Feasibility study of an adjustable-power laser cutting head for TBM applications: Focus on rock fragmentation efficiency and energy consumption

Mechanical rock-breaking tools generally perform poorly in cutting. To meet the “double carbon” target, it is important to reduce the consumption of metal materials and the waste of metallurgical energy. These issues are often caused by the frequent failures of rock-breaking tools in extreme geological formations. Such formations are characterized by high ground stress, high rock strength, and high quartz content. To address this, research has been conducted to support efficient rock breaking by full-face tunnel boring machines (TBMs) using disc cutters. This research includes establishing a laser theoretical model, designing a prototype laser cutting head, proposing a laser-assisted rock-breaking mode, and validating its feasibility. Initially, the introduction of a perforated spherical concave lens was proposed without altering the basic components of traditional laser cutting systems. This lens was aimed to improve the beam shaping principle of straight round lasers, thus suggesting a new adjustable power density distributed laser theoretical model. Subsequently, the structure of the prototype distributed laser cutting head was designed, and an integration scheme with the existing TBM cutterhead cutting system was provided. Based on the disc cutter rock-breaking mechanism, a laser pre-cutting groove-assisted adjacent disc cutters rock-breaking mode was proposed. Later, to analyze the rock-breaking effects of distributed lasers, on one hand, an improved plan for the laser cutting head optical assembly was proposed and simulated for verification; on the other hand, a laser rock-breaking experimental platform was further set up, and the rock-breaking effects of straight round/distributed lasers were compared and analyzed to determine the optimal object distance for subsequent experiments. Finally, experiments on disc cutter penetration into rock samples irradiated by straight round/distributed lasers under different distances from the cutter to the groove (DCG) were conducted. By comparing and analyzing the macroscopic rock fragmentation phenomena and the energy consumption of disc cutter penetration into rock, the feasibility of the new rock-breaking mode was preliminarily verified. The research results show that distributed lasers can fundamentally suppress the formation of vitreous glaze by reducing the laser power density in the outer non-core areas. By converting traditional straight round lasers into distributed lasers, the energy consumption during the penetration of tools into rock can be significantly reduced Additionally, the optimal DCG is increased. Compared to the traditional disc cutter rock-breaking mode, the proposed rock-breaking mode offers advantages such as better rock-breaking effects, lower energy consumption, and fewer required laser cutting heads and disc cutters.