Dynamical behaviour of machine tools during friction stir welding

Abstract

Friction stir welding (FSW) is a promising joining technology that is quickly becoming the preferred joining process for a wide range of applications. Because of their high static values, the process forces occurring during FSW still are a major factor concerning the development or the choice of friction stir welding machines. However, until now, the vast majority of research projects only consider the static force components or the maximum loads that occur during a given welding operation. But, like during turning or milling, the tool does generate oscillating process forces that induce vibrations into the machine structure and should not be neglected. Thus, the key aspect of this work is the comprehensive characterization of the dynamical nature of the process forces and their effect on the machine structure. These results are then used for the development of a process force model and the design of a machine model to simulate the response to these loads. These two models are combined in one simulation environment and interact with each other to predict the process stability for a certain combination of process parameters and machine.

Tool eccentricity in friction stir welding: a comprehensive review

“…As mentioned, it is inherent in all milling operations. Related works on FSW report eccentricities in the range of 0.001-0.06 mm [79,[92][93][94]. Research on eccentric motion in this range mainly focuses on the fundamental understanding of FSW, how this motion affects the process control and response variables (welding speed, force, power, etc.)…”

“…However, minor geometrical variations in the material flow in an AA2017-T4 sample, compared to the plasticine, suggest that eccentricity may also be caused by the different transverse forces on the advancing and retreating sides of the weld. This can be understood through the simple model of material transportation around the pin during FSW shown in Figure 3 [94, 103]. The tool region is divided into quadrants, namely advancing/leading, retreating/leading, advancing/trailing and retreating/trailing [88].…”

“…On the other hand, Zaeh and Gephard [94] examined the effect of tool eccentricity on the process force. Force measurements showed that tool runout has a major influence on the process force ( F x and F y ) oscillating amplitude when a 0.03 mm tool runout was applied using 1400 rev min −1 without any welding speed (0 mm min −1 ), but this effect became negligible for extremely low runout (0.001 mm).…”

Formation of the periodic material flow behaviour in friction stir welding

“…This kind of feature can be optically observed as periodic material flow behaviour or alternating light and dark banded structures in the horizontal cross-section, and also as onion ring structures of weld nugget in the transverse cross-section. Numerous researches have detected that the periodic feature has substantial influence on the variation of texture, grain size, fracture behaviour and micro-hardness of the joint, and could be correlated with the periodic fluctuation of welding loads during FSW process [4][5][6]9,[13][14][15]. However, few works have focused on its formation mechanism.…”

Dynamic Interaction between Machine, Tool, and Substrate in Bobbin Friction Stir Welding

“…Others have adopted signal processing methods, namely, fast Fourier transform (FFT), to reveal frequencies of the force signal [16]. This method has been used to characterise the trends for different tool run-out [17]. Imbalanced and force magnitudes have been associated with greater tendency to produce voids in the weld [13], though the mechanisms are incompletely understood.…”