Beom-Soo Kang

Various design techniques to reduce cogging torque by controlling energy variation in permanent magnet motors

Using energy method, this paper analytically reveals that the cogging torque can be reduced by controlling N/sub L/th harmonic components of the square of airgap permeance function and flux density function, where N/sub L/ denotes the least common multiple of number of poles and number of slots. As for design tools, it introduces various design techniques to reduce cogging torque with analytical formulation and FEM examples.

Design and manufacturing of fiber reinforced elastomeric isolator for seismic isolation

Abstract In this paper an experimental analysis is presented for the mechanical characteristics of multi-layer elastomeric isolation bearings where the reinforcing element—normally steel plates—are replaced by a fiber reinforcement. The fiber reinforced elastomeric isolator (FREI), in contrast to the steel reinforced elastomeric isolator (SREI) which is assumed to be rigid both in extension and flexure, is assumed to be flexible in extension, but completely lacking flexural rigidity. The FREI is designed and fabricated for evaluation of the performance on seismic isolation. Experiments are carried out to evaluate and compare the performances of fiber reinforcement with performance of steel reinforcement, and the differences in performance among different kinds of fiber reinforcements. From the experiments, the performance of the FREI is shown to be superior to that of the SREI in view of horizontal stiffness and vertical stiffness of the isolator. Therefore, it is possible to produce an FREI that matches the behavior of an SREI. Consequently, the FREI could replace the conventional SREI for seismic isolation with low-cost manufacturing and lightweight installation.

Finite element analysis and design in stainless steel sheet forming and its experimental comparison

Abstract Bending and drawing processes are analyzed in stainless steel sheet forming using solid element and finite-strain formulation by the Finite Element Code MARC. In bending deformation, the springback increases through augmentations of the clearance between punch and workpiece. Divergences between theoretical and experimental results occur due to the simplification of the contact condition at the die–workpiece interface. For the square cup deep drawing process which includes bending and drawing deformation modes, the lubrication conditions are critical factors for producing sound products. All the results derived from the FEM analysis show reasonable agreement with the experimental data.

Bursting failure prediction in tube hydroforming processes by using rigid–plastic FEM combined with ductile fracture criterion

Abstract The most common failure in tube hydroforming is the bursting failure due to excessive thinning of large deformation. To evaluate the forming limit of hydroforming processes, the Oyanes ductile fracture integral I was introduced and calculated from the histories of stress and strain according to every element by using the rigid–plastic finite element method. The region of fracture initiation and the forming limit for three hydroforming processes, such as a tee extrusion, an automobile rear axle housing, and a lower arm under different forming conditions are predicted in this study. Also it is shown that the material parameters used in the ductile failure can be obtained from the experimental forming limit diagram. From the results, the prediction of the bursting failure and the plastic deformation for the three hydroforming examples demonstrates to be reasonable so that this approach can be extended to a wide range of practical tube hydroforming processes.

Prediction of the forming limit in hydroforming processes using the finite element method and a ductile fracture criterion

Abstract Using the finite element method, Oyane’s ductile fracture integral I was calculated from the histories of stress and strain according to every element and then the forming limit of the hydroforming process was evaluated. The fracture initiation site and the forming limit for two typical hydroforming processes, a bumper rail and a subframe, under different forming conditions are predicted in this study. For these products, the ductile fracture integral I is not only affected by the process parameters, but also by the shape of the pre-forming blank. Due to no axial feeding at the end of the blank, the possibility of cracking in hydroforming of these products is influenced by the friction condition more strongly than for the axial feeding of products such as a the tee extrusion. All the simulation results show reasonable plastic deformation and the applications of the method could be extended to a wide range of hydroforming processes.

Finite Element Analysis of Multi-Stage Deep Drawing Process for High Precision Rectangular Case with Extreme Aspect Ratio

Abstract Deep drawing process for rectangular drawn section is different with that for axisymmetric circular one. Therefore deep drawing process for rectangular drawn section requires several intermediate steps to generate the final configuration without any significant defect. In this study, finite element analysis for multi-stage deep drawing process for high-precision rectangular cases is carried out especially for an extreme aspect ratio. The results of analysis show that the irregular contact condition between blank and die affects the occurrence of failure, and the difference of aspect ratio in the drawn section leads to non-uniform metal flow, which may cause failure. A series of experiments for multi-stage deep drawing process for the rectangular cases are conducted, and the deformation configuration and the thickness distribution of the drawn rectangular cases are investigated by comparing with the results of the numerical analysis. The numerical analysis with an explicit time integration scheme shows good agreement with the experimental observation.

Comparison of vibration sources between symmetric and asymmetric HDD spindle motors with rotor eccentricity

The permanent magnet motor is often the most important element in hard disk drive (HDD) spindles and also a frequent source of vibration and acoustic noise. The eccentricity between stator and rotor is inevitably introduced during manufacturing process, such as mass unbalance, shaft bow and bearing tolerances. This paper analytically discusses effects of rotor eccentricity on motor performances for symmetric and asymmetric motors, such as local traction, unbalanced force, cogging torque, back EMF, phase current and torque ripple. An asymmetric motor, mostly chosen to reduce the cogging torque, shows a worse effect on cogging torque and unbalanced force when the eccentricity exists. It also adversely affects the flux linkage and introduces variation of the phase back EMF depending on winding and rotating eccentricity, thus yielding increased mutual torque ripple.

Development of brushless and sensorless vibration motor used for mobile phone

With the wide use of mobile phones, a paging signal by a sound transducer acts as an environmental noise on many occasions, thus necessitating an alternative paging signal by a vibration motor. Conventional vibration motors employ three-phase windings with mechanical brushes for commutation, which is disadvantageous to manufacturing cost and productivity. In this paper, a new one-phase brushless and sensorless vibration motor is introduced utilizing digital signal processor chips in mobile phones. For electromagnetic field analysis, two-dimensional modeling can be implemented to determine the back electromotive force using axisymmetric boundary conditions. Geometric design parameters, such as coil pitch and magnet pitch. are considered for performance optimization. Through the experiments, it is shown that the proposed design has the equivalent performance with reduced number of parts, thus enhancing manufacturing productivity and reducing manufacturing cost.

Manufacture of an automobile lower arm by hydroforming

Abstract An automobile lower arm has been fabricated in a prototype form by hydroforming with the aids of numerical analysis and experiments. For the numerical process design, a program called HydroFORM-3D developed here on the basis of a rigid–plastic model, has been applied to the lower arm hydroforming. The friction calculation between die and workpiece has been dealt with carefully by introducing a new scheme in three-dimensional surface integration. To accomplish successful hydroforming process design, thorough investigation on the proper combination of process parameters such as internal hydraulic pressure, axial feeding and tool geometry has been performed. Results obtained from numerical simulation for a lower arm in the hydroforming process are compared with a series of experiments. The comparison shows that the numerical analysis successfully provides the manufacturing information on the lower arm hydroforming, and it predicts the geometrical deformation and the thinning.

Analysis of a dynamic speaker in mobile phones by considering mechanical, electrical, and magnetic coupling effects

With the advent of 3G mobile phones, a combined laptop personal computer and mobile phone can be realized that enables multimedia data communication such as TV streaming, web searching, music play, etc. A dynamic speaker is an essential part to generate high quality sound in the next generation mobile phones. Noting that characteristics of a dynamic speaker are a coupled phenomenon of mechanical, electrical, and magnetic system, a systematic analysis must be implemented to fully consider the coupling effects for an improved design. This paper presents a complete analysis of a dynamic speaker by considering mechanical, electrical and magnetic coupling effects. Results of the analysis are confirmed by the experiments. An improved design of a dynamic speaker is also proposed with enhanced performance.