Tool life improvement by peck drilling and thrust force monitoring during deep-micro-hole drilling of steel

An unstable drilling process results from the insufficient supply of cutting fluid and bad chip removal as machining depth increases. These causes of unstable drilling lead to serious problems in micro-drilling. All drills were broken while drilling the first hole in the micro-deep-hole drilling of steel with an aspect ratio over 10, regardless of the cutting conditions. Peck drilling, which utilizes an intermittent feed, is widely used in drilling deep holes. Generally, the one-step feed-length (OSFL) of peck drilling is one and a half times longer than the drill diameter in conventional drilling. An OSFL between one half and twice the micro-drill diameter was used by some workers for micro-drilling. However, this range of OSFL was an arbitrary decision. This paper proposes the peck drilling method using thrust force signal monitoring. The monitoring parameters for peck drilling (MPPDs) are introduced through the analysis of thrust force in both the time and frequency domain. The monitoring system was embodied using LabVIEW. Through this monitoring system, the proper OSFL for stable machining in the deep-micro-hole drilling of steel was determined to be about a tenth of the tool diameter.