Mechanism And Forming Control Of Arc Additive Repair Process In Self-shielded Flux Cored Wire

Aiming at the problem of how to urgently,quickly and accurately complete the additive repair of key parts of weapons in wartime environment and field harsh environment(high temperature,strong wind,plateau and desert),this paper innovatively putted forward a selfshielded flux cored wire additive repair technology to suitable for wartime and field working environment.The proposal of this technology will solve the problems of rapid emergency repair and rapid and accurate supply of equipment parts under battlefield and some field extreme working conditions.The application of this technology will greatly shorten the supply chain of parts,simplify logistics supply and improve maintenance efficiency.In addition,the research of this technology will support the development of intelligent,modular and integrated arc additive repair equipment and on-board and shipborne "shelter" systems,and provide theoretical and practical guidance for the reform of equipment maintenance system.Due to the addition of flux core components in self-shielded flux cored wire,special wire structure and interference of working environment,there were some problems in the process of addition repair in self-shielded flux cored wire,such as poor stability and forming accuracy.In order to solve these problems,this paper mainly focused on the process mechanism of arc additive repair of self-shielded flux cored wire.The main research contents of this paper are as follows:(1)In order to meet the design requirements of field additive repair equipment and additive materials,a miniaturized and highly mobile additive repair prototype device suitable for field environment was developed by using customized special titanium calcium self-shielded flux cored wire,robot system,welding system,three-dimensional scanning system and other software and hardware systems were designed;in order to accurately observe and analyze the droplet transition process,a synchronous acquisition system of droplet transition image and electrical signal was built through the design of high-speed camera system and electrical parameter acquisition system;in order to analyze the physical characteristics of arc in the process of self-shielded flux cored wire arc welding,an arc spectrum acquisition system based on spectrum analyzer was designed in this paper;at the same time,in order to analyze the variation of base metal temperature field in the process of single-layer multi pass forming,a base metal temperature measurement system was built based on infrared thermometer;in order to efficiently and accurately analyze the characteristics of droplet transition,an analysis system for automatic detection,tracking,counting and automatic calculation of droplet average size was designed and developed in this paper.The automatic statistics and analysis of droplet average size and droplet transition frequency were realized.The verification results shown that the accuracy of the statistical results in the analysis system was more than 93%,the system meet the requirements of design and application.(2)According to the special design of flux core composition of customized welding wire,combined with the characteristics of flux core metallurgical reaction,the effects of current,voltage and electrode polarity on droplet transfer mode and arc behavior was analyzed,the key process factors affecting droplet transfer mode and arc behavior were found.The results shown that electrode polarity was the main factor determining droplet transfer mode and arc behavior,and current and voltage were the main factors affecting droplet average size and frequency;in order to study the characteristics and laws of metallurgical reaction in droplet reaction zone under different electrode polarities,the morphology and element distribution characteristics of droplet bottom reaction zone under different electrode polarities were analyzed.The results shown that there were great differences in the morphology and element distribution characteristics of droplet reaction zone under different electrode polarities,and the arc behavior under different electrode polarities become the main affecting factor;in order to explore the influence mechanism of different electrode polarities on droplet transition mode,a droplet force model was established.The analysis results were shown that under different electrode polarities,distribution characteristics of a large number of low ionized oxides and a small amount of low melting point fluoride in droplet reaction zone determine the direction of electromagnetic force acting on the droplet,so that when the direct current electrode negative(DCEN),the electromagnetic force was the main force to promote the droplet transition,and the droplet transfer mode was the spray transfer.Under the direct current electrode positive(DCEP),the electromagnetic force become the main force to hinder the droplet transition,and the droplet transfer mode performed the large droplet repulsion transition;in order to reveal the causes of instability in droplet transition process and the formation mechanism of spatter,the process of droplet spatter was analyzed.The results shown that in DCEP,there was mainly deviation spatter,which always exists,which has become the main reason for deteriorating welding quality.Under DCEN,high current and voltage parameters would cause an obvious explosion splash process.(3)In this paper,from the perspective of arc physics,and the electron density field,temperature field and the distribution characteristics of active elements in arc plasma with different electrode polarities were calculated quantitatively.It was shown that the different conductive channel models at the bottom of droplets determine the distribution characteristics of active elements,arc electron density and arc temperature field.The establishment of the conductive channel model provides a theoretical basis for the analysis of arc dynamic behavior.(4)In order to realize the low heat input of the substrate,control the droplet transfer process and improve the stability of the forming process,the feasibility of controlling the droplet transfer process in the customized self-shielded flux cored wire based on the shortcircuit waveform was explored.The results shown that due to the short-circuit explosion phenomenon and the insufficient metallurgical reaction of the flux core in the short-circuit stage,the short-circuit transition mode in the short-circuit stage become the main reason for deteriorating the stability of the forming process;Considering the method of controlling droplet transfer process by pulse current waveform,various main functional characteristics of strong and weak pulse peak groups in double pulse current waveform were analyzed,and the quantitative calculation models of deposition efficiency and arc force were established.The results shown that under the same arc power,double pulse arc mode has lower heat input,higher deposition rate and easier droplet transition;In order to observe the influence of key parameters of double pulse arc on droplet transfer characteristics,the change law of droplet transfer characteristics was statistically analyzed.The results showed that when the droplet size is 0.5 ?0.9 mm,the process of droplet transfer was mainly one pulse and one drop,among which the current variation coefficient was the smallest and the arc additive repair process is the most stable.When the droplet size was less than 0.5 mm,it mainly showed that there were many droplets in one pulse,resulting in the explosion of delayed melting slag column,which seriously affects the stability of material addition process;In order to realize the stable transition by one pulse and one drop,a droplet size control scheme based on optimal adjustment of pulse parameters was proposed,and a droplet size prediction model based on RBF-BP neural network was established.(5)The characteristic parameters of weld morphology have become a necessary part in slice design based on 3D scanning reconstruction model.Therefore,this paper mainly established a weld forming prediction model based on GA-BP neural network;based on the goal of real-time closed-loop feedback control of weld width,an RBF neural network PID controller was designed,and the performance of the controller was verified by simulation experiments to meet various performance indexes;by observing the thermal cycle curves and residual stress curves under three conventional scanning paths,the rationality of scanning path planning was verified.The results showed that the path mode of short side reciprocating scanning mode has lower base metal heat input and smaller residual stress after welding.(6)Designed and successfully carried out the additive repair experiment in the highaltitude field working environment,and verified the effectiveness of the technology in the field working environment.The performance and accuracy after repair meet the emergency repair requirements under wartime conditions,and satisfied the technical indexes of field additive repair;In order to normalize and standardize the field additive repair process,the additive repair process specification was formulated,it was suitable for the field working environment.