Rock cutting mechanisms were used for the prediction of the cutting performance of mechanical excavators in the mid of 1900s. However, rock cutting tests performed in the laboratory both in small and full scales have been successfully applied for the same purpose as a more realistic method for the last few decades. Daily advance rate, the specific energy, and the performance of the excavation machine can accurately be predicted by means of those tests. In accordance with the advanced technology, the cutting tests can also be modeled by utilizing the discrete element method as in Particle Flow Code in 3D (PFC3D) and hence the performance of a machine can be assessed from this code as well. This paper initially summarizes the methods which have been applied to predict the forces. Then, rock cutting simulations by using a conical bit in PFC3D are discussed and the pick forces recorded in the course of modeling are given. The results are compared with the ones obtained from rock cutting mechanisms. In addition, an understanding of how discrete assemblies are failed during cutting and how the tool forces on the bit are influenced by the failure type are examined.
Rock cutting tools have been widely employed on excavation machines in mining and tunneling industry. Several types of them, particularly, drag and conical bits are used on soft-medium rock environment and mounted in an array on the front of cutterhead. As the cutterhead begins to move, the rock is excavated. At the same time, the cracks occur and propagate in the direction of cutting. The chips are also formed around the cutter. The size of chips produced by the machine let the manufacturers know the excavation efficiency. However, the efficiency, i.e. the performance of machine, is also evaluated depending on the cuttability and abrasivity properties of rock. For instance, hard and abrasive rocks result in excessive wear on the bit. Therefore, the effects of cutting parameters should be investigated prior to cutting process and the descriptive information about the formation is obtained. Hence, optimum cutting conditions are determined.
The cutting parameters are examined under linear cutting sets(LCM)in the laboratories. Measurement of tool forces during tool-rock interaction at the LCM is a valuable method to have an idea about the cuttability of rock. Tool forces are basically composed of normal and cutting forces. As the wear on the bit progress, the geometry of the tip changes and causes to increase the forces (Martin & Fowell 1997). In addition, tool forces can be estimated by numerical modeling of cutting action. This method is more convenient since it has the opportunity of controlling the cutting parameters easily. Particle Flow Code in 3 Dimension running under discrete element method is a suitable program to model rock cutting. It is able to model the behavior of solids and the stresses developed within them due to different loading conditions (Tawadrous et al. 2009) It has been widely used around the world to numerically solve the various problems. In the rock cutting area, the development of different models are still in progress.