Brief introduction of CNC machine tool fixture

Classified according to the characteristics of the use of fixtures 　　 　　 

According to the general characteristics of fixtures in different production types, machine tool fixtures can be divided into five categories: general fixtures, special fixtures, adjustable fixtures, modular fixtures and assembly fixtures. 　　

General-purpose fixtures are standardized fixtures that can process different workpieces within a certain range. They are called general-purpose fixtures. Their structure and dimensions have been standardized, and they have certain versatility, such as three-jaw self-centering chucks, flat-nose vise for machine tools, and four Claw single-action chuck, bench vise, indexing head, center frame, magnetic table, etc. This type of fixture is highly adaptable and can be used to clamp various workpieces within a certain shape and size range. These fixtures have been manufactured and supplied by specialized factories as machine tool accessories, and only need to be purchased. The disadvantage is that the accuracy of the fixture is not high, the productivity is also low, and it is difficult to clamp the workpiece with complex shape, so it is generally suitable for single-piece small batch production. 　　 　　

Special Fixture A fixture designed and manufactured specifically for a certain process of a certain workpiece is called a special fixture. In the production of relatively stable products and large batches, various special fixtures are used to obtain higher productivity and processing accuracy. The design cycle of the special fixture is longer and the investment is larger. Special fixtures are generally used in mass production. In addition to mass production, some special fixtures are also needed in small and medium batch production, but specific technical and economic analysis should be carried out during structural design. 　　 　　

Adjustable fixture Some components can be adjusted or replaced to adapt to a variety of workpiece processing fixtures, called adjustable fixtures. Adjustable fixtures are a new type of fixture developed for the defects of general fixtures and special fixtures. For workpieces of different types and sizes, it can be used only by adjusting or replacing individual positioning elements and clamping elements on the original fixture. It can generally be divided into general adjustable clamps and group clamps. The former has a larger general range than the general fixture; the latter is a special adjustable fixture, which is designed according to the group principle and can process a family of similar workpieces, so it is better to use in the production of multiple varieties, medium and small batches Economic effect. 　　 　　Combined fixtures use standard combined components and parts, which are specially assembled for a certain process of a workpiece, called modular fixtures. Modular fixture is a modular fixture. Standard modular components have high precision and wear resistance, and can be assembled into various fixtures. The fixture can be disassembled after use, and it is left to assemble a new fixture after cleaning. Since the use of modular fixtures can shorten the production preparation cycle, components can be used repeatedly, and has the advantages of reducing the number of special fixtures, so modular fixtures are more economical in single-piece, medium and small batch multi-variety production and CNC machining Fixture. 　　 　　

Assembling fixtures The fixtures assembled with special standardized and serialized assembled parts are called assembling fixtures. It has the advantages of modular fixtures, but it has higher precision, higher efficiency and compact structure than modular fixtures. Its base plate and clamping parts often contain small hydraulic cylinders. This type of fixture is more suitable for use on CNC machine tools. 　　 　　

Classified by machine tool 　　 　　

Fixtures can be divided into lathe fixtures, milling machine fixtures, drilling machine fixtures, boring machine fixtures, gear machine fixtures, CNC machine tool fixtures, automatic machine tool fixtures, automatic line accompanying fixtures, and other machine tool fixtures according to different machine tools. According to the clamping power source, the clamps can be divided into manual clamps, pneumatic clamps, hydraulic clamps, pneumatic and hydraulic clamps, electromagnetic clamps and vacuum clamps. 　　 Features of fixture 　　 　　

Features of CNC machining fixtures As a machine tool fixture, first of all, it must meet the clamping requirements of the workpiece during machining. At the same time, the CNC machining fixture has its own characteristics. These characteristics are: 　　 　　

CNC machining is suitable for multi-variety, medium and small batch production. In order to clamp multiple types of workpieces of different sizes and shapes, the CNC machining fixture should be flexible and can clamp workpieces of various shapes and sizes after proper adjustment. 　　 　　

Traditional special fixtures have four functions: positioning, clamping, guiding and tool setting. CNC machine tools are generally equipped with contact test probes, tool presetters and tool setting parts, which can solve the problem of tool setting by the machine tool. The precise positioning accuracy controlled by the program on the CNC machine tool can realize the tool guiding function in the fixture. Therefore, fixtures in CNC machining generally do not require guiding and tool setting functions, and only require positioning and clamping functions to meet the requirements of use, which can simplify the structure of the fixture. 　　 　　

In order to adapt to the rate of CNC machining, the CNC machining fixture should be clamped quickly with pneumatic, hydraulic, electric and other automatic clamping devices as much as possible to shorten the auxiliary time. 　　 　　 

The fixture itself should have enough rigidity to adapt to cutting with large cutting amount. Numerical control machining has the characteristics of concentrated processes. In one clamping of the workpiece, both rough machining with a large cutting force and finishing machining to meet the requirements of the final accuracy of the workpiece are required. Therefore, the rigidity and clamping force of the fixture must be satisfied. Cutting force requirements. 　　 　　 

In order to adapt to the multi-faceted CNC machining, it is necessary to avoid the interference of the fixture structure, including the components on the fixture, on the tool movement trajectory, and the fixture structure should not hinder the multi-faceted machining of various parts of the workpiece. 　　 　　

The positioning of the fixture should be reliable, the positioning components should have high positioning accuracy, and the positioning position should be easy to clean chips, without chip accumulation. If the positioning surface of the workpiece is too small, consider adding a process boss or auxiliary reference. 　　 　　

For the workpiece with low rigidity, small clamping deformation should be ensured, such as making the clamping point close to the supporting point, avoiding the clamping force acting on the hollow area of the workpiece, etc. When rough machining and finishing are completed in the same process, if the above measures cannot control the deformation of the workpiece within the range of machining accuracy requirements, the program should be paused before finishing, and the operator can change before finishing after roughing. Clamping force (appropriately reduced) to reduce the impact of clamping deformation on machining accuracy. 　　 　　

There are many types of CNC machine tool fixtures, and the fixtures used on metal cutting machine tools are collectively called machine tool fixtures. In modern production, machine tool fixtures are an indispensable process equipment, which directly affects the accuracy of workpiece processing, labor productivity, and product manufacturing costs.