To say that compared with general machine products, motors have similar mechanical structures and similar casting, forging, machining, stamping and assembly processes;

But the difference is more obvious. The motor has a special conductive, magnetic and insulating structure , and has unique processes such as iron core punching, winding manufacturing, dipping and plastic packaging, which are rare in ordinary products.

The manufacturing process of the motor mainly has the following characteristics:

• There are many types of work, and the process involves a wide range of areas.

• There are many non-standard equipment and non-standard tooling,

• There are many types of manufacturing materials;

• High processing precision requirements;

• Large amount of manual labor.

The motor iron core is a whole made up of many punched sheets. The quality of the punched sheets directly affects the quality of the core pressing, and the quality of the iron core will have a great impact on the quality of the motor product.

If the groove shape is not neat, it will affect the quality of money embedded, if the burr is too large, the size accuracy and tightness of the core will affect the magnetic permeability and loss.

Therefore, ensuring the manufacturing quality of punching sheets and iron cores is an important part of improving the quality of motor products.

The quality of the stamping is related to the quality of the die, the structure, the precision of the stamping equipment, the stamping process, the mechanical properties of the stamping material, and the shape and size of the stamping .

The dimensional accuracy, coaxiality, and groove position accuracy of the stamping sheet can be guaranteed from the aspects of silicon steel sheet, punching die, punching scheme and punching machine.

From the perspective of punching die, reasonable clearance and die manufacturing precision are necessary conditions to ensure the accuracy of die size.

When a compound die is used, the dimensional accuracy of the working part is mainly determined by the manufacturing accuracy of the die, and has nothing to do with the working state of the punch.

According to the technical conditions, the precision difference of the stator tooth width is not more than 0.12mm, and the allowable difference of individual teeth is 0.20mm.

Excessive die clearance, incorrectly installed dies, or blunted die edges can cause burrs on the punch.

To fundamentally reduce burrs, it is necessary to strictly control the gap between the punch and the die during mold manufacturing;

When installing the die, it is necessary to ensure that the clearance on each side is even, and when punching, it is also necessary to ensure the normal operation of the die, check the size of the burr frequently, and sharpen the cutting edge in time;

The burr will cause the short circuit between the sheets of the iron core, which will increase the iron loss and temperature rise. Strictly control the size of the iron core to achieve press-fitting. Due to the existence of burrs, the number of punching pieces will be reduced, resulting in an increase in excitation current and a decrease in efficiency. The burrs in the slot will puncture the winding insulation and cause the teeth to expand.

Excessive burrs at the rotor shaft hole may cause hole size reduction or ellipticity, making it difficult to press-fit the core on the shaft. When the burr exceeds the specified limit, the mold should be repaired in time.

When there is corrugation, rust, oil or dust, the press fit coefficient will be reduced. In addition, the length should be controlled during press-fitting. Too much reduction will make the core weight insufficient, the magnetic circuit section will be reduced, and the excitation current will increase.

The punching sheet insulation is not handled well or managed poorly, and the insulation layer is destroyed after pressing, which makes the iron core moderate and the eddy current loss increases.

The length of the stator core is too much longer than that of the rotor core, which is equivalent to the increase of the effective length of the air gap, which increases the magnetic force of the air gap (increases the excitation current) and increases the stator current (increases the copper loss of the stator) .

In addition, the effective length of the iron core increases, which increases the leakage reactance coefficient and the leakage reactance of the motor.

This is mainly due to the excessive burr of the stator punching sheet , and its impact is the same as above.

It reduces the net length of the stator core, reduces the cross-sectional area of the stator teeth and stator yoke, and increases the magnetic flux density.

The reasons for the insufficient weight of the iron core are:

• Stator punching burrs are too large;

• The thickness of the silicon steel sheet is uneven;

• The punch is rusty or stained with dirt;

• The pressure is not enough due to oil leakage of the hydraulic press or other reasons during pressing.

For a closed motor, the outer circle of the stator core is in poor contact with the inner circle of the frame, which affects heat conduction and increases the temperature of the motor. Because the thermal conductivity of air is very poor, only 0.04% of the iron core, even if there is a small gap, the thermal conductivity will be greatly affected.

If the inner circle is not ground, the iron core of the stator and rotor may rub against each other; if the inner circle is ground, it will not only increase the working hours, but also increase the iron consumption.

If the notch is not filed, it will be difficult to insert the wire; if the notch is filed, the stator clamp coefficient will increase, the effective length of the air gap will increase, the excitation current will increase, and the rotating iron loss (that is, the rotor surface loss and pulsation loss) will increase . .

The reasons for the unevenness of the stator core are:

• The punches are not pressed in order;

• The punching burr is too large;

• Slotted rods become smaller due to poor manufacture or wear;

• The inner circle of the lamination tool cannot expand the inner circle of the stator core due to wear;

• Stator punching slots are not neat, etc.

The stator core is uneven and needs filing grooves, which will reduce the quality of the motor. In order to prevent the stator core from grinding or filing , the following measures should be taken:

• Improve the precision of die manufacturing;

• Realize single-machine automation, so that the punching order is stacked in the forward direction, and the order is pressed in the forward direction;

• Ensure the accuracy of the application of process equipment such as molds and groove-like rods produced during the press-fitting of the stator core

• Strengthen the quality inspection of each process in the punching and pressing process.

The quality of the cast aluminum rotor directly affects the technical and economic indicators and operating performance of the asynchronous motor. When studying the quality of the cast aluminum rotor, it is not only necessary to analyze the casting defects of the rotor, but also to understand the effect of the quality of the cast aluminum rotor on the efficiency and power factor of the motor . And the influence of starting and running performance .

The additional loss of the cast aluminum rotor is much larger than that of the copper bar rotor asynchronous motor, and the method of casting aluminum is different. The additional loss is also different, and the additional loss of the die-cast aluminum rotor motor is the largest.

This is because the strong pressure during die-casting makes the cage bar and the iron core contact very closely, and even aluminum water is squeezed between the laminations, and the transverse current increases, which greatly increases the additional loss of the motor.

In addition, due to the fast pressurization speed and high pressure during die-casting, the air in the cavity cannot be completely removed, and a large amount of gas is densely distributed in the rotor cage, end ring, fan blade, etc. in the form of "pinholes", resulting in the aluminum alloy in the cast aluminum rotor The specific gravity decreases (about 8% less than that of centrifugal cast aluminum) and the average resistance increases by 13% , which greatly reduces the main technical and economic indicators of the motor. Although the centrifugal cast aluminum rotor is affected by various factors, it is prone to defects, but the additional motor The loss is small.

Aluminum water comes directly from the inside of the crucible during low-pressure aluminum casting, and "slow" low-pressure pouring is used, with better exhaust; when the guide bar is solidified, the aluminum water is replenished from the upper and lower end rings. Therefore, the quality of the low-pressure cast aluminum rotor is excellent.

Electrical performance of motors with different cast aluminum rotors

It can be seen that the low-pressure cast aluminum rotor has the best electrical performance, followed by the centrifugal cast aluminum rotor, and the pressure cast aluminum rotor is the worst.

The quality of the cast aluminum rotor has a great influence on the performance of the motor. The reasons for these defects and their influence on the performance of the motor will be discussed in detail below.

The reasons for the insufficient weight of the rotor core are:

• The burr of the rotor punch is too large;

• Uneven thickness of silicon steel sheet;
  

• The rotor punch is rusty or not clean;

• The pressure during pressing is small (the pressing pressure of the rotor core is generally 2.5~.MPa) .

• The preheating temperature of the cast aluminum rotor core is too high and the time is too long, the core burns seriously, and the net length of the core decreases.

The weight of the rotor core is not enough, which is equivalent to the reduction of the net length of the rotor core, so that the cross-sectional area of the rotor teeth and the rotor yoke is reduced, and the magnetic flux density is increased. The effects on motor performance are:

• The excitation current increases, the power factor decreases, the motor stator current increases, the rotor copper loss increases, the efficiency decreases, and the temperature rise increases.

The reasons for rotor misalignment are:

• When the rotor core is press-fitted, the groove-like rod is not used for positioning, and the groove wall is not neat.

• The matching gap between the oblique key on the dummy shaft and the keyway on the punch is too large;

• The pressure during press-fitting is small, and the burrs and oil stains of the punching sheet are burned off after preheating, which makes the rotor sheet loose;

• After the rotor is preheated, it throws and rolls on the ground, and the rotor punches produce angular displacement.

The above defects will reduce the rotor notch, increase the leakage reactance of the rotor slot, reduce the cross section of the bar, increase the resistance of the bar , and have the following effects on the performance of the motor:

• The maximum torque decreases, the starting torque decreases, the reactance current increases at full load, and the power factor decreases;

• The stator and rotor current increase, and the stator copper loss increases;

• The rotor loss increases, the efficiency decreases, the temperature rises, and the slip rate is large.

The reason why the chute width is larger or smaller than the allowable value is mainly that the oblique key on the dummy shaft is not used for positioning when the rotor core is press-fitted, or the inclination dimension of the oblique key is out of tolerance when the dummy shaft is designed .

The effects on motor performance are:

• If the width of the chute is larger than the allowable value, the leakage reactance of the rotor chute will increase, and the total leakage reactance of the motor will increase;

• The length of the guide bar increases, the resistance of the guide bar increases, and the impact on the performance of the motor is the same as the following;

• When the chute width is smaller than the allowable value, the leakage reactance of the rotor chute decreases, the total leakage reactance of the motor decreases, and the starting current increases;

• The noise and vibration of the motor are large.

The reason for the broken bar is:

• The rotor core is pressed too tightly, and the rotor core expands after aluminum casting, and excessive tension is applied to the aluminum strip, which breaks the aluminum strip.

• After aluminum casting, demoulding is too early, the aluminum water is not solidified, and the aluminum strip is broken due to the expansion force of the iron core.

• Before aluminum casting, there are inclusions in the rotor core slot.

The winding is the heart of the motor, and its life and operating reliability mainly depend on the manufacturing quality of the winding and the electromagnetic effect during operation, mechanical vibration and environmental factors;

The selection of insulating material and structure, the insulation defect and the quality of insulation treatment in the manufacturing process directly affect the quality of the winding, so attention should be paid to winding manufacturing, winding drop and insulation treatment .

Most of the magnet wires commonly used in motor windings are insulated wires, so the wire insulation is required to have sufficient mechanical strength, electrical strength, good solvent resistance, and high heat resistance. The thinner the insulation, the better.

Insulating material is a material with high resistivity, the current flowing through it can be considered negligible, and the general resistivity is greater than 107Ω*M

• Dielectric strength

• Insulation resistivity KV/mm MΩ The ratio of the applied voltage of the insulating material to the leakage current of the insulating material;

• The dielectric constant, the energy of the ability to store electrostatic charges;

• Dielectric loss, the energy loss generated in an alternating magnetic field;

• Corona resistance, arc resistance and anti-leakage trace performance.

The thermal properties of insulating materials include thermal rating, thermal shock resistance, thermal expansion coefficient, thermal conductivity and curing temperature;

For example, enameled wire enamel is anti-stripping, scratch-resistant, and bending-resistant. For slot insulation and heat-resistant insulation, it requires certain compression, tensile, bending, shear, bonding humidity, impact toughness, and hardness .

Refers to water absorption, acid resistance, alkali resistance and solvent resistance, mildew resistance, etc.

The quality inspection after stator winding embedding includes appearance inspection, DC resistance measurement and withstand voltage test.

• Check that the size and specifications of the materials used should meet the requirements of the drawings and technical standards.

• The winding pitch should comply with the drawings, the connection between the windings should be correct, the straight line part is straight and tidy, there is no serious crossing phenomenon at the end, and the insulation shape of the end should meet the regulations.

• The slot wedge should have sufficient tightness, check with a spring scale if necessary, there should be no cracks at the end, the slot wedge should not be higher than the inner circle of the iron core, and the length extending from both ends of the iron core should be equal.

• Use the template to check that the shape and size of the winding end should meet the requirements of the drawings, and the end binding should be firm.

• The cracked repair at both ends of the slot insulation should be reliable. For motors with less than 36 slots, there should be no more than three places and no cracks to the iron core are allowed.

• DC resistance allows ±4%

The purpose of the withstand voltage test is to check whether the insulation strength of the winding to the ground and between the windings is qualified. The withstand voltage test is carried out twice, one is carried out after inserting the wire, and the other is carried out during the factory test of the motor.

The test voltage is AC, the frequency is 50Hz and the actual sinusoidal waveform. During the factory test, the effective value of the test voltage is 1260V (when P2<1KW) or 1760V (when P2≥1KW) ;

When testing after embedding wires, the effective value of the test voltage is 1760V (P2<1KW) or 2260V (P2≥1KW) .

The stator winding should be able to withstand the above voltage for 1min without breakdown.

The electrical breakdown strength of insulating varnish is several tens of times that of air. After insulation treatment, the air in the winding is replaced by insulating varnish, which improves the initial free voltage and other electrical properties of the winding;

After the winding is impregnated, the insulating varnish fills the capillaries and gaps of the insulating material, and forms a dense and smooth paint film on the surface, making it difficult for moisture to penetrate into the winding, thereby significantly improving the moisture resistance of the winding.

Insulation has a much better thermal conductivity than air. After the winding is impregnated, its thermal conductivity can be significantly improved. At the same time, the aging speed of the insulating material is slowed down and the heat resistance is improved.

After the winding is impregnated, the wire and the insulating material are bonded into a solid whole, which improves the mechanical properties of the winding and can effectively prevent insulation loosening and wear caused by vibration, electromagnetic force, thermal expansion and contraction.

The paint film formed after insulation treatment can prevent the insulation material from being damaged due to direct contact with harmful chemical media.

After special insulation treatment, the winding can also have the ability of anti-mildew, anti-corona and anti-oil, so as to improve the chemical stability of the winding.

The characteristics of motor assembly are mainly determined by the use requirements and structural features, mainly including:

That is to say, when the structural design is required, each part should have clear dimensions, shape tolerances and surface roughness requirements, which is the basis for ensuring the quality of micro-motor products. Some more sophisticated micro-motor parts are completely interchangeable and cannot meet the requirements, they need to be assembled in groups.

Shaft assembly has a great impact on motor life, noise, static friction, temperature rise, etc. Each motor has different shaft precision and installation requirements , and there should be clear regulations, and the process must be guaranteed.

If necessary, the inspection of assembly coaxiality and verticality can be added during the assembly process.

Because static unbalance and dynamic unbalance make the motor produce additional torque when it is working, the light ones have vibration and noise, and the heavy ones may cause bore sweeping and resonance. Special equipment is required for careful calibration.

There are many light and small parts and thin-walled parts of the motor, which have poor rigidity and are easy to deform. During processing and assembly, special tools must be used for transmission, transfer and storage. Do not subject it to undue external force, causing deformation and damage.

For mass-produced motors, they can be assembled in a flow-line operation. The assembly process is very detailed, and the quality can be guaranteed step by step. For multi-variety and small-batch products, Yicai group process assembly is often divided into stator and rotor. The general assembly process can formulate a unified special process procedure, including the specific requirements of each product. This is convenient for quality assurance, and intermediate inspection procedures can be added if necessary.

Relevant Ministry of the State: According to the commonality of various types of motors and a certain category of motors, a part of general standards has been formulated. Standards are formulated according to the special requirements of a certain series or a certain variety.

Each enterprise formulates standard implementation rules according to its own situation and formulates enterprise special product standards.

In standards at all levels, especially national standards, there are mandatory standards, recommended standards and guiding standards.

The first part is composed of letters/Chinese/Hanyin. Indicates: standard level, international industry standard, enterprise standard; nature: compulsory, recommended, guided;

The second part: For example, GB755 is the No. 755 national standard, and Arabic numerals are used to indicate the serial number in this level of standard.

The third part: Yes - separate from the second part and use Arabic numerals to indicate the year of implementation.

• GB/T755—2000 Rating and performance of rotating electrical machines

• GB/T12350—2000 Safety requirements for small power motors

• GB/T9651—1998 Test method for one-way stepping motor

• JB/J4270—2002 General Technical Specifications for Internal Motors of Room Air Conditioners.

• GB/T10069.1—2004 Noise measurement method and limit value of rotating electrical machines, noise measurement method

• GB/T12665—1990 Damp heat test requirements for motors used in general environments