Apr 052012
 

A large set of orthogonal metal cutting tests was carried out, for Aluminium 2014_T6 using HSS and carbide tools, with the main objective of observing transient dynamic response during the first few revolutions after tool-workpiece engagement. Thesis StatementThe parametric study covers a wide range of various combinations of depth, width of cut as well as spindle speed. Depth of cut is assumed to rises linearly to its nominal steady state value after one spindle revolution (the wedge effect). Both of the two force components as well as tool acceleration in the thrust direction are monitored, and recorded on FM tape recorder for further analysis. Experimental results show that forces rise up to their quasi-steady state values, but not necessarily after one spindle revolution. Often, more than one revolution is taken. This rise duration increases with decreasing depth of cut and increasing spindle speed. This behaviour can not be explained using classical quasi-static models.

Steady state force values are found to be in agreement with established models in the literature. Root mean square of acceleration in the thrust direction was found to be a good measure of energy involved in the process and to be very sensitive to cutting conditions and their dynamic changes. It is shown that with reasonable simplifying assumption and using standard system identification techniques, experimental cutting force transient response can be fitted to a first order model. This model states that the forces depend not only on depth of cut but on the rate of change of depth of cut and rate of change of force as well.

In order to explain this transient force response on physical bases, it is proposed that metal cutting, usually, occurs under adiabatic shear band conditions. This comes in agreement with earlier views about the dual nature of metal cutting as a shearing-cracking process. Yet, for adiabatic shear banding to occur, metal deformation is to be modelled as a Thermo-Visco-Plastic large deformation large strain rate process.

Finally, a simplified one-dimensional verification of the proposed time dependent force model is presented. Possible implications of using such a model in more practical metal cutting situations is discussed. Moreover, some applications of the obtained results in adaptive control, material testing, and machinability data prediction are briefly discussed. Possible extensions and continuation of the present work are also suggested. The appendices include a comprehensive graphical report of most of the cutting tests performed as well as a literature survey in support of this new physical model.

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  1. Y.M. Ali, Experimental Investigation on The Dynamics of Orthogonal Metal Cutting, Master Thesis, The American University in Cairo, May 1993.

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