Extension of durability theory through correlation of wear with acoustic emission to the characteristic values of the ball screw drive

点击翻译按钮获取中文摘要

Ball screw drives are currently used in the vast majority of all metal cutting machine tools as the essential drive element. Therefore, the precise knowledge of service life and assurance of availability of the ball screw drive is of decisive economic importance. Currently, the dimensioning of ball screw drives only takes into account fatigue life. This is due to the fact that it is unknown how fatigue life, wear mechanisms and the mechanical behavior of the ball screw drive are correlated.Ball screw drives are subjected to complex and combined wear mechanisms due to the complex movement and the return of the ball. This results in complex presences of wear such as abrasion, adhesion and fatigue. This influences distinctively the service life of the ball screw drive. Additionally the wear mechanisms influence the mechanical characteristics of the ball screw drive e.g. the nut preload or stiffness of the nut. Current methods for wear diagnostics only focus on individual presences of wear and on individual mechanical characteristics. Therefore an integrated understanding of wear mechanisms, wear presences and the mechanical characteristics of the ball screw drive is currently not available. Acoustic Emission is a measurement method with which wear mechanisms can be observed. Acoustic Emission allows better feature extraction because of the higher information density, leading to the observation of the formation of wear. This is currently used for diagnostics in gear boxes and bearings.Objective of this research proposal is an integrated approach correlating wear mechanisms, presences of wear and the mechanical characteristics of the ball screw drive over time with the use of Acoustic Emission. In addition to the established characteristic values for condition monitoring, acoustic emission constitutes a method to more precisely identify signs of wear (e.g. pitting) over time and to spatially assign them to the track of nut and screw or ball and therefore create a depiction of damage progression. This allows to draw conclusions on the effective wear mechanisms. This research attains the goal of correlating the depiction of damage progression received with Acoustic Emission with the mechanical characteristics and the presence of wear (structure-borne noise, temperature, frictional torque, nut preload and characteristic curve of stiffness). By matching these observations a conclusion on the chronological sequence of effective wear mechanism can be drawn. Additionally the effective service and fatigue life of the ball screw drive is quantified by identifying static and dynamic properties as a function of wear development. As a result more precise predictions of the effective service and fatigue life can be derived.