Increasing critical depth of cut in ductile mode machining of tungsten carbide by process parameter controlling

摘要

Ductile mode machining is usually applied for the optical finishing operation of e.g. tungsten carbide molds. One requestfor this mode is not to exceed the critical depth of cut hcu,crit characterized by the transition point from ductile to brittlematerial removal.Based on experimental investigations a formula for the critical depth of cut, relating the material specific propertiesYoung's-Modulus E, material hardness H and fracture toughness KC was developed by Bifano et. all. Even when theinfluence of cutting conditions, like tool or process characteristics, are neglected the formula is widely used for setting upUPM machines ever since. However, previous investigations have shown that hcu,crit strongly depends on coolant fluidcharacteristic as well as on the compressive stress applied into the cutting zone by the use of tools with e.g. negative rankangles.In this paper, we report on a ductile process analysis applying a recently developed method for process optimization inoptics fabrication. Following that trail, critical process parameters have been identified and their influences on thecritical depth of cut hcu,crit have been tested experimentally in fundamental ruling tests.Among others, following parameters were identified and tested: (a) characteristics of the coolant used, (b) the pH valueof the coolant, (c) the tool specifications of the applied diamond and (d) whether ultrasonic assistance (US) is beingswitched on or off. Depending on the applied set of process parameters and for the experimental data collected,maximum ductile mode material removal rates could be achieved with dcmax = 1600 nm.That way, a new formula was developed, which allows the prediction of the critical depth of cut depending on criticalprocess parameters while machining binderless nanocrystalline tungsten carbide. The formula was set up based onexperimental results and is one step towards extending Bifanos formula taking the influences of critical processparameters into account.