The Research of The Dynamic Characteristics of Horizontal Jig Boring Machine Z.Li 1, a, X.S.Zhao 2,b and D.W.Zhang 3,c

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1 Advanced Materials Research Online: ISSN: , Vols , pp doi: / Trans Tech Publications, Switzerland The Research of The Dynamic Characteristics of Horizontal Jig Boring Machine Z.Li 1, a, X.S.Zhao 2,b and D.W.Zhang 3,c 1, 2, 3 Department of Mechanical Engineering TianJin University,Tianjin,China a lizhi@tju.edu.cn b zhaoxiangsong@hotmail.com c medzhang@tju.edu.cn Keywords: Experiemtal Modal;Dynamic Characteristics;Finite Element Analysis. Abstract. Modal analysis is one way of studying the dynamic characteristics of the mechanical. In order to study the dynamic characteristics of machine tool,numerical machine model is set up with finite element analysis software,of which validity is verified by experimental modal analysis.the experimental test also provide the boundary conditions, so as to further structure modification and dynamic characteristic design. Introduction Digital design is the direction for precision numerical machine tool designing in the future[1]. The fast reasonable design of whole structure is realized by CAD/CAE and multi-objective optimization software which integrate performance optimization and virtual prototype together. Dynamic characteristics designing is very important to machine tool and is one of the important indicators for machine evaluation and structure modification[2]. The research methods of dynamic characters of machine tool can be classified into calculating modal analysis and experiment modal analysis.the calculating modal analysis method use the characteristic value and characteristic vector of mechanical system motion differential equation, to determine the system modal parameters (natural frequency and damping ratio and modal shape). Experimental modal analysis begins with measuring the input power and output response from measurepoint on the structure,and then converts the measured data into frequency response function.finally, estimates the modal parameters by using frequency response function. Experimental method can verify the validity of the theoretical model, and provides boundary conditions to it[3,4,5]. 1. Domestic and international research status The commonly method to test the dynamica character of whole machine tool is single input multiple output (SIMO). SIMO method measure one input and multiple output signal at the same time,then get the frequency response function of whole machine tool by changing the response point. SIMO method can use vibration exciter or hammer to excite machine tool. Due to the machine tool belong to high rigid structure, vibration exciter is the relatively ideal excition of which excition force and exciton signal can be completely control, a variety of signal can be chosen,good coherence and high precision.it is more suitable for machine tools with high rigid structure. The modal experiment on machine tool is mostly on only one direction which called error sensitive direction, but for modern numerical machine tool,the error sensitive direction is not unchangeable, especially for the multiple axis machining center, these is no obvious error sensitive direction, single direction excition is obviously not very reasonable.the study on dynamic characteristics of the machine tool for different direction excition, has been done little. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-09/05/16,19:29:12)

2 1392 Advances in Manufacturing Science and Engineering 2. Horizontal jig boring machine dynamics model analysis The dynamics model of horizontal jig boring machine is established by finite element software ANSYS. Considering the actual situation and the finite element analysis software calculation rules, the model is simplified according the following principles: 1. Remove the screw part; 2. Remove gear transmission mechanism of turntable, only keep the shell; 3. Remove the broach mechanism in the spindle, only keep the shell; 4. Ignore the bolt hole,screw hole, process hole, chamfering,round, and other small structure on the machine tool; 5.Delete some groove which size less than 5 mm,bosses and tool withdrawal groove. In the model, material properties is set as follows: material is 45 # steel, modulus of elasticity is Pa, poisson's ratio is 0.3, material density is 7800 kg/m 3.Establish spring element with combin14 at x,y and z direction along the guide-slide junction surface.thethe machine tool is meshed with eight nodes Solid 45 in intelligent mesh way. The boundary conditions of the model are set as that every edge of bed bottom entirely constraint. Modal frequency and modal shape within the range of 80 Hz are listed in Table 1. Each modal shape as shown in Fig.1, Fig.2,Fig.3. Table1 Modal frequency and modal shape Modal order Frequency(Hz) Modal shape Column bending and torsion Column torsion along Y axis Column torsion along Y axis Fig.1 Modal 1 Fig.2 Modal 2 Fig.3 Modal 3 3. Dynamic characteristic test research of horizontal jig boring machine The dynamic characteristics of the machine tool, to a great extent, depends on the characteristics of junction surface. The joint surface parameters used in dynamic model are mostly experience value and do not take damping parameter into account.further more, some parts of numeral machine tool are nonlinear.so experiment test is needed to check the validity of the dynamic model and provides boundary conditions to it Experimental system composition Fig.4 Experimental system composition

3 Advanced Materials Research Vols Experimental system composition shows in Fig.4. The main instruments are listed in Table 2. Table 2 Main instrument Serial number Name 1 B&K3560 system 2 B&K4824 exciter 3 B&K8230C-003 force sensor 4 B&K3624 power amplifier 5 B&K4370 charge sensor 6 B&K2692charge amplifier 7 Notebook computer 3.2. Excition signal and measurepoint arrangement Excition signal as input information, has an important effect on the test accuracy. Random signal is a non-deterministic signal of which energy distribution is uniformed in 0 ~ frequency range.random signal is more comform to the actual processing state. Therefore, random signal is choosen as the excitation signal. The leakage is minished by adding hanning window to the response signal.test result is obtained from 50 times average.bandwidth is set at Hz. Regarding the machine tool as spindle, slidder, column and bed fourmain parts, totally 162 measurepoints are arranged on them,as shown in Fig.5. Fig.5 Measurepoint arrangment 3.3. Experiment processor Fix the exciter on the working table with bending plate,set ejector rod at the front of the spindle,give narrow band random signal along x,y,z axis direction respectively to excite the machine tool,as shown in Fig.6, Fig.7, Fig.8.Measure force signal by narrow band signal at front of the ejector rod, response signal of x,y,z direction by three B&K4370 charge sensor at spindle, slidder, column and bed. Fig.6 X axis vibration system Fig.7 Y axis vibration system Fig.8 Z axis vibration system 3.4. Experiment result Seting the noise level at 0.01and using OrthogonalPolynomial, 7 modals are found in the frequency range of Hz. Modal frequency and modal shape are listed in Table 3 Exprimental modal 1 andmodal 2 are as shown in Fig.9 and Fig.10.Modal shape from modal 3 to modal 7 are almost the same,as shown in Fig.11.

4 1394 Advances in Manufacturing Science and Engineering Table 3 Experimental modal frequency and modal shape Modal Frequency(Hz) Damping ratio Modal shape Column bending along X axis Column torsion along Y axis Column bending and torsion along Y axis Fig.9 Experimental modal1 Fig.10 Experimental modal2 Fig.11 Experimental modal3 4. Result analysis The experiment modals are more dense, finite element calculation modal 1,modal 2,modal 3 coinside with experimental modal 1,modal 4,modal 5,the max error is within 10%; modal shapes are also consistent. The validity of the dynamic model is verified by experimental test. The first natural frequency of the machine tool is 48.5 Hz, which indicates that it has good dynamic characteristic. In the low frequency phase, the modal shape is the column s bending and torsion. Table 4 The comparison of calculating modal and experiment modal Calculating modal Frequency(Hz) Experiment modal Frequency (Hz) Error(%) Acknowledgement This work was supported by the National High Technology Foundtion 863 Project under grant No.2012AA and No.2012AA Reference [1] J.R. Niu,The overview of foreign processing center and techological development trend.journal of Metal Processing,15(2012)p [2] B.Bediz,U.Kumar,Modeling and experimentation for three-dimensional dynamics of endmill. International Journal of Machine Tools&Manufacture 53(2012)p [3] J.F.Lin, X.B.Ma, Nc machine tool dynamic characteristic test and analysis. Machinery manufacturing,08(2010)p.5-9. [4] H.Z.Li,B.N.Xu, Relative excition test analysis on machine tool, Journal of Vibration,Test and Diagnosis,02(1998)p [5] J.P.Hung,Y.L.Lai,Modeling the machining stability of a vertical milling machine under the influence of the preloaded linear guide. International Journal of Machine Tools&Manufacture, 51(2011)p [6] J.X.Zheng,M.J.Zhang,The application of experimental modal technology in study the structure of machine tool.control Technology,12(2007)P

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