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在电阻点焊过程中喷溅的产生直接降低焊接接头的强度,因此是最不希望出现的焊接缺陷.文中引入基于显微接触理论的接触电阻模型,通过轴对称有限元模型分析了镁合金电阻点焊过程中的温度场分布及塑性变形过程,以揭示内部喷溅产生的原因.结果表明,由于AZ31镁合金高热导率、低熔点、低比热容和大的线膨胀系数,焊接中需要采用大电流短时间的强参数焊接,所以相对于铝合金和钢铁来说,喷溅在镁合金焊接中更容易发生.内部喷溅产生的原因主要与金属熔化导致熔核内部压强增大相关,增加的压力致使周围的塑性环产生缺口,保护液态金属冲破周围固态金属的束缚,形成喷溅. 相似文献
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电阻点焊是一种多物理场耦合且封闭不可见的金属成形过程,焊接过程中电流大且通电时间短,电极力与熔核区热熔化程度匹配不当,极易造成飞溅问题,影响表面成形并降低焊点强度. 针对此问题,文中提出了一种压电致动器辅助电阻点焊的方法,利用压电致动器自身响应时间短、输出推力大的特点,将压电致动器辅助压力施加于焊接过程,实现电阻点焊过程中宏观静压力与压电致动器辅助快速动态可编程压力调节. 结果表明,压电致动器在电阻点焊气缸宏观预紧力下可实现可控的压力输出,不同频率的振动可辅助加载于原始压力波形之上,在保持焊接参数不变的情况下,压电致动器的振动输入可有效改善熔核区热分布,实现对焊接飞溅的抑制并增大熔核直径,综合提升接头性能. 相似文献
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为了研究焊接工艺参数对钛合金微电阻点焊焊接质量的影响规律以及获得最优的焊接工艺参数,利用中心组合试验设计对0.4 mm厚的TC2钛合金进行焊接试验,对焊接试样进行准静态拉伸试验,获取了表征焊点质量优劣的熔核直径、拉伸力、拉伸位移和失效能量. 利用灰熵法得到了每个焊接质量指标的权值,将其加权为焊接综合质量指标. 采用逐步回归分析方法得到了焊接工艺参数(焊接电流、焊接时间以及电极压力)与焊接综合质量指标之间的回归方程. 在此基础上分析了焊接工艺参数两两交互作用对焊接质量的影响规律,采用爬山优化算法得到了最优的焊接工艺参数. 相似文献
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《Science & Technology of Welding & Joining》2013,18(5):386-392
AbstractThe weld expulsion is prone to occur and severely affects the nugget quality when the initial gap between dual phase (DP) steel sheets exist in resistance spot welding (RSW). To investigate the effect of initial gap on weld expulsion, a finite element model was developed to analyse the weld nugget formation process with different initial gaps for DP steels. An estimation method of expulsion occurrence based on the ratio of the nugget radius Rn and the contact radius Rc between sheets was proposed to get the critical initial gap without expulsion. The simulation and experimental results showed that the weld expulsion would not happen until the gap spacing reaches the critical value. The critical initial gap of DP steel is much smaller than that of low carbon steel. For both DP steel and low carbon steel, the critical initial gap would increase with the thickening of the steel sheet. 相似文献
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《Science & Technology of Welding & Joining》2013,18(3):250-254
AbstractThe present paper presents the influence of welding current shape on weld strength of resistance spot welds of zinc coated mild steel sheets. The influence is analysed at different levels of the electrode wear. Welding currents with different peak values and different RMS (root mean square) values were used in the experiment. The results show that welding current with high peak values implies higher weld strength. 相似文献
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研究了用小波分析方法从电极压力曲线上提取判定铝合金冲击波点焊过程发生喷溅的特征信息的方法.采用db5小波对发生喷溅焊点的电极压力曲线信号上的不规则信号突变进行了检测.结果表明,小波分解中高频部分重构信号可准确检测到电极压力曲线上信号发生突变时的位置及突变程度,也就是说能够将发生喷溅缺陷的时刻准确地表现出来.利用超过一定阈值的小波分解高频重构信号的全局最大值作为判定点焊过程发生喷溅缺陷的特征信息是准确可靠的,从而实现了将电极压力曲线上的信号特征转化为计算机容易识别的数值特征. 相似文献
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The effects of expulsion on microstructure and tensile shear strength of spot welds have been investigated for a high-strength
cold rolled sheet steel. Spot welds with expulsion are characteristic for a “double im-age” near the fusion line, an equiaxed
dendritic grain zone along the faying surface, and deep indenta-tions on the outer surfaces. Microstructural examinations
and tensile shear tests of spot welding specimens were conducted to determine the correlation between microstructure and strength.
It was found that the equiaxed dendritic structure was associated with significant solidification cracking. Frac-tography
on tensile specimens reveals that brittle failure is associated with an equiaxed microstructure. Furthermore, the surface
indentation will change the stress at the nugget edge, and deep surface inden-tations are expected to promote premature failure. 相似文献
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《Science & Technology of Welding & Joining》2013,18(2):135-142
AbstractThe current path area is a significant factor in estimating the temperature distribution via numerical modelling for resistance spot welding. This paper presents a method for the estimation of the current path area at the faying surface during small scale resistance spot welding between bulk metallic glass and stainless steel. Observation of cross-sections and fracture surfaces reveals the welding process at the faying surface for both dissimilar and similar welding. The equipotential surface that depends on the difference between the contact area of the electrode-to-sheet and sheet-to-sheet interfaces is estimated by numerical modelling. The current path area at the faying surface is estimated by measuring the electric potential between the sheets, taking into account the current distribution. 相似文献
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Lü Jiaheng 《中国焊接》2007,16(4):42-46
The conventional methods of determining the dynamic resistance were mostly done by measuring the voltage and current at secondary side of transformer in resistance welding machines, in which the measuring set-up normally interferes with the movement of electrode, and the measuring precision is influenced by inductive noise caused by the high welding current. In this study, the dynamic resistance is determined by measuring the voltage at primary side and current at secondary side. This increases the accuracy of measurement because of higher signal-noise ratio, and allows to apply to in-process system without any wires connected to electrodes. 相似文献
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通过建立基于多物理场耦合的焊点模型,得到焊接参数与焊点力学性能之间的窗口关系;对焊点进行车身综合工况下的受力分析,将焊点所受到的拉、剪力以及装配节拍要求的焊接时间作为约束条件,以最低焊接能耗为优化目标,提出了基于焊点“质量—能耗”均衡模型的焊接参数优化方法. 通过该优化方法,可以得到焊点力学性能及工业能耗的均衡优点. 结果表明,以某车型安全带固定座结构为算例,相比传统方法,优选的焊接参数在保证焊点性能要求的同时,还能使生产能耗降低超55%,这对保证质量及降低企业生产成本具有重要意义. 相似文献
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基于Windows环境、高速数据采集卡PCL1800和工控机通用平台,采用VC++开发了一套信号采集、信号处理、实时显示的焊接电信号测试分析软件。该系统能精确采集点焊过程的电极间电压和焊接电流波形,并提取出焊接过程动特性的喷溅特征信息,从而为高性能焊机的研制和焊接参数的优化提供了一个强有力的工具。 相似文献
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Results of temperature measurements during welding of 12.7 mm thick AA6061-T6 alloy plates by modified indirect electric arc (MIEA) are presented. This study describes the thermal cycles in the heat-affected zone (HAZ) and also in the fusion zone. Depending upon the position of the transducers, the maximum temperatures measured in the HAZ ranged from 308 to 693°C, these measurements were related with the tensile test results and the failure zone reported previously by the authors (Ambriz et al., S&;I 2006;11:10–17). It was observed that there is a decrease in the mechanical strength of the welded joints, due to the microstructural changes undergone by the AA6061-T6 alloy in which formation of the β′ occurs according to the time–temperature transformation diagram. The inherent cooling conditions of the weld pool observed for the MIEA technique (single welding pass) have made it possible to establish the characteristics of solidification and microstructure for a specific cooling rate. 相似文献
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以采集的电阻点焊接头表面的数字图像作为信息源,探索了一种新的点焊质量无损监测方法.首先,通过图像特征分析,焊点表面图像被划分为4个环形特征区域,提取环形特征区域面积作为表征焊点质量的特征参数.其次,根据特征区域面积与焊点抗剪强度的相关性分析结果,选择了相关性显著的3个特征参数作为输入向量,焊点抗剪强度作为输出向量,建立了点焊质量的RBF神经网络监测模型.仿真分析和验证结果表明,基于焊点表面图像特征信息处理监测点焊质量的方法是可行的. 相似文献
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