## 1 Introduction  
Mineral resources are the foundation for the development of human society. For metal mines, blasting is the main form of mining [1, 2]. However, there are difficulties in controlling the stability of surrounding rocks in the blasting mining process. In addition, simultaneous blasting of ore and waste rock increases the workload of washing [3, 4, 5]. In recent years, the continuous mining of metal mines, which draws on the successful experience of mechanized mining in non-metallic mines, such as coal mines [6, 7, 8], has attracted the attention of scholars. However, the hardness of ores in metal mines is generally high, and the conical picks on shearer drum suffer great forces due to hard rock cutting. Improving the cutting ability of hard ores has become a current research hotspot. This article takes the shearer drum, which is widely used for coal cutting in fully mechanized mining equipment as the research object and conducts research on methods to improve the cutting ability of hard rocks. At present, many factors influence the material properties of rock, and confining pressure is one of them [9]. [PERSON] et al. [10] found that crack closure happens under the compression effect. Rock is considered a porous and fractured material, and under external pressure, cracks and voids will close. Therefore, the compactness of the rock increaseswith the compression effect, which has some influence on the mechanical properties of the rock. According to [PERSON] et al. [11], with the increase of confining pressure, the strength of granite increased. [PERSON] et al. [12] found that an increase in confining pressure on rock mass would reduce the elastic modulus of the rock mass. Therefore, confining pressure on rock mass is proved to be a factor that increases the compressive strength of rock mass. Then, the cutting performance of cutting tools behaves differently [13]. According to [PERSON] et al. [14,15], with the increase of confining pressure, the critical stress of the sample increases and the fragmentation of particles increases. [PERSON] et al. [16] found that as the confining pressure increased, the cutting force on single cutters increased as well. From this, it can be seen that rock with loose and porous become denser under confining pressure. Then, denser rock could be resistant to higher cutting force, which increases the difficulty of rock fragmentation. Therefore, it is harder for rock cutting with the increase of confining pressure. However, those studies focused on single cutters rather than multiple cutters, such as shearer drums, which would be studied in the paper. Therefore, this article will consider it in subsequent research content. Previous studies have shown that under the confining pressure, the compressive strength of rocks increases, and the cutting force increases as well. For the shearer drum cutting process, confining pressure not only increases the compactness of the rock but also increases the squeezing force between the shearer drum and the rock mass. According to [PERSON] et al. [17,18], the working environment of the cutters on the end plate of the shearer drum is harsher than the cutters on the other positions because the cutter's shearer drum worked inside the coal body and extrusion from the coal body aggravated the working condition. Therefore, reducing the frictional resistance between the rock mass and the shearer drum is not only beneficial for reducing the wear of the cutter but also good for reducing the cutting force. One of the methods to reduce the squeezing force is to add free surfaces to the rock mass according to [PERSON] et al. [19] and it is found that the number of free surfaces in the rock mass can effectively reduce the cutting force on the cutter. Till now, there are several methods for the creation of free surfaces on rock mass if necessary, such as water jet-assisted technology [20]. According to that research, the appearance of free surfaces in rock mass can effectively reduce cutting force.