How to choose a CNC machine tool?

Three aspects can be considered when purchasing CNC machine tools

The first is whether the machine tool body can meet its own processing requirements and the quality of the machine tool.

The second is the numerical control system. There are many types of numerical control systems. Choosing the right system is the key to purchasing CNC machine tools.

The last is the drive unit, which is also the key to machine tool control. Different drive units can achieve different machining accuracy. When choosing a drive unit, choose a suitable drive unit according to the accuracy requirements of the workpiece to be processed.

The CNC system is the control center of the CNC machine tool and is known as the "brain" of the machine tool. The machine tool equipped with the CNC system greatly improves the accuracy, speed and efficiency of parts processing.

The function of the CNC system is undoubtedly an important restrictive factor for the design and selection of CNC machine tools. The following important factors must be considered in the selection of a CNC system:

1. Driving ability

2. Fully closed loop demand and dual drive demand

Three and five-axis control requirements

Fourth, RTCP, the choice will be relatively large. At the same time, the numerical control system suppliers that may be involved in the five-axis function must also carefully consider the export license, after-sales service, and so on.

The following analysis from the CNC system

Selection of CNC system

The CNC system is the "brain" of the CNC machine tool, which operates and processes the control information of the machine tool. According to the principle of numerical control system, it can be divided into two categories: economical numerical control system and standard numerical control system.

Economical CNC system From the point of view of control method, economical CNC system generally refers to an open-loop CNC system. It has the advantages of simple structure, low cost, convenient maintenance and debugging, and low operation and maintenance costs. However, it is affected by the torque-frequency characteristics and accuracy of the stepping motor. The feed speed and torque are mutually restricted, and the improvement of performance is limited. Economical CNC systems are often used in CNC wire cutting and some economical CNC lathes and milling machines that do not require high speed and accuracy. They are also widely used in the CNC transformation of ordinary machine tools. The open-loop numerical control system is the index control system itself without a position detection device. The numerical control system sends out a certain number and frequency of command pulses, and the drive unit performs machine tool positioning. Under the influence of external factors in the open-loop system, the machine tool does not move or does not move properly, but the system has reached the designated position when the machine tool has reached the specified position, and the machining accuracy of the machine tool will be greatly reduced. However, because of its simple structure, rapid response, stable and reliable work, convenient debugging and maintenance, and very low price, it still has the largest market in China so far.

Standard CNC system

Standard CNC systems include semi-closed-loop CNC systems and fully-closed-loop CNC systems.

Semi-closed-loop CNC system generally refers to the feedback of the position signal (photoelectric encoder) of the machine tool's servo motor to the CNC system. The system can automatically perform position detection and error comparison, and can compensate for some errors. Therefore, its control accuracy is better than that of an open-loop CNC system. It is higher, but lower than the fully closed-loop CNC system.

In addition to the position feedback of the servo motor of the machine tool, the fully closed-loop numerical control system also feedbacks the position signal of the position detection device of the machine tool table (usually with a grating ruler) to the system, thereby forming all position follow-up control. The system is in the process of processing. Automatic detection and compensation of all position errors.

The processing accuracy of the fully closed-loop CNC system is the highest, but the debugging and maintenance of this system is extremely difficult, and the price of the system is very high, which is only suitable for medium and high-end CNC machine tools.

Because the price of an open-loop control system is much lower than that of a closed-loop control system, when choosing a numerical control system, consider the proportion of the numerical control system to the price of the entire CNC machine tool. Then, according to the configuration of the machine tool and the requirements of the machine itself, , The low-end machine tool adopts an open-loop control system, and the middle and high-end machine tool adopts a closed-loop control system.