Efficiency in contamination-free machining using microfluidic structures

• Microfluidic structures internal to cutting inserts were designed and manufactured to cool the cutting insert during machining operations.
• Efficiency ratios for the cooling systems were defined accounting for the fraction of the mechanical power requested to cut the metal that is dissipated as thermal power by the cooling system.
• Mixed-effects linear statistical models fitted to the experimental results (cutting of AA6082-T6) showed that the efficiency ratio depends on the feed rate and the cutting speed but not on the depth of cut.
• The maximum efficiency achieved was about 11 %. The models also show that decreasing feed rate and cutting speed increases the efficiency ratio.

The plastic deformation of the material in the chip formation and the friction when the chip slides on the rake face of the insert generate heat. The heat generation is responsible for a temperature rise of the chip, of the insert and of the newly created surface on the workpiece. Adhesion and diffusion between the chip and the insert are thus facilitated with detrimental effects on the tool wear. A cooling system based on microfluidic structures internal to the insert is considered in this study as a means of controlling the temperature at the chip–insert interface. The coolant and the part never enter in contact. Hence contamination of the part by coolant molecules is prevented. The aim of this study is to identify and to quantify the effect of the cutting parameters on the effectiveness of the internal cooling system. To measure this effectiveness an efficiency ratio r is defined as the percentage of the mechanical power actually needed at the tool to remove material that is thermally dissipated by the internal flow of the coolant. Similarly, a specific efficiency ratio r′ is also defined by considering the mechanical power per volume flow rate of the material removed and the dissipated thermal power per volume flow rate of the coolant. Both r and r′ are then analysed in a 33 factorial experiment within the space of the technological variables depth of cut, feed rate and cutting speed. The cutting trials were conducted in turning operations of AA6082-T6 aluminium alloy. Linear mixed-effects models were fitted to the experimental results using the maximum likelihood method. The main finding was that the efficiency ratio r depends only on the feed rate and the cutting speed but not on the depth of cut. An interaction effect of the feed rate and the cutting speed on the efficiency was also found significant. Higher efficiency is attainable by decreasing cutting speed and feed rate. The maximum efficiency predicted in the technological region investigated was 10.96 %. The specific efficiency once log-transformed was found linearly increasing with the depth of cut and the feed rate, whereas being insensitive to the cutting speed.

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