Plastic sealed motor is a type of motor that uses a new type of insulation material to encapsulate the stator as a whole, mainly used in household appliances. Due to its various advantages over traditional motors, its development prospects are quite broad.

The design of its molds has a significant impact on the quality and price of the finished plastic products. The quality of a set of molds can be determined during the design phase. A good set of chess equipment must have the following conditions: 1. Shape and dimensional accuracy that meet the requirements of plastic sealed products; 2. Easy and efficient molding, easy removal of finished products, short molding cycle, and continuous production capability; 3. Good appearance and no need for further processing after molding; 4. The mold structure is sturdy and has a long lifespan.

The design of plastic sealed motor molds should not only have the characteristics of general plastic molds. It should be considered based on the special requirements of the motor stator, such as the possible problems that may occur during the plastic sealing process of the stator components: coil damage caused by impact; Insufficient filling; The outlet part is covered with sticky material; Injury lines, etc. To ensure the long-term and efficient operation of the mold, its structure, materials, and processing methods must be carefully considered.

2、 Mold Design for BMC Plastic Sealed Motor Stator

2.1 The preparation stage of mold design should focus on the following tasks

1. Choose a molding machine and understand its specific parameters

There are various types of injection molding machines, and as BMC material for thermoplastic materials, imported BMC specialized injection molding machines are often used, but the price is relatively expensive. The plastic sealed motor that I am currently developing and researching. The cutting adopts a domestically designed and manufactured plunger type (vertical and horizontal) injection molding machine, which uses a vertical oil cylinder to directly lock the mold, heats the mold itself, and a horizontal oil cylinder for injection. One sweet mold and two negative molds are alternately shifted and matched left and right. The machine is easy to operate, easy to maintain, reliable in performance, low in price, and has high production efficiency. It can be controlled manually or semi automatically.

The specific parameter values of the machine are as follows: large injection volume: 1000cm3; Large locking force: 57t; High injection pressure: 20t; Injection stroke zlOOmm; Mold Large Size: 360× 500× 280； Mold small size: 240× 500× 280； Spray nozzle size R18; The center height of the mold is 200mm.

2. Gain a detailed understanding of the characteristics of the finished product

The stator of the plastic sealed motor is made of unsaturated polyvinyl acetate short glass fiber reinforced molding compound; The use of BMC as a packaging insulation for short pants has higher advantages compared to traditional iron shell motors. In terms of electrical insulation, heat resistance, moisture resistance, and corrosion resistance, it surpasses traditional iron shell motors. BMC material itself has good mechanical properties, smaller linear expansion parameters and shrinkage rates, making the finished product size more stable, higher precision, and better surface smoothness. It can meet the high requirements of manufacturers for its surface smoothness.

3. Basic concept of mold

According to the manufacturer's requirements for the batch and total output of finished products, as well as the specific situation of the magnesium mold force of the molding machine, the number of mold cavities and the setting of the parting surface of the mold are determined; Due to the problem of the stator of the motor always encountering the problem of the lead wire being led out from the cavity, the parting surface is usually set in the middle of the lead wire; The choice of mold material is often determined by factors such as the manufacturer's frequency of use, service life, and steel price of the mold.

In addition, the processing of molds should make use of basic processing methods such as turning and milling as much as possible to reduce production costs. There are requirements for the surface of plastic sealed motors; Mirror” The effect is that the post-processing of the mold cavity is mostly done by circular grinding.

2.2 Mold Design Stage

When designing a plastic sealed motor, there are usually two situations: the shape and material of the stator are determined by the manufacturer, and then modified by the designer, or the designer comprehensively considers the purpose, performance, appearance, etc. provided by the manufacturer before redesigning. The plastic sealed motor of the dryer, as shown in the following figure, belongs to the former case. The manufacturer provides parameters such as the stator, rotor, shape, and installation dimensions of the motor, and we provide the finished product drawing design. After obtaining the manufacturer's approval, we proceed with the mold design.

1. Design principles of molds

① The circulation part of BMC material includes injection channels, runners, gates, and exhaust ducts.

Note&dash& mdash; The conical channel between the injection molding machine nozzle and the flow channel. Its front end aperture is smaller, the rear end aperture is larger, and the taper angle of the conical hole is about 3— 5. The R at the front end of the injection channel must be greater than the R at the nozzle by about 0.1mm in order to closely fit with the nozzle, and the small end aperture must be greater than the nozzle aperture by about lnm, with the H part being about 3‐ 5mm, as shown in Figure 1.

Flow channel&dash& mdash; The passage between the end of the injection channel and the gate. It is the part that closely affects the flow relationship of materials. The cross-sectional shape is shown in Figure 2, preferably circular or trapezoidal. To reduce flow resistance, its surface needs to be ground. The appropriate cross-sectional area for the flow channel is approximately 16mm2-50mm2.

Gate - the entrance of the mold cavity. It has the following functions: controlling the flow rate and velocity of materials; Reduce stress; Make the flow channel easy to detach after the zigzag shape. The usual practice is to set up a small gate at the beginning. Make appropriate adjustments based on the actual situation. There are many types of gates, and in plastic sealed motors, we use fan-shaped gates. This gate is not prone to defects near it. As shown in Figure 3. When designing a multi-mode cavity, it is important to ensure that the material reaches all the gates simultaneously.

② Demoulding device for stator

The mold cavity is equipped with a demolding slope, with a minimum depth of 0.25 for depths above 20mm, and the angle should be as large as possible when possible. However, the inner ring of the stator core should have a smaller demolding angle due to its tight fit with the core. Due to the easy processing, long service life, and easy replacement of the ejector rod, we use this mechanism to ejector the stator and flow channel. The setting of the stator ejection position should be based on the principle of not affecting the appearance. From the top end face to 25mm below the end face, the clearance between the left and right mating holes must be less than 0.1mm, and the lower part can be slightly increased to about 0.5mm.

③ Handling of outgoing line parts

The stator of a motor is different from general plastic products, as its lead wires must extend from the mold cavity. So the parting surface of the mold is often set in the central part of the lead wire. When the manufacturer requires asymmetrical wire clamps, the male and female molds cannot be opened and closed smoothly. At this time, inserts (movable or fixed) must be placed to make demolding easier, but placing inserts increases the production cost of the mold.

④ The strength of the mold

Due to the usage temperature of the mold being around 150 ℃. Moreover, repeated high pressure can easily cause deformation of the mold, so the wall thickness between multiple cavities or from the cavity to the edge of the mold should be around 30mm.

⑤ Temperature control of molds

Due to the fact that the injected BM C material is a thermosetting plastic, it has the property of being softened at the beginning of heating and having plasticity, and then becoming a solidified product when further heated. Therefore, the material cylinder of the injection molding machine does not need to be heated, and the mold itself needs to maintain a constant temperature as much as possible. We place heating rods on the upper and middle parts of the mold, connected to temperature controllers for control. Attention should be paid to the good connection between the temperature control meter probe and the mold, and to prevent rust in the gap between the heating rod and the mold.

⑥ Control of stator size, positional accuracy, and surface smoothness

The coordination requirements between the stator and rotor of the motor are quite high, so the dimensional accuracy of the stator must be strictly controlled. Generally speaking, the shrinkage rate of a material often determines its dimensional accuracy. Shrinkage rate refers to the ratio of the difference between the size of the mold cavity and the size of the finished product at room temperature to the size of the mold cavity. The main reason for the shrinkage of finished products is that the expansion coefficient of the material is not equal to that of the mold material. The volume shrinkage caused by double bond crosslinking during BMC material recycling can be controlled between 0.1% and 0.15%. The shrinkage rate is much lower than other plastics, which provides a guarantee for the high dimensional accuracy of the motor stator.

Due to the application of plastic sealed motors in household appliances, their appearance requirements are high, with both color and appearance requiring a beautiful and square appearance. In order to provide high surface quality, the surface smoothness of the mold cavity itself needs to be achieved and strictly controlled in terms of temperature, pressure, insulation, and post curing. Of course, these are all calculated rigorously and accumulated experience.

The flowability of BN C material is good, and the insulation thickness of the motor stator is generally around 2mm. Even in the slightly thicker parts at the corner transition, it is not easy to produce bubbles, dents, and other phenomena.

Also, because the entire stator is axially positioned with a core and the finished product after plastic sealing has a high coaxiality with the rotor, the vibration of the motor is reduced and the noise is low during operation.

2. The basic structure of the mold is described as follows (taking the plastic sealed motor of the dryer as an example), as shown in Figure 4:

(I) Injection nozzle: makes mold installation easy, for the population of materials:

(2) Male mold heating plate: The male mold is fixed on this plate. It is installed on the injection molding machine using a pressing plate method. The sheet thickness must be above 20mm. Jing uses this sheet metal to install a heating rod to heat the male mold, and at this time, an asbestos sheet needs to be placed between the injection molding machine and this sheet metal to prevent heat transfer.

(3) The shape of the finished product is determined by the male mold sheet metal. The surface processing must meet the dimensional accuracy requirements of the drawing. In order to facilitate demolding, too much demolding slope is left.

(4) Negative mold plate: The core is often placed on this plate, which also determines the shape of the finished product. The number of mold cavities for the finished product after mold opening is calculated based on the injection pressure of the injection molding machine and the projected area of the finished product.

(5) Core: The positioning center of the finished product is used to unify the center of the motor stator and rotor.

(6) Negative mold heating plate: Place the negative mold heating tube and heat the negative mold. Plays a supporting role for the female mold plate, preventing deformation due to injection pressure and making mold processing easier.

(7) The top rod is fixed around the sheet metal to ensure the correct, balanced, and stable position of the finished product. The hole diameter of the top rod on the sheet metal is about 0.25mm larger than that of the top rod; 0.5 mm.

(8) Pad plate: a fixed plate for supporting the top rod.

(9) Bottom plate: Connect the entire mold to the injection molding machine and form an ejection space with the cushion plate.

(10) Pushing rod: to push the finished product out of the negative mold. Its size is determined by the shape of the finished product being too small. The diameter is generally 3‐ Above a. Its material must have wear resistance and toughness. The clearance between it and the mold core should be less than 0.01mm.

(11) Supporting plate: Ensure the top out distance of the finished product.

(12) Guide post and guide sleeve: To ensure smooth coordination between the male mold and the visible mold, wear-resistant materials should be used due to their high friction frequency.

(13) Reverse push rod and spring: restore the fixing plate of the top rod to its normal position after the finished product is pushed out: during the mold stage. Note: (12) and (13) are not shown in the figures

3. Main materials for each component of the mold

The materials used for molds are differentiated according to the purpose of each part. Here, only the stator of the plastic sealed motor is taken as an example to illustrate:

(1) Guide post and guide sleeve: require surface resistance, use T8A, surface quenching, HRC≥ 55;

(2) Mold cavity and core: High strength, wear-resistant surface, minimal quenching deformation, made of crl2 steel;

(3) Injection nozzle: surface wear-resistant, corrosion-resistant, thermosetting, made of Cd2 steel;

(4) Top out rod and reverse push rod: certain strength and wear resistance. Use T8A;

(5) Various mold plates: require a certain strength, 45 steel quenched and tempered;

(6) Screws and connectors: General strength, made of A1 steel.

4. Quality of finished products

The quality of the finished product is ultimately determined by the requirements of its intended use. It includes the following four aspects:

(1) The dimensional accuracy of the stator meets the requirements of the drawing;

(2) Sufficient strength and hardness;

(3) Bright and smooth appearance, uniform color, no cracking, blistering, or pinholes:

(4) Meet other performance requirements, such as insulation, coaxiality with the rotor, noise and vibration characteristics.

Only when all four of these requirements are met, can the design of the tool be considered successful.

3、 Conclusion

The stator of a plastic sealed motor is formed by encapsulating the stator core, windings, leads, etc. together with BMC material, forming a whole with good insulation and mechanical reinforcement. Compared with iron shell motors, it has smaller volume, lighter weight, less vibration, lower noise, good integrity, high mechanical strength, moisture resistance, corrosion resistance, and high production efficiency. Although it is a new type of motor for household appliances, its development is quite fast. I have designed and manufactured plastic sealed stators for dryers, range hoods, and air conditioner motors, and have applied them in batches to products from various manufacturers, achieving good results. The mold design for BMC plastic sealed motor stators is also becoming increasingly perfect, which can meet the requirements for mass production of BMC plastic sealed stators.