Electrical Steel Laminations Research Articles

Investigation of the influence of cobalt content and grain size of WC-Co cemented carbides on wear when shear cutting electric sheet metal

In the production of electrical machines, shear cutting of electrical steel laminations before further processing into rotors and stators represents an essential manufacturing process. Investigations have shown that using abrasively worn active elements while shear cutting increases the hysteresis losses in the electrical steel sheet due to introduced deformations and resulting residual stresses. Therefore, knowledge of suitable tool materials is of great importance for producing high-quality electric motors. Due to its high silicon content, electrical steel has a strong abrasive effect on the tools, which is why Tungsten carbide cobalt (WC-Co) cemented carbides are commonly used. In this work, continuous stroke tests are carried out on an electric sheet with punches made of different WC-Co cemented carbides, differing in cobalt content and grain size. The punches are examined with increasing wear regarding cutting-edge geometry, surface condition and microstructure. The resulting cutting parts are inspected for cutting surface characteristics. In addition, the influence of geometry and tribology of the punches regarding residual stresses in the material is investigated by FEM-Simulation. The investigations will provide information on the wear development and causes when shear cutting electrical sheets and the effects on electric losses.

Computation of Core Losses in Electrical Steel Laminations With Impacts of Normal Flux and PWM Switching Considered

Computation of Core Losses in Electrical Steel Laminations With Impacts of Normal Flux and PWM Switching Considered

Analyzing the impact of interlocking on non-oriented electrical steel (NOES) laminations: A microstructural and mechanical property perspective

Non-oriented electrical steel laminations are widely used in electric motor cores and are manufactured using various techniques such as cutting, punching, interlocking, and welding. These manufacturing processes can have a detrimental effect on the performance of the electric motor. Thus, in order to enhance the performance of the electric motor, it is essential to comprehend the microstructural, mechanical, and magnetic property changes resulting from manufacturing. The current study focuses on the microstructural modifications caused by interlocking, which is known to impact the core magnetic properties of motors, and its relation to mechanical properties like hardness. Six interlocked non-oriented electrical steel samples were prepared by incomplete punching at different loads from 500 N to 4000 N. Scanning Electron Microscopy (SEM) and Electron backscattered diffraction (EBSD) analysis was performed on the interlocked samples to study the microstructure and crystallographic texture near the edge whereas nanoindentation was used to determine the hardness profile. Pop-in analysis was done to study the extent of work hardening due to punching and its effect on hardness. The hardness change due to residual stress was determined, which was used to estimate the induced residual stress near the edge. It ranged from 0.04 GPa at 550 N load to 11 GPa at 4000 N load near the punched edge.

Water jet guided laser cutting of electrical steel laminations

The state-of-the-art process for manufacturing electric machine laminations, die stamping, lacks flexibility and is only applicable for high-volume production, thus prototyping is often done via laser cutting or electrical discharge machining (EDM). The water jet guided laser (WJGL) is proposed as an alternative method for prototyping. This paper investigates the impact on magnetic characteristics of WJGL cutting electrical steel laminations. A 532 nm nanosecond laser with a maximum average power of 400 W was used to cut 0.2 mm thick non-grain oriented electrical steel (NO20-1200). WJGL process parameters were down-selected through experimental trials. Strips of the electrical steel containing slits were created using two sets of WJGL parameters to examine the effect on the material’s magnetic characteristics. The results indicate that using lower powers could minimise the impact on the relative permeability and core loss. With further development on scaling up, the WJGL has potential for rapid prototyping of laminations.

A Review on the Effect of Electrical Steel Manufacturing Processes on the Performance of Electric Machines

The manufacturing processing of Electrical Steel Laminations (ESLs) for electric machines comprises cutting, stacking, and housing techniques which can result in plastic deformation and residual stress in the soft magnetic material. These manufacturing processes result in decreasing the magnetic quality and a local increase in both the static and dynamic hysteresis losses near the cut edges and consequently a reduction in the performance of the designed motor. The iron losses resulting from cutting can vary by a factor of two or more depending on geometrical, material, and processing parameters as well as the magnetic field strength. It is advantageous to consider these manufacturing effects in the design stage to reduce the probability of underperforming mass production. In this paper, the manufacturing processes of ESLs and their modelling methods are comprehensively surveyed. The gaps in scientific understanding and the research need for the expansion of accurate modelling of the cutting and joining of ESLs are subsequently discussed.

Investigation of Insulation Layers on Additive Manufactured Electrical Steel Laminations in Electric Motors

In this paper, the insulation properties of printed electrical steel laminations for high-efficiency electric machines are investigated. In contrast to conventionally produced electrical steel laminations made from rolled coil material, additive manufacturing from powder material allows extremely thin and complex near-net-shape geometries with no scrap material. At the same time, the printed electrical steel laminations offer the advantage that no additional cutting steps are required and specific material characteristics are adjustable which enables special machine modifications. To avoid global eddy current paths between the single sheet layers after the stacking process, the laminations must be insulated from each other in order to keep losses low, especially at high operating frequencies. This requires a sufficiently high surface insulation resistance on the sheets. Since the insulation coating cannot be applied continuously during rolling, as in conventional production, alternative approaches for application are required. The investigations characterize and evaluate potential insulation systems for additive manufactured laminations. The printed sheets are analyzed geometrically, electrically and metallurgically at first and characterized for the next process steps. Afterwards, potential insulation systems are analyzed and investigated in practical tests. The coating systems are characterized in terms of application, thickness, electrical and mechanical insulation properties, and options for further processing. This is crucial as the coating needs a sufficient level of adhesion to the substrate and allows successive bonding.

Effects of WEDM and AWJ cutting methods on induction motor efficiency and total magnetic losses: Experimental design and response surface methodology

In this study, the effect of cutting electrical steel laminations using abrasive water jet (AWJ) and wire electrical discharge machining (WEDM) techniques on 5.5 kW induction motor efficiency (MEfficiency) and total magnetic losses (TLosses) was investigated. After the stator and rotor packages were formed, winding, varnishing and mechanical assembly processes were carried out and the motors were prepared for MEfficiency and TLosses tests according to the IEC 60034-2-1-1A standard. Tests were performed using different frequencies (f) and motor loading rates (MLoad). While burr formation was observed with the effect of plastic deformation on the cutting edge of electrical steels with AWJ, recast layer formation was observed with the effect of heat in WEDM. MEfficiency decreased while TLosses increased due to increasing f and MLoad in both cutting methods. Maximum MEfficiency and minimum TLosses values were measured in WEDM, it was determined that optimum results using Response Surface Methodology (RSM) were measured at f of 50 Hz and MLoad of 100% values in both cutting methods. The statistical effects of f and MLoad on MEfficiency and TLosses were revealed with ANOVA (Analysis of variance). In addition, mathematical models were developed for the prediction of MEfficiency and TLosses.

Development and Optimization of a Mechanically Robust Novel Rotor Topology for Very-High-Speed IPMSMs

Due to the trade-off between rotor mechanical strength and magnetic leakage, the high-speed capability of interior permanent magnet machines (IPMSM) is severely limited. This paper proposes a novel rotor topology capable of delivering 5 kW at 100,000 rpm using commercialized electrical steel laminations. By implementing the mechanical analysis in an iterative evolution process, two promising new topologies were developed. The first topology uses smooth compound curves (CC) to minimize the stress concentration and will be referred to as CC-type; the second topology is developed based on the CC-type with the aim to strengthen the structure further using the concept of a double-tied arch bridge (DAB) and referred as the DAB-type henceforward. After comparing the designs obtained from a detailed multiphysics optimization process, the DAB-type design was found to outperform the CC-type in all aspects, especially the mechanical robustness. This design was selected for experimental verification and a prototype was constructed. The mechanical and electromagnetic performances of the design were fully verified experimentally. The DAB-type prototype has achieved 2.31×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> rpm√kW, which is 1.5 times higher than other laminated rotor high-speed IPMSM designs found in the literature.

Identification of the scalar Preisach model with a single branch of descending hysteresis loop and numerical interpolation for the electrical steel sheet lamination with soft magnetic properties

The developed scalar Preisach model predicts the hysteresis behavior of the soft magnetic, electrical steel sheet. The experimental hysteresis loops of the electrical steel lamination prepare the Everett function required to predict the hysteresis behavior of the electrical steel lamination. We obtain the Everett function in two ways, from the series of minor loops and a single descending branch of a hysteresis loop. The Everett function has a closed algebraic form in the method using the minor loops. A genetic algorithm carries out the subsequent fitting based on the closed algebraic equation and optimization; however, the calculated flux values have highly deviated from the measured values. In another way, the Everett function consists of numerically driven Fs and B factorable functions. The values extracted from a limiting hysteresis loop determine the function Fs and B. The predicted values are correct, and the proposed method for determining the Everett function is only valid for soft magnetic materials representing symmetric and non-exchange-bias hysteresis behavior. While the method has application limitations to general magnetic hysteresis, it demonstrates the validity of using a function derived from experimentally measured hysteresis loops rather than a closed-algebraic equation to determine the Everett function. With the Everett surface the Preisach distribution function (PDF) is numerically derived and represents the difference in domain structure between two specimens.

Material Engineering of 3D-Printed Silicon Steel Alloys for the Next Generation of Electrical Machines and Sustainable Electromobility

Recently, there has been a growing need for sustainable and efficient electromobility. Also, the interest in highly-flexible resource-saving production has been increasing. To this aim, standardized manufacturing of electrified powertrains is being replaced by scalable production solutions. With this being said, additive manufacturing (AM) technology through its unmatched flexibility, can be used to manufacture the next generation of electrical machines. One of the main challenges of the existing electrical machines is that the stator and rotor are manufactured only using 2D electrical steel laminations without any design freedom for the third dimension. This research is targeting 3D printing of high quality magnetic materials. Multiple AM technologies allow industrialization of unconventional solutions and different chemical compositions of magnetic material powders can be customized for a wide range of applications including transportation electrification. This study is focusing on 3D micro extrusion technology of highly viscous silicon steel (FeSi) powder pastes. Different soft magnetic cores are printed with different silicon contents. The magnetic BH characteristics and losses of the cores are measured and compared and the best Si content with a higher limitation for eddy current losses is identified. Finally, advanced shape-profiled cores are printed and characterized to evaluate their magnetic properties in comparison to the standard electrical steel. The findings indicate that the utilization of a 3D printed core successfully mitigates eddy current losses within the high-frequency range, while also offering the added benefit of constructing intricate structures.

Loss performance of an additively manufactured axial flux machine stator with an eddy-current limiting structure

AC electrical machines have mostly been limited to 2D magnetic circuits due to the use of electrical-steel laminations, however, in recent years advances in non-traditional motor architectures such as axial flux show promise for increased torque and power densities. 3D magnetic circuits as required by axial flux motors are difficult to manufacture using laminations, and for other architectures impossible. Soft magnetic composites enable 3D flux pathways but at the expense of magnetic properties. In this study, an axial flux stator is fabricated from high-silicon electrical steel (Fe-6.5 wt%Si) using additive manufacturing with Hilbert cross-sectional geometry to limit eddy current losses and compared with electrical steel laminations of 0.127 mm and 0.35 mm. This shows comparable performance between the additively manufactured Hilbert stator and 0.35 mm laminations below 500 Hz. A torque loss of approximately 20% was observed due to 34% less magnetic material in the Hilbert stator than 0.127 mm laminations, but improved torque density for the stator by 13%. By designing for additive manufacturing, tooth area could be scaled up providing an electrical machine with 3D magnetic flux pathways with acceptable loss behaviour and good magnetic circuit properties, enabling further flexibility to electrical engineers in their pursuit of higher torque and power density.

Experimental and statistical analysis of the effects of punching and laser cutting methods on induction motor efficiency and total magnetic losses in silicon lamination sheets

In this study, M400-50A electrical steel laminations (ESLs) used in electrical machines were cut with punching and laser methods and the effect of these cutting methods on the efficiency and total losses of induction motors was investigated. ESLs were prepared by laser and punching cutting methods concerning an induction motor with a power of 5.5 kW. After the stator and rotor packages were created, processes such as winding, varnishing, and mechanical assembly were performed on the motors. It is prepared for motor efficiency (MEfficiency) and total magnetic losses (TLosses) tests according to the direct measurement method specified in the IEC 60034-2-1-1A standard. Four different frequencies (f: 50, 75, 100 and 125 Hz) and five different motor loading rates (MLoad: 25, 50, 75, 100 and 125%) were defined as independent variables in the tests. MEfficiency and TLosses values were measured as dependent variables. Plastic deformation and edge rounding were observed on the edges cut with punching and edge rounding and angled edge formation on the edges cut with the laser. The average surface roughness of the laser-cut edges was determined to be higher than the ESLs cut by punching. It was observed that TLosses increased while MEfficiency decreased with increasing frequency and MLoad value in motor tests. It was determined that the training, testing, and experimental data are quite compatible with each other and the R2 values are close to 1 in the statistical analyzes performed with ANN (Artificial neural network). In addition, it was specified that RMSE (Root mean square error) and MAPE (Mean absolute percentage error) values vary between 0.007 and 13.310% for each cutting method and mathematical models can be used to predict MEfficiency and TLosses with ANN.

Blue laser welding of laminated electrical steels: Dynamic process, weld bead characteristics, mechanical and magnetic properties

Laminated electrical steels are the key material structure of the stator and rotator of a motor, where high-quality welding is crucial for improving the performance of the electric machine. However, it is challenging to achieve a desired balance among the magnetic properties, mechanical properties, and welding efficiency for the laminated electrical steels at present. This work first adopted a 450 nm flat-top blue laser with a maximum power of 2000 W, which has a higher primary absorption rate to Fe compared to that of the conventionally used 980-1080 nm infrared laser, to join the laminated electrical steels. The dynamic process, weld bead characteristics, mechanical properties, and magnetic properties of the blue laser welding of laminated electric steels were investigated. The results show that a flat-top and large-spot blue laser can make the molten pool have a self-stabilizing ability to keep the continuity when encountering the gap and unsmooth surface. Moreover, a further improved self-stabilizing ability is observed for a small welding speed. The largest depth and width of the blue laser weld bead in this work are 2.30 and 0.57 mm, respectively, with a shear strength of up to 1700 N, which are achieved at the laser power of 1500 W and welding speed of 10 mm/s. In addition, the work also validated that the blue laser could significantly reduce the splashing in welding of electrical steel laminations and improve the welding efficiency, which provides a promising solution for high-performance electrical machine manufacturing.

Stress-Dependent Magnetic Equivalent Circuit for Modeling Welding Effects in Electrical Steel Laminations

Welding has a severe impact on the efficiency of electrical machines. The heat added during the welding process affects the microstructure of the material and causes residual stress. This results in local degradation of the magnetic permeability and facilitates additional iron losses in the machine core. With the purpose of modeling and simulating welding effects in electric machines, this paper proposes a stress-dependent magnetic equivalent circuit (MEC) model for welded non-grain-oriented electrical steel laminations. A modified iron loss model is proposed to accommodate these welding effects. Furthermore, the proposed MEC model is applied to a M270-35A stator core as a case study. It was demonstrated that the core losses increase by 25% when four welding joints are applied. With a limited number of magnetic measurements on a welded and unwelded core, the model can be fully parametrized. Finally, the model was successfully validated on a core with eight welding seams at 100 Hz. The proposed model can be integrated into the design of electric machines to consider the welding effects.

Researches on the geometrical and dimensional accuracy for complex thin parts made of electrical steel by abrasive waterjet machining

The electrical steel laminations which compose the rotor and stator core for electrical motors have complex 2D shapes. When these parts require small batches of production, they can be efficiently manufactured only by flexible methods. The paper presents the results of using abrasive waterjet machining (AWJ) to obtain such parts within the frame of a research project with EU funding. The main objective of the research was the analysis of geometrical and dimensional accuracy of the parts which will confirm that AWJ is a suitable process in this case. The parts were measured on an optical digital profilometer. The measurement process was not simple because the parts are relatively large and cannot be focused only by one shot by the camera. Also, another important issue were the profile edges inconsistencies due to the burrs. Those problems and the limitations of the measurement technology did not allow the automation of measurement. The results and discussions proved that AWJ can be used successfully for manufacturing such parts and the machining process is traceable.

Experimental study of grain oriented electrical steel laminations under 3D magnetic flux excitation

The magnetic behavior of a lamination stack made of grain-oriented electrical steel (GOES) is investigated under non-conventional 3D magnetic flux excitations. An experimental demonstrator has been designed to study a normal orientation of the magnetic flux path, with regard to the lamination plane, combined with different in-plane orientations of the easy magnetization axis of the lamination stack. The results in terms of the magnetic flux distribution and the iron losses are presented and discussed.

Analysis of magnetic properties degradation following industrial impregnation process of electrical steel laminations

This paper deals with the analysis of the magnetic properties degradation following an industrial impregnation process of electrical steels employed in stators of large generators. First, the impregnation process is studied directly on industrial stators to emphasize the significance of the process effect. Then, to have a controlled approach of the impregnation conditions, laminated ring cores were subjected to the same process but for different configurations. The ring cores were magnetically characterized to highlight the influence of the resin on the magnetic properties. Also, in order to distinguish the effect of the resin from potential other phenomena during the curing phase (i.e. the ageing effect), an experimental protocol is proposed: the results allow to emphasize the impact of such process on the magnetic properties.

A Material Law Based on Neural Networks and Homogenization for the Accurate Finite Element Simulation of Laminated Ferromagnetic Cores in the Periodic Regime

Electromagnetic fields and eddy currents in thin electrical steel laminations are governed by the laws of magnetodynamics with hysteresis. If the lamination is large with respect to its thickness, field and current distributions are accurately resolved by solving a 1-D finite element magnetodynamic problem with hysteresis across half the lamination thickness. This 1-D model is able to deliver mesoscopic information to be used, after appropriate homogenization, in the macroscopic modeling of an electrical machine or transformer. As each evaluation of such a homogenized model implies a finite element simulation at the mesoscale, a monolithic coupling might be very time-consuming. This article proposes an alternative approach, assuming a periodic excitation of the system, where the parameters of a parametric homogenized material law are determined in each finite element with a neural network. The local material law can then be used as a conventional constitutive relationship in a 2-D or 3-D modeling, with a massive speed-up with respect to the monolithic coupling.

Quantitative characterisation and modelling of the effect of cut edge damage on the magnetic properties in NGO electrical steel

The cut edges of electrical steel NGO laminations in electric motors experience mechanically induced plastic deformation and residual elastic stress, which deteriorate the magnetic performance of the material. This deterioration is accounted for empirically in electric machine modelling tools by introducing a ‘build factor’ on the iron losses. Currently, a wide range of cut edge deteriorated widths have been reported in the literature, depending on the method used for characterisation, the material and the cutting method. In this paper, cut edge plastic damage characterisation was carried out using EBSD kernel average misorientation (KAM) maps and nano-indentation to quantify the magnitude and width of the plastic damage at the cut edge for a stamped tooth of a segmented stator and a guillotined single sheet tester (SST) sample. The relationship between the EBSD KAM and nano-hardness values and plastic strain was found using tensile samples tested to varying applied strain levels. Therefore, the plastic strain gradient with respect to distance from the cut edge was determined. It was found that both EBSD and nano-indentation gave similar predictions of effective plastic strain values and damage width: up to 1.45–1.50 at stamped cut edge over 180 µm width and up to 1.35–1.4 at guillotine cut edge over 250 µm width. The relationships between the magnetic performance and elastic stress, plastic strain, and plastic strain with elastic stress were determined using single sheet tester (SST) measurements. In addition, SST 3D FEA models of the cut edge sample were built using COMSOL Multi-Physics software considering a single layer for plastic damage only and two layers for plastic damage + elastic stress and elastic stress. The modelling results for the guillotine cut edge SST samples were compared to measured data. It was found that to obtain accurate cut edge magnetic property deterioration for NGO electrical steel laminations both the plastic strain and residual elastic stress cut edge effects need to be included. In the cut edge model, a first layer width of 250 µm with magnetic properties for an effective plastic strain of 1.17 under residual compressive elastic stress of −133 MPa and a second layer width of 220 µm with magnetic properties for residual compressive elastic stress of −119 MPa give excellent results for hysteretic BH curves and specific iron loss evaluation.

An Update to a New Method of Stator Core Repair: Saving Time and Reducing Costs

This article provides an update to a paper presented in 2006, sharing the results of a decade of core repair. The process described is for a microconversion coreplate of electrical steel laminations used in ac stators, ac rotors, and dc armatures. The treatment process restores the coreplate and avoids the laborious restack process, saving time and reducing the cost to the end user.