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A new, small dimensioned drill for stainless steel

15 August 2014 - Small dimensions, stainless steel and process-reliability - a definite challenge for drills!

With characteristics such as bad thermal conductivity, high ductility and long chips, stainless steel is not a favorite of the chip removal specialist. These properties are synonymous for material cementing at the cutting edges, jammed and blocked flutes and therefore often the cause for premature drill breakage. Process-reliable machining is difficult, especially in small diameters where an efficient cooling is nearly impossible. The development engineers of Mikron Tool SA Agno accepted the challenge and with CrazyDrill SST-Inox they developed a small drill especially adapted for stainless and acid-resistant steels.

Compared with presently available products on the market, this drill differs in various important factors to guarantee a successful use. Starting with the material, a solid carbide with exceptional flexibility and thermal shock resistance but also with high breakage ductility. The geometry, the most important element of this development, has been revised and adapted to the pertinent requirements. The reduced transverse cutting edge reduces the feed force, guarantees a good self-centering of the drill and generates short chips even with „long-chip-production“ materials.  Cutting edge breakages are thus avoided. The result for the customer is a better tool life, more process-reliability and better productivity. A special difference to standard tools consists in the drill top profile: the slightly reduced drill diameter after the short top section reduces the friction and therefore the heat development, reducing the torque. A benefit for process reliability as well as for surface quality. The digressive flute, divided in two areas, is responsible for a good chip removal: a „chip breakage“ area with a 32° flute facilitate the chip breakup, the area „chip removal“ with a 12° flute allows quicker chip removal.

The new coating lives up to the requirements for the above mentioned materials: it resists to thermal load, due to a smooth surface the friction is limited and allows a good chip removal. The adhesion to other materials is low, avoiding therefore chip cementing at the cutting edges (no material build up at cutting edges).   

The new drill CrazyDrill SST-Inox affords, so to speak „crazy“ performances not only regarding tool life and process-reliability but also when it comes to the drilling speed. The Swiss cutting tool specialist Mikron Tool confirms the possibility to machine with CrazyDrill SST-Inox, compared to standard drills, with 1.5 to 2 times higher cutting speeds and feed rates and with steps up to 1 x d. To date, usually we talk about steps of max. ½ x d, on average about steps of ¼ x d or smaller.

Well aware that internal cooling is an important question, Mikron Tool stepped it up a notch and developed a version of the drill with integrated cooling.  In this version, 3 to 4 cooling channels pass through the shaft and exiting at the conical neck. This provides an efficient cooling jet on the top of the drill, controlled heat and a continuous chip removal. The advantage is once more a clearly better tool life expectancy, the producer in fact talks about 2 to 4 times better tool life. In the meantime, the optimized cooling influences the cutting parameters: steps from 1 to
2 x d are foreseen, cutting speed and feed can be increased from 20% to 30% compared to drills of the same product family but without through cooling. All in all, a clearly more efficient tool. Thus Mikron Tool generally recommends this through coolant version where a through cooled spindle is available.

As for all its standard products, also for CrazyDrill SST-Inox Mikron Tool specializes on small dimensions. The version without internal cooling as well as the one with integrated cooling channels are available from inventory from 0.3 to 2 mm (.0118 to .0787”) with increments of 0.05mm (.00197) and a usable length of 8 x d. Special executions with different dimensions are available on request.

The new drill achieved good results in the watch industry, but the producer foresees the good applications also in other industry segments where an efficient machining of stainless materials is required. To mention are the medical industry with implants and instruments, aerospace, food industry or the electronic industry, especially optoelectronic.

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