High speed effects and dynamic analysis of motorized spindles for high speed end milling
Abstract
High-speed machining (HSM) has become a critical manufacturing technology for industry to meet fierce international competition. Aerospace industry is the first and most successful in implementing HSM due to its use of aluminum and their very large size of parts which require very long machining time. The main objective of this thesis is to develop a finite element dynamic model to characterize the mechanical and thermal influence on the dynamic behavior of the spindle-bearing system for high-speed end milling. The finite element spindle dynamic model is validated via a state-of-the-art high speed spindle/milling test bed. In particular, several systematic tests are also developed to enable the measurement of system natural frequencies at high speeds while the spindle is rotating at very high speeds. Based on the experimental and theoretical results, we conclude that: (1) System stiffness increases as the front bearing preload increases. (2) When the high-speed spindle is under appropriate cooling and lubrication conditions, the thermal preload of the spindle bearing increases due to its radial thermal expansions, resulting in higher bearing stiffness. (3) The system is softened due to the centrifugal effects of the spindle shaft when the bearing preload is kept constant. (4) The centrifugal effects are more significant to the system dynamics than the gyroscopic effects. (5) The system is softened mainly due to centrifugal effects of spindle shaft, instead of bearings. The above results can be applied to lobe diagram for regenerative stability analysis, in which the centrifugal effects must be considered in the evaluation of a system's transfer function. It can also be applied to review the centrifugal effects based on the cutter receptance. This analysis is useful to assist the use of ISO 1940/1 standard. The proposed model can provide machine tool builders a design tool to estimate necessary bearing stiffness, bearing positions, bearing spacing, and system dynamics in their machine tool designs for different operating conditions.
Degree
Ph.D.
Advisors
Tu, Purdue University.
Subject Area
Industrial engineering|Mechanical engineering
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