Research on Bending & Forming Of TA18 High-Strength Titanium Pipes For Aviation
1. Research Progress
Pipe CNC bending and forming technology is a very complex process, which is affected by many factors such as material properties, pipe wall thickness factors, bending technology, mold design and manufacturing level. Pipe bending and forming are prone to various defects, such as thinning of the outer wall thickness, thickening of the inner wall thickness, interface distortion, wrinkling and cracking, which seriously restricts the development of China's aerospace piping system. In view of the current pipe bending and forming technology, research scholars have mainly done a lot of work from the following aspects and have achieved certain results.
In terms of theoretical analysis and research, research scholars have mainly derived a large number of theoretical formulas and established models of characterization formulas from various aspects such as pipe cross-section shrinkage, wall thickness thinning rate, neutral layer offset, pipe length, bending moment and cross-section distortion rate, and the theoretical analysis results are in good agreement with the experimental verification results. However, in the process of theoretical analysis, a large number of hypotheses and formulas have been simplified, and the influence of some factors has been ignored, so the accuracy and scope of application of the formula are limited.
In terms of numerical simulation and analysis, research scholars used finite element analysis software to model the bending and forming process of pipes, and to varying degrees they developed algorithms twice. Through finite element simulation analysis, the material flow law, stress and strain distribution state, pipe wall thickness change, elbow rebound law, bending and forming defect generation mechanism and change law during pipe bending and forming process are studied, and the influence of bending and forming process parameters, such as mandrel parameters, friction parameters, bending speed and pipe mold gap, etc. , on the pipe forming process is revealed.
In terms of experimental research, the current experiments mainly focus on the theoretical analysis and numerical simulation results of universities and scientific research institutes. Scholars have conducted some research on the influence of bending process parameters and heat treatment system on the organizational morphology and mechanical properties of pipes, but research on the process and uniformity control of mass production has rarely been reported.
2. Existing Problems
Although great progress has been made in the bending and forming research of high-strength TA18 titanium alloy pipes in my country, it is still in its infancy, and no mass production technology and control method have been formed, and it still faces new challenges.
First of all, theoretical research and numerical simulation analysis are disconnected from production test research. Due to the limitations of equipment and production test conditions, universities and other research institutions have concentrated a lot of research in the direction of theoretical analysis and numerical simulation. The production unit has certain experimental trial production conditions, but due to the existing operating mechanism, it has not yet invested a lot of research work.
Secondly, in terms of process technology, during the cold bending process of TA18 high-strength titanium alloy pipes, the tonnage of the equipment is required, the angle control accuracy is low, and defects such as rebound and wrinkling are prone to occur; during thermal shaping, “bite edge” defects are prone to occur during mold closing, and high-temperature creep is easy to occur when heated for a long time, which makes it difficult to control the roundness of the cross-section of the product.
Finally, the two-step cold bending + hot shaping currently used has a longer forming cycle and a higher cost.
TA18 titanium alloy pipes have become the preferred material for aerospace piping systems and are widely used abroad, but they are still in their infancy in China. Due to the current demand for lean aviation products, the research on high-efficiency, high-precision, high-yield and low-cost forming technology of titanium alloy pipes is imminent in the future. In order to achieve precise cnc bending and forming of titanium alloy pipes, it is urgent to study and establish a more comprehensive bending and forming process system and numerical simulation system for titanium alloy pipes.
