KOMET has developed a 6xD indexable insert high-performance drill bit that retains its stability even when working without a centring point or guide rails.
5xD is as good as it gets when it comes to the length/diameter ratio of drilling tools. Or at least, that’s what was previously thought, since larger ratios have a considerable adverse effect on stiffness; until now, stable machining operations and adequate feed rates have been mutually exclusive. But the KOMET GROUP has been hard at work, pooling its many years of experience and sophisticated development methods to come up with a new, 6xD drill bit with performance data that will not fail to impress.
The impetus for the project was provided by a customer who enquired about the possibility of a productive 6xD 33-mm drill bit for making large screw holes for bearing rings of the kind used in wind turbines, for example. Tools of this size normally have guide elements, such as a centring point or guide rails, which makes the manufacturing process significantly more complex and drives costs skywards. In the words of Dr. Michel Maes, Head of Development at the KOMET GROUP, “Although you can find cheap 6xD drilling tools on the market that do not feature guide geometries, these are generally only able to work at relatively low feed rates and are therefore not particularly productive.”
The new KOMET KUB Pentron® 6xD indexable insert drill bit has been designed to be a low-cost, high-performance alternative without guide elements, which does not compromise on productivity or process reliability – just like the successful KOMET KUB Pentron® 5xD, which the Besigheim-based drilling specialists used as the gold standard for stiffness in this latest endeavour. Development Engineer Julius Osterried explains, “Our finite element analyses concluded that the stiffness of a 6xD tool was up to 45 per cent less than that of a 5xD tool.” To counteract this, the developers had to make changes to the basic body, since both the substrate from the KOMET KUB Pentron® and the successful Pentron W80 indexable inserts were to be retained for the new tool design.
Julius Osterried describes the next stage in the development process: “To establish the kinds of loads that would be encountered, machining tests were conducted in which forces were measured, and the results from these were compared with results achieved using simulation tools – both numerical and hybrid.” “We collaborated with other organisations such as universities, who were able to bring the latest scientific expertise to the table.” In a screening, the KOMET developers then established which geometric characteristics have a significant influence on stiffness. Armed with these findings and their experience, they used the design of experiments (DoE) and finite element (FEM) methods to optimise the geometry of the basic body in order to achieve a stiffness that is sufficient to withstand the specific loads to which it is subjected on the lateral force plane. The development team turned promising design variants into prototypes and validated them by means of drilling tests.
The results of this testing were used to create the final design of the new, 6xD drill bit, which was then taken to the customer for field testing. The drill bit needed to prove itself for roughing operations in 42CrMo4 quenched and tempered steel. At feed rates of up to 0.12 mm/rev and cutting speeds of up to 176 m/min, the new, 6xD drill bit has done just that, achieving positive results in terms of the hole diameters it can drill, which are within the tolerance limits set out in the specifications. In addition to this, the anti-penetration cutting forces of the drill bit, chip evacuation and quality of the drilled hole fulfil the customer’s requirements.
Head of Development Dr. Michel Maes concludes, “With this kind of cutting data and the results it has achieved in testing, the new KOMET®KUB Pentron® 6xD indexable insert drill bit without additional centring point is set to be a highly productive tool for 42CrMo4V machining. It allows us to achieve tool life travel of up to 9.9 m. Not only are these figures considerably higher than comparable drill bits without guide elements, but they also demonstrate that the new tool can hold its own against its guided counterparts. Ultimately, our customers are very pleased with the outcome.”
The new KOMET KUB Pentron® 6xD indexable insert drill bit is now already in use in the field, and developers have wasted no time getting to work on additional 6xD drill bits with other diameters.