What are the structural components of automatic CNC lathes?
Although there are many types of CNC lathes, they are generally composed of three parts: the main body of the lathe, the numerical control device and the servo system.
1) Except for some economical CNC lathes that basically maintain the traditional layout of ordinary lathes, most of the CNC lathes have been specially designed and finalized for production.
1) Spindle and headstock
a) Spindle CNC lathe spindle's rotation accuracy directly affects the machining accuracy of the parts; its power and rotation speed affect the processing efficiency; its synchronous operation, automatic speed change and directional accurate stop requirements affect the automation degree of the lathe.
b) A CNC lathe with a stepped automatic speed regulation function in the spindle box, and the transmission mechanism in the spindle box has been greatly simplified; a CNC lathe with stepless automatic speed regulation (including directional exact stop), which plays the role of mechanical transmission speed change and direction change The mechanism no longer exists, and its spindle box has become synonymous with "bearing seat" and "lubrication box"; for the retrofit type (with dual functions of manual operation and automatic control processing), it basically retains its original Headstock.
2) Guide rail The guide rail of the CNC lathe is an important part to ensure the accuracy of the feed movement. It largely affects the rigidity, accuracy and stability of the lathe at low speed feed, and is one of the important factors affecting the quality of parts processing. Except that some CNC lathes still use the traditional sliding guide rail (metal type), the CNC lathes produced by stereotypes have used more plastic guide rails. This new type of sliding guide has a low coefficient of friction, good wear resistance, corrosion resistance and shock absorption, as well as superior lubrication conditions.
3) The mechanical transmission mechanism has been greatly simplified on the basis of the original ordinary lathe transmission chain, except for the gear transmission in part of the spindle box. For example, the hanging wheel box, feed box, slide box and most of the transmission mechanism are cancelled, and only the spiral transmission mechanism of longitudinal and horizontal feeding is retained, and the drive motor to the lead screw is added (a few lathes have not Add) gear pair that can eliminate its backlash.
a) Spiral transmission mechanism The screw pair in the numerical control lathe is a pair of movement that converts the rotary motion output by the drive motor into a linear motion of the tool post in the vertical and horizontal directions. The component that constitutes the screw transmission mechanism is generally a ball screw pair. The friction resistance of the ball screw pair is small, which can eliminate the axial gap and preload, so the transmission efficiency and precision are high, the movement is stable, and the movement is sensitive. However, the structure is more complicated and the manufacturing technology requirements are higher, so the cost is also higher. In addition, it is more difficult to adjust the gap size by yourself.
b) Gear pair. In the drive mechanism of many CNC lathes, a simple gear box (frame) is set between the drive motor and the feed screw. The main function of the gear pair is to ensure that the pulse equivalent of the feed motion of the lathe meets the requirements, and to avoid the adverse effect of the possible axial movement of the lead screw on the drive motor.
4) Auto-rotating tool post In addition to the automatic tool changer with random tool change (with tool magazine) in the turning center, CNC lathes generally have an automatic indexing tool post with a fixed tool position, and some lathes also have various forms Double knife holder.
5) Detection feedback device The detection feedback device is an important part of the CNC lathe, which has a great influence on the processing accuracy, production efficiency and automation degree. The detection device includes two categories: displacement detection device and workpiece size detection device. Among them, the workpiece size detection device is divided into two types: the internal size detection device and the external size detection device. The workpiece size detection device is only used on a small number of CNC lathes.
6) Tool setting device, except for a few special-purpose CNC lathes, almost all ordinary CNC lathes use various forms of automatic indexing tool holders for multi-tool turning. In this way, the position where the tool position of each tool is installed on the tool holder, or the position relative to the fixed origin of the lathe, requires tool calibration, adjustment, measurement, and confirmation to ensure the processing quality of the parts.
(2) Numerical control device and servo system The main difference between numerical control lathe and ordinary lathe is whether it has two major parts: numerical control device and servo system. If the detection device of the CNC lathe is equivalent to the human eye, then the CNC device is equivalent to the human brain, and the servo system is equivalent to the human hands. In this way, it is not difficult to see the important position of these two parts in the CNC lathe. a) Numerical control device The core of the numerical control device is the computer and its software, which plays a "command" role in the numerical control lathe: the numerical control device receives various information sent by the processing program, and after processing and deployment, it sends execution to the drive mechanism Command; in the execution process, its drive, detection and other institutions will feed back relevant information to the numerical control device at the same time, so that a new execution command can be issued after processing.
A CNC machine tool is an automated machine tool equipped with a program control system (numerical control system). The system can logically process programs that have use numbers or other symbol coding instructions (tool movement trajectory information). Specifically, the digitized tool movement trajectory information is input to the numerical control device, and after decoding and calculation, the machine tool that controls the relative movement of the tool and the workpiece and processes the required parts is the numerical control machine tool.
1. Working principle of CNC machine tool According to the technical requirements and process requirements of the part processing, the processing program of the part is written, and then the processing program is input to the CNC device. The CNC device controls the spindle movement, feed movement, tool replacement, and workpiece Clamping and unclamping, cooling and lubrication pumps are turned on and off, so that tools, workpieces and other auxiliary devices work strictly in accordance with the sequence, trajectory and parameters specified by the processing procedure, so as to process parts that meet the requirements of the drawings.
2. CNC machine tool structure CNC machine tool is mainly composed of four parts: control medium, CNC device, servo system and machine tool body. The machining process of CNC machine tools:
1) Control medium
The control medium records various processing information in the form of instructions, such as the process of part processing, process parameters and tool movement, etc., and inputs this information to the CNC device to control the CNC machine tool to cut the part.
2) Numerical control device
The numerical control device is the core of the numerical control machine tool. Its function is to accept the input processing information, decode, calculate and logically process through the system software and logic circuit of the numerical control device, send corresponding pulses to the servo system, and control the movement of the machine tool through the servo system The parts move according to the instructions of the processing program.
3) Servo system
The servo system consists of a servo motor and a servo drive device. Generally speaking, the numerical control system is the integration of the index control device and the servo system, so the servo system is the execution system of the numerical control system. The speed and displacement commands issued by the numerical control device control the displacement of the execution part according to the feed speed and the feed direction. Each execution part of the feed motion is equipped with a servo system, and some servo systems also have a position measuring device, which directly or indirectly measures the actual displacement of the execution part, and feeds it back to the numerical control device to compensate for machining errors.
4) Machine tool body
The body of CNC machine tools is basically similar to that of ordinary machine tools. The difference is that the structure of CNC machine tools is simple and rigid. The transmission system uses ball screws to replace the lead screws and rack drives of ordinary machine tools. The spindle speed change system simplifies the gear box and generally uses frequency conversion. Speed regulation and servo control.
Tools for CNC lathes:
(1) Requirements for cutting tools The CNC lathe can both be used for roughing and finishing. In order to make rough machining with a larger cutting depth and a larger feed rate, the rough turning tool is required to have high strength and good durability. Fine turning is first of all to ensure the machining accuracy, so the cutting tools are required to have high precision and good durability. In order to reduce the time of tool change and facilitate tool setting, it should be possible to use machine clamp tools more often. CNC lathes also require good consistency of blade durability to facilitate the use of tool life management functions. When using tool life management, the blade durability setting principle is based on the blade with the lowest durability among the batch of blades. In this case, the consistency of blade durability is even more important than its average life.
(2) CNC lathe tools. CNC turning tools are generally divided into three categories, namely, pointed turning tools, arc-shaped turning tools and forming turning tools. Turning tools characterized by straight cutting edges are generally called pointed turning tools. The tip of this type of turning tool (also its tool location point) is composed of straight main and secondary cutting edges, such as 90? internal and external turning tools, left and right end face turning tools, grooving (broken) turning A variety of external and internal turning tools with very small cutting edges and small chamfers. When machining parts with this type of turning tool, the contour shape of the part is mainly obtained by the displacement of an independent tool tip or a linear main cutting edge, which is completely in principle with the other two types of turning tools. different.
The arc-shaped turning tool is a special turning tool for CNC machining. Its characteristic is that the shape of the blade forming the main cutting edge is an arc with small roundness error or line profile error; each point of the arc blade is the tip of an arc-shaped turning tool, therefore, the tool location point is not On the arc, but at the center of the arc; the turning tool arc radius is theoretically independent of the shape of the processed part, and can be flexibly determined or confirmed after measurement as required. When the tip of some pointed or shaped turning tools (such as threaded turning tools) has a certain arc shape, it can also be used as this type of turning tool.
The arc-shaped turning tool can be used for turning inner and outer surfaces, and is particularly suitable for turning various smoothly connected (concave) forming surfaces. Forming turning tools are commonly known as model turning tools, and the contour shape of the processed parts is completely determined by the shape and size of the turning tool blade. In CNC turning processing, common forming turning tools include small radius arc turning tools, non-rectangular turning tools and thread turning tools. In CNC machining, the forming turning tool should be used as little as possible or not, and when it is really necessary to select it, it should be explained in detail in the process preparation document or the processing procedure sheet. In order to meet the needs of automatic processing of CNC machine tools (such as tool setting or pre-adjustment, automatic tool change or revolving, automatic detection and management, etc.), and continuously improve product processing quality and production efficiency, and save tool costs, more Use modular and standardized tools.
2. The chuck hydraulic chuck of the CNC lathe is an important accessory for clamping the workpiece during CNC turning. Ordinary hydraulic chuck can be used for general rotary parts; for parts whose clamping part is not cylindrical, special purpose is required. Chuck; spring chuck is required when directly machining parts with bar stock.
3. The tailstock of the CNC lathe has a large ratio between the axial size and the radial size, and the movable top installed on the hydraulic tailstock needs to be used to support the end of the part to ensure the correct processing of the part. The tailstock has ordinary hydraulic tailstock and programmable hydraulic tailstock.
4. The tool rest of the CNC lathe is a very important part of the CNC lathe. According to the function of CNC lathe, the number of tools that can be installed on the tool post is generally 8, 10, 12 or 16, and some CNC lathes can be equipped with more tools. The structure of the tool holder is generally rotary, and the tool is installed on the tool holder in the circumferential direction, and radial turning tools, axial turning tools, drills, and boring tools can be installed. The turning machining center can also be equipped with axial milling cutters and radial milling cutters. The tool holders of a few CNC lathes are in-line, and the tools are installed along a straight line. CNC lathes can be equipped with two tool holders:
(1) The special tool holder is developed by the lathe manufacturer itself, and the tool holder used is also special. The advantage of this tool holder is low manufacturing cost, but lacks versatility.
(2) General tool holders. The tool holders produced according to certain general standards. CNC lathe manufacturers can choose and configure according to the functional requirements of CNC lathes.
5. Milling power head of CNC lathe The milling power head installed on the tool post of the CNC lathe can greatly expand the processing capacity of the CNC lathe.
