| Because of light quality ancd compact structure,thin-walled parts are widely used in many industries Such as aerospace,automobile manufacturing and so on.The thin-walled parts have small wall thickness and irregular structural shape,which make it difficult to keep high quality and low cost in traditional process.Metal additive maunufacturing technology provides an efficient method,but the heat inpiut of traditional method is more likely to lead to bad forming.Magnetic control welding technology is an emerging technology that gradually developing and improving in recent years,which control the shape of arc,flow of molten pool and droplet transfer to regulate the formation of weld seam and improve the quality of weld seam by exert non-contact electromagnetic force.Therefore,it is of great significance to study how to apply magnetic control welding technology on metal additive manufacturing of thin-walled parts effectively.The paper takes microbeam plasma surfacing for thin-walled parts as experimental object,and builds magnetic conrol welding test system.The different kinds of externtenal transverse magnetic field can be obtained by adjusting the excitation parameters.The CCD can be used to get molten pool shape of surfacing for thn-walled parts.The welding forming experiment of thin-walled parts was carried out under the external forward DC magnetic field,revcerse DC magnctic field,low frequency AC magnetic diels and intermediate frequency AC magnetic field.The change of the characteristics of arc and molten pool shape,the forming law of the surfacing layer and the evolvement of structure was analyzed.The results show that the welding are has a magnetic bias under the effect of the DC magnetic Held,and the deflection direction is related to the direction of the magnetic field.The welding are is oscillating periodically under AC magnetic field,the cross-section of surfacing layer in the non-magnetic region of thin-walled parts is "inverted gold ingot".The effect of external forward DC magnetic field on controlling the forming size of surfacing layer is obvious,in which the width decreases by 1.23mm at 45mT,decreasing by 35%.When a reverse 26mT DC magnetic field is applied,the fusion line of surfacing layer in magnetic region shows "wavy" after applying magnetic field,the effect of grain refinemnt is more obvious and the dislribution of grain structure is periodic.When the low frequency AC magnetic field is applied,and the magnetic induction is controlled at 6mT to 14mT,the periodic deflection of the welding arc has a stir function on the molten pool and the effect on the shape of the surfacing layer is small,meanwhile the original thick cell-shape crystals change to cellular dendritic crystals and equiaxed crystals.When the intermediate frequency alternating magnetic field is applied,the shape of surfacing layer changes obviously with the increase of the magnetic induction,and the shape of surfacing layer changes gradually from "inverted gold ingot" to "peach" at the same time.Aiming at the side images of the molten pool collected by CCD during the welding process,the technology of open window is adopted to select the characteristic area for image processing.And the Matlab was used to process the real-time digital images of molten pool collected by the experiment,such as median filtering,image enhancement,edge extraction and edge extraction etal,and a clear marginal curve of the molten pool was obtained finally.It is of great significance to realize the intelligent control of magnetic control welding for the subsequent extraction of image feature parameters.It is of great significance to extract image feature parameters for realizing the intelligent control of magnetic control welding technology. |
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