Finite Element Analysis of Centreless-Lunette Turning of Heavy Shaft

Abstract

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...

FEA-Analysis of Shaft and Supports Deformations for Huge Precise Lathe. Statics and Resonances

“…EHL model will be simulated onwards for full situation review. RHL machine was described and simulated in case of centerless turning (Vasilevich and Dounar, 2017). Techniques that work are implied in the present investigation.…”