The tool:workpiece interaction when machining welded hardfacing using PCBN tools

Ren, Xuejun

Abstract

The work presented in this thesis is concerned with turning chromium carbide based hardfacings using PCBN tools. The chip formation and tool wear process was studied by quick-stop and machining tests. Cutting temperature was investigated by means of a remote thermocouple and the chip-tool interface temperature was simulated by an ANSYS Finite Element Analysis model. Cutting performance of PBN tools from different suppliers was compared in field cutting tests. Hardness, microstructure and the adhesion between the workpiece and cutting tool material were assessed.
ln the turning process, saw-tooth chips were formed, with a short chip:tool contact length. Quick-stop tests revealed that the machining process involved fracture of large carbides ahead of the cutting edge in the primary zone. Temperature measurements showed that the cutting temperature for the hard facing material was lower than that with titanium alloy but much higher than that with machining mild steel. The cutting temperature predicted at the tool chip interface was in the range of 600-700°C when cutting hard facing.
The tool wear process was found to involve three main progressive stages - from small scale edge chipping to large scale flaking and fracture. Four types of wear were identified: flank wear, microchipping, flaking of the rake face and delamination of the flank face. Abrasion appears to be the principal flank wear mechanism and it showed a minimum value for different speeds but increased with feedrate. The main mechanism for microchipping involved failure through the CBN particle boundaries. Flaking of the rake face occurred in the later stages and transgranular fracture was the main mechanism.
In field tests, PCBN material from various sources achieved different cutting performance, which reflected the structural differences in the PBN materials. A dense structure with strong particle binding is essential for satisfactory performance of PCBN in this application.

Citation

Ren, X. (2000). The tool:workpiece interaction when machining welded hardfacing using PCBN tools. (Thesis). University of Hull. Retrieved from https://hull-repository.worktribe.com/output/4224369

• Thesis Type: Thesis
• Deposit Date: Oct 12, 2022
• Publicly Available Date: Feb 24, 2023
• Keywords: Engineering
• Public URL: https://hull-repository.worktribe.com/output/4224369
• Additional Information: Department of Engineering, The University of Hull
• Award Date: May 1, 2000