Working Principle, Characteristics and Application of Combination Fixture
Due to the rapid development of science and technology, the mechanical industry products are not only increasingly diverse, but also the products are updated and improved quickly, therefore, it becomes a prominent problem to shorten the production cycle of process equipment, ensure processing quality, improve productivity and reduce processing costs in machining. So, on the basis of standardization of fixture parts, there is a combination of fixtures. The emergence and development of the combination of fixtures for CNC machine tools in the machinery industry, single-piece small batch production and new product trial work, creating extremely favorable conditions.
A combination of the working principle, characteristics and application of the fixture
1, the working principle and characteristics of the combination of fixtures. Combination fixture is a new type of process equipment with high degree of standardization, serialization and generalization in machine tool fixture. It is a combination of a set of prefabricated standard components. These components have various shapes, sizes and specifications, and have good interchangeability, wear resistance and high precision. According to the process requirements of the workpiece, it is assembled into various special fixtures by building blocks. After use, the components can be easily disassembled, washed and stored away for reuse when reassembled. Figure 2 – 20 shows a set of combined rotary drill press fixture and the components of this fixture.
Combination clamps have the following characteristics.
(1) flexible and versatile, allowing rapid availability of fixtures and shortening production preparation cycles.
(2) Ensuring machining quality and improving production efficiency.
(3) Save manpower, material and financial resources, and improve economic efficiency.
(4) Reduce the storage area of fixtures and improve management work.
There are some shortcomings of the combination jig, such as it is bulky and not as rigid as the special jig, but with the continuous development of the combination jig components and the continuous improvement of the assembly technology, its performance will be gradually improved. In addition, the assembly of complete sets of combination jigs, must have a large number of components in reserve, therefore, the cost of the beginning of the investment is larger.
2、The application of combination fixture. Combination fixture has a wide range of applications, it is not only maturely used in machine tools, automobiles, agricultural machinery, instrumentation and other industries, but also promoted in heavy, mining and other machinery industries.
(1) From the viewpoint of production type, the characteristics of combination jig determine that it is most suitable for the production of products that change frequently, such as single-piece small batch production, new product trial production and temporary surprise production tasks. For mass-produced products, the combination fixture can also be used to supplement the number of special fixtures, or when the special fixtures are damaged or the production process is changed. For mass-produced products, sometimes the combination fixture can be considered appropriately.
(2) From the viewpoint of processing work, the combination jig can be used for drilling, turning, milling, planing, grinding, boring, inspection and other work types, among which the drilling machine jig is the largest application. If combined with pneumatic, hydraulic and other transmission devices, it can also form a high-efficiency fixture.
(3) From the viewpoint of geometry and size of the workpiece, the combined fixture is generally not restricted by the complexity of the workpiece shape, and rarely encounters the situation that the fixture cannot be assembled because of the special shape of the workpiece. At present, our country adopts a large number of medium-sized series of combination fixture, generally applicable to the workpiece with the shape size of 20-600mm, and sometimes according to the production needs, it can also assemble a larger combination fixture.
(4) From the perspective of the tolerance level of the processed workpiece, since the components of the combination fixture itself are IT2 tolerance level, therefore, under normal circumstances, through the accumulated error of each assembly link, the workpiece processing tolerance level can reach IT3, and if it is carefully matched and adjusted, the workpiece processing tolerance level can also reach IT2 or higher.
Second, the series and basic elements of combination fixture
There are three series of combination jigs: small, medium and large according to their sizes, and the difference mainly lies in the basic elements of the components. The basic elements of the combination jig are outline size, T-slot width and diameter of bolts and screw holes.
Small series of combination jig is mainly used in instrument, meter, telecommunication and electronic industry, the diameter of bolt of this series is M8×1.25, the width of positioning key and keyway is 8H7/js6, and the distance between T-slots is 30mm.
Medium-sized series of combination jig is mainly used in machinery manufacturing industry, the diameter of the bolt of this series of components is M12×1.5, and the size of the key positioning and the width of the keyway is 12H7/h6, and the distance between the T-slots is 60mm.
Large series of combination jig is mainly used in heavy machinery manufacturing, the diameter of the bolt of this series of components is M16×2, and the size of the key positioning and the width of the keyway is 16H7/h6, and the distance between the T-slots is 60mm.