Experimental investigation of hole quality in drilling of additive manufacturing Ti6Al4V parts produced by hole features

Abstract

Although additive manufacturing (AM) applications are on the rise, machining processes such as drilling are required to complete the manufacturing process successfully. This study envisaged that after the Ti6Al4V alloy designed as a pre-hole feature is produced by the Selective Laser Melting (SLM) method, there will be significant advantages to drilling the holes the desired diameter size will bring to the production costs. Hole accuracy, hole surface roughness, cutting forces, cutting tool wear, and chip form were determined as evaluation criteria. Their relations with drilling parameters were evaluated. After drilling, the deviation values from the average diameter, circularity, and cylindricity in the AM holes improved about 98%. The increases in cutting forces in uncoated twist drills negatively affected the hole quality. The increased cutting forces increased deviation values from diameter, cylindricity, and circularity. Better values were obtained in coated twist drills. The lowest surface roughness (0.58 μm) was recorded at 50 m/min cutting speed and 0.15 mm/rev feed in coated drills. Minimum deviation from cylindricality and circularity were obtained in uncoated drills. It was determined that the diameter deviation of the coated tool was 76% less than the uncoated tool. With the study, it has been revealed that it may be advantageous to drill AM parts produced with unsupported front holes instead of drilling a full hole. Considering the smaller chip cross-section in the drilling process, the cutting speed and feed values could be increased to increase the drilling efficiency. In addition, in the study, it was determined that the proper drilling of the pre-drilled hole has a sensitive relationship with the fact that the pre-drilled hole centre and the drill centre come to the same point during drilling.