## 5 Discussion
### The Relationship Between the Height of Extrusion Zone and Cutting Depth
Therefore, if the variations in \(\mathbf{GDC}\) are not considered, and the rock-cutting model is established with \(\mathbf{h}_{c}=\mathbf{h}\), it may lead to some deviation in the results of the analysis. This deviation may be particularly significant when the cutting depth is large. For instance, in numerical simulations and laboratory tests [35], the minimum value of \(\mathbf{GDC}\) has been as low as 0.40. In such cases, it is not appropriate to treat the cutting depth as the height of the extrusion zone. Thus, before constructing the rock-cutting model, it is recommended to perform a series of single-tooth pre-cutting tests on the rock to determine the height of the extrusion zone based on experimental results. The new dynamic model constructed in this study visualizes the change in tool-rock interaction in the process of cutting rock breaking, and theoretically reveals the mechanism of dynamic rock breaking. The influence of cutting parameters on cutting frequency and \(\mathbf{GDC}\) reveals the influence of tool inclination, cutting speed and cutting depth on tool-rock interaction and contact relationship. Therefore, this study can provide new ideas and references for cutting-related research and design. Firstly, in the aspect of cutting model construction, this study proposes a method based on the dominant frequency of single tool cutting force to determine the height of extrusion zone \(\mathbf{h}_{c}\) in cutting, which provides a new idea for accurate modeling. For example, in the study of tool wear, tool wear is closely related to the range of tool-rock contact position. If the model is modeled according to the previous static cutting model, the longitudinal projection of the tool-rock contact range is a fixed value of the cutting depth \(\mathbf{h}\). According to this study, the acquisition of \(\mathbf{GDC}\) based on the new dynamic single-tooth cutting model provides a new way to determine the tool-rock contact range. Secondly, according to the change in GDC with cutting depth, it can be seen that when the cutting depth is small (\(\mathbf{h}\leq\) 0.5 mm in this study), the longitudinal scale of the contact range can be considered as \(\mathbf{h}\) in the construction of the cutting model or the analysis of the tool-rock contact range. When the cutting depth gradually becomes larger, to accurately determine the \(\mathbf{h}_{c}\) or \(\mathbf{GDC}\), it is best to carry out a certain pre-cutting experiment according to the method in this paper. In addition, according to the influence of three cutting parameters on cutting frequency and \(\mathbf{GDC}\), when analyzing the contact relationship between tool and rock in the range of tool inclination angle of 10-20\({}^{\circ}\) and cutting speed of 15 mm/s-55 mm/s, only the depth can be explored without paying too  
Figure 18.0 The relationship between experimental \(\mathbf{GDC}\) and \(\mathbf{h}\). (a) Rock 1, (b) rock 2.  
much attention to the changes in the other two parameters. This provides a good reference for the design and optimization of the cutting scheme in the subsequent research. At the same time, due to the limitations of research level and objective conditions, there are still some shortcomings in this study. First, on the basis of comprehensive consideration of the research focus and problem simplification, this study ignores or assumes some factors that will affect the cutting process in practice. For example, when constructing and analyzing the new dynamic cutting model, the influence of temperature, humidity and other factors on the cutting parameters is ignored, and the cutting tool is regarded as a rigid body without considering its wear in the cutting process. Secondly, the research focus of this paper is to propose a new method of dynamic cutting model, and accordingly put forward the corresponding research method of cutting dynamic characteristics. Therefore, only the Tuffeau rock type is selected to carry out relevant research and verification.