Development of a New Model for the Varying Dynamics of Flexible Pocket-Structures During Machining

Many of the aerospace components are characterized by having pocket-shaped thin-walled structures. During milling, the varying dynamics of the workpiece due to the change of thickness affects the final part quality. Available dynamic models rely on computationally prohibitive techniques that limit their use in the aerospace industry. In this paper, a new dynamic model was developed to predict the vibrations of thin-walled pocket structures during milling while taking into account the continuous change of thickness. The model is based on representing the change of thickness of a pocket-structure with a two-directional multispan plate. For the model formulation, the Rayleigh–Ritz method is used together with multispan beam models for the trial functions in both the x- and y-directions. An extensive finite element (FE) validation of the developed model was performed for different aspect ratios of rectangular and nonrectangular pockets and various change of thickness schemes. It was shown that the proposed model can accurately capture the dynamic effect of the change of thickness with prediction errors of less than 5% and at least 20 times reduction in the computation time. Experimental validation of the models was performed through the machining of thin-walled components. The predictions of the developed models were found to be in excellent agreement with the measured dynamic responses.

[1]  J. Douglas Faires,et al.  Numerical Analysis , 1981 .

[2]  W. Kline,et al.  The Prediction of Surface Accuracy in End Milling , 1982 .

[3]  John W. Sutherland,et al.  An Improved Method for Cutting Force and Surface Error Prediction in Flexible End Milling Systems , 1986 .

[4]  P.A.A. Laura,et al.  Analytical and experimental investigation on vibrating, continuous rectangular plates of non-uniform thickness , 1987 .

[5]  M. A. Elbestawi,et al.  A simulation system for improving machining accuracy in milling , 1990 .

[6]  Yusuf Altintas,et al.  Prediction of Cutting Forces and Tool Breakage in Milling from Feed Drive Current Measurements , 1992 .

[7]  Yusuf Altintas,et al.  Dynamic peripheral milling of flexible structures , 1992 .

[8]  Rong Tyai Wang,et al.  Vibration analysis of a multi-span beam , 1994 .

[9]  L. Meirovitch.  Principles and techniques of vibrations , 1996 .

[10]  Farid Abrari,et al.  Multi-Axis Milling of Flexible Parts , 1998 .

[11]  Luigi Garibaldi,et al.  Dynamics of multi-span continuous straight bridges subject to multi-degrees of freedom moving vehicle excitation , 1999 .

[12]  Jer-Shyong Tsai,et al.  Finite-element modeling of static surface errors in the peripheral milling of thin-walled workpieces , 1999 .

[13]  V. Prabhu Raja,et al.  Dynamics of High-speed Machining of Aerospace Structures using Finite-element Analysis , 2002 .

[14]  Daniel Brissaud,et al.  A model of milled surface generation for time domain simulation of high-speed cutting , 2003 .

[15]  Yusuf Altintas,et al.  An Improved Time Domain Simulation for Dynamic Milling at Small Radial Immersions , 2003 .

[16]  Svetan Ratchev,et al.  Milling error prediction and compensation in machining of low-rigidity parts , 2004 .

[17]  Svetan Ratchev,et al.  Modelling and simulation environment for machining of low-rigidity components , 2004 .

[18]  Svetan Ratchev,et al.  Material removal simulation of peripheral milling of thin wall low-rigidity structures using FEA , 2004 .

[19]  Daniel Brissaud,et al.  Impact of the cutting dynamics of small radial immersion milling operations on machined surface roughness , 2004 .

[20]  Shun-Chang Chang,et al.  Free vibration analysis of multi-span beams with intermediate flexible constraints , 2005 .

[21]  D. J. Gorman,et al.  Accurate analytical type solutions for free vibration frequencies and mode shapes of multi-span bridge decks: the span-by-span approach , 2006 .

[22]  Balakumar Balachandran,et al.  Stability analysis for milling process , 2007 .

[23]  Paul Xirouchakis,et al.  Finite element method based machining simulation environment for analyzing part errors induced during milling of thin-walled components , 2008 .

[24]  József Kövecses,et al.  Dynamics Modeling and Analysis of Thin-Walled Aerospace Structures for Fixture Design in Multiaxis Milling , 2008 .

[25]  B. Balachandran,et al.  Stability of Up-milling and Down-milling Operations with Variable Spindle Speed , 2010 .

[26]  József Kövecses,et al.  A New Analytical Formulation for the Dynamics of Multipocket Thin-Walled Structures Considering the Fixture Constraints , 2011 .