WHAT IS WELDING?

Welding is the process of joining metas

FILLER MATERIAL

HEAT

MELTING OF METAL

JOINING OF METAL

1. 2 3

E. CURRENT GAS CHEMICAL REACTION

NO FILLER MATERIAL

HOW MANY TYPES WELDING ARE THERE?

1. 2. 3. 4. 5. ARC WELDING RESISTANCE WELDING GAS WELDING LASER BEAM WELDING THERMIT WELDING ETC.

TYPES OF WELDING POWER SUPPLIES

1.A.C Welding power supply 2.Capacitor-Discharge power supply 3.Transistor power supply 4.Frequency Inverter power supply 5.A.C Inverter welding power supply

TYPES OF RESISTANCE WELDING

1. SPOT WELDING 2. PROJECTION WELDING 3. FLASH WELDING 4. SEAM WELDING 5. BUTT WELDING

WHAT IS RESISTANCE WELDING?

In this process, an electrical current flows through resistive circuit to generate enough heat between two pieces of sheet metal so that the metal reaches molten stage.The resistance to the flow of current is provided by the work piece.The maximum heat is generated at the point of maximum resistance.

Principles of Resistance welding

A spot welding is made by pressing two or more overlapping piece together while an electrical current is passed through a localized contact area. The heat in the welding zone should be generated rapidly so that only minimum heat is dissipated by conduction to cooler area. The current is high but the voltage is very low and there is no danger of an electric shock. Resistance Welding is suitable for low cost and mass production and is widely used in the automotive and electronics parts industries.

MAJOR ELEMENTS OF SPOT WELDING

* WELD CURRENT * WELD TIME * PRESSURE * RESISTANCE * ELECTRODE SHAPE (CURRENT DENSITY)

Current
Is the rate of flow of a given no of electrons through a particular cross section of a conductor The unit of current is amps ( A )

WELD TIME CONTROL FOR SPOT WELDING

1 . SQUEEZE TIME TIME REQUIRED FOR THE ELECTRODE TO CLOSE ON METAL AND APPLY PROPER PRESSURE. IT VARIES WITH THE GAP BETWEEN THE ELECTRODES . 2. UPSLOPE TIME TIME TAKEN FOR THE CURRENT TO REACH FROM ZERO THE PEAK VALUE. 3. WELD TIME TIME REQUIRED FOR PEAK CURRENT TO FLOW AND HEAT THE METAL 4. DOWN SLOPE TIME TIME TAKEN FOR THE CURRENT TO CUT OFF I.e, FROM PEAK TO ZERO

WELD TIME CONTROL FOR SPOT WELDING

5. HOLD TIME TIME TAKEN BY THE ELECTRODES TO HOLD THE SHEETS TOGETHER AFTER THE CURRENT FLOW STOPS. PRESSURE STILL APPLIED TO ALLOW THE MOLTEN METAL TO SOLIDIFY. 6. OFF TIME IT IS THE TIME BETWEEN THE END OF ONE SPOT SEQUENCE TO START OF NEXT SPOT SEQUENCE

CURRENT

WELD TIME CONTROL FOR SPOT WELDING

SQEEZE UP SLOPE WELD

DN SLOPE TIME

HOLD

OFF

TIMER CONTROLLER

WELDING CURRENT FEATURES AND MEASUREMENT

WHY CURRENT CAN NOT MEASURE WITH AMETER In spot welding ,large current flows for very short time (0.02 sec -0.5 sec ), AMETER cannot respond so quickly. HOW TO MEASURE THE CURRENT In spot welding current is measured with Toroidal coil When high current flows it generates magnetic field and magnetic flux interlink with the coil generate Electromotive force in proportion to rate of change of current to time V = K di/dt K is constant

Flux

Coil i

Coil output V is in proportion to the coil

Current i Electromoti ve force V

area and nos. of turns This type of sensor can measure any large current in differential value To get absolute value it is interlink with electronic circuit.

How to check current?

Toroidal coil

Weld checker

Resistance welding
Relation between Current and time A :- WILL HAVE Current A B C Time
A: Strong current and short time C: Small Current and long time B:Medium current and medium time LESS WORK DISTORTION LESS OXIDATION GOOD WELDABILITY

Change in Current Density

Effect of Pressure
*Electrode brings sheet into intimate contact thus effect contact resistance *Ensures completion of electric circuit *Ensures heat dissipation in weld zone and prevents surface fusion. *If low: Surface burning and pitting of electrode *If High: More current is required. *Measure the pressure between electrodes with calibrated pressure gauge only.

PROPERTIES AND FUNCTION OF ELECTRODES

REQUIREMENT OF ELECTRODES
1. 2. 3. 4. 5. ELECTRODES CENTERED AND FIXED SECURILY TO ELECRODES HOLDER FREE MOVEMENT ALLOWING FOR CONSITTENT PRESSURE REPEATABILITY QUICK RESPONSE OF THE ELECTRODE ARM ALLOWS FOR PRESSURE TO BE MAINTAINED DURING WELDING ELECRODES MUST HAVE LOW NATURAL RESITANCE, HIGH HEAT CONDUCTIVITY AND MAINTAINED HARDNESS EVEN AT HIGH TEMPERATURES HIGH CONDUCTIVITY ELECTRODES ARE USED FOR LOW CONDUCTIVE MATERIALS AND LOW CONDUCTIVE ELECTRODES BEING USED FOR HIGH CONDUCTIVE MATERIAL THEY SUPPLY THE SUFFICIENT WELDING CURRENT TO THE WORK ( GOOD ELECTRICAL CONDUCTOR ) THEY HELP DISSIPATE THE THE HEAT FROM THE WELD ZONE (HIGH THERMAL CONDUCTIVITY) THEY TRANSMIT THE REQD. FORCE TO THE WORK (GOOD MECHANICAL STRENGTH ) AS TIP OF THE ELECRODE DETERMINE THE WELDING AREA ON THE WORK PIECE IT IS NECESSARY TO MAINTAIN THE CONTANT SHAPE FREE FROM WEAR MANY TYPES OF SHAPES ARE USED IN ELECTRODES

FUNCTIONS OF ELECTRODES
1. 2. 3. 1. 2.

SHAPE OF ELECTRODES

F - TYPES

P - TYPES

R - TYPES

CF - TYPES

CR - TYPES

THE MOST COMMONLY USED ELECTRODES SHAPES ARE P AND CR TYPES.

Electrode tip length

The endurance life of electrode tips depends from the length of the copper part of the electrode tip besides the material.

Resistance welding
Relation between Current and Pressure No Nugget
Large Nugget Dia (Strength) Small

Splash
B - will have Good Weld Less Spatters Optimum Nugget Dia

Explosion Current

A:High Current and High Pressure B:Medium current and medium Pressure C: Small Current and High Pressure

How to check pressure?

Pressure gauge

Electrode

Resistance
Is the internal opposition a material offers to the flow of electrical current. The unit is Ohms (:)
( when very small value is referred, resistance is often represented using micro ( Q:) = 10-6 Ohms

The Magnitude depends on the material and varies as the length changes, but inversely proportional to the cross sectional area of the conductor. R=V( L/A)
V=resistivity , L= Length, A= Cross section

Resistance also changes as the temperature of the material changes.

RT= R20 (1+E(T-20)) RT= Resistance at T0C, R20= Resistance at 200C E=Temperature coefficient of the material

Contact Resistance

Impedence
When an alternating current passes through a conductor, an inductive reactance will oppose the flow of current. ( X) The combination of the inductance and the resistance is called the impedence ( Z ) Z= (R2 + X2 )1/2

Generation of heat
Heat energy is generated when ever electrical current is passed through an electrical resistance. Q=I2Rt
Q= watt-seconds or joules I=Current in amperes R=Resistance in Ohms t= Time in cycles ( 1 cycle = 20 milli sec )

Temperature gradient

Temperature gradient

Change in Contact Resistance during Welding

Heat Zone

PSW WELDING SYSTEM

Welding gun Transformer Controller ELCB

ELCB

TYPES OF SPOT WELDING GUNS

1. Portable spot welding (PSW ) gun 2. IT spot welding gun 3. SSW(Stationary Spot Welder) 4. Servo gun 5. Fixture gun

PSW (X TYPE GUN)

Gun Body

PARAMETER FOR SELECTION OF TIPS

Tip Dia Sheet thickness 12 0.4 ~0.8 13 16 0.4 ~ 0.8 0.6 ~ 2.0

Conditions Used in PSW and SSW Used generally in Cap tip in PSW Used both as Cap and normal in PSW &SSW

Tip Material should be ( CRM 16-CuCr 1Zr) Cr 0.4 - 1 % , Zr 0.02 -0.1 % & Cu - Bal. Properties Conductivity:- 75 ~ 80 Hardness :- 130~170 Brinel

PROPERTIES AND APPLICATIONS OF ELECTRODES

ELECTRODES MATERIAL Copper Chrome copper NBC alloys Beryllium copper Tungsten silver Tungsten copper Tungsten Molybdenum Cu CuCr Ni Be Cu Cu Be AgW CuW W Mo CONDUCTANCE ( IACS % ) 97 75-80 55 50 40-45 30-35 29 30 APPLICATIONS Few applications but good for F types of electrodes Generally used for Ferrous materials and stainless steel Good for ferrous materials , SUS and Nickel Good for SUS and ferrous material High hardness and less abrasion High hardness and less abrasion Good for Copper and Brass Same as tungsten electrodes

Electrode cooling

Why cooling?
The electrodes with its tips are tightly on a work piece made of steel that temperature must be that high to melt its material. The electrodes must be cooled for protection and endurance live purposes Increases the temperature of the secondary circuit from 20C up to 80C, in that case increases the resistance in the secondary circuit. Copper parts increase their resistance by 6 x 4% = 24%, brass parts by 6 x 1,5% = 9%. It can be assumed that the resistances of secondary circuits are dominated 90% by copper parts. In the case the welding current in the secondary circuit at a temperature of 20Current is 10 kA then

Does the temperature of the secondary circuit rise up to 80C:

The welding current falls down to 8 kA. To keep the welding current constant, the secondary circuit must be cooled. With rising temperature the electrodes get less hard. The danger of deformation occurs and the contacting areas of the tips get larger. Therefore the welding current density reduces and the welding spot quality gets worse. Well cooling makes the endurance life of the electrode tips longer. Good cooling of the secondary circuit secures a constant welding current and a constant current density!

EFFECT OF WATER COOLING

Water Flow Rate in PSW Should be 20~25 Ltr/Min Water temp for circulation should be 25 deg C

Less Water flow result in

High consumption of Tip Bigger nugget Dia Low strength of Welds

Preparation for MS Spot welding

*Material to be welded should be free from Dust, Rust, Paint, Grease & Acid substance *The Electrode should be of RWMA CLASS - II (Conductance 75% & Hardness 130 ~170 Brinnel *Min Pitch is to be maintained as per table to avoid the *Shunting of current due to adjacent spots.It can also be corrected by increasing current with due consideration of shunting current * If the lap between two plates goes less , it will reduce the strength and lead to undulation and Distortion *In case of welding 2 sheets of different thickness ,condition of thinner sheet is applicable.However in principle ratio should be kept max between 1:3. In case of three or more sheet,Total sheet thickness should not exceed the 4 times of thinner sheet. Condition for mean value is applicable

USE OF COATED SHEET Flange width Welding condition has to be raised for welding coated sheets. As the heat disspating capacity of dia 13 tip is less as compared to dai 16 tip ( volume ratio is 1:1.6) , life of dia 13 tip will be reduced requiring large no. of changeovers as comapred to dia 16 tip and also it needs more time to weld same quantity of spots as compared to dia 16 tip as shown in the table . There is a difference of 1:1.6 in the volume ratio of the tips and this controls the weldability greatly For instance, when you weld the steel board of t0.7 mm

Uncoated 2 sheets Dia 16 tip Dia 13 tip 3 sheets Dia 16 tip Dia 13 tip 7.8KA, 14 cycles 54 spots/min or less 21spots/min or less 8.2 KA, 14 cycles 49 spots/min or less 19 spots/min or less

Coated 9.2 KA, 14 cycles 39 spots/min or less 15 spots/min or less 9.7 KA, 14 cycles 35 spots/min or less 13 spots/min or less

Lets take the case of YD2 weldingline There are 1805 respot ( about 70% of total spots) and on an average operator can weld about 25spots/min and the tact time is 2.55 min Incase of Dia 16 tip, 29 welding guns will be needed whereas in case of dia 13 tip, 48 welding guns will be needed thus requiring more investment and space ( asuming 2 nos. coated sheets).

Direction of Flange As for zinc that is the surface treatment material of the coated sheet, the melting point is relieved by the dispersion of low straightening spatter. As a result, it becomes a pockmarked pattern on externals and the decrease in the quality is caused in the part where zinc is relieved. Moreover, the steel sheet might get transformed by receiving heat from spatter from the short distance and causes irregularity. It doesn't completely return to the original shape though finish is required in both cases. Moreover, the plated layer given with great pains as the result is peeled off. In the design of the body, consideration where the skin is not located in the welding flange extension is necessary.

USE OF SUPER DEEP DRAWING MATERIAL Decrease in strength Incase of deep drawing material like SPCX, ultimate tensile strength is less as compared to the normal material like SPCC. Due to heat affected zone, strength falls further resulting in degradation of strength by about 15% as comapred to normal steel. Minimum welding pitch ; Standard for minimum welding pitch is 20mm In case the spot pitch is reduced more than this, the strength of each spot will decrease so this minimum pitch has to be secured. Incase more spots are needed to secure proper strength, spots should be staggered as shown below As staggering of spots require more flange width, this has to be checked in the drawing.

20

REFERENCE FOR MS SPOT WELDING (A-class )

Thic knes s rank Weld Time (cyc) Weld Curre nt (kA) Electrod e Force (kN) Thic knes s rank Wel d Tim e (cyc) Weld Curre nt (kA) Electrod e Force (kN) Thi ckn ess ran k Wel d Tim e (cyc) Weld Curren t (kA) Electrode Force (kN) Thickness rank Wel d Tim e (cyc) Weld Curre nt (kA) Electrode Force (kN)

11 12 13 14 22 23 24 33 34 44

13 13 13 13 15 15 15 17 17 17

7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 8.0

1.96 1.96 1.96 1.96 1.96 1.96 1.96 1.96 1.96 1.96

111 112 113 114 121 122 123 124 131 132 133 134 141 142 143 144

13 13 13 13 13 15 15 17 13 15 17 17 13 15 17 21

7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 8.0

1.96 1.96 1.96 1.96 1.96 1.96 1.96 1.96 1.96 1.96 1.96 1.96 1.96 1.96 1.96 2.94

212 213 214 222 223 224 232 233 234 242 243 244

13 13 13 15 17 17 17 17 17 17 17 21

7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 8.0 7.5 8.0 8.0

1.96 1.96 1.96 1.96 1.96 1.96 1.96 1.96 2.94 1.96 2.94 2.94

313 314 323 324 333 334 343 344 414 424 434 444

13 15 17 17 17 17 17 17 15 17 17 21

7.5 8.0 7.5 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.5 8.5

1.96 2.94 1.96 2.94 2.94 2.94 2.94 2.94 2.94 2.94 2.94 2.94

Only General sheet is applied.

Thickness rank table Thickness(mm) Rank 0.9 1 0.9 1.2 2 1.2 1.6 3 1.6 4

REFERENCE FOR MS SPOT WELDING (A-class )

SHEET THICKNESS TIP DIA Max 'd' mm 0.4 0.5 0.6 0.8 1 1.2 1.6 1.8 2 2.3 3.2 mm 3.2 4.8 4.8 4.8 6.4 6.4 6.4 8 8 8 8 MIN 'D mm 10 10 10 10 13 13 13 16 16 16 16 mm 8 9 10 12 18 20 27 31 35 40 50 mm 10 11 11 11 12 14 16 17 18 20 22 PITCH MIN LAP MIN BEST CONDITION (A - CLASS )
WELD TIP CURRENT TIME PRESSU RE cycle Kgf Amprs NUGGET DIA SHEAR STRENGTH

5 6 7 8 10 12 16 18 20 24 32

115 135 150 190 225 270 360 410 470 580 820

5200 6000 6600 7800 8800 9800 11500 12500 13300 15000 17400

mm 4 4.3 4.7 5.3 5.8 6.2 6.9 7.4 7.9 8.6 10.3

Kgf 180 240 300 440 610 780 1060 1300 1450 1850 3100

* The welding Speed is high * The dispersion of welding strength is small *Welding machine of high capacity is required *Welding is done for particular stength

lap

REFERENCE FOR MS SPOT WELDING ( B & C Class )

SHEET TIP DIA THICKN Max MIN ESS 'd' 'D mm 0.4 0.5 0.6 0.8 1 1.2 1.6 1.8 2 2.3 3.2 mm 3.2 4.8 4.8 4.8 6.4 6.4 6.4 8 8 8 8 mm 10 10 10 10 13 13 13 16 16 16 16 PITCH MIN LAP MIN

B - CLASS
WELD TIME TIP CURRE NUGGE PRESS NT T DIA URE

C- CLASS
SHEAR WELD TIP CURRE NUGGE SHEAR STREN TIME PRESS NT T DIA STREN GTH URE GTH

mm 8 9 10 12 18 20 27 31 35 40 50

mm 10 11 11 11 12 14 16 17 18 20 22

cycle 8 10 12 15 20 23 30 32 36 44 60

Kgf 75 90 100 125 150 175 240 275 300 370 500

Amprs 4500 5000 5500 6500 7200 7800 9100 9500 10300 11300 12900

mm 3.6 4 4.3 4.8 5.4 5.8 6.7 7.2 7.6 8.4 9.9

Kgf 160 210 280 400 540 680 1000 1200 1370 1770 2850

cycle 20 24 26 30 36 40 50 55 58 65 78

Kgf 40 45 50 60 75 85 115 130 150 180 260

Amprs 3500 4000 4500 5000 5600 6100 7000 7500 8000 8600 10000

mm 3.3 3.6 4 4.6 5.3 5.5 6.3 6.6 7.1 7.9 9.4

Kgf 125 175 225 355 530 650 925 110 1305 1685 2665

*Welding speed is medium * The welding speedis low *The dispersion of welding strength is average *The dispersion of welding strength is large *Welding machine of small capacity is sufficien *Welding is done for strength *Welding strength is not a criteria

Welding parameters board

ELECTRODE TIP
WATER TEFLON TUBE

ELECTRODE
USED NEW

WEAR LINE

2~3 mm 0.5 mm 6 mm

TIP DIA BE CHECKED AFTER DRESSING WITH GO / NOGO GAUGE

GO 6~8 mm NOGO < 8mm

GAUGE FOR TIP DIA

How to do the dressing of electrode?

Electode Dressing

ALIGNMENT OF TIPS

100 % Matching

90 % Matching

< 90 % Matching NOT OK

ACCEPTABLE BEST SPOT TIP ALIGNMENT OK

GUN ALIGNMENT FOR UNDLATION

NOT OK

NOT OK

OK

Electrode Pushing

TESTING METHOD AND ACCEPTANCE CRITERIA

SL. NO TYPE OF TEST NON-DESTRUCTIVE TEST 1 a. APPEARANCE TEST METHOD OF CHECKING VISUAL CHECK FOR I. NO CRACK ii NO PIN HOLE iii NO UNDULATION DRIVE CHIESEL IN B/W TWO PLATES BY HAMMER TILL YOU HEAR METALLIC SOUND BY CHIESEL DRIVE CHIESEL IN B/W TWO PLATES BY HAMMER TILLNUGGET IS FOUND BY UTM STANDARD TEST SHEETS ARE TESTED IN UTM FOR SHEAR STRENGTH FREQUENCY ALL SPOTS

b. CHIESEL TEST

EVERY ONE HOUR

DESTRCUCTIVE TEST a. SHEAR TEST

ONCE IN 2 Hrs on ( Test Pc )

B. TENSILE SHEAR TEST

ONCE IN A MONTHS

Verifying Weld spot

300Kg

Size of the welded spot

The size of the nugget depends on the thickness of the sheets as well as on the size of the electrode tips. To avoid unwanted deformations on the outer surface of car panels, the concerning electrode should have a large contacting area.

Weld defects

Spot Weld defects

o o o o o o o o Expulsion Surface fusion Excessive indentation Blow hole Crack in nugget Insufficient nugget Too much fusion Deformed nugget

Causes
Electrode tip diameter Weld force Weld time Surface condition Cooling Current shunting Impedance / resistance Input power Work piece

Spot welding defects

Sl no.

DEFECTS

CAUSES
DIRTY AND SCALY MATERIAL POOR FIT UP OF PARTS TIP MATCHING NG

COUNTERMEASURES

SPOT BURR (EXPUSION ) AND TIP STICKY

SQUEEZE TIME TOO LESS WELD CURRENT VERY HIGHT WELD TIME VERY HIGH WELD PRESSURE LESS GUN POSITION NOT OK HOLD TIME VERY LESS TIP WORN OUT HIGH CURRENT

TIP DRESSING TO BE DONE EVERY ONE HOUR ENSURE THE CORRECT SQ TIME ENSURE THE CURRENT SETTING OK (CURRENT TO BE CHECKED WITH CALIBERATED WELD CHECKER ) ENSURE THE TIP PRESSURE RIGHT AFTER CHECKING WITH CALIBERATED PRESSURE GAUGE OPERATER EDUCATION FOR GUN BALANCING AND COMP BALANCING INCREASE THE HOLD TIME REPLACE THE TIP ENSURE THE CURRENT SETTING CORRECTLY (CHECK IT WITH CALIBERATED WELDCHECKER ) CLEAN THE PARTS
ENSURE THE TIP PRESSURE RIGHT AFTER CHECKING WITH CALIBERATED PRESSURE GAUGE

PIN HOLE
DIRTY , SCALY AND RUSTED MATERIAL TIP PRESSURE LESS GUN POSITION NG ELECTRODE ALIGHNMENT NG SHEET OVERLAP LESS TIP PRESSURE HIGH PARTS ARE NOT FITTED PROPERLY IN THE FIXTURE

UNDULATION

OPERATER EDUCATION FOR GUN BALANCING AND COMP BALANCING GUN ARMS PLAY ,TO BE CORRECTED OPERATER EDUCATION
ENSURE THE TIP PRESSURE RIGHT AFTER CHECKING WITH CALIBERATED PRESSURE GAUGE

CLAMPING OF PARTS TO BE DONE

Spot welding defects

Sl no.

DEFECTS

CAUSES
WELD CURRENT VERY LOW WELD FORCE VERY LOW WELD TIME VERY LOW POOR FIT UP OF PARTS IN THE FIXTURE EXCESS UNDULATION

COUNTERMEASURES
ENSURE THE CURRENT IS CORRECT (CHECK WITH CALIBERATED WELD CHECKER ) ENSURE THE TIP PRESSURE IS CORRECT (CHECK WITH CALIBERATED PRESSURE GAUGE ) ENSURE THE CORRECT WELD TIME OPERATER EDUCATION FOR GUN BALANCING AND COMP BALANCING OPERATER EDUCATION FOR GUN BALANCING AND COMP BALANCING TIP DRESSING TO BE DONE EVERY HOUR AND ENSURE THE TIP MATCHING CLEAN THE SURFACE ENSURE PROPER GUN POSITION TIP TO BE REPLACED. INSIDE TEFLON TUBE TO BE CHECKED ENSURE STANDARD QUALITY OF TIPS. WATER FLOW TO BE CHECKED GUN ARM INSULATION / OBSTACKLE TO BE RECTIFIED PROPER PITCH TO BE MAINTAINED. OPERATER EDUCATION FOOL PROOFING TO BE DONE FOR LINE VOLTAGE

SPOT FAILURE ( NO NUGGET OR LITTLE NUGGET - WELD NOT HOLDING )

GUN POSITION NG TIP MATCHING NG DIRTY OR SCALY MATERIAL SHEET SPOT ON ROOT RADIUS ELECRODE FACE TOO LARGE /TIP WORN OUT / DEFORMED TIP RAW MATERIAL NG POOR HEAT BALANCE / TIP COOLING NG GUN ARM TOUCHING/ ( SHORT CKTING OF CURRENT ) SPOT PITCH LESS ( SPOT TOO CLOSE ) LOW LINE VOLTAGE

Error caused by work pieces.

Error caused by work pieces 2

Spatters
Generally spatters are caused by an incorrect adjustment! With correct adjusted welding parameters und electrodes well lined up no spatters will occur!

Calculation of the time needed to weld a spot -1

Calculation of the time needed to weld a spot -2

Calculation of the time needed to weld a spot -3

COATED SHEETS PRESENTATION

Galvanized steel sheets

Galvanized steel sheets require a higher welding current in alliance of a higher electrode-force (approximately 10%) than not coated steel sheets!

zinc splatters
Due to possible zinc splatters galvanized sheets need a correct adjusted welding current

Reference for Galvanized sheet Spot welding

TYPE SHEET THICKNESS mm 0.6 0.8 1 1.2 1.6 2 0.6 0.8 1 1.2 1.6 2 0.6 0.8 1 1.2 1.6 2 ONE SIDE PLATING THICKNESS MICRONES WELD TIP CURRENT PRESSURE cycle 9000 10000 10000 12000 15000 19000 9000 10000 10500 11500 13500 17000 9000 10000 11000 12500 15000 20000 Kgf 250 270 300 350 450 600 250 270 300 350 450 600 250 270 330 400 450 650 WELD TIME Amprs 7 8 9 10 12 15 7 8 9 10 12 15 7 8 9 10 12 15 SHEAR STRENGTH Kgf 300 450 600 700 1150 1550 330 500 650 850 1300 1600 330 500 650 900 1300 1600

ELECTROP LATING

2~3

ALLOY PLATING

8 ~ 12

HOT DIP PLATING

10 ~ 15

PROJECTION WELDING

PROJECTION WELDING
* PROJECTION WELDING IS A TYPE OF RESISTANCE WELDING. * AS THE NAME IMPLIES IN THIS TYPE OF WELDING ONLY THE PROJECTED PORTION IS MELTED AND JOINED TO THE BASE METAL.. * HIGH CURRENT IN LESS TIME IS THE MAIN FEATURE OF THIS WELDING. * PROJECTION NUT AND PROJECTION STUD OF STANDARD SPECIFICATION CAN BE WELDED.

PROJECTION NUT WELDING

NG
UPPER ELECTRODE

OK

PIN SPRING LOWER ELECTRODE PIN

NUGGET

Reference for projection nut welding

NUT SIZE SHEET WELD TIME WELD TIP THICKNESS CURRENT PRESSURE PROJECTION HEXAGONAL NUT cycle amp Kgf 5 9000 225 5 10000 225 6 11000 225 6 9500 230 6 11000 230 6 13000 260 PROJECTION SQUARE NUT 5 9000 200 5 10000 240 5 10500 300 5 9500 220 5 10000 240 6 11000 270 6 12000 300 6 13000 370 6 13000 300 6 14000 370 SHEAR STRENGTH

mm

M5/M6

M8

mm 0.7 0.8 1.2 0.7 0.8 1.2 0.7 0.8 1.2 0.7 0.8 1.2 0.8 1.2 0.8 1.2

Kgf 250/350 250/350 250/350 450 450 450 250/350 250/350 250/350 450 450 450 600 600 800 800

M5/M6

M8

M 10 M 12

PROJECTION STUD WELDING

BEFORE UPPER ELECTRODE AFTER
WATER CIRCULATION

FUSION

WORK PC.

LOWER ELECTRODE

Reference for projection Stud welding

SCREW SIZE SHEET THICKNESS WELD TIME WELD CURRENT TIP PRESSURE WELDING STRENGTH TWIST Kgcm M8 2.6 1 M6 2.6 1 2.6 1 2.6 1 9 9 9 9 9 9 9 9 11000 9000 6500 5800 5500 4800 5000 4000 570 340 210 190 180 160 140 90 800 1900 290 420 400 1100 180 320 M5 200 800 120 260 M4 100 500 60 240 TENSILE Kg

STUD WELDING (FLASH WELDING )

STUD LIFT PLUNGE

BASE METAL EXCITATION OF COIL

LIFTED CONDITION

LIFTING ACTION

WELDING PULSE PILOT ARC VOLTAGE PILOT ARC

PLUNGE POINT

WELDING CURRENT MELT CONDITION HEATING TEMPERATURE

Reference condition for Stud welding

STUD SIZE M3 M4 M5 M6 M8 SHEET THICKNESS 0.6-1.2 0.6-1.2 0.6-1.2 0.6-1.2 0.6-1.2 DIA OF STUD TO BE WELDED 4.5 5.5 6.5 7.5 9.5 CHARGING VOLTAGE 60-90 70-100 90-130 130-170 180-240 STRENGTH OF SPRING mm 15-25 SPRING FORCE 15-25 15-25 18-30 18-30 REMARKS

SET STICK OUT TO 2 ~ 2.5 MM IN ALL CASE SET LIFT 1 ~ 1.5 MM SET CURRENTAND TIME FOR PILOT ARC MOST SUITED

A M.S.

15 100

30 200

50 400

THANKS
extra files ahead

EXTRA slides

Resistance welding
Resistance & Effect of Pressure
R1&R5 Resistance between tip and sheet R2 & R4 sheet individual resistance R3 Surface contact resistance

R1 R2 R3 R4 R5 In welding it is desirable to have R1,R2,R4,R5 low R3 high

Electrode Type & Size

Welding processing-parameters
Welding processing-parameters cannot be determined by theoretical calculations. Only with test rows welding process parameters can be optimized. Start a test row with the lower theoretical welding process parameter and increase one of the parameters (for example the welding current) step by step. The test rows should be focused to the most important object, as there are quality, strength or process pace. Research for the best welding spot can be done for example by verifying the grinding pattern.

Diameter of the welded connection

Welding two sheets with different thickness or welding more than two sheets the lens diameter doesnt correspond with the diameter of the mating area. Decisive for the tightness of the welded spot is the mating area between the sheets. The required minimum diameter can be calculated as shown in the example:

 The secondary current depends directly from the secondary voltage. Important to solve the welding job is the voltage over the work piece.
U work piece = U total (U upper electrode arm + U lower electrode arm)

SPOT CHECKING METHOD

WELD SPOTS

CHIESEL NUGGET DIA

NUGGET CHECKING METHOD IF METAL SOUND ----- OK

UTM
SPOT SHOULD NOT FAIL

TENSILE STRENGTH CHECKING METHOD

Weld defects

Expulsion at weld interface

Dirty , scaly material Poor fit-up squeeze time too short Weld force too low Weld current too high Weld time too high

Surface expulsion, electrode sticking

Dirty , scaly material Poor fit-up squeeze time too short Weld force too low Weld current too high Weld time too high Tip dirty

Electrode Mushrooming
weld time too long. Weld force too high Weld current high Insufficient cooling Electrode area too small Electrode alloy too soft

Excessive weld indentation

weld time too long. Weld force too high Weld current high Insufficient cooling Electrode area too small Poor fit-up

Little or no weld nugget

Weld time too short Weld force too high Weld current too low Electrode face too large Poor heat balance Welds too close together Dirty or coated material Low line voltage

Cracks in weld nuggets

Hold time too short Weld force too low Dirty, scaly material

Displaced weld nugget

Electrode misaligned Poor heat balance Poor fit-up

Weld not holding

Weld force too high Weld force too low Poor fit-up of parts Weld current too low Weld time too short Poor set up of tools.