Signature images for arc welding fault detection

Abstract

The present work elucidates the signature image approach to welding fault detection, covering the calculation of signature image data objects from blocks of welding electrical data (voltage and current), the definition of appropriate vector operations, and the manipulation of the signatures to permit detection of welding faults. Detection of out of position welds in overlap joints is illustrated, and the relevant changes in signature features are related to the physics of the short arc welding process. Finally, it is shown how fault detection performance can be improved by optimising the way the signatures are calculated.     

Random nature of droplet size and its origins in short circuit CO2 arc welding

Abstract

The nature of the droplet size variation and its effect on the process behaviour were investigated for short circuit CO₂ arc welding using a power supply with constant voltage output. To obtain the droplet images and record the welding current and voltage transient waveforms in phase, an integrated experimental system was established by combining a high speed charge coupled device camera based on laser shadowing and a related optical system with a dual channel analog/digital converter. The droplet size in short circuit transfer mode is defined as the maximum diameter of the molten droplet just before short circuiting. The experimental results reveal that the distribution of droplet size typically has a random nature with a range of between 1 and 2 times the electrode diameter. Excessively large or small droplet size is markedly unfavourable to the process stability. The droplet shape just before short circuiting and the short circuiting experience are also critical factors affecting the process behaviour. The main factors influencing the droplet size and shape are analysed in detail and approaches to control their evolution are then proposed.     

Parametric approach to positional fault detection in short arc welding

Abstract

This work investigates a parametric technique for short arc welding fault detection. The independent component analysis algorithm is applied to split welding voltage and current signals into arcing and short circuiting regions. A series of parameters including means, medians and normalised inner products are calculated by processing the different sections of welding electrical data. Out of position welds in overlap joints are studied with investigation of the connection between parameters and short arc welding features. The effect of changing shielding gas is also illustrated. Figures of merit to quantify the change in various parameters between faulty and good welds are compared and discussed. It is shown that the data separation into two regions with independent component analysis is useful in providing various parameters that can assist in short arc welding fault detection under different conditions.     

Experimental study on welding characteristics of CO2 laser TIG hybrid welding process

Abstract

The experiments of CO₂ laser TIG paraxial hybrid welding with 4 mm thick AISI 321 stainless steel sheet have been performed. The arc images and welding characteristics have been investigated with different energy ratios between laser and arc. The experimental results indicate that the hybrid welding is similar to laser welding and has also two welding mechanisms: deep penetration welding and heat conduction welding. Because of the effect of keyhole induced by laser, the arc root can be stabilised and compressed, and the current density and the penetration depth are all increased significantly, which show the characteristics of deep penetration welding. However, when the current is increased to a critical value, the laser induced keyhole disappears and the arc expands obviously, which decreases the penetration depth, so that the welding mechanism has been changed from deep penetration welding to heat conduction welding. Furthermore, the effects of distance between laser beam and electrode, pulsed laser and hybrid manners on hybrid welding characteristics have also been studied.     

Development of low spatter CO2 arc welding process with high frequency pulse current

Abstract

Metal transfer phenomena and spatter generation in CO₂ arc welding with a solid wire were investigated, and a low spatter welding process using a high frequency pulse rectangular current was developed. The optimal conditions of high frequency pulse CO₂ arc welding were determined to be a peak current of 450–550 A and pulse frequency of 450–750 Hz. These high frequency pulse currents influenced the droplet oscillation due to resonance between the applied pulse frequency and the natural frequency of the droplet. A droplet was regularly transferred by 9–11 pulses, and the average interval of metal transfer was ～16 ms, which was half of that in conventional CO₂ arc welding. The average droplet weight is 34 mg, showing a large reduction in comparison with that of the conventional method. As a result, the total spatter weight was reduced by 70% in comparison with the conventional method, and particularly large spatters more than 0·5 mm in diameter were reduced from 25 to 3 mg s^?1.     

CO2电弧焊电源动特性评定指标的实验分析

针对CO2电弧焊电源,对我国提出的动特性评定指标进行了实验分析,得出了几点有意义的结论。说明了只根据原有动特性评定指标,并不能准确地评定CO2电弧焊源的动特性,需要CO2电弧焊电源的动特性的评定方法进行深入研究,寻找能准确评定CO2电弧焊电源动特性的新指标。     

Statistics of signature images for arc welding fault detection

Abstract

The present work covers the statistical analysis of signature images for weld quality monitoring and fault detection. Welding signature images are two-dimensional histograms of voltage and current data. Signatures from production welding are compared with reference good welding using a statistical analysis of both the principal components, which are fitted with shifted normal distributions, and the remainders not explained by the principal components, which are fitted with a multidimensional normal distribution. A signature basis set is employed, allowing efficient real time computations. The statistical data fits are illustrated with data from overlap welds, and examples of fault detection with out of position welds are given.     

波形控制CO2弧焊电源设计

针对CO2焊接工艺的特点,设计了一种实现波形控制的逆变弧焊电源,电源采用单片机控制,对焊接电压、焊接电流实时采样,可准确控制短路电流值.当短路发生后,电流先保持在一较低值,然后以指数规律上升,当检测到缩颈时,降低电流直到熔滴过渡后再燃孤;同时在燃孤阶段,控制燃弧电流的变化速度,保证充足的燃弧能量.以实现减小金属飞溅和改善焊缝成形.     

软开关逆变器在CO2弧焊电源中的应用研究

通过将新型软开关电路拓扑和逆变技术引入CO2孤焊电源，保证电源在全范围内实现软开关，使开关管在零电压下开通和关断。开关损耗、开关应力及电磁干扰得到明显改善。同时，开关管工作在较高的逆变频率，通过微机控制，以软件编程的方式对各控制参数进行优化匹配，获得了较合理的电源动特性和较好的焊接效果。     

CO2短路过渡焊接熔池图像传感器

针对CO2短路过渡焊接熔池图像实时检测的要求，研制了一种基于普通工业CCD摄像机的专用传感器。介绍了该传感器紧凑的机械结构和独特的光学设计，设计了可消除CCD摄像机固定工作时序与CO2短路过渡发生的随机性之间的矛盾的实时检测熔池图像的控制时序，给出了相应的图像检测系统的工作原理。试验表明，采用该图像传感器可以围绕焊枪轴线从不同角度快速、准确地获得清晰的熔池图像。     

Arc power and efficiency in gas tungsten arc welding of aluminium

Abstract

A calorimetric study of gas tungsten arc welding of aluminium is described. The present study comprised experiments in which autogenous welding runs were each made on a block of electrical conductor grade aluminium. The blocks were all approximately cubic in shape which, when combined with the high thermal conductivity of aluminium, ensured that their temperature equalised soon after the completion of a run. Each sample was immersed in insulating material before welding so that heat losses to the surroundings were minimised. Thermocouples were attached to the block in each experiment and the bulk temperature rise was related to the energy input associated with the welding run. The effects of arc polarity, alternating current balance, shielding gas composition, arc length and welding current on the arc power and arc efficiency were investigated. The results obtained with alternating current are compared to those for direct current, and the differences are explained.     

Effect of boundary conditions and heat source distribution on temperature distribution in friction stir welding

Abstract

Welding experiments on Al-6005A have been carried out using a fully instrumented milling machine. The power input was calculated from the measured torque and forces. The thermal cycles were measured at various locations close to the weld centreline. A finite element pseudo-steady-state uncoupled thermal model was developed, taking into account the influence of the welding parameters on the power input. The distribution of the total power input between surface and volume heat sources was also studied. The measured and predicted thermal cycles are in good agreement when proper contact conditions between the workpiece and the backing plate are introduced.     

逆变式CO2焊接电源控制电路设计

介绍了逆变式CO2焊接电源的基本工作原理，详细讨论了逆变电源驱动电路和电源外特性控制电路。研制的电源输出L形外特性，短路峰值电流采用恒流控制，引弧性能好，焊接飞溅小。驱动电路适合于MOSFET或IGBT的驱动，既可以用于全桥式逆变电路，又可以用于半桥式变电路，控制电路工作稳定可靠。     

Study on elimination of interlayer defects in horizontal joints made by rotating arc narrow gap welding

Abstract

In this work, the characteristics of interlayer defects were studied in horizontal welds made by rotating arc narrow gap welding. The interlayer defects existed in the form of incomplete fusion and slag inclusions, occurring near the lower sidewall. In the rotating arc process, the instantaneous velocity of the arc with respect to the sample is higher when the arc is close to the lower sidewall, whereas it is lower when it is near the upper sidewall. This results in a lower effective heat input to the lower sidewall, and a corresponding reduction in the enthalpy that is transferred along with the deposited metal. Fortunately, this asymmetric nature of rotating arc welding can be exploited to minimise or eliminate interlayer defects. It is shown that, by controlling the direction of rotation for the arc, removing slag, selecting an appropriate groove size and resetting the torch position, defect free horizontal welds in heavy plates can be achieved.     

CO2气体保护焊在钢管拱桥上的应用

介绍了CO2气体保护焊在钢管混凝土拱桥上钢管环缝焊接应用的优势,用实例说明了采用CO2气体保护焊后,生产效率有了明显的提高,同时降低了工人的劳动强度.该工艺完全可以替代焊条电弧焊.采用该工艺能有效地缩短工程制造的周期,大大降低工程制造的成本.     

CO2短路过渡焊工艺参数优化的研究

由于CO2短路过渡焊接过程是一个非线性、时变的过程,所以对其焊接工艺参数的优化研究一直是焊接界的热点.运用正交试验,结合自行研制的焊接电弧动态小波分析仪对焊接电流、电弧电压、焊接速度等主要焊接工艺参数进行了优化研究.根据试验结果分析了主要焊接工艺参数与焊接质量之间的关系,为焊接工艺参数的优化及焊机性能的改进奠定了必要的基础.     

软开关逆变式MAG/CO2弧焊电源的可靠性研究

针对软开关逆变式MAG/CO2弧焊电源的可靠性问题，进行了比较系统的分析研究；并对设计和制造阶段影响逆变器各个环节可靠性的主要因素进行研究，提出相应的措施。重点介绍逆变主电路、系统硬件、软件受干扰及其抗干扰措施，逆变频率、IGBT安全工作对可靠性影响等方面的试验研究工作。     

CO2焊短路过程动特性与外特性的关系

CO2短路过渡焊在制造业上的应用非常广泛，对系统动特性有较高要求。该文结合电路理论和焊接短路过程的特点对过程动特性及其与外特性进行了细致的分析，突破了以往在外特性控制和动特性控制之间的关系上互不清楚、互不相关、相互分离的传统观念，认识到在CO2焊短路过渡过程中，动特性和外特性密切相关，既不能用外特性来解释动态过程；也不能认为动特性与外特性无关，动特性会受到外特性的制约，它们之间的关系可以用明确的数学语言进行分析，提出了动特性的最大响应能力及可控性的思想，分析结果有很大的理论意义。     

熔滴短路过渡频率对CO_2焊接过程稳定性的影响

在依次改变送丝速度v_e。电弧电压U_a、保护气体流量Q、焊接速度v_w和焊丝伸出长度l_e等多种工艺参数的条件下,基于数值分析,全面评估了CO_2焊接过程熔滴短路过渡频率与焊接过程稳定性的定量关系,证明了在改变送丝速度v_e、电弧电压U_a和焊丝伸出长度l_e的条件下,熔滴短路过渡频率f与焊接过程的稳定性成正相关关系,而在改变保护气体流量Q和焊接速度v_w的条件下,熔滴过渡频率f却失去了表征焊接过程稳定性的能力,不能够作为焊接过程稳定性的评价指标。     

Microstructures of gas metal arc weld metal of 950 MPa class steel

Abstract

The effects of shielding gas composition on the properties and microstructure of single pass weld metals produced by GMA (gas metal arc) groove welding of 950 MPa class steel plates have been investigated. The shielding gas employed was a mixture of argon (Ar) and carbon dioxide (CO₂) (0–25%), and the weld heat input was ～3 kJ mm. With increasing CO₂ content, the hardness of the weld metal decreased from 380 HV to 280 HV, and the absorbed energy of the Charpy impact test decreased from 130 J to 90 J. The microstructures of the weld metal, consisting primarily of low carbon martensite and carbide free bainite, became more bainitic as the CO₂ content of the shielding gas was increased. It was also found that the MA constituent, embrittling microstructure, was formed in the granular bainitic area, the volume fraction of which increased with the CO₂ content of the shielding gas.