A Novel Method of laser coating process on worn-out cutter rings of tunnel boring machine for eco-friendly reuse

Abstract

Cutter rings form an integral part of tunnel boring machines (TBM). These cutters are deployed in various hard rock tunneling projects. The life of the cutter rings governs the economics of tunneling significantly. This paper presents a novel methodology to enhance hardness and wear resistance of used worn out disc cutters in TBM for eco-friendly reuse. Disc cutters are mainly made of H13 tool steel. To improve the hardness and wear resistance, a layer of tungsten carbide is coated on the used cutter rings. Considering the long operating hours of TBM, cutter rings get worn out due to severe interaction with the hard rock both in compression and rolling mode. Replacement of the cutter-ring is costly, and quite a time consuming and cumbersome job. Refurbishment is always a better option and laser cladding is a novel technique for enhanced life of cutters. It increases the hardness and wear resistance of the cutters to a considerable extent. Cladding is carried out with the help of a laser beam. In this method, a layer of nanoparticles of tungsten carbide powder is deposited on the worn-out surface of the cutters. For carrying out the investigation, different coating parameters are selected based on the central composite design (CCD). With different capacities of laser, a total of 13 samples were prepared at various scanning speeds varying between 200 to 300 mm/min and a level of laser power varying between 100 to 200W. The coating is critically inspected by various means such as an optical microscope, FESEM, and EDS. Hardness testing was accomplished by Vicker's hardness testing machine. Wear testing was carried out with the aid of pin on disc setup. The results shows an asymmetrical behavior between the yield parameters (hardness and wear rate) and process parameters (scanning speed and laser power). The hardness values increased from 16% to 95%. A correlation test was conducted between the hardness and wear rate. The results depict a clear negative correlation between them, indicating the advantage of laser coating for reducing cutter ring wear in TBM.