Uncoated Twist Drills Research Articles

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

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.

Application of Taguchi Method and Surface Response Methodology to Evaluate Of Mathematical Models to Chip Deformation when Drilling With Coated and Uncoated Twist Drills

The paper deals with the methodology and suitability of mathematical models applying analysis of the signal-to-noise (S/N) ratio as well as analysis of variance (ANOVA) and surface response methodology (RSM) on effect of TiAlN coating on chip ratio when drilling with HSS Co5 twist drill with diameter of 8 mm. Experimental work was performed according to design of experiment (DoE) Taguchi method. Cutting speed vc (m/min) and feed f (mm/rev) were selected as control factors in three levels and chip ratio K was used as a response variable. The main aim of this study is to establish relevant methodology for short term testing and find adequate mathematical model for chip ratio parameter K = f(vc, f) as a function of cutting condition when drilling with PVD coated and uncoated tool. Statistical software Minitab 14 was employed to process and evaluate of experimental data. The effect of feed and cutting speed on chip ratio was investigated through analysis of the signal-to-noise (S/N) ratio and analysis of variance. Equations for chip ratio K as a function of control factors were developed.

A study of the wear mechanisms of Ti 1− xAl xN and Ti 1− x− yAl xCr yN coated high-speed steel twist drills under dry machining conditions

Recent advances in cutting tool materials and PVD surface coatings are making high-speed dry machining an increasingly viable machining operation in commercial manufacturing sectors. High oxidation resistant coatings, such as TiAlN, are used extensively in global manufacturing for reducing production costs and improving productivity in such aggressive metal-cutting operations. In this investigation, the performance of TiN, Ti 1− x Al x N and Ti 1− x− y Al x Cr y N coatings was assessed on Co-HSS twist drills used to machine an automotive grade grey cast iron. As part of the study, two experimental methods were used to characterise the performance of the twist drills, namely, by an audible ‘screech’ and measurement of the progression of outer corner flank wear lands. Both techniques showed that a single layer TiN coating failed to outperform even uncoated twist drills when dry machining grey cast iron under aggressive machining conditions. However, using the measurement of outer corner flank wear technique, the average tool life of uncoated twist drills was increased by factors of 4.5, 6.5 and 6.9 by Ti 0.59Al 0.41N, Ti 0.27Al 0.19Cr 0.54N and Ti 0.21Al 0.14Cr 0.65N coatings, respectively. In the case of ‘screech’ failure, the average tool life of uncoated twist drills was increased by factors of 3.9, 7.3 and 10.8 by Ti 0.59Al 0.41N, Ti 0.27Al 0.19Cr 0.54N and Ti 0.21Al 0.14Cr 0.65N coatings, respectively. The performance of twist drills was also assessed using a number of quantitative techniques, namely, measurement of thrust and torque, hole diameter and drill wear. The latter was also observed using scanning electron microscopy (SEM) which showed an early onset of workpiece material transfer at the margins of the uncoated drills. In the case of the PVD coated drills, an improvement in the tribological interaction between the coatings and the grey cast iron workpiece resulted in a significant reduction in material transfer at the drill margins. The above results are discussed in terms of their affect on hole diameter and cutting forces.

Influence of chromium content on the dry machining performance of cathodic arc evaporated TiAlN coatings

Physical vapour deposition (PVD) titanium aluminium nitride coated cutting tools are used extensively in global manufacturing for reducing production costs and improving productivity in a number of aggressive metal-cutting operations, namely, dry and high-speed machining. In this investigation, the performance of Ti 1− x Al x N and Ti 1− x− y Al x Cr y N coatings was assessed on Co-HSS twist drills used to machine grey cast iron. The failure criterion for drills was defined as a critical sized flank wear land at the outer corners of the drills. Using this criterion, the average tool life of uncoated twist drills was increased by factors of 2.5, 3.0 and 3.0 by Ti 0.59Al 0.41N, Ti 0.27Al 0.19Cr 0.54N and Ti 0.21Al 0.14Cr 0.65N coatings, respectively. Notwithstanding the similar increase in average tool life, the Ti 1− x− y Al x Cr y N coatings produced more consistent results than the Ti 1− x Al x N coated drills with standard deviations of 67, 3 and 19 holes, respectively. This result has significant practical implications in manufacturing, since drills are not replaced on an individual basis, but rather on a preset tool change frequency. The present paper discusses the performance of Ti 1− x Al x N and Ti 1− x− y Al x Cr y N coated drills in terms of average and practical drill life and concludes with remarks on the characterisation of PVD coatings and their significance on the performance of Co-HSS twist drills when dry machining grey cast iron.