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Overview of resistance spot welding control

Abstract This paper presents an overview of resistance spot welding control. The presentation of the physical background of the resistance welding process is followed by the description of the main problems concerning the appurtenant control theory. Solutions to these problems are presented primarily according to the measured signals used and to the type of control strategies.

Estimating the strength of resistance spot welds based on sonic emission

Abstract Audible sound signals detected during the resistance spot welding (RSW) of zinc coated steels were investigated in order to assess their suitability for estimating the strength of the weld. A new sonic emission indicator was introduced and compared to a commonly used emission count indicator. A new method of spot weld strength estimation based on the two indicators is presented. The advantage of the method is that it makes it possible to establish the stage when the electrode is worn out. The method enables the development of improved RSW process control algorithms.

Resistance spot welding control based on the temperature measurement

Abstract In this paper a novel approach for temperature measurement during resistance spot welding is presented. The temperature is measured by two thermocouples mounted at the ends of both the electrode tips. The authors chose to mount them there because it was expected that it would be possible to measure the temperature at this point using a digital camera in the near future. The research was, therefore, motivated to obtain various pieces of information about the welding process from the measured temperature profiles. The measured temperature profiles showed a good correlation with the weld strength. Other phenomena, such as expulsion and electrode wear, can also be related to a temperature profile.

Influence of welding current shape on expulsion and weld strength of resistance spot welds

Abstract The 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.

Image-based electrode tip displacement in resistance spot welding

The paper presents a new image processing-based algorithm for electrode tip displacement measurement. Its accuracy is evaluated by a comparison with a conventional optical sensor. The results show a clear advantage of the proposed image processing algorithm. A special program was written in order to analyze the algorithm. The electrode tips are detected by the program. It also determines the size of the reference areas on the electrode tips and tracks these areas during the welding process. Due to a multi-thread implementation of the algorithm the execution time was reduced significantly as compared to previously presented work. Consequently this approach is now applicable for control-related resistance spot welding purposes.

Resistance spot weld strength estimation based on electrode tip displacement/velocity curve obtained by image processing

Abstract This paper presents a machine vision based electrode tip displacement measurement. The displacement is obtained by the observation of a certain area (mask) in a sequence of images. Based on the obtained displacement measurement a tip velocity was calculated as well. For this signal Kalman filtering was used in order to reduce noise. The relation between the electrode tip displacement/velocity curve parameters and weld strength was investigated. Among maximum displacement, indentation depth, maximal velocity in cooling phase and maximal velocity in heating phase the latter turned out to be the best parameter for weld strength estimation.

A machine vision-based electrode displacement measurement

The document presents a novel approach for electrode tip displacement measurement. It is based on digital image analysis using a custom-made lighting system, CCD camera, and an image analysis algorithm. Results show accurate displacement measurements and the influence of thermal expansion of the machine components on other displacement-measuring methods.

Vision-based control of a line-tracing mobile robot

In this article, a vision‐based control of a line‐tracing mobile robot is presented. The position of the robot is determined based on the analysis of the images obtained by a ceiling mounted camera. Such an approach has some advantages compared to the more common robot mounted camera approach. The robot detection algorithm uses some well‐known image processing algorithms. As the PC is common these days and the mobile robot is quite easy to build or buy, the only prerequisite is a camera. The time delay of a web camera is too large so a FireWire CCD camera is preferred for better performance. The control system presented can be an ideal educational tool for an introductory level course in image processing, image analysis, or machine vision. As the line‐tracing problem is well known to everyone studying mechatronics or robotics, the approach presented in this article should be of great interest to all students in these fields, because it offers an alternative solution to the line‐tracing problem. Besides that this approach makes it possible to implement a more advanced predictive control algorithm. In order to make the experiment even more interesting, an obstacle avoidance algorithm is presented as well.

3D Measurement of Electrode Contact Area in Resistance Spot Welding of Coated Steel

The document discusses the possibility of contact area estimation during resistance spot welding employing post-weld 3D measurement of electrode indentation. Experimental welding of a common type of mild zinc-coated steel was conducted using two different electrode tip types varying welding time, RMS current and number of successive welds. The other parameters (clamping force, voltage, pre- and post-weld time, weld-piece thickness) were constant. The results show that this approach gives valuable information on the conditions under which the weld-spot was formed.

The applicability of welding force for spot weld quality assurance

This paper presents research about the possible usage of welding force for the estimation of the weld strength. Other signals such as welding current or electrode displacement are commonly used for this purpose. Our previous research has, however, shown that welding force is a very good indicator of expulsion occurrence. In this paper, we presented the relationship between time needed for expulsion occurrence and weld strength. The results are better than in the case of welding current. In order not to limit this approach only to welds with expulsion, another variable is calculated from the welding force signal. The welding force variation is the sum of square differences of welding force and mean welding force. Although slightly less accurate than time needed for expulsion variable, it is not limited to expulsion welds.