Fast, process-secure ways to complete very deep drilling

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Increasing productivity with the right cutting tool

Sebastian Richarz, senior engineer at the Institute for Machine Tools and Factory Operation (IWF) at the Technical University in Berlin, said: “The use of long spiraled solid carbide borers enables, in comparison to single-lip deep-hole drills, significant raising of productivity due to the substantially higher feed rates realisable.” Besides raising productivity by a factor of around 6 to 8, a decisive role in the use of spiral drills, depending on the application, is played by the specified bore quality and, in particular, process security.

One focus at the IWF is on looking at the process chain for manufacturing tools for hard drilling processes with a high aspect ratio. A second focus is on the development of holistic production strategies, with the aim of being able to use the tools process-securely and with long service lifetimes in processing hardened heat-treated steel on universal processing centres.

How to work hard materials

In deep drilling in hard working materials, carbide tools combined with a PVD coating are used. The substrate as bearer of the coating has a decisive influence here on the service lifetime of the tool, as Richarz emphasised: “In current developments in drilling tools, ultrafine hard grain metals are proving to be particularly suitable as substrate materials, uniting simultaneously, in comparison with conventional hard metals, the characteristics of great hardness with great toughness – it has thus only become possible in the last few years to use spiraled tools with twisted coolant channels at high feed rates at all.”

For hard deep drilling to be carried out process-securely on processing centres, of particular importance, besides the drilling tool and a process sequence precisely matched to the working material, is the examination of the production unit with its additional functions and clamping situation. “The state of the art in this technology is to have an adequate supply of cooling lubricant in order to be able to remove chips along relatively small chip channel cross-sections, even from great drilling depths, and to ensure a sufficient cooling and lubrication of the cutting edges,” Richarz explained. One method for reducing increased friction is to employ cooling lubricants that have a fat content which is higher than 10%.

Slight inaccuracies in the machine tool, such as concentric run-out errors in the main spindle or positioning inaccuracies in the linear axes, can lead to overloading of the tools and thus to breakage. “In particular, the need is for the lowest possible angular deviations of the linear feed axis,” Richarz said, pointing to the results of comparative experiments on various drilling/milling machining centres at the IWF. Depending on the process, even slight angular deviations could have a fatal effect on positively driven tools with an aspect ratio of 30 × D, leading to breakage of the tool.

A version of this article originally appeared in MM MaschinenmarktETMM

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Technology

Fast, process-secure ways to complete very deep drilling

Increasing productivity with the right cutting tool

How to work hard materials