Ball-nose end milling: Development of criteria for automatic selection of spindle speed and feed rate

Dies and molds usually contain a large number of sculptured surfaces. The most common processes used in the production of this type of sculptured surfaces are Numerically Controlled (NC) milling and electro-discharge machining. In terms of machine tools and cutting tools, this work focused on 3-axis NC milling and ball-nose end mills.; In today's Computer Aided Manufacturing (CAM) systems, the physics of the milling process are hardly taken into account for the generation of NC programs. This results in some inefficiency and adverse process conditions during ball-nose end milling.; The objective of this work was to develop a methodology for enhancement of NC programs used during milling of sculptured surfaces. Such NC programs contain a large number of linearly interpolated tool paths. The computer program (OPTIMILL), developed for tool path enhancement, analyzes every tool path to determine the appropriate combination of spindle speed and feed rate that produces prescribed values of maximum chip thickness and maximum cutting speed. Significant reductions of milling time were expected with the proposed approach for tool path enhancement.; The milling process analysis conducted by OPTIMILL is based on the estimation of the uncut chip geometry (i.e., the volume of material removed during one revolution of the ball-nose end mill). A combination of discrete geometry (for the workpiece and cutting tool) and analytical expressions is required for this estimation. This work presents a methodology to derive these analytical expressions and investigates the impact of the discretization resolution on the estimation accuracy and computation time.; A limited number of tool wear experiments were conducted in order to determine the appropriate range of cutting conditions for ball-nose end milling operations. The tool material was uncoated tungsten carbide. The workpiece material was P-20 mold steel with a hardness of 30 HRC. An adhesive wear mechanism was determined to influence the observed increases in flank wear rate at relatively slow cutting speeds.; Application examples are shown for the proposed approach for tool path enhancement. The resulting enhanced NC programs reduce the time necessary to machine sculptured surfaces. Some benefits in terms of tool wear were also observed.