Frameless torque motors serve as the core power source for modern precision equipment, with their performance directly determining the accuracy and reliability of high-end devices. Unlike framed motors, they lack a housing and bearing structure, allowing equipment manufacturers to integrate the motor directly into their mechanical systems, thereby saving space, reducing weight, and improving overall system performance.
The production of frameless torque motors is an art that combines materials science, precision machinery, and electromagnetics. Among the processes, winding, insertion, and segmented round assembly are the core of the core.
01 Fundamentals of Frameless Torque Motors
The biggest difference between frameless torque motors and traditional motors is that they have no housing, bearings, or output mechanism, consisting only of two components: the stator and the rotor.
This design allows for direct integration into the customer's mechanical system, making it particularly suitable for applications with extremely high requirements for space, weight, and precision, such as industrial robots, aerospace, and precision medical equipment.
The stator, as the static part of the motor, contains the windings and iron core, responsible for generating the electromagnetic field; the rotor is the rotating part, usually equipped with permanent magnets. The accuracy of the air gap between them typically needs to be controlled at the micrometer level, which directly determines the motor's performance and efficiency.
02 Winding Process: The Birth of Precision Coils
Winding is the first key process in frameless torque motor production, aiming to wind copper wire into the specified coil shape according to the design requirements.
Material Selection and Preparation
Winding typically uses high-purity oxygen-free copper enameled wire (purity ≥ 99.95%), whose surface insulation may be made of materials like polyimide. For high-power applications, rectangular copper wire might be chosen to improve slot fill factor and heat dissipation performance.
Winding Process and Control
The winding process needs to be performed on a dedicated winding machine, equipped with precise tension control systems and counters. During operation, the starting end of the wire is first left with an appropriate length and secured. The winding machine is then started, causing the wire to be arranged neatly and tightly from left to right in the slot without crossing.
Precision control is crucial: the number of coil turns must meet the design requirements with minimal tolerance; the wire arrangement must be tight and flat, avoiding crosses or overlaps; tension must be uniform to prevent damage to the insulation.
Process Challenges and Innovations
Winding is particularly challenging for the small stators of frameless torque motors. In recent years, universal insertion fixtures have emerged. Through adjustable baffle and clamp plate designs, they can adapt to the insertion needs of different motor models, greatly improving production efficiency and mold utilization.
03 Insertion Process: The Art of Placing Coils into the Iron Core
Insertion is the process of embedding the wound coils into the slots of the stator iron core. This is an extremely delicate task requiring superb skill and extensive experience.
Preparation Before Insertion
Various tools need to be prepared before insertion: pressing plates, slot liners, curved scissors, insertion needles, mallets, bamboo strips, etc. Simultaneously, slot insulation needs to be placed by folding insulation paper into a "U" shape and inserting it into the slot to provide insulation protection for the coils.
Insertion Techniques and Skills
Insertion operations require a series of precise techniques :
1. Pinching Flat: Use both hands to pinch and compress the straight corner parts of the coil, reducing its width so it can enter the stator bore without touching the iron core.
2. Twisting: Twist both sides of the coil in the same direction, causing the wires to twist to one side.
3. Combing: Pinch the lower straight edge near the corner flat and slide it downwards to comb it, making it form a flat row shape.
During insertion, the pinched effective edge's rear end needs to be tilted towards the slot opening on the iron core end face. Reach from the other end of the stator to receive the coil, and use both hands cooperatively to press the effective edge into the slot opening.
Quality Control and Insulation Treatment
After the wires are inserted, a slot liner is used to comb the wires straight in one direction within the slot. Then, a pressing plate is used to flatten the wires in the slot, and slot closure strips and wedges are inserted.
For the small stators of frameless torque motors, it is difficult to control stability during insertion. New universal insertion fixtures use an adjustable design with sliding baffles and special clamp plates, effectively securing stators of different sizes and ensuring stability during the insertion process.
04 Segmented Round Assembly Process: The Key to Ensuring Precision
Segmented stators are a common structure in frameless torque motors, where the entire stator is divided into several segments, wound separately, and then assembled into a complete circle. This design can improve the slot fill factor, shorten the coil end turns, and greatly benefit the motor's electromagnetic performance.
Challenges in Round Assembly
The biggest challenge when assembling segmented stators into a complete circle is ensuring the roundness tolerance of the stator's inner diameter. If the force on the segments is uneven, it can lead to a large roundness tolerance in the stator's inner circle, subsequently causing uneven motor air gap, increasing cogging torque and torque ripple, and even generating issues like unilateral magnetic pull.
Innovative Round Assembly Methods
To solve this problem, advanced round assembly processes employ various innovative methods:
Thermal Shrinking with Fixture Method: The inner arc surface of each stator iron core segment is closely fitted to the outer cylindrical surface of the assembly fixture. After being tightly fastened with an outer hoop fixture, the motor housing, heated to 220°C-240°C, is thermally shrunk onto the outer cylindrical surface of the segmented stator iron core. After the housing cools, the fixture is removed. This method can control the roundness tolerance of the stator's inner circle to within 0.05mm, an improvement of 3-4 tolerance grades compared to traditional methods.
Electromagnetic Round Assembly Method: This is a newer method where all segmented stator iron cores with wound coils are vertically placed into the base of an assembly fixture, with positioning keys inserted for radial positioning. A stator pressure plate is then inserted between the base and the inner bore of the stator iron cores and fixed with bolts.
Subsequently, the coil windings on each segmented stator iron core are connected to a DC power supply, giving each stator segment magnetism, which causes them to be sucked tight together with the magnetic stator pressure plate. Welding or thermal shrinking of the housing then follows. This method ensures round assembly accuracy through magnetic force, and the magnitude of the force can be controlled by adjusting the current.
Automated Round Assembly Equipment
Automated round assembly mechanisms can complete the round assembly of multiple coil stators using just one rotary motor to drive a turntable. The edge of the turntable has oblique slots set crossing with the turntable's radius. Through a U-shaped slider and roller mechanism, the rotary motion is converted into linear motion, pushing the stator segments towards the center to gather.
The advantage of this mechanism is that one drive unit can complete the synchronous movement of multiple segments, greatly reducing resource waste and production costs. By controlling the rotation amplitude of the turntable, the assembly size can also be adjusted to accommodate the round assembly needs of different stator specifications.
05 Quality Inspection: The Pursuit of Excellence
In the production process of frameless torque motors, quality inspection runs throughout, ensuring every step meets design requirements.
After winding, it is necessary to check the number of coil turns and the DC resistance to ensure they comply with the design. During insertion, it is necessary to constantly check whether the wires in the slots are neat and parallel, and whether the insulation has shifted. After round assembly, the roundness tolerance of the stator's inner circle needs to be inspected to ensure it is within the allowable range.
For welded parts, the quality of the solder joints needs to be checked to ensure good contact and sufficient mechanical strength . Insulation performance needs to be verified through withstand voltage tests to ensure no risk of short circuit or leakage.
06 Future Development Trends
The production technology for frameless torque motors is still continuously developing and innovating. Future trends mainly include:
Automation and Intelligence: With the development of industrial robotics and intelligent control technology, the production process of frameless torque motors is moving towards comprehensive automation and intelligence to improve precision and efficiency.
Application of New Materials: The use of new insulating materials, magnetic materials, and conductive materials will further improve motor performance and reliability.
Process Innovation: New processes are emerging constantly, such as laser welding, vacuum pressure impregnation (VPI), etc., continuously enhancing the quality grade of motors.
Modularization and Standardization: Through modular and standardized design, production costs are reduced, product applicability is improved, enabling frameless torque motors to be applied in broader fields.
With advancing processes, frameless torque motors will achieve higher power density, smaller size, and greater accuracy. The round assembly accuracy of segmented stators will reach the micrometer level, and the winding and insertion processes will be fully completed by automated equipment.
The production process of frameless torque motors is a microcosm of precision manufacturing, where every link embodies the wisdom and craftsmanship of engineers.
