With the new CoroDrill DS20, Sandvik Coromant has introduced a 7×D indexable insert drill that makes drilling from both sides of a component obsolete in the area of short-hole drilling. This is made possible by a new design for both the basic body and the indexable inserts. The differences to its predecessor, the CoroDrill 880, are therefore immediately apparent: instead of a conventional, constant, helical helix, the new 7×D indexable insert drill has an initially strongly curved chip channel, followed by a straight chip channel. This design not only enables high performance, but also stability and a balance of forces. The latter in particular is necessary for a long, asymmetrical drill.

Key aspects of development

Controlled cutting forces, reliable chip evacuation with predictable chip deflection and high centering capability are among the most important requirements for drills for depths greater than 5×D. As the bending tendency of a 7×D drill is three times higher than that of a 5×D drill, the requirements for stability and optimum force distribution increase with the length of the drill. Consequently, one of the first challenges during development was to find the ideal design and the best possible position of the indexable insert - especially with regard to determining the optimum resulting force, as both indexable inserts are arranged asymmetrically. A solid basic geometry and a hard-wearing indexable insert design with four full cutting edges on both the inner and peripheral inserts also ensure robustness.

The basic geometry has been redeveloped, as has the indexable insert design. © Sandvik Coromant

Another important aspect in the development of the CoroDrill DS20 was to find the optimum combination of material and design for the drill body and tool cooling. This required extensive research, analysis and testing, as the drill body needed to be durable and more rigid than before. In addition, the chip channel shapes had to be individually designed for each drill size and indexable insert in order to achieve less vibration, predictable wear patterns and a longer tool life. The team needed around two years just to develop the optimum chip channel design while maintaining the required internal cooling.

The challenge was to achieve the greatest possible rigidity of the drill body on the one hand and to design the chip removal in such a way that high process reliability, repeat accuracy and consistent quality are guaranteed at all times on the other. The design of the chip flute plays a decisive role in this conflict between high drill rigidity and optimum chip evacuation. The "straighter" the chip channel, the less material is removed - this increases rigidity. On the other hand, a steeper helix angle increases the speed of chip removal, which increases process reliability. Both capabilities are required in every drill, but must be optimized for bores larger than 5xD - a challenge that the team successfully solved with meticulous work and intensive testing.

A total of 50 different parameters had to be adjusted during the development of the drill. Each time a parameter was changed, the 49 others also had to be adjusted accordingly. In order to manage this effort efficiently and without errors, experts from Sandvik Coromant developed special software that enabled all parameters to be controlled, modulated and analyzed in a virtual environment. Only on this basis was the team able to develop the next generation of two-stage technology, which reduces cutting forces on entry by up to 75 percent compared to CoroDrill 880 and improves centering capability.

From the development to the field test

Parallel to the CoroDrill DS20, the company developed the new Modular Drilling Interface (MDI), which serves as an interface between the drill and adapter. © Sandvik Coromant

In order to test the new indexable insert drill under real conditions, initial trials were carried out at a user that manufactures slewing rings for the wind turbine industry. With success: By switching from a 6×D competition drill to the CoroDrill DS20, a complete component could be machined safely and faster, as there were no unpredictable stops or insert changes. The company was also able to double its productivity.

Further tests allowed conclusions to be drawn about the potential advantages of the 7×D indexable insert drill. For example, the CoroDrill DS20 can increase tool life by 25 percent when drilling steel, cast iron or hardened workpieces and by 10 percent when drilling stainless steel and non-ferrous materials. Productivity increases are also achieved: typically 10 percent when machining steel, stainless steel and cast iron and 5 percent for hardened materials, non-ferrous materials, super alloys and titanium.

This performance is due in particular to the chip control and feed speeds in all 4×D to 7×D applications. Process reliability is ensured by lower forces and easier cutting, especially during entry. Users of the CoroDrill DS20 benefit from lower costs per hole, the ability to drill deeper and lower noise levels. In addition, no pilot holes are required.