Approach to photorealistic halo simulations

A multiple-scattering Monte Carlo model that can produce near-photographic quality images is developed and used to simulate several dramatic halo displays. The model atmosphere contains an absorbing ozone layer plus two clear, molecular air layers with Rayleigh scattering surrounding a cloud layer and an atmospheric boundary layer with aerosol particles subject to Lorentz-Mie scattering. Halos are produced by right hexagonal or pyramidal crystals that reflect and refract according to geometric optics without diffraction, although "junk" crystals with a pronounced forward-scattering peak but no halo peaks may be included to simulate typical, faint halos. Model parameters include ozone height and content, surface and cloud pressure, cloud optical thickness, crystal shapes, orientations and abundances, atmospheric turbidity, aerosol radius, and albedo. Beams for each wavelength are sorted into small bins as halo beams if they have been scattered once only by a single crystal and otherwise as sky beams, which are smoothed and combined with the halo beams to produce images. Multiple scattering generally vitiates halos, but extremely rare halos, such as Kern's arc, can be produced if a significant fraction of crystals in optically thick clouds have identical shapes and are highly oriented. Albedo is a model by-product with potential value in climate studies.     

Numerical simulation on interaction between TIG welding arc and weld pool

The interface deformation between welding arc and weld pool is important in dynamic coupling numerical simulation on arc and pool. To reveal the interaction between welding arc and weld pool, unified mathematic model of TIG welding arc and pool was established in this paper. The moving interface was solved by updating the calculation region of arc and weld pool continually. Fluid flow and heat transfer of TIG welding arc and weld pool were analyzed basing on this model. The weld pool shape calculated by dynamic coupling welding arc and pool is more close to the experiment than that of non coupling calculation.     

Effects of applied magnetic field on twin-wire indirect arc shapes

Research on regularity of indirect arc shapes change with variation of applied magnetic field is studied. Results show that indirect arc would be elongated or compressed in XOZ plane with variation of applied transverse magnetic field’s direction and intensity, while the indirect arc would be deflected with the application of longitude magnetic field in YOZ plane, and the deflection degree and direction will be also changed by the variation of longitude magnetic field’s intensity and direction. It is considered that change of arc shapes is caused by variation of arc forces. The influence of Ampere force on indirect arc deformation and deflection is analyzed in this paper.     

Robust sensing of arc length

During arc welding, the arc heats and melts the workpiece as heat flux. When the welding current is given, the distribution and the intensity of the heat flux are determined by the length of the are. The measurement and control of the are length are fundamental in robotic and automated welding operations. Length of welding arc determines the distribution of the arc energy and thus the heat input and width of the weld. This work aims at improving the measurement accuracy of arc length using the spectrum of are light at a particular wavelength during gas tungsten arc welding (GTAW) with argon shield. To this end, effects of welding parameters on spectral distributions were studied. To verify the effects of base metal and arc length, the arc column was also sampled horizontally as Layers for spectral analysis. Results show that spectral lines of argon atoms are determined by are length, independent of welding parameters other than the current. Based on these findings, a compact arc light sensor has been designed to measure the arc length with adequate accuracy. A closed-loop arc length control system has been developed with the proposed sensor     

Effects of applied magnetic field on twin-wire indirect arc shapes

Research on regularity of indirect arc shapes change with variation of applied magnetic field is studied. Results show that indirect arc would be elongated or compressed in XOZ plane with variation of applied transverse magnetic field’s direction and intensity, while the indirect arc would be deflected with the application of longitude magnetic field in YOZ plane, and the deflection degree and direction will be also changed by the variation of longitude magnetic field’s intensity and direction. It is considered that change of arc shapes is caused by variation of arc forces. The influence of Ampere force on indirect arc deformation and deflection is analyzed in this paper.     

Flow turbulence in a cylindrical channel encompassing an electric arc

The effect of an electric arc on the gas flow in a cylindrical channel is investigated. It is shown that the striking of an arc in a laminar flow leads to its turbulence at the boundary of the arc column. Within the arc column, the flow is rendered laminar by the high viscosity of the arc plasma. However, thermal turbulence may develop in the central part of the arc.Academic Scientific Combine A. V. Lykov institute of Heat and Mass Exchange, Academy of Sciences of Belarus', Minsk. Translated from Inzhenerno-Fizicheski Zhurnal, Vol. 62, No. 4, pp. 601–607, April, 1992.     

Temperature, stress and microstructure in 10Ni5CrMoV steel plate during air–arc cutting process

Although the air–arc cutting process has been widely used in the material processing engineering, little information about temperature, stress and microstructure in the plate air–arc cut is known. A three-dimensional finite element model including the material removal and the thermal effect of the arc is developed to study the temperature and stress fields of 10Ni5CrMoV steel plate during air–arc cutting process in this paper. The microstructures and micro-mechanical properties of the parts near the groove especially in heat affected zone (HAZ) are studied by experimental methods, and they also can be used as a method to verify the numerical results. Effects of stresses induced by air–arc cutting process on the initial residual stress fields of base materials are also researched. The results show that the cooling velocity in HAZ is higher than the one of the welding process for the same base material, and the zone with high temperature is very narrow, which means that the temperature gradients near the groove are very steep during the air–arc cutting process; this special temperature field depresses multiphase transformations and coarse microstructures. The evolution of the stress during the air–arc cutting is described, and the numerical results indicate that the characteristics of the evolution of stresses and the residual stresses distribution in the plate in air–arc cutting process seem to be similar to the ones of the butt welding for flat plates. The influences of air–arc cutting process on initial stress fields present two aspects: thermal effect and material removal effect, and the former plays a primary role. Both numerical temperature and stress fields are compared with the experimental ones. It is very important for researchers to clarify the temperatures, stresses and microstructures in the plate during air–arc cutting process, and understand fully the mechanism of influences of air–arc cutting on the plate; it is also very valuable for engineering application of the air–arc cutting process.     

水或液氮中电弧放电制备炭纳米材料

利用特制的电弧放电装置，研究了水或液氮中碳电弧放电形成炭纳米材料的机理。借助高分辨率透射电子显微镜对电弧放电生成的产物进行了观察和分析。结果表明：在水或液氮中碳电弧放电可以生成多壁碳纳米管和碳纳米洋葱结构，液氮中碳电弧放电可以生成单壁碳纳米角，水中钴催化碳电弧放电可以生成碳包裹的纳米钴颗粒。横向低频交变磁场会影响碳纳米材料的形核过程，并且可以推测磁场交变的频率5Hz与纳米管、纳米洋葱等结构的生长周期存在某种拟合。根据实验现象，提出了一种解释液体中碳电弧放电过程纳米材料生成的理论模型。     

CO2-shielded arc as a high-intensity heat source

The characteristics of a CO₂-shielded arc are studied to evaluate its potential as a novel heat source for material processing, with lower costs and higher productivity than that of the tungsten–inert gas (TIG) arc. A double-gas-shielded system, using both CO₂ and an inert gas, is employed for the arc torch; this minimizes consumption of the tungsten electrode and gives arc stability equivalent to an argon TIG arc for 1800 s operation. The arc voltage of the CO₂-shielded arc is about 19 V for an arc current of 150 A and an arc gap of 3 mm, which is much higher than the 12 V obtained for an argon TIG arc. The CO₂ constricts the arc, resulting in an increase in the maximum heat flux density at the anode surface by a factor of about 10 relative to the TIG arc. The penetration depth of stainless steel melted by the CO₂-shielded arc is much larger than that for the argon TIG arc. It is concluded that the greater heating power of the CO₂-shielded arc, which is due to the greater arc constriction, in turn a consequence of the greater specific heat of CO₂, should lead to a large increase in material processing productivity.     

基于拉格朗日乘子法的空间圆弧拟合优化方法

针对传统的空间圆弧拟合方法鲁棒性低、拟合精度不高等问题,提出了一种鲁棒性较强的空间圆弧拟合优化方法。首先,以拉格朗日乘子法为基础,基于平面条件约束建立目标函数,从而得出空间圆弧拟合方程;其次,采用RANSAC（random sample consensus,随机抽样一致）算法剔除错误跟踪点,将RANSAC算法的高稳定性应用到空间圆弧拟合的点云优化中,进而提高拟合精度。最后,通过实验分析验证了所提空间圆弧拟合优化方法的可行性,并与传统拟合方法进行比较,分析所提方法的拟合精度。实验结果表明：普通圆弧点云拟合的相对精度在0.003左右,复杂圆弧点云拟合的相对精度在0.01左右;相较于传统拟合方法,所提方法有效解决了拟合精度低及鲁棒性差等问题。研究结果表明提出的空间圆弧拟合优化方法一方面可运用拉格朗日乘子法增强鲁棒性,另一方面可通过采用RANSAC方法剔除错误点以提高拟合精度,具有广泛的工程实际应用价值。     

Mathematical Modeling of Metal Active Gas (MAG) Arc Welding

In the present paper. a numerical model for MAG (metal active gas) arc welding of thin plate has been developed. In MAG arc welding, the electrode wire is melted and supplied into the molten pool intermittently. Accordingly, it is assumed on the modeling that the thermal energy enters the base-plates through two following mechanisms, i.e., direct heating from arc plasma and "indirect" heating from the deposited metal. In the second part of the paper, MAG arc welding process is numerically-analyzed by using the model. and the calculated weld bead dimension and surface profile have been compared with the experimental MAG welds on steel plate. As the result. it is made clear that the model is capable of predicting the bead profile of thin-plate MAG arc welding, including weld bead with undercutting.     

碳纳米管工具电极的制备

纳米工具电极是进行纳米电解加工的必备条件,其特征尺寸直接影响纳米结构的最终尺寸.提出了利用电弧放电将碳纳米管束焊接在钨针尖上的纳米工具电极制备方法,并通过试验研究了钨针的针尖圆弧半径和放电电压对制备碳纳米管工具电极的影响.试验结果表明,不同尖端圆弧半径的钨针,所需有效放电电压不同,圆弧半径越小,有效放电电压越小,强电场分布越集中,越容易将碳纳米管束焊接在针尖的顶端;圆弧半径越大,强电场分布区域越大,越不容易控制碳纳米管束焊接的方向性.在针尖圆弧半径约为100 nm和300 nm的钨针上,放电电压分别为25 V和35 V时,成功制备出碳纳米管工具电极.     

高铬铁基药芯焊丝不同堆焊工艺下的显微组织与性能研究

采用高铬铁基耐磨合金细粉做成药芯焊丝,分别用埋弧堆焊和等离子束堆焊方法制备耐磨试样,对试样的显微组织、硬度分布、耐磨性分别进行研究。实验表明：埋弧堆焊和等离子束堆焊组织具有较明显的区别,埋弧堆焊试样结晶定向性更好,晶粒更细化;埋弧堆焊涂层显微硬度平均值为791 HV0.2,等离子束堆焊涂层显微硬度平均值为774HV0.2,埋弧堆焊涂层的显微硬度分布更均匀;耐干砂磨粒磨损性能埋弧堆焊是等离子束堆焊的1.7倍。     

一种新型基于小波奇异性分析的故障电弧检测方法

在分析了故障电弧特性的基础上,提出了故障电弧周期零休的特征信息,该信息用小波分析时表现为周期性的奇异点,据此提出了周期性奇异点检测故障电弧的新算法。以LabWindows/CVI为平台,设计开发了基于小波奇异性检测原理的故障电弧在线检测系统,该系统运用多线程技术实现了对故障电弧的实时在线检测。     

Formation of stainless steel layer on mild steel by welding arc cladding

The discrete microstructural characterization and the formation of stainless steel layer on mild steel where produced in cladding deposits, and fusion boundary region were investigated using tungsten inert gas (TIG) arc, high current pulsed arc and constricted plasma arc. The experimental procedure involved making bead-on-plate method for controlled travel speed, employing filler metal by using tungsten inert gas arc, pulsed current gas tungsten arc and transferred plasma arc, with subsequent sectioning and examination of the reaction interface. For TIG arc cladding, using filler metal of small diameter the deposit does not become stainless steel, but on using 3.2 mm diameter filler metal it becomes stainless steel with less than 50% dilution. For pulsed arc cladding, the complete stainless steel is not obtained on account of the existence of an incomplete mixture, particularly at the fusion boundary region. However, on using a large diameter filler metal at a pulse frequency of 500 Hz, the complete stainless steel microstructure has been accomplished. The plasma arc cladding can be achieved in such a way that the conversion into stainless steel on the mild steel surface — which is the microstructures of cellular austenite in cladding deposit and cellular dendritic austenite containing δ or σ-phase in fusion boundary region — is possible irrespective of the melt penetration and the dilution. The following conditions were found to be beneficial for the formation of stainless steel microstructure layer on the mild steel: using large diameter filler metal, below 50% dilution, and further rendering arc localized and constricted.     

Distribution of heat flux transported by a magnetically driven arc

An alternating magnetic field is applied to a transferred arc to create a plasma arc for heating a large metal surface. The arc root oscillates on the metal surface at the frequency of alternating electromagnetic force (I × B force). The magnitude of the applied magnetic field controls the amplitude of the oscillatory motion. By changing the waveform of the applied field, the distribution of the heat flux density is adjustable. An overly strong magnetic field renders the oscillatory arc motion unstable. Experimental observations reveal that the heat flux is affected considerably by the neutral gas flow surrounding the arc.     

超音速电弧与普通电弧喷涂FeCrNiB涂层的耐磨损性能

为了提高电弧喷涂涂层的结合强度及耐磨损性能,采用超音速电弧喷涂技术和普通电弧喷涂技术在Q235钢表面分别制备了Fe17Cr5NiB涂层,通过扫描电镜(SEM)、X射线衍射仪(XRD)、显微硬度计、摩擦磨损试验机等手段对比分析了2种涂层的微观结构及性能。结果表明:超音速电弧涂层具有更加致密的结构,其平均孔隙率为0.95%,远低于普通电弧涂层;超音速电弧涂层与基体呈紧密结合,其结合强度为60 MPa,而普通电弧涂层与基体之间呈明显的分层状态,其结合强度仅为28 MPa;超音速电弧涂层具有良好的非晶态结构及致密性,使其具有远高于普通电弧涂层的硬度以及耐磨损性能,显微硬度高出普通电弧涂层32.27%,耐磨损性能是普通电弧涂层的2倍以上(是基体的14倍以上)。     

Laser-Monitor-Assisted Investigation of the Regions of Closure of Current on the Electrodes of an Atmospheric-Pressure Low-Current Carbon Arc

The results are given of observations of regions of closure of current on the electrodes of an atmospheric-pressure low-current carbon arc, performed using a laser monitor immediately during the time of burning of the arc. It is found that the time of existence of a cathode crater on a graphite cathode is 0.2–0.3 s. An analysis of images of the region of closure of current on a pyrographite cathode reveals evidence of melting of pyrographite. A comparison of images of the region of closure of current on the electrodes of a carbon arc with the available literature data on the conditions of closure of current on the anode and cathode enables one to establish the origins of the various details of images of the region of closure of current on the cathode and anode of a low-current carbon arc. The results of this comparison further lead one to conclude that a low-current electric arc is an arc with liquid cathode and anode spots, and that the melting process is a stabilizing factor as regards the current density in those spots.     

Role of arc mode in laser-metal active gas arc hybrid welding of mild steel

Arc mode plays an important role in joint characterizations of arc welding, but it has been seldom considered in laser-arc hybrid welding. This paper investigated the role of arc mode on laser-metal active gas (MAG) arc hybrid welding of mild steel. Three arc modes were employed, which were cold metal transfer (CMT), pulsed spray arc and standard short circuiting arc. Microtexture of the joints were observed and measured via electron back scattering diffraction (EBSD) system to reveal the effect of arc mode on microstructure. Mechanical properties of the joints were evaluated by tensile and Charpy V-notch impact tests. It was found that both the stability and mechanical properties of laser-CMT hybrid welding (LCHW) is the best, while those of laser-standard short circuiting arc welding (LSHW) is the worst. OM and EBSD results showed that the fraction of acicular ferrite and high-angle grain boundaries in fusion zone decreases gradually in the sequence of LCHW, laser-pulsed spray arc welding and LSHW, while the mean grain size increases gradually. Finally, the microstructure formation mechanisms and the relationship between microstructure and mechanical properties were summarized by the loss of alloying element and the stirring effect in molten pool.     

Mechanism of Metal Transfer in DE-GMAW

Modification of conventional gas metal arc welding (GMAW) process is of great potential to achieve high productivity with low cost and strong usability.Double-Electrode GMAW (DE-GMAW) is such a modified arc welding process which is formed by adding a bypass torch (gas tungsten arc welding torch) to a conventional GMAW system.The mechanism of metal transfer in DE-GMAW was proposed and verified in this paper.Experiments show that the critical current is decreased so that spray transfer can be obtained at a lower current level in DE-GMAW.Analysis of this significant change in metal transfer phenomena is conducted, and explanation is given out.It is found that the bypass arc in DE-GMAW lifts the anode point on the droplets such that the electromagnetic force becomes larger and squeezes the droplets so that spray transfer can take place under welding current lower than that in conventional GMAW.