Cesnik D.,Hidria Rotomatika |
Bratus V.,Hidria AET
HTM - Journal of Heat Treatment and Materials | Year: 2013
The distortion of steel flat ring type products after fine-blanking and subsequent carbonitriding was investigated. All the analyzed products were produced from the same coil and under the same conditions of fine-blanking. The fine blanked products were afterwards heat treated by using three different procedures - carbonitriting, stress relief annealing and heat treatment in a neutral atmosphere under the same temperature regime as for carbonitriding. The contribution of fine-blanking, relief of residual stresses, uneven heating and cooling and the formation of carbonitrided cases on the overall distortion were determined. The results were complemented with hardness measurements, residual stresses measurements and observations of microstructure. The presented research work is the first step towards the understanding of the mechanisms and factors that influence the quality of the final products during the production cycle. © 2013 Carl Hanser Verlag, München.
Cebron M.,Hidria Rotomatika |
Kosel F.,University of Ljubljana
Strojniski Vestnik/Journal of Mechanical Engineering | Year: 2014
Stored energy analyses by differential scanning calorimetry (DSC) and indentation hardness measurement were performed on crosssectional samples cut from the gauge length of tensile-deformed copper specimens. The stress-strain curve was described using dislocationbased hardening models integrated into a visco-plastic Taylor-type model of polycrystal deformation. Three approaches in reproducing the experimental stress-strain curve were used to evaluate the differences in dislocation density predictions resulting from different modelling options. A good description of hardening was achieved by all three approaches and constitutive models and only negligible differences were found in the predicted dislocation density between assumed homogeneous and heterogeneous dislocation distribution throughout the polycrystal. Measured values of stored energy are somewhat lower than those published in research studies in which one-step and slow annealing methods were used. A simple model predicting a nearly linear increase of stored energy with dislocation density was found to adequately describe retained energy evolution. Since different dislocation arrangements result in different yield stress and energy predictions, both results can be used to determine values of parameters in two-internal-variable hardening models. Even though both measured quantities were satisfyingly described, uncertainties regarding material parameters and the applied polycrystal and stored energy models prevent us from claiming that the evaluated dislocation density distributions represent the actual dislocation structure in the material. As expected for strongly hardening materials, the relationship between yield stress and hardness could not be adequately approximated by a linear function. Instead, a linear combination of yield stress and hardening rate was used, finally providing a relation between hardness and stored energy through their mutual dependence on yield stress. © 2014 Journal of Mechanical Engineering. All rights reserved.
Bizjan B.,University of Ljubljana |
Milavec M.,Hidria Rotomatika |
Sirok B.,University of Ljubljana |
Trenc F.,University of Ljubljana |
Hocevar M.,University of Ljubljana
Journal of Sound and Vibration | Year: 2016
A study of velocity and pressure fluctuations in the tip clearance flow of an axial fan is presented in this paper. Two different rotor blade tip designs were investigated: the standard one with straight blade tips and the modified one with swept-back tip winglets. Comparison of integral sound parameters indicates a significant noise level reduction for the modified blade tip design. To study the underlying mechanisms of the energy conversion and noise generation, a novel experimental method based on simultaneous measurements of local flow velocity and pressure has also been developed and is presented here. The method is based on the phase space analysis by the use of attractors, which enable more accurate identification and determination of the local flow structures and turbulent flow properties. Specific gap flow energy derived from the pressure and velocity time series was introduced as an additional attractor parameter to assess the flow energy distribution and dissipation within the phase space, and thus determines characteristic sources of the fan acoustic emission. The attractors reveal a more efficient conversion of the pressure to kinetic flow energy in the case of the modified (tip winglet) fan blade design, and also a reduction in emitted noise levels. The findings of the attractor analysis are in a good agreement with integral fan characteristics (efficiency and noise level), while offering a much more accurate and detailed representation of gap flow phenomena. © 2016 Elsevier Ltd.
Bolka S.,Hidria Rotomatika |
Slavic J.,University of Ljubljana |
Boltezar M.,University of Ljubljana
Strojniski Vestnik/Journal of Mechanical Engineering | Year: 2015
The mechanical characteristics of sheet metals are typically identified in the in-plane direction, although the sheet-metal forming processes (e.g., blanking, deep-drawing) are normally applied in the out-of-plane direction. As the mechanical characteristics are not necessarily constant, their direct experimental evaluation through the forming process would enable material monitoring and process optimization, and, additionally, material characterization in the out-of-plane direction. Full, partial (to a certain depth) and sequential (consecutive partial steps to full penetration) blanking experiments are performed on a laboratory blanking apparatus to correlate the out-of-plane material characteristics with the in-plane ones. The well-established in-plane approach to damage is introduced for the out-of-plane direction to determine the isotropic Lemaitre damage variable. Furthermore, yield and ultimate shear stresses are determined and correlated to their respective in-plane counterparts, offering a new insight in the sheet-metal blanking process. © 2015 Journal of Mechanical Engineering. All rights reserved.
Kontarcek A.,Hidria AET |
Bajec P.,Hidria Rotomatika |
Nemec M.,University of Ljubljana |
Ambrozic V.,University of Ljubljana |
Nedeljkovic D.,University of Ljubljana
IEEE Transactions on Industrial Electronics | Year: 2015
This paper presents a low-cost fault-tolerant system for open-phase fault (OPF) in a power-converter-fed permanent-magnet synchronous machine. The proposed fault-tolerant system is based on field orientation control with additional fault tolerance functionality. A current predictive method for OPF detection is presented, together with an estimation of the threshold level for detection. The proposed method is based on the prediction of stator current for the next sampling interval. Furthermore, a new method for postfault operation of the machine is proposed. For optimal performance of the complete drive, a prefiring angle is introduced in order to avoid the temporary generation of negative torque. This improvement increases the average generated postfault electromagnetic torque, and consequently, it reduces the mechanical stress on various machine parts. The proposed fault detection and postfault operation solutions were simulated in MATLAB, and they were also tested on an experimental setup. The results show several advantages of the proposed fault-tolerant solution, like its short fault-detection time, substantial robustness against variation of machine parameters or load fluctuations, and negligible implementation costs, since no hardware modifications are needed. The fault detection algorithm does not require high computing power, and it operates well even during transients. © 1982-2012 IEEE.