The paper presents an overview of different types of defects at friction stir welding. In order to explain the reasons for their occurrence a short theoretical background of the process is given ...first. The main emphasis is on the parameters that influence the process. An energy supply based division of defects into three disjoint groups was used. The occurring defects are demonstrated on various materials.
In the last decade, digital image correlation (DIC) has become the most widely used non-contact technique for measuring full-field motion and deformation in image sequences. As permanent hardware ...improvements make it possible to readily obtain digital images with higher and higher resolutions at ever-increasing frame rates, the efficiency of image registration methods is becoming increasingly important. Another aspect of this problem is the desire to improve the accuracy of these methods, which in general implies additional computational time. This problem is addressed by applying the inverse compositional Gauss-Newton (IC-GN) algorithm, which is modified to include the parametric sum of squared differences (PSSD) correlation criterion. However, the classical IC-GN algorithm with the sum of squared differences (SSD) correlation criterion cannot be used in cases in which lighting variations are of considerable importance. In this paper, a solution to this disadvantage is presented. The lighting variation is directly included in the IC-GN minimization procedure, which reduces the additional calculation time. Moreover, this IC-GN algorithm does not need to re-evaluate and invert the Hessian matrix. This results in a more computationally efficient algorithm. Experimental results show that the proposed algorithm is insensitive to the linear intensity variation in the target image; consequently, it has a faster convergence rate than the IC-GN algorithm with the zero-mean normalized sum of squared differences (ZNSSD) correlation criterion. As a result, computational time can be reduced by up to 30% in the case of convergence condition
𝜖
=0.001. Owing to the above mentioned advantages of the proposed IC-GN algorithm, it could become a new standard for efficient and robust full-field displacement tracking in image sequences with varying lighting intensity.
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.
Overview of resistance spot welding control Podržaj, P.; Polajnar, I.; Diaci, J. ...
Science and technology of welding and joining,
04/2008, Letnik:
13, Številka:
3
Journal Article
Recenzirano
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.
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.
Information about the dynamic loading of a steel structure is important for its static design as well as for an assessment of its fatigue life. In the case of tower cranes, these loads are mainly ...caused by vibrations and load sway, which occurs as a result of the slewing motion of the jib around the vertical axis and from the radial movement of the load's suspension point. In this paper, only the slewing motion that produces the spatial motion of the pendulum is considered, because this kind of motion has received much less attention than the translation of the suspension point. In order to achieve this, a non-linear mathematical model of the load sway during the slewing motion was formulated, and the non-linear nature of the swinging motion for large angles and the non-linearity of the power transmission were considered. The structure's elasticity and damping, the friction in the main bearing, and the air resistance were also taken into account. The dynamic forces acting on the steel structure of the crane during payload transport were obtained. In order to confirm the mathematical model, an actual model of a crane was built and used as the basis for measurements. A comparison of the results shows good agreement between the predicted and the measured values.
This paper presents the nanorobotic resistance spot welding (RSW) of ultra-thin film three-dimensional helical nanobelts(HNBs) for the assembly of nanoelectromechanical systems (NEMS) from ...as-fabricated building blocks. Three-dimensional HNBs with metal pads firstly placed onto as-fabricated micropipette electrode. using nanorobotic manipulation, then fixed with RSW. The spot-welded structures are then electro-mechanically characterized to show the ohmic conductivity and electromechanical stability. Experiments show that RSW can enable stable ohmic contacts with sufficient mechanical strength for constructing devices such as force sensors from HNBs.
Undergraduate students are often uncomfortable about using frequency methods. Therefore, a decision was made to try to explain this concept by using a real-life example. A common second-order damped ...spring-mass system was used for this purpose. Viscous dampers are known to be nonlinear. Therefore, the system's damper was modified, and an electromagnetic damper was used instead of the viscous damper in order to get closer to linearity. In this way, the results obtained should more closely resemble the results predicted by theory.
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.
