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    Topic review

    Joining Laminated Electrical Steels

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    Submitted by: Hongze Wang


    In recent years, the motor has been increasingly used to replace the conventional gasoline engine for carbon emission reduction, and the high-performance motor is urgently required. The stator and rotor in a motor are made of hundreds of joined and laminated electrical steels. This paper covers the current research in joining the laminated electrical steels for the motor application, together with the critical assessment of our understanding. It includes the representative joining method, modeling of the joining process, microstructure of the weld zone, mechanical strength and magnetic properties. The gaps in the scientific understanding, and the research needs for the expansion of joining laminated electrical steels, are provided.

    1. Introduction

    As a machine to transform the electrical energy into mechanical energy, a motor has been widely used as the traction machine in industry equipment [1][2][3][4][5][6][7], e.g., electrical vehicle, electrical airplane, electric ship, and so on. Electrical steel [8][9][10][11], a high silicon (2–5.5 wt% Si) [12][13] and thin sheet (0.2–0.65 mm) steel [14], is the soft magnetic material for the stator and rotor in a motor [15][16][17]. The addition of silicon to iron results in a decrease in coercivity and an increase in resistivity [12][18][19][20][21][22]. Furthermore, the reduction of the sheet thickness results in the reduction of the eddy current loss in the electrical steel when put in the alternating magnetic field environment [14][23][24]. The stator and rotor in a motor are made of hundreds of laminated and joined thin electrical steel sheets [25], which could reduce the eddy current loss and improve efficiency. There are insulation coatings on both sides of the electrical steel sheet to cut off the interlaminar eddy current when hundreds of electrical steels are laminated in the motor application [26][27][28][29][30][31][32][33][34][35][36]. Generally, the goal of joining the laminated electrical steels is to ensure the mechanical strength of the laminations [37], while the joining process will lead to the degradation of the magnetic properties due to the damage of the insulation coating [38], the modification of the microstructure [39][40], the introduction of the residual stress [41], and so on. It is a great challenge to reach the trade-off between mechanical strength and magnetic properties [42]. Besides, the structure of the laminated electrical steels is different from the conventional lapped or butted sample, and the conventional knowledge about joining may not work for joining the laminations. Finally, it is important to study the joining of the laminated electrical steels, which could speed up the roadmap towards high-quality motor manufacturing.

    2. The Representative Joining Method

    Currently, the joining method for the laminated electrical steels could be generally categorized into three types: glue join [26][43], mechanical join [44] and fusion welding [45], as shown in Figure 1 [40]. The advantage of the glue-join method was that it did not destroy the insulation coating. Kaido et al. [26] measured the magnetic and mechanical characteristics of adhesive coating non-oriented electrical steel sheet cores in the conditions of motor and found that the deteriorations of iron losses and exciting currents by adhesion were less than those by welding. Schoppa et al. [46] coated the electrical steel laminations with the adhesive varnish, then the laminations were stuck together during a thermally activated process. Their experimental results showed that the increase of the specific core loss after sticking was very low, and they concluded that sticking was from the magnetic point of view one of the best methods of assembling laminations into magnetic cores. The glue-join method also allowed homogenous electrical isolation, reduced acoustic emission, and behaved high thermal conductivity in service [26][43]. Generally, the composition of the glue varies with the supplier, including the organic glue, inorganic glue and their combinations. However, the biggest obstacle for the large-scale application of this technique was the concern about the mechanical failure of the adhesion under the periodic load condition at an elevated temperature during the operation of the motor [47]. Besides, the cost was also higher than the other joining methods [46].

    Figure 1. Schematic of the representative join methods for laminated electrical steels: (a) Glue join; (b) mechanical join; (c) fusion welding [40].

    Both mechanical joining [44][48][49][50] and fusion welding [37][38][46][51][52] are widely used to join the laminated electrical steels at present. Senda et al. [44] compared the effects of two representative V-type mechanical interlocking methods, dowel formation and dowel jointing on the magnetic properties of the joined ring core sample made of the electrical steel laminations, they found that two methods showed comparable contributions to iron loss increase at low frequencies (e.g., 50 Hz), whereas, increases in iron loss due to dowel jointing were greater than those due to dowel formation at high frequencies. Imamori et al. [49] investigated the influence of interlocking on the magnetic properties of ring cores by measurement, and they observed that the inverse of permeability and iron loss increased linearly with the number of interlocks. The mechanical joining process is usually combined with the punching process in the progressive stamping die process. Finally, the cost of the mechanical joining process is a bit lower than that of the welding process. The disadvantage of the mechanical joining method is the lower strength at the direction perpendicular to the electrical steel surface compared to that of the fusion welded joint. Besides, the mechanically joined joint has a lower fatigue life under the periodic loads than that of the welded joint. In the case with the high strength requirement, several fusion welding passes were jointly used to enhance the strength of the mechanically joined sample.

    The heat source used in fusion welding of the electrical steel laminations includes laser [37], electron beams [53], plasma arcs [39], electric arcs (TIG, GTA, CMT) [51][54], and so on. As a high efficiency and high-quality fusion welding method, laser welding was thought to be a potential method for welding of the electrical steel laminations in the high-performance motor application [37][40][42][51][55]. Compared to the other fusion welding methods, laser welding could achieve a smaller heat affected zone, induce lower residual stress, and finally obtain the welded electrical steel laminations with higher magnetic properties. Figure 2 shows the schematic of laser welding of laminated electrical steel laminations [40]. The moving energy beam melt the edge of the laminations continuously and the effective joint was formed at the interfaces of the laminations.

    Figure 2. Schematic of the fusion welding process [40].

    Table 1 shows the representative research in the joining of laminated electrical steels. The critical factors affecting joining the laminated electrical steel laminations are as follows: (a) the special structure of the laminations made of hundreds of electrical steel sheets; (b) the insulation coating on both sides of the electrical steel sheet, which affects the dynamics of the molten pool during the fusion welding process because of the entrapped bubbles due to the pyrolysis of the coating and may induce pores in the weld seam; (c) the comprehensive requirement of the strength and magnetic property. The following sections will summarize the current research in joining of laminated electrical steels, which provides a better understanding of the joining process with great demands from the industry.

    Table 1. Representative research in the joining of laminated electrical steels.

    Joining method

    Research content



    Continuous laser welding

    Strength: both the strength and the fatigue behavior of the weld material showed no appreciable

    difference to the base material;

    Microstructure: completely ferritic in both the base material and the weld seam; Defect: pores observed in the weld seam



    Continuous laser welding

    Model for torsion strength: mathematical model with the function to estimate the strength of the welded laminations based on the welding parameters



    Continuous laser welding

    Strength of the welded ring stator: increase with the heat input; Microstructure ferrite in the weld seam; Magnetic property: deteriorate with the heat input



    Continuous laser welding

    Simulation of temperature distribution: discontinuous temperature distribution in the heat affected zone due to the hinder of the interface



    Continuous TIG welding

    Strength, microstructure, magnetic property: TIG welded joint has higher strength, coarser grain and worse magnetic property than laser welded joint



    Continuous welding

    Magnetic property: mathematical model and FEM model were developed to estimate the eddy current loss



    Mechanical joining

    Interlaminar eddy currents mainly affect the iron loss of the local zone.




    Mechanical property: critical adhesive shear angle values of about 5° were obtained for all laminate samples, independent of the steel substrates used to create the laminates



    Adaptive pulsed spot welding

    Possibility of the adaptive pulsed spot welding for laminated electrical steels was proved.



    Statistical distribution of single welding spots

    The strategy of distributed welding spot shows promising results to decrease the

    magnetic deterioration, especially as an approach for higher

    frequency applications



    The entry is from 10.3390/ma13204583


    1. Enokizono, M. Construction of Development Technology of Next Generation Applied Electromagnetic Machinery in Japan. Mater. Sci. Forum 2010, 670, 51–59, doi:10.4028/
    2. Miyabe, Y.; Kakema, M.; Saito, T. Searching for Optimal Solutions for Motor Performance Design. SAE Tech. Pap. Ser. 2020.
    3. Mehdi, M.; He, Y.; Hilinski, E.J.; Kar, N.C.; Edrisy, A. Non-Oriented Electrical Steel with Core Losses Comparable to Grain-Oriented Electrical Steel. J. Magn. Magn. Mater. 2019, 491, 165597, doi:10.1016/j.jmmm.2019.165597.
    4. Lopez-Perez, D.; Antonino-Daviu, J. Application of Infrared Thermography to Failure Detection in Industrial Induction Motors: Case Stories. IEEE Trans. Ind. Appl. 2017, 53, 1901–1908, doi:10.1109/tia.2017.2655008.
    5. Liu, C.; Lei, G.; Wang, T.; Guo, Y.; Wang, Y.; Zhu, J. Comparative Study of Small Electrical Machines with Soft Magnetic Composite Cores. IEEE Trans. Ind. Electron. 2016, 64, 1049–1060, doi:10.1109/tie.2016.2583409.
    6. Krings, A.; Cossale, M.; Tenconi, A.; Soulard, J.; Cavagnino, A.; Boglietti, A. Magnetic Materials Used in Electrical Machines: A Comparison and Selection Guide for Early Machine Design. IEEE Ind. Appl. Mag. 2017, 23, 21–28, doi:10.1109/mias.2016.2600721.
    7. Krings, A.; Boglietti, A.; Cavagnino, A.; Sprague, S. Soft Magnetic Material Status and Trends in Electric Machines. IEEE Trans. Ind. Electron. 2016, 64, 2405–2414, doi:10.1109/tie.2016.2613844.
    8. Pluta, W.A. Prediction of Influence of Magnetic Anisotropy on Specific Total Loss in Electrical Steel with Goss Texture. In Proceedings of the 2018 Progress in Applied Electrical Engineering Conference, Koscielisko, Poland, 18–22 June 2018.
    9. Tanaka, I.; Nitomi, H.; Imanishi, K.; Okamura, K.; Yashiki, H. Application of High-Strength Nonoriented Electrical Steel to Interior Permanent Magnet Synchronous Motor. IEEE Trans. Magn. 2013, 49, 2997–3001, doi:10.1109/tmag.2012.2236101.
    10. Tietz, M.; Biele, P.; Janßen, A.; Herget, F.; Telger, K.; Hameyer, K. Application-Specific Development of Non-Oriented Electrical Steel for EV Traction Drives. In Proceedings of the 2012 2nd International Electric Drives Production Conference, Nuremberg, Germany, 15 October 2012.
    11. Oda, Y.; Kohno, M.; Honda, A. Recent Development of Non-Oriented Electrical Steel Sheet for Automobile Electrical Devices. J. Magn. Magn. Mater. 2008, 320, 2430–2435, doi:10.1016/j.jmmm.2008.03.054.
    12. Takajo, S.; Hiratani, T.; Okubo, T.; Oda, Y. Effect of Silicon Content on Iron Loss and Magnetic Domain Structure of Grain-Oriented Electrical Steel Sheet. IEEE Trans. Magn. 2018, 54, 1–6, doi:10.1109/tmag.2017.2759103.
    13. Sidor, Y.; Kovac, F.; Kvačkaj, T.; Sidor, J. Grain Growth Phenomena and Heat Transport in Non-Oriented Electrical Steels. Acta Mater. 2007, 55, 1711–1722, doi:10.1016/j.actamat.2006.10.032.
    14. Hanitsch, R.E. Rotary and Linear Machines. In Encyclopedia of Materials: Science and Technology; Elsevier: Amsterdam, The Netherlands, 2001; 8221-8227.
    15. Beckley, P. Electrical Steels for Rotating Machines; Institution of Engineering and Technology: London, UK, 2002.
    16. Mehdi, M.; He, Y.; Hilinski, E.J. The Evolution of Cube ({001}) Texture in Non-Oriented Electrical Steel. Acta Mater. 2020, 185, 540–554.
    17. Birosca, S.; Nadoum, A.; Hawezy, D.; Robinson, F.; Kockelmann, W. Mechanistic Approach of Goss Abnormal Grain Growth in Electrical Steel: Theory and Argument. Acta Mater. 2020, 185, 370–381, doi:10.1016/j.actamat.2019.12.023.
    18. Ahn Y.K., Jeong Y.K., Kim T.Y., Cho J.U., Hwang N.M. Texture evolution of non-oriented electrical steel analyzed by EBSD and in-situ XRD during the phase transformation from γ to α. Mater. Today Com. 2020, 25, 101307.
    19. Qin, J.; Liu, D.F.; Zhang, Y.H. Application Status and Development Prospect of Rare Earth in Electrical Steels. J. Iron Steel Res. 2018, 30, 163–170.
    20. Wu, J.; Zhang, L.; Gong, T.; Zhu, J.; Hao, Q.; Qin, Z.; Cong, S.; Zhan, D.; Xiang, Z. Texture Evolution of the Surface Layer of High Silicon Gradient Electrical Steel and Influence on the Magnetic Properties. Vacuum 2015, 119, 189–195, doi:10.1016/j.vacuum.2015.05.016.
    21. Belyaevskikh, A.S.; Lobanov, M.L.; Rusakov, G.M.; Redikul’Tsev, A.A. Improving the Production of Superthin Anisotropic Electrical Steel. Steel Transl. 2015, 45, 982–986, doi:10.3103/s0967091215120037.
    22. Mouriopoulos, C. Production of Silicon Steel Sheet at Dofasco. Steel Times Int. 1989, 13, 36–37.
    23. Petryshynets, I.; Kováč, F.; Füzer, J.; Falat, L.; Puchý, V.; Kollár, P. Evolution of Power Losses in Bending Rolled Fully Finished No Electrical Steel Treated under Unconventional Annealing Conditions. Materials 2019, 12, 2200, doi:10.3390/ma12132200.
    24. Uesaka, M.; Senda, K.; Oomura, T.; Okabe, S. Influence of Thickness of Non-oriented Electrical Steel on Iron loss under Inverter Excitation. IEEJ Trans. Fundam. Mater. 2018, 138, 367–372, doi:10.1541/ieejfms.138.367.
    25. Tsuchida, Y.; Yoshino, N.; Enokizono, M. Reduction of Iron Loss on Laminated Electrical Steel Sheet Cores by means of Secondary Current Heating Method. IEEE Trans. Magn. 2017, 53, 1, doi:10.1109/TMAG.2017.2705168.
    26. Pugstaller, R.; Wallner, G.M.; Strauß, B.; Fluch, R. Advanced Characterization of Laminated Electrical Steel Structures Under Shear Loading. J. Adhes. 2018, 95, 834–848, doi:10.1080/00218464.2018.1450747.
    27. Peng, K.Y. Advanced Chromium-Free Coating for Electrical Steels. Iron Steel Technol. 2015, 12, 65–70.
    28. Chivavibul, P.; Enoki, M.; Konda, S.; Inada, Y.; Tomizawa, T.; Toda, A. Reduction of Core Loss in Non-Oriented (No) Electrical Steel by Electroless-Plated Magnetic Coating. J. Magn. Magn. Mater. 2011, 323, 306–310, doi:10.1016/j.jmmm.2010.09.024.
    29. Lin, A.; Zhang, X.; Fang, D.; Yang, M.; Gan, F. Study of an Environment‐Friendly Insulating Coating with High Corrosion Resistance on Electrical Steel. Anti-Corros. Methods Mater. 2010, 57, 297–304, doi:10.1108/00035591011087154.
    30. Ke, S.; Qian, X.; Zhu, S. Application of X-Ray Fluorescence Method in the Analysis of Electrical Steel Coating. In Proceedings of the 10th International Conference on Steel Rolling, Beijing, China, 15 September 2010.
    31. Chivavibul, P.; Enoki, M.; Konda, S.; Inada, Y.; Tomizawa, T.; Toda, A. Application of Electroless-Plated Magnetic Coating to Reduce Core Loss of Electrical Steel. Adv. Mater. Res. 2010, 117, 21–25, doi:10.4028/
    32. Puzhevich, R.B.; Korzunin, G. Quality Control of the Insulating Coating on Electrical Steel. Russ. J. Nondestruct. Test. 2006, 42, 468–473, doi:10.1134/s1061830906070060.
    33. Loisos, G.; Moses, A.; Beckley, P. Electrical Stress on Electrical Steel Coatings. J. Magn. Magn. Mater. 2003, 254, 340–342, doi:10.1016/s0304-8853(02)00839-9.
    34. Coombs, A.; Lindenmo, M.; Snell, D.; Power, D. Review of the Types, Properties, Advantages, and Latest Developments in Insulating Coatings on Nonoriented Electrical Steels. IEEE Trans. Magn. 2001, 37, 544–557, doi:10.1109/20.914376.
    35. Snell, D.; Coombs, A. Novel Coating Technology for Non-Oriented Electrical Steels. J. Magn. Magn. Mater. 2000, 215, 133–135, doi:10.1016/s0304-8853(00)00095-0.
    36. Lindenmo, M.; Coombs, A.; Snell, D. Advantages, Properties and Types of Coatings on Non-Oriented Electrical Steels. J. Magn. Magn. Mater. 2000, 215, 79–82, doi:10.1016/s0304-8853(00)00071-8.
    37. Schade, T.; Ramsayer, R.M.; Bergmann, J.P. Laser Welding of Electrical Steel Stacks Investigation of the Weldability. In Proceedings of the 4th International Electric Drives Production Conference, Nuremberg, Germany, 30 September 2014.
    38. Sundaria, R.; Daem, A.; Osemwinyen, O. Effects of Stator Core Welding on an Induction Machine—Measurements and Modeling. J. Magn. Magn. Mater. 2020, 499, 166280.
    39. Vourna, P.; Ktena, A. Metallurgical, Mechanical and Magnetic Properties of Electrical Steel Sheets in TIG and PLASMA Welding. Key Eng. Mater. 2013, 543, 479–482, doi:10.4028/
    40. Wang, H.; Zhang, Y.; Li, S. Laser Welding of Laminated Electrical Steels. J. Mater. Process. Technol. 2016, 230, 99–108, doi:10.1016/j.jmatprotec.2015.11.018.
    41. Leuning, N.; Steentjes, S.; Weiss, H.A.; Volk, W.; Hameyer, K. Magnetic Material Deterioration of Non-Oriented Electrical Steels as a Result of Plastic Deformation Considering Residual Stress Distribution. IEEE Trans. Magn. 2018, 54, 1–5, doi:10.1109/tmag.2018.2848365.
    42. Leuning, N.; Steentjes, S.; Hameyer, K.; Gerhards, B.; Reisgen, U. Analysis of a Novel Laser Welding Strategy for Electrical Steel Laminations. In Proceedings of the 7th International Electric Drives Production Conference, Wurzburg, Germany, 5 December 2017.
    43. Kaido, C.; Takeda, K.; Wakisaka, T.; Mizokami, M. Characteristics of Adhesive Coating Non-oriented Electrical Steel Sheet Cores. IEEJ Trans. Ind. Appl. 1999, 119, 1010–1015, doi:10.1541/ieejias.119.1010.
    44. Senda, K.; Toda, H.; Kawano, M. Influence of Interlocking on Core Magnetic Properties. IEEJ J. Ind. Appl. 2015, 4, 496–502, doi:10.1541/ieejjia.4.496.
    45. Dharmik, B.Y.; Lautre, N.K. A Study on Hardness of CRNO Electrical Sheets for Edge Joining Through TIG Welding. In Operations Management and Systems Engineering; Springer Science and Business Media LLC: Singapore, 2019; pp. 689–698.
    46. Schoppa, A.; Schneider, J.; Wuppermann, C.-D.; Bakon, T. Influence of Welding and Sticking of Laminations on the Magnetic Properties of Non-Oriented Electrical Steels. J. Magn. Magn. Mater. 2003, 255, 367–369, doi:10.1016/s0304-8853(02)00877-6.
    47. Wang, H.; Zhang, Y.; Lai, X. Effects of Interfaces on Heat Transfer in Laser Welding of Electrical Steel Laminations. Int. J. Heat Mass Transf. 2015, 90, 665–677, doi:10.1016/j.ijheatmasstransfer.2015.07.027.
    48. Imamori, S.; Aihara, S.; Shimoji, H.; Kutsukake, A.; Hameyer, K. Evaluation of Local Magnetic Degradation by Interlocking Electrical Steel Sheets for an Effective Modelling of Electrical Machines. J. Magn. Magn. Mater. 2020, 500, 166372, doi:10.1016/j.jmmm.2019.166372.
    49. Imamori, S.; Steentjes, S.; Hameyer, K. Influence of Interlocking on Magnetic Properties of Electrical Steel Laminations. IEEE Trans. Magn. 2017, 53, 1–4, doi:10.1109/TMAG.2017.2713446.
    50. Kaido, C.; Mogi, H.; Hanzawa, K. The Effect of Short Circuit between Laminated Steel Sheets on the Performance of Lamination Core of Motor. IEEJ Trans. Fundam. Mater. 2003, 123, 857–862, doi:10.1541/ieejfms.123.857.
    51. Zhang, Y.; Wang, H.; Chen, K.; Li, S. Comparison of Laser and TIG Welding of Laminated Electrical Steels. J. Mater. Process. Technol. 2017, 247, 55–63, doi:10.1016/j.jmatprotec.2017.04.010.
    52. Cui, R.; Li, S. Pulsed Laser Welding of Laminated Electrical Steels. J. Mater. Process. Technol. 2020, 285, 116778, doi:10.1016/j.jmatprotec.2020.116778.
    53. Vourna, P. Characterization of Electron Beam Welded Non-Oriented Electrical Steel with Magnetic Barkhausen Noise. Key Eng. Mater. 2014, 605, 39–42, doi:10.4028/
    54. Dharmik, B.Y.; Lautre, N.K. Performance Assessment of CMT over GTA Welding on Stacked Thin Sheets of CRNGO Electrical Steel. Mater. Lett. 2020, 272, 127901, doi:10.1016/j.matlet.2020.127901.
    55. Vegelj, D.; Zajec, B.; Kanitz, A.; Možina, J. Adaptive Pulsed-Laser Welding of Electrical Laminations. Stroj. Vestn. J. Mech. Eng. 2014, 60, doi:10.5545/sv-jme.2013.1407.
    56. Wang, H.; Zhang, Y.; Lai, X. A Model for the Torsion Strength of a Laser-Welded Stator. J. Mater. Process. Technol. 2015, 223, 319–327, doi:10.1016/j.jmatprotec.2015.04.012.
    57. Wang, H.; Zhang, Y. Modeling of Eddy-Current Losses of Welded Laminated Electrical Steels. IEEE Trans. Ind. Electron. 2017, 64, 2992–3000, doi:10.1109/tie.2016.2636203.
    58. Shimoji, H.; Todaka, T.; Aihara, S. A Thermographic Camera Method for Measuring the Core Loss Distribution. J. Magn. Magn. Mater. 2020, 505, 166679, doi:10.1016/j.jmmm.2020.166679.
    59. Neuwirth, T.; Backs, A.; Gustschin, A.; Vogt, S.; Pfeiffer, F.; Böni, P.; Schulz, M. A High Visibility Talbot-Lau Neutron Grating Interferometer to Investigate Stress-Induced Magnetic Degradation in Electrical Steel. Sci. Rep. 2020, 10, 1764–12, doi:10.1038/s41598-020-58504-7.
    60. Kopecký, V.; Fekete, L.; Perevertov, O.; Heczko, O. Changes in Magnetic Domain Structure During Twin Boundary Motion in Single Crystal Ni-Mn-Ga Exhibiting Magnetic Shape Memory Effect. AIP Adv. 2016, 6, 056208, doi:10.1063/1.4943363.
    61. D’Silva, G.J.; Feigenbaum, H.P.; Ciocanel, C. Visualization of Magnetic Domains and Magnetization Vectors in Magnetic Shape Memory Alloys Under Magneto-Mechanical Loading. Shape Mem. Superelasticity 2020, 6, 67–88, doi:10.1007/s40830-020-00262-6.