The hidden cost of tool wear in CFRP drilling is the tool changes, extra inspection, rework and rejected parts a worn edge creates before it ever breaks. Managing it means setting a safe tool-change point based on acceptable holes, not on tool failure.
The first most common tool wear we see is a loss of control over the hole. The tool continues to rotate and produces what appears to be a completed feature. Yet as its cutting edge changes, so does the way it interacts with CFRP.
- Cutting forces and pressure rise.
- Fibres are pushed rather than severed cleanly.
- Entry and exit condition deteriorate.
The process that produced excellent-quality holes at the start of the run can become progressively less secure before you see a change in the tool. That is why we developed the Diamond Coated 2 Flute Drill, a new coating with increased product lines suitable for high-quality holes with longer runs and greater benefits compared to uncoated carbide.
Why CFRP Wears Cutting Edges So Quickly
CFRP is highly abrasive, but it is not one consistent material. Different fibre orientations and fibre cutting angles, laminate structures, stack geometry, resin systems and thicknesses can change how the same composite drill performs. As the cutting edge repeatedly meets the carbon fibres, abrasion gradually removes material from the edge. The wear commonly appears as a bright, polished land along the area doing the cutting.
At first, this wear is small and even. The drill retains enough of its intended geometry to continue cutting effectively. As the wear land widens, however, the geometry presented to the material changes. The edge becomes less sharp, cutting pressure increases and the drill begins to push fibres rather than sever them cleanly.
This is why abrasion is both predictable and dangerous. It normally develops progressively, giving the manufacturer an opportunity to identify it. But once it reaches a critical point, wear can accelerate and hole quality can deteriorate quickly.
Diamond coating slows that progression by placing a highly wear-resistant barrier between the abrasive material and the carbide substrate. The purpose is not to make the drill suitable for every CFRP application. It is to help preserve the geometry that produced the good holes at the beginning of the run.
Because Aero-CARB is available as an off-the-shelf range from Ø3.0 to Ø12.0 mm, manufacturers can evaluate that additional wear resistance without beginning with a bespoke PCD tool. Whether it provides the best commercial result still has to be confirmed within the actual material, machine and hole requirements.
The Warning Signs to Review
If the first holes are acceptable and drilling damage appears later in the run, inspect the drill before changing the complete drilling strategy.
Look for:
- A bright or polished wear land on the cutting edge.
- Increasing peel-up or push-out delamination.
- Frayed or uncut fibres at the hole exit.
- A change in hole size, position or surface condition.
- Increasing machine load, cutting pressure or vibration.
- More frequent inspection or operator intervention.
A dull drill can still complete a hole. The warning is that it no longer completes the hole in the same condition.
Where the Cost Really Appears
The tool purchase price is visible and easy to compare. The process costs created by wear are less obvious:
- Tool changes and lost machine time: every unplanned change stops production while the drill is replaced and the process is checked.
- Additional inspection: an uncertain end-of-life point forces more frequent checks to protect the component.
- Rework: fibre breakout or delamination may require repair, curing, reinspection and an additional setup.
- Rejected components: if the hole cannot be recovered, the loss includes the material and every previous operation invested in the part.
Getting the change point right is far cheaper than discovering the end of tool life through a rejected part.
Cost Per Tool vs Cost Per Acceptable Hole
A lower-priced drill is not automatically the lower-cost option. Equally, a more wear-resistant drill is not automatically commercially justified.
The correct comparison begins with:
Tooling cost per acceptable hole = total usable tool cost ÷ acceptable holes produced
For a more complete production calculation, add the costs of:
- Machine time used for tool changes.
- Inspection beyond the normal process requirement.
- Manual rework and additional setups.
- Rejected components.
- Operator intervention needed to keep the process secure.
This is the difference between measuring tool life and understanding production cost. The cheapest tool to buy may become more expensive once it is placed in the process.
It is also the right way to evaluate a diamond-coated drill. Aero-CARB has a higher purchase price than uncoated carbide, so the case for changing should be demonstrated through more acceptable holes, fewer interruptions or a more predictable change point, not through the coating alone.
Setting a Safe Tool-Change Point
It is not practical to wait for a rejected hole before changing every drill. The answer is to define an acceptable hole and identify when wear begins to affect it.
Inspect the tool and hole at planned intervals during a controlled trial. Record the cutting data, visible edge wear, entry and exit condition, hole measurements and the number of acceptable holes produced.
Once the deterioration point becomes clear, reduce the expected tool life to create a safe working limit. This gives the operator a planned change point before quality is placed at risk.
As with the adjustments described in Part 1, make the first change large enough to produce a measurable result. A 15 to 20 percent reduction in expected tool life or cutting speed can provide a practical starting point while the process is being secured.
Extending Tool Life Without Moving the Problem
Cutting speed has one of the strongest influences on wear. Reducing it can allow the edge to remain in a usable condition for longer, but the effect must be measured against cycle time and output.
Stability also matters. Runout, tool overhang, component support, toolholding and vibration can all increase edge damage. A more wear-resistant drill cannot compensate for an unstable setup.
Review the process as a complete system:
- Confirm the drill bit geometry is suitable for the hole.
- Inspect the cutting edge and identify the wear pattern.
- Review cutting speed and feed rate.
- Check runout, toolholding and component support.
- Decide whether the tool material provides enough wear resistance.
When to Change the Tooling Route
Carbide can remain suitable for development work or shorter runs when it completes the required quantity securely.
Diamond-coated carbide becomes relevant when abrasive wear causes the uncoated edge to lose its cutting condition too early. The Aero-CARB 2 Flute Double Margin Diamond-Coated Drill adds an 8 μm CVD diamond coating to help protect the drill geometry and slow the development of wear.
PCD may be the stronger option for established, higher-volume production where maximum tool life and long-term process stability justify the initial investment. Suitable PCD tools may also be relapped and, depending on their design and condition, retipped.
The decision should not be driven by purchase price or production volume alone. Component value, quality requirements, tool-change time and cost per acceptable hole all influence the most appropriate route. If the edge is still losing its cutting condition too early, our support team can help review the drill geometry, cutting data and setup as a complete system.
Frequently Asked Questions
Why do drills wear quickly in CFRP?
Carbon fibres are highly abrasive. Repeated contact gradually wears the cutting edge, while cutting data, runout, vibration and tool geometry influence how quickly that wear develops.
What does CFRP drill wear look like?
It often appears as a bright or polished land on the cutting edge. As that land widens, cutting pressure increases and the drill becomes less able to sever fibres cleanly.
Can a worn drill still produce holes?
Yes. A drill may continue machining after the hole condition has begun to deteriorate. Tool life should be based on acceptable holes, not simply the point at which the drill breaks.
How should tool cost be compared?
Compare the tool cost per acceptable hole and include tool-change time, additional inspection, rework and scrap exposure where the data is available.