Introduction to modern machine tool fixtures

With the rapid development of science and technology, the ever-changing market demand and the increasingly fierce competition for commodities have made the cycle of upgrading mechanical products shorter and shorter, and the proportion of multi-species and small-batch production has become higher and higher. In order to adapt to this situation, various new types of fixtures have emerged.

The direction of development of modern machine tool fixtures is mainly manifested in precision, high efficiency, and flexibility. Here are some examples of modern machine tool fixtures.

One, adjustable fixture

Adjustable fixtures are divided into two types: universal adjustable fixtures and group fixtures (also called special adjustable fixtures). Their common feature is that as long as the individual positioning, clamping, or guiding elements are replaced or adjusted, they can be used for the processing of various parts, thus enabling the single-piece, small-batch production of multiple parts to become one set of parts on the same fixture. Batch production." After the product is replaced, parts can still be processed on this jig as long as they belong to the same type of part. Because the adjustable fixture has strong adaptability and good inheritance, the use of adjustable fixtures can greatly reduce the number of special fixtures, shorten the production preparation cycle, and reduce costs.

(a) Universal adjustable fixture

The general adjustable fixture has a wide range of processing objects, and the processing target is sometimes inaccurate. Such as the stud type drilling jig, as long as the replacement of different positioning, clamping, guiding elements, can be used for drilling different types of workpieces.

(B) Group fixture

A group fixture is a fixture designed specifically for a group of parts in a group process.

The group of components processed by the jigs should all conform to the similar principle of the group process. The similarity principles mainly include the following: similar processes; similar surfaces for mounting; similar shapes; similar sizes; similar materials; similar precision. Figure 10-7 shows a set of process parts for machining the arc surface and one end face of the yoke, which conforms to the similarity principle of the group process.

Figure 10-8 shows the set of lathe fixtures for machining this part set. Two pieces are processed at the same time. There are four pairs of positioning sleeves 2 (positioning holes φ16H7) on the clamp 1 and can be used to install four interchangeable positioning shafts KH1 for processing four different center distance L components. If the exchangeable positioning shaft is installed in the T-shaped groove in the C-C cross section, various parts whose center distance L changes within a certain range can be machined. The replaceable cushion cover KH2 and the replaceable pressure plate KH3 are replaced according to the height H of the fork part of the part, and are fixed in the T-shaped groove where the two positioning shafts are perpendicular to each other, so that the rotation-proof positioning and auxiliary clamping are used.

The design method of group fixtures is similar to that of special fixtures. First, a “composite part” is identified. This part can represent the main features of the parts within the group. Then the fixtures are designed for “composite parts” and the design can be adjusted according to the processing range of the parts within the group. Parts and replaceable parts. It should be easy to make adjustments, change quickly, and have a simple structure. Because the jigs can be mass-produced, efficient clamping devices such as various pneumatic and hydraulic devices can be used.

Second, the combination of fixture

(I. Overview

The combination fixture is a standardized, serialized and generalized process equipment. China began to promote the use of the beginning of the 60s, has now been basically universal, all cities and major factories have their own combination fixture station.

The assembly jig is assembled from a set of pre-manufactured standard components and assemblies of different shapes, sizes, and sizes.

A combination fixture is generally a special fixture that is assembled for a certain process of a workpiece, and can also be assembled into a universal adjustable fixture or a group fixture. Combination clamps are suitable for all types of machine tools.

The combination fixture transforms the one-way process of designing, manufacturing, using, and scrapping the special fixture into a cyclic process of assembly, diffusion, cleaning and storage, and reassembly. A few hours of assembly can be used to replace the design manufacturing cycle of several months, thereby shortening the production cycle; saving man-hours and materials, and reducing production costs; it can also reduce the fixture storage area and facilitate management.

The components of the combination fixture have high precision and wear resistance, and they are completely interchangeable. The component precision is generally IT6 to IT7. Workpieces machined with a combination of jigs, the position accuracy is generally up to IT8 ~ IT9 level, if carefully adjusted up to IT7 level.

Third, CNC machine tool fixture

In the modern automated production, the application of CNC machine tools has become more and more extensive. During CNC machining, the movement of the tool or table is controlled by the program and is performed at a certain coordinate position.

When designing a CNC machine tool fixture, the following points should be noted:

1. The origin (cutting point) should be set on the fixture of the CNC machine tool.

2. CNC machine tools do not need to set the tool guide. This is because when the CNC machine tool is processed, the machine tool, the fixture, the tool, and the workpiece always maintain a strict coordinate relationship, and there is no need for a guide element between the tool and the workpiece to determine the position.

3. CNC machine tools often need to machine workpieces in several directions, so the CNC machine tool fixtures should be open.

4. CNC machine tools should try to use adjustable fixtures, assembly fixtures and combination fixtures. Because the workpieces machined on CNC machine tools are often single-piece and small-batch production, fixtures with good flexibility and short preparation time must be used.

5. The clamping of the CNC machine tool fixture should be firm and reliable and easy to operate. The position of the clamping element should be fixed to prevent the component and the tool from colliding during automatic machining.

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