Influence of Interlocking on Magnetic Properties of Electrical Steel Laminations

Abstract

1. Introduction Electrical steel sheets are widely used for magnetic cores in electrical machines such as motors and transformers. To produce motor cores, for example, electrical steel sheets are punched, stacked, vertically fixed by interlocking or welding and finally combined with a frame by shrink fitting. In the vertical fixing process, interlocking is an especially suitable method for mass production. On the other hand, it is well known that electrical steel sheets are magnetically deteriorated by such manufacturing processes. After the processes, permeability decreases and iron loss increases, which lead e.g. to a lower performance of motors. To take these influences into account, finite element method (FEM) analyses considering magnetic deterioration are performed. For such FEM analyses, magnetic data for electrical steel sheets considering such manufacturing processes are required. It has been reported that compressive stress [1][2][3], which often appears in motor cores with shrink fitting, and punching [4][5][6][7] deteriorate electrical steel sheets significantly. However, there are few reports on magnetic deterioration by interlocking electrical steel sheets and it is required to systematically study the influence of interlocking. In this contribution, measurement results for ring cores with interlocking are presented and the cause of the magnetic deterioration is discussed. 2. Experimental procedure Interlocking was applied to ring cores made of electrical steel sheets. This is because it is difficult to apply interlocking to samples for Epstein frames or single sheet testers. The structure of the studied ring cores is shown in Fig. 1 (a). The material used is non-oriented electrical steel containing about 3 wt% of silicon and some other elements to improve soft magnetic properties. The thickness of the sheets t 1 is 0.5 mm. The outer and inner diameters of the ring cores, d o and d i respectively, are 60 mm and 48 mm. The overall height of the stack T is 5 mm. There are 0, 2, 4, or 8 interlocks equally distributed along the circumference of the ring cores. The length and the width of each interlock, a and b respectively, are 4 mm and 1 mm. Fig. 1 (b) shows the schematic drawing of the cross section of an interlock. BH curves and iron losses at the frequency of 50 Hz were measured. 3. Magnetic model We assume here that an interlocked ring core is represented by a magnetic series circuit with undamaged and damaged regions. If there is no leakage of flux from the ring core, the following equations are valid. l/μ a =Nd/μ + +(l-Nd)/μ -(1) W a =NdW + /l+(l-Nd)W -/l (2) Here, μ a and W a show the measured permeability and iron loss. μ + and μ -show the permeability of damaged and undamaged regions. W + and W -show the iron losses of damaged and undamaged regions. N is the number of interlocks in a ring core. l is the average length of the entire magnetic circuit approximated by π(d o + d i )/2. d is the length of a damaged region. These equations show that the inverse of permeability and iron loss should ...

Localized magnetic properties measurement of interlocking core laminations

“…The effect of the interlocks’ number, sizes and shapes on the overall magnetic properties of lamination ring cores has been investigated by many researchers (Liu and Liu, 2018; Senda et al , 2015). The main conclusions are as follows: The inverse of permeability and iron loss increases linearly with the number of interlocks. Interlocks along the radial direction have a more significant impact on magnetic properties than those along the circumferential direction (Imamori et al , 2017). The shape of the interlock also affects the fastened strength between the laminations.…”

“…Interlocks along the radial direction have a more significant impact on magnetic properties than those along the circumferential direction (Imamori et al , 2017).…”

Joining of the Laminated Electrical Steels in Motor Manufacturing: A Review

“…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.…”

“…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.…”

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

“…In [86], the effect of interlocking on magnetic properties of ESLs was investigated using ring specimens. It found that with an increasing number of interlocks, the inverse of permeability and iron loss both increase linearly.…”