Fault Maintenance of Spindle Drive System of CNC Machine Tool

The spindle drive system of the CNC machine tool is also the main transmission system. Its performance directly determines the surface quality of the workpiece. It has a complex structure, mechanical, electrical, and pneumatic linkages, and has a high failure rate. Its reliability will directly affect the CNC machine tool. safety and productivity. Therefore, in the repair and maintenance of CNC machine tools, the spindle drive system is very important. According to the maintenance order, the maintenance personnel go to the site to conduct fault inquiry and investigation, determine the maintenance plan, draw up the maintenance work plan, plan the working hours and costs; check the relevant display interface and circuit schematic diagram of the PLC of the CNC machine tool, the CNC system and the instruction manual of the inverter, etc. Data, analyze the cause of the failure; use general tools and multimeters to detect and judge the location of the failure, quickly troubleshoot the machine tool site, fill in the maintenance record and hand it over for acceptance.
Knowledge about the spindle
The CNC machine tool spindle drive system is a high-power actuator of the CNC machine tool, and its function is to accept the S-code speed command and the M-code auxiliary function command of the CNC system (CNC) , to drive the spindle for cutting. It includes a main shaft driving device, a main shaft motor, a main shaft position detection device, a transmission mechanism and a main shaft. Usually, the spindle drives the workpiece to be processed to rotate, and the corresponding machine tool is a lathe; the spindle drives the cutting tool to rotate, which is milling, and the corresponding machine tool is a milling machine.
Spindle system classification and characteristics
Most of the main drive systems of full-function CNC machine tools adopt stepless speed change. At present, the continuously variable speed system mainly includes frequency conversion spindle system and servo spindle system according to different control methods. Generally, DC or AC spindle motor is used to drive the spindle to rotate through belt transmission, or through belt transmission and reduction gear in the spindle box ( to obtain greater torque) to drive the spindle to rotate. In addition, according to the difference of the spindle speed control signal, it can be divided into two types: the spindle drive device controlled by analog quantity and the spindle drive device controlled by serial number. The spindle drive device controlled by analog quantity adopts frequency converter to realize the control of the spindle motor, and there are two forms: general frequency converter to control general motor and special frequency converter to control special motor. At present, most economical machine tools adopt the form of CNC system analog output + frequency converter + induction (asynchronous) motor, which is very cost-effective. At this time, the analog spindle can also be called a variable frequency spindle. Serial spindle drive devices are generally developed and produced by various CNC companies, such as the 611 series of Siemens and the α series of Fanuc Corporation of Japan.
1. Ordinary cage-type asynchronous motor with gear gearbox
This is the most economical way to configure the main shaft, but it can only achieve step-by-step speed regulation, because the motor always works at At the rated speed, after being decelerated by the gear, the output torque is large at the low speed of the spindle, and the heavy cutting ability is strong, which is very suitable forMeet the requirements of rough machining and semi-finishing. If the processed product is relatively single and there is no high requirement on the spindle speed, it can also play a very good effect when configured on a CNC machine tool; its disadvantage is that the noise is relatively large, and the spindle speed range is not large because the motor works at power frequency. , not suitable for non-ferrous metals and processing occasions that require frequent changes in spindle speed.
2. Ordinary cage-type asynchronous motor with simple frequency converter
can realize the stepless speed regulation of the spindle. Torque output, otherwise, especially lathes are prone to stalling. Generally, two-speed gears or belts are used to change speed, but the spindle can still only work in the medium and high speed range. In addition, due to the limitation of the maximum speed of ordinary motors, the speed of The range is more limited.
This scheme is suitable for occasions that require stepless speed regulation but do not require low speed and high speed, such as CNC drilling and milling machines. There are many simple frequency converters produced in China.
3. Through-cage asynchronous motor with general-purpose frequency converter
In addition to the U/f curve adjustment, the current imported general-purpose frequency converter also has the function of vector control without feedback, which will The low-speed characteristics of the motor have been improved, and with the two-stage gear transmission, it can basically meet the processing of low-speed lathes (100-200 rpm) with small machining allowances, but it is also limited by the maximum motor speed. This is the most commonly used spindle drive system for economical CNC machine tools.
4. Dedicated frequency conversion motor with general frequency converter
Generally, vector control with feedback is adopted, which can have large torque output at low speed or even zero speed, and some have orientation or even indexing The feed function is a very competitive product. Take Xianma YPNC series frequency conversion motor as an example, voltage: three-phase 200V, 220V, 380V, 400V optional; output power: 1.5-18.5KW; frequency conversion range 2-200Hz; (maximum speed r/min); 30min150% overload capacity ;Support V/f control, V/f+PG (encoder) control, vector control without PG, vector control with PG. The manufacturers that provide general-purpose inverters are mainly foreign companies, such as: Siemens, Yaskawa, Fuji, Mitsubishi, Hitachi, etc.
Mid-range CNC machine tools mainly adopt this scheme. The two-speed shifting of the spindle drive or even only one gear can realize the gravity cutting of turning and milling at a speed of about 100-200r/min. Some directional functions can also be applied to CNC boring and milling machines that require fine boring processing. If applied to machining centers, it is not ideal. Other auxiliary mechanisms must be used to complete the function of directional tool change, and rigid tapping cannot be achieved. Require.
The machine tool with electric spindle is mainly used for finishing and high-speed processingworkers, such as high-speed precision machining centers. In addition, it is widely used in engraving machines and non-ferrous metal and non-metallic material processing machine tools. Because these machine tools only require high spindle speed, spindle drives are often not used.
As far as electrical control is concerned, the control of the machine tool spindle is different from the machine tool servo axis. In general, the control system of the machine tool spindle is a speed control system, while the control system of the machine tool servo axis is a position control system. In other words, the spindle encoder is generally not used for position feedback (nor for speed feedback), but only used as a speed measurement component. The data obtained from the spindle encoder generally has two purposes, One is used to display the spindle speed; the other is used for the occasion where the spindle and the servo axis work together (such as thread cutting, constant line speed processing, G95 rotation feed, etc.).

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