEMENTS OF CNC SYSTEM. FIG. 36.21 SHOWS THE MAJOR FUNCTIONAL UNITS OF A CNC SYSTEM

THE VARIOUS UNITS ARE DISCUSSED BELOW:

INPUT UNIT. IT RECEIVES ALL THE COMMANDS FROM OPERATOR INTERFACE (OPERATION STATION CONTAINING ALL THE SWITCHES, PUSH BUTTONS DISPLAYS, ETC, REQUIRED TO OPERATE AND MONITOR MACHINE ACTIVITIES) AND FEEDBACK OR STATUS OF MACHINE IN THE FORM OF A.C., D.C., AND ANALOG SIGNALS. ALL INPUT SIGNALS ARE MADE COMPATIBLE (BY INPUT UNIT) TO BE UNDERSTOOD BY CONTROL UNIT (LIKE CONVERSION OF SIGNAL TO DIGITAL FORM BY A/D CONVERTER, ETC.), SOFTWARE (SYSTEM OPERATING PROGRAM, PART PROGRAMS AND DIAGNOSTICS) ARE INPUT BY MEANS OF PAPER TAPE, OR MAGNETIC DEVICES STORED IN MEMORY UNTIL NEEDED BY CONTROL UNIT..

CONTROL UNIT. IT TAKES INSTRUCTIONS FROM THE MEMORY UNIT AND INTERPRETS THEM ONE AT A TIME. IT PROCESSES INFORMATION RECEIVED FROM THE OPERATOR AND MACHINE INTERFACE. THIS INFORMATION IS INTERPRETED AND MANIPULATED WITH HARDWARE LOGIC AND COMPUTER PROGRAMS..

MEMORY UNIT. IT STORES INSTRUCTIONS AND DATA RECEIVED FROM THE INPUT. IT ALSO STORES THE RESULTS OF ARITHMETIC OPERATIONS AND SUPPLIES INFORMATION TO THE OUTPUT UNIT. THE SIZE OF THE PROGRAMS AND SPACE REQUIRED TO MANIPULATE DATA DETERMINE THE AMOUNT OF MEMORY REQUIRED. PART PROGRAMS AND USUALLY STORED IN RANDOM ACCESS MEMORY (RAM) WHICH PROVIDE IMMEDIATE ACCESS TO ANY STORAGE LOCATION POINT IN MEMORY. FIXED PROGRAMS (SUCH AS THE SYSTEM OPERATING PROGRAM

AND DIAGNOSTICS) ARE STORED ON READ ONLY MEMORY (ROM) WHICH STORES INFORMATION PERMANENTLY. INFORMATION ON ROM CAN BE READ BUT CAN'T BE ALTERED.

ARITHMETIC UNIT-IT PERFORMS CALCULATIONS AND MAKES DECISIONS. ITS RESULTS ARE STORED IN THE MEMORY UNIT.

OUTPUT UNIT-IT RECEIVES DATA FROM MEMORY AT THE COMMAND OF CONTROL UNIT. THE SIGNALS ARE MADE COMPATIBLE WITH OUTPUT DEVICES SO THAT COMMANDS ISSUED BY OUTPUT UNIT CAN BE OBEYED BY THEM. DIGITAL SIGNALS ARE FIRST CONVERTED TO ANALOG FORM TO CONTROL AXIS DRIVE SERVOMOTORS. OUTPUT SIGNALS ARE USED TO TURN ON AND OFF DEVICES, DISPLAY INFORMATION, POSITION AXES, ETC.

OPERATOR INTERFACE. VARIOUS UNITS WHICH COMPRISE OPERATOR INTERFACE ARE AS FOLLOWS.

PUNCHED TAPE IS THE MOST COMMONLY USED INPUT SYSTEM FOR NC SYSTEM TYPEWRITERS HAVING A TAPE-PUNCH ATTACHMENT ARE FREQUENTLY USED TO PREPARE NC PUNCHED-TAPE PROGRAMS. THE INSTRUCTIONS FOR A GIVEN OPERATION ARE CONTAINED IN SEVERAL ROWS OF INFORMATION CALLED A BLOCK. BY MEANS OF THE HOLE PATTERNS PUNCHED IN THE TAPE, ALL THE LETTERS OF THE ALPHABET AS WELL AS DIGITS 0 TO 9 CAN BE CODED TO FORM WORDS WITHIN A BLOCK. VARIOUS OTHER SYMBOLS USEFUL FOR CONTROLLING MACHINE FUNCTIONS CAN ALSO BE CODED. TAPE READERS MAY BE EITHER ELECTROMECHANICAL TYPE (USING FINGERS OR OTHER DEVICES TO MAKE ELECTRICAL CONTACT THROUGH HOLES OF THE TAPE, USUALLY SLOW TYPE) OR PHOTOELECTRIC TYPE DETECTED LIGHT OR REFLECTED LIGHT TYPE-FASTER THAN ELECTROMECHANICAL TYPE). SOME TAPE-READERS ARE CAPABLE OF READING AN ENTIRE BLOCK OF HOLES SIMULTANEOUSLY. SUCH TAPE-READERS ARE USED ON SIMPLE POSITIONING MACHINES.

MAGNETIC DEVICES (MAGNETIC TAPE, DISK, DRUM) HAVING THE ABILITY TO STORE LARGE AMOUNTS OF DATA ON A SMALL AMOUNT OF SURFACE ARE ALSO USED TO FEED INPUT TO MEMORY UNIT.

OPERATOR STATION FORMS A MAJOR OPERATOR INTERFACE. IT IS USED TO INITIATE AUTOMATIC OPERATION, TO INPUT DATA, AND TO MONITOR ACTIVITIES USING DISPLAY DEVICES LIKE CRT (CATHODE RAY - :•=• LEDS (LIGHT EMITTING DIODES), PLASMA DISPLAYS ETC. MANUAL DATA INPUT TO OVERRIDE THE PROGRAM IS ALSO PROVIDED ON OPERATOR STATION.

MACHINE INTERFACE. IT CONSISTS OF ALL DEVICES USED TO MONITOR AND CONTROL MACHINE TOOL, LIKE EXTREME TRAVEL LIMIT SWITCHES, MISCELLANEOUS POSITION LOCATION, SOLENOIDS FOR HYDRAULIC AND AIR CONTROL, CONTROL VALVES,SERVOMECHANISMS ETC.

USUALLY TWO LIMIT SWITCHES ARE PROVIDED TO DETECT END OF TRAVEL ON ANY AXIS. MANY MACHINE FUNCTIONS ARE PERFORMED BY APPLYING AIR OR OIL PRESSURE TO DEVICES LIKE POWER DRAWBARS, TURRET INDEXES, TOOL CHANGER MAGAZINES, COOLANT FLOW ETC. MANY MACHINE TOOLS USE HYDRAULIC OR AIR OPERATED CYLINDERS TO CONTROL SPINDLE SPEED AND AXIS FEED TRANSMISSIONS. THE CONTROL OF THESE DEVICES IS PROGRAMMED IN THE CONTROLLER AND ACTIVATED BY CONTROL CODES.

A SERVOMECHANISM IS A GROUP OF ELEMENTS WHICH CONVERT THE NC OUTPUT INTO PRECISION MECHANICAL DISPLACEMENTS. THESE ELEMENTS INCLUDE MOTORS (HYDRAULIC OR ELECTRIC), GEAR TRAINS AND TRANSDUCERS (VELOCITY OR POSITION). THE DRIVE TO SPINDLE AND SLIDES IN NC TOOLS IS USUALLY PROVIDED BY EITHER HYDRAULIC OR ELECTRIC MOTORS. SERVOMECHANISMS MAY BE EITHER OPEN OR CLOSED LOOP. FIG. 36.22 SHOWS THE MECHANICAL ELEMENTS OF A CNC SYSTEM.

SIGNALS FROM MACHINE CONTROL UNIT AND FROM THE FEEDBACK DEVICE ARE FED TO COMMAND SIGNAL CIRCUIT AND THEN TO SERVOMECHANISM WHICH AMPLIFIES IT AND PROVIDES POWER TO MOVE THE DESIRED MACHINE SLIDE OR CARRY OUT A MECHANICAL MOVEMENT AS REQUIRED. THE SERVOMECHANISM MAY BE AN ELECTRIC MOTOR WHICH DRIVES THE MACHINE TABLE THROUGH A LEAD SCREW, OR THE SYSTEM MAY INVOLVE HYDRAULIC MOTORS, HYDRAULIC RAMS OR OTHER DEVICES FOR MOVING THE CONTROLLED MACHINE ELEMENTS OR SLIDES AS REQUIRED. MOTORS MAY DRIVE THE SLIDES THROUGH LOW-FRICTION LEAD SCREWS EMPLOYING CIRCULATING BALL NUTS OR THROUGH RACK-AND-PINION ARRANGEMENTS. THE ROTARY HYDRAULIC MOTOR USES THE PRESSURE OF FLUID FLOWING THROUGH GEARS OR AGAINST PISTONS TO EFFECT A SHAFT ROTATION. THESE MOTORS ARE USUALLY SMALL IN SIZE AND OF THE POSITIVE DISPLACEMENT VARIETY. OIL FLOW TO THE MOTOR IS CONTROLLED BY A SERVO VALVE (WHICH IS TYPICALLY AN ELECTRO HYDRAULIC UNIT USING AN ELECTRICAL SOLENOID TO ACTUATE A SMALL FLAPPER WHICH CONTROLS HYDRAULIC PRESSURE ON A SPOOL VALVE ; THE SPOOL VALVE DIRECTING OIL TO HYDRAULIC MOTOR, WHICH PRODUCES THE DESIRED MECHANICAL MOTION). HIGH-TORQUE ELECTRICAL MOTORS WHICH CAN BE DIRECTLY COUPLED TO LEAD SCREWS ARE USED. A STEPPING MOTOR IS USUALLY USED WHICH IS ACTUATED BY PLUSES AND MOVES A FIXED ANGULAR UNIT (SAY 15°) FOR EACH ELECTRICAL PULSE. THE MOTOR IS USUALLY CLAMPED MAGNETICALLY AT FIXED ANGULAR POSITION. ON ISSUING ONE ELECTRICAL PULSE, MOTOR ADVANCES BY 15° AND REMAINS HELD IN POSITION BY A MAGNETIC DETENT UNTIL THE NEXT ELECTRICAL PULSE ADVANCES IT BY ANOTHER 15°. A SLIDE DRIVEN BY THE MOTOR WOULD

NORMALLY BE GEARED SO THAT EACH 15° STEP WOULD MOVE THE TABLE (0.003 TO 0.013 MM).

FLOW OF TIMING CONTROL SIGNAL

GAS METAL ARC WELDING IS A PROCESS IN WHICH COALESCENCE IS PRODUCED BY HEATING ARC BETWEEN A CONTINUOUS FILLER METAL (CONSUMABLE) ELECTRODE AND THE WORK. SHIELDING IS OBTAINED ENTIRELY FROM AN EXTERNALLY SUPPLIED GAS OR GAS MIXTURE. THERE ARE A NUMBER OF VARIATION OF THE GAS METAL ARC WELDING PROCESS AND THE PROCESS HAS BEEN GIVEN MANY DIFFERENT TRADE NAMES, E.G. VARIATIONS ARE CALLED MIG WELDING, CO₂ WELDING, FINE WIRE WELDING, SPRAY ARC WELDING, PULSATED ARC WELDING, ELECTRO SLAG WELDING AND SHORT-CIRCUIT WELDING.

PRINCIPLE OF OPERATION: -

THE MIG WELDING PROCESS IS SHOWN BY FIGURE. THE MIG WELDING PROCESS UTILIZES THE HEAT OF AN ARC BETWEEN A CONTINUOUSLY FEED CONSUMABLE ELECTRODE AND THE WORK TO BE WELDED. THE HEAT OF THE ARC MELTS THE SURFACE OF THE BASE METAL AND THE END OF THE ELECTRODE. THE METAL MELTED OF THE ELECTRODE IS TRANSFERRED THROUGH THE ARC TO THE WORK WHERE IT BECOMES THE DEPOSITED WELD METAL. SHIELDING IS OBTAINED FROM AN ENVELOP OF GAS WHICH MAY BE AN INERT GAS AN ACTIVE GAS OR A MIXTURE THE SHIELDING GAS SURROUNDS THE ARC AREA TO PROTECT IT FROM CONTAMINATION FROM THE ATMOSPHERE THE ELECTRODE IS FED IN TO THE ARC AUTOMATICALLY IS USUALLY FROM A COIL. THE ARC IS MAINTAINED AUTOMATICALLY AND TRAVEL CAN BE MANUALLY OR BY MACHINE.

THE GAS METAL ARC WELDING PROCESS, INTRODUCES IN THE LATE 1940S HAS BEEN BECOME ONE OF THE MOST POPULAR ARC WELDING PROCESS. EARLY DEVELOPMENT WAS FOR WELDING OF ALUMINUM USING INERT GAS FOR SHIELDING. HENCE THE NAME "METAL INERT GAS" OR MIG WELDING. FOR WELDING STEELS INERT GASES SEEMED TO BE TOO EXPENSIVE AND AN ACTIVE GAS, CC>2 WAS SELECTED. THE SELECTION OF CC>2 WAS BASED ON THE ANALYSIS OF GASES FORMED BY THE DISINTEGRATION OF THE COATING OF COVERED ELECTRODES. THIS VARIATION, NAMED CO2 WELDING, WAS WELL ADAPTED FOR WELDING MILD STEEL.

FURTHER DEVELOPMENT WITH DIFFERENT SHIELDING GASES LED TO THE "SPRAY ARC" VARIATION, WHICH UTILIZES LARGER DIAMETER ELECTRODES; WITH A SHIELDING GAS MIXTURE OF 95% ARGON AND 5% OXYGEN (OTHER MIXTURES WERE 98-2 AND 99-1 ARGON - OXYGEN MIXTURES). THESE GAS MIXTURES PRODUCED A SPRAY TYPE METAL TRANSFER AND WELDS WITH AN EXTREMELY SMOOTH SURFACE.

EXPERIMENT NO - 8

AIM: - TO CARRY OUT WELDING USING TIG/MIG WELDING SET

THE GAS METAL ARC WELDING PROCESS IS THE FASTEST GROWING PROCESS IN USE TODAY. ITS GROWTH IS BASED ON REPLACING SHIELDED METAL ARC WELDING FOR WELDING THIN METALS, AND FOR REPLACING GAS TUNGSTEN ARC WELDING FOR NON-FERROUS METALS. IT IS REPLACING SUBMERGED ARC IN AUTOMATIC APPLICATIONS.

WELDING CIRCUIT AND CURRENT: -

THE GAS METAL ARC WELDING USES A WIRE FEEDER SYSTEM THAT CONTROLS THE ELECTRODE WIRE FEED AND WELDING ARC, AS WELL AS THE FLOW OF SHIELDING GAS AND COOLING WATER. THE POWER SUPPLY IS NORMALLY THE CONSTANT VOLTAGE TYPE. A GUN OR TORCH IS USED FOR DIRECTING THE ELECTRODE AND SHIELDING GAS TO THE ARC AREA. FOR THE ELECTRO SLAG METHOD TRAVEL MECHANISM AND RETAINING SHOES ARE ALSO REQUIRED.

THE GAS METAL ARC WELDING PROCESS USES DIRECT CURRENT. ALTERNATING CURRENT HAS NOT BEEN SUCCESSFULLY USED. DIRECT CURRENT ELECTRODE NEGATIVE DCEN (STRAIGHT POLARITY) CAN BE USED WITH SPECIAL EMISSIVE COATED ELECTRODE WIRES, WHICH PROVIDES FOR BETTER ELECTRON EMISSION. DCEN IS RARELY USED BECAUSE THE EMISSIVE-COATED ELECTRODES ARE MORE EXPENSIVE. THE WELDING CURRENT VARIES FROM AS LOW AS 20 AMPERES AT A VOLTAGE OF 18 VOLTS TO AS HIGH AS 750 AMPERES AT AN ARC VOLTAGE OF 50 VOLTS. THE EQUIPMENT REQUIRED FOR MIG WELDING ARE 1) POWER SOURCE 2) THE ELECTRODE WIRE FEEDER AND CONTROL SYSTEM 3) THE WELDING GUN AND CABLE ASSEMBLY FOR SEMIAUTOMATIC WELDING FOR AUTOMATIC WELDING 4) THE GAS AND WATER CONTROL SYSTEM FOR THE SHIELDING GAS AND COOLING WATER WHEN USED, AND 5) TRAVEL MECHANISM AND GUIDANCE FOR AUTOMATIC WELDING. THERE IS THE EXTRA FACTOR OF MOLDING SHOES WHEN USING THE ELECTRO GAS METHOD. THE POWER SOURCE FOR GAS METAL ARC WELDING SHALL BE RATED FOR 100 % DUTY CYCLE

TOOL AND EQUIPMENT: LATHE, THREE JAW CHUCK, HSS FACING AND TURNING TOOL 12X12MM, THREADING TOOL, VARNIER CALLIPER.

MATERIAL REQUIRED: MILD STEEL ROUND 25X94 MM. LENGTHS

PROCEDURE:

1. SELECT SUITABLE RPM TURNING USING FORMULA CUTTING SPEED WHERE DIAMETER IS IN MM.

2. USE MAX. DEPTH OF CUT 0.5MM, FEED 0.2-0.3MM/REV.

3. HOLD THE WORK PIECE IN THREE JAW CHUCK FACING ON ONE SIDE.

4. CHANGE THE WORK PIECE DIRECTION START FACING AND COMPLETE 90.0 MM LENGTH.

5. THEN HOLD WORK PIECE ABOUT 22.0MM IN CHUCK.

6. TOOL POSITION 90* TO WORK PIECE AXIS AND STAR PLAIN TURNING MAKE 22X60MM TO ONE SIDE.

7. CHAMFER ON WORK PIECE 5X45* ON THE SIDE.

8. CHANGE GROOVING TOOL AND MAKE GROOVE 18X10MM WIDTH AFTER 50MM LENGTH TO THE SIDE.

9. INSPECT THE WORK PIECE AS PER DRAWING.

ADVANTAGES: -

THE MAJOR ADVANTAGES OF THE MIG WELDING ARE:

1. HIGH DEPOSITION RATE WHEN RELATED TO SHIELDED METAL ARC WELDING.

2. HIGH OPERATOR FACTOR WITH RESPECT TO SHIELDED METAL ARC WELDING

3. HIGH UTILIZATION OF FILLER MATERIAL

4. ELIMINATION OF SLAG AND FLUX REMOVAL

5. REDUCTION OF SMOKE AND FUMES.

6. MAY BE AUTOMATED FOR HIGH - OPERATOR FACTOR.

7. SKILL LEVEL IN THE SEMIAUTOMATIC METHOD OF APPLICATION SLIGHTLY LOWER THANREQUIRED FOR MANUAL SHIELDED METAL ARC WELDING.

8. EXTREMELY VERSATILE AND WIDE AND BROAD APPLICATION ABILITY.

SAFETY PRECAUTION:

1 HOLD THE WORK PIECE TIGHTLY IN THREE JAW CHUCK.

2. HEIGHT OF CUTTING TOOL POINT AND WORK PIECE CENTRE SHOULD BE EQUAL.

3. LEAD SCREW CONTINUE RUNNING POSITION WHEN THREAD MAKING.