Simulation-based Control of Tool Wear and Lifetime for Titanium Machining

The prediction of tool life time in machining processes has been subject to research since the beginning of machining technology itself. Already in the early 1900s Taylor [1] found a basic correlation between tool life time and cutting velocity in turning. The Taylor equation has later been improved by also taking the chip thickness into account. However, not the equation is the problem in computing the tool life time but the parametrization for a certain pair of tool and work material. Especially for the machining of titanium alloys with sharp tools where the tool wear mainly consists of smaller or greater splintering of the cutting edges it is hard to determine the state of a somehow worn cutting edge as a scalar value. This makes it hard to measure the progression of the tool wear from a new tool towards a finally worn one. Especially the point in time at which the final wear, i. e. the end of the tool life, is reached is hard to determine. Another problem that is related to tool wear is the effect on the cutting forces. As far as it is not possible to simulate the tool wear progression it does not make sense to try to predict the point in time where the end of tool life is reached. Measurements of the spindle torque with differently worn tools have shown that a simple extension of the Kienzle equation enables the inclusion of the tool wear into the cutting force computation. Vice versa, when the undeformed chip form is known it is possible to recompute the current wear state from the spindle torque. This enables the measurement of both the tool wear progression and the end of tool life and therefore to develop a tool wear model that is taking the undeformed chip form into account. This allows the computation of the tool wear progression even along any NC-program with continuously changing undeformed chip forms.