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The punching method of iron core laminations

There are several punching methods for stator and rotor punching, and the punching dies required by them are different.

 

1. Single punching

Punching out a continuous contour line (with at most one break) each time. For example, shaft holes and keyways, a stator slot or a rotor slot. The advantages of single punching are that the single punching die has a simple structure, is easy to manufacture, and has good versatility; the production preparation work is simple; and the tonnage of the punching machine is small. Its disadvantage is that the punching process is carried out multiple times, which will inevitably bring about errors in the concentricity of the inner and outer circles of the stator punching, as well as the indexing errors of the stator slot and the rotor slot. Single punching is mainly used in single-piece production or small-batch production, which can reduce the time and cost of tooling preparation. In addition, single punching is often used when there is a lack of large-tonnage punching machines.

 

2. Multiple punching

Punching out several continuous contour lines each time. The shaft hole, the keyway and balance slot on the shaft hole, and all the rotor slots can be punched out at one time. Or punch out the inner and outer circles of the stator sheet at one time. The advantages of compound punching are high labor productivity and good sheet quality. The disadvantages are that the manufacturing process of compound dies is relatively complicated, the working hours are long, the cost is high, and a large-tonnage punching machine is required. Compound punching is mainly used in mass production.

 

3. Progressive punching

Combine several single dies or compound dies and arrange them in a straight line at the same distance. The upper die is installed on the same upper die seat and the lower die is installed on the same lower die seat to form a pair of progressive dies. The advantage of progressive punching is high labor productivity, and the disadvantage is that progressive dies are difficult to manufacture. Progressive punching is mainly used for mass production of small and micro motors, because the size of the motor sheets with large capacity is large. To arrange several dies, the punching machine must have a large tonnage and a large workbench. Progressive punching can only play its advantages when using coils.

 

4. Oscillating punching process:

Through continuous feeding of steel coils and adjustment of die eccentric angle, synchronous punching and parting of stator and rotor sheets are realized. The core process is as follows:

​Steel coil blanking: Use unwinder and leveling machine to pre-treat silicon steel coils to ensure material flatness (flatness ≤0.1mm/100mm)

​Oscillating punching: ​Stator sheet: Through die eccentric angle control, the composite punching of outer circle, keyway (positioning accuracy ±0.05mm), balance groove (elimination of dynamic imbalance), dovetail groove (overlapping locking) and mark groove (assembly alignment) is completed in one stroke.

​Rotor sheet: Use eccentric angle to adjust tooth profile distribution, and synchronously punch out rotor sheets with tooth grooves, tooth profile accuracy ≤0.06mm, tooth top burr ≤0.04mm (satisfying dynamic balance pass rate ≥98%).

​Automatic sorting: After stamping, the stator and rotor sheets are separated by a manipulator or pneumatic device to avoid the risk of deformation caused by manual intervention.

The above punching methods each have their own advantages and disadvantages and application scope. They should be appropriately combined based on the size of the factory's production batch, mold manufacturing capacity, punching equipment conditions, etc., while striving to improve labor productivity and punching quality, to give full play to their respective advantages, avoid disadvantages, and meet the needs of production development.

 

5. High-speed punching process is a technology that uses a high-speed punching machine

(punching speed usually reaches 200~1500 times/minute) with a precision progressive die to complete the punching, forming, lamination and other processes of metal sheets (such as silicon steel sheets) in a short time. Its core goal is to achieve efficient, high-precision, and large-scale production of motor core sheets.

 

​6. High-speed punching

1. Silicon steel sheets (electrical steel) are used as raw materials, which are suitable for motor cores due to their high magnetic permeability and low iron loss.

The material is usually supplied continuously in the form of coils to ensure the continuity of high-speed production.

2. Feeding and positioning​

A servo feeding system is used to accurately control the feeding speed and position of the material.

High-precision positioning is achieved through optical or mechanical sensors to ensure the accuracy of the punching position.

3. Stamping and forming​

On a high-speed punching machine, the following are completed in sequence through a multi-station progressive die:

​Punching​: Punching out core slots, shaft holes, positioning holes, etc.

​Blanking​: Forming the outer contour of the core.

​Stacking riveting​ (optional): directly stack the core sheets during the stamping process to form a stacking group (reducing the subsequent stacking process).

3. Discharging and collection​

The waste after stamping is automatically discharged through the die discharging system.

The finished core sheets are collected by conveyor belts or manipulators, and some processes can achieve automatic stacking.

4. Quality inspection​

Online inspection equipment (such as visual systems) monitors dimensional accuracy, burrs, surface defects, etc. in real time.

 

Technical features​

1. High punching speed and high efficiency​

The punching speed can reach hundreds to thousands of times per minute, which is suitable for mass production. For example, a high-speed punching machine can produce millions of cores per year.

2. High precision and consistency​

The mold precision reaches ±0.002mm, and the core sheet size error is controlled at the micron level. The multi-station design of the progressive mold ensures the synchronization and consistency of each process.

3. High material utilization​

By optimizing the layout design (such as rotating layout and nested layout), reducing corner waste, the utilization rate of silicon steel sheets can reach more than 90%.

 

Our company's main process:

"One drop, two", that is, re-punching the inner and outer circles of the stator punching sheet (including the orientation mark on the outer circle of the stator punching sheet); the second step is to position the stator punching sheet with the inner circle, the orientation mark is oriented, and all the stator slots and the dovetail slots and marking slots on the outer circle are re-punched; the third step is to position the rotor punching sheet with the shaft hole,

 

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Re-punch all rotor slots, shaft holes and the keyways and balance slots of the shaft holes. The advantages of this scheme are:

1) High labor productivity;

2) Can be cut by nesting, the utilization rate of silicon steel sheet is high;

3) The stator and rotor slots are punched out together with their respective marking slots at the same time, and the quality of the punched sheet is good;

4) The inner and outer circles of the stator punching sheet are punched out at the same time, and the coaxiality can be easily ensured by the mold;

5) It is easy to realize single machine automation, that is, the robot feeds and the robot takes the material;

6) The stator and rotor slots can be punched again on two punching machines at the same time, which shortens the processing cycle compared with the first scheme. The disadvantage is that if the inner circle positioning plate is worn during the re-punching of the stator slot, the circumference of the slot bottom will be non-concentric with the inner circle. When stacking, the inner circle expansion tire is used as the reference, which will make the slot hole uneven.

 

"One drop three" re-punching:first drop the material, then punch the slot. It is divided into three steps (Figure 3-20): the first step is "one drop three", that is, re-punching the inner circle and outer circle of the stator punching sheet (including the orientation mark on the outer circle of the stator punching sheet) and the process hole on the rotor punching sheet;

 

The second step is to position the stator punching sheet with the inner circle:orient the orientation mark, and re-punch all the stator slots and the dovetail slots and mark slots on the outer circle; the third step is to position the rotor punching sheet with the process hole, and re-punch all the rotor slots, shaft holes and keyways on the shaft holes. This scheme has the same advantages and disadvantages as the second scheme. Because the rotor sheet is positioned with the process hole on the rotor punching sheet when re-punching, the outer circle rough positioning plate on the lower die does not require high precision, has a simple structure, and is easy to manufacture; the outer circle rough positioning plate can be made into a semicircle, which is easy to feed and relatively safe. However, the blanking die and the rotor compound punching die are more complicated due to the additional process hole surface on the rotor punching sheet.

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Figure 3-20 Re-punching, first blanking (one blank three), then punching slots