Investigation on the stepping arc stud welding process

158CHINA WELDING Vol. 14 No. 2 November 2005Investigation on the stepping arc stud welding processChi Qiang, Zhang Jianxun, Fu Jijfei and Zhang Youquan池强,张建勋,付继飞,张友权 *Abtract Through the inestigation on traditional arc stud welding process, a new welding gun and its control system weredeveloped in this paper. The stepping arc stud welding gun was mainly made by a sepping motor as actuating wnit and ascrew-driven device as moving wnit. A control system with a MCS-5 1 single-chip microcomputer as main control component wasused to realise the new stud welding procedure. This new welding process with stepping stud welding gun is named as steppingarc stud welding. In the new welding process , the stud action can be looked as constituted by some micro steps. The sttingand adjusting of the stepping are welding gun behaxior paramneters are accomplished independently. It is indicated fom theresults of process lests and bending test that the stepping arc stud welding procss is practicable.Key words stud, arc stud welding, welding gun, single-chip microcomputer0 Introduction1 Stepping arc stud welding gun and its control sys-Arc stud welding is gradually becoming an increasingtemimportant joining process from the first practial applica- 1. 1 Stepping are stud welding guntion developed originally for the shipbuilding industry as aThe arc stud welding gun as an actuating mechanismreplacement of the time consuming drilling and boltingis controlled to accomplish the stud lift and plunge in theprocess in 193911. The are stud welding fasteners atta-welding process. The structure of the stud welding gun de-ched to one side of the workpiece can replace ones madetermines the implementation procedure and characteristicsby riveting and tapping. Up to now, it has been widelyof welding. At present, the welding gun widely used is theused in the manufacture of automobile , multistoried build-electromagnetic arc stud welding gun. From the inventionings, construction of bridges ，appliance industries and soof arc stud welding, the design principle of welding gunon“hold the line and the improvement mostly fasten on the fig-The equipment of arc stud welding consists of a d-curation and capability. It is one of the important character-power source, a control unit, and a welding gun. Accord-istics in the gun design that the actuating unit consists of aing to the power source used, arc stud welding has beenmagnetic coil and a mechanical spring.separated into two basic types, common are and capacitorThe stepping arc stud welding gun differs completelydischarget6].from electromagnetic welding gun in structure design. TheIn this paper， through the investigation on theprincipal parts of the welding gun consist of a stepping mo-process of common arc stud welding and traditional arestud welding gun, a new arc stud welding gun driven by ator and a screw-driven device. The machine structure ofstepping motor and its control system were developed. Thestepping arc stud welding gun is shown in Fig. 1, inclu-welding process based on the developed welding gun wasding an actuating unit, a moving unit and a fixing and pro-tection unit.evaluated.中国煤化工YHCNMHG。Chi Qiang and Zhang Janxun, School of Material Science and Engineering, Xi' an Jiaotong University, Xi' an, 710049. E mail:chiqiang2004@ sina. com ( Chi Qiang) Fu Jifei and Zhang Youquan, Central Research Institute of Building and Construction, ChinaMetallurgial Construction Group, Beijing, 10008.Investigation on the stepping arc stud welding process159Steppingschematic diagram.motpmolorLead screw .1.2 Control systemThe control of welding gun is realized by contollingNutthe stepping motor. In this paper, a control system with aShock absorbingMCS-51 single -chip-microcomputer as the main controlspring device-component was designed to realize an accurate control ofChuckStud.the stepping motor and welding procedure. The block dia-gram of control system is shown in Fig.2. The P1 port ofsingle-chip microcomputer sends out the rectangular waveFig.1 Machine structure of stepping are stud welding gunpulse signal to drive the motor. The signal contrlling rota-tion direction is generated by P1 port also.(1) As the actuating unit of stepping arc stud weld-ing gun, the stepping motor has some advantages such asless inertia , needless for arresting gear , favorable workingOptoelectronic| Weldingisolatormotor drivegunperformance, etc. In addition it can start, reverse andstall for an instant. The stepping motor is controlled bySingle-chip microcomputerEPROMpulse signal. lIts rotational angle is in proportion to pulse87512764counts and its rotational speed is mostly concemed withRAM1/0 device Welding parameterspulse frequency. The rotation of motor has no direct rela-62648255settingtionship with the voltage and current. And the error of ro-tation will not be accumulated.Fig.2 Block diagram of welding gun control system(2) The main body of the moving unit is a screw-driven device, namely a pair of screw and nut. It changes2 Stepping arc stud welding processthe angular displacement originating from stepping motor 2. 1 Weld sequence of stepping arc stud weldinginto straight-line displacement with a stud motion aspect,The welding process based on stepping are stud weld-which realizes the stud action procedure requested by arc ing gun is named as stepping are stud welding. Its weldstud welding. The screw is joined to the motor shaft. withsequence is ilustrated in Fig. 3.mechanical means to receive the angular displacement.The nut does only axial straigt-ine motion through aguide apparatus. The change of nut moving direction is ac-tud、日1用Work-complished by changing the rotation direction of steppingpieceLnmotor. A stud is loaded into the stud-holding chuck, mov-(1)(2)(3)(4)(5)ing with the nut to accomplish the stud lift and plunge inthe welding process.Fig.3 Sequence of stepping are stud welding(3) The fixing and protection unit involve gun frame-work. , shock absorbing spring device and motor shaft pro-(1) Loading a stud into the stepping arc stud weldingtector. The action of shock absorbing spring device isgun, positioning the gun properly against the workpiece,changing the stud displacement into spring compressionand m中国煤化I工the workpiece.when the stud plunge depth is excessive, which protects:YHCNMH at, and lfting the studmotor and other parts against breakage. And the motorby driving the stepping motor positive rotation, then resul-shaft protector decreases the stress of motor shaft. The gunting in an are between the stud and workpiece.framework and motor shaft protector are not marked in(3) Keeping the arc in the gap lfed for melting both160CHINA WELDING Vol. 14 No.2 November 2005the stud and the workpiece.2.3 Realization of the slow stud plunge(4) The stud is plunged into the welding pool byIn common arc stud welding process with an electro-means of the reverse of motor and the welding current is magnetic welding gun, the stud plunge speed is high. It isautomatically shut off when the arc period is over. The arcincreasing gradually as stud entering to the welding pool inperiod is preset in the control system.the stud welding process. When the stud enters to the(5) The weldment is completed and the gun is liftedwelding pool, the plunge speed reaches to the climax.off the stud.Such a process can be called fast stud plunge. The suff-cient stud plunge speed could insure an adequate extrusion2.2 Welding gun behavior parameterspressure between stud and workpiece at the completion ofThe welding gun behavior parameters such as the liftthe weld, however, it could also bring serious spatter. Indistance, the plunge depth, and the lift and plunge speedorder to reduce the spatter, the stud plunge speed some-are very important for higher welding quality.times needs to be controlled strictly. Generally, the studBecause of the changes in the structure of the studplunge speed is chosen according to the diameter of wel-welding gun, stepping arc stud welding process differsded stud. A rather slow plunge speed should be adoptedfrom common arc stud welding. Comparing with commonfor welding large diameter stud.are stud welding, it is not need to preset the length of theThe slow stud plunge means that the stud enters tostud burn-off in the stepping arc stud welding. It is one ofthe molten pool with a comparatively slow speed and a suf-its important characteristics that the stud action can beficient joint extrusion pressure. Because of the slow studlooked as constituted by some micro-steps. The parametersplunge, the spatter can be reduced in great extent. Thedealing with the stting and adjusting of the welding gunslow stud plunge can hardly be realized in common arcbehavior can be programmed in the control system.stud welding, for the structure of electromagnetic arc studThe speeds of stud lift and plunge, U, can be compu-welding gun determines that the joint extrusion pressureted as follows:and the stud plunge speed is direct ration.The special actuating and moving unit of stepping arc: f0tv=360(1)stud welding gun can satisfly the requirement of the slowstud plunge.here,f is the pulse frequency, θ is the stepping angle ofThe screw-driven device of stepping arc stud weldingthe motor and t is the pitch of screw. The distance of liftgun transfers not only movement but also dynamic force inand plunge, h is determined according to the fllwing for-the direction of the stud moving. The force, Q is adjustedmula.by torque of stepping motor and some parameters of screwh=360_aθt(2)pair. And if the friction force of screw pair is not calculat-ed, then:here, a is the pulse count.FThe stting and adjusting of the welding gun behavior(3)tgλparameters is relatively independent. It can be obtainedp=2I(4)according to equations (1) and (2) that the adjusting ofdparameters is only alied to the controlled variable of motortgλ=型(5)rotation and screw dimension. It results in a litle affectπwith each other. In the common arc stud welding, therewher中国煤化工guide screw, λ the liftare some influents with each other among the parameters.angletorque of stepping mo-For example, different stud plunge depth stting will altertor ,HHCNMH Gscrew, n the count ofthe decrement of spring, and finally afeets the stud plungethread and p the pitch. The final force, Q is obtained byspeed.combining equations (3) -(5)Investigation on the stepping are stud welding process1610:2πT(6)process after the stud is drawn from the workpiece. Thetesting process shows that the stepping arc stud weldingAccording to equation (6)，the extrusion pressure ofcan be accomplished successfully and the welding processwelded joint, namely Q can be estimated cursorily. Foris feasible.example, ifn=1,p=6 mm and T=1N. m, then Q=1 000 N. Such a pressure meets completely the demand of80slow stud plunge as long as the friction force is not too big-Open-cireuitger. In order to obtain a more extrusion pressure, a step-60voltageping motor with good torque-frequency charactersticshould be selected to hold a biggish torque when its rota-40Welding volageional speed changed with limits.203 Welding testWelding tests based on stepping arc stud welding gun-100 0 100 200 300 400 500and its control system are done to testify the feasibility oft/msstepping arc stud welding process and the rationalty of thewelding gun. A magnetic amplifier type arc welding recti-Fig.4 Timing diagram of the elding voltagefier ( model ZXG-300) is used as the welding powersource. One of its characterstics is a steep dropping volt-In some circumstances, welded stud is used for enlar-ampere characteritic with a no-load volage about 75 V,ging radiating surface or tightening coat and insulating lay-which satisfies the requirements of arc starting and weld-er. In this case, the requirement of joint strength is noting. The deficiency of the rectifer is lack of the functionstrict and the mechanical test can be done according toadjusting welding circuit automaically, which results inpractical situation. In the other case， when the joinlthat the welding circuit control cannot be realized duringstrength is demanded, the bend test is a generally usedstepping arc stud welding.method. Bend testing of small studs should be done with aThe material of stud and workpiece is a kind of low-tube- type bending tool. The testing device used in the testcarbon steel ( Q235). The stud is round with diameter 5is shown in Fig. 5. The welded stud should be bent to 45mm. And the end of the stud is flat without flux. The- 90 degree from its axis without weld failure for somethickness of workpiece is 5 mm. The area to weld shouldstrict applications, as well as a bend of 10 - 15 degreebe cleaned before welding to remove the deleterious sub-may be adequate for some applications. For mild carbonstances such as heavy rust, oxide layer, paint， grease ,steel and stainless steel, the bend degree is generally reheavy oil, moisture, etc. According to the material andquired as 60 degree. The qualification testing of weldeddimension of stud, welding conditions are chosen as thePfollows, lift height: 1. 7 mm, plunge speed: 30 mm/s,-Tubewelding current: 300 A.The welding voltage during welding is collected in thewelding process as showm in Fig. 4. The open-circuit volt-Sudage measured actually before welding is used to prove the :Workpieceaccuracy of date acquisition. Refrring to the welding volt-中国煤化工-age in Fig. 4, it will be noted that the welding volage is aMHCNMHGbout 30 V and the value is comparatively stable in thecomplete arc buming course. It means that the arc is igni-ted sucesfully and keeps normal burming in weldingFig.5 Schematic diagram of bend test.162CHINA WELDING Vol. 14 No. 2 November 2005joint of stepping are stud welding is done by bend test and(3) The welding gun behavior parameters such as thethe result is shown in Fig. 6. The bend degree proves thatlift distance, the plunge depth, and the lift and plungethe joint is sound.speed can be set via program control. The interaction ofparameters is reduced because of the adjustable character-istice of relative independence.(4) It is indicated from welding tests that steppingarc stud welding process is practicable. Furthermore, theresults of bend test prove that the joint is sound.References[1] Singleton R C. The growth of stud welding. Welding Engi-neering, 1963, 48(7):27 -31Fig.6 Bend joint2]Ramasamy S. Drawn arc stud welding: Crossing over fromsteel to aluminum. Welding Joumnal, 2000, 79(1):35 -394 Conclusions(1) The welding process with stepping arc stud weld-[3] Strigel R M, PincheiraJ A, Oliva M G, et al. Reliability of3/8 in. stud-welded deformned bar anchors subject to tensileing gun is named as stepping arc stud welding. One of itsloads. PCI Journal, 2000, 45(6): 72 -82important characteristics is that in welding process the stud[ 4] Chambers H A. Principles and practices of stud welding. PCIaction can be looked as constituted by some micro-steps.Jourmal, 2001, 46(5): 46 -58(2) A stepping are stud welding gun controlled by [5] Masubuchi K, Imakita A, Miyake M. An initial study of resingle-chip microcomputer system is developed. A step-motely manipulated stud welding for space applications.ping motor is taken as the actuating unit and a screw-driv-Welding Jourmal, 1988, 67(4): 25 -34en device as the moving unit to realize the stud action pro-[6Shoup T E. Sud welding. Welding Rescarch Council Bulle-tin, 1976(214):1-22cedure requested by arc stud welding.中国煤化工MYHCNMHG