穿孔型双面电弧焊的传热与小孔形成

建立了穿孔型双面电弧焊小孔形态和传热的数学模型,考虑了作用于熔池上的各种力学因素,并采用帖体曲线坐标系处理复杂的熔池表面和小孔与熔池的边界。计算结果表明,熔透是穿孔的必要条件,熔透之后穿孔的速度远远大于熔透之前的。随着板厚的增加,熔透和穿孔所需的时间增加,并且熔透到穿孔的时间间隔也增大,但熔池的最小跨距变化不大,熔池的最小跨距可作为小孔建立的评价指标。小孔的形成使得焊接能量更加集中于电弧中心线附近,从而可以采用较小的焊接热输入,不开坡口一次焊透焊件。     

基于焊缝熔透检测的机器人深熔K-TIG焊接系统

开发了一套基于熔透检测的机器人深熔锁孔非熔化极惰性气体保护焊接(Keyhole tungsten inert gas, K-TIG)系统,实现焊接高度(Contact tip-to-work distance, CTWD)自动调节与熔透状态的在线检测。利用电弧电压与焊接高度的对应关系,通过弧压传感器实时采集电弧电压信号并换算成焊接高度值,然后将实际高度值与预设高度值之间的差值经由过程控制对象连接与嵌入协议(OLE for process control, OPC)通信系统反馈给机器人控制系统,从而控制机器人实现焊接高度的自动调节。同时,构建了熔透检测系统,使用电荷耦合器件(Charge coupled device, CCD)相机采集熔池与小孔图像,从中提取熔池-小孔特征,并建立熔池-小孔特征与熔透状态之间的相关性,在此基础上建立识别熔透状态的反向传播(Back propagation, BP)神经网络,实现不同焊接高度下熔透状态的间接检测,最后根据该检测结果得到最佳的焊接高度。经过试验验证,整个系统可靠稳定,能准确检测焊缝的熔透程度,并实现焊接高度自动调节,从而提高了焊接质量。     

熔透状态识别预测与控制技术研究现状

焊接过程中,熔透是保证焊缝质量的前提,实时监控焊缝熔透状态对实现自动化焊接和保证焊接质量具有重要的工程意义.在焊接过程中,可以通过分析熔池动态特征参数、焊接电参数、电弧声信号等识别预测熔透状态,从而实现控制熔透.近几年来,国内外专家学者在焊缝熔透方面取得了大量的研究成果.本文综述了较前沿的基于学习模型、数学建模、神经网...     

逆变脉冲熔化极气体保护焊机的工艺特性

众所周知,脉冲熔化极气体保护焊是在一定平均电流下,焊接电源的输出电流以一定的频率和幅值变化来控制熔滴有节奏的过渡到熔池;可在平均电流小于临界电流值的条件下获得射流过渡,稳定地实现一个脉冲过渡一个(或多个)熔滴的理想状态,熔滴过渡无飞溅。并具有较宽的电流调节范围,适合板厚≥1.6mm工件的全位置焊接,尤其对一些热敏感性较强的材料,可有效地控制热输入量,改善接头性能。由于脉冲电弧具有较强的熔池     

MIG焊电弧声信号与熔透状态相关性

电弧声作为焊缝熔透状态监控的潜在源信号,对焊接过程质量控制和自动化生产的实现具有重要意义.以MIG焊平板对接射流过渡过程中产生的非平稳电弧声信号为研究对象,采用小波变换技术取得了良好的信噪分离效果,达到有效抑制噪声目的.在此基础上,通过合理地选择样本数据,从时域、频域和时频联合3个角度研究分析电弧声信号与焊缝熔透状态之间的内在相关性,发现电弧声信号能量及其频谱特性与熔透状态高度相关,其中1 500～4 500 Hz频率段信号能量的变化可准确地检测出焊接过程熔透状态的改变.结果表明利用电弧声信号进行熔透状态监控是可行的,为MIG焊接过程质量监控提供了一种廉价而有效的新途径.     

基于Hammerstein模型的GMAW-P焊接熔深自适应预测控制

针对脉冲熔化极气体保护焊(Pulsed gas metal arc welding,GMAW-P)过程中焊接熔深的实时控制,使用脉冲峰值期间的电压变化幅值(ΔU)来表征焊接熔深变化,并且通过测量和控制ΔU的大小来间接达到熔深控制的目的。建立了以ΔU为输出和脉冲基值电流为输入的单输入单输出熔深控制系统。系统输入输出之间的静态关系模型显示该熔深控制系统具有一定非线性,因此,采用加入干扰的Hammerstein模型描述该非线性系统。在基于该Hammerstein模型的经典预测控制算法基础上,在控制过程中加入递推最小二乘法在线辨识模型参数,从而实现焊接熔深自适应控制。控制算法仿真和实时焊接试验表明该熔深控制算法能够较好地实现GMAW-P焊接过程中的熔深控制。变散热试验结果验证了该控制算法的有效性和适应性。     

全熔透钨极惰性气体保护电弧焊熔池表面变形动态过程的数值分析

基于能量守恒和质量守恒原理,并依据能量最小化理论,推导出全熔透钨极惰性气体保护电弧焊(Gas tungsten arc welding,GTAW)熔池自由上、下表面变形的控制方程组,并探讨与文献给出的熔透熔池上、下表面变形控制方程组的异同,给出控制方程组中将熔池上表面变形和下表面变形耦合为一个统一整体的拉格朗日参数的求解方案。分别对GTAW焊接不锈钢和低碳钢薄板从引弧到熔透并达到准稳态的全过程中熔池上、下表面变形的动态演变进行预测和分析,从中提取出了可用于表征工件熔透与否的参数,为基于正面视觉检测的背面熔透智能控制提供了依据。     

Nd:YAG激光焊接殷钢薄板材料的工艺研究

利用Nd:YAG脉冲激光作为焊接热源,对殷钢材料Invar36分别进行了平板单道焊接试验和对焊试验,分析了工艺参数（激光功率、焊接速度、脉冲宽度和离焦量）变化对焊缝的表面形貌、熔宽以及熔透性的影响。对0.85mm厚度的殷钢薄板对焊接头的硬度和成分的变化以及拉伸强度进行了检测。结果表明：激光功率和脉宽是影响焊缝熔深、熔宽和热影响区大小的主要因素;扫描速度对焊缝表面的鱼鳞状条纹间距影响尤为明显;离焦量主要影响焊缝的宽度和熔透性;合理匹配工艺参数能够实现0.85mm厚度薄板对焊,并且获得形貌良好的焊缝。焊缝的组织成分没有发生明显变化,拉伸强度和基体的相当,显微硬度略低于基体硬度。     

激光熔覆时粉末流温度场的仿真模拟

粉末流与激光束相互作用中,粉末流整体温度分布直接影响激光熔覆的熔覆层质量。以热粉末流为研究对象。使用FLUENT进行了温度场及速度场的仿真模拟。结果表明。FLUENT可以很方便的对激光束与粉末流相互作用的过程进行模拟,其输出的计算结果可以直观的揭示热粉末流的温度场和速度场变化情况。FLUENT软件的成功应用对于研究激光束与粉末流相互作用过程和指导熔覆的生产实践有着积极的意义。     

用Nd:YAG激光焊接殷钢薄板材料

用Nd:YAG脉冲激光作为焊接热源,对殷钢材料Invar36分别进行了平板单道焊接试验和对焊试验,分析了工艺参数(激光功率、焊接速度、脉冲宽度和离焦量)变化对焊缝的表面形貌、熔宽以及熔透性的影响.检测了0.85 mm厚的殷钢薄板对焊接头的硬度、成分以及拉伸强度.结果表明:激光功率和脉宽是影响焊缝熔深、熔宽和热影响区面积的主要因素;扫描速度对焊缝表面的鱼鳞状条纹间距影响尤为明显;离焦量主要影响焊缝的宽度和熔透性;合理匹配工艺参数能够实现0.85 mm厚度薄板的对焊,并且获得形貌良好的焊缝.焊缝的组织成分没有发生明显变化,拉伸强度和基体强度相当,显微硬度略低于基体硬度.     

MODELING, VALIDATION AND OPTIMAL DESIGN OF THE CLAMPING FORCE CONTROL VALVE USED IN CONTINUOUSLY VARIABLE TRANSMISSION

Associated dynamic performance of the clamping force control valve used in continuously variable transmission （CVT） is optimized. Firstly, the structure and working principle of the valve are analyzed, and then a dynamic model is set up by means of mechanism analysis. For the purpose of checking the validity of the modeling method, a prototype workpiece of the valve is manufactured for comparison test, and its simulation result follows the experimental result quite well. An associated performance index is founded considering the response time, overshoot and saving energy, and five structural parameters are selected to adjust for deriving the optimal associated performance index. The optimization problem is solved by the genetic algorithm （GA） with necessary constraints. Finally, the properties of the optimized valve are compared with those of the prototype workpiece, and the results prove that the dynamic performance indexes of the optimized valve are much better than those of the prototype workpiece.     

General temperature rise solution for a moving plane heat source problem in surface grinding

In the present study, the general solutions for a transient state as well as for the temperature rise formed everywhere in the workpiece due to a rectangular-shaped moving plane heat source arising at the grinding zone are derived. The present analysis starts from a point heat source solution by applying the method of separation of variables to a three-dimensional heat conduction problem. Because the workpiece moving velocity is quite small, the convective term related to the workpiece velocity is first excluded from the heat conduction equation. This workpiece velocity effect will be included in the model by slightly modifying the coordinate variable in the sliding direction shown in the solution of the point heat source. Therefore, the general three-dimensional solution of the stationary temperature rise can be expressed in an integral form as a function of the product value of the unknown initial condition and the particular solution of temperature rise. The unknown initial temperature rise in the solution can be replaced by the point heat source due to frictional that multiplying the product of the Dirac delta functions defined for three directions. Using the definition of the Dirac delta function, the temperature rise solution for a point heat source can thus be obtained. This solution is further extended to obtain the moving and uniform heat sources arising in a rectangular grinding zone. A comparison among the experimental result and the theoretical results predicted by the present model and Jaeger’s model [Jaeger JC (1942) Proc Roy Soc, NSW 76:203–224.] show that the present model is quite accurate and is generally superior to Jaeger’s model; it can be applied to predict the three-dimensional temperature rise distributions in the workpiece.     

NUMERICAL SIMULATION AND EXPERIMENTAL VALIDATION OF THE TEMPERATURE FIELD IN SURFACE GRINDING

Three-dimensional numerical simulations are carried out to investigate the temperature field in the contact zone due to the thermal loading of the workpiece in surface grinding. This technique considers that the thermophysical properties of the workpiece material are non-linear according to temperature, the contact zone between the wheel and the workpiece is assumed as an arc surface, and the heat flux entering the workpiece is assumed as proportional to the local undeformed chip thickness. A good agreement is found between the simulated results and the experimental observations. The high grinding temperature leads to the thermal expansion of the workpiece material, which causes the thickness of the actual material removal layer to be larger than the cutting depth. The grinding temperature at the central portion is higher than that on the side of the workpiece during the wet grinding, thus the material removal layer in the central zone is thicker than that on the side zone, and the workpiece surface is concave across the grinding width.     

Numerical modeling of heat transfer and fluid flow in hybrid laser–TIG welding of aluminum alloy AA6082

This paper describes a three-dimensional numerical model based on finite volume method to simulate heat transfer and fluid flow in laser–tungsten inert gas (TIG) hybrid welding process. To simplify the model and reduce the calculation time, keyhole dynamics are not considered; instead, a new modified volumetric heat source model is presented for the laser source to take into account the effect of the keyhole on the heat transfer into the workpiece. Due to the presence of arc current, an appropriate electromagnetic model based on the Maxwell equations are also solved to calculate electromagnetic forces in the weld pool. The results of computer simulation, including temperature, current density, electromagnetic, and melted material velocity field, are presented here. Furthermore, several dimensionless numbers are employed to recognize the importance of fluid flow driving forces in the weld pool. It is deduced that the fluid flow has an important effect on the weld pool shape. It is also founded that among the driving forces, Marangoni force is dominant fluid force in the weld pool. Besides, calculated results of hybrid welding process are compared with those of TIG and laser welding processes. The weld pool depth is relatively the same, but the width of the weld pool is highly larger in hybrid welding than lone laser welding. Eventually, the presented model is validated by comparison between calculated and experimental weld pool shape. It is founded that there is a good agreement as the capability of this model can be proved.     

变极性等离子弧立焊穿孔熔池的稳定建立

改进焊接工艺控制时序,编制起弧系统控制平台及信号采集程序。采用改进的起弧系统对2219铝合金和LF6铝合金薄板及中厚板进行变极性等离子弧立焊工艺试验,利用红外线测温仪检测起弧过程中焊接熔池区域附近的点随预热时间的温度变化,并把该曲线上的临界温度作为检测穿孔熔池是否形成的标志,计算机根据穿孔时刻的临界温度控制焊件行走的使能信号。研究表明：改进的起弧系统能够简化设备操作,提高自动化程度与工作效率;在穿孔形成的瞬间,检测点的温度有一个从高到低的突变过程(穿孔前的瞬间温度达到临界值),而且对于同一检测点,多次测量得到的临界温度基本稳定;起弧阶段向主焊接阶段过渡稳定,能够实现穿孔熔池的稳定建立,从而验证改进的起弧控制系统的可行性及可靠性。     

细长轴磨削变形的变速优化智能预测控制研究

在建立细长轴磨削过程中工件弹性变形数学模型的基础上，打破了传统的恒速控制方法，提出了一种控制细长轴磨削弹性变形的变速优化适应控制策略：根据磨削系统沿工件轴向各点刚度的不同，通过不断改变工件转速和纵向进给速度，控制法向磨削力的变化，进而控制工件的弹性变形；同时，由一个神经网络预测系统和一个模糊控制系统实时控制加工过程中的磨削深度，进一步控制加工中由于砂轮磨损而引起的细长轴形状误差。仿真和实验结果表明：变速优化适应控制策略和模糊神经网络预测控制方法是可行的，可极大地提高磨削生产率，减小细长轴的形状误差。     

外加高频磁场下电弧快速成形过程的电磁-流体耦合数值模拟

外加电磁作用是改善电弧快速成形零件组织和性能的有效方式之一。为了揭示高频磁场对熔池传热、对流和形态的影响机理,采用有限元电磁计算和有限体积流体分析耦合的方法,建立电磁场、熔池温度场和流体流动场分析的三维模型,分析工件和熔池中高频电磁力/热的分布特征,研究高频电磁力与表面张力、电弧力以及熔滴冲击共同作用下的熔池表面动态变形,对比分析有/无外加高频磁场情况下熔池温度分布和流体流动模式上的差异,并由此预测外加高频磁场对凝固组织和熔池形态的改变。结果表明,高频电磁力驱动熔池流体在垂直焊接方向的平面内形成单漩涡旋转对流,有利于熔断枝晶细化晶粒,熔池表面形状向远离线圈一侧倾斜,熔宽增大。金相和焊道横截面测试证实了上述模拟结果。     

基于线性规划的工件稳定性建模及其应用

工件在实现定位后,在加工过程中将要受到工件重力和切削力等外力的作用。为使工件保持定位精度与生产安全性,必须保证工件在整个加工过程中具有稳定性。系统地讨论了工件稳定性建模及其求解方法,在摩擦锥线性近似以及变量非负转换的基础上,提出了工件稳定性的定量判断准则;利用线性规划方法对工件稳定性模型进行分析。结果表明,稳定性模型不仅能够验证工件的稳定性,而且还能够分析夹紧力大小、作用点以及夹紧顺序的合理性。这种方法既适用于夹具夹持稳定性分析,也适用于机械手的抓取稳定性分析。     

The study for stability of closed-loop control system based on multiple-step incremental air-bending forming of sheet metal

To solve the springback problem for sheet metal forming, feedback control idea in automatic control theory is introduced to incremental air-bending forming process. The advanced control techniques are used to solve precision forming for workpiece of sheet metal. However, stability, accuracy, and rapidity of closed-loop control can directly affect system normal operation. Aiming to analyze the effect of stability on the quality of the formed workpiece, a closed-loop control system model for incremental air-bending forming is established. The transfer function and characteristic equation of the closed-loop system are solved through theory deduction and minor incremental linearization method. Both simulations with Matlab/Simulink and root locus results show that, as the overall gain is equal to one, the shape of formed part could converge to the target shape at the fastest rate. Finally, a semiellipse-shape workpiece is manufactured with the corrected mold obtained by the closed-loop forming method. The experimental results show that the closed-loop forming way is feasible and the means of correcting the mold parameters by iterative compensation of the stable closed-loop control system is effective. It can be taken as a new approach for sheet metal incremental air-bending forming and mold design.     

搅拌摩擦焊工具的研究现状

搅拌焊工具技术是搅拌摩擦焊工艺最重要的因素。搅拌焊工具主要由肩部和焊针组成，焊接薄板时，旋转的肩部和工件之间摩擦产生的热量是主要热源，而随着板厚的增加，更多的热量必须靠旋转的焊针和工件摩擦产生。焊接工具的主要作用是保证连接区材料产生足够的塑性变形，并控制焊针周围塑性体的流动，形成优质的焊接接头。