Deep drilling works by utilizing specialized tools and setups to overcome the unique challenges of creating deep, narrow holes in materials like metal, extending beyond the capabilities of standard drilling methods.
Deep drilling processes employ special tools and setups specifically designed for the task. The core function of these setups is to efficiently deliver high pressure coolant directly to the cutting edge and effectively evacuate chips cleanly from the deep bore. This combination is crucial for successfully achieving depth-to-diameter holes into metal beyond what a common CNC machine can reach.
The Challenges of Deep Holes
Drilling a shallow hole on a standard CNC machine is relatively simple. However, as the hole gets deeper relative to its diameter (high depth-to-diameter ratio), several challenges arise:
- Chip Evacuation: Chips generated during cutting struggle to exit the deep, narrow bore, leading to clogging, tool breakage, and poor finish.
- Heat Buildup: Friction between the tool, workpiece, and chips generates significant heat, which can damage the tool and the material.
- Tool Stability: Maintaining a straight path and preventing tool wandering becomes difficult over long distances.
- Lubrication & Cooling: Getting coolant effectively to the cutting zone deep inside the hole is challenging.
Specialized Solutions in Deep Drilling
Deep drilling methods, such as Gundrilling or BTA (Boring and Trepanning Association) drilling, address these challenges through their design and operation:
- Special Tools & Setups: Deep drilling tools often have unique geometries. For example, a gundrill is a single-lipped tool with a v-shaped flute and a through-hole for coolant. BTA tools may have multiple cutting edges and a different chip evacuation path. The machine setups provide the stability and power needed for the process.
- High Pressure Coolant Delivery: Unlike standard drilling where coolant is often flood-applied externally, deep drilling systems force coolant at high pressure directly through the tool or around it. This serves multiple purposes:
- Cooling: Dissipates heat effectively at the cutting zone.
- Lubrication: Reduces friction between the tool and the workpiece.
- Chip Flushing: Provides the force needed to push chips out of the bore.
- Clean Chip Evacuation: The high-pressure coolant is engineered to carry the chips away efficiently. In gundrilling, chips flow back along the v-shaped flute. In BTA drilling, coolant is fed externally around the tool, and chips and coolant exit through the center of the drill tube. This prevents chip accumulation.
- Achieving High Depth-to-Diameter Ratios: By managing heat, friction, and chip buildup, these processes can create holes with depth-to-diameter ratios ranging from 10:1 up to 100:1 or more, far exceeding the typical 5:1 or 10:1 limits of conventional drilling on standard CNC equipment.
In essence, deep drilling is a specialized manufacturing process that modifies the fundamental drilling principle with specific tooling, high-pressure fluid dynamics, and machine rigidity to create precise, very deep holes that would be impossible or impractical with standard machining techniques.
