Last modified: 2016-07-08
Abstract
Modern high-pressure, high-temperature IC engines call for increasingly hard valve seat materials, in turn calling for even higher performance cutting tool materials, such as, polycrystalline cubic-Boron Nitride (p-cBN). This work focuses on a process used by Ford Motor Company in which the three angles of three-angle valve seats are cut simultaneously with a single tool holder hosting three p-cBN inserts spaced 120° about the axis of rotation. When used in this way, the life of p-cBN tools is highly variable thus negating any advantages offered by p-cBN. P-cBN, of low fracture strength, is particularly vulnerable throughout three-angle cutting due to vibration which develops as a result of unopposed radial forces from each angle (cutting insert) [1,2].
In this study, experimental cutting force data are captured from a series of cutting experiments performed using a custom built measurement tool (shown in figure 1) which has been designed to hold the p-cBN insert (shown in figure 2). The cutting force data (figure 3) are used as parametric input into a representative friction model for the cutting system. Using the friction model, a numerical simulation is created which takes into account measured friction characteristics of the system, copper-filled porosity (figure 4) of AR20 and chatter-induced fracture damage of the p-cBN substrate.
The numerical model shows good agreement with experimentally captured results. Furthermore the model allows for easy investigation on the effect of edge preparation of the p-cBN insert which highlights the importance of edge preparation when cutting with high-hardness materials such as p-cBN.