2010 Full-Line Drill Catalog - Desanto

Machining technologygood chip evacuation, whereby the tool geometry also playsan important role. Short chips, large flutes with polishedsurfaces – possibly MolyGlide-coated – can provide thesolution.In a few dry machining applications, air is used for cooling.Obviously, tools with coolant ducts are applied, throughwhich air is delivered to the hole. Air not only cools tool andworkpiece, but under the correct pressure also improveschip evacuation.Interestingly, dry and HSC machining do not exclude oneanother, as one would expect. On the contrary, moderncarbide drills and coatings allow so-called dry HSC – dryhigh speed machining, combining the advantages of the twomachining trends, as for example, a reduction in productioncosts in certain applications.To optimise drills for the MQL technology, Guhring is increasinglyapplying the Finite-Element-Method (FEM). FEMallows the dimensioning and optimisation of the tools duringthe design phase. The flute in the area directly behindthe cutting edge has the task to mould the chip in order tobreak it as small as possible. In the rear area its task is toevacuate the chip as quickly as possible. These tasks applyto wet machining, minimal quantity lubrication as well asdry machining. With minimal quantity lubrication and drymachining, however, it is extremely important to providethe chip with minimal frictional resistance in the rear area,in order to ensure a problem-free chip evacuation. This isaided by an optimised flute form as well as a specially polishedfute surface.Flute design to suit MQLWith the assistance of the aforementioned FEM-analysis,it is possible to simulate the flow resistance of a flutewith chip, subsequently providing optimised flute formsfor different material classes. The following image showsa flow optimised flute form and point design, providingoptimal chip flow and also minimising the thermal load ofthe cutting edge thanks to an optimised throughflow of thepoint area and the flute by the MQL aerosol.Minimal quantity lubrication MQLMQL or minimal quantity lubrication works with an air-lubricant-mixture,that only contains a small part of lubricant.TechnicalIn the past, the technology of minimal quantity lubricationwas generally applied on the own initiative of the user, inorder to reduce costs. Often, tools for wet machining weresimply applied under MQL conditions. With this approach,the limits of the tools’ efficiency were reached very quicklyand it became clear that a mere substitution of the lubricantwas not a targeted approach.A professional approach during the design of MQL suitabletools nowadays allows considerable performance increaseswhilst maintaining process reliability. Hereby, all the drill’srelevant attributes for providing efficiency and process reliability,from the cutting edge to the flute as well as theshank end, are adapted to satisfy the special demands ofMQL. As well as the choice of carbide, this also includes thespecial tool geometry, the tool coating and the design of theshank end for MQL drills.In addition, improved chip evacuation and therefore increasedprocess reliability is provided by a MQL-suitablecoating. Guhring has developed a double coating, consistingof a hard coating with an additional soft coating, MolyGlide.Tests confirm a considerably higher chip evacuation speedfor the MQL tool with the above coating in comparison withconventional tools.Coolant delivery to suit MQLBecause an extremely low volume of lubricant is appliedwith minimal quantity lubrication, the delivery of theselow coolant quantities to the effective area is of utmostimportance. Hereby, the geometric design of the shank endis of main significance for a safe delivery of the lubricant.310