Effects of Process Parameters On Tool Vibration And Force Transmissibility In High-Speed Micro-Milling Machine

High-speed micro-milling is an emerging technology used to produce micro and miniaturized products with smooth surface finish and high dimensional precision. However, tool vibration is a major problem in micro-milling as it directly affects the product accuracy, surface quality and tool life. Inappropriate selection of process parameters increases radial and axial thrust as well as force transmitted to structure during micro-machining which results in rapid tool vibration. This work focuses on the experimental investigation of process parameters (cutting speed and depth of cut) in order to reduce tool vibration due to axial and radial thrust in high-speed micro-milling. The tool used in this experiment is a 2-flute end mill cutter (1 mm cutter diameter) and workpiece is a commercially pure titanium (CpTi) plate. The operation was performed at different depth of cut and varying cutting speeds keeping the chip load constant. Vibration signals were acquired and processed to obtain the vibration thrust of the tool and the force transmitted to the structure. The results indicated that as the depth of cut and cutting speed increases, both axial as well as radial thrust decreases leading to lower vibration amplitude of the cutting tool and reduction in force transmitted to the machine structure.

Optimization for Far-distance Cooperative Rendezvous with Multiple Direction-fixed Thrusts

The continuous-thrust far-distance cooperative rendezvous problem between two spacecraft is investigated. The indirect optimization method, based on Pontryagin’s maximum principle (PMP), is applied to optimize fuel consumption. To overcome the difficulty in nonsmooth integration caused by the bang-bang control, the homotopy method is adopted to solve the fuel-optimal problem from a related energy-optimal problem. The quantum-behaved particle swarm optimization (QPSO) algorithm is used to obtain the energy-optimal solutions. The energy-optimal solutions are used as the initial values for the homotopic procedure to obtain the fuel-optimal solutions and optimal bang-bang control law. A hybrid algorithm combined homotopy method and sequential quadratic programming (SQP) algorithm is proposed. This hybrid algorithm can effectively obtain feasible optimal solutions even though the indirect optimization method exhibits a narrow convergence domain. Simulations of high-thrust and low-thrust rendezvous problems are provided and the proposed hybrid algorithm is verified. Moreover, the necessity of radial thrust is investigated.

Automatic Unloading Liquid Rocket Engine Fuel Feed System Booster Pump Radial Thrust Bearings from Axial Force

Increasing the suction capacity, efficiency and energy parameters of high-speed pumps is an important task in the development of power systems in the aerospace industry, as well as in their application in energy and oil production. With improved cavitation properties, the pumps can operate at a higher shaft speed, and at its given value - with lower cavitation reserves, i.e. at a reduced inlet pressure. When the shaft speed increases, the pump weight and overall dimensions decrease. To increase the anti-cavitation qualities of pumps in the power system, auxiliary (booster) pumping units are used, creating the pressure necessary for the cavitation-free operation of high-pressure and high-speed main pumps of the engine fuel supply system. In accordance with its purpose, the booster pump must provide the required supply pressure of the specified flow rate at the lowest possible liquid pressure at the inlet. At the same time, the efficiency of the booster pump unit should be maximum, and the overall dimensions and weight should be minimal. The last two characteristics predetermine the maximum possible number of revolutions of the pump shaft. Ensuring the operability of the ball-bearing supports of the fuel supply units is one of the most important and complex tasks in the development of modern and promising liquid rocket engines (LRE), especially reusable ones. This task has always been one of the priorities in the fine-tuning the fuel feed units of such engines. The article proposes a method for calculating and controlling the unloading liquid rocket engine booster pump radial thrust bearings from axial force. The method can be applied in the entire range of liquid rocket engine calculations. The further development of this work will be mathematical modeling of the operation of the booster pump automatic axial force unloading.

CONSTRUCTION MODIFICATION OF RADIAL THRUST ROLLER BEARINGS

Analytical relationships have been developed for the design of modified tapered roller bearings based on standard bearings of the 7000 type. The modification consists in replacing the rolling elements in the form of tapered rollers with a straight generatrix by concave rollers with an arc generatrix, which are in contact with the convex raceways of the rings. By calculation, the advantage of modified roller bearings in terms of service life in comparison with standard roller bearings of similar overall dimensions is shown.

Spiral trajectories induced by radial thrust with applications to generalized sails

In this study, new analytical solutions to the equations of motion of a propelled spacecraft are investigated using a shape-based approach. There is an assumption that the spacecraft travels a two-dimensional spiral trajectory in which the orbital radius is proportional to an assigned power of the spacecraft angular coordinate. The exact solution to the equations of motion is obtained as a function of time in the case of a purely radial thrust, and the propulsive acceleration magnitude necessary for the spacecraft to track the prescribed spiral trajectory is found in a closed form. The analytical results are then specialized to the case of a generalized sail, that is, a propulsion system capable of providing an outward radial propulsive acceleration, the magnitude of which depends on a given power of the Sun-spacecraft distance. In particular, the conditions for an outward radial thrust and the required sail performance are quantified and thoroughly discussed. It is worth noting that these propulsion systems provide a purely radial thrust when their orientation is Sun-facing. This is an important advantage from an engineering point of view because, depending on the particular propulsion system, a Sun-facing attitude can be stable or obtainable in a passive way. A case study is finally presented, where the generalized sail is assumed to start the spiral trajectory from the Earth’s heliocentric orbit. The main outcome is that the required sail performance is in principle achievable on the basis of many results available in the literature.

Space radar terrain survey and the joint flight of a spacecraft pair

The paper considers the concept of space radar monitoring complex performing Earth observation by two spacecrafts according to the technology of synthesized aperture in an interferometry scheme that allows obtaining a global high-precision digital model of the Earth’s relief. The first key problem when creating the complex is the development of an algorithm for determining the heights of the resulting image relative to the relativity surface. Unlike the traditional interferometer scheme using angular coordinates, radar gives the current coordinates of all points involved in the measurement scheme. This allows new algorithm using the difference between two space phase measurements of the downrange to the same surface element to be proposed. Both measurements are performed from two points of common position, spaced apart and representing the interferometry base. As a result, a simple estimate of the potential accuracy of altitude measurement and conditions of its implementation required for the structural scheme of space interferometry are obtained. The second key problem is the arranging coordinated kinematics of the flight of two spacecrafts, forming the base of the space interferometer with the orientation and dimensions that provide the necessary accuracy of altitude measurement. It is shown that both problems are systemically interrelated and the selection of principal solutions to optimize the complex as a whole requires simultaneous consideration and interdisciplinary coordination of the requirements determined by the specifics of each of the two problems. The technique for preliminary project evaluation of results obtained from the orbital group, visually representing all the relationships between individual characteristics of key problem areas of the complex and output target indicators of its work is proposed. The characteristics of the passive flight of spacecraft pair and the conditions for the obtaining high-quality interferometer measurement are considered. It is shown that these conditions are ensured only for a certain part of the orbit, resulting in decreasing efficiency of using the orbital group flight time, and the global survey of the planet relief takes about a year. In this context the possibility of using a small radial thrust applied for a long enough time exceeding a day is shown. As a result, the measurement conditions are stabilized, and the duration of the global survey of the planet relief is reduced to a few months. In addition, the efficiency of using the flight time of the orbital group increases, which allows performing Earth sounding using other possible programs.

Study on the performance of novel gas foil conical bearings

To reduce the mass and size of low-power turbine machinery, a new type of gas foil conical bearing was proposed, and its static and dynamic performance was systematically studied. Based on a nonlinear bump stiffness model considering rounding and friction, the structural stiffness distribution, load capacity, dynamic stiffness, and damping coefficients of gas foil conical bearing were calculated, and the influence of bearing parameters on its static and dynamic characteristics was studied. In addition, a pair of gas foil conical bearings was used to replace the traditional radial-thrust foil bearing support scheme on an air compressor to explore the practicability of the novel bearing. The results show that the new gas foil conical bearing has an excellent supporting performance and broad prospects for application. The bump radius, rounding radius, friction coefficients, and foil thickness will significantly influence the bump foil stiffness. The bearing parameters such as structural stiffness, nominal clearance, cone angle, and eccentricity have a large effect on its static and dynamic performance, and we can obtain the desired bearing characteristics by tailoring these parameters.