Recent studies in CGI machining have focused on continuous cutting conditions that occur during high-speed cylinder boring.1,2  Boring of engine cylinders is one of the more critical operations in engine production, requiring high-quality surfaces to be produced at relatively high cutting speeds. It is at these elevated cutting speeds (250-700 m/min) where the machinability differences between CGI and conventional gray cast irons are most pronounced.

Previous studies have reported insert wear rates to be 20-30 times greater in the continuous cutting of CGI relative to results obtained in machining of gray cast iron under equivalent conditions.1 The differences in machinability between gray cast iron and CGI have been attributed to differences in graphite structure and also to the presence of manganese sulfide inclusions in gray cast iron.

Manganese sulfide inclusions, (not present in CGI), form a protective and lubricating film on the cutting tool surface during machining of gray cast iron, protecting the tool surface and decreasing rates of tool wear.3,4,5  It has been shown that the formation and activity of these lubricating films is highly dependent on cutting speed (likely cutting temperatures) with gray iron machinability and tool life improving as cutting speeds increase.6

Based on these factors and the current level of understanding of the microstructural and compositional features of CGI, recent work at Quaker Chemical has led to the development of new metalworking fluid technology — Quakercool 7020-CG — useful for increasing tool life in CGI machining.7

To assess further the utility of this new technology and especially its impact during CGI machining at high speeds under continuous cutting conditions, tests were conducted to assess the performance of this fluid in a turning operation using tungsten carbide cutting inserts at cutting speeds of 250 m/min, and also PCBN cutting inserts at cutting speeds of 700 m/min.

Fluid 37, a fluid commonly used during machining of conventional gray cast iron, was included in this testing and served as a baseline for this study. In addition to assessing fluid performance in the machining of both gray cast iron and CGI, dry machining of CGI was performed using both tool materials and conditions. This was done to assess the impact of wet versus dry machining in this operation.