| Summary: | 碩士 === 國立臺灣科技大學 === 機械工程系 === 106 === The objective of the study was to develop a program used to generate compensation tool path by the measured data of a workpiece using two-dimensional coordinate measuring machine (2D CMM). The error compensation program improved the dimension errors and skewed contour. It can also help to reduce the effect of tool wear on the dimensions during the machining process .
In the study, the workpiece was positioned by using a scroll chuck, machined on a three-axis CNC milling machine and measured on the 2D CMM. The programming language of the compensation program was Visual C#. The program was composed of two algorithms: mirroring tool path and generating orthogonal regression line. The program can import measured data from the 2D CMM and export compensated NC code into the three-axis machine tool in order to compensate the workpiece’s dimension error.
In two-dimensional measurement and compensation experiment, several different types of workpiece were used. The workpieces’ geometric features included a square with 0∘rotation, a square with 3∘rotation, a square with 30∘ rotation and a circle. The decreased absolute errors of features ranged between 88% and 99% after compensation. The result shows that milling accuracy was appreciably improved. Also, the standard deviation was reduced to between 0.6 μm and 1.5μm. The reduced standard diviation indicates that the skewed contour was improved by this
compensation program.
In the experiment that adopted simulated ISO 10791-7 test piece, the workpiece was randomly placed at four locations on the table of the machine tool. The dimension errors of the workpieces were successfully compensated at each location. The result shows that this compensation method is feasible in the working area of the three-axis machine tool.
In the dimension-monitoring experiment, both new and wear tools were used to simulate the effect of the prolonged machining time on the dimension error of the workpiece. In the experiment, the 2D CMM was served as a monitoring apparatus to inspect the dimension errors. If the errors of the workpiece deviated from the tolerance, the workpiece was compensated so that the final dimensions were within the tolerance. The result suggests that controlling the dimensional of the workpieces during the mass production is feasible.
The compensation method was also verified on a five-axis machine tool. The absolute error of a feature was 0.8 μm and the standard deviation was 2.8 μm. The results show that this compensation method was also feasible on machine tools with different accuracy capability.
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