Fuzzy Reliability Estimation for Cutting
Tools Based on State Space Model
Shujie Liu, Chao Li, Hongchao Zhang
Sustainable Manufacturing Research Institute
Mechanical Engineering Academy, Dalian University of Technology
Dalian, China
liushujie@dlut.edu.cn
Abstract
A cutting tool is an important part of machine tools and its reliability influences the total manufacturing
effectiveness and stability of machine tools. The paper presents the application of state space model in
the cutting tools reliability assessment. As the single evaluation threshold is not easy to determine, the
paper puts forward the concept of fuzzy sets to solve this problem. The performance variable acquired
through feature extraction is used to fuzzify the states of the cutting tools and the degeneration state is
treated as a fuzzy event which is uniquely characterized by membership function. The deterioration of
the tool is seen as a stochastic dynamic process with continuous degrading and the deterioration
tendency is predicted by the Kalman filter algorithm. Fuzzy reliability is defined and the
condition-based replacement strategy is introduced. In the case study, the acoustic emission signal is
measured, and wavelet packet (WP) energy extracted from the acoustic emission signals is used to
estimate the tool state. The corresponding fuzzy reliability is calculated based on the distribution of the
forecasted state and a pre-set fuzzy membership function. The best time of when the tool should be
replaced is obtained from a cost model. The positive results show the plausibility and effectiveness of the
proposed approach, which can facilitate machine performance and reliability estimation.
Key words: Cutting tool, state space model, Kalman filter, fuzzy reliability, condition-based
replacement.
1Introduction
As an important part of CNC machine, cutting tools will be aging in the long-term operation. The
reliability of cutting tools influences the whole manufacturing effectiveness and stability of equipment.
The malfunction of machine tools may result in the halt of the whole production and bring about
tremendous financial losses. For example, in the case of complex installations such as automobile
assembly lines, it can be as high as $20,000 per minute. With an accurate estimate of tool lifetime,
worn tools can be changed in time to reduce waste product and tools costs noticeably. It is even
possible to guarantee a certain surface quality(Chen et al. 2011). Requirements for increased plant
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