Quality control of the induction hardened layer and the grinding process in aerospace ball screws via magnetic Barkhausen noise analysis
Reducing the weight of aircraft and helicopters is a common way to reduce fuel consumption and achieve greener operations. Nowadays, hydraulic actuators are used to move the control surfaces that are responsible for commanding the flight. Hydraulic systems have a considerable weight and therefore one of the major challenges in the aeronautic sector is to substitute these actuators with lighter electrical actuators. However, electrical actuators must be highly reliable and able to work under severe conditions. In this respect, electro-mechanical actuators (EMA) represent the next generation of actuation systems for commercial aircraft and aero engines. EMAs are equipped with a motor, a ball/roller screw and the control electronics. Actuators are safety-critical components of an aerospace system and an undetected failure can lead to serious consequences. Therefore, the quality of these ball screws has to be controlled and certified with the most advanced non-destructive techniques. In this context, the present work presents magnetic Barkhausen noise analysis (BNA) as a non-destructive technique for controlling the quality of ball screws, thereby ensuring the induction hardened layer has formed properly and detecting the local overheating regions, known as grinding burns, which may have occurred during the grinding process. With the aim of analysing the sensitivity of the BNA, several induction hardening treatments were applied to produce samples with different profiles and hardened layer depths. Moreover, grinding conditions were varied to obtain grinding burns of different intensities. Magnetic Barkhausen noise measurements were taken with a system designed and implemented by the authors, and the derived parameters were compared with microhardness measurements made at various depths after the different induction hardening and grinding processes. The results show that various parameters derived from the magnetic Barkhausen noise envelope can be used to identify both the different layer depths after induction hardening and the decrease in hardness produced by the grinding burns in such a way that a set of thresholds can be used to determine and assure the quality of the hardened layer and the grinding process of the ball screws. More info about this article: http://ndt.net/?id=19690
Magnetic Barkhausen emission measurements for evaluation of material properties in gears
The magnetic Barkhausen emission (MBE) technique is considered as a potential non-destructive evaluation (NDE) method for assessing material properties in case-hardened gears. For gear manufacturing industries, the evaluation of material properties such as tempering induced changes in hardness level and the associated microstuctural changes, variations in case-depth of hardened layer, grinding process induced alteration in microstructure, hardness and residual stress distributions are of primary importance in order to ensure the quality of gears during service. This paper presents an overview of different research and developmental studies carried out at Design Unit, Newcastle University on the MBE technique suitable for different applications in the evaluation of quality of gears.
Joint strength of aluminum ultrasonic soldered under liquidus temperature of Sn–Zn hypereutectic solder
Abstract In order to obtain high-strength aluminum joints, ultrasonic soldering of 1070 aluminum was conducted under liquidus temperature of Sn–Zn hypereutectic solder. A device for ultrasonic soldering was assembled, which propagated ultrasonic vibrations in a direction perpendicular to joining surfaces. This device joined 1070-Al using quasi-melting Sn–Zn hypereutectic solder without using any artificial spacers. The strength of the solder joints was evaluated by tensile tests. The optimum joining conditions were determined, and the effects of solder compositions and soldering temperature on the joint strength and the solder layer thickness were examined. In this ultrasonic soldering process, the highest tensile strength was obtained for the solder joints fabricated at 220 °C for the Sn–23Zn and Sn–40Zn solder compositions. The joint strength was equivalent to that of 1070-Al heat treated at 220 °C. The sound joints were obtained at 300 °C using Sn–82Zn solder, the liquid phase volume fraction of which was theoretically only 0.24. The present work also revealed that the thickness of retained solder layer in the joint after ultrasonic soldering could be estimated. Accordingly, ultrasonic soldering under the liquidus temperature of Sn–Zn hypereutectic solder could be a spacer-free soldering method to obtain high-strength aluminum joints.