CrazyDrill Cool SST-Inox

Small, deep and fast, these are the characteristics of the small drill CrazyDrill Cool SST-Inox. Due to internal coolant ducts, innovative geometry and innovative coating, the machining of stainless steels, nickel based super alloys and CrCo-alloys has become significantly simpler and process stable. This goes also for small diameters, as well as deep bores.

The range includes through coolant drills in six different working lengths: up to 6 x d, to 10 x d, to 15 x d, to 20 x d, to 30 x d and to 40 x d. In addition, there is a short i.e. pilot drill for a max bore depth of 3 x d. Up to a bore depth of 20 x d these tools are available from dia. 0.039” (1 mm), the longest one from .078” (2 mm). The entire range goes to a max diameter of 0.236” (6 mm).

Drills with spiralized coolant ducts are available already; also in the small-diameter ranges. However, many get into trouble with tough-elastic materials or with the poor heat conductivity of super alloys. Here the cooling through “classic” round ducts is even with high pressure insufficient. A premature edge chipping, packing of chips, buildup of the flutes prevents a process stable drilling. Exactly this is important for industries which produce from valuable material even more valuable finished parts.

Markus Schnyder, head of Mikron Tool International and one of the initiators of the new tool, knows all about the problematic: “For many years our customers reached the limit when drilling stainless steel. The process was not stable and too slow; thus, machining became extremely expensive. We wanted to find a solution. The development took us several years. Besides we depended on a close cooperation with our partners, for instance to find the right blank material or truly efficient coating. “

^{Markus Schnyder is president of Mikron Tool International.}

Independent whether short or long bore, the principle is always the same. A new geometry provides a chipbreaking effect at the front. Short and curved chips are the result. In the back an open flute profile facilitates a perfect evacuation of microchips. There is a variant for long drills: in addition to the open profile a polishing of the flutes helps the easy evacuation of chips from the bore. Also, the new coating, special for machining of stainless steels helps.

Performance and process stability is mainly given by the cooling of the tool: two spiralized, internal coolant ducts up to the drill tip, guarantee a constant and massive coolant flow during the entire drilling process. An important factor to prevent overheating of the tool even with high cutting speeds.

The coolant ducts have the largest possible diameter and are drop shaped. These ducts are located in an area with little stress and therefore the stability of the tools is not jeopardized. Comparing to the conventional round diameter, these ducts afford a four-time higher coolant flow. At diameters under 0.118” (3 mm) a power chamber in the shaft reduces the length of the ducts and provides higher coolant pressure.

The advantage of the efficient supply of coolant to the drill tip, increases tool life because an overheating of the cutting edges is avoided right from the beginning. Combined with the innovative tip geometry, the cooling helps greatly to break and flush out the chips from the flutes. All these characteristics make it possible to work with higher cutting parameters (speed and feed) and to drill in one single stroke.

Starting with drills for a depth of 10 x d, little by little new and longer versions were introduced until the presentation of the complete range including 30 x d and 40 x d as a global novelty in 2019.

“One single stroke is sufficient to reach the entire depth – without chip evacuation – from 6 to 40 x d”, confirms Schnyder and adds right away that this is an absolute unique achievement. The same goes for the speeds and feeds, which can be set equally for a depth up to 20 x d. Merely for depths starting at 30 x d these settings need to be reduced at an average of one third.

When drilling deeper holes of 15 x d or more it helps to have a short pilot operation to reach a high positioning accuracy. It also helps to guide the subsequent long drill and guarantees good straightness. So that this centering fits perfect, Mikron Tool developed the complimentary pilot drill whose tolerances are precisely tuned to the long drills. If requested the tool can also simultaneously do a chamfer of 90 degrees. According to the long drill It has the internal coolant to the tip and is available in diameters from 0.039” to .0236” (1 to 6 mm).

There are various reasons which motivate a user to test these new drills: one argument is saving time, cost reduction with higher tool life or simply the quest for a stable drilling process especially with difficult materials.

A customer works with a “classical” drill with round cross section coolant channels and reaches a tool life of 3,900 bores per tool. With the new tool he reaches right away a duration of 18,000 parts. This represents for changing one single tool a cost saving of $ 15,000 per year.

For the machining of a medical part (bore diameter  0.156”, depth 2.68”) made from chrome-cobalt a user had trouble to find the right drill, guaranteeing a stable process. Only with this new tool he had success – drilling in one stroke without pecking.

Schnyder gives a short summary of the first positive feedbacks he received from the industry: A bore of up to 10 times faster is achieved. 3 x better tool life was reached. The bore quality is excellent in regard to cylindricity, diameter and concentricity. Surface quality, depending on material in the range of R_a 0.1 to 0.3 (grinding quality).