Roundness Error in Deep Hole Drilling using Twist Drills and Cold Mold Steel 718

Applications: Deep hole drilling is one of the machining processes which currently has been applied in the manufacturing area. The sophistication in some area such as aerospace, automotive, wind energy and nuclear power encourage the application of deep hole drilling. Objectives: In this study the effect of machining parameters on the roundness error during the drilling multiple deep holes of steel alloy using HSS Co5 DH100 straight shank twist drills for deep hole drilling of cold mold steel 718 towards the value of roundness error was investigated. Method: Drilling tests were carried out using a CNC milling machine under three different levels of minimum quantity lubricant (20, 30, 40 ml/hour) by drilling three different levels of depth of holes (65, 70, 75 mm), three different levels of spindle speeds (700, 800, 900 rpm) and three different levels of feed rates (50, 60, 70 mm/min). Findings: It was observed that the minimum value of roundness error obtained when using DoE approach and regression model is when cutting speed (V) is 700 rpm, minimum quantity lubricant (l) is 40 ml/hr and feed rate (f) equals 50 mm/min, depth of hole (d) is 65 mm. ANOVA analysis also proves that the combination of machining parameters obtained is significantly to the roundness error value that results in the roundness error minimum value and F statistic also showed that the model is important at the significance level of 95%.