Surface roughness and diametral consistency of holes drilled into DDGS/phenolic resin blends

In this study, corn-based distillers dried grains with solubles (DDGS) has been utilized as a filler and blended with phenolic resin. The blends were compression molded into rectangular test specimens, into which holes have been machined using a standard 9.52 mm (3/8 in) diameter, two-fluted twist drill. A series of tests was then conducted to examine the effects of DDGS content, cutting speed, and feed rate upon the surface finish (roughness) of the interior hole slot, as well as the consistency of the drilled hole diameter. DDGS content was 0, 25, 50, and 75%, by weight. Cutting speed was 17, 30, and 46 m/min (55, 100, and 150 ft/min). Feed rate was 0.025, 0.152, and 0.279 mm/rev (0.001, 0.006, and 0.011 in/rev). Results indicate that as the DDGS content increased, roughness exhibited a weak but statistically significant decrease. When the cutting speed increased, roughness increased slightly. However, when feed rate increased, roughness increased at a greater rate than that due to cutting speed. In terms of diametral consistency, the effect of adding DDGS resulted in holes with diameters less than the nominal drill size. As cutting speed increased, the holes tended to be oversized. Based on the cutting speed and feed rate levels used, optimal machining conditions which would reduce roughness occurred for 75% DDGS, cutting speed of 17 m/min (55 ft/min), and feed rate of 0.025 mm/rev (0.001 in/rev). However, to maintain consistent hole diameter, optimal conditions were found to be 40% DDGS, 30 m/min (100 ft/min), and 0.152 mm/rev (0.006 in/rev) and would produce a drilled hole with a diameter of 9.52 mm (0.375 in). As the use of biofillers in plastic composites evolves, it will become increasingly important to examine the machinability of these novel materials.