| The rapid and multidisciplinary development of modern industry has brought enormous challenges to the improvement of welding quality and production efficiency.Due to the advantages of low welding material consumption,high production efficiency,precise control of line energy,and high weld forming quality,the ultra-narrow gap TIG welding process has good application prospects in the manufacturing of medium and thick plate steel structures.As a large proportion of steel,austenitic stainless steel is widely used in the welding field due to its good plasticity and corrosion resistance.However,because austenitic stainless steel is sensitive to heat input,grain boundary corrosion is prone to occur within the sensitized temperature range,resulting in welding defect.For this reason,this paper proposes an insulated solid wall constrained slice tungsten electrode pulse arc ultra narrow gap welding process,which can accurately regulate the line energy.However,in the process of ultra-narrow gap welding,the pulse arc is very sensitive to groove configuration.Even small changes in groove configuration can have a significant impact on the characteristics of the pulse arc,and the main manifestation of groove configuration changes is transverse shrinkage deformation.This article investigates the influence and control mechanism of transverse shrinkage deformation of groove on the characteristics of pulse arc during ultra narrow gap welding.On the basis of the continuity equation,momentum conservation equation,energy conservation equation,and Maxwell equation system,a three-dimensional mathematical model of slice tungsten pulsed arc with insulating wall constrain in ultra-narrow gap welding process has been established.By solving and comparing the temperature field,flow field,current density field,and electromagnetic force distribution of pulse arc under different transverse shrinkage deformation of groove,the evolution law of the constrained pulse arc characteristics over time and the influence law and control mechanism of transverse shrinkage deformation of groove on the pulse arc characteristics were clarified.The results indicate that the guiding effect of the front end of the slice tungsten electrode and the hysteresis of the pulse arc shape on the change of pulse current are the main factors affecting the characteristics of the constrain pulsed arc.The guiding effect causes the current density of the pulse arc to concentrate and flow towards the position with small discharge gap,thus making the physical field of the pulse arc tend to be distributed in the position with small discharge gap.However,the hysteresis of the pulse arc shape on the change of pulse current will cause the arc shape to be unable to expand and contract synchronously when the base current transitions to the peak current and when the peak current transitions to the base current.Thus making it difficult for the arc shape to expand and contract synchronously when the base current transitions to the peak current.When the current rapidly increases while the arc shape still maintains the base current,the smaller arc shape results in a significant increase in current density,and a significant increase in pulse arc temperature,flow rate,and electromagnetic force.When the peak current transitions to the base current,the current rapidly decreases,while the arc shape remains in the extended state at the peak current.The current density significantly decreases,and the temperature,flow rate,and electromagnetic force of the pulse arc all significantly decrease.As the peak current increases,the heat generation of the arc also increases,leading to an increase in the peak temperature of the pulse arc and an expansion of the temperature field distribution.At the same time,it also enhances the electromagnetic contraction force,limits the expansion of the arc shape,increases the current density,and enhances the flow rate and electromagnetic force peak of the pulse arc.As the peak current increases,transverse shrinkage deformation of groove also increases.Transverse shrinkage deformation of groove will reduce the distance between groove sidewall and the tungsten electrode,generate stronger solid wall compression and constraint on the arc,causing the arc shape to shrink,increase current density,and increase arc temperature.At the same time,the increase in current density will also enhance the electromagnetic contraction force,increase the electromagnetic force,strengthen the Maker effect,and enhance the guiding effect.The cathode jet is enhanced,and the flow trend of the cathode jet towards the position with small discharge gap is enhanced.The combined effect of the two makes the thermal characteristics of the pulse arc improved.An increase in arc length will lead to the expansion of arc shape,a decrease in current density,and a decrease in current density,resulting in a decrease in pulse arc temperature,jet strength,and electromagnetic force.As the arc length increases,transverse shrinkage deformation of groove also increases,strengthening the compression effect of the solid wall and the constraint effect on the arc,increasing the current density and guiding effect,resulting in an increase in pulse arc temperature,jet strength,and electromagnetic force.The flow trend of the cathode jet towards the position with small discharge gap is enhanced.The joint influence of the two ultimately leads to an improvement in the thermal characteristics of the pulse arc,indicating that the lateral contraction deformation of groove is the main factor affecting the characteristics of the pulse arc.However,an increase in arc length will lead to a decrease in current density,which will weaken the strengthening of the thermal characteristics of the pulse arc by transverse shrinkage deformation of groove.An increase in the duty cycle will lead to an extension of the peak current action time,the arc shape will be fully expanded,the current density has decreased slightly,thereby weakening the guiding effect,resulting in a decrease in the temperature,jet strength,and electromagnetic force of the pulse arc.As the duty cycle increases,transverse shrinkage deformation of groove also increases.The compression effect of the solid wall and the constraint effect of the insulation solid wall on the arc are enhanced,resulting in an increase in current density,thereby increasing the temperature,jet strength,and electromagnetic force of the pulse arc.At the same time,the guiding effect is enhanced,leading to an increased flow trend of the cathode jet towards the position with small discharge gap.Due to an increase in the duty cycle,the current density will slightly decrease,which will slightly weaken the strengthening effect of transverse shrinkage deformation of groove on the thermal characteristics of the constrained pulse arc,and ultimately weaken the improvement effect of the thermal characteristics of the constrained pulse arc. |
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