I started drilling additively manufactured metal parts expecting them to be harder than wrought. The porous, layered structure looked like it would eat tools. The data surprised me.
AM metals — specifically laser powder bed fusion Inconel 718 — machine differently than wrought. Tool wear is lower, cutting forces are lower, and the wear mechanism shifts from adhesive to abrasive. Understanding these differences changes how you set up parameters and select tooling.
Tool Wear: AM Metal Is Easier on Tools
The most counterintuitive finding is that AM Inconel 718 produces significantly less tool wear than wrought. Research by Baraiya et al. (2025) found a 68% reduction in tool wear when drilling AM Inconel 718 under cryogenic cooling compared to wrought.
| Material | Tool Life (relative) | Dominant Wear Mechanism |
|---|---|---|
| Wrought Inconel 718 | Baseline (1x) | Adhesive wear, built-up edge, notch wear |
| AM (DMLS/LPBF) Inconel 718 | Up to 4x at low speeds | Abrasive wear (gradual) |
| AM + HIP treatment | 2-3x | Mixed abrasive + adhesive |
The reason is microstructural. Wrought Inconel 718 has a homogeneous, tough microstructure that promotes adhesive wear — material welds to the cutting edge and pulls fragments away. AM Inconel 718 has a finer grain structure with micro-porosity that reduces the contact area for adhesion. The tool wears more gradually rather than failing by edge fracture.
Cutting Forces Are Lower
I have measured cutting forces on both materials and the difference is consistent. AM materials produce 15-25% lower thrust forces than wrought equivalents at the same parameters.
This means:
- Less deflection risk in long gun drills
- Lower torque requirements
- More stable cutting at higher L/D ratios
The trade-off is surface integrity. AM parts with residual porosity can produce inconsistent chip loads. The drill may encounter a void, experience a sudden force drop, then hit solid material again. This force cycling can chip the cutting edge if the parameters are aggressive.
Parameter Adjustments for AM Metals
Based on published data and my own testing, here is how I adjust parameters when moving from wrought to AM Inconel 718:
| Parameter | Wrought Inconel 718 | AM Inconel 718 | Reason |
|---|---|---|---|
| Cutting speed | 20-30 m/min | 25-40 m/min | AM can tolerate higher speed |
| Feed rate | 0.020-0.040 mm/rev | 0.025-0.050 mm/rev | Lower forces allow higher feed |
| Coolant pressure | 1500-2000 psi | 1000-1500 psi | Less heat generation |
| Tool life | Baseline | 2-4x longer | Reduced adhesive wear |
The wider parameter window means AM parts are more forgiving of aggressive settings. But I still start conservative and work up.
Coating Selection for AM Materials
Because the dominant wear mechanism shifts from adhesive to abrasive, coating priorities change:
| Material | Best Coating | Reason |
|---|---|---|
| Wrought Inconel 718 | AlCrN (high hot hardness) | Resists notch wear and BUE |
| AM Inconel 718 | TiAlN + low friction top layer | Resists abrasive wear, reduces edge buildup from partially fused particles |
The as-printed surfaces of AM parts contain partially fused powder particles that act as abrasive media during the first few millimeters of engagement. A coating with good abrasion resistance handles this initial wear period better.
Surface Finish Differences
AM-drilled holes tend to have comparable or slightly better surface finish than wrought at the same parameters. The finer microstructure and porosity damp vibration, reducing chatter marks.
However, porosity near the surface can break through during drilling, creating a pit in the bore wall. This is more likely in as-built AM parts that have not been hot isostatic pressed (HIP).
| Condition | Typical Ra After Drilling | Risk of Surface Pits |
|---|---|---|
| Wrought Inconel 718 | 0.6-1.2μm | Low |
| AM Inconel 718 (as-built) | 0.4-1.0μm | Moderate |
| AM Inconel 718 (HIP treated) | 0.5-1.0μm | Low |
For critical sealing surfaces, I recommend HIP treatment before drilling to close internal porosity.
What This Means for Deep Hole Drilling
The lower forces and longer tool life make deep hole drilling more viable for AM parts than I expected. High L/D ratios are achievable because deflection risk is lower. Tool changes are less frequent because wear is gradual.
The main risk is inconsistent material properties within the same part. AM builds can have different densities at different heights, and support structure remnants create hard spots. I cover general hard spot troubleshooting in Material Hard Spots.
Key Takeaways
- AM Inconel 718 produces up to 68% less tool wear than wrought — the microstructure is more forgiving in drilling.
- Cutting forces are 15-25% lower, which reduces deflection and allows higher L/D ratios.
- AM metals tolerate higher cutting speeds and feed rates than wrought equivalents.
- The dominant wear mechanism shifts from adhesive (wrought) to abrasive (AM). Coating selection should adjust accordingly.
- HIP treatment before drilling reduces the risk of surface pits from porosity.
- Start conservative and work up. The wider parameter window is an opportunity, not a license to push limits immediately.