The numerical control (NC) system is the core component of a machine tool. When choosing an NC system, it's essential to evaluate its performance, cost-effectiveness, and after-sales support comprehensively. Hardware Machine Tool Network Jinjitong recommends using well-known brands for better reliability and service. The selection of the CNC system should be based on the machine’s structure, performance, and the required accuracy of the parts being machined. As one of the largest countries in terms of machine tool production, China has recognized the importance of improving the CNC rate of its machines. A smart strategy is to retrofit traditional machine tools with CNC systems. Countries like Germany, the U.S., and Japan have long emphasized the modernization of old equipment and have developed comprehensive systems that integrate research, production, and application. With continuous technological advancements, machine tool transformation remains a key topic. China should promote this approach more widely and develop a CNC transformation path that fits its national conditions.
First, the significance of CNC machine tool retrofitting:
1. **Cost-effective**: Compared to buying new machines, retrofitting can save between 60% to 80% of the cost, especially for large or special equipment. In many cases, the cost of upgrading an existing machine is only one-third of purchasing a new one. Even when completely overhauling the original structure, it still costs about 60% of the price of a new machine, while making full use of the existing infrastructure.
2. **Stable and reliable performance**: Since the basic components of the original machine are aged, they rarely experience stress deformation, ensuring consistent accuracy over time.
3. **Improved productivity**: After CNC retrofitting, automation can be achieved, increasing efficiency by 3 to 7 times compared to traditional machines. For complex parts, the higher the difficulty, the greater the efficiency gain. Additionally, fewer fixtures are needed, reducing both cost and production preparation time.
Second, the CNC transformation plan:
1. **Choosing the right CNC system**: The CNC system is the heart of the machine. It must be selected based on performance, economy, and maintenance. Jinjitong advises choosing reputable brands. The system should match the machine’s needs without unnecessary features to avoid waste and reduce failure risks. There are three main types: open-loop systems using stepping motors, closed-loop systems with asynchronous or DC motors and grating feedback, and semi-closed loop systems using AC/DC servo motors with encoder feedback. Open-loop systems are simple, low-cost, and ideal for small and medium-sized machines. Closed-loop systems offer high precision but are more complex and expensive. Semi-closed loop systems provide a balance between cost and precision, suitable for larger machines requiring high control accuracy.
2. **Mechanical part modifications**: After retrofitting, the machine should achieve high static and dynamic stiffness. This includes minimizing friction, ensuring no transmission gaps, and improving ease of operation and maintenance. For CNC lathes, the guide rails should have good friction resistance and low friction. Bonding Teflon soft belts on the original rails helps prevent crawling and improves rail life. Ball screws are preferred for their high efficiency, precision, and long lifespan, while sliding screws may not meet high-precision requirements. Gear pairs must be precise and gapless, with either flexible or rigid adjustment methods used to eliminate backlash.
Third, an example of CNC retrofitting:
Take an economical CNC lathe as an example. The digital control system should include linear and circular interpolation, thread cutting, tool compensation, and other functions. Domestic systems like Huazhong and Guangzhou CNC are cost-effective and user-friendly. Ball screw modification is optional if the original machine doesn’t require high precision. Stepper motors are used to drive the lead screw through gears or timing belts, replacing the original mechanical transmission. Automatic tool holders replace manual ones, improving efficiency. Photoelectric encoders ensure synchronization between the spindle and feed movement during threading. Guide rails can be modified with Teflon belts or replaced with rolling guides. Spindle speed control can be upgraded with frequency converters for automatic variable speed. If automation level is low, the original spindle mechanism can remain unchanged to reduce costs.
CNC retrofitting is a practical and effective way to modernize machine tools, offering significant economic and technical benefits.
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