CNC lathes have entered the market since the early 1970s. So far, through the unremitting efforts of major machine tool manufacturers, through measures such as cooperation with foreign well-known machine tool manufacturers, joint ventures, technology introduction, prototype digestion and absorption, China’s machine tool manufacturing level has become Greatly improved, its output occupies a large proportion in metal cutting machine tools. At present, the varieties and specifications of domestic CNC lathes are relatively complete, and the quality is basically stable and reliable. It has entered the stage of practical and comprehensive development.
1) Lathe
According to the relative position of the rail surface of the bed and the horizontal plane, there are 5 layout forms of the bed. Generally speaking, the small and medium-sized CNC lathes mostly use inclined beds and inclined bed slides. Only large CNC lathes or small precision CNC lathes use flat beds, but few vertical beds. The flat bed has good manufacturability and is easy to manufacture. Because the tool post is placed horizontally, it is good for improving the motion accuracy of the tool post, but it is difficult to evacuate chips; the horizontal slide of the tool post is longer, which increases the width of the machine tool and affects the appearance. The oblique sliding plate structure of the flat bed body is equipped with an inclined guide rail cover, so that the advantages of the flat bed body with good manufacturability are maintained, and the width of the bed body is not too large.
The structure of CNC lathe and oblique sliding board body is widely used in modern CNC lathe, because this layout has the following characteristics:
- ①The machine tool is neat and beautiful in appearance, and covers a small area;
- ②Easy to realize mechanical and electrical integration;
- ③ The hot chips cut from the workpiece will not accumulate on the guide rail and affect the accuracy of the guide rail;
- ④ Easy chip removal and installation of automatic chip removal device;
- ⑤Easy to install closed protective device;
- ⑥ It is pleasant and easy to operate; ☆ It is convenient to install the manipulator and realize the stand-alone automation.
2) Guide rail
The guide rail of CNC lathe can be divided into two kinds of sliding guide rail and rolling guide rail. The sliding guide rail has the advantages of simple structure, convenient manufacturing, and large contact rigidity. However, the traditional sliding guide has high friction resistance, fast wear, and a large difference between the dynamic and static friction coefficients. It is easy to produce crawling at low speed. At present, CNC lathes no longer use traditional sliding guides, but use sliding guides with wear-resistant adhesive tape and a new type of plastic sliding guides. They have the characteristics of good friction performance and long service life. The advantage of the rolling guide is that the friction coefficient is small, the dynamic and static friction coefficients are very close, and there will be no creeping phenomenon. Grease lubrication can be used. According to different rolling elements, rolling guides can be divided into ball linear guides and roller linear guides. The latter has higher bearing capacity and stiffness than the former, but the coefficient of friction is slightly larger.
3) Tool holder system
According to the different tool change methods, the tool holder system of CNC lathes mainly includes rotary tool holder, row tool holder and automatic tool changer with tool magazine. The row type tool holder is generally used for small-sized CNC lathes, mainly for processing bar stock or disc parts. Rotary tool post is the most commonly used tool change tool post for CNC lathes. It can realize the automatic tool change action of the machine tool through the rotary indexing of the tool post. frame. According to the relative position of the rotary axis of the knife holder and the bottom surface of the installation, the rotary knife holder is divided into two types: a vertical knife holder and a horizontal knife holder. The row-type tool holder and the rotary tool holder have a certain limit on the number of tools. When a large number of tools are needed, an automatic tool changer with a tool magazine should be used.
4) Spindle drive system
The main transmission system of CNC lathe can be divided into graded variable speed transmission and continuously variable transmission. Hierarchical variable speed transmission is a uniformly and discretely distributed limited number of speeds in a certain range, which is mainly used for ordinary machine tools. The stepless speed change mode can continuously change the speed within a certain range, so as to obtain the best speed to meet the processing requirements, can change speed during operation, and facilitate automatic speed change. The drive system of the winner of the CNC lathe usually adopts stepless speed change. Compared with ordinary lathes, the main drive of CNC lathes uses AC and Straight spindle speed regulating motors. The motor speed range is large, and the stepless speed regulation can be used, which greatly simplifies the spindle structure. In order to adapt to different processing needs, there are three ways of the main transmission system of the CNC lathe.
5) Feed drive system
The feed drive system of CNC lathes generally adopts feed servo system, which can be divided into open-loop system and closed-loop system according to their different control methods. The former has low positioning accuracy, but it has a simple structure, reliable operation, and low cost; the latter has high control accuracy and good fast performance, but it has higher requirements for machine tools and is more expensive. The position detection devices used in the closed-loop system are: pulse encoder, resolver, induction synchronizer, magnetic ruler, grating ruler and laser interferometer. The driving device commonly used in the feed servo system of the CNC lathe is a servo motor. Servo motors are divided into DC servo motors and AC servo motors. The former is widely used because of its high reliability and low cost.
