Application Of VFD in CNC Machine Tools

The application advantages of conventional frequency converters in the CNC machine tool industry are closely centered around processing accuracy, production efficiency, equipment reliability, and intelligent requirements, offering significant technical advantages over traditional control solutions (such as relay control or fixed-speed motors). The following is a detailed analysis from core application scenarios and technical characteristics:

I. High-precision Speed Control to Ensure Processing Consistency

1. Stepless Speed Regulation and Wide-range Speed Adaptation

· Full-process coverage: Supports stepless adjustment from 0.1r/min to rated speed (e.g., 0–15,000r/min), meeting the differentiated needs of rough machining (high-speed cutting for material removal) and finish machining (low-speed precision grinding). For example:

· During milling of automotive engine cylinder blocks, the spindle speed can be real-time adjusted from 10,000r/min to 3,000r/min according to tool wear, ensuring surface roughness Ra < 1.6μm.

· Speed stability advantage: When using vector control technology , speed fluctuation can be controlled within ±0.5% of the rated speed, which is 2–10 times more precise than traditional V/f control (±1%–±5%), avoiding workpiece dimension errors caused by speed fluctuations (e.g., shaft diameter error < 0.01mm).

2. Dynamic Load Response and Torque Compensation

· Instantaneous torque adjustment: When the cutting load suddenly changes (e.g., tool 切入 cast iron workpiece), the frequency converter can increase output torque within 50–100ms (e.g., Siemens G120 series torque response < 80ms), preventing tool edge chipping or workpiece vibration due to insufficient torque.

· Low-speed high-torque characteristics: At 10% of the rated speed (e.g., 1,000r/min), conventional frequency converters can output 120%–150% of the rated torque, adapting to heavy-duty cutting of difficult-to-machine materials like titanium alloys and hardened steels.

II. Energy Saving and Efficiency Optimization in Variable Load Scenarios

1. Energy-saving Logic of On-demand Speed Regulation

· Energy consumption pain points of traditional modes: During empty strokes (e.g., tool changing, table moving) of CNC milling machines, fixed-speed motors still consume 30%–50% of the rated power. Taking an 11kW spindle motor as an example, 8 hours of daily no-load operation will waste 20–30kWh of electricity.

· Frequency conversion energy-saving strategies:

· No-load speed reduction: When no cutting load is detected, the speed is automatically reduced to 30%–40% of the rated value, with an energy-saving rate of 50%–60%;

· Load-linked speed regulation: The speed is real-time adjusted through current sensors. For example, when the cutting depth increases from 0.5mm to 2mm, the spindle speed decreases from 6,000r/min to 3,000r/min while increasing torque, with comprehensive energy saving of 10%–25% (based on FANUC 0i-TF system data).

2. Regenerative Energy Recycling

· Brake energy reuse: When the feed axis decelerates after rapid positioning, the motor switches to generating state, and the frequency converter stores the regenerative power in the DC bus or converts it into heat through a braking unit (some high-end models can feed back to the grid). For example, a three-axis machining center can recover 3–5kWh of energy daily, accounting for 5%–8% of total power consumption.

III. Soft Start/Stop and System Protection to Extend Equipment Life

1. Reducing Electrical and Mechanical Impacts

· Soft start characteristics: Starting current is controlled within 2–3 times the rated value (traditional direct start is 5–7 times), reducing grid voltage fluctuations and motor winding heating. When a 22kW spindle motor uses frequency conversion start, the starting current can be reduced from 400–600A to 150–200A, extending motor life by 20%–30%.

· Smooth stop control: Avoids processing defects caused by sudden stops (e.g., in thread cutting, the frequency converter decelerates to 0 with a slope of 0.5–1s to ensure complete thread profile).

2. Multi-level Fault Protection Mechanisms

· Built-in protection functions: Including overcurrent (trip within 1 minute at 150% rated current), overvoltage (grid surge protection), overheating (power module temperature alarm), phase loss protection, etc. For example, when a tool is stuck, the frequency converter detects sudden current increase and stops within 0.1s to prevent spindle bearing burnout.

IV. Standardized Communication and System Integration Capability

1. Seamless Collaboration with CNC Systems

· Support for mainstream industrial buses: Communicates with CNC systems via protocols like Modbus, CANopen, EtherNet/IP , with data update cycles ≤1ms, ensuring speed synchronization during multi-axis linkage (e.g., speed deviation of each axis <0.1% in four-axis machining).

· Direct control by PLC programs: Can receive speed commands from CNC programs (e.g., G-code M03 S2000), real-time adjusting spindle speed without additional hardware interfaces.

2. Digital Operation and Maintenance Monitoring

· Real-time parameter visualization: Data such as motor current, speed, and temperature can be displayed on the CNC panel (e.g., FANUC iHMI), with intuitive fault codes (e.g., E001 overcurrent) prompting, shortening fault troubleshooting time by over 50%.

· Basic status monitoring: Some frequency converters support running time counting and motor overload frequency statistics, assisting in formulating maintenance plans (e.g., scheduling lubrication in advance based on bearing running time).

V. Adaptation to Typical Processing Technology Requirements

1. Stable Control of Medium-low Speed Spindles

· Adaptation to conventional speed ranges: Suitable for spindles below 10,000r/min (e.g., lathes, drilling machines), ensuring processing accuracy in scenarios like gear machining and thread cutting. For example, when a hobbing machine processes a gear with a module of 2mm, the frequency converter controls spindle speed fluctuation within ±5r/min, ensuring tooth profile error <0.02mm.

2. Simple Multi-axis Linkage Scenarios

· Economical multi-axis control: In three-axis machining centers (e.g., vertical milling), frequency converters can synchronously control spindle and feed axis speeds, meeting conventional process needs such as plane contour and hole system machining, with costs 30%–50% lower than servo systems.

VI. Comparison with Traditional Solutions/Servo Systems

Comparison Dimension	Traditional Relay Control	Conventional Frequency Converter	Servo System
Speed Control Accuracy	Step adjustment, error >5%	Stepless speed regulation, error <0.5%	Error <0.01%, higher precision
Dynamic Response	Response time >200ms	Response time <100ms	Response time <20ms, suitable for high-speed dynamic scenarios
Energy Consumption	Fixed-speed operation, no energy saving	Energy-saving rate 10%–25%	Energy-saving rate 25%–40%, more efficient regenerative energy recovery
Cost	Low (simple hardware)	Medium (higher than relays, lower than servos)	High (suitable for high-end scenarios)
Applicable Scenarios	Rough machining, simple cutting	Conventional precision machining (e.g., automotive parts)	Precision machining (aerospace, molds)

Conclusion

In the CNC machine tool industry, conventional frequency converters cover over 80% of conventional machining scenarios with the advantage of "priority on cost-performance ratio". Their core value lies in: improving processing qualification rate through precise speed control (defect rate reduced by 15%–20%), achieving energy consumption optimization through on-demand speed regulation (electricity cost saved by 10%–25%), and simplifying equipment maintenance through standardized integration (maintenance cost reduced by 30%). Although servo systems are required for ultra-high-speed and ultra-precision scenarios, conventional frequency converters remain the mainstream choice for equipment such as CNC lathes and ordinary machining centers, especially suitable for small and medium-sized enterprises to balance cost and performance needs. With the advancement of Industry 4.0, their integration with edge computing and simple AI algorithms (such as automatic speed optimization based on load) will further expand their application boundaries.

This equipment is composed of a frequency converter, a water pump motor, a PID controller and a pressure sensor. The built-in PID regulation function can adjust the frequency in real time to maintain a constant pressure in the pipeline network. Its energy-saving principle is based on the cube proportional relationship between the shaft power of the water pump and its rotational speed. By reducing the power supply frequency, it significantly reduces energy consumption, and the measured power-saving rate reaches 20% to 60%. It is equipped with a soft start-stop function to eliminate the water hammer effect and extend the service life of the equipment. At the same time, it supports time-segmented pressure timing control and unattended operation mode, and integrates automated management and multiple safety protection mechanisms.

 Excellent energy-saving effect: 

  

Under VFD drive, as the motor power factor improves, the operating current decreases, thereby reducing equipment power consumption and saving operating costs.