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
A review of the influence of grinding conditions on resulting residual stresses after induction surface hardening and grinding
Abstract Internal stresses which are, since the completion of manufacturing, termed residual stresses very much reflect the manufacturing procedures and machining conditions. Residual stresses are analysed in terms of different induction surface hardening conditions and then also after finish grinding in terms of different machining conditions. Induction surface hardening creates very desirable residual stresses in the hardened surface layer. Residual stresses are always of a compressive nature and are usually present to the depth of the induction-hardened layer. By the appropriate selection of grinding wheel and grinding conditions and taking into account the physical and mechanical properties of the workpiece material very favourable compressive residual stresses in the hardened surface layer can be retained. How is it possible to assure a desirable surface and surface layer quality after induction-hardening and fine grinding? Finding an answer to this question requires a very good knowledge of the process of grinding on the micro-level as well as knowledge of mechanical and heat effects acting on the layer of the workpiece including the type and condition of the grinding wheel. An all-inclusive consideration of the numerous influences of the kind and condition of the tool on the changes on the surface and in the surface layer of the workpiece in the given machining conditions is described by the term “surface integrity”.
Tunable scaling behaviour observed in Barkhausen criticality of a ferromagnetic film
A ferromagnetic material shows a sequence of discrete and jerky domain jumps, known as the Barkhausen avalanche1,2, in the presence of an external magnetic field. Studies of Barkhausen avalanches reveal power-law scaling behaviour that suggests an underlying criticality3,4,5,6,7,8, as observed in a wide variety of systems such as superconductor vortices9, microfractures10, earthquakes11, lung inflations12, mass extinctions13, financial markets14 and charge-density waves15. The most interesting unsolved fundamental question is whether the universality in the scaling exponent holds regardless of the material and its detailed microstructure. Here we show that the scaling behaviour of Barkhausen criticality in a given ferromagnetic film is experimentally tunable by varying the temperature (not dimensionality). We observe for the first time that the scaling behaviour in the Barkhausen criticality of a given system crosses over between two universality classes when the relative contributions from the dipolar interaction and domain-wall energies are altered by an experimental parameter.