Key technical requirements for the manufacturing process of electric vehicle drive motors

The technical and economic indicators of electric motors are largely related to their manufacturing materials and manufacturing processes. In electric motor manufacturing plants, the quality of products made from the same design structure and the same batch of raw materials often varies greatly. Without advanced manufacturing technology, it is difficult to produce advanced products. Let’s take a look at several key processes in motor manufacturing.

1. Stator core

The requirements for hedging sheets are as follows:

a. The punched sheets should meet the dimensional tolerances specified in the drawings.

b. The surface of the punched film should be smooth and uniform in thickness. Stator and rotor punching burrs are ≤0.05mm.

c. The coaxiality between the inner circle or the center hole and the outer circle of the punched piece: Φ0.04 ~ 0.06mm for one punch for the inner and outer circles, and appropriately relaxed for two punches for the inner and outer circles.

d. The uneven distribution of punching groove teeth, that is, the difference between the maximum and minimum tooth widths is level 3 or 4.

e. The center line of the groove should pass through the center of the circle and there should be no obvious skew.

f. The insulation layer on the surface of the punched sheet should be thin and uniform, and have sufficient dielectric, oil resistance, and moisture-proof properties.

g. The number of punched sheets with missing edges shall not exceed 2%, and the height of the missing edges shall not exceed 20% of the yoke height.

The requirements for stamping and lamination are as follows:

The task of core pressing is to arrange and press a certain number of punched sheets into a complete, compact and suitable whole with accurate dimensions, neat appearance.

a. The core weight or lamination coefficient must comply with the drawings. Insufficient weight of the iron core will increase the magnetic induction intensity, causing the motor's iron loss to increase, the excitation current to increase, and the power factor and efficiency to decrease.

b. The pressure should be uniform and the tightness should be appropriate. The iron core should not loosen or deform under the combined effects of mechanical vibration, electromagnetism and heat. If the iron core is too loose, the number of punched pieces within a certain length will be reduced, which will not only cause insufficient magnetic conductivity cross-section, but also cause vibration noise and damage the insulation; if the iron core is too tight, the insulation resistance between the pieces will be reduced, and even the insulation between the pieces will be damaged, which will cause the iron core to Consumption increased dramatically. If the pressure is uneven, the insulation will be easily damaged if it is too tight, and the core will become loose if it is too loose.

c. Geometric dimensions should be accurate. The total length of the iron core, slot size, and the size and position of the radial ventilation slots should all meet the specified requirements. The outer diameter tolerance of the iron core should ensure the process requirements for the coaxiality of the externally pressed stator core.

d. Shape requirements. The core coaxiality should be within the specified range, and the punched sheets should not be wavy after press-fitting. The edges of the iron core, especially the teeth, should not be warped.

e. The axial centerline position of the iron core should meet the specified requirements to ensure that the stator and rotor centers are symmetrical.

f. The insulation between core sheets should not be damaged.

2. Rotor cast aluminum

Surface quality requirements:

a. There should be no cracks in the end rings, blades and balance columns.

b. The size and depth of shrinkage holes on the surface of the end ring should be less than 20% of the height of the end ring, and the maximum should not be greater than 3mm. Only one hole is allowed on each end.

c. The defects of wind blades and sharp corners should be less than 3mm.

Size requirements:

a. Rotor core length tolerance.

       Core length L＜160mm, allowable tolerance +2.0mm;

       Core length L≥160mm, allowable tolerance +2.5mm.

b. The deflection of the outer circle of the end ring and the outer circle of the iron core.

       The outer diameter of the core is Φ<100mm, and the maximum deflection is not greater than 1.0mm;

       The outer diameter of the core is Φ<250mm, and the maximum deflection is not more than 2.0mm;

       The outer diameter of the iron core is Φ250~400mm, and the maximum deflection is not more than 3.0mm;

       The outer diameter of the core is Φ＞400mm, and the maximum deflection is not more than 4.0mm.

c. The end ring end face deflects the core end face: Same as b.

d. The allowable deviation of the rotor slot slope is ±1.0mm.

e. The inclined groove line on the outer surface of the rotor must be straight. The rotor disc deviation should generally be less than 0.5mm when viewed from the groove inclined line.

Internal quality requirements:

Check for defects such as broken strips, cracks, pores, looseness and shrinkage holes.

3. Winding

The winding is a key component of the motor and the weakest link that is most susceptible to damage. It is affected by electromagnetic, thermal, mechanical vibration, and environmental factors. Motor life and operational reliability mainly depend on the windings.

Coil manufacturing technical requirements:

a. The diameter and number of turns of the winding should be accurate. There should be no more than one joint for each coil, no more than two for each phase coil, and no more than four for each unit. The joints must be at the end bevel, and the wrapping should meet the regulations.

b. The size is moderate and meets the requirements, guaranteed by the winding mold.

c. The coils should be arranged neatly without crossing or damaging the insulation. The insulation between turns of multi-turn coils and to the ground should be good and reliable.

Technical requirements for winding embedding, shaping and wiring:

a. The iron core should be inspected and cleaned before inlaying wires. Any protrusions on the surface of the stator and in the slots must be filed flat and blown clean (should not be in the wire inlay area).

b. The winding pitch (slot pitch), connections between coils, and relative positions of lead wires must be correct.

c. Winding slot insulation, layer insulation, and phase insulation should be good and reliable. The quality of insulation materials and structural dimensions should comply with regulations.

d. The surface of the slot wedge should be flat and smooth. The winding insulation should not be damaged when inserted. It should be appropriately tight. There should be no cracks at the end and it should not be higher than the inner circle of the core. The lengths of windings, insulation and slot wedges exposed at both ends of the stator core should be symmetrical.

e. The wires at the end of the winding should be arranged neatly without serious crossover. End binding and insulation should meet the requirements.

f. When inlaying or shaping wires, metal tools must not be used to directly contact the windings, and excessive force must not be used to avoid damaging the insulation.

g. The lead wire joints should be welded firmly to ensure good contact, sufficient mechanical strength, smooth surface, and no desoldering or false soldering. Strict precautions should be taken to prevent copper dust, welding slag and other spatter from damaging the winding insulation and mixing into the winding.

h. The lead wires should be arranged neatly, have the same length and meet the requirements. If the outlet mark needs to be marked, it should be marked at the same specified position.

i. The end dimensions should comply with the drawing or tooling requirements.

j． There should be no cracks in the insulation at the bottom of the slot, and there should be no insulation damage in the wires. If there is a crack in the slot, it must be padded with the same material as the slot insulation, but the total number of cracks must not exceed 3, and the cracks must not reach the core.

k． The stator core with windings is not allowed to roll on the ground, and the coil insulation must not be damaged during its stacking and transportation.

Technical requirements for winding dipping and drying:

The winding insulation of small and medium-sized motors is often dipped in paint. The paint dipping process is: 1. Pre-baking; 2. Paint dipping; 3. Drying after paint dripping. Depending on the requirements, the windings are sometimes dipped several times.

a. The process parameters and insulation resistance of pre-baking, dipping and drying should meet the specified requirements.

b. The impregnating paint is uniform and transparent, without impurities, lumps, or deterioration. The viscosity of the paint should meet the process requirements.

c. After drying, the color of the paint film on the winding surface should be uniform. The paint film should be non-sticky and slightly elastic when touched. There should be no cracks and wrinkles on the surface. There should be no deformation at the ends and no bumps, exposed copper, separation of lead wires, or grooves in the copper wires. There is no misalignment of the wedge.

4. Machine base

a. The dimensional tolerance and roughness of each processing part should comply with the drawings.

b. The geometric tolerance of each machined surface shall comply with the drawings. Among them, the coaxiality between the two ends of the stop and the inner circle, and the jump of both ends facing the axis of the stop are the key to machine base processing. The inner circle and the iron core should have appropriate tightness to ensure that the stator core does not loosen or move in series during the operation of the motor.

c. For motors with feet, the plane of the feet should be parallel to the axis line. The distance between the foot holes and the centerline of the base should be symmetrical and meet the specified tolerances.

5. End cap

The stiffness of the end cover structure, the dimensional accuracy and shape deviation of the stop and the bearing chamber will affect the uniformity of the air gap between the stator and the rotor. This should be noted during design and processing.

a. Dimensional tolerances, cylindricity and roughness of bearing housings.

b. Dimensional tolerance, cylindricity and roughness of the stop.

c. Coaxiality of bearing chamber and stop.

d. The jump of the end face to the axis of the stop.

e. Depth from the end face of the stop to the bearing chamber. The wall thickness of the end cover should generally not be less than 5mm, the end cover stop should be chamfered, and the machining allowance should be more than 3mm.

6. Motor shaft

Spindles are commonly made of 45 high-quality carbon structural steel or 40Cr alloy steel. Spindle processing is divided into two stages: preliminary processing and forming processing. The preparatory processing includes straightening the round bar, blanking the blank, flattening the end face and drilling the center hole. Forming processing includes rough turning, semi-finishing turning, cylindrical grinding, keyway milling, etc.

The core diameter of the rotating shaft, the diameter and roughness of the bearing gears, the outer diameter size and roughness of the rotor core, the distance between the bearing gears at both ends, and the coaxiality between the outer circle of the iron core and the rotating shaft are all key to processing. The rotation shaft, iron core, and fan blades should have appropriate tightness to ensure that the rotor core and fan blades are not loose or loose during the operation of the motor. In addition, the dimensional tolerances of the shaft extension and keyway should comply with the installation dimensional tolerance requirements of relevant product standards.