Abstract
Ultrasonic welding of titanium alloy Ti6Al4V to carbon fibre reinforced polymer (CFRP) at 20 kHz frequency requires suitable welding tools, so called sonotrodes. The basic function of ultrasonic welding sonotrodes is to oscillate with displacement amplitudes typically up to 50 µm at frequencies close to the eigenfrequency of the oscillation unit. Material properties, the geometry of the sonotrode, and the sonotrode tip topography together determine the longevity of the sonotrode. Durable sonotrodes for ultrasonic welding of high-strength joining partners, e.g., titanium alloys, have not been investigated so far. In this paper, finite element simulations were used to establish a suitable design assuring the oscillation of a longitudinal eigenmode at the operation frequency of the welding machine and to calculate local mechanical stresses. The primary aim of this work is to design a sonotrode that can be used to join high-strength materials such as Ti6Al4V by ultrasonic welding considering the longevity of the welding tools and high-strength joints. Material, sonotrode geometry, and sonotrode tip topography were designed and investigated experimentally to identify the most promising sonotrode design for continuous ultrasonic welding of Ti6AlV4 and CFRP. Eigenfrequency and modal shape were measured in order to examine the reliability of the calculations and to compare the performance of all investigated sonotrodes.
Highlights
The performance of components for aeronautical or automotive industries is constantly being improved
Further investigations of similar rod-shaped sonotrodes were performed by solving the equation of motion and by the finite element method (FEM)
Since joining the strength andsonotrodes hardness of the sonosonotrode mustisbe higher thanofthat the upper partner, made from trode must be higher than that of the upper joining partner, sonotrodes made from alualuminium or titanium were not considered in this work
Summary
The performance of components for aeronautical or automotive industries is constantly being improved. Dissimilar metal/titanium joints have been investigated in the past, but in contrast to this work, titanium was the lower joining partner during ultrasonic welding [8,15]. Suitable materials and sonotrode geometries have to be considered in order to achieve reproducible high joint strength and longevity of the tools. Used sonotrode materials have been investigated by Emmer et al [23,24] who examined sonotrodes made from the tool steel CPM10V, 16MnCr5 and the metal matrix composite Ferrotitanit WFN in relation to displacement amplitude and microstructural effects. Besides mechanical properties of the used material, acoustic characteristics of sonotrodes are strongly dependent on geometry, especially the mass distribution along the axis of oscillation [25]. There is a need for superimposition of modes in some cases, such as ultrasonic drilling tools [30,32], or sonotrodes that operate in a combined longitudinal-torsional mode [33,34,35]
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