The manufacturing of laminated iron cores is one of the crucial stages in motor production. This stage involves the largest workload, has the strictest technical requirements, and places the highest demands on tooling—making it a key factor influencing economic efficiency. Therefore, it is essential to pay close attention to studying the manufacturing processes for laminated iron cores as well as related issues concerning die structures.

I. Types of Film Processing

To facilitate the study of the structure and manufacturing process of motor iron cores, punched laminations are classified according to their shapes into circular laminations, sector-shaped laminations, and pole-lamination laminations.

1. Circular punching die

Figure 1–4 show the stator and rotor laminations for AC motors and the armature laminations for DC machines. The maximum width of electrical steel sheets is 1200 mm; taking into account machining allowances during punching, the diameter of the fully circular punched laminations shall be Φ ≤ 1180 mm.

Figure 1 Stator laminations for small asynchronous motors

 

Figure Figure 1 shows the stator laminations for a small asynchronous motor. The outer circumference of these laminations is stamped with dovetail slots, which allow snap-in clips to be installed during the press-fitting of the iron core, thereby securely fastening the laminations together as a single unit.

 

 

Figure Figure 2 shows the rotor laminations for a small induction motor. The shaft hole in the rotor lamination features a keyway (whose corner serves as a marking reference) and a balance groove. The balance groove is provided to reduce rotor imbalance.

 

 

The figure above shows the stator laminations for a medium-sized AC motor, featuring an embedded press-fit structure. These are solid circular laminations that are directly stacked inside the motor frame.

 

The figure above shows the armature laminations for a DC motor, which feature axial ventilation holes (this type of lamination structure is also used in AC motors). Unlike conventional armature laminations that have grooves for slot wedges, these laminations consist of two different diameters of laminations within the iron core. The smaller-diameter laminations are positioned at specific locations; after the windings are inserted, non-magnetic steel wires or non-woven fiberglass tapes are tightly wound around the small-diameter core sections to secure the shims or windings.

 

2. Sector-shaped piece

The core diameter of steam turbine generators, hydroelectric generators, and other medium- and large-sized motors exceeds... At 1180 mm, sector-shaped laminations must be used. Considering material utilization and the current equipment conditions, some small motor stator cores also adopt a sector-lamination structure.

1) Stator扇形冲片

Although these stamped laminations have a similar fan-shaped appearance, they come in various visual forms due to differences in their stacking methods. Two common types of stator fan-shaped laminations are shown in the figure. As shown in Figure 5.

2) Rotating sector-shaped punch blade

 

The rotor core diameter is greater than At 1180 mm, a fan-shaped laminated core is used for assembly. Figure 6 shows even-numbered-slot rotor fan-shaped laminations (where α represents the angle between adjacent slots and z denotes the number of slots per fan-shaped lamination). Figure 7 depicts odd-numbered-slot rotor fan-shaped laminations. Figure 8 illustrates three commonly used structural types of rotating armature fan-shaped laminations.

3. Magnetic-grade laminations

Magnetic pole laminations generally use thicker ones ( (1–2 mm) Made from A3 or 16Mn steel plates by stamping. Figure 9a shows a stator pole lamination for a DC motor; Figures 9b and 9c show rotor pole laminations; and Figures 9d and 9e show pole laminations for eddy-current brakes.

 

II. Technical Requirements for Film Processing

1. Dimensional accuracy

The film sheets come in various sizes and can be categorized as: There are two types: “internal dimensions” and “fitting dimensions.” Internal dimensions—such as the dimensions of slots, ventilation holes, marking grooves, and hole diameters on magnetic pole laminations—generally use the H10 tolerance grade. Higher precision grades are unnecessary, because the errors caused by the inner parts protruding outward and the outer parts retracting inward after lamination far exceed the inherent tolerances of the laminations themselves. As for “fitting dimensions”—which refer to the dimensions of the inner circle, outer circle, shaft holes, and other features that mate with other components—the selection of the appropriate precision grade depends on the machining process employed.

 

The dimensional accuracy of the inner and outer diameters of stator laminations for small- and medium-sized induction motors is related to their assembly and pressing method. Typically, when stator laminations are pressed from the outside, the inner diameter is usually achieved by: H8—The outer diameter accuracy is also related to the process plan that ensures the stator's coaxiality.

1) In the “external circular light” scheme, a machining allowance of 0.5 mm is left on the outer diameter of the punched part, with a tolerance grade of H8 or H9.

2) The tolerances for the outer diameters of the stamped laminations in the “Two No-Lights” and “Light-Stop-Port” schemes are determined based on the precision of both the stamped laminations and the iron core. Since the outer diameter dimension tends to increase after the iron core is pressed into place, the upper tolerance limit for the lamination outer diameter is 0.035 to 0.045 mm smaller than the corresponding upper tolerance limit for the iron core outer diameter (a value of 0.035 mm is chosen for smaller diameters). The lower tolerance limit is generally set according to the H7 tolerance grade. Table 1 lists the tolerances for the outer diameters of the stator laminations and iron cores for the JO2 series externally press-fitted small asynchronous motors.

The outer diameter of the stator laminations for internal mounting typically uses... H7, with an inner diameter of H8. Table 2 lists the tolerance for the inner diameter of the stator core installed internally.

2. Film edge burrs

1) The thickness of the stator laminations is generally controlled within 0.05 mm. For certain parts of multi-layer laminations (with lengths around 30 mm), the thickness is controlled within 0.12 mm; however, these parts must undergo deburring treatment and, after processing, their thickness should be reduced to within 0.08 mm.

2) The burr on the rotor laminations shall be controlled within 0.07 mm; in individual slot areas, the burr shall not exceed 0.10 mm.

3) For stamped parts that have been painted, the burrs shall not exceed 0.05 mm.

 

3. Film Curling

After punching, the punched laminations will exhibit varying degrees of warping. Laminations punched in single slots tend to warp more significantly—especially rotor laminations with closed slots. After single-slot punching, the warping is particularly severe, and the outer diameter of the laminations... For items 230mm or less, the deviation is not allowed to exceed 2mm; for items over 230mm, the deviation is not allowed to exceed 3mm.

1) When the coaxiality between the inner circle or shaft hole and the outer circle is achieved in a single stamping operation, it is generally controlled within 0.04 to 0.06 mm. However, when the inner and outer circles are stamped in two separate operations, the required coaxiality can be appropriately relaxed.

2) The unevenness of the tooth distribution in the punching slot (also known as "large-tooth" or "small-tooth" variation)—that is, the difference between the maximum and minimum tooth widths—shall comply with the specifications outlined in the drawings and relevant process documents. If no specific requirements are provided, reference may be made to Inspection Grade 3 or Grade 4 as shown in Table 3.

 

Some factories stipulate that the difference between the number of teeth on the driving and driven gears should not exceed. 0.12 mm; the difference between fixed-size teeth does not exceed 0.2 mm.

3) The centerline of the groove should pass through the center of the circle and should not exhibit any obvious deviation. During inspection, align the shaft holes (or outer diameters) of the two halves—front and back—and ensure that, with one end of the groove root aligned, the distance between the teeth on the two halves does not exceed 0.8 mm.

4) The insulating layer on the film surface should be thin and uniform, with sufficient dielectric properties, oil resistance, moisture resistance, and adhesion.

New Horizons for Motors Posted on January 4, 2024, 17:49 in Shanghai