The status quo of numerical control transformation of machine tools in China

Abstract CNC machine tools are widely used in the manufacturing industry due to their high precision and productivity, which significantly improves product quality and output. As a result, the demand for CNC technology continues to grow. Purchasing new CNC machines is one way to enhance numerical control efficiency, but retrofitting existing machines is also a viable and cost-effective option. CNC machine tool transformation not only reduces costs but also allows companies to modernize their equipment without fully replacing it. In recent years, with the increasing need for various types of machine tools in China, the CNC transformation industry has developed rapidly. Most projects focus on upgrading old CNC machines, while some involve converting traditional machines into CNC systems. Below are key considerations during the CNC transformation process.

I. Cost-Effective Analysis of CNC Machine Tool Retrofit and Replacement

Before deciding to retrofit an old machine, it’s essential to compare the price of new CNC machines with similar performance. Delivery time should also be considered. For small CNC lathes or milling machines that aren’t expensive, it may be more efficient to purchase new models rather than retrofit old ones, as the cost difference is minimal and the transformation process can take up to two months. Many manufacturers keep these models in stock. However, for large, high-cost machines, retrofitting is often a better choice, saving money and reducing acquisition time. For example, a 2000 × 1800 mm work surface, three-axis linkage, 60-tool horizontal machining center could benefit significantly from such an upgrade.

II. Current Condition of the Machine to Be Retrofitted

Not all old machine tools are suitable for CNC conversion. A thorough assessment of the machine’s condition is necessary before proceeding. The mechanical system must be in good working order, as this is the foundation for a successful transformation. If the machine has serious mechanical issues, such as design flaws or manufacturing defects, the retrofit may not provide significant benefits. Before starting the transformation, it’s important to test the machine’s mechanical accuracy and repair any problems found.

The electrical system of the old machine is another critical factor, especially if components have aged or failed. Understanding the original CNC system model, number of control axes, spindle configuration, motor power, and drive setup is essential. Additionally, checking the completeness of technical documentation—such as electrical diagrams, PLC programs, maintenance manuals, hydraulic and pneumatic schematics, and mechanical assembly drawings—is crucial. These documents help speed up the transformation process. However, it's important to verify that the data matches the actual machine, as some manufacturers may provide generic drawings that don't reflect individual modifications.

III. Determination of the CNC Transformation Plan

Based on the machine’s condition and user requirements, a comprehensive transformation plan should be developed.

1. CNC System Upgrade Plan

The first step in the transformation is upgrading the CNC system. The choice depends on the current control level, the complexity of the workpieces being processed, and the company’s budget. It’s advisable to select systems from mainstream manufacturers, such as FANUC or Siemens for foreign options, and Huazhong or Kanedi for domestic alternatives. Compatibility with existing CNC systems used by the company is also important, as it simplifies maintenance and reduces spare parts inventory. The selected system should be practical, avoiding unnecessary expenses on overly advanced features.

2. Spindle Servo System Upgrade Plan

Older CNC machines often use DC or AC analog servo systems. Depending on the application, the original drive unit and motor can be replaced with an AC digital servo system, or an inverter can be used instead. If the original system is still in good condition, it can be retained. Similarly, a well-functioning DC motor can be kept, and the old drive unit can be replaced with a new DC servo controller.

3. Feed Servo System Upgrade Plan

Similar to the spindle system, the feed system can either be upgraded to an AC digital servo or retain the original setup if it’s still functional. This decision depends on the machine’s needs and the available budget.

4. Closed-Loop Control and Sensor Upgrade Plan

For older machines using inductive synchronizers or circular gratings, these can be replaced with digital encoders or grating rulers. When selecting the type, ensure compatibility between the detection component and the new system, whether it uses square wave or voltage signals. If the original current signal is retained, it must be converted to a voltage signal to match the new system, as most modern CNC systems do not support current signals.