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System Identification of Controlled Pulse keyhole Plasma Arc Welding Process

Chinese Journal of Mechanical Engineering 2012年第6期25卷 1274-1280页

作者： JIA Chuanbao DU Yongpeng GUO Ning WANG Fang HAN Yanfei Shandong Provincial Key Laboratory of Special Welding Technology Institute of Oceanographic InstrumentationShandong Academy of SciencesQingdao 266001China

The development of closed-loop control systems is one of the most effective ways to improve the stability of the keyhole status during keyhole plasma arc welding （K-PAW）. Due to the disadvantages of the ＂one-pulse-one-keyhole＂ technology based on the conventional square current waveform, the controlled pulse welding current waveform is newly applied to control the keyhole open and close periodically. In order to realize the real-time control on the keyhole behavior with this advanced current waveform, welding experiments and system identification are conducted based on the classical control theory. One complete welding cycle can be divided into 3 periods. The keyhole establishing time is the most important time variable, which determines the keyhole behavior and welding process stability. At the same time, the averaged effiux plasma arc voltage during one pulse cycle can reflect the real keyhole dimension and status in a real-time manner. Therefore, two single-input-single-output （SISO） systems are proposed, in which keyhole establishing time and keyhole average dimension are taken as the system controlled variables respectively. Welding experiments are designed with the peak current varying randomly. Experiments show that the keyhole establishing time changes in an opposite direction to the varied peak current, and the averaged efflux plasma arc voltage varies with the same trend as the peak current. Based on the least squares technique and F test of classical system identification, second order difference equation for keyhole establishing time/peak current system and first order difference equation for keyhole average dimension/peak current system are obtained. It is proved that the calculated data by the two mathematical expressions are well matched with the measured data. The proposed research provides mathematical expressions and theoretical analysis to develop closed-loop systems for the controlled pulse K-PAW.

关键词： controlled pulse plasma arc welding keyhole system identification control

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NUMERICAL CALCULATION FOR 2-DIMENSIONAL HEAT TRANSFER IN keyhole LASER WELDING

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Chinese Journal of Mechanical Engineering 1998年第3期11卷 20-25页

作者： Xu Jiuhua Zhang Jingzhou Jiang Chengyu Luo Yumei Mechanical Engineering Institute, Nanjing University of Aeronautics and Astronautics Nanjing Univ of Aeronautics and Astronautics Nanjing China

A numerical method is presented for analysing 2 dimensional quasi steady state heat transfer in high power density laser keyhole welding processes. The mathematical model is established according to the conservation of mass, momentum and energy. Computation is performed by using the finite control volume method in the curvilinear coordinate system. A position prediction correction procedure is employed to identify the solid liquid interface location. This method is applied to the study of a typical keyhole welding process of an AISI 304 stainless steel plate and its feasibility is verified.

关键词： Laser welding Heat transfer keyhole Temperature distribution

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Driving mechanism of keyhole evolution during multi-pulse drilling with a millisecond laser

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Science China(Physics,Mechanics & Astronomy) 2019年第10期62卷 112-118页

作者： Yue Zhang Gang Yu XiuLi He ShaoXia Li WeiJian Ning Key Laboratory of Mechanics in Advanced Manufacturing Institute of MechanicsChinese Academy of SciencesBeijing 100190China Center of Materials Science and Optoelectronics Engineering University of Chinese Academy of SciencesBeijing 100049China School of Engineering Science University of Chinese Academy of SciencesBeijing 100049China

To better understand the physical processes of multi-pulse laser drilling,this study investigates the keyhole evolution and its driving mechanism in a time-resolved observation *** evolution characteristics suggested a two-phase process of rapid penetration followed by moderate *** revealed in the ejection and vaporization behavior,the keyhole evolution was dominated by ejection and vaporization during the rapid and moderate penetration stages,*** a single laser-pulsed drilling experiment,the driving mechanism itself was found to be affected by the dimensionless laser power *** effect of dimensionless laser power density on depth increment was then discussed by comparing the experimental observations with numerical simulation *** results further confirmed the driving mechanism of the keyhole *** results in this paper are useful for understanding the driving mechanism of the keyhole evolution during multi-pulse laser drilling.

关键词： multi-pulse laser drilling melt ejection vaporization keyhole evolution driving mechanism

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Numerical Simulation of Current Density Distribution in keyhole Double-Sided Arc Welding

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Journal of Materials Science & Technology 2004年第2期20卷 228-231页

作者： JunshengSUN ChuansongWU MinZHANG HouxiaoWANG NationalKeyLaboratoryofAdvancedWeldingProductionTechnology HarbinInstituteofTechnologyHarbin150001China KeyLab.ofLiquidStructureandHeredityofMaterial MinisityofEducationShandongUniversityJinan250061China

In the double-sided arc welding system (DSAW) composing of PAW+TIG arcs, the PAW arc is guided by the TIG arc so that the current mostly flows through the direction of the workpiece thickness and the penetration is greatly improved. To analyze the current density distribution in DSAW is beneficial to understanding of this process. Considering all kinds of dynamic factors acting on the weldpool, this paper discusses firstly the surface deformation of the weldpool and the keyhole formation in PAW+TIG DSAW process on the basis of the magnetohydrodynamic theory and variation principles. Hence, a model of the current density distribution is developed. Through numerical simulation, the current density distribution in PAW+TIG DSAW process is quantitatively analyzed. It shows that the minimal radius of keyhole formed in PAW+TIG DSAW process is 0.5 mm and 89.5 percent of current flows through the keyhole.

关键词： PAW+TIG double-sided arc welding Surface deformation of the weldpool keyhole Current density distribution

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Numerical analysis of transient keyhole shape in pulsed current plasma arc welding

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China Welding 2014年第4期23卷 69-75页

作者：孙俊华武传松 School of Materials Science and Engineering Shandong Jianzhu University Jinan 250101 Provincial Key Lab ofAdvanced Welding Technology Jiangsu University of Science and Technology Zhenjiang 212003. Institute of MaterialsJoining Shandong University Jinan 250061

Based on the characteristics of ＂one keyhole in a pulse＂ in pulsed current plasma arc welding （PAW） , the transient variation process of weld pool in a pulse cycle is simulated through the establishment of corresponding heat source model. And considering the effects of gravitational force, plasma arc pressure and surface tension on the weld pool surface, the dynamic change features of the keyhole shape in a pulse cycle are calculated by using surface deformation equation. Experiments are conducted and validate that the calctdated weld fusion line is in good agreement with the experimental results.

关键词： pulsed current plasma arc welding weld pool keyhole numerical analysis

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Experimental determination of the weld penetration evolution in keyhole plasma arc welding

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China Welding 2007年第1期16卷 6-8页

作者：胡庆贤武传松张裕明 Institute for Materials Joining Shandong University Jinan250061 Center for Manufacturing and Department of Electrical and Computer Engineering University of Kentucky Lexington KY 40506

keyhole plasma arc welding experiments are conducted to measure the weld geometry and penetration at different moments during the initial phase from igniting arc to quasi-steady state. Indirect information on keyhole formation and evolution in plasma arc welding can be extracted based on the weld macrophotograph at cross section. It has laid foundation to verify the mathematical models of keyhole plasma arc welding.

关键词： weld penetration keyhole plasma arc welding

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Acquisition and processing of coaxial image of molten pool and keyhole in Nd:YAG laser welding with high power

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China Welding 2004年第1期13卷 51-55页

作者：秦国梁齐秀滨杨永波王旭友林尚扬 State Key Laboratory of Advanced Welding Production Technology Harbin Institute of Technology Harbin Welding Institute

An experimental setup of acquiring the coaxial visual image of the molten pool and keyhole in high power Nd:YAG laser welding is introduced in this paper. It is one of the most difficult problems in acquiring coaxial image that the coaxial imaging signal of molten pool and keyhole must be separated from the laser beam with high power. This problem was resolved by designing a dichroitic spectroscope. The characteristics of imaging signal were analyzed and the coaxial image of molten pool and keyhole was acquired. A smoothing filter and a homomorphic filter were designed to remove the low frequency noise and to enhance the image according to the characteristics of imaging signal. At last, edges of molten pool and keyhole were detected and extracted based on image segmentation with threshold.

关键词： laser welding molten pool keyhole coaxial visual image image processing

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Simulation on the Melt Flow in Laser Full Penetration Welding with a Model Including a Non-Rotational Symme-try keyhole Based on Energy Balance

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稀有金属材料与工程 2011年第S4期40卷 120-124页

作者： Zhang L J1,Zhang J X1,Wu B1,2,Chen L2,Gong S L2,Wang H R3 1 State Key Laboratory of Mechanical Behavior for Materials,Xi’an Jiaotong University,Xi’an 710049,China2 Power Beam Processing Dept.,Avic Beijing Aeronautical Manufacturing Technology Research Institute,Beijing 100024,China3 School of Energy and Power Engineering,Xi’an Jiaotong University,Xi’an 710049,China Xi An Jiao Tong Univ Sch Energy & Power Engn Xian 710049 Peoples R China Xi An Jiao Tong Univ State Key Lab Mech Behav Mat Xian 710049 Peoples R China Avic Beijing Aeronaut Mfg Technol Res Inst Power Beam Proc Dept Beijing 100024 Peoples R China

A three dimensional model including a non-rotational symmetry keyhole of which the geometry is calculated base on the energy balance at keyhole wall is created to simulate the heat transfer and fluid flow within the molten pool during laser full penetration welding of titanium alloy *** order to take into account the effects of multiple reflections within the keyhole,a ray tracing method is employed and the coordinate dependent heat flux obtained is exerted on keyhole wall during the simulation on the heat transfer and fluid flow within molten ***,the computed weld cross sectional profile is compared with the experimental result to verify the model and it is fond that the simulation result is consists with experimental result.

关键词： laser welding titanium alloy non-rotational symmetry keyhole simulation

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NTWV-based sensing keyhole dimension in plasma arc welding

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China Welding 2008年第3期17卷 1-5页

作者：贾传宝武传松张裕明 Institute for Materials Joining Shandong University Center for Manufacturing and Department of Electrical and Computer Engineering Universityof Kentucky

During stable keyhole plasma arc welding, the pilot arc and the transferred arc exist at the meantime, and the arcs can be considered as a composition of two parts inside and outside the nozzle, respectively. Under the mechanical constriction and thermal contraction effects, the inside arc has certain arc length, electron density and arc profile etc. inducing constant tungsten-to-nozzle voltage. However, the arc outside the nozzle diverges at about 5 degrees and has certain characteristics similar to the free arcs. The nozzle-to-workpiece voltage （NTWV） depends mainly on the length of the arc, which gets bigger as increasing of the weld penetration and keyhole size. The NTWV sensor is developed for monitoring NTWV in real time. The welding experiments are designed to get different penetrations and keyhole sizes. It is found that as the weld penetration and the keyhole size increase, NTWV also increases linearly. The NTWV signals can be used as the feedback variable in automatic control of keyhole plasma arc welding.

关键词： keyhole plasma arc welding nozzle-to-workpiece voltage penetration keyhole sensor

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A computer-based control system for keyhole plasma arc welding

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China Welding 2007年第4期16卷 7-10页

作者：贾传宝武传松张裕明 Institute for Materials Joining Shandong University Center for Manufacturing and Department of Electrical and Computer Engineering University of KentuckyLexingtonKY 40506USA

A new kind of control system for keyhole plasma arc welding （K-PAW） was developed based on the computer and the Graphics Language--LabVIEW. It can set and output the required current waveforms with desired decreasing slopes so that the corresponding ＂opening and closing＂ of keyhole can occur periodically. With this control strategy of welding current waveforms, the workpiece is fully penetrated while no burn-through Occurs. keyhole plasma arc welding experiments were conducted to verify the stability and reliability of the developed system.

关键词： control system keyhole plasma arc welding

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