Research On Mechanism Of Flash Beam Blasting Based On Digital Imaging Technology And Pertinence Of Welded Joint Property

The mechanism of the two welding modes,AC and DC,is investigated from the aspects of flash beam blasting,welding surface status,heating efficiency and welding temperature field,based on digital imaging technology such as high-speed photography system,infrared imaging system.In this paper,the mobile rail welding machine is mainly researched.Therefore,the process of power frequency AC and intermediate frequency inverter DC welding is mainly studied;At the same time,normalizing of flash butt welding joint was tested and analyzed based on a new digital IGBT induction heating system,that verified this new equipment can be used for rail postweld heat treatment,at the same time,it further validatedproperties ofthe flash butt welding joints were improvedthrough postweld heat theatment.Through the above experiments and analysis,the main conclusions are as follows:(1)In flash flat stagethe two modes welding,craters with large area are most located in the railhead,and the formation of craters with large area and depth are mainly caused by the adhesion;Craters smaller in area anddepthmostly caused by flash beam blasting;The shape factorsof the crater are related with its formation reasons,the shape is regular when the crater is simultaneous affected by flash and adhesion.But the flash beam blasting will cause the shape to break away from the basic circle,whenflash beam blasting and adhesion simultaneous happening at the same site,the formation of the crater shape is more irregular,and most of them occur on the rail bottom,which is more in conformity with the appearance of the observed flat spots;(2)Accelerate flash stage has the highest flash frequency,pulse flashstage has the lowst;Continuous flash stage has the strongest flash intensity,pulse flashstage has the weakest;Pulse flash stagehas the highest flash heating factor,accelerate phasehas the lowest;hand flash uniformity,In terms of flash uniformity,flash-flatstage is most uneven,pulse flash stage is the most uniform;(3)The flash characteristic values of each stage are matched with the mechanism of each stage,and the theoretical analysis is verified quantitatively;In the whole flash stages,heating from the flash is much lower thanthe short circuit in the pulse flash stage;(4)There is very small arc discharge phenomenon between end faces when they are closing to each other but without contact,the duration is very short;In the early process of flash,the splash droplets of liquid metal seem to have a certain direction,but then changed to evenly around patterm,it is not observed that the drift of the splash is affected by the electromagnetic force of the transformer;(5)There are unstable flash in the early stage of flash in the two modes of welding,and the heating zone temperature both reached the highest in the end of pulse flash stage;but in terms of temperature gradients,the DC mode is slightly higher than the mode of AC;(6)The average flash frequency at each stage of DC welding is higher than that of AC welding,the flash intensity and flash heating factor are smaller than AC welding;(7)The short-circuit resistance value of DC welding is much lower than that of AC welding,which is more beneficial to the stability of flash in welding process and is beneficial to improve welding quality;(8)From the observation of fracture surface and the result of flat spot scanning,there is no obvious difference between the two patterms;(9)The new digital series resonant IGBT rail postweld heat treatment equipment can effectively reduce the heat treatment power size,solves the high maintenance requirements and large volume of the exiting power;In the process of heat treatment,the constant power method is used with its better temperature uniformity and repeatability;The equipment can satisfy postweld treatment of the flash butt welded joint,and through the performance test,the significantly improved of the joint's performance with postweld heat treatment is verified.