Dynamics of heavy lathe tool ta be renovated has been simulated in the paper. Original turning scheme concerns finish-machining of large rotor shafts. High-positioned parts and a milling head may create dynamic problems. For this very reason FEM-simulation has been carried in static, modal and harmonic arrangements. A carrying system for shaft support consists of a bed, a support, a tool and a tailstock. A headstock is not involved in the given turning scheme. It has emerged that static and dynamic rigidity for a support is 3-4-fold less than for a shaft. Tool rigidity is decreasing from 186.5 to 11.9 N/µm when passing from statics to turning rather close to support resonance. Twelve resonance modes have been evaluated in the paper. Two modes have been considered as dangerous. These modes are "shaft swinging in lunettes" (M1, 26.7 Hz) and "support pecking" (M3, 54.4 Hz). The paper shows excessive mechanical compliance of the bed that has insufficiently rigid ribbing and through holes. Bed filling with polymer concrete is moderately effective. Transition from twolunette (2L) scheme of shaft support to three-lunette (3L) scheme makes it possible to increase significantly rigidity in statics (by 2.09-fold) but there is a limited effect dynamics. Heights of resonance peaks are decreasing not more than 1.32-fold for M1, M3. Effect of dynamic damping has been revealed in case when high support closes with a middle lunette. The support serves as a dynamic damper. Measures for strengthening of machine tool carrying system have been analyzed in the paper. It has been established that swinging of a shaft which is to be machined according to M1 is badly blocked by passive and mechanical means. It is better to bypass a resonance while setting cutting modes. "Support pecking" resonance (M3) can be raised in the zone of high frequencies and at the same time it is possible to decrease its amplitude. This effect can be obtained while using all strengthening measures. Partial strengthening has rather low efficiency. While using a heavy machine tool three ranges are recommended for milling and turning: pre-resonance (<20 Hz), inter-resonance (35-45 Hz) and super-resonance (>65 Hz). The last range is preferable due to super-resonance damping of the shaft and the support as well. The next design step is to add triangle connecting rods or caissons for the bed. Анализ методом конечных элементов бесцентрово-люнетного точения крупных валовДокт. физ.-мат. наук, проф. Ю. В. Василевич 1) , канд. техн. наук, доц. С. С. Довнар 1) 1) Белорусский национальный технический университет (Минск, Республика Беларусь) Реферат. Смоделирована динамика тяжелого токарного станка после планируемой реновации. Оригинальная схема точения касается чистовой обработки крупных роторных валов. Высокорасположенные детали и фрезерная головка могут создавать динамические проблемы. Поэтому проведено МКЭ-моделирование в статической, модальной и гармонической постановках. Несущая система для удержания вала состояла из станины, суппорта, инструмента и задней бабки. Пере...
Research of breakage of the chestnut tree branch on the planting of university campus is provided. Collapse is caused by a severe accidental wind gust. Due to collapse in the student environment, the investigation has additional methodical value for the teaching of FEA simulation. The model includes roots, trunk, branch, and conditional crown, where the trunk-branch junction is steady enough. The load-bearing system of tree is taken as an example of an effective bionic design. The branch has grown with the implementation of the idea of “equal-strength console”—the change of sections along the branch provides constant stress level and near uniform dispensation of their without stress concentrators. Static simulation of the tree loading is provided both in the linear formulation and in the geometrically nonlinear one. It is proved that in the trunk-branch junction area the stresses are twice lower than the branch itself, and it is not the place for fracture. For the given wind pressure, the work stress in the branch has exceeded twice the allowable level under bending with some torsion. In such construction (of the tree), the breakage could happen even in the perfect branch condition due to her severe overloading.
Load bearing system simulation is provided for a huge lathe to be renovated. Static and modal analyses are done by FEM. Focus was centerline rising, needed for larger rotor shaft machining. Forces between shaft and three supports were applied. Shaft static stiffness is lowered at 1.15 times only for 600 mm centerline rising. Supports have lost its rigidity at 1.42 times. Concrete pouring into bed cavities is recommended for supports flexibility limitation such as tailstock reinforcement. Robustness of bottom resonances is revealed both for rotor shaft (14.5–18.2 Hz) and supports (42.7–55.4 Hz). Centerline rising is allowed on 300 mm at least. It gives possibility to machine extremely large (up to ø2750 mm) shafts.
FEM simulation of Eddystone lighthouse is provided. Incorporated bionic tower is modelled as well. Load cases including gravity force, wind thrust, water stream and 50-year wave impulse are accomplished. Stress concentrator system is described. Effect of tension stress concentrator compensation caused by gravity is showed. Low gradient stress dispensation is demonstrated for bionic tower outer surfaces. Recommendation touching places to monitor are given.Methodic experience related to interactive one-command student – professor FEM simulation of responsible load-bearing systems is collected.
Original experimental technical equipment for making samples in the form of permeable tubes of porous material, i.e. coiled wire. The article describes the construction of the equipment, the processes of forming and pressing the wire semi-product and methods of fixing the ends of the wire product.
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