Development and implementation of a magnetoplasmadynamic thruster for welding and cutting

The main aim of this work was to construct and study an electromagnetic device to weld and cut materials. This device, known as magnetoplasmadynamic thruster (MPDT) ionizes gas, forming a plasma jet at high temperatures. Firstly, tests were performed analyzing the influence of physical variables (electric current intensity, relative position of electrodes, gas flow rates and angle of the extremity of the cathode) on the plasma jet. Based on the results of theses tests, the parameters best adapted for welding and cutting were chosen. So, autogenous welding of stainless steel sheets was performed, as well as cutting of sheets with different thicknesses and different materials.

The results have shown that this electromagnetic device can be used for welding and cutting.     

Measurement of surface temperature of weld pools by infrared two colour pyrometry

Abstract

In this research, two colour pyrometry was conducted to obtain the surface temperature of weld pools, in which the weld pool was photographed by a high speed camera during arc welding. Two wavelengths (950 and 980 nm) of light in the infrared range were selected from the thermal radiation light emitted from the weld pool at the instant when the arc was extinguished, using an imaging spectroscope. Consequently, in gas tungsten arc welding, it was shown that the surface temperature distribution of a weld pool is affected by the sulphur content in the base metal. It is thought that this temperature distribution is determined by the balance between the driving forces of viscous drag from the cathode jet of plasma and Marangoni surface tension. In gas metal arc welding, it was seen that the surface temperature distribution becomes uniform and the temperature is 1715–1845 K, which is obviously lower than that of the metal droplet.     

双钨极TIG电弧压强分布及其与等离子体喷射的关系

建立一个三维的统一的双钨极TIG焊模型,利用磁流体动力学理论对双钨极、电弧、阳极三个区域进行统一求解,获到双钨极电弧的压强分布,探究等离子体喷射与对电弧压强的关系。研究发现,双钨极TIG在钨极下方、阳极上方以及两束等离子体流交汇处存在较大的电弧压强,这些高压区的形成与等离子体喷射存在因果关系。计算发现,双钨极TIG焊在阳极表面上的最大压强远小于单钨极TIG焊的,这为双钨极TIG焊的应用提供了一些理论基础。     

扫描速度对球墨铸铁表面等离子束硬化组织和性能的影响

对不同扫描速度下球墨铸铁表面等离子束处理的组织和性能进行了分析研究.结果表明,在保持工作电流为60 A,工作电压为30 V的条件下,扫描速度从10 mm/s增加到50 mm/s,球墨铸铁表面发生了熔凝硬化;扫描速度增大,熔凝层和硬化层的深度、宽度减小,硬化层的最高硬度值增大,熔凝硬化区石墨相消失,其室温组织为细小的变态莱氏体+残余奥氏体,相变淬火区组织为针状马氏体+变态莱氏体+包围球状石墨的变态莱氏体、马氏体双壳组织;双壳组织硬度达到917.8 HV0.1,对提高耐磨性有利.     

等离子束表面冶金与激光溶覆技术

介绍了等离子束表面冶金和激光熔覆技术的原理、特点和研究现状,分析比较了两种技术的工艺特点及涂层组织结构特点.由于等离子束表面冶金技术具有突出的优质高效低成本综合优势,且涂层原料来源广,在市场竞争中具有潜力.     

Modeling the keyhole shape and dimension in plasma arc welding

It is of great significance to model the keyhole shape and dimensions to optimize the plasma arc welding process parameters. In this study, through employing a combined volumetric heat source mode, the weld pool in keyhole plasma arc welding is determined firstly, and then the dynamic force-balance condition on the interface between the plasma jet and the molten metal is dealt with in describing the keyhole formation inside the weld pool. The effects of welding current on the shape and size of keyhole are numerically analyzed. The sharp transformation from a partial keyhole to a full-penetration keyhole is quantitatively demonstrated.     

织构化热处理对钢轨钢耐磨性和寿命的影响

目的减小钢轨钢表面因离散硬化产生的硬化区与基材边界处的硬度突变,从而消除磨损过程中硬化区与基材边界处因材质不连续而产生的早期碎裂现象,进一步提高钢轨钢的耐磨性和寿命。方法提出了一种基于层流等离子体束离散硬化的表面织构化热处理方法。与之前的离散圆点状硬化不同,通过调节等离子体束在试样表面的运动速度,改变试样表面的加热时间,在硬化区与基材之间人为地附加了一个过渡区。为了揭示织构化热处理对钢轨钢滚滑性能的影响,在摩擦磨损试验机上进行了磨损试验。磨损后的试样经切割、打磨、抛光和腐蚀,在光学显微镜和扫描电子显微镜下进行了观察,以分析试样的磨损过程和织构化热处理提高试样耐磨性的机理。结果由于附加过渡区的存在,相变区的一边被拉长,形状变为泪滴状。硬化区到基材的硬度变化率由3500 HV/mm降低至200 HV/mm,在圆点状硬化中可观察到的硬度突变消失。同时,在磨损实验中,泪滴状硬化试样的磨损量较圆点状硬化试样降低了27%,边界碎裂消失。结论具有附加过渡区的试样比圆点状硬化的试样具有更好的耐磨性和抗塑性变形能力,该方法对提高钢轨钢的使用寿命具有一定的应用前景。     

大型挖掘机铲斗高锰钢焊接工艺的研究

高锰钢在较大的冲击载荷或接触应力作用下,其表层迅速产生加工硬化,生成高密度位错和形变孪晶,产生高耐磨的表面层,内层奥氏体仍保持着良好的韧性。当焊接、切割、碳弧气刨等工序使高锰钢再次加热,极易使碳化物沿晶界析出,从而使其热影响区失去韧性而变脆。本文通过对大型挖掘机铲斗材料和结构的研究,制定出既能保证焊接接头质量又经济的大型挖掘机铲斗的高锰钢焊接工艺。     

水下局部干法焊接圆形排水罩的流体仿真分析

对于水下局部干法焊接,其局部排水装置的排水效果及装置内流体湍流状态决定了焊接过程的稳定性,是影响焊接质量的关键因素之一. 以圆形排水罩结构作为局部排水装置进行研究,基于流体力学,利用FLUENT软件进行模拟仿真,探索圆形排水罩的排水过程,分析不同的进气方式和排水方式对罩内相分布的影响,以及对工件表面流体湍流状态的影响. 并将模拟仿真的排水过程与试验进行对比,验证仿真的准确性. 结果表明,模拟仿真与实际排水过程演变趋势基本一致,模拟仿真结果具有一定的可信度. 通过对比分析,确定合理的排水罩进气和排水方式,为局部水下焊接的稳定性提供基础数据.     

Modelling the Plasma Jet in Multi-Arc Plasma Spraying

Particle in-flight characteristics in atmospheric plasma spraying process are determined by impulse and heat energy transferred between the plasma jet and injected powder particles. One of the important factors for the quality of the plasma-sprayed coatings is thus the distribution of plasma gas temperatures and velocities in plasma jet. Plasma jets generated by conventional single-arc plasma spraying systems and their interaction with powder particles were subject matter of intensive research. However, this does not apply to plasma jets generated by means of multi-arc plasma spraying systems yet. In this study, a numerical model has been developed which is designated to dealing with the flow characteristics of the plasma jet generated by means of a three-cathode spraying system. The upstream flow conditions, which were calculated using a priori conducted plasma generator simulations, have been coupled to the plasma jet simulations. The significances of the relevant numerical assumptions and aspects of the models are analyzed. The focus is placed on to the turbulence and diffusion/demixing modelling. A critical evaluation of the prediction power of the models is conducted by comparing the numerical results to the experimental results determined by means of emission spectroscopic computed tomography. It is evident that the numerical models exhibit a good accuracy for their intended use.     

复合材料用碳纤维等离子体表面改性技术进展

近年来复合材料得到了广泛的应用,尤其在航空工业领域,已成为了世界强国竞相发展的核心技术。碳纤维树脂基复合材料作为复合材料中的优秀代表,由于其独特的性能优势,具有很大的发展潜力,但是界面结合强度是制约其应用的关键瓶颈。等离子体表面改性技术能提高碳纤维与树脂基的界面结合强度。总结了国内外学者工作,从等离子体处理装备发展和工艺参数影响两个角度对碳纤维等离子体表面改性技术的研究进展进行了阐述。在装备发展方面,重点介绍了在碳纤维表面处理研究中三类处理装置,包括射频等离子体处理装置、DBD等离子体处理装置和滑动弧射流等离子体处理装置,分析了各自的优缺点。在工艺参数方面,重点介绍了不同等离子体种类、等离子体处理时间、等离子体放电功率对碳纤维表面状态的影响规律。在此基础上,对碳纤维等离子体表面处理技术的未来发展方向进行了展望。     

Hybrid machining of Inconel 718

A new approach for machining of Inconel 718 is presented in this paper. It combines traditional turning with cryogenically enhanced machining and plasma enhanced machining. Cryogenically enhanced machining is used to reduce the temperatures in the cutting tool, and thus reduces temperature-dependent tool wear to prolong tool life, whereas plasma enhanced machining is used to increase the temperatures in the workpiece to soften it. By joining these two non-traditional techniques with opposite effects on the cutting tool and the workpiece, it has been found that the surface roughness was reduced by 250%; the cutting forces was decreased by approximately 30–50%; and the tool life was extended up to 170% over conventional machining.     

焊接与切割设备的使用和维修(六十二)——空气等离子弧切割机的使用与维修

焊接和切割时等离子体是利用电弧在高度压缩的情况下弧柱的温度大大提高,从而使气体电离而获得.介绍了焊接与切割时等离子的产生过程,等离子孤切割的最大优点,以及等离子切割技术的最新发展.     

Kerf characteristics in abrasive waterjet cutting of ceramic materials

An abrasive water jet (AWJ) can provide a more effective means for precision cutting of ceramic materials as compared with conventional machining methods, but many aspects about this cutting technology are still under flux and development. In this study, experimental techniques based on statistical experimental design principles and theoretical investigations were conducted to study AWJ cutting of alumina-based ceramics. Semi-empirical cutting depth equations are determined for the prediction and optimization of the AWJ cutting performance. Topographical characteristics of uncut-through kerf and the effects of various parameters are discussed. In addition, visualization studies are conducted to develop further understanding of the macromechanics of the AWJ cutting process.     

等离子喷焊在三偏心蝶阀上的应用

三偏心金属密封蝶阀由于具有耐腐蚀性好、密封可靠、开启力矩小等优点,逐步得到广泛应用.为提高密封面耐磨性,延长使用寿命,需时密封面进行改性处理.在采用自动等离子喷焊代替手弧焊实现三偏心蝶阀密封面喷焊的过程中,出现了喷焊面非线性位移、焊层开裂等问题.在研制以单片机80C196KC和CPM2A-60CDR-A可编程控制器为核心组成的喷焊自动跟踪控制系统的基础上,经过大量工艺试验,合理选择喷焊材料和工艺参数,在不预热条件下,得到成形均匀、无裂纹等缺陷、质量符合要求的自动等离子喷焊层,此成果已成功应用于实际产品的生产上.     

Hump formation mechanism in gas-jet-assisted keyhole laser welding of HR-2 stainless steel

Gas-jet-assisted keyhole laser welding offers the possibility of a breakthrough in the limitations of penetration depth in laser welding,which currently suffers from equipment restrictions.A gas jet of sufficient intensity to assist the keyhole should be used to obtain suppressed plasma,a deepened keyhole,and increased penetration depth.However,an excessively strong gas jet gives rise to humps.The incident angle of the keyhole-assisted gas jet is 60°,with a nozzle ahead of the laser beam.A series of experiments were carried out with different welding velocities and gas parameters by using HR-2 hydrogen-resistant stainless steel and a slab CO_2 continuous-wave laser welding machine.The weld profiles can be categorized into four types,welds of traditional laser welding,welds of enhanced laser welding,undercut welds,and humping welds with increased gas pressure.A high-speed camera was employed in the experiments to monitor the formation of humps under an excessively strong gas jet.The results of analysis show that hump formation can be divided into six stages.Its main driving force is the intense turbulence of gas jet.There are two main reasons for hump formation:premature solidification of the molten pool caused by the large temperature gradient between the front and rear parts of the molten pool,and the emergence of a thin layer liquid bridge with one-directional flow under the enhanced cooling effect of excessively strong gas.     

车削速度对GH4169加工表面完整性的影响

加工表面完整性对材料的服役性能有着重要的作用。使用陶瓷刀具,对高温合金GH4169进行车削加工,分析不同车削速度对表面完整性各特征参量的影响,采用光学显微镜、扫描电子显微镜、显微硬度仪和XRD等仪器对表面微观结构、显微硬度和残余应力进行观测。结果表明:表面粗糙度随切削速度的增大而减小;加工表层存在滑移,且有明显的加工硬化现象,表层显微硬度随着车削速度的增大呈现增大趋势;轴向表面残余应力均为拉应力,且随着车削速度的增大拉应力先增大后减小,原因在于当速度增大至一定程度时,热量短时间内无法传递到工件内部,导致热效应的作用效果减弱。     

The corrosion and corrosion-wear behaviour of plasma nitrided 17-4PH precipitation hardening stainless steel

Plasma surface nitriding of 17-4 PH martensitic precipitation hardening stainless steels was conducted at 350 °C, 420 °C and 500 °C for 10 h using a DC plasma nitriding unit, and the surface properties of the plasma surface engineered samples were systematically evaluated. Experimental results have shown that the surface properties of the plasma nitrided layers in terms of hardness, wear resistance, corrosion behaviour and corrosion-wear resistance are highly process condition dependent, and it is feasible to provide considerable improvement in wear, corrosion and corrosion-wear resistance of 17-4PH steel using optimised plasma treatment conditions. All three treatments can effectively improve the surface hardness and the sliding wear resistance under unlubricated conditions; high temperature (420 °C and 500 °C) treated materials revealed improved corrosion and corrosion-wear properties due to the formation of surface compound layers.     

等离子切割用的水帘除尘器及其技术经济效益比较

在普通压缩空气等离子切割机上加装水帘除尘器，可以消除因超高温切割而广：生的含有金属蒸气的大量烟尘，减少环境污染，改善不锈钢板切口金相组织。与其它设备或技改方案相比，具有较高的技术经济效益。     

Plasma polymerized hexamethyl disiloxane in adhesion applications

The plasma polymer of hexamethyl disiloxane (HMDSO) was investigated as an adhesive for the gluing of silicon-to-silicon for potential application in microelectronic device and sensor fabrication. The aim of this work was to determine whether nm-thick films of HMDSO deposited in excess oxygen could be used as an adhesion layer for the bonding of silicon or glass to itself or other materials. The adhesive should be stable at high temperature and it should not outgas. The chemical nature of the thin films was analysed using Fourier transform infra red spectroscopy (FTIR) and contact angle measurements. Thermal stability was investigated using gas chromatography combined with mass spectroscopy (GC/MS). Adhesive strength was determined using an Instron tensile testing apparatus. Results show that a combination of plasma surface modification and plasma deposition reactions allow for the fabrication of Si-Si sandwiches that show shear strength up to 6 MPa, which would be sufficient for bonding applications in many microelectronic devices. The deposited materials were temperature stable. Sources of errors and methods to overcome these are discussed.