1 Classification of machining centers
The machining center is often divided into a vertical machining center and a horizontal machining center according to the status of the main shaft in the space. The main shaft of the machining center is called a vertical machining center in the vertical state of the machining center, and the main shaft is in a horizontal state called a horizontal machining center. Machining center. as the picture shows,
The spindle can be used for vertical and horizontal conversions. It is called vertical and horizontal machining center or five-sided machining center, also called compound machining center. According to the number of columns in the processing center; single column type and double column type (gantry type).
Gantry machining center
According to the coordinates of the processing center and the coordinates of the simultaneous control points: There are three-axis two linkage, three-axis three linkage, four-axis three linkage, five-axis four linkage, six-axis five linkage and so on. Three-axis and four-axis refer to the coordinates of the movement coordinates of the machining center. The linkage means that the control system can control the coordinates of the movement at the same time, thus realizing the position and speed control of the tool relative to the workpiece.
According to the number and function of the workbench, there are a single-table machining center, a dual-table machining center, and a multi-table machining center.
According to processing precision points: There are general machining centers and high-precision machining centers. General machining center with a resolution of 1μm, a maximum feed rate of 15 to 25m/min, and a positioning accuracy of about 10μm. High-precision machining center, resolution of 0.1μm, maximum feed rate of 15 to 100m/min, positioning accuracy of about 2μm. Between 2 ~ 10μm, more ± 5μm, can be called precision grade.
2 Structure of the machining centerSince machining centers have been invented for more than 30 years, various types of machining centers have emerged in various countries of the world. Although the overall structure of the various types of structures, they are generally composed of the following major components.
1, the basic components. It is the basic structure of the machining center and consists of a bed, a column and a work bench.
Due to the static load of the machining center and the cutting load generated during machining, it is necessary to have sufficient rigidity. These large items can be
Therefore, the cast iron pieces can also be welded steel structural pieces, which are the largest parts and components in the machining center.
2. Spindle components. It consists of spindle box, spindle motor, spindle and spindle bearing. Spindle start, stop, and shifting are all controlled by the CNC system. The cutter mounted on the spindle participates in the cutting movement and is the power output part of the cutting process.
3, CNC system. The CNC part of the machining process is composed of cNc devices, programmable controllers, servo drives, and operation panels. It is the control center that performs sequential control actions and completes the machining process.
4, automatic tool change system. It consists of a magazine, a robot, and other components. When a tool change is required, the CNC issues a command to remove the tool from the magazine into the spindle hole by the robot (or by other means).
5, auxiliary devices. Including eddy-slip, cooling, chip removal, protection, hydraulics, pneumatics, and inspection systems. Although these devices do not directly participate in cutting motions, they provide a guarantee for the machining center's machining efficiency, machining accuracy, and reliability. Therefore, these devices are also an indispensable part of the machining center.
3 Structure features of machining centers1. The machine has high rigidity and good vibration resistance. In order to meet the requirements of high automation, high speed, high precision, and high reliability of machining centers, the static stiffness, dynamic stiffness, and damping ratio of the mechanical structural system of the machining center are all higher than those of ordinary machine tools (the stiffness of the machine tool under the action of static forces). It is called the static stiffness of the machine tool; the stiffness of the machine tool under dynamic force is called the dynamic stiffness of the machine tool.
2. The machine's drive system has a simple structure, high transmission accuracy, and high speed. There are three main types of machining center transmissions, namely ball screw pairs, hydrostatic worm-worm gear strips, and preloaded double gear-racks. They are directly driven by a servo motor, eliminating the need for a gear train, delivering high precision and speed. General speed up to 15m/min, up to 100m/min;
3. The spindle system has a simple structure and no gearbox transmission system (only special 1st to 2nd gear transmissions are reserved). Large spindle power, wide speed range, and stepless speed regulation. At present, more than 95% of spindles in machining centers use AC spindle servo system, and the speed can be infinitely variable from 10 to 20000 r/min. Servo motor drive spindle power is generally very large, is 1 to 2 times that of ordinary machine tools, due to the use of AC servo spindle system, spindle motor power is large, but the output power and the actual power consumption to maintain synchronization, there is no large horse car The kind of waste of electricity, so its highest efficiency, from the perspective of energy conservation, processing centers and energy-saving equipment;
4. The guide rails of the machining center are all made of wear-resistant materials and new structures, which can maintain the accuracy of the guide rails for a long period of time. Under high-speed heavy cutting, the moving parts do not vibrate, and at low feed speed, they do not crawl and have high sensitivity in motion. The guide rails are made of steel guide rails, quenching hardness ≥HRC, and PTFE mating surfaces with guide rails. The advantages of this treatment: a. The friction coefficient is small; b. Good wear resistance; c. Vibration damping; d. Good craftsmanship. Therefore, the precision life of the machining center is higher than that of general machine tools;
5. There is a magazine and tool changer. This is the main difference between machining centers and CNC milling machines and CNC boring machines, which makes the functions of the machining center and the ability of automatic processing stronger. The machining center has a few magazines with a small capacity, and many more than a few hundred. These tools are automatically called and replaced by the tool changer, and the tool life can also be managed through the control system.
6. The control system function is more complete. It not only controls the automatic machining of the tool, but also controls and manages the tool magazine and realizes automatic tool exchange. Some machining centers have multiple worktables. Worktables can be exchanged automatically. Not only can a workpiece be automatically processed, but also a batch of workpieces can be automatically processed. This kind of multi-table machining center is called a flexible processing unit. With the development of the machining center's control system, the degree of intelligence is becoming higher and higher. For example, the FANUC L6 system can realize human-machine dialogue and online automatic programming. Through the cooperation of the color display and the manual operation keyboard, the program can be input and edited. , modify, delete, with foreground operation, background editing front and back functions. During the processing, online inspection can be realized, and the detected deviation can be automatically corrected to ensure that the first part is successfully processed once, thereby preventing the production of waste products.
DMG DMC 70 H Horizontal Machining Center
4. The main processing object of the machining centerThe machining center is suitable for parts that require complex machining, multiple processes, high requirements, multiple types of common machine tools and many tool holders, and that can be machined after many installations and adjustments. The main objects of its processing are box-type parts, complex surfaces, special-shaped pieces, disk and plate parts and special processing and other five categories.
Box parts
Box-type parts generally refer to having more than one hole system, an internal cavity, and a certain proportion of parts in the length, width, and height directions. Such parts are used in machine tools, automobiles, and aircraft manufacturing industries. as the picture shows,
Box parts
Box-type parts generally require multi-position hole system and plane machining, high tolerance requirements, especially the strict requirements of shape and position tolerance, usually through milling, drilling, expansion, boring, hinge, boring, tapping and other processes Requires more tools, it is difficult to process on ordinary machine tools, tool sets, high cost, long processing cycle, multiple clamping, correcting, manual measurement times, the tool must be frequently changed when processing, the process is difficult to develop More importantly, accuracy is difficult to guarantee.
The machining center for machining box parts has a large number of machining stations and parts that can be completed by multiple rotations of the table. Generally, horizontal machining centers are selected. When the processing station is small and the span is not large, the vertical machining center can be selected and processed from one end.
2. Complex surfaces
Complex surfaces occupy a special important position in the machinery manufacturing industry, especially the aerospace industry. The use of ordinary machining methods for complex surfaces is difficult or even impossible. In China, the traditional method is the use of precision casting, and one can imagine the accuracy is low. Complex surface parts such as: various impellers, wind deflectors, spherical surfaces, various surface forming dies, propellers and propellers for underwater vehicles, and some other shapes of freeform surfaces.
impeller
This type of part can be processed by a machining center. The milling cutter acts as an envelope surface to approximate the sphere. When a complex surface is machined with a machining center, the programming workload is large, and most of them require automatic programming techniques.
3. Shaped pieces
Shaped parts are irregularly shaped parts, and most of them require multiple processing of points, lines, and surfaces. The deformed parts are generally poor in rigidity, difficult to control due to clamping and deformation, and it is difficult to ensure the processing accuracy. Even some of the machining parts of some parts are difficult to be completed by ordinary machine tools. When processing with a machining center, reasonable process measures should be adopted, one or two times clamping, and the multiple machining center or line and surface mixed processing characteristics of the machining center should be used to complete multiple processes or all process contents.
4. Plate, sleeve and board parts
With keyway, or radial hole, or distribution of holes in the end face, curved disc sleeve or shaft parts, such as flanged bushings, shafts with keyways or square heads, etc., as well as more porous Processed board parts, such as various motor covers. End-surface distribution of holes, curved disk parts should choose vertical machining center, there are radial hole optional horizontal machining center.
5. Special processing
After mastering the functions of the machining center, with a certain tooling and special tools, the use of machining center can complete some special process work, such as engraving, engraving, and engraving on the metal surface, and installing high on the spindle of the machining center. Frequency spark power supply, the surface of the metal surface can be line-scanning quenching; equipped with a high-speed grinding head machining center, can achieve a small modulus involute bevel gear grinding and a variety of curve, surface grinding and so on.
5. Accessories for machining centersChain knife library
2. Disk magazine
3. Exchange workbench
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