Discussion on Some Problems in Design and Manufacture of High Speed ​​Motorized Spindle

Over the past decade, the rapid advancement of high-speed processing technology has led to a growing demand for high-speed CNC machine tools across various industries, particularly in aerospace, automotive, mold manufacturing, and motorcycle production. Industrialized nations such as the United States, Japan, Germany, Italy, and Switzerland have developed a wide range of commercial high-speed machine tools. The following table highlights several high-speed machining centers from internationally recognized brands that have emerged in recent years. **New High-Speed Machining Center Watch** Manufacturer (Country) | Machine Name and Model | Spindle Maximum Speed (r/min) | Maximum Feed Rate (m/min) | Spindle Drive Power (kW) ---|---|---|---|--- Cincinati Milacron (US) | Maxim 500 Horizontal Machining Center | 20,000 | 28 | 12 Ingersoll (US) | HVM800 High-Speed Horizontal Machining Center | 20,000 | 76.2 | 45 Mikron (US) | HSM700 High-Speed Vertical Machining Center | 42,000 | 40 | 14 Ex-cell-O (DE) | XHC241 High-Speed Horizontal Machining Center | 24,000 | 120 | 40 RODERS (Germany) | RFM1000 Machining Center | 42,000 | 30 | 20–30 Makino (Japan) | A55-A128 Machining Center | 40,000 | 50 | 22 Niigata Ironworks (Japan) | VZ40 Machining Center | 50,000 | 20 | 18.5 Mazak (Japan) | Super-400H Machining Center | 25,000 | 15 | 18.5 ![Figure 1a: No vector control](http://i.bosscdn.com/blog/20/08/03/05074634174.gif) **(a) No vector control** ![Figure 1b: With vector control](http://i.bosscdn.com/blog/20/08/03/05074634869.gif) **(b) With vector control** **Figure 1: Torque-Power Characteristics** High-speed machine tools are essentially CNC and precision machines. One of their most significant features is the realization of "zero drive" in the transmission system. This means eliminating all mechanical components—such as belts, gears, and clutches—between the main motor and the spindle, thereby integrating the motor directly with the spindle. This design offers advantages such as a simpler mechanical structure, reduced inertia, faster response times, and the ability to achieve extremely high speeds, rapid acceleration, and precise positioning (C-axis control). The use of AC variable frequency speed control and vector control technologies ensures a wide speed range and ideal torque-power characteristics (as shown in Figure 1b), enabling both roughing and high-speed finishing in a single setup. The integration of spindle components allows for standardized, mass-produced functional units, making it easier for machine tool manufacturers to customize high-speed machines based on user requirements. This approach aligns with modern modular design principles. Despite the simplified mechanical structure, the manufacturing process for high-speed spindles is highly demanding. Challenges include heat dissipation from built-in motors, balancing high-speed spindles, and designing optimal support and lubrication systems. These issues must be addressed to ensure stable, reliable operation and high-precision machining. This paper discusses the challenges involved in the design and manufacture of high-speed, high-power spindles for milling and boring, drawing on research conducted at our institution. ### 1. Basic Parameters and Structure of Motor Spindles Key parameters of motor spindles include maximum spindle speed, constant power speed range, rated power, maximum torque, front journal diameter, and bearing span. The maximum spindle speed, front journal diameter, and rated power are fundamental design considerations. Electric spindles are typically used in high-speed machining centers, and their design depends on statistical analysis of typical parts based on user process requirements. Machine tool manufacturers usually produce two types of high-speed machine tools of similar size: "high-speed type" and "high-rigidity type." The former is suitable for processing light alloys, composites, and cast iron in aerospace and aviation, while the latter is used for mold manufacturing, automotive parts, and difficult-to-machine materials like high-strength steel and heat-resistant alloys. When designing electric spindles, it's essential to select a variable frequency motor and control module with excellent torque-power characteristics and a wide speed range. There are two common layout methods for high-speed motor spindles based on the relative position of the main motor and the bearings: ![GD-2 Electric Spindle](http://i.bosscdn.com/blog/20/08/03/05074634354.jpg) **Figure 2: GD-2 Electric Spindle** 1. Coding disk 2. Spindle housing 3. Cooling water jacket 4. Motor stator 5. Oil gas nozzle 6. Motor rotor 7. Stepped interference sleeve 8. Balance disk 9. Angular contact ceramic ball bearing ![Electric Spindle with Main Motor Behind Rear Bearing](http://i.bosscdn.com/blog/20/08/03/05074635951.gif) **Figure 3: Electric Spindle with Main Motor Behind the Rear Bearing** 1. Hydraulic cylinder 2. Pull rod 3. Spindle bearing 4. Disc spring 5. Collet 6. Spindle 7. Built-in motor The first layout places the main motor between the front and rear bearings, resulting in a compact and stiff spindle unit suitable for medium and large-scale machining centers. The second layout positions the motor behind the rear bearing, reducing the radial size of the front end and improving cooling conditions but increasing the axial length, which is more suitable for small, high-precision machine tools. ### 2. Main Heat Sources of the Electric Spindle and Their Solutions Heat generation in high-speed electric spindles used in milling and boring operations is a critical concern. The primary heat sources are the main motor and the spindle bearings. Unlike conventional spindles, the proximity of the motor to the bearing can significantly affect its accuracy. Poor heat dissipation can also impact the machine tool’s reliability. To address this, an external circulating oil and water cooling system was implemented for the GD-2 high-speed electric spindle. An aluminum jacket with spiral grooves is placed around the motor stator. During operation, coolant flows through these grooves, efficiently removing heat. The flow rate of the coolant is calculated based on the motor’s heat output. ![Oil-Water Heat Exchange System of GD-2 Electric Spindle](http://i.bosscdn.com/blog/20/08/03/05074635644.gif) **Figure 4: Oil-Water Heat Exchange System of GD-2 Electric Spindle** Additionally, the spindle bearings generate significant heat due to high-speed rotation. The dm·n value (diameter × speed) is crucial for determining the dynamic and thermal performance of the bearings. Most high-speed spindles use angular contact ceramic ball bearings made of silicon nitride, offering lower density, higher hardness, and better thermal stability. These bearings enable high-speed operation, minimal temperature rise, and long service life. An oil-air lubrication system was also employed on the GD-2 electric spindle to further reduce bearing temperatures. Measurements show that under high-speed conditions, the bearing temperature can decrease by 9 to 16°C compared to traditional oil mist lubrication, with improved cooling efficiency as the dm·n value increases. ### 3. Dynamic Balance Design of the Electric Spindle Electric spindles often operate at speeds exceeding 10,000 rpm, with some reaching up to 60,000–100,000 rpm. Even a small imbalance can create significant centrifugal forces, leading to vibration and reduced machining accuracy. Therefore, strict dynamic balance is required. Components must be precisely manufactured and assembled to achieve a dynamic balance level of 0.4 or higher. ![Dynamic Balance Design of Rotor of High-Speed Electric Spindle](http://i.bosscdn.com/blog/20/08/03/05074636516.gif) **Figure 6: Dynamic Balance Design of Rotor of High-Speed Electric Spindle** 1. Rotor inner sleeve 2, 4. End cap 3. Rotor silicon steel sheet During design, structural symmetry is crucial. Key connections and threaded fasteners are avoided. The rotor and spindle are connected via an interference fit, ensuring secure torque transmission. For maintenance, an oil press system allows easy removal of the rotor without damaging the assembly. To ensure accurate dynamic balance after assembly, the rotor’s outer diameter is machined with a slight allowance before installation. After hot pressing, the rotor is mounted on a lathe, and the outer diameter is finely machined. Additionally, symmetrically drilled screw holes on the end caps allow for fine-tuning of the balance using adjustment screws. ### 4. Conclusion As the core component of high-speed CNC machine tools, the performance of the spindle greatly influences the overall efficiency and precision of the machine. Countries worldwide invest heavily in research and development, establishing specialized production facilities with advanced equipment and controlled environments. While China’s high-speed motorized spindle technology is still in its early stages, there is significant potential for growth. To accelerate the adoption of high-speed processing technology and improve CNC machine tools, further research and development are essential to achieve professional mass production of electric spindles.

ROAD ROLLER

1. According to the compaction principle, it can be divided into static action roller and vibratory roller. Static action roller (including static smooth wheel roller and tire roller) compacts the soil by the static pressure generated by the self weight and load of the roller. Vibratory roller relies on the combined action of high-frequency vibration and exciting force generated by the vibrating mechanism
2. According to the number of rolling wheels, it can be divided into single wheel roller, double wheel roller, three wheel roller, etc.
3. Self propelled roller can be divided into mechanical transmission roller, mechanical hydraulic transmission roller and full hydraulic transmission roller according to its power transmission mode.

4. According to its structural weight, it can be divided into light, small, medium, heavy and ultra heavy rollers.

The road roller, also known as the soil compactor, is a kind of equipment for road construction.Road rollers belong to the category of road equipment in construction machinery. They are widely used in filling and compacting operations of large-scale engineering projects such as high-grade highways, railways, airport runways, dams, and stadiums. They can roll sandy, semi-cohesive and cohesive soils, Subgrade stabilized soil and asphalt concrete pavement layer.With the gravity of the machine itself, the road roller is suitable for various compaction operations, so that the rolled layer can be permanently deformed and compacted.Road rollers are divided into two types: steel wheel type and tire type.

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