INVESTIGATION OF DIE POLISHING STRATEGIES USING FIVE-AXIS MACHINING CENTRE

This paper investigates the automated grinding and polishing of dies and molds using a five-axis milling machine. Automating the die bench working process not only saves on labour costs and removes workers from a difficult and dirty task, but also reduces lead times as well as shape errors. Bench working is the process of bring the die to its final shape and appearance with only a minimal of metal removal. The removal of cusps from the surface of the die is the first stage. Once the net shape has been obtained the die is polished to a mirror like surface finish. The first stage of the project was the development of a mechanistic grinding model to help determine the forces that would be encountered during cusp removal. Using this information a passive polishing tool was designed and constructed that fit inside a standard 25.4mm (1") collet as would any other tool. The rotational velocity for the force control polishing tool was supplied by the spindle itself. The mechanistic model was verified with subsequent grinding tests. Both O1 and P20 tool steel were used while employing the Taguchi method to determine the optimal parameters (rotational speed, force, feed, etc.) for the polishing of the die. Additionally, the traditional S-pattern polishing path was compared to a fractal pattern proposed by Mizugaki and Sakamoto (1992). The system has proven to be a viable alternative to manual polishing of dies.