Deep hole drilling

Drilling holes with high length-to-diameter ratios

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

Definition of deep hole drilling

According to the VDI Standard, deep hole drilling processes are manufacturing processes for the machining of bore holes with diameters between D = 0.2 ... mm and whose drilling depth is usually greater than three times the diameter. For small diameters, length-to-diameter ratios of up to l/D ≈ 100 can be achieved, in special cases even up to l/D = 900. With large diameters, the l/D ratio is usually limited by the travel or the bed length of the deep hole drilling machine.

Deep hole drilling

Deep hole drilling is distinct from conventional drilling methods as it requires large quantities of coolant to be supplied to the cutting edges under high pressure, depending on the drilling process and diameter. This method ensures effective cooling and lubrication at critical contact points between the workpiece and tool, thereby enhancing the quality of the hole and overall productivity. Two primary tool types are used: asymmetrical single cutting-edge tools, which include single-lip deep hole drills and BTA deep-hole drilling, and symmetrical tools like spiral deep hole drills. Historically, deep hole drilling originated in China.

The tools vary in their operational capabilities with respect to diameter range, achievable l/D ratios, surface quality, and productivity. Symmetrical tools are limited to the smaller diameter range of D = 0.2 ... 32 mm, yielding an l/D ratio typically around l/D = 30. In contrast, asymmetrical tools facilitate hole production in the D = 0.5 ... mm diameter range, with l/D ratios generally constrained by machine dimensions. It is evidenced that these deep drilling techniques do not universally compete across all diameter ranges, and symmetrical tools can achieve significantly higher feed rates compared to the classical methods in their specific range.

Deep hole drilling methods

Single-lip deep hole drilling

Single-lip deep hole drilling is typically employed for holes in the D = 0.5...40 mm range. This method requires careful design to house coolant channels within the tool. The internal cooling system enables high-pressure coolant flow that efficiently removes chips through a v-shaped longitudinal groove in the tool.

Tools

Visuals illustrate that a single-lip deep hole drill features a tool holder, shank, and drill head. This design ensures compatibility for efficient coolant flow to expel chips while maintaining tool stability. The asymmetrical cutting edge arrangement facilitates the transfer of cutting forces to the borehole wall, producing superior results.

BTA deep hole drilling

The BTA method evolved as a modification of single-lip deep hole drilling to address its limitations. Known as the Boring and Trepanning Association, it combines innovative tool designs and methods that enhance coolant handling and chip removal. This technique is primarily utilized for D = 6... mm applications, showcasing its efficacy compared to previous technologies.

Ejector deep hole drilling

This variant operates in a D = 18 ... 250 mm diameter range, utilizing an ejector system to enhance chip removal efficiency while using additional coolant discharge outlets. The efficacy of this system makes it compatible with varied machine environments.

Methods associated with deep hole drilling

In addition to classical methods, post-processing methods for surface finishing and complex contours are prevalent. Various techniques are tailored to specific functions, ensuring flexibility across industrial applications.

Internal profiling

This process produces symmetrical contours like those of centrifugal casting molds or propeller shafts, using NC-controlled tools to achieve precise internal profiles in deep cavities.

Skiving and smooth rolling

These methods serve to enhance bore hole features and surface finish, particularly in hydraulic cylinder manufacturing, where hybrid processes combine chip removal and forming.

Single edge reaming

Reaming serves to refine pre-drilled holes, utilizing geometrically similar designs to single-lip drills to achieve high-quality outcomes.

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