A fixture is a process equipment for clamping workpieces. It is widely used in machining, heat treatment, assembly, welding and testing processes in the mechanical manufacturing process. The fixtures used on metal cutting machine tools are collectively referred to as 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. There are many types of machine tool fixtures, and machine tool fixtures can be classified from different angles. The following are some commonly used classification methods.
(1) Classification by the use characteristics of the fixture According to the common characteristics of the fixture in different production types, machine tool fixtures can be divided into five categories: general fixtures, special fixtures, adjustable fixtures, combination fixtures and assembled fixtures.
① General fixtures are standardized fixtures that can process different workpieces within a certain range. They are called general fixtures. Their structure and size have been standardized and have a certain degree of versatility, such as three-jaw self-centering chucks, flat vises for machine tools, four-jaw single-action chucks, bench vises, universal indexing heads, centers, center stands and magnetic workbenches. This type of fixture has strong adaptability and can be used to clamp various workpieces within a certain shape and size range. These fixtures have been manufactured and supplied by special factories as machine tool accessories. They are not very accurate, have low productivity, and are difficult to clamp workpieces with complex shapes. Therefore, they are generally suitable for single-piece small-batch production.
② Special fixtures are fixtures designed and manufactured specifically for a certain process of a certain workpiece. In the production of relatively stable products and large batches, the use of various special fixtures can achieve higher productivity and processing accuracy. The design cycle of special fixtures is long and the investment is large. Special fixtures are generally used in batch production. In addition to large-scale 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.
③ Adjustable fixtures Some components of which can be adjusted or replaced to adapt to the processing of various workpieces are called adjustable fixtures. Adjustable fixtures are a new type of fixture developed to address the defects of general fixtures and special fixtures. For workpieces of different types and sizes, it is only necessary to adjust or replace individual positioning elements and clamping elements on the original fixture to use it. It can generally be divided into two types: general adjustable fixtures and group fixtures. The former has a wider range of general use than general fixtures; the latter is a special adjustable fixture designed according to the grouping principle and can process a family of similar workpieces, so it has better economic effects when used in multi-variety, medium and small batch production.
④ Combination fixtures use standard combination components and parts, and are specially assembled for a certain process of a certain workpiece, which is called a combination fixture. Combination fixtures are modular fixtures. Standard modular components have high precision and wear resistance and can be assembled into various fixtures. The fixture can be disassembled after use, cleaned and left for assembly of new fixtures. Since the use of modular fixtures can shorten the production preparation cycle, the components can be reused many times, and it has the advantages of reducing the number of special fixtures, modular fixtures are a more economical fixture in single-piece, medium and small batch multi-variety production and CNC machining.
⑤ Assembly fixtures are assembled with special standardized and serialized assembly parts, which are called assembly fixtures. It has the advantages of modular fixtures, but it has higher precision, higher efficiency and more compact structure than modular fixtures. Its base plate and clamping parts often have small hydraulic cylinders. This type of fixture is more suitable for use on CNC machine tools.
(2) Classification by machine tool
According to the machine tool used, fixtures can be divided into lathe fixtures, milling machine fixtures, boring machine fixtures, gear machine tool fixtures, CNC machine tool fixtures, automatic machine tool fixtures, automatic line follow-up fixtures and other machine tool fixtures.
(3) Classification by clamping power source
According to the clamping power source, fixtures can be divided into manual fixtures, pneumatic fixtures, hydraulic fixtures, magnetic fixtures, etc.