Compact graphite iron (CGI) is a promising material that could replace conventional gray cast iron for making diesel engine blocks and heads to increase fuel economy and reduce emissions. However, the poor machinability of CGI evidenced by rapid tool wear leads to significantly increased manufacturing cost. To improve the machinability, a novel machining technique, modulation-assisted machining (MAM), is employed to provide low-frequency (tens or hundreds of Hz) modulation on the tool feed motion. This study intends to explore the feasibility and understand the effects of MAM in improving the machinability of CGI with coated carbide cutting tools.First, tool wear performance was compared between conventional machining (CM) and MAM using a dry turning configuration for a range of cutting speeds (150, 250 and 350 m/min) while measuring cutting forces and tool temperature. The results show that MAM can significantly increase tool life up to several folds especially at higher cutting speeds (250 and 350 m/min) compared to CM. It was found the cutting force and tool temperature are strongly influenced by the tool wear and the extent of iron adhesion.Next, tool wear was characterized in detail using high-resolution digital microscopy, SEM and EDS techniques for CM and MAM turning at 250 m/min in both dry and lubricated conditions. Significant wear reductions with MAM were achieved compared to CM in both dry and lubricated conditions. However, MAM dry turning resulted in significant reduction of tool wear compared to MAM lubricated turning. It was found that two wear phenomena account for the wear reduction in MAM: 1) the formation of SiO2 deposition layer on tool flank and 2) the preservation of the coatings on the cutting edge. The mechanisms on how the wear progression is slowed down by the observed wear phenomena as well as how these phenomena are enabled by MAM are discussed.Finally, the effects of modulation frequency on the tool wear and cutting temperature were investigated. Tool wear and cutting temperature were characterized for a range of modulation frequency and the ratio between modulation and rotation frequencies (1.5 - 9.5) in MAM turning at 350 m/min. It was found that higher modulation frequency leads to lower crater wear but higher nose wear. The main flank wear however seems to mainly depend on the formation of SiO2 deposition layer. There is an optimal frequency ratio due to the conflicting impacts on the crater wear and nose wear, which is also supported by the result that the lowest tool temperature is achieved at an intermediate frequency ratio.
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