Application of VFD (Variable-frequency Drive) on CNC machine tool spindle

1 Introduction

Numerical control machine tool, referred to as numerical control machine tool (NC, Numerical Control), is a mechatronics product integrated with mechanical, electrical, hydraulic, pneumatic, microelectronics and information technologies in the past 30 years. It has the advantages of high precision, high efficiency, high automation and high flexibility. This article mainly introduces the advantages of Sunwoele HSF600 series VFD (Variable-frequency Drive) on CNC machine tools.

2 Introduction to CNC machine tools

The technical level of CNC machine tools and their percentages in the output and total ownership of metal cutting machine tools are one of the important indicators to measure a country's national economic development and the overall level of industrial manufacturing. CNC lathe is one of the main varieties of CNC machine tools. It occupies a very important position in CNC machine tools. It has been widely valued by countries all over the world for decades and has developed rapidly. The spindle is an important part of the lathe, which plays an important role in improving the processing efficiency, expanding the range of processing materials, and improving the processing quality. Most of the economical CNC lathes cannot change the speed automatically. When the speed needs to be changed, the machine tool can only be stopped, and then the speed can be changed manually. The main drive system of full-function CNC lathes mostly adopts stepless speed change. There are mainly two types of continuously variable transmission systems: servo spindle system and DC spindle system, and DC or AC spindle motors are generally used. Drive the main shaft to rotate through the belt drive, or drive the main shaft to rotate through the belt drive and the reduction gear in the headstock (to obtain greater torque). Due to the wide range of speed regulation of the spindle motor and the stepless speed regulation, the structure of the spindle box is greatly simplified.

3 Main parameters of CNC lathe and functional requirements for VFD (Variable-frequency Drive)

Main parameters and performance indicators:

(1) 3.0kW CNC lathe

Motor parameters:

Rated power: 3.0kW;

Rated frequency: 50Hz;

Rated voltage: 380V;

Rated current: 7.8A;

Rated speed: 970r/min;

Mechanical transmission ratio: 1:1.5;

Processing material: 45# steel;

Actual test performance indicators:

Spindle speed: 200r/min (VFD (Variable-frequency Drive) operating frequency around 15Hz) feed performance and speed.

(2) 5.5kW CNC lathe

Motor parameters: rated power: 5.5kW;

Rated frequency: 50Hz;

Rated voltage: 380V;

Rated current: 13A;

Rated speed: 1400r/min;

Mechanical transmission ratio: 1:1.5;

Processing material: 45# steel;

Actual test performance indicators:

Spindle speed: 200r/min (VFD (Variable-frequency Drive) operating frequency 9 ~ 10Hz);

Spindle speed: 450r/min (VFD (Variable-frequency Drive) operating frequency around 22Hz) feed performance and speed.

4 HSF600 series VFD (Variable-frequency Drive)

HSF600 series VFD (Variable-frequency Drive) adopts advanced magnetic flux control technology, the motor has large torque at low speed, high speed accuracy, reasonable price, complete functions, and has instantaneous power failure processing and speed tracking restart functions to ensure continuous operation of the system mechanism to ensure that the motor operates at the highest efficiency state, therefore, the use of HSF600 high-performance VFD (Variable-frequency Drive) to replace the spindle AC servo system is the best choice for the machine tool industry. As shown in Figure 1.

Figure 1 Schematic diagram of CNC system

(1) Introduction to the features of HSF600VFD (Variable-frequency Drive)

l Small size, belonging to miniature products, occupying less space in the control cabinet;

l The control method is sine wave SPWM, the control performance is greatly improved compared with the previous VF control method, especially in the low-speed torque to meet the needs of the machine tool spindle, and the starting torque can reach more than 100% at 5Hz;

l The carrier frequency range is 0~16kHz, which can reduce the electromagnetic noise of the motor;

l Provide standard 0~10V analog interface, which is compatible with most CNC system interfaces and has strong versatility;

l Strong overload capacity, more than 150% of the rated output current exceeds one minute;

l Provide multi-functional output terminal signals, such as abnormal signal, running signal, speed arrival signal, fault indication, to meet the system's monitoring of the spindle speed state;

l Automatic torque compensation to meet the processing needs of the machine tool spindle at low speed.

(2) Debugging environment, wiring and debugging methods

The motor selected by the customer is 3.0kW/50Hz/380V, the VFD (Variable-frequency Drive) model Sunwoele-HSF600-3R7-T3B is selected, and the braking resistor is 400W/150Ω, as shown in Figure 2.

Figure 2 Application of VFD (Variable-frequency Drive) on CNC machine tools

The VFD (Variable-frequency Drive) VS/GND terminal provides the analog speed of the CNC system, VS is connected to the positive signal of the analog interface of the CNC system, and GND is connected to the negative signal. The signal is a 0-10V analog voltage signal to control the spindle speed. S1/S2/COM is the forward/reverse signal terminal of VFD (Variable-frequency Drive). Usually, the CNC system sends a forward or reverse signal to drive the intermediate relay. The normally open contact of the intermediate relay is connected to the VFD ( Variable-frequency Drive) S1/S2/COM, so as to control the forward and reverse of VFD (Variable-frequency Drive). The parameters are set as follows:

l F005 and F006 are acceleration time and deceleration time, according to customer requirements, F001=5S, F002=1S;

l F030 and F031 are set according to the nameplate of the motor, F010=9A, F031=1;

l F012 upper limit operating frequency selection, corresponding to the output frequency of VFD (Variable-frequency Drive) when the analog signal is 10V input, since the speed is adjusted within the range of 0-2000rpm, after including the mechanical reduction ratio, this parameter needs to be set to 66.7 Hz;

l The F002 parameter is the setting of the running signal and frequency source, and it is set as the external terminal signal control (3).

(3) Debugging results

The spindle motor is driven by HSF600 high-performance VFD (Variable-frequency Drive), which meets the processing requirements and prolongs the service life of the tool. Due to the advanced magnetic flux algorithm, it can output 100% torque smoothly even at low speed (low frequency) to meet the processing needs of different parts, and can completely replace the traditional rolling shaft