Effects of cryogenic cooling on machining of acrylonitrile-butadiene rubber

The basic idea of cryogenic machining of elastomers is to lower the process temperature under glass transition temperature, causing the transformation of the viscoelastic properties of elastomers into brittle with better machinability outcomes. However, because of the heat generated by plastic deformation and chip formation in the primary shear zone and friction between the tool and the workspace, even with cryogenic cooling, the resulting temperature in the cutting area is often higher than the glass transition temperature. As a result, it can cause a partially rubbery state of the workpiece. In this paper, the effect of cryogenic cooling on the milling of acrylonitrile-butadiene rubber was analysed. Three different cooling setups, namely, indirect, direct and flow cooling, were proposed and their influence on temperature distribution in the cutting zone was studied in conjunction with different tool geometries and parameters (depth of cut, rotational speed, and feed rate). Direct cooling provides the best-resulting temperature distribution with the lowest surface roughness (1.27 to 1.47 mu m) as it acts as a lubricant between the tool and workpiece and cools the tool and workpiece simultaneously.On the other hand, increasing the depth of cut and rotational speed also increases surface roughness. The best results show samples with grooves obtained with a rotational speed of 5000 rpm, depth of cut 0.25 mm and feed rates between 75 and 300 mm/min with surface roughness between 0.86 and 1.29 mu m. Those samples show clean grooves with sharp edges, minimal surface roughness and geometric deviation, with defined ductile chip formation.

Automated summary

The basic idea of cryogenic machining of elastomers is to lower the temperature to make them brittle and easier to machine. However, the heat generated during the process can still result in a partially rubbery state. This study analyzed the effect of cryogenic cooling on milling acrylonitrile-butadiene rubber, considering different cooling setups and tool parameters. Direct cooling provided the best temperature distribution and surface roughness, while increasing the depth of cut and rotational speed increased surface roughness. The best results were achieved with specific parameters, showing clean grooves with sharp edges and minimal surface roughness.