基于MSC.NASTRAN的点焊模型及其比较分析

点焊是汽车车身结构常用的一种连接方式,为对这种结构进行有限元分析必须建立相应的点焊模型。本文介绍了MSC.NASTRAN中常用的3种点焊模型,并用一个例子说明了不同的点焊模型对分析结果的影响。     

基于超声参数化和熵模型的汽车焊点质量识别

汽车焊点的超声波检测过程中,超声回波为非稳态信号,特征不易提取,同时焊点缺陷类型众多,导致汽车焊点质量的自动判定与识别比较困难。因此,提出一种基于超声信号参数化和判别熵模型的汽车焊点质量智能识别方法。通过建立汽车焊点超声回波信号的参数化模型,再基于EM算法思想,提出多回波超声信号的特征参数估计算法。根据提取的超声信号时频特征值,结合判别熵对特征值的有效性进行监督,提取最优特征值子集,最终实现汽车焊点质量类型的智能识别。焊点的实际检测结果验证了方法的有效性和识别的准确性。     

Evaluation on Spot Weld Models in Structural Dynamic Analysis of Automotive Body in White

Spot weld models are widely used in finite element analysis(FEA) of automotive body in white(BIW) to predict static,dynamic,durability and other characteristics of automotive BIW.However,few researches are done on evaluation of the validity of these spot weld models in structural dynamic analysis of BIW.To evaluate the validity and accuracy of spot weld models in structural dynamic analysis of BIW,two object functions,error function and deviation function,are introduced innovatively.Modal analysis of Two-panel and Double-hat structures,which are the dominated structures in BIW,is conducted,and the values of these two object functions are obtained.Based on the values of object functions,the validity of these spot weld models are evaluated.It is found that the area contact method(ACM2) and weld element connection(CWELD) can give more precise prediction in modal analysis of these two classical structures,thus are more applicable to structural dynamic analysis of automotive BIW.Modal analysis of a classical BIW is performed,which further confirms this evaluation.The error function and deviation function proposed in this research can give guidance on the adaptability of spot weld models in structural dynamic analysis of BIW.And this evaluation method can also be adopted in evaluation of other finite element models in static,dynamic and other kinds of analysis for automotive structures.     

Ultrasonic thermometry for friction stir spot welding

This investigation presents the feasibility of ultrasonic temperature measurement of friction stir spot welding (FSSW). FSSW is an automated solid state joining process. Thermal profiles of the weld zone are crucial for implementing informed process changes to improve weld quality. Ultrasonics present a novel and non-invasive method of monitoring changes in temperature.Ultrasonic time of flight (TOF) measurement method is used to calculate the temperature of Al 6061 as it is heated. Comparisons of the ultrasonic temperature calculations with thermocouple readings confirm the accuracy of the ultrasonic system. The ultrasonic signal is then recorded during spot welding and processed. The results show that ultrasonic technology is a feasible method of monitoring the heating and cooling profiles of the weld zone during welding. The paper also discusses challenges presented by the system as well as recommendations for its future implementation in the friction stir welding manufacturing industry.     

A study on using scanning acoustic microscopy and neural network techniques to evaluate the quality of resistance spot welding

This paper shows that the quality of resistance spot welds can be evaluated using scanning acoustic microscopy (SAM). Two-layered coated spot-welded samples are investigated utilising a wide-field short-pulse scanning acoustic microscope with operation frequencies of 25, 50 and 100 MHz. Geometrical parameters, e.g. nugget area, maximum axis of nugget, and minimum axis of nugget, are acquired from C-scan images of weld nuggets using mathematical morphology techniques. These parameters serve as inputs for an artificial neural network (ANN) model to evaluate the quality of spot welds. The output of the model during the training process comprises the results of nugget peeling tests and expert opinions. The ANN can provide suggestions on weld quality with a higher than 95% correctness. A JAVA computer program is developed for image processing, ANN training, and ANN testing. With this model, the computer program can render the quality of spot welds that are close to those achieved using off-line destructive method.     

Robust design of spot welds in automotive structures: A decision-making methodology

Automotive structures include thousands of spot welds whose design must allow the assembled vehicle to satisfy a wide variety of performance constraints including static, dynamic and crash criteria. The objective of a standard optimization strategy is to reduce the number of spot welds as much as possible while satisfying all the design objectives. However, a classical optimization of the spot weld distribution using an exhaustive search approach is simply not feasible due to the very high order of the design space and the subsequently prohibitive calculation costs. Moreover, even if this calculation could be done, the result would not necessarily be very informative with respect to the design robustness to manufacturing uncertainties (location of welds and defective welds) and to the degradation of spot welds due to fatigue effects over the lifetime of the vehicle. In this paper, a decision-making methodology is presented which allows some aspects of the robustness issues to be integrated into the spot weld design process. The starting point is a given distribution of spot welds on the structure, which is based on both engineering know-how and preliminary critical numerical results, in particular criteria such as crash behavior. An over-populated spot weld distribution is then built in order to satisfy the remaining design criteria, such as static torsion angle and modal behavior. Then, an efficient optimization procedure based on energy considerations is used to eliminate redundant spot welds while preserving as far as possible the nominal structural behavior. The resulting sub-optimal solution is then used to provide a decision indicator for defining effective quality control procedures (e.g. visual post-assembly inspection of a small number of critical spot welds) as well as designing redundancy into critical zones. The final part of the paper is related to comparing the robustness of competing designs. Some decision-making indicators are presented to help the analyst to plan robust resistance spot welds designs along with quality controls in order to insure a specified level of structural performance. All examples are presented on a full body-in-white structure (one million dofs and thousands spot welds).     

管道对接焊缝超声检测爬行器的研制

介绍了一种用于管道对接焊缝内部缺陷检测的自动检测爬行器的工作原理、系统结构和工作特点。该系统在PC机的控制下相对焊缝运动，实现了超声检测的自动化。试验结果表明，该系统在灵活性和易于使用等方面取得了较满意的结果，具有较广泛的适用性。     

Weld quality analysis and evaluation of plasma arc welds in electrical stators

The use of plasma arc welding (PAW) has increased in the last years as a substitute for the gas tungsten arc welding in the automotive, electrical and appliance industries. Although the use of PAW in the industry has increased, there are still a limited number of theoretical methods and simulation tools to predict the metal flow characteristics and its interaction with the process parameters during the welding process. Therefore, weld design must still rely on the designer’s experience and the trial-and-error method. As a consequence, the process parameters and the weld quality may not be as originally expected at the design process. In this paper, a weld quality analysis of the PAW process is presented to guarantee a good quality of the product. To measure the influence of process parameters on weld quality, first, “quality” is defined. Weld quality measurement methods are then proposed based on visual inspection, electrical tests and mechanical tests of the welds. Using these methods and the experimental data obtained from the actual welding process at the production line, a new approach to evaluate the weld quality is proposed based on a circular shape model of the weld cross-section area. Finally, a relationship between the weld geometry and weld quality is proposed and intended to be used as a practical online monitoring method of weld quality.     

基于超声波串列扫查的自动扫查装置控制系统研究

针对高压容器焊缝常存在边界未融合、未焊透、裂纹等危害性缺陷，设计了一种利用磁带导航、光纤传感器检测、磁轮驱动的自动扫查装置。利用超声波自动串列扫查原理．在工控机的控制下，自动扫查装置沿焊缝方向运动，实现对焊缝超声串列检测的自动化，可以在线对扫查装置进行监视和控制。对容器缺陷参数进行数据采集、处理等，当运动方向偏离串列扫查基准线时，控制系统根据调整算法进行实时校正。试验结果表明，该装置具有很高的定位精度和导航性能，利用扫查装置检测探伤，提高了缺陷检测性能，保证焊接的质量，也节省了大量的人力和物力。     

Characterization and mechanical properties of TiN/TiAlN multilayer coatings with different modulation periods

In this paper, laser welding for the stainless steel lap joint used in the railway vehicle body has been studied based on the analysis of the ultrasonic test. The weld width is evaluated by the analysis of ultrasonic testing signals during the ultrasonic scanning process. The changes of the echo and main frequency are in good agreement with the positions of the probe. The semi-attenuation method and frequency domain analysis are established based on the A-scan signals and frequency spectrum characteristic curves. From the analysis of the error statistics, the frequency domain analysis has a higher accuracy and stability, which can meet the requirements of engineering applications. The equivalent weld width is defined based on the C-scan imaging and the quantitative ultrasonic test is achieved. The tensile shear measurements of welds show that the equivalent weld widths have the same change rules with the values of the tensile shear strength and provide an important basis for the quality evaluation of the laser welding.     

薄镀锌钢板点焊超声成像分析

采用水浸超声聚焦直入射法对镀锌薄板点焊焊核进行超声C扫描成像检测,分析C扫描图像中各特征部分的超声A扫描信号。超声波C扫描成像方法能够测量点焊焊核直径,检测焊核中常见的几种缺陷如气孔、裂纹以及飞溅,此外采用该方法还能对焊核的外观进行检测。为了获得更为精确的焊核内部结构信息,进一步分析了焊核内部不同形状缺陷的C扫描图像特征及A扫描信号特征,通过这些图像特征和信号特征能够判断焊核内部缺陷的形状及类型。因此,超声C扫描成像法能够在不破坏点焊焊核的前提下全面直观地显示焊核的内外部结构。该方法不仅能够用于评价点焊质量,而且还可以作为辅助手段用于点焊的其他研究中。     

Analytical studies for buckling and vibration of weld-bonded beam shells of rectangular cross-section

An approach to analytical solution is presented for vibration and buckling of thin-walled tubular beam shells typical of automotive structures, which are fabricated by joining sheet metal stampings along the two longitudinal edges with periodic spot welds, adhesive bonding, or combination of spot welds and bonding, known as weld bonding. Solutions are obtained for such beam shells of rectangular cross-section with two opposite ends simply supported. The beam shell is modeled as an assembly of the constituent walls and Levy-type formulation is used to obtain a series solution for the transverse displacement of each of the walls. The challenge of expressing the discrete point support conditions at the spot welds by a continuous function is addressed using the flexibility function approach used in literature. The flexibility function, used earlier to represent the flexibility distribution along weld-bonded edges of rectangular plates with periodic spot welds, is used here. The characteristic equations are obtained by satisfying the displacement, slope, shear, and moment equilibrium at the mating edges of the walls including the two weld-bonded edges and the compatibility conditions at the spot-weld locations. This approach to analytical solution, described here for thin-walled beam shells of rectangular cross-section, can be suitably adopted for more general cross-sections and joints along non-symmetric edges. A parametric study is undertaken to show the effect of aspect ratio of the beam shell, adhesive joint parameters, and the number of spot welds on the elastic buckling loads and the natural frequencies. Such parametric studies can be of use to designers in arriving at an optimal joint configuration of weld-bonded beam shells from buckling and vibration considerations.     

Process Characterisation of Pulsed Nd:YAG Laser Seam Welding

A wide range of pulsed laser welding parameters was identified. These include average peak power density (APPD), peak power, mean laser power, traverse speed, pulse repetition rate, duty cycle, pulse energy, spot size, and pulse duration. The type of laser beam temporal pulse shape studied was a rectangular power pulse. The effects of pulsed laser welding parameters on heat flow, weld dimension, and weldability are investigated. The study shows that weld quality is principally affected by APPD, mean power, and traverse speed, of which APPD is the most critical process parameter. A processing map containing the APPD effects is constructed as a guide for producing good welds.     

车身焊点虚焊案例分析及解决方法

焊点虚焊是车身焊接的主要问题之一,对产品的质量影响很大。就某些焊点虚焊的质量问题进行分析,识别焊点虚焊失效的潜在原因,解决虚焊的质量问题,从而提升车身焊接质量。     

汽车油箱焊缝检查机的设计

汽车油箱用来装汽车用的燃料,箱体是由金属板材卷制成型,再由缝焊机进行纵向缝焊,由于各种因素的影响,有时箱体焊缝处会泄漏。而油箱生产企业在此工序结束后无检查手段,就会产生油箱次品。介绍了一种汽车油箱焊缝检查机,可以及时检查焊缝的质量,降低产品的次品率。     

Online qualitative nugget classification by using a linear vector quantization neural network for resistance spot welding

Real-time estimation of weld quality from process data is one of the key objectives in current weld control systems for resistance spot-welding processes. This task can be alleviated if the weld controller is equipped with a voltage sensor in the secondary circuit. Replacing the goal of quantifying the weld quality in terms of button size by the more modest objective of indirect estimation of the class of the weld, e.g., satisfactory (acceptable, “normal” button size), unsatisfactory (undersized, “cold” welds), and defects (“expulsion”), further improves the feasibility of the mission of indirect estimation of the weld quality. This paper proposes an algorithmic framework based on a linear vector quantization (LVQ) neural network for estimation of the button size class based on a small number of dynamic resistance patterns for cold, normal, and expulsion welds that are collected during the stabilization process. Nugget quality classification by using an LVQ network was tested on two types of controllers; medium-frequency direct current (MFDC) with constant current controller and alternating current (AC) with constant heat controller. In order to reduce the dimensionality of the input data vector, different sets of features are extracted from the dynamic resistance profile and are compared by using power of the test criteria. The results from all of these investigations are very promising and are reported here in detail.     

A small-size multichannel scanning acoustic microscope

A multichannel scanning acoustic microscope, the ultrasonic element of which consists of several focused transducers, is proposed. In this device, images are generated by the electronic switching of the transducers with simultaneous mechanical translation of the acoustic element, thus reducing the data acquisition time. The design of the microscope, the acoustic element of which contains eight transducers with a 100-MHz central frequency, a 6.7-mm focal distance, and a 16° angular aperture, is considered. The multichannel acoustic element and mechanical scanner are physically combined into a remote smadelay linell-size module, enabling studies of large-size complex-shaped objects. As an example, acoustical images of the inner structure of spot welds of aluminum sheets are presented. The comparison of the acoustical images and results of destructive tests has shown that, based on ultrasonic data, it is possible to estimate sizes of weld cores and detect inner defects.     

Effect of projection on joint properties of friction welding of tube-to-tube plate using an external tool

Friction welding is widely used as a mass-production method in various industries. Friction welding of tube-to-tube plate using an external tool (FWTPET) is an innovative friction welding process and has potential applications in aerospace, railways, automotive, and marine industries. FWTPET is capable of welding tube-to-tube plate of similar and dissimilar metals and is capable of producing good-quality leak-proof weld joints. In this work, FWTPET welds have been produced with six different tube projections. Tool steel has been used to join the FWTPET process. After the completion of welding, macrostructural and microstructural studies have been conducted and it reveals the weld configuration that is capable of generating defect-free welds. Further, hardness and pull strength of welds obtained with six different tube projections have been studied. When compared to other weld conditions, 1 mm projection has resulted in better strength. The weld strength and average weld interface hardness with 1 mm projection are 84.72 MPa and 70.58 Hv respectively. The sufficient heat generation has been occurred at optimum projection in FWTPET process.     

Optimization of pulsed current in resistance spot welding of Zn-coated hot-stamped boron steels

Metallic coatings have been widely used for hot-stamped boron steel in automotive applications. Surface coating in hot-stamped boron steels has improved corrosion resistance. However, a thick coating layer degrades resistance spot weldability. In the case of a Zn-coated hot-stamped boron steel, the high contact resistance and material stiffness with low vaporization temperature of the alloyed layers result in a narrow current passage at the faying surface. Expulsion occurs at low current due to rapid heat development, resulting in a narrow weld current range. The pulsed current can control the heat input by applying a fast cool time during welding to improve the mechanical properties of the joint and acceptable current range. In this study, Zn-coated hot-stamped steels were resistance spot welded using various pulse current procedures, and welding condition was optimized via three pulsed current steps. Step 1: Contact area was controlled without nugget formation. Step 2: Nugget growth was minimized and contact area was maximized. Step 3: The maximum acceptable current range and nugget diameter were achieved. These welding conditions improved the acceptable current range and mechanical properties of spot welds due to increased spot weld size.