MM Science Journal | www.mmscience.eu ISSN 1803-1269 (Print) | ISSN 1805-0476 (On-line) Special Issue | HSM 2019 15 th International Conference on High Speed Machining October 8-9, 2019, Prague, Czech Republic DOI: 10.17973/MMSJ.2019_11_2019057 MM Science Journal | 2019 | Special Issue on HSM2019 3099 HSM2019-044 FREQUENCY RESPONSE PREDICTION FOR ROBOT ASSISTED MACHINING A. Barrios 1 *, S. Mata 1 , A. Fernandez 1 , J. Munoa 1 , C. Sun 2 , E. Ozturk 2 1 IDEKO, Dynamics and Control, Elgoibar, Spain 2 AMRC with Boeing, The University of Sheffield, Sheffield, UK *Corresponding author; e-mail: abarrios@ideko.es Abstract Robotics is increasing its presence in the machine tool sector. One interesting application for robot assisted machining involves a robot locally increasing the stiffness of a thin walled part to suppress regenerative vibrations and minimize part deformations during machining. Simulating the dynamics improvement achieved when coupling the robot and the part is of high concern, in order to guarantee the appropriate performance of the assisted machining. Receptance Coupling Substructure Analysis (RCSA) technique for High Speed Machining (HSM) dynamics simulation has been expanded to derive the frequency response of the assembled system composed by the coupling of the thin walled part and the robot. Keywords: Robot; Dynamics; Frequency response; Receptance coupling; Machining 1 INTRODUCTION Robotics is revolutionizing manufacturing as robots become smarter, faster and cheaper, increasing its presence for high value tasks rather than traditional repetitive or dangerous tasks [Pricewaterhouse 2014]. Machining of thin walled parts is a challenging manufacturing process since the low stiffness of thin walled parts leads to undesirable vibrations and deformations of the part, due to instability in the machining process, causing a negative effect on machining accuracy and surface quality of the final part. Traditionally milling stability theory [Altintas 2012] is applied to eliminate vibrations and increase productivity by tuning process parameters. However, occasionally additional actions are required to modify the dynamics of the part and obtain a stable machining operation. Acting on the fixturing of the part provides a considerable effect on the improvement of the dynamics of the part. Usually the part is clamped to the table at a discrete number of predefined surfaces and the part can be further stiffened by adding more fixed supports to the default fixturing. These fixed supports range from simple clamps to novel intelligent fixtures that enable the identification of critical process conditions, the compensation of error influences and the minimization of defective parts [Möhring 2016]. Vibrations during thin walled part machining are mainly related to the dynamics of the area of the part where the tool is interacting and the use of additional fixtures all around the part may require a large amount of clamping elements. Considering this fact, a mobile support system can be used to provide increased stiffness to the part precisely at the tool-part contact zone, following the tool around the part at the same velocity. Fei [Fei 2017, Fei 2018] introduces an ad hoc mobile support system attached to the ram of the machine tool to stiffen and damp the thin walled part while machining in order to suppress vibrations. In the literature the trend is to use robots as mobile supports for thin walled part machining, because of the additional flexibility and adaptability that robots provide. The robotic mobile support allows the suppression of vibrations and reduces deflections by improving the stiffness of the thin walled parts in the direction of the main vibration mode. Some authors focus their research on the coordination for dual-robot mirror milling system consisting of a machining hybrid robot, a supporting hybrid robot, and a fixture [Xiao 2018]. Other authors develop a force control solution in an industrial robot to be used in a milling machine in order to supress vibrations and deformation of the thin walled part [Esfandi 2017, Ozturk 2018]. A robot as mobile support provides a clear improvement in the dynamic response of the thin walled part, which has been demonstrated. Therefore, it is of high interest to predict the dynamic response of the combined robot and part system in order to simulate the dynamic response and stability of the machining operation. This machining capability prediction allows determining the viability of the robotic mobile support, saving time and costs compared to the experimental verification that requires physically moving the robot to the machining workshop. A range of techniques has been developed to help dynamic design and vibration analysis of complex structures or systems. These techniques represent the structure through models so that the dynamic properties of the structure can be studied [Urgueira 1989]. These models can be broadly categorized as:  Spatial Models. Analytical models based on the mass, stiffness and damping matrices representing physical properties of the Degrees of Freedom (DoF) of the