No abstract

This paper presents a new approach to the structural integration of piezoceramics into thin-walled steel components for condition-monitoring applications. The procedure for integrating the sensors into metal components is described, and their functionality is experimentally examined with a 2 mm-thick steel sheet. The signal quality of the produced sensors is investigated in a frequency range from 100 Hz to 50,000 Hz and is compared with the results of piezo patches and strain gauges under the same conditions. The results show that due to a higher signal-to-noise ratio and a better coherence, the structurally integrated piezoceramics and the piezo patches are more qualified sensors for vibration measurement in the examined frequency range than the strain gauges. The measurements also indicate that the patches provide higher amplitudes for the frequency range up to 20 kHz. Beyond that, up to 40 kHz, the integrated sensors supplied higher amplitudes. The better signal quality in different frequency ranges as well as the different manufacturing and application methods can be interpreted as an advantage or disadvantage depending on the boundary conditions of the condition-monitoring system. In summary, structural integrated piezoceramics extend the options of monitoring technology.

When applying a magnetic field parallel or perpendicular to the long edge of a parallelepiped Ni-Mn-Ga stick, twin boundaries move instantaneously or gradullay through the sample. We evaluate the sample shape dependence on twin boundary motion with a micromagnetics computational study of magnetic domain structures and their energies. Due to the sample shape, the demagnetization factor varies with the direction of external magnetic field. When the external magnetic field is applied perpendicular to the long edge of the sample, i.e. in the direction in which the demagnetizing field is highest, the magnetic energy intermittently increases when the strength 2 of the applied magnetic field is low. This energy gain hinders the twin boundary motion and results in a gradual switching, i.e. a gradual magnetization reversal as the applied magnetic field is increased. The formation of 180⁰ magnetic domains offsets this effect partially. In contrast, when the applied magnetic field is parallel to the long edge of the sample, i.e. in the direction in which the demagnetizing field is lowest, the energy decreases with each subsequent magnetization domain reversal and the twin boundary moves instantaneously with ongoing switching. The actuation mode with the field parallel to the long sample edge lends itself for on-off actuators whereas the actuation mode with the field perpendicular to the long sample edge lends itself to gradual positioning devices.

Magnetostrictive materials are a group of smart materials with comparable properties to piezoelectric materials regarding strain and operating frequency. In contrast, the Curie temperature is much higher and the principle effect allows different actuator designs. Especially in the case of rotating actuators in ultrasonic assisted machining, a high potential is seen for a simplified energy transmission. In the study, a test stand for a rotating actuator with simultaneous vibration in longitudinal direction was designed to show the proof of principle for this idea. It was shown that the current inducing the magnetic field as well as its frequency influence the amplitude of the rotating actuator. This is a first step to developing a rotating actuator for ultrasonic machining.

Abstract. The application of ultrasonic vibration assistance in machining offers many benefits over conventional machining. In some machining processes, like the generation of geometrically defined microstructures by cutting, the interaction of the system components and the machining process can be particularly crucial with respect to the production result. Monitoring of ultrasonic vibration-assisted machining in terms of the in-process measurement of frequency and amplitude is currently realized by measurement inside the actuator; thus, measurement is presently undertaken relatively far away from the cutting process. In this paper an in-process measurement set-up based on strain gauges positioned close to the cutting edges is presented. It is used to investigate the induced vibration in the ultrasonic horn. Experiments on machine samples with and without ultrasonic vibration assistance are performed using the in-process measurement set-up described. The results of the strain gauges are analysed in comparison to internal feedback signal and surface measurements. The experiments show the high sensitivity of the measurement set-up presented and a huge gain of information compared with the conventional measurement approach. This enables improved controllability of the excited mode shapes as well as in-process adjustment of the ultrasonic vibration frequency and amplitude for the manufacturing of defined microstructures.