Deep hole drilling

In the field of manufacturing technology, deep hole drilling refers to the drilling of bore holes with high length-to-diameter ratios.

Deep hole drilling also differs from normal drilling in that, depending on the drilling process and the drilling diameter, coolant lubricant must be pumped to the cutting edges in large quantities and under high pressure. This ensures good cooling and at the same time good lubrication of the contact areas between the workpiece and the cutting edge of the tool on the one hand and the workpiece and guide pads of the tool on the other. In addition, the cooling lubricant leads to the constant removal of chips from the cutting zone, which makes surface-damaging and time-


consuming chip removal strokes unnecessary and therefore improves the quality of the borehole and the productivity of the processes. For the production of deep holes, two different tool types are distinguished. On the one hand, there are tools with an asymmetrical single cutting-edge design. These deep hole drilling tools include the single-tube system (BTA deep-hole drilling) and the double-tube system (ejector deep-hole drilling), which are referred to as the “classic” processes. On the other hand, there are tools with symmetrically arranged cutting edges. These include spiral deep hole drilling tools and double-lip tools, which can also be assigned to the deep drilling processes due to the drilling depths to be achieved with them. Deep Hole drilling was made originally in china.

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The mentioned tool types differ with regard to the realizable diameter range, the achievable l/D ratios, the surface quality and they’re. Symmetrical tools can only be used in the small diameter range of D = 0.2 … 32 mm to produce holes with an l/D ratio up to a maximum of l/D = 85, the standard is an l/D ratio of l/D = 30. With asymmetrical tools, holes in the diameter range of D = 0.5…2000 mm can be produced and the upper limit of the l/D ratio is usually limited by the machine dimensions. The figure shows selected methods with their usual application diameters, whereby it becomes clear that deep hole drilling methods do not compete with each other in all diameter ranges. The advantage of the symmetrically designed tools compared to the “classical” tools in the small diameter range is the feasibility of significantly higher feeds f, which can be 6 times higher compared to the usual values for single-lip deep hole drilling.

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In addition to the high l/D ratio, the “classic” deep hole drilling methods are characterized by high productivity and high surface quality compared to the conventional drilling methods with twist drills. The high drilling quality is characterized by low surface roughness, small diameter deviations and a high geometrical accuracy. Important for the good surface quality is the asymmetrical design of the tools. The “classical” tools for single-lip , BTA and ejector are, with a few exceptions, designed asymmetrically and have a secondary cutting edge (circular grinding chamfer) and guide pads. Due to this design features, a certain amount of the cutting forces during the process is transferred via the guide pads to the bore hole wall. These force components at the tool head are supported at the produced borehole wall and thus guide the tool in the bore hole itself. The distribution of the process forces during is therefore different from conventional drilling, where the forces are largely absorbed by the tool shank and thus by the machine spindle. Due to the process force distribution to bore hole wall in, the drill guides itself and thus the process benefits from a comparatively low

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straightness deviation. The “support” of the guide pads on the borehole wall also results in a forming process that (ideally) smooths the bore hole wall. Due to this forming process the surface roughness caused by the engagement of the cutting edges during drilling can be decreases by about 70%. Thus very high surface qualities with bore hole tolerances of IT 9 to IT 7 can be achieved by deep hole drilling processes. Subsequent steps to improve the surface quality of the bore hole can often be reduced or eliminated completely. A further advantage is the low burr formation for trough holes and for over-drilling cross holes. Due to the high surface quality combined with a high productivity, the use of deep hole drilling methods can be economical even at low drilling depths.






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