THE ANALYSES OF MACHINED SURFACE ACCURACIES IN THE END MILLING OF AL6061-T6：A STUDY OF THE DIMENSIONAL ACCURACY AND SURFACE ROUGHNESS
| Autor: | Hung-Yen Chang, 張弘彥 |
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| Rok vydání: | 2003 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 91 This dissertation presents the theoretical and experimental analyses of the dimensional accuracy and surface roughness in the end milling of aluminum alloys. In the end milling operation, the helical end mill supports one end with the spindle and drive on the other, hence it is easily deflected by the cutting force and results in dimensional errors on the machined surface. Due to the side cutting edges taking the major work of metal removal and the cutting forces acting on the circumference of the tool, the theoretical analyses of the tool deflection including the bending, torsion and the teeth deformation are assumed. In order to analyze the deflection of the nonprismatic tool, the mill and the cutting chips are sliced into small segments along the tool axis. The dynamic flexural rigidity is built from rotating the true cross-sections of the segments. The unit cutting forces on the chip segments of Aluminum 6061-T6, including the effect of tool run-out, are calculated by Kline’s cutting force model. According to the properties of the cross-sections, the analyses of tool deflection by torsion are divided into uniform and non-uniform portions. Since the teeth-flanges on the mill have a larger sidewise bending stiffness, the warp on cross-sections by torsion is also derived. To compute the tooth deformation, the finite element method using the ANSYS software is applied. An auxiliary experiments and measurements of data are used to verify the adequacy of the theoretical model. The results show the theoretical model with closed shapes to the experimental measurements. For the more aluminum alloys may be used in the practical process, the experimental model including the factors such as the hardness of workpiece, cutting speed, feed, axial and radial depths of cuts is supposed. The central composite design with the Response Surface Methodology is adopted to build the experimental model. Variance analysis is then used to test the significant factors and verify the appropriation of this model. The results indicate that the dimensional accuracy is reduced with the increasing values of workpiece hardness, feed, radial and axial depths of cut, but it increases with greater cutting speed when the cutting speed is above 100 m/min. The practical roughness models with dry cutting and coolant conditions are developed and compared with the theoretical model. Factors included in the developed models are, the cutting speed, feed, depth of cut, concavity and axial relief angles on end cutting edge by Response Surface Methodology for Aluminum 2014-T6. The adequacy and prediction of the machined surface accuracy models were verified with variance analyses and concluded well. The results show that the surface roughness greatly improves when the cutting fluid is applied. The significant factors affecting the finished surface with dry conditions are the cutting speed, feed, concavity and axial relief angles; respectively, the feed and concavity angles are for coolant conditions. For a given concavity angle more than 2.5o, surface roughness increases with the growths of feed, concavity and axial relief angles. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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