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How much do you know about the principle of CNC machine tools?

  1. The emergence of CNC machine tools

With the development of science and technology, society’s demand for product diversification is becoming stronger and stronger, which requires the cycle of product replacement to be shorter and shorter, making the proportion of multi-variety and small-batch production significantly increased. At the same time, with the continuous improvement of product performance requirements in aerospace, shipbuilding, military industry, automobile, agricultural machinery and other industries, there are more and more complex parts in the products, and the processing quality requirements are also constantly improving. The use of traditional ordinary processing equipment has been difficult to adapt to this diversification, flexibility and high efficiency and high quality requirements of complex shape parts. To solve the above problems. A high-precision, high-efficiency “flexible” automated production equipment-CNC machine tools came into being.

  1. The composition of CNC machine tools

CNC machine tools are typical mechatronics products. They are modern mechanical processing equipment with high efficiency, high precision, high flexibility and high automation that integrates modern mechanical manufacturing technology, automatic control technology, detection technology, and computer information technology. Like other mechatronics products, it is also composed of a mechanical body, a power source, an electronic control unit, a detection sensor part and an execution machine. Servo system, composition.

(1) Mechanical body
It is the body of the CNC machine tool and is the mechanical part used for various cutting processes.

(2) Power source
It is the part that provides power for the CNC machine tool, mainly using electricity.

(3) Electronic control unit
Its core is the computer numerical control, referred to as the CNC device. It decodes, calculates and logically processes the various digital information received, generates various command information and outputs it to the servo system, so that the machine tool can operate according to the specified operation. This part also includes corresponding peripheral equipment, such as displays, printers, etc.

(4) Detection sensor part
It mainly detects the linear displacement of the worktable and the angular displacement of the rotary table. The detection results are sent to the computer, or used for position display or feedback control.

(5) Actuator, servo system
It is used to drive the displacement components on the machine tool to make corresponding movements and control their positioning accuracy. For example, the tool movement of many CNC machine tools is completed by using servo motors to drive ball screws.

  1. Classification of CNC machine tools

(1) Classification by process use of CNC machine tools

1) General CNC machine tools. It is a variety of CNC machine tools with similar process feasibility to ordinary machine tools. Its types are the same as ordinary machine tools (such as CNC lathes, CNC milling machines, CNC grinders, CNC drilling machines, etc.)

2) Machining centers are CNC machine tools with reverse storage and automatic tool changing devices.

3) Special CNC machine tools are special processing machine tools equipped with CNC devices (such as CNC wire cutting machines, CNC laser processing machines, etc.)

(2) Classification by the motion trajectory of CNC machine tools

1) Point control CNC machine tools. Its CNC device only controls the movement of the machine tool moving parts from one position point to another, but does not control the motion trajectory between points. The tool does not perform cutting processing during the movement process. (Such as CNC drilling machines, CNC punching machines, etc.)

2) Linear control CNC machine tools. In addition to controlling the accurate position of the starting and end points of the machine tool moving parts, its CNC device also controls the moving parts to perform linear cutting processing at an appropriate speed along the direction parallel to the machine tool coordinate axis or in a direction 450 degrees to the machine tool coordinate axis. (Such as simple CNC lathes, simple CNC grinders, etc.)

3) Contour control CNC machine tools. Its CNC device can simultaneously control two or more coordinates in linkage, thereby realizing the processing of curved contours and surfaces. (Such as CNC milling machines and CNC lathes with linkage of more than two coordinates)

(3) Classification by servo system control method

1) Open-loop control system.

2) Semi-closed-loop control system.

3) Closed-loop control system.

(4) Classification by the number of controlled coordinate axes

1) Two-coordinate CNC machine tools, which refer to machine tools that can simultaneously control two coordinate axes to process curved contour parts (such as CNC lathes)

2) Three-coordinate CNC machine tools, which refer to CNC machine tools that can control three coordinate axes in a linked manner, and can be used to process less complex spatial surfaces (such as three-coordinate CNC milling machines)

3) Two and a half coordinate CNC machine tools (such as economical CNC milling machines)

4) Multi-coordinate CNC machine tools, which have complex machine tool structures, high control accuracy, and complex processing procedures. They are mainly used to process parts with complex shapes (such as non-coordinate CNC milling machines)

  1. Processing characteristics of CNC machine tools

(1) Strong applicability to part processing
Different parts can be processed by changing the processing program, which is particularly suitable for the current characteristics of multiple varieties, small batches, and fast product updates.

(2) High degree of automation
Generally speaking, except for loading and unloading workpieces, most other processing processes are completed automatically by the machine tool, which greatly reduces the labor intensity of workers.

(3) Stable processing quality
During the processing, the machine tool works under the specified control instructions from beginning to end, eliminating the influence of the operator’s technical level and emotional changes on the processing quality, so the processing quality is stable and the size consistency of a batch of parts is good.

(4) High productivity
The spindle speed and feed rate of CNC machine tools have a wide range, allowing the machine tool to perform powerful cutting of large cuts. In addition, in the machining center. Due to the use of tool magazine. It can realize continuous processing of multiple processes on one machine tool, greatly reducing the processing time and auxiliary time of parts, so the productivity is high.

(5) Conducive to the modernization of production management
CNC machine tools use digital signals and standard codes as control information, which is easy to realize the standardization of processing information. At present, it has been organically combined with computer-aided design and manufacturing CNC/CAM, and is the foundation of modern integrated manufacturing technology.

  1. Basic working principle of CNC machine tools

When processing parts on ordinary machine tools, the operator constantly changes the relative motion trajectory between the tool and the workpiece according to the requirements of the part drawing. The required parts are processed by the tool cutting. When processing parts on CNC machine tools. The processing sequence of the processed parts, process parameters and machine tool motion requirements are compiled into a processing program in numerical control language, and then input into the CNC device. After the CNC device performs a series of processing on the processing program, it sends an execution instruction to the servo system, which drives the moving parts of the machine tool to move, thereby automatically completing the processing of the parts.

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