Technology Fast, process-secure ways to complete very deep drilling

Editor: Rüdiger Kroh

Boring deep holes presents a special challenge for tools. With large length-to-depth ratios, the process has to be optimally planned, especially for hardened steel. Required is a combination of high process speed and top boring precision, journalist Bernhard Kuttkat reports.

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Deep-hole drilling makes special demands on the tools. The cooling lubricant plays a decisive role here in chip removal.
Deep-hole drilling makes special demands on the tools. The cooling lubricant plays a decisive role here in chip removal.
(Photo: Hoffmann Group)

When looking at the demands on boring tools, deep drills certainly represent one of the more important niches. This is how Ulrich Kreuzer, technical manager of the Mapal Competence Centre in Altenstadt, Germany, said he sees the market for such precision tools. More specifically, “Around 80% of all bores are less than 5 × D, for example, while bores of over 20 × D constitute hardly 5% of all bores required, but these are without doubt critical for the functioning of the components in question and cannot be done without more elaborate technical work.”

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He explained that one should not underestimate the positive effects that the development of deep-hole borers have on shorter borers because the sophisticated geometries of the deep borers do of course improve the performance and service lifetime of shorter tools when they are used there.

Defining the process of deep hole drilling

And when does one begin to talk of deep-hole drilling? Helmut Gschrey, senior product manager of hole-making at Germany’s Walter, Tübingen, spelled it out: “In our view, deep-hole boring starts at 16 × D; there, it is important to be process-secure.” These tools must represent the highest quality. Moreover, above 16 × D, a certain drilling strategy is required – pilot bore, insertion, start main bore, withdrawal with reduced rotational speed. “For bores of up to 8 or 12 × D there are many manufacturers, above 12 × D there are really only the top makers,” Gschrey emphasised.

Because no separate official statistics are available for deep borers, only a rough estimate is possible regarding their annual market volume. For example, the requirement of German industry for solid carbide and single-lip deep borers lies between €20 million and €25 million, Krenzer estimated. HSS spiral drills, ejector and BTA systems could account for up to €15 million.

Mapal has two models of spiral deep borers in stock as standard. In its cutting material and geometry, the Mega-Deep-Drill is designed for cutting steels, while the Mega-Alu-Deep-Drill is for aluminium and non-ferrous metals. As Krenzer noted, “Pilot drilling is absolutely decisive for the functioning of the deep drills, and this very often has to be done on inclined workpiece surfaces.” Mapal has reportedly developed, with the Mega 180, a tool that not only masters this difficult task, but can also be used at feed rates otherwise only encountered with spiral drills.

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