1、 The structural composition of the electric spindle

Electric spindle is a new technology in the field of CNC machine tools that integrates machine tool spindle and spindle motor in recent years. The main transmission system of high-speed CNC machine tools has eliminated pulley transmission and gear transmission. The spindle of the machine tool is directly driven by a built-in electric motor, reducing the length of the main transmission chain to zero and achieving "zero drive" of the machine tool. This type of transmission structure combines the spindle motor and machine tool spindle into one, making the spindle part relatively independent of the machine tool's transmission system and overall structure. Therefore, it can be made into a "spindle unit", commonly known as an "electric spindle".

Electric spindle is a new technology in the field of CNC machine tools that integrates machine tool spindle and spindle motor. Along with linear motor technology and high-speed cutting tool technology, electric spindle pushes high-speed machining into a new era. Electric spindle is a set of components, including the electric spindle itself and its accessories: electric spindle, high-frequency frequency converter, oil mist lubricator, cooling device, built-in encoder, tool changer, etc. The rotor of the electric motor is directly used as the spindle of the machine tool, and the housing of the spindle unit is the motor base, which, together with other parts, realizes the integration of the electric motor and the machine tool spindle.

2、 Drive mode

The electric motors of electric spindles are all AC asynchronous induction motors, because they are used in high-speed machining machines. The starting speed needs to be quickly increased from static to tens of thousands or even hundreds of thousands of revolutions per minute, and the starting torque is large. Therefore, the starting current is 5-7 times higher than the rated current of ordinary motors. There are two driving methods: variable frequency drive and vector control drive. The driving control characteristic of a frequency converter is constant torque drive, and the output power is proportional to the torque. The latest frequency converter of the machine tool adopts advanced transistor technology, which can achieve stepless speed change of the spindle. The drive control of the machine tool vector control driver is constant torque drive at the low-speed end, and constant power drive at the medium and high-speed ends.

Electric spindle has the advantages of compact structure, light weight, low inertia, low noise, fast response, etc. Moreover, it has high speed and high power, simplifies machine tool design, and is easy to achieve spindle positioning. It is an ideal structure in high-speed spindle units. The electric spindle bearing adopts high-speed bearing technology, which is wear-resistant and heat-resistant, and has a service life several times longer than traditional bearings.

3、 The application of high-speed electric spindle in the machine tool industry

Simplify the structure and promote the modularization of machine tool structures

Electric spindles can form standardized and serialized products based on their application, structure, performance parameters, and other characteristics, which can be selected by the host to promote the modularization of machine tool structures.

Reduce machine tool costs and shorten the development cycle of machine tools

On the one hand, standardized and serialized electric spindle products are easy to form specialization and mass production, and can also shorten the development cycle of machine tools and adapt to the rapidly changing market trends.

Improve the performance and reliability of machine tools

The CNC machine tool with electric spindle structure simplifies the structure, reduces transmission and connection links, and improves the reliability of the machine tool; The mature technology, complete functions, excellent performance, and reliable quality of the electric spindle components make the performance of the machine tool more perfect and the reliability further improved.

Implement special requirements for some high-end CNC machine tools

Some high-end CNC machine tools, such as parallel motion machine tools, pentahedral machining centers, small hole and ultra small hole machining machines, require the use of electric spindles to meet complete functional requirements. To promote the widespread application of high-speed cutting technology in the field of mechanical processing, the electric spindle system is directly driven by a built-in motor, meeting the high-speed cutting requirements of "high speed, high precision, high reliability, and small vibration" of machine tools. Together with the high-speed feed system and high-speed tool system of machine tools, it is a necessary condition for high-speed cutting. The combination of electric spindle technology with motor frequency conversion, closed-loop vector control, AC servo control, and other technologies can meet the needs of metal cutting processes such as turning, milling, boring, drilling, and grinding.

4、 Application of high-speed electric spindle in robots

With the continuous development of computer technology towards intelligence, the continuous expansion and deepening of robot application fields, and the group application of robots in FMS and CIMS systems, industrial robots are also constantly developing towards intelligence to adapt to agile manufacturing and meet diverse and personalized needs. At present, industrial robots have been widely used in fields such as automobile and automotive parts manufacturing, mechanical processing industry, electronic and electrical industry, rubber and plastic industry, food industry, wood and furniture manufacturing, etc. In industrial production, industrial robots such as arc welding robots, spot welding robots, distribution robots, assembly robots, painting robots, and handling robots have been widely used.

The perfect combination of spindle and robotic arm is applied in cutting, deburring, drilling and polishing of alloy materials and SMC materials for car trunk, closely linking the spindle industry with industrial automation.

The front end of the spindle is installed on the chuck for milling drills. The high torque of the spindle can easily cut thick alloy plates, and the ventilation and sealing function solves the problem of a large amount of dust entering the spindle during the cutting process. During the cutting process, cutting fluid is often used to cool the tool, and the IP57 protection level completely avoids the concern of liquid entering the spindle. At the same time, the sealed air pressure cooling spindle is beneficial for long-term machining of the spindle.

The front end is extended by 40 millimeters, and the robotic arm can avoid tooling when rotating, making it convenient for cutting products; When used in conjunction with heat shrink cylinder clamps, it saves time for tool replacement and re alignment, improving work efficiency. The maximum power of the spindle reaches 5000 watts, with powerful power output and an expanded range of materials that can be processed. It weighs 3.5KG and is lightweight. It uses HSK clamps with high precision, and the maximum clamping range can reach 10mm. The cutting tools can be automatically replaced through ventilation, improving work efficiency.

5、 Summary of common faults in the spindle section

1. Fault phenomenon: Severe abnormal noise from the spindle; There is noise when the rotation speed is high; The temperature rise is relatively high.

Root cause analysis:

① The spindle bearings may be worn or damaged;

② The spindle may not be well lubricated, resulting in a lack of oil; Or the lubricating oil may be dirty or have impurities;

③ There may be dirt on the end face of the spacer ring;

④ The preload force of the main shaft bearing may be too large;

⑤ The position and tension of the belt may not be appropriate;

⑥ Dynamic balance difference of spindle components;

Solution:

① Replace the spindle bearings;

② Add appropriate spindle oil; Replace with new oil to ensure the cleanliness of the spindle;

③ After disassembling the spindle, clean the spacer ring;

④ Readjust the preload force;

⑤ Adjust the position and tension of the belt again;

⑥ Adjust the dynamic balance again;

2. Fault phenomenon: There is abnormal noise from the spindle, and it takes a lot of effort to rotate it by hand, with a noticeable sense of jamming.

Reason analysis: It may be due to the loosening of the bolts that lock the cylinder and hit the block, causing the block to loosen, resulting in no gap between the locking butterfly spring nut and the block, thus generating friction.

Solution: Tighten the loose nuts to ensure that the gap between them is appropriate.

3. Fault phenomenon: Large vibration during cutting process.

Root cause analysis:

① The main shaft bearings may become rough or damaged;

② The loosening of the bearing pre tightening nut causes the spindle to move;

③ Insufficient pre tightening force and excessive clearance of bearings;

④ Other factors;

Solution:

① Replace bearings;

② Tighten the nut to ensure the spindle accuracy is qualified;

③ Adjust the bearing clearance again, but the preload should not be too large;

④ Check the cutting tool or change the cutting parameters.

6、 Main categories and commonalities

1. Classification of electric spindles:

a、 Turning spindle; b、 Milling spindle; c、 Grinding spindle.

2. Common structural points:

The knife pulling mechanism includes (tension sensor, knife pulling sensor, knife loosening sensor, pull rod, claw, disc spring).

Lubrication mechanism (grease lubrication within 6000 rpm, oil mist lubrication within 20000 rpm, oil air lubrication above 20000 rpm).

Cooling mechanism (air-cooled, self cooled, oil cooled).

Functional mechanism, rotating unit (easy to jump and reduce impact).

Bearings (ceramic ball bearings, combination methods: front four, back one, front two, back two, front three, back one, etc., with a spacer ring between bearings, and the position of the bearings will give way to the bearings during assembly).

3. Structural differences:

Encoder (gear magnetic grid type), central outlet (OTT).