Machining of Compacted Graphite Iron (CGI) and Spheroidal Graphite Iron (SGI): A fundamental study of tribological issues and progressive cutting tool wear.

摘要

This dissertation presents the results of extensive experimental studies conducted on gaining a detailed and comparative understanding of the tribological issues and progressive cutting tool wear mechanisms encountered in the machining of important grades of cast iron: Compacted Graphite Iron (CGI), Spheroidal Graphite Iron (SGI) and Gray Cast Iron (CI).;The interactions among tool material, tool topography, and Minimal Quantity Lubrication (MQL) on the tribology of CGI machining, under different cutting speeds, are studied through short duration turning experiments on CGI with flat faced, grooved and chamfered tools; constituting of silicon nitride, coated carbide and coated cermet grades. The results from the study reveal an increase in cutting forces with the application of MQL at high cutting speeds (400 m/min) on all tool types; symptomatic of the negative influence of using MQL at these conditions. Results also show an enhanced performance of grooved coated cermets.;Progressive tool wear tests conducted on cylindrical CGI and SGI test specimens with a wide variety of cutting tools (uncoated and coated carbide, uncoated and coated cermet, uncoated silicon nitride ceramic and uncoated cubic boron nitride), under different cutting speed regimes (250 m/min, 400 m/min), reveal the collaborative nature of crater wear, flank wear and nose wear in effecting the edge failure of cutting tools. Results also show the existence of a complex relationship between tool-substrate and tool-coating in machining CGI and SGI with a cermet tool; where a TiN coating on the tool effectively increases tool wear instead of reducing it. It is observed that tools (irrespective of the tool substrate material or tool coating) fail relatively faster during SGI machining, owing to the better physical and mechanical properties of SGI, in comparison to CGI.;An experimental study conducted on machining the three grades of cast iron with uncoated and coated cermet tools reveals the unique occurrence of flank face buildup/layers on uncoated tools used to machine CGI and SGI. This is shown to be on account of microchip generation in machining. The study also reveals the absence of such flank face buildup on TiN coated tools and tools used to machine CI.