This is the ARJ21 wing box being assembled by AVIC Xifei. It seems ordinary, but it was made through a breakthrough technology that won the second prize of the 2020 National Technological Invention Award.
This new generation of high-precision aviation scientific research results called "Multi-flexible matching cutting manufacturing technology and application of large and complex thin-walled structures" (hereinafter referred to as: multi-flexible matching cutting technology) will significantly improve my country's large aircraft processing and production field The stable batch production capacity.
1. It is the first time in the global numerical control machining field to propose and realize the pre-stress adjustable multi-face dovetail slot clamping method.
2. The cutting parameter optimization method it proposes solves the chatter and low efficiency of 30,000 rpm high-speed milling of large and complex thin-walled structures in five-axis machining.
3. For the first time, it is proposed to open a ring-shaped stress relief groove, which is widely used in the processing of large-scale wall panels, frames, beams and other parts, forming a complete set of CNC programming technical standards for large-scale complex thin-walled structural parts.
In order to achieve this breakthrough achievement, the scientific research team of AVIC Xifei CNC Processing Plant has studied for 11 years.
Facing difficulties and working hard to tackle key problems
Aeronautical structural parts, such as long trusses, are an important part of the aircraft body skeleton, which is not only an important bearing structure of the aircraft, but also an important part of the weight of the aircraft. However, its manufacturing is a difficult problem: the parts are large in size, difficult to clamp and inefficient, the structure of the parts is more complex, the machining accuracy is more strict, and the deformation of the parts is more difficult to control... These "hard bones" are more difficult to chew than each.
In order to achieve a breakthrough in this field, in 2008, the scientific research team of AVIC Xifei CNC Processing Plant launched a scientific research project on the processing and manufacturing of wing truss, and thus embarked on the road of research.
In the past, the wing truss of large aircraft was processed by profiling. However, profiling is a processing technology in the 1950s, and the surface quality of the processed parts is very poor, and the amount of grinding is relatively large. Too much polishing will seriously affect the fatigue strength of the parts, and the processing equipment is aging, and the production capacity cannot meet the production needs. Moreover, the wing truss are slender, flexible, thin-walled and weak rigid parts, which are prone to flutter during processing.
In order to realize low-vibration and stable cutting during the machining process, the scientific research team of the AVIC Xifei CNC processing plant has tried to develop several milling fixtures. After years of research, it is the first time in the global CNC machining field to propose and realize the pre-stress adjustable multi-face dovetail slot clamping. Method, hydraulic integrated clamping-such a method is fast and stable, solves the problem of processing vibration of weakly rigid long truss, and realizes a key breakthrough in this field in our country.
In order to reduce the cutting chatter during machining, the R&D team also proposed a cutting parameter optimization method that takes into account the rigidity of the workpiece and the time-varying characteristics of the machine tool. Through a large number of experiments, collecting and analyzing massive data, the chatter problem of five-axis milling of large and complex thin-walled parts has been completely solved.
On the outer wing of a large aircraft, the largest wall panel is nearly 20 meters long and more than 2 meters wide, while the thinnest part of the web is less than 2 mm. The problem to be solved by the R&D team of the CNC processing plant is to perform CNC machining on such a large, thin, and extremely rigid wall panel to ensure that there is no chatter. This is like moving a knife on the paper to ensure that the paper does not break.
After adopting the new technology of vibration suppression and efficiency enhancement, the cutting chatter of 8 types of parts such as wall panels, long trusses, frames, beams, ribs, skins, joints, and slide rails are effectively suppressed, the manufacturing accuracy is doubled, and the parts are qualified. The rate is as high as 100%, which greatly improves production efficiency.
After the "competition", the data is stunning
The next "episode" can better reflect our country's surpassing in this field.
A few years ago, an internationally renowned civil aircraft main engine manufacturer invited a number of domestic suppliers to provide technical improvement solutions for it. In addition to rigid manufacturing standards, the shorter the manufacturing time, the better.
Many domestic suppliers have participated in and demonstrated their plans, but without exception, they have all failed in comparison with the "standard plan" provided by them-the processing time is overtime.
At this time, AVIC Xifei CNC Processing Plant was also invited to come up with the self-invented "multi-flexible matching cutting technology". It only takes less than four hours to use this technology to process the edge of the vertical tail beam of a large aircraft, which is 12 minutes less than the "standard plan"!
In addition to being fast, stable and time-saving, this technology can also significantly reduce labor intensity.
In the previous processing of large aircraft structural parts, the labor intensity of workers was mainly reflected in the replacement of special milling fixtures and the fine adjustment of parts processing positions. The original special fixture has to be replaced once facing the long stringers of different cross-sections. And when facing longer long stringers, nearly 70 to more than 80 bolt pressing plates are required.
The "multi-flexible matching cutting technology" can greatly reduce the number of fixture replacements through universal fixtures; through flexible hydraulic adjustable fixtures, the difficulty of positioning parts is also reduced, and workers can easily align and process quickly; through the invention of embedded fixtures, reduce This reduces the tedious labor caused by workers changing the bolt pressing position during the processing.
After applying "multi-flexible matching cutting technology", the part manufacturing cycle is effectively shortened by 40%, and the single-piece cycle is shortened by an average of 5 days.
The tooling manufacturing cost has been reduced by more than 90%, and the processing efficiency has been increased by 56 times.
At the same time, the manufacturing accuracy is doubled, and the qualified rate of parts is as high as 100%.
Today, AVIC XAC has realized the pre-stress adjustable multi-point clamping and conformal clamping of typical aerospace structural parts such as the fuselage frame, wing stiffened wall panels, and wing ribs one by one. This technology is widely used in the development and production of the long truss of the wing of the C919 project.
This technology has greatly improved the level of digital aircraft manufacturing in my country. In the future, the model and output of my country's aviation manufacturing industry will gradually increase, bringing more considerable economic benefits.
