Cutting methods and machine tool issues in die and mold machining.

摘要

The objective of this research project was to develop a technique for the direct machining of dies and molds in their hardened state. The technique was applied to the milling of hardened dies with ball end mills. The cutting geometry of the multi-path ball end milling and inclined ball end milling was identified and the mathematical expressions for the instant depth of cut were derived. It was found that the "step-up" path increment mode and inclined ball end milling create the best cutting conditions. The poor cutting condition of "zero speed zone" could be avoided by applying those methods. Experimental data showed that the cutting force was decreased by using those methods. Finite element analyses were conducted on the SETCO high speed spindle with different ball end mills. The results showed that for the insert type cutter with high stiffness, the major vibration mode was the spindle mode, while for the solid cutter with low stiffness, the tool mode dominated. The cutting experiments supported the judgement concluded from the finite element model. An open architecture NC controller was developed and installed in a three-axis milling machine. A user interface software for the controller was developed. The controller and the user interface software create a user-friendly operation environment for machining dies and molds. A high pressure coolant system has been built and the effect of the coolant in hardened steel machining was investigated. The high pressure coolant greatly reduced the temperature in the cutting area. It was also observed that the cutting force was decreased by using coolant. The disadvantage of using coolant in the machining of hardened die and mold steel was the increasing of tool wear due to chipping.; This research indicates that the direct machining of die and mold steel in the hardened state is feasible. High stiffness of the machine tool particularly of the tool-tool holder-spindle system, promotes successful machining of hardened dies and molds. For a three-axis milling machine, "step-up" increment mode is recommended, while if five-axis machining ability is available, an inclined tool will create the best cutting condition in ball end milling. An open architecture NC controller will benefit the machining of dies and molds by allowing such enhancements as tool breakage detection and chatter recognition to be easily added. The high pressure coolant was effective to reduce the cutting temperature and decrease the cutting force, but attention needs to be paid to tool wear.