OPTIMIZATION OF SPOT WELDING PROCESS PARAMETERS …

1 506 Int. J. Mech. Eng. & Rob. Res. 2014 Manoj Raut and Vishal Achwal, 2014 OPTIMIZATION OF SPOT WELDING PROCESSPARAMETERS FOR MAXIMUM TENSILESTRENGTHM anoj Raut1* and Vishal Achwal1*Corresponding Author:Manoj Raut, experimental study is based on an investigation of the effect and OPTIMIZATION of weldingparameters on the tensile shear strength in the Resistance Spot WELDING (RSW) PROCESS . Theexperimental studies were conducted under varying electrode forces, WELDING currents, andwelding times. The settings of WELDING PARAMETERS were determined by using the Taguchiexperimental design of L18 Orthogonal array method. The combination of the optimum weldingparameters have determined by using the analysis of Signal-to-Noise (S/N) ratio. The confirmationtest performed clearly shows that it is possible to increase the tensile shear strength of the jointby the combination of the suitable WELDING PARAMETERS .

2 Hence, the experimental results confirmedthe validity of the used Taguchi method for enhancing the WELDING performance and optimizingthe WELDING PARAMETERS in resistance spot WELDING :Resistance Spot WELDING (RSW), Tensile shear strength, Taguchi method, S/Nratio, OptimizationINTRODUCTIONR esistance spot WELDING is getting significantimportance in car, bus and railway bodies etcdue to automatic and fast PROCESS . The majorfactors controlling this PROCESS are current,time, electrode force, contact resistance,property of electrode material, sheet materials,surface condition etc. the quality is bestjudged by nugget size and joint strength. Thisstudy presents a systematic approach todetermine effect of PROCESS parametersISSN 2278 0149 3, No. 4, October 2014 2014 IJMERR. All Rights ReservedInt. J. Mech. Eng. & Rob. Res. 20141 Truba College of Engineering and Technology, Indore, Madhya Pradesh, India.

3 (electrode force, weld time and current) ontensile shear strength of resistance weld jointof mild steel using Taguchi general introduction for principle,working and PARAMETERS of spot WELDING isgiven Spot WELDING (RSW) is amongthe oldest of the electric WELDING method thatused in the industry and it is useful andaccepted method in joining Paper507 Int. J. Mech. Eng. & Rob. Res. 2014 Manoj Raut and Vishal Achwal, 2014 Spot WELDING is widely used in weldingcarbon steel because they have higherelectrical resistance and lower thermalconductivity than the electrode that made fromcopper. The Spot WELDING is commonly beingused in automobile industry, where it is usedto weld the sheet metal forming a welders can also be completelyautomated, and many of the industrial robotsfound on assembly lines are spot WELDING also being used in the of Operation forResistance Spot WeldingResistance Spot WELDING (RSW) is includedin the group of resistance WELDING processesthat heat is used in joining the work parts ofmetal.

4 Heat is generated from electricalresistance across the two work parts InResistance Spot WELDING two work part ofmetal are joined together by applying electriccurrent and pressure in the zone to be weldand resistance WELDING is different From arcwelding because it s not required filler metalor fluxes added to the weld area during thewelding WELDING operates based on fourfactors that of current that passes through thework that the electrodes applied on thework time the current flow through the area of the electrode tip contact withthe work the WELDING PROCESS the amount ofelectric current is flow from the electrodes tothe work pieces. The weld force is applied byleg the electrode to the work pieces,the right amount of pressure that applied onthe work pieces is very important in order toobtain the good quality of welds. During thewelding PROCESS , the electric current is flowFigure 1: Resistance Spot WeldingFigure 2: Resistance WELDING MachineCircuits508 Int.

5 J. Mech. Eng. & Rob. Res. 2014 Manoj Raut and Vishal Achwal, 2014through electrode tips to the separate workpieces of metal to be resistance of the base metal toelectrical current flow causes heat, the heat islimited to the area which the tip of the electrodeand weld area contacts. While the WELDING forceis maintained, the heat is generating. In theholding stage (where the pressure is stillmaintained), the current is switched off and thenugget is cooled under the pressure. The heatthat generated in spot WELDING is basicallydepend on the electric current and the timebeing used and on the electrical resistance ofmaterial between amount of heat generated is a functionof current, time and resistance between theelectrode the heat that generates in resistancespot WELDING according to Joule s law isexpressed by the =I2 RtwhereH = Heat is generated in joulesI = Current (in amperes)R = Resistance (in ohms)t = Time to current flow (in seconds)Resistance Spot WeldingParametersThe spot WELDING PROCESS PARAMETERS havetheir own importance.

6 A small change of oneparameter will affect all the other PARAMETERS will determine the qualityof the welds. The appropriate combination ofthe spot WELDING parameter will produce strongjoining and good quality of WELDING . Spotwelding PARAMETERS of the electrode contact currentElectrode ForceThe purpose of the electrode force is tosqueeze the parts to be weld and the primarypurpose is to hold the parts to ensure the partsin intimate contact at the joining the electrode force is increased the heatenergy will decrease, a high pressure thatexerted on the weld joint will decrease theresistance at the point of contact between theelectrode tips and the parts surface. Thismeans that the higher electrode force requiresa higher weld current. Weld spatter can behappen because the pressure on the tips istoo light or when weld current becomes toohigh.

7 Too heavy pressure will cause small spotweld. In other words when the pressureincreases, the electrical current andsubsequent heat are transfer to a wider area,Figure 3: Time Sequence of the ResistanceSpot WELDING Cycle: (1) Clamping Time,(2) Weld Time, (3) Hold Time, (4) Off Time509 Int. J. Mech. Eng. & Rob. Res. 2014 Manoj Raut and Vishal Achwal, 2014the penetration and area of the weld of the Electrode ContactSurfaceOne general criterion of resistance spot- WELDING is that the weld shall have a nuggetdiameter of 5 t1/2, t being the thickness ofthe steel sheet. Thus, a spot weld made in twosheets, each 1 mm in thickness, wouldgenerate a nugget 5 mm in diameteraccording to the 5 t -rules. Diameter of theelectrode contact surface should be slightlylarger than the nugget TimeSqueeze Time is the time interval between theinitial application of the electrode force on thework and the first application of time is necessary to delay the weldcurrent until the electrode force has attainedthe desired TimeWeld time is the time during which weldingcurrent is applied to the metal sheets.

8 The weldtime is measured and adjusted in cycles of linevoltage as are all timing functions. One cycleis 1/50 of a second in a 50 Hz power the weld time is, more or less, related towhat is required for the weld spot, it is difficultto give an exact value of the optimum time (Cooling-Time)Hold time is the time, after the WELDING , whenthe electrodes are still applied to the sheet tochill the weld. Considered from a weldingtechnical point of view, the hold time is the mostinteresting WELDING parameter. Hold time isnecessary to allow the weld nugget to solidifybefore releasing the welded parts, but it mustnot be to long as this may cause the heat inthe weld spot to spread to the electrode andheat it. The electrode will then get moreexposed to wear. Further, if the hold time istoo long and the carbon content of the materialis high (more than ), there is a risk theweld will become brittle.

9 W hen weldinggalvanized carbon steel a longer hold time CurrentThe amount of weld current is controlled by twothings: The setting of the transformer tap switchdetermines the maximum amount of weldcurrent available. The percent of current control determinesthe percent of the available current to beused for making the low percent current settings are notrecommended because it may harm the qualityof the weld. The weld current should be keptas low as possible. When determining thecurrent to be used, the current is steadilyincreased until weld spatter occurs betweenthe metal sheets. This indicates that thecorrect weld current has been reached. Thetemperature rises rapidly at the joined portionof the metal where the resistance is greatest ifthe current becomes too great internal spatterwill REVIEWR esistance Spot WELDING (RSW) is gettingsignificant importance in manufacturing car,bus and railway bodies, etc.

10 , due to automaticand fast PROCESS . As the automobile joints aresubjected to higher loading condition hence510 Int. J. Mech. Eng. & Rob. Res. 2014 Manoj Raut and Vishal Achwal, 2014to avoid the failure higher strength of spotwelded joint is required (Thakur andNandedkar, 2010). When the spot welded jointis subjected to pure opening condition then itfails in the direction of load applied and whenit subjected to combined opening and shearloading conditions it fails inclined from thesurface of weld nugget (Linet al., 2003).Therefore the spot welded joint should bestrong in both in pure opening condition andin combined opening and shear loadingconditions. Though the PROCESS PARAMETERS ofthe spot WELDING also affect the mechanicalbehavior of welded joint in the loadingconditions so the PARAMETERS should also besuitable for the higher strength of joint (ChetanPatel, Dhaval Patel, 2012).