Innovations that lead the way in drilling

The change that saw numerically-controlled machine tools coming into use took place on a large scale during the seventies, bringing with it turning-centres and machining-centres to replace most lathes and milling machines . New turning and milling cutting tools with cemented-carbide indexable inserts were raising machining rates continually to reduce machining times. But drilling stood out as a very slow operation thanks to the continued use of the twist-drill, which had remained the same for decades. The cutting action of this tool is primitive in relation to other tools and very much so compared to today`s drills. It has a large, centre chisel-edge betwee the two cutting edges which to a large extent deforms the metal being drilled and takes up a large proportion of the power neededd to make a hole.

Being an established innovator of cutting tools, Sandvik Coromant developed various indexable-insert tools. Insert geometry, carbide-grades, insert-manufacturing and new ways of securing inserts in the holder were some of the main steps forward. In 1977, Sandvik Coromant pioneered the indexable-insert short-hole drill – the T-Max drill with diameters from 25 mm upwards. In a capable machine, the T-Max drill could make the same hole ten times faster than the high-speed steel twist-drills.

The T-Max drill was groundbreaking at the time. There were two inserts, a peripheral and a centre insert, each dedicated to its role in the drill and overlapping to give good cutting action across the hole diameter. Cutting edges were provided with specially-developed chipbreakers in the form of rills along the edges. These reduced the width of chips, making them easier to evacuate. The biggest risk to an indexable-insert drill then, and now, is chip congestion in the flute as these drills penetrate material very quickly and need to evacuate chips quickly and effciently. Any problems in chip evacuation will very quickly lead to congestion and catastrophy. Monitoring the form and colour of chips, especially to set the operation initially was very important – and still is today. The evolution to the T-Max U drill during the eighties led to drills with diameters of 17.5 mm, new insert grades and stronger geometries – with the effect that fifteen of the same holes could be drilled per minute.

But the second really big leap in the development of indexable insert drills came in in the mid-nineties. The new Coromant U drill did not have much in common with the first T-max drill atall as regards design or performance – the new drill made twenty of the same holes, double that of the pioneer-drill.

The Coromant U drill was technically advanced. Instead of the straight flutes in the drill body, the new drill had twisted flutes shaped to be channels for the best chip evacuation with internal coolant supplied to the cutting zone. Chips of different shapes could be streamed out efficiently when drilling different materials. It was also the much extended application area of the drill that was a big new advantage, with drill-depths of five times the diameter. Also the drill could be made to a diameter down to 12.5 mm. The newly developed Wiper-edge concept for inserts had also been incorporated in the peripheral insert design to increase productivity by allowing a higher penetration rate for the same surface finish. A wide range of semi-standard options made the drill suitable for many different operations and holes, and there were radial setting possibilities to improve the achievable tolerance limits, with boring also an option.

Stage three of the Sandvik Coromant leading development of indexable insert drills came in 2005 - the CoroDrill 880. It is still out in front today through the steady evolution of its basic technology and components. It has shown itself to be even more capable over an even larger application area, in all workpiece materials - making twenty-five of the same holes per minute.

Although indexable insert drills are still basically seen as roughing tools, with holes of IT13 tolerances, they can today make holes closer than previous indexable-insert drills. This has made the application area of indexable-insert drills much broader. Its capability is much due to a newly-developed cutting action thanks to a new innovation : Step Technology. But it was also the result of even further developments in chip evacuation technology as well as advances in indexable-insert technology. Further cutting data increases became possible with newly developed insert-grades.

A unique Sandvik Cormant innovation, Step Technology is achieved through the central and peripheral inserts working together in a completely new way, particularily when entering the workpiece. Lower cutting forces are distributed step-by-step between the inserts and the resulting closely-balanced cutting forces have a marked positive influence on the how the drill makes and finishes the hole. Step Technology is also achieved through a new insert design, with the cutting-area covered by the central insert giving much more drilling harmony. This is very much a high-tech tool solution developed with high-tech methods, made possible by IT and with new metrology.The CoroDrill 880 needed several years of R&D with specially developed programmes for detail monitoring of the drilling process.

Indexable-insert drills are, however, limited through their cutting action when it comes to hole-depth. Also, the accumulated tolerances of the tooling elemetnts limits the suitablity for precison holes without individual tool-setting. Not surprisingly then that Sandvik Cormant have introduced new innovations in the form of two other types of drills : exchangeble-tip drills and solid-carbide drills.

As the latest concept in exchangeable-tip drills, the CoroDrill 870 has been developed mainly out of the requirement to change tools in the machine. Being ideal for holes, as deep as eight times the diameter, the hole-tolerances that can be achieved are as close as IT9 in the diameter area of 12 to 26 mm. Exchangeable tips can also be an advantage from a tool-stock and -cost aspect depending upon the type of production. The unique coupling-interface, between tip and drill-body, is a key-feature of this drill. Also, a new flute-concept as well as new geometry for the tips have provided improved chipbreaking, with insert-grade developments providing higher cutting speeds. Added reliability, penetration rates, finishing capability and handling ease are the main new benefits of this latest innovation for an established drill-type.

Solid carbide drills have tradionally been associated with holes of closer tolerances - IT8 - which is still the case today. The CoroDrill 860 is a new innovation in solid carbide drills, covering diameters fro 3 to 20 mm. But the 860-drill has also added a new important dimension to this type of drill : very fast penetration rates. In this way broadening the application area as the drill becomes a competitor, not just as regards precision, but also speed. The unique, advanced drill-point geometry provides a much more effective cutting action and the new flute-design and cemented carbide grade have broadened the basis for selection for this type of drill.

This drill should still be seen as superior in making high-precison holes in one pass, but, as the high-tech tool it is, the 860-drill should equally be seen as the means with which to more generally achieve higher productivity – in some cases whatever the tolerances. In many applications, in machinery capable of high cutting data, it out-performs the modern indexable-insert drill, making even more holes per minute.

Sandvik Coormant innovations in drilling during the past few decades have transformed machining and dramatically improved productivity in machining. While the typical machine shop in the mid-seventies would make one hole per minute, today`s can make up to thirty – with a lot better precision, eliminating additional finishing operations, and with higher security.

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Sandvik Coromant

Sandvik Coromant is a world-leading supplier of cutting tools and tooling systems for the metalworking industry and is represented in 130 countries. 27 state-of-the art Productivity Centers located around the world provide customers and staff with continuous training in tooling solutions and methods to increase productivity. Sandvik Coromant is part of the Tooling business area of the Sandvik Group.

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Contact: Lianne Mills
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Email: Catherine.li@sandvik.com

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