By trial and error...
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Gleb Gubanov, the employee of the TsAGI research and production complex
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The handmade bench at which Gleb Gubanov carried out experiments in the course of damper creation
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Oscillations may do significant damage to a part under production. On the photo left – example of such adverse effect
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Now, TsAGI specialists of the research and production complex have dampers of several sizes. This arsenal is sufficient for the production of vanes of various types
At the creation of aerodynamic models and their components, i.e., compressor vanes of gas turbine engines, the final stage of work determines the success of the whole process. The issue is the finish milling by means of a modern high precision CNC machining center, during which vibration of the parts may occur. Such adverse events are caused by impact of a milling cutter and may “ruin” a vane in a literal sense. At TsAGI, we found the solution to this issue. Gleb Gubanov, a young specialist of the Institute research and production complex, tells us about this solution
Our conversation partner has graduated from the Department of Aeromechanics and Flight Engineering of MIPT and is among a new generation of the employees who are ready to use critical approaches to the work. The manager set the task before Gleb — to design a damper (vibration damper) to be fastened directly to the part and prevent vibration caused by milling cutter impact. An inertia damper was taken as a basis; it is a system executing free oscillations. It was expected that in the course of milling its vibrations would dampen oscillations of the part being milled.
Prior to tests of real vanes in the milling cutter, Gleb created a small bench. A trial model was meant to simulate the process of milling, but a metal plate played the part of a part to be machined, and an arm with the load (in the form of an ordinary eraser) fastened to it — a damper. It was easy to manufacture such a load and to move it along the arm, changing the frequency of free oscillations of the damper. Vibrations in the model were set up by a small motor with the eccentric on the shaft. According to the young scientist, the result of the experiments surpassed all expectations. “Vibrations of the part disappeared, when the damper oscillation frequency coincided with the motor rotation frequency,” Gleb said.
Then experiments were carried out directly on the metal vanes. The result was that the inertia damper eliminated constrained oscillations of the part, caused by operation of the milling cutter on the specified frequency, and very effectively: a vibration damper weighing 1% of the part weight allowed to decrease the amplitude of its constrained oscillations by 100 times. Nevertheless, the damper failed to manage so-called self-oscillations, which could occur on the frequency other than the frequency of external action. “This phenomenon is challenging for study, and in actual practice it occurs on a regular basis,” our conversation partner explains. To clearly demonstrate this negative effect, caused by self-oscillations, Gleb showed various specimens of metal plates. The surface of some of them covered by the particular relief pattern similar to window frost.
Thus, the problem of constrained oscillations of the part on the specified frequency was solved, but not the problem of self-oscillations. A new idea immerged: “Instead of a small weight, why not a more massive device on the part to be machined? If the vibration damper weight is 100 % of the part weight, then it will be effective within the wide range of frequencies,” Gleb decided. The idea helped to develop a universal damper which may handle self-oscillations without specific settings for a certain part.
This resulted in a damper which is a “load” (of cylindrical shape), placed with a small gap in a metal housing (sleeve) filled with viscous fluid. The sleeve is fixed to the part, and the load freely “travels” inside. When the part starts to oscillate, the housing of the vibration damper displaces relative to the inertia load, forcing the inner viscous fluid to flow through a thin gap between the side surfaces of the housing and load, which ensures dissipation of oscillation energy.
Said dampers are manufactured from brass, duralumin and other materials at TsAGI’s research and production complex. The vibration dampers are of four sizes, which differ from each other in mass. They do not require adjustment for a specific task rather, the selection of an appropriate size for a specific part. During milling the dampers are installed to the side opposite to the part to be machined, and then the procedure is repeated. They are fastened with an adhesive or by vacuum.
A range of sets of vanes for fans and turbines of various purpose has been manufactured using these dampers. The main advantage of this milling method is the essential simplification of part fixation, reduction of time for production preparation, and maintenance of design process efficiency.
“Now we are working toward large-scale implementation of the technology,” Gleg explained. “The application of the dampers is plausible not only for vane production, but also for all soft parts.” As an example, he explains a production process of stiffened panels for aircraft. “TsAGI takes interest in our development results, but we hope that its importance will have wider application,” the young scientist notes. Gleb has defended the Ph.D. thesis on this subject, thus the invention is a benchmark for him personally.