Key technical requirements for motor manufacturing process

The technical and economic indicators of electric motors are largely related to their manufacturing materials and manufacturing processes. In the motor manufacturing plant, the quality of products made of 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.

The following key processes in motor manufacturing

1. Motor shaft

The main shaft is usually made of 45 high-quality carbon structural steel or 40Cr alloy steel. Spindle processing is divided into two stages: preparatory processing and forming processing. Preparatory processing is round steel straightening, rough blank blanking, flat end face and center hole punching. Forming processing is rough turning, semi-finishing turning, grinding outer circle, milling keyway, etc.

The core gear diameter, bearing gear diameter and roughness of the rotating shaft, the outer diameter and roughness of the rotor core, the distance between the bearing gears at both ends, and the coaxiality between the outer circle of the core and the shaft are all key to processing. There should be appropriate tightness for the shaft, iron core and fan blades to ensure that the rotor core and fan blades do not loosen or move in series during the operation of the motor. In addition, the dimensional tolerances of shaft extension and keyway should meet the requirements of relevant product standards for installation dimensional tolerances.

2. Stator core

The requirements for the punching sheet are as follows:

a The punched sheet should reach the dimensional tolerance specified in the drawing.

b The surface of punched sheet should be smooth and uniform in thickness. Stator and rotor punching burr ≤ 0.05mm.

c The coaxiality between the inner circle or central hole and the outer circle of the punched sheet: Φ0.04 ~ 0.06mm for one punching of the inner and outer circles, and a proper relaxation for two punches of the inner and outer circles.

d The unevenness of the groove tooth distribution of the punching sheet, that is, the difference between the maximum and minimum tooth width is 3 or 4 grades.

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

f The insulating layer on the surface of the stamping sheet should be thin and uniform, and have sufficient dielectric, oil-resistant, and moisture-proof properties.

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

The requirements for stacking of punching sheets are as follows: the task of pressing the iron core is to arrange and compress a certain number of punching sheets, and fix them into a whole with accurate size, neat shape and tight fit.

a The core weight or lamination factor must comply with the drawings. Insufficient core weight will increase the magnetic induction intensity, resulting in increased iron consumption of the motor, increased excitation current, and reduced power factor and efficiency.

b The pressure should be uniform and the tightness should be appropriate. The iron core should not be loosened or deformed under the comprehensive action of mechanical vibration, electromagnetism and heat. If the iron core is too loose, the number of punched pieces in a certain length will be reduced, not only the magnetic cross-section is insufficient, but also cause vibration noise and damage the insulation; Consumption increased dramatically. If the pressure is uneven, the insulation is easily damaged if it is too tight, and the iron core is often loosened if it is too loose.

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

d Shape requirements. The coaxiality of the iron core should be within the specified range, and the punched sheet should not appear wavy after pressing. The edges of the core, especially the teeth, should not be lifted.

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

f The insulation between core pieces should not be damaged.

3. Cast aluminum rotor

Surface quality requirements:

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

b The size and depth of the shrinkage cavity on the surface of the end ring shall be less than 20% of the height of the end ring, and the maximum shall not be greater than 3mm, and only one cavity is allowed at each end.

c The defect of fan blades and sharp corners should be less than 3mm.

Internal quality requirements:

Check for defects such as broken strips, cracks, pores, porosity and shrinkage cavities.

4. Winding

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

Coil manufacturing technical requirements:

a. The diameter and number of turns of the winding wire should be accurate. There should be no more than one joint for each coil, no more than two joints for each phase coil, and no more than four joints for each coil.

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

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

Technical requirements for winding embedding, shaping and wiring:

a. Check and clean the iron core before embedding wires. If there are protruding parts on the surface of the stator and in the groove, they must be filed and blown clean (not in the wire embedding area).

b The relative position of the winding pitch (slot pitch), connecting wires between coils and lead wires must be correct.

c Winding slot insulation, layer insulation, and phase-to-phase insulation should be good and reliable. The quality and structure size of the insulating material shall comply with the regulations.

d The surface of the slot wedge should be flat and smooth, and the winding insulation should not be damaged when inserted. Windings, insulation, and slot wedges should be symmetrical in length at both ends of the stator core.

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

f Do not use metal tools to directly contact the winding when inserting wires and shaping, and do not use excessive force to avoid damage to the insulation.

g Lead wire joints should be welded firmly to ensure good contact, sufficient mechanical strength, smooth surface, and no desoldering or virtual welding. Strictly prevent copper powder, welding slag and other spatters from damaging the winding insulation and mixing into the winding.

h The lead-out wires should be arranged neatly, have the same length and meet the requirements. Those that need to mark the line mark should be marked at the same specified position.

i The size of the end should conform to 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 damage to the insulation of the wires. If there is a crack in the slot, it must be cushioned with the same material as the slot insulation, but the total number of cracks must not exceed 3, and the cracks are not allowed to 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 handling.

Technical requirements for winding varnish drying:

The winding insulation of small and medium-sized motors is often dipped in varnish. The paint dipping process is: pre-baking - dipping paint - drying after dripping paint. Depending on the requirements, the windings are sometimes dipped in paint multiple times.

a Pre-baking, dipping, drying process parameters, insulation resistance should meet the specified requirements.

b Dip varnish is uniform and transparent, free from impurities and blocky substances, and without deterioration. The viscosity of the paint should meet the process requirements.

c After drying, the color of the paint film on the surface of the winding should be uniform. The paint film should be non-sticky and slightly elastic when touched by hands. There should be no cracks and wrinkles on the surface. There is no misalignment of the slot wedge.

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