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  1. 1. 1 CHAPTER 1 INTRODUCTION List of welding processes prevailing in the company • Arc welding • Inert Gas (CO2) welding • Spot welding • Stud Welding • TIG Welding 1.1 ARC WELDING: Arc welding is a type of welding that uses a welding power supply to create an electric arc between an electrode and the base material to melt the metals at the welding point. They can use either direct (DC) or alternating (AC) current, and consumable or non-consumable electrodes. The welding region is usually protected by some type of shielding gas, vapour, or slag. Arc welding processes may be manual, semi-automatic, or fully automated. First developed in the early part of the 20th century, arc welding became commercially important in shipbuilding during the Second World War. Today it remains an important process for the fabrication of steel structures and vehicles. 1.2 METAL INERT GAS WELDING: Metal inert gas (MIG) welding or metal active gas (MAG) welding, is a welding process in which an electric arc forms between a consumable wire electrode and the work piece metal(s), which heats the work
  2. 2. 2 piece metal(s), causing them to melt, and join. Along with the wire electrode, a shielding gas feeds through the welding gun, which shields the process from contaminants in the air. The process can be semi-automatic or automatic. A constant voltage, direct current power source is most commonly used with GMAW, but constant current systems, as well as alternating current, can be used. There are four primary methods of metal transfer in GMAW, called globular, short-circuiting, spray, and pulsed-spray, each of which has distinct properties and corresponding advantages and limitations. 1.3 TIG WELDING Tungsten inert gas (TIG) welding is an arc welding process that uses a non- consumable tungsten electrode to produce the weld. The weld area is protected from atmospheric contamination by an inert shielding gas(argon or helium), and a filler metal is normally used, though some welds, known as autogenous welds, do not require it. A constant-current welding power supply produces energy which is conducted across the arc through a column of highly ionized gas and metal vapours known as a plasma. 1.4 STUD WELDING: Stud welding is a form of spot welding where a bolt or specially formed nut is welded onto another metal part. The bolts may be automatically fed into the spot welder. Weld nuts generally have a flange with small nubs that melt to form the weld. Studs have a necked down, un-threaded area for the same purpose. Weld studs are used in stud welding systems. Capacitor discharge weld studs range from 14 gauge to 3/8" diameter. They can come in many different lengths ranging from 1/4" to 5" and larger. The tip on the weld end of the stud serves a twofold purpose.
  3. 3. 3 1.5 SPOT WELDING: Spot welding is a process in which contacting metal surfaces are joined by the heat obtained from resistance to electric current. Work-pieces are held together under pressure exerted by electrodes. Typically the sheets are in the 0.5 to 3 mm (0.020 to 0.12 in) thickness range. The process uses two shaped copper alloy electrodes to concentrate welding current into a small "spot" and to simultaneously clamp the sheets together. Forcing a large current through the spot will melt the metal and form the weld. The attractive feature of spot welding is a lot of energy can be delivered to the spot in a very short time . The amount of heat (energy) delivered to the spot is determined by the resistance between the electrodes and the amperage and duration of the current. The amount of energy is chosen to match the sheet's material properties, its thickness, and type of electrodes. Applying too little energy won't melt the metal or will make a poor weld. Applying too much energy will melt too much metal, eject molten material, and make a hole rather than a weld. Another attractive feature of spot welding is the energy delivered to the spot can be controlled to produce reliable welds. The advantages of the method include efficient energy use, limited work piece deformation, high production rates, easy automation, and no required filler materials. While the shear strength of each weld is high, the fact that the weld spots do not form a continuous seam means that the overall strength is often significantly lower than with other welding methods, limiting the usefulness of the process. It is used extensively in the automotive industry cars can have several thousand spot welds.
  4. 4. 4 CHAPTER 2 LITERATURE SURVEY 2.1 RESISTANCE WELDING THEORY Resistance welding process is applicable for joining electrically conducting aerials, the joint s are made by raising the temperature of the weld zone and the parts together during the plastic stage. Spot welding projection welding seam welding and upset butt welding are all basically resistance welding, the difference are mainly in the geometrical arrangement of parts. In all these cases the heat required to raise the temperature of the metal is generated due to the passage of electrical current through the joint. The contact resistance (of the order of milli ohms) causes the heat to localize at the point of interest and the current carrying electrodes are adjusted to increase this effect. No fillers are required therefore the process is cheaper, neater and faster than most of the other methods of metal joining. CURRENT SOURCE: The source of current is in general a special step down transformer. The primary side of this fed from the power supply. In small machines up to about (5kva) the transformers are designed to work from 220 volts ac. In case of larger machines the power is fed from 2 lines of a three phase 440 volts system. Another type of power source employed consists of a regulated dc supply which is momentarily connected to a pulse transformer. Since any machine should be adaptable for different jobs, normal type of resistance welding transformer is provided with a number of taps on its windings. The secondary voltage is thus adjusted depending upon the job to be weld.
  5. 5. 5 2.2 TIMING CONTROLS: 2.2.1 WELD TIME: A very important requirement of spot welding is that the welding current is delivered to the job only for a very short time, typical timings are only about 0.1 sec to 3 sec. Precision welding of highest quality are done with a timing less than 1 sec therefore the unit of time preferred by the industry is the cycle. One cycle corresponds to 1/50th of a second when referred to the power supply frequency of 50 cycles per second. In simple machines a electromagnetic contactor is kept energised or a time period suited to each requirement. The contacts of this conactor connect the primary of the welding transformer to the power supply. The timing period is determined by the settings of a variable resistor through which a capacitor is charged to a predetermined level. 2.2.2 SEQUENCE TIMINGS: A spot welding operator preferably must have to operate only a simple switch or a foot lever. The electrodes should contact the job pieces and when a desired pressure is developed the current should flow for a selected time and the electrodes should part after the weld is forged. In pneumatically operated machines the sequence of events as well as the duration of each event are controlled by electronic timers. If the feeding of job is made fast and regular it is possible to get a stitching type by recycling through the sequence
  6. 6. 6 2.2.3 SEAM WELDING: For manufacturing leak tight drums and similar items the method used is seam welding. Electrodes are rotating wheels the speed of which is adjustable. A series of overlapping welds are made. Typical timings are 2 cycles on followed by 2 cycles off and periods. Heavy current 100-500 amps are therefore required to be switched at the rate of 10-20 times a second and an electronic device is absolutely necessary. There are several products which are produced by this type of welding 2.2.4 ELECTRODE FORCE: Small and inexpensive machines utilize the force provided by the operator, transferred through suitable lever mechanisms. Usually a spring is employed to adjust the limit of force required when the spring is compressed to a set point a switch is operated to start the weld. Larger machines intended for heavy jobs and/or mass production utilizes compressed air for delivering the force required. A pneumatic cylinder is connected one of the welding electrodes and compressed air at a regulated pressure is introduced into the cylinder at the start of the weld. The pressure is removed after the weld is forged the switching of air being done by an electromagnetic valve. In some equipments different pressures are utilized during weld and forge. All the programmes is achieved through electronic controls.
  7. 7. 7 2.3 INSTALLATION OF SPOT WELDING MACHINE The original installation of a piece of a equipment has a large bearing on its subsequent operation and trouble free performance. This then deserves first preference in the overall subject of service. This is especially true for resistance welding machine because of the numerous utility services required electric power, often two one for motor power and the other for the welding power. In addition the welding machine may also require cooling water, air, hydraulic and sometimes even gas services. 2.3.1 PREPARATION FOR INSTALLATION Upon receipt the equipment should be checked thoroughly, with all packing lists, instructions, special tools, etc., properly accounted for. Also at the time of receipt, the machine, motor and control nameplates should be checked for proper service requirements 2.3.2 SETTING THE MACHINE Any machine that has mechanical motions, whether air hydraulic or electrical actuation should be anchored to a rigid stationary surface to prevent creeping or walking. The extent of this attachment to the floor or other surface will depend upon the size weight or operation of the equipment also on the type of building or floor. Pits are especially desirable for large splash welding machines to act as a receptable for the flash metal from the weld. In any case the machine should be leveled at its weight equally distributed on all legs or hold down member. Careless setting of the machine may cause undue strain on its members or binding of ways slides etc.
  8. 8. 8 2.3.3 SAFETY REQUIREMENTS Safety for the operating personnel and the elimination of fire hazards are of paramount importance. Welding equipment manufacturers provide their machine with majority safety features. Adequate guarding of gearing and other moving parts safe and approved electrical wiring as well as various types and kinds of safety controls such as simple palm buttons to prevent operating the machine without both hand on the buttons interlocks etc. Never attempt to override or evade these safety measures. In addition users may install additional safety precautions: area barricades exhaust systems, flash shield, etc. Rigorous maintenance of good housekeeping procedures should be exercised at all the times. 2.3.4 ELECTRICAL INSTALLATION With the machine set properly in position, electrical service is run through the weld controls to the welding transformers and to the motors when required. The electrical service to the motors will be the same as any normal electrical motor service which is adequately covered by city or national electric codes. The voltage rating of the cables used for welding transformer supply is important. Welding cable which is not marked or stamped 600v is not acceptable for resistance welding primary lines. The cable must a rating of 600v ac or above. When machine are installed in a temporary manner a proper electrical earth found must be provided to prevent electrically hazardous condition.
  9. 9. 9 2.3.5 SETUP OF EQUIPMENT With the equipment completely installed and with electrical power turned off, the installation personnel must: 1. Check motors for proper rotation. 2. Check all bolts , nuts etc., for tightness including electrical connections. 3. Check air water oil lines for possible leakages. 4. Make sure all cylinders function properly and see that hydraulic oil is adequate 5. If water saver valves are supplied the manual valve should be closed prior to turning on the power for the first time. Turn on electrical power. 6. Turn on hydraulically operated equipment. After checking pumps for proper rotation, it is necessary to exhaust all air from the system as any air at all, even a bubble, may cause faculty operation. 7. See that all guards and safety devices are in place. Operate properly, and adequately protect personnel from all moving parts of machine. 8. Set the weld control to the 'NO WELD' position. Set the 'SQUEEZE TIME', 'HOLD TIME' and 'COOL TIME' functions at maximum. If everything is functioning properly , the machine is ready for the operating department, which will set the machine and weld controls as required for the parts to be joined. Proper weld schedules may be defined by the machine manufacturer, to proceed with production.
  10. 10. 10 2.4 SERVICE REQUIREMENTS 2.4.1 Compressed air: Moisture free air at a recommended flow volume is required at a working pressure of 5.6kg/cm2.compressed air is useful for determining the reservoir size and flow rate. The values are calculated without considering the piston rod diameter varies for a given size of cylinder. The cylinder is supposed to work at 5.7 gauge pressure and perform 100 operations. 2.4.2 Cooling water: Clean residue water at minimum 2.1kg/cm2 pressure across machine and temperature below 30 degree Celsius at recommended flow rate is required. Each water cooling water circuit should have 5lpm flow rate hence cooling water rate required is (5*n) plum, where n is the number of cooling water circuits. 2.5 COOLING SYSTEM Resistance welding equipment develops very high secondary currents. this coupled with compact design makes the need for proper cooling mandatory. Water supply must be sufficient and at the proper temperature and pressure difference as recommended. If supply of city water does not meet specifications and if high in lime content , a re-circulating system using distilled water should be considered.
  11. 11. 11 Water circulation should be checked often to assure that all parts of the welder requiring cooling, receive water. Water flow should be checked at the outlet of the machine. If a water system becomes plugged or if flow gets restricted, an air line may be utilized to remove the obstruction. The usual procedure is to remove both inlet and drain lines from the machine and connect airline to the drain and force air in the direction opposite to water flow. When equipment is not to be used for a period of time, the water should be shut off by closing the water shut off valve. Hoses which have become worn, cracked or swollen should be replaced by new ones. when replacing be sure that the water circuit is not changed. Cooling the thyristor must always be considered important, Water should enter each tube at the bottom of the metal jacket and be discharged at the top. the jumper hose in series between two pads of the thyristor pair should be atleast 600mm long. 2.6 ELECTRODES AND DIES All the high current generated by the water secondary is concentrated at the contact points of the electrodes or dies. This current must be transmitted under pressure to the work piece to be welded. Therefore, electrodes must have good electrical and thermal conductivity and be able to withstand high pressures. It is important to maintain the cleanliness and smoothness of electrode contact points to assure consistent, good quality welds.
  12. 12. 12 Electrodes must be dressed whenever pitting, metal pickup or deformation is noticed. Metal pickup by electrodes must be immediately removed before next weld. An adequate supply of spare electrodes is recommended to reduce downtime the electrode dressing needed. Frequent cleaning of the electrode in the machine helps maintain weld quality and lengthen the electrode replacement. When dressing electrodes, always maintain the required contour. Electrodes often have a radius or shape to conform to the part being welded or to properly concentrate the weld current. A poorly dressed electrode directly contributes to poor weld quality. 2.7 PNEUMATIC SYSTEM Most machines will be entirely or partially air operated. For this reason basic knowledge of pneumatics is essential for efficient welder maintenance. The pneumatic system will usually consists of one or more of following items: 1. A filter(s) 2. A lubricator(s) 3. A regulator(s) 4. Valves 5. Cylinders 6. Intensifier (In Hydro-Pneumatic machines).
  13. 13. 13 All will require some type of maintenance to ensure proper and efficient operation. It is good practice to have spares for each of the above so that the equipment downtime can be minimized when extensive maintenance is required. 2.7.1 AIR LINE FILTER: A filter, if used, may be of the manual or automatic type. The manual type will require periodic removal of the trapped water and other foreign particles. Usually, this is done by opening a petcock at the bottom of the bowl and catching the liquid in a container. A filter with an automatic drain will empty itself as necessary. occasionally, it will be necessary to replace or disassemble and clean the filter. 2.7.2 AIR LINE REGULATOR: The air line regulator is used to reduce the supply line air pressure to the desired pressure for welding. This adjustment is an important part of every weld schedule. The regulator must be kept clean and operating accurately. Pressure losses and air leaks can result from dirty regulators. 2.7.3 AIR LINE LUBRICATOR: The lubricator should always contain oil at the specified level. The oil recommended is a light machinery oil and is usually specified as a type having a viscosity of 150 SSU at 100oF. The oil level should never be above the line indicated on the bowl. When filling, be sure that the air supply is turned off before removing the filter plug.
  14. 14. 14 All air systems require lubricating oil. The amount of the oil to be provided by the lubricator cannot be specified but a good ' rule of thumb ' is one drop for each three strokes of the most frequently operating cylinder. To adjust the lubricator, turn the adjustment screw as indicated. 2.7.4 AIR VALVES: Directional control valves are one of the most fundamental parts in hydraulic machinery as well and pneumatic machinery. They allow fluid flow into different paths from one or more sources. They usually consist of a spool inside a cylinder which is mechanically or electrically controlled. The movement of the spool restricts or permits the flow, thus it controls the fluid flow. Manually operated valves work with simple levers or paddles where the operator applies force to operate the valve. Spring force is sometimes used to recover the position of valve. Some manual valves utilize either a lever or an external pneumatic or hydraulic signal to return the spool. Solenoid operated are widely used in the hydraulics industry. These valves make use of electromechanical solenoids for sliding of the spool. Because simple application of electrical power provides control, these valves are used extensively. However, electrical solenoids cannot generate large forces unless supplied with large amounts of electrical power. Heat generation poses a threat to extended use of these valves when energized over time. Many have a limited duty cycle. This makes their direct acting use commonly limited to low actuating forces.
  15. 15. 15 2.7.5 AIR CYLINDERS: Pneumatic cylinders (sometimes known as air cylinders) are mechanical devices which use the power of compressed gas to produce a force in a reciprocating linear motion. Pneumatic cylinders use the stored potential energy of a compressed air and convert it into kinetic energy as the air expands in an attempt to reach atmospheric pressure. This air expansion forces a piston to move in the desired direction. The piston is a disc or cylinder, and the piston rod transfers the force it develops to the object to be moved. They prefer to use pneumatics sometime because they are quieter, cleaner, and do not require large amounts of space for fluid storage. Because the operating fluid is a gas, leakage from a pneumatic cylinder will not drip out and contaminate the surroundings, making pneumatics more desirable where cleanliness is a requirement. AFTER ASSURING ALL SERVICE CONNECTIONS ARE TIGHT: 1) Switch on power supply (before switching on power check up insulation resistance of power line and transformer, it should be more than two mega ohms). This should be done by experienced supervisor. In case of machine with thyristor contactor insulation resistance may be very low due to water in thyristor 2) Open air supply set welding pressure to the recommended value. 3) Check the operation of the machine without applying the welding current.
  16. 16. 16 4) Ensure that water is circulating freely and at recommended flow rate and in proper direction 5) The machine is now ready to make test weld. 2.8 CALCULATION OF DUTY CYCLES AT OTHER LOADS: Duty cycle is defined as the ratio of time during which the output side of the transformer is loaded to the integrating period Integrating period is the sum of the load and no-load period during which the equipment is operated for a particular application. Standard integrating period is 60secs. The electrical data under short cut conditions have been compiled from the average of test measurements taken on actual machine. Such tests are made in accordance of IS: 4804. These data under short circuit conditions are sufficiently accurate to give the maximum power requirements. Percent duty cycle at any kva demand can be calculated as follows: Pc = rating 50perc duty cycle(KVA) PX = kva demand at other duty cycle(KVA) X = other duty cycle in percent(%)
  17. 17. 17 Table 2.1 RECOMMENDATIONS FOR MILD STEEL SHEETS When determining per cent duty cycle it must be remembered that the basic kva rating of the welding transformer at 50 per duty cycle only applies when using the maximum secondary voltage available at that this kva rating varies directly with secondary voltage. Thickness “t” of the thinnest member (mm) Minimum contacting overlap (mm) Electrode tip diameter “d” in (mm) Weld quality 0.250 08 3.0 Best satisfactory 0.500 10 3.0 Best satisfactory 0.710 10 4.5 Best satisfactory 1.000 12 5.0 Best satisfactory 1.250 15 6.0 Best satisfactory 1.600 16 6.0 Best satisfactory 2.000 10 7.0 Best satisfactory 2.500 20 8.0 Best satisfactory
  18. 18. 18 2.9 SPOT WELDING PARAMETERS Spot welding parameters include:  Electrode force  Diameter of the electrode contact surface  Squeeze time  Weld time  Hold time  Weld current  Off time The determination of appropriate welding parameters for spot welding is a very complex issue. A small change of one parameter will affect all the other parameters. This, and the fact that the contact surface of the electrode is gradually increasing, makes it difficult to design a welding parameter table, which shows the optimum welding parameters for different circumstances. 2.9.1 ELECTRODE FORCE The purpose of the electrode force is to squeeze the metal sheets to be joined together. This requires a large electrode force because else the weld quality will not be good enough. However, the force must not be to large as it might cause other problems. When the electrode force is increased the heat energy will decrease. This means that the higher electrode force requires a higher weld current. When weld current becomes to high spatter will occur between electrodes and sheets. This will cause the electrodes to get stuck to the sheet.
  19. 19. 19 An adequate target value for the electrode force is 90 N per mm2. One problem, though, is that the size of the contact surface will increase during welding. To keep the same conditions during the hole welding process, the electrode force needs to be gradually increased. As it is rather difficult to change the electrode force in the same rate as the electrodes are "mushroomed", usually an average value is chosen. 2.9.2 DIAMETER OF THE ELECTRODE CONTACT SURFACE One general criterion of resistance spot-welding is that the weld shall have a nugget diameter of 5*t1/2, “t” being the thickness of the steel sheet. Thus, a spot weld made in two sheets, each 1 mm in thickness, would generate a nugget 5 mm in diameter according to the 5*t½-rule. Diameter of the electrode contact surface should be slightly larger than the nugget diameter. For example, spot welding two sheets of 1 mm thickness would require an electrode with a contact diameter of 6 mm. In practice, an electrode with a contact diameter of 6 mm is standard for sheet thickness of 0.5 to 1.25 mm. This contact diameter of 6 mm conforms to the ISO standard for new electrodes. 2.9.3 SQUEEZE TIME Squeeze Time is the time interval between the initial application of the electrode force on the work and the first application of current. Squeeze time is necessary to delay the weld current until the electrode force has attained the desired level. 2.9.4 WELD TIME Weld time is the time during which welding current is applied to the metal sheets. The weld time is measured and adjusted in cycles of line voltage as are all timing functions. One cycle is 1/50 of a second in a 50 Hz power system. (When the weld
  20. 20. 20 time is taken from American literature, the number of cycles has to be reduced due to the higher frequency (60Hz) that is used in the USA.) As the weld time is, more or less, related to what is required for the weld spot, it is difficult to give an exact value of the optimum weld time. For instance:  Weld time should be as short as possible.  The weld current should give the best weld quality as possible.  The weld parameters should be chosen to give as little wearing of the electrodes as possible. (Often this means a short weld time.)  The weld time shall cause the nugget diameter to be big when welding thick sheets.  The weld time might have to be adjusted to fit the welding equipment in case it does not fulfil the requirements for the weld current and the electrode force. (This means that a longer weld time may be needed.)  The weld time shall cause the indentation due to the electrode to be as small as possible. (This is achieved by using a short weld time.) When welding sheets with a thickness greater than 2 mm it might be appropriate to divide the weld time into a number of impulses to avoid the heat energy to increase. This method will give good-looking spot welds but the strength of the weld might be poor. By multiplying the thickness of the sheet by ten, a good target value for the weld time can be reached. When welding two sheets with the thickness 1 mm each, an appropriate weld time is 10 periods (50Hz).
  21. 21. 21 2.9.5 HOLD TIME (COOLING-TIME) Hold time is the time, after the welding, when the electrodes are still applied to the sheet to chill the weld. Considered from a welding technical point of view, the hold time is the most interesting welding parameter. Hold time is necessary to allow the weld nugget to solidify before releasing the welded parts, but it must not be to long as this may cause the heat in the weld spot to spread to the electrode and heat it. The electrode will then get more exposed to wear. Further, if the hold time is to long and the carbon content of the material is high (more than 0.1%), there is a risk the weld will become brittle. When welding galvanized carbon steel a longer hold time is recommended. 2.9.6 WELD CURRENT The weld current is the current in the welding circuit during the making of a weld. The amount of weld current is controlled by two things; first, the setting of the transformer tap switch determines the maximum amount of weld current available; second the percent of current control determines the percent of the available current to be used for making the weld. Low percent current settings are not normally recommended as this may impair the quality of the weld. Adjust the tap switch so that proper welding current can be obtained with the percent current set between seventy and ninety percent. The weld current should be kept as low as possible. When determining the current to be used, the current is gradually increased until weld spatter occurs between the metal sheets. This indicates that the correct weld current has been reached.
  22. 22. 22 2.9.7 OFF TIME Begins automatically after Hold Time. The time allotted for the Movable Electrode to remain retracted. Once the time has elapsed, the Welding Control automatically reinitiates the Weld Schedule. This timing function is only used when the "Repeat Switch" is ON. Programmable in Cycles. (1 Cycle = 1/60 of a second) 2.10 WELD TESTING: The purpose of quality control is to assure duplication of welding results under controlled combination. Without quality control, poor welds may occur for a long period of time before detected. Defects undetected may result in scrap , re-work, lost production and failure of final product. Sizes of samplings can be statistically established to yield a very accurate control over the process. The number of welds per hour will usually govern the frequency of the sample selection and the size of the sampling. Occasionally, a process will require non-destructive testing of 100% of the welds. The type of test used will depend on the type of welding process to be tested. A specific type test is recommended for each welding technique. Good control over the welding process can usually be achieved by making regular tests on the weld and maintaining the electrodes in proper condition. 2.10.1 TENSION SHEAR TEST: Perhaps a common test of a weld is the Tension Shear Test. In this test the specimen is pulled to destruction in a standard tension testing machine. The size and shape of this specimen is very important. Each test specimen should have its failure point recorded.
  23. 23. 23 2.10.2 OTHER TESTS: Other weld tests are as follows:- 1. Tension Test a) Cross tension test. b) U-tension test 2. Impact test a) Shear impact test. b) Drop impact test. 3. Fatigue test 4. Microtech test 5. Radiographic test 6. Twist test 7. Hardness test 8. Pillow test Most satisfactory tests are of a destruction type. For very expensive products, a destruction test is usually not economical or practical. Usually, some type of X-ray is adopted for these products and only qualified are permitted to judge result. 2.10.3 VISUAL INSPECTION: Surface conditions often indicate weld quality. Some of the more undesirable common spot, seam and projection weld surface conditions and their effects are listed below;
  24. 24. 24 Table 2.2 SURFACE CONDITIONS OF SPOT WELDS TYPE CAUSE EFFECT Deep electrode indentation Improperly dressed electrode face; lack of control of electrode force; high contactresistance. Loss of weld strength due to reduction of metal thickness at periphery of weld area bad appearance Surface fusion Scaly or dirty metal; low electrode force; misalignment of work, high welding current, electrodes improperly dressed. Under size welds due to heavy expulsion of molten metal; large cavity in weld zone extending through to the surface increased costof removing burrs from surface of work. Irregularly shaped weld Misalignment of work in electrodes; bad electrode or improper electrode bearing on radius of flange. Bad appearance; reduced corrosionresistance; reduced weld strength if molten metal is expelled. Cracks, deep cavities or pin holes Removing electrode force before thoroughly quenching weld to a temp well below visible red heat; excessive heat generation resulting in expulsion of metal Reduction of fatigue strength if weld is in a tension member or if crack of imperfection extends into periphery of weld area corrosive in recess of cavity
  25. 25. 25 CHAPTER 3 PROJECT DESCRIPTION OUR AREA OF CONCERN: Spotwelding of stiffeners on Power Operated Doors. USE OF STIFFENERS: To prevent bending of Power Operated Doors 3.1 CURRENT PROCESS: • Spotwelding is done between the stiffener and the door (both 1mm thickness) with the help of a single electrode (copper) • Total number of spots onthe sides of the stiffener are 1. Vertical Stiffener(both sides) = 16 spots(8+8) 2. Horizontal top Stiffener(both sides) = 10 spots (5+5) 3. Horizontal bottomStiffener(one side) = 5 spots
  26. 26. 26 3.2 USAGE OF SPOT WELDING IN THE COMPANY TO WELD S.NO THICKNESS CURRENT(amps) 1 3.0mm + nut (mild steel) 75/99 2 1.0mm + 1.0mm/0.6mm(mild steel) 40/60 3 1.2mm + 2.0/3.0mm(mild steel) 60/90 4 2.0mm + 2.0 mm (mild steel) 80/90 5 1.0mm + 1.0mm (galvanized iron) 90/100 6 1.0mm + 2.0mm (galvanized iron) 90/100 Table 3.1 Usage of Spot Welding in the company 3.3 STIFFENERSUSED: S.NO TYPES WIDTH(mm) THICKNESS 1 Horizontal top stiffener 415 1 mm 2 Horizontal bottomstiffener 420 1 mm 3 Vertical stiffener 1840 1 mm Table 3.2 Stiffeners Used
  27. 27. 27 Fig 3.1 Design of an electrode
  28. 28. 28 3.4 ELECTRODE CHARACTERISTICS 3.4.1 CHROMIUM ZIRCONIUM COPPER Many applications demands Copper to have higher mechanical properties and to be capable of use at elevated operating temperatures while still retaining the good conductivity for which it is selected in the first place. The high-copper alloy family includes Beryllium Coppers, 2% Beryllium Copper, Chromium Coppers, Zirconium Copper , Chromium Zirconium Copper and Nickel Silicon Chromium Copper. The Chromium Zirconium Copper is essentially Chromium Copper alloys which has a small addition of Zirconium. The addition of Zirconium inhibits chemical reaction of Copper at elevated temperatures. It also helps to retain the physical properties at elevated temperatures. Also it marginally increases annealing temperature. Chromium Zirconium Coppers are used widely in areas where high electrical and thermal conductivity are required combined with good mechanical properties. Uses include Resistance Welding Machine Electrodes, Seam Welding Wheels, Spot Welding Tips, Flash Butt Welding Electrodes, Anvil Contact Bars, Electrical Switch Gear Contacts & Terminals, Electrode Holders, Cable Connectors, Current Carrying Arms and Shafts, Circuit Breaker Parts, Heat Sinks, Short Circuit Rings, MIG welding contact tubes and many other applications where Copper would normally be the ideal choice for High Conductivity but is just not Strong enough. C18150 Chromium Zirconium Copper is used extensively for cap style resistance welding electrodes. Evidence suggests that it can provide less sticking and resist deformation longer than its chromium copper counterpart in some specific situations.
  29. 29. 29 C18150 (Chromium Zirconium Copper) Chemical Composition (%max., unless shown as range or min.) Cu (1) Cr Zr Min./Max. Rem. .50-1.5 .05-.25 Nominal 98.9 1.0 .10 Table 3.3 Chemical composition of C18150 (1) Cu value includes Ag. Note: Cu + Sum of Named Elements, 99.7% min. Table 3.4 Physical Properties 3.4.2 Typical Uses Consumer: Pencil-type & Light Soldering Guns: Tips, Rod Extensions Electrical: Resistance Welding Electrodes Industrial: Welding Electrodes, Welding Wheels, Tips and Rod Extensions Physical Properties Metric Melting Point - Liquidus 1080 C Melting Point - Solidus 1070 C Density 8.89 gm/cm3 @ 20 C Specific Gravity 8.89 Electrical Conductivity 0.464 Mega Siemens/cm @ 20 C Thermal Conductivity 323.9 W/m · o K at 20 C Coefficient of Thermal Expansion 16.45 ·10-6 per o C (20-100 C) Modules of Elasticity in Tension 117200 MPa
  30. 30. 30 WELDING ELECTRODE The figure 3.2 represents a 3D view of a single electrode. This electrode is placed within the tool holder. The electrode used here is Chromium Zirconium Copper material. Fig 3.2 Welding electrode in current process
  31. 31. 31 DOOR BODY WITH STIFFENER The figure 3.3 represents the 3D view of doorbodywith stiffener. The stiffener is used mainly to prevent the doorfrom bending. Fig 3.3 Door body with Stiffener
  32. 32. 32 INFERENCE: 1. The above graph represents number of doors spotwelded in a day. 2. It is noticed that an average of 55 doors are welded in a day. 3. It takes about 3 minutes for spotwelding a stiffener on door using single electrode.
  33. 33. 33 CHAPTER 4 METHODOLOGY ADOPTED 4.1 ALTERNATIVE IMPROVEMENT FOUND OUT PRACTICALLY • Changing the toolholder in such a way that two electrodes of coppercan be fitted to it. • To design a template to make sure that the two electrodes can be used in a single spotoperation. • To practice and study about an alternative to spotwelding i.e clinching process ( optional) • To change the bed of the machine accordingly. 4.2 Pictorial Representation Of Modified Working Process Our aim is develop a tool holder containing two electrodes. Fig 4.1 Pictorial Representation Of Modified Working Process
  34. 34. 34 4.3 TO DESIGN A TOOL HOLDER Fig 4.2 Design of a Tool holder
  35. 35. 35 TOOL HOLDER The figure 4.3 represents the 3D view of a tool holder connected to inlet and outlet pipe. Inlet and outlet pipe is used in transportation of the coolant. Fig 4.3 Tool holder
  36. 36. 36 Fig 4.4 Design of a tool with electrode
  37. 37. 37 TOOL HOLDER WITH ELECTRODE The figure 4.5 represents the 3D view of toolholder containing the electrode. This model is developed to reduce the time consumption by 50%. Fig 4.5 Tool holder with electrode
  38. 38. 38 The figure 4.6 represents the three dimensional view of tool holder placed on the stiffener. The tool holder makes sure that two spots are welded in a single press. Fig 4.6 Tool holder placed on stiffener The figure 4.7 represents the front view of the tool holder placed on the stiffener. The distance of separation between two electrodes is 80mm. Fig 4.7 Front view
  39. 39. 39 4.4 TO DESIGN A TEMPLATE The figure 4.8 represents the different views of the designed template. Fig 4.8 Design of a Template
  40. 40. 40 TEMPLATE The figure 4.9 represents the 3D view of the template. The template is designed in such a way that it can be used freely by a lay man with minimum effort. Fig 4.9 Template
  41. 41. 41 WITH TEMPLATE The figure 4.10 represents the 3D view of template placed in the doorbody. The template makes sure that the stiffener placed within the doorbodyis aligned properly with it. Fig 4.10 Usage of template
  42. 42. 42 CHAPTER 5 RESULT ANALYSIS 5.1 CALCULATIONS: (a) To determine electrode force: ELECTRODEFORCE= 6000 x (T1 +T2) 6000 = constant T1 = thickness of first sheet T2 = thickness of second sheet T1=T2= 0.1cm. 6000 x (0.1 + 0.1) = 1200lbs 600 = necessary electrode force in lbs. (b) To determine weld time: WELD TIME = 100 x (T1 +T2) 100 = constant 100 x (0.1 + 0.1) = 20 20 = necessary weld time in cycles
  43. 43. 43 (c) To determine weld current: WELD CURRENT = 100,000 x(T1 +T2) 100,000 = constant T1 = thickness of first sheet T2 = thickness of second sheet 100,000 x (0.1+0.1) = 20,000 20,000 = necessary secondary current in amperes. (d) To determine tip face diameter TIP FACE DIAMETER = 0.1 + (T1 +T2) 0.1 = constant T1 = thickness of first sheet T2 = thickness of second sheet .1 + (0.1+0.1) = 0.3 .3 = tip face diameter in inches
  44. 44. 44 5.2 CURRENT DISTRIBUTION BETWEEN 2 ELECTRODES: The Current Divider Rule(CDR) is useful in determining the current flow through one branch of a parallel circuit. Two resistors in parallel. For only two resistors in parallel: I1 = (RT/R1) * IT Where RT is the total resistance of the parallel branches under examination. (1/RT)= (1/R1) + (1/R2) RT = (R1R2) / (R1+R2) On substituting RT, I1 = [R2/(R1+R2)] * IT In this case, R1 = R2 , Since two electrodes are of same material. I1 = [R2/2R2] * IT Cancelling R2, we get , I1 = IT/2 Total current flowing through the electrode = 100 amps. Therefore, I1 = 100/2 , I1 = 50 amps. So, the current flowing through each electrode is 50 amps. If current enters a parallel network with a number of equal resistors, the current will split equally between the resistors.
  45. 45. 45 5.3 ANALYSIS OF DESIGN The design represents the 3D view of toolholder with electrode. This design is analyzed to make sure that there is tool wear. Fig 5.1 Tool holder imported into ANSYS
  46. 46. 46 Meshing: The design represents the tool holder with electrode being meshed. Meshing is done to make sure that the whole design is constrained with required stress. Fig 5.2 Meshing
  47. 47. 47 The design is analyzed and following inferences are made: 1) The blue and green color shown in the tool holder containing the electrode represents that the design is safe and there is no tool wear. Fig 5.3 Result analysis of tool holder
  48. 48. 48 CHAPTER 6 CONCLUSION The project has been designed in such a way that it suits to the working process prevailing in the company. We have also analysed the strength of the material using the necessary software. We have ensured that the design introduced make sure that the time taken is reduced by fifty percent. Efforts to develop a template for efficient working of a lay man have been successfully developed. We hope that the project will be useful in the field of engineering.
  49. 49. 49 CHAPTER 7 FUTURE WORK 1. Instead of using holder containing two electrodes efforts can be made in further developing the tool holder in such a way that more than two electrodes can be used at a time. 2. Flexible spot welding is a type of welding in which welding can be done by free movement. Efforts can be done by implementing this type of welding which is easy to use as efficient. 3. Efforts can be done by studying about clinching process which is nothing but using adhesives for joining to metals. This reduces the effect of heat.
  50. 50. 50 CHAPTER 8 REFERENCES 1. wikipedia.org 2. Design of Jigs And Fixtures- Edward G Hoffman 3. www.millerwelds.com 4. www.spotweldequip.com 5. www.robot-welding.com 6. www.mipalloy.com 7. www.wisc-online.com