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Development Status Of CNC Machining Fixtures For Domestic Structural Parts

Development Status Of CNC Machining Fixtures For Domestic Structural Parts

For the clamping of structural parts, manual methods are still used at present, such as the screw pressing method, which takes time and effort. In many cases, fixture assembly time and workpiece clamping time are much longer than workpiece cutting time, resulting in low production efficiency.
At present, the country’s investment in large-scale industrial machinery construction in important areas is increasing. In aviation, the main method of machining mechanical parts of aircraft is still CNC machining, especially CNC milling. The development of CNC machining fixtures for structural parts has greatly affected the improvement of my country’s aircraft manufacturing. However, there are still some common problems in the CNC machining fixtures for structural parts.

High-speed cutting methods are commonly used. For example, Xifei large complex structural parts are processed in Xifei CNC center. The types of structural parts include wing beams, wall plates, beam ribs, frames, large support joints and butt joints. These structures In addition to the characteristics of many grooves, thin walls, and high accuracy, the parts need to meet the usual characteristics of aircraft wing structural parts such as the aircraft’s variable bevel theoretical surface, and also have the requirements of large part size, groove depth and reference plane profile. Yan et al. [1], the processing of Chengfei structural parts is carried out in CNC branch and structural parts branch respectively, large structural parts are completed in CNC branch, and small structural parts are carried out in structural branch. At present, in domestic machine manufacturers, the CNC machining fixtures for structural parts have the following general problems.

1 The number of special fixtures is large, and the scope of fixtures is narrow.

In a subcontracting project and the development of large aircraft, a structural component factory of a company of AVIC needs to process a large number of structural components that use profiles as raw materials. Such parts are mainly milling and drilling. Due to the uncertainty of subcontracting tasks, and the domestic large aircraft are still in the development process, the number of parts is small but there are many types. In order to ensure the processing quality, special fixtures have been developed for each part, the base is a relatively heavy casting, and the positioning accuracy is not high. The workshop tool library and even the workshop floor are full of various fixtures. When converting from producing one part to producing another part, the recombination time of the fixture recombination is about 2h, which seriously affects the production efficiency. Large integral structural parts on the aircraft, such as integral skins and siding, are still partly using large die tires for milling and trimming. Mold tire design and manufacturing cost is high, and strong specificity. A large number of mold tires occupy the plant area, and the warehouse backlog is serious.

2 Lack of computer-aided fixture assembly system and fixture production process management system.

At present, the fixture design or fixture assembly plan planning is basically still carried out manually. The designer has a lot of labor and low efficiency; the design quality depends on personal experience and habits, the quality is unstable, and the standardization is poor. The search for fixture components and the assembly of fixtures are time-consuming and laborious. The jig production process management is chaotic, and there is a lack of classified retrieval methods for jigs and jig components. For new structural parts, there may be suitable tooling, but because it is difficult to find, or after finding similar tooling, the lack of scientific methods to guide assembly, designers often eventually give up using existing fixtures or fixture components, and redesign and manufacture, this Caused a huge waste. After the assembling jig completes the workpiece processing task, it cannot be disassembled and assembled in time and orderly.

3 Low degree of automation of the fixture.

For the clamping of structural parts, manual methods are still used at present, such as the screw pressing method, which takes time and effort. In many cases, fixture assembly time and workpiece clamping time are much longer than workpiece cutting time, resulting in low production efficiency.

The fixture and CNC machine tool are independent in terms of structure and control. It is difficult to coordinate, consistently position, clamp and advance and retract the workpiece through CNC commands.

4 The degree of standardization and modularity of the fixture components are low, which results in low reusability of fixture components, poor interchangeability of fixtures, and difficulty in assembling.

5 Can not support the design of aircraft parts using MBD technology, lack of three-dimensional fixtures and fixture components digital model, and the three-dimensional digital coordination of aircraft parts design is not enough.

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