Large-scale CNC lathe processing is a high-tech processing method for machining precision hardware parts. At present, there are many kinds of large-scale CNC lathe processing, which can be classified according to a variety of different principles. Let's take a look at 4 common classifications about large-scale CNC lathe processing.
1. Classified according to process use
(1) General large-scale CNC lathe processing. This kind of large-scale CNC lathe processing is the same as the traditional general-purpose lathe processing. There are CNC turning, milling, boring, drilling, grinding and other mechanical processing methods. The processing possibilities of such large-scale CNC lathes are similar to those of general-purpose machine tools. Parts with complex shapes can be processed.
(2) CNC large-scale numerical control lathe processing. This kind of large-scale CNC lathe processing is developed on the basis of general large-scale CNC lathe processing. It is a kind of CNC lathe with automatic tool changer (also known as multi-process CNC lathe or boring machine), which is composed of a tool magazine (which can accommodate more than 10-100 tools) and an automatic tool changer on a general large CNC lathe. Milling machining center, commonly referred to as machining center), which makes the processing of large CNC lathes further develop towards automation and high efficiency.
(3) Multi-coordinate large-scale CNC lathe processing. Some complex-shaped parts cannot be processed by large-scale CNC lathes with three coordinates, such as the processing of propellers, aircraft surface parts, etc., which require composite movements of more than three coordinates to process the desired shape. Therefore, multi-coordinate CNC lathe processing appears, which is characterized by a large number of axes controlled by the CNC device and a complex lathe structure. The number of coordinate axes usually depends on the machining process requirements of the machined parts.
2. Classification according to the motion trajectory of CNC large-scale CNC lathes
(1) Point-controlled large-scale CNC lathe processing. The CNC device processed by such large CNC lathes can only control the moving parts of the lathe to move accurately from one position to another, that is, only control the coordinate value of the end point of the stroke, and do not perform any cutting during the movement process. The speed and route of movement in between depends on productivity. In order to have the highest possible productivity on the basis of precise positioning, the movement between the two related points is first to move quickly to approach the new position, and then reduce the speed by 1-3 steps to make it approach the positioning point at a slow speed to ensure its positioning accuracy.
(2) Large-scale CNC lathe processing with point position linear control. When processing such large CNC lathes, it is not only necessary to control the position between the two related points, but also control the moving speed and route between the two related points. Its route is generally composed of straight line segments parallel to each axis. The difference between it and point-controlled large-scale CNC lathe processing is that when the moving part of the lathe moves, it can be cut along the direction of one coordinate axis (generally it can be cut along a 45° oblique line, but it cannot be cut along a straight line with any slope). machining, and its auxiliary functions are more than point-controlled CNC lathes. For example, functions such as spindle speed control, cycle feed processing, and tool selection should be added.
(3) Contour control large-scale CNC lathe processing. The control device for this kind of large CNC lathe can continuously control two or more coordinate axes at the same time. During processing, it is necessary to control not only the starting point and the end point, but also the speed and position of each point in the entire processing process, so that the large CNC lathe can process the complex shape parts that meet the requirements of the drawings. Its auxiliary functions are also relatively complete.
3. Classification according to the control mode of the servo system
(1) Open-loop control large-scale CNC lathe processing. In open-loop control, there is no detection and feedback device for large-scale CNC lathe processing. The flow of signals from the numerical control device is one-way, so there is no system stability problem. It is precisely because of the one-way flow of the signal that it does not check the actual position of the moving parts of the CNC lathe, so the machining accuracy of the large CNC lathe is not high, and its accuracy mainly depends on the performance of the servo system. The working process is as follows: the input data is distributed by the numerical control device to distribute the command pulse, and the controlled workbench is moved by the servo mechanism (the servo element is often a stepper motor).
(2) Closed-loop control of large-scale CNC lathe processing. Since the open-loop control accuracy cannot meet the requirements of precision CNC lathes and large CNC lathes, its actual working position must be detected. For this reason, a detection feedback device is added to the open-loop control CNC lathe to detect the movement of the CNC lathe at all times during processing. The position of the parts is matched with the position required by the numerical control device, in order to achieve high machining accuracy.
(3) Open-loop compensation type large-scale CNC lathe processing. The characteristics of open-loop control large-scale CNC lathe processing and closed-loop control large-scale CNC lathe processing are selectively concentrated to form a mixed control scheme. Large-scale CNC lathe processing requires high feed speed and return speed, as well as relatively high precision. If only fully closed-loop control is used, the CNC lathe drive chain and worktable are all placed in the control link, and the factors are very complicated. In order to avoid these contradictions, a hybrid control method can be used
4. Classification by numerical control device
(1) Hard-wired large-scale CNC lathe processing (called ordinary CNC, or NC). The input, interpolation operation, control and other functions of this kind of numerical control system are realized by devices such as integrated circuits or discrete components. Generally speaking, different CNC lathes have different control circuits, so the universality of the system is poor, and because it is all composed of hardware, its function and flexibility are also poor. Such systems were widely used before the 1970s.
(2) Soft wire large-scale CNC lathe processing (also known as computer numerical control or microcomputer numerical control, ie CNC or MNC). This type of system uses medium, large-scale and ultra-large-scale integrated circuits to form CNC devices, or uses microcomputers and special-purpose integrated chips. Its main numerical control functions are almost entirely realized by software. For different CNC lathes, only different software needs to be compiled. can be achieved, and the hardware can be almost universal. Therefore, the flexibility and adaptability are strong, and it is also convenient for mass production. The modularized software and hardware improve the quality and reliability of the system. Therefore, modern CNC lathes use CNC devices.