Investigation and Evaluation on Influence of Machining (CNC) Conditions on Surface Quality of Paulownia Wood

The aim of this study was to investigate the effective factors on surface quality of paulownia wood during machining by advanced computer numerical controled (CNC) machine. For this aim paulownia logs were provided and were converted to proper sizes (2. 5 x 10 x 15 cm) and then air dried. The Variable of this study were cutting speed (8. 37 and 15. 07 m/s)، feeding rate (6 and 12 m/min)، cutting depth (1and 5 mm)، cutting method (down and up-milling) and cutting pattern (tangential and radial). Roughness of cut specimens edge were evaluated by profilometer method according to ISO 13565 standard. For evaluation of surface quality، average roughness (Ra)، maximum roughness (R max)، valley roughness (Rv) and peak roughness (Rp) were used. Degrees of effectiveness of the parameters were evaluated by fractional factorial design as completely random design at confidence level of 95%. The result showed that cutting speed، cutting method and feed rate are influencive factors on surface quality of machined specimens and their effects were significant. With increasing cutting speed and decreasing feeding rate the roughness decreased and surface quality improved. In up-milling cutting method، degree of roughness was higher and consequently surface quality was inferior. It is to be noted that cutting method in comparison to other factors had the high influence on surface quality. The rest variables did now have independent influence on surface quality at 95% Confidence level. This study for achieving the optimum surface quality recommends that cutting speed of 15. 07 m/s، feeding rate of 6 m/min، cutting method of down-milling and cutting depth of 1 mm for tangential cross section.