Improving Endmilling Surface Finish by Workpiece Rotation and Adaptive Toolpath Spacing

Free-form surfaces are being used in a growing number of engineering applications, especially in injection molding of consumer products. Decreasing the manufacturing cost and time of these molds will improve the efficiency of manufacturing injection molded consumer products. This paper is motivated by the need for simple strategies to improve the quality of and decrease the time required to machine free-form surfaces. We present two methods to improve the surface finish of parts finished with ball-nose endmilling. In the first method the surface finish is improved by finding an optimal orientation angle for the workpiece relative to the machining axis. In the second method finish is improved by adaptively varying the step-size when using raster toolpaths. The adaptive variation is controlled by a user-defined finish improvement factor, where the spacing density is increased only if the improvement in surface finish is greater than the finish improvement factor. These methods are implemented using an analytical model of the workpiece surface finish based on the mean scallop height of the machined surface. Results from the analytical model are verified with machining experiments, and we show that the adaptive spacing strategy can improve the surface quality by more than 50% with a small increase in the toolpath length. To achieve a similar improvement in surface quality by uniformly decreasing the path spacing results in a much larger increase in the toolpath length. The strategies discussed in this paper allow process planners intuitive control over the toolpath layout and spacing and improve the efficiency of machining high quality parts.

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