Classification of CNC Machines

In addition to being widely used in various types of machine tools, CNC technology is also applied to the motion control of various mechanical devices. Due to the development of control systems and sensing elements, the intelligence level of machine tools has been increasing, and the range of processes has also been expanding. From the perspective of control principles and main performance, the following classification can be made.

1. Classification by process purpose

According to the process characteristics, it can be divided into general CNC machine tools and machining centers.

General CNC machine tools include CNC lathes, CNC boring and milling machines, CNC grinders, CNC gear processing machines, CNC pressure processing machines, and CNC electrical processing machines, etc.

A machining center is a CNC machine tool with a tool magazine and an automatic tool changer. On the machine tool, different process operations can be realized, and it can usually complete drilling, reaming, broaching, tapping, boring, milling, etc. for multiple process operations. To expand the processing range and reduce auxiliary time, some machining centers can also automatically replace the worktable, tool magazine, and spindle. The turning-milling center is developed from CNC lathes and has turning and milling functions.

2. Classification by processing route

(1) Point position control CNC machine tools

These only require the positioning accuracy of the moving parts from one point to another.The route of their movement is not required.

(2) Contour processing CNC machine tools.

The CNC system of this type of machine tool can simultaneously control multiple coordinate axes to perform combined actions and process the contours of different shapes of workpieces.

3. Classification by the presence or absence of detection devices

It can be divided into open-loop, full-closed-loop, and semi-closed-loop control systems of CNC machine tools.

(1) CNC machine tools with open-loop control have no position detection devices, so the processing accuracy is relatively low. They are usually driven by stepper motors. This system is simple in result, inexpensive, and is used in CNC milling machines with low precision requirements.

(2) CNC machine tools with full-closed-loop control have position detection devices installed on the machine tool and the moving parts. They can detect the accurate position of the coordinate movement and feed it back to the computer. Therefore, CNC machine tools with full-closed-loop systems have high processing accuracy.

(3) CNC machine tools with semi-closed-loop control also have position detection device components. The difference from CNC machine tools with full-closed-loop control is that the detection element is disc-shaped and installed at the tail of the servo motor. The position of the coordinate movement is detected by measuring the motor angle. Due to the transmission components between the motor and the worktable having gaps, elastic deformation, and thermal deformation, the detected data has errors compared to the actual coordinate values. However, due to the advantages of semi-closed-loop CNC systems, such as relatively low price, simple structure, convenient installation and debugging, and less susceptibility to damage to the detection element, they are mostly used in CNC machine tools with relatively low precision requirements.

4. Classification by the number of coordinated coordinate axes

There are two-axis, three-axis, four-axis, and five-axis coordinated CNC machine tools, etc. The different number of coordinated coordinate axes makes a significant difference in the processing capabilities of the machine tools. For example, a boring and milling machine with only two coordinate axes coordinated can only process planar curved surface. If it can be three-coordinate axes coordinated, it can process three-dimensional space curved surfaces. When processing multi-dimensional curved surfaces, to ensure that the tool can cut reasonably, the centerline of the tool rotation also needs to rotate. Therefore, more coordinate axes need to be coordinated. The boring and milling machine with five-axis coordination can process the surface of a helical propeller. When understanding the number of coordinated coordinate axes, it is necessary to examine the functions of the control software, the number of coordinate axes the machine tool has, and the number of servo motors it has. The number of coordinated coordinate axes refers to the number of moving coordinate axes controlled by the same interpolation program. The movement rules of these coordinate axes are determined by the processed contour surface.