Appearance
Laser drilling does not cut — it vaporises. A focused beam of light delivers energy densities exceeding 10⁶ W/cm² to the workpiece surface, vapourising material before it can melt. There is no tool to wear, no cutting force to cause deflection, and no material too hard to drill. The challenge is not making the hole — it is making the hole round, straight, and clean. Laser-drilled holes are inherently tapered, lined with recast material, and surrounded by a heat-affected zone. Laser drilling is chosen not because it produces the best holes, but because it can produce holes where no other method can.
Laser Drilling Methods
Percussion Drilling
Percussion drilling is the simplest and fastest method. A series of laser pulses are applied to the same spot, each pulse removing a small amount of material.
| Parameter | Typical Range |
|---|---|
| Hole diameter | 50–700 μm (standard); 1–50 μm (micro) |
| Maximum depth | < 20 mm |
| Time per hole | 0.1–20 seconds |
| Aspect ratio | Up to 100:1 (through) |
| Taper | Higher than other methods |
Best for: High-speed production where hole quality is secondary — cooling holes, filters, lubrication holes.
Trepanning
Trepanning first drills a pilot hole (percussion), then moves the laser beam in a circular path to enlarge the hole to the final diameter.
| Parameter | Typical Range |
|---|---|
| Hole diameter | 0.3–10 mm |
| Maximum depth | < 10 mm |
| Time per hole | 1–20 seconds |
| Circularity | Good — controlled by beam movement |
| Taper | Less than percussion |
Best for: Large-diameter holes where good circularity and low taper are required.
Helical Drilling
Helical drilling moves the laser beam in a circular path while simultaneously feeding the focus position downward, creating a helical tool path.
| Parameter | Typical Range |
|---|---|
| Hole diameter | 10–200 μm |
| Maximum depth | < 2 mm |
| Time per hole | > 10 seconds |
| Circularity | Excellent — best of all methods |
| Taper | Minimal — near-cylindrical holes possible |
Best for: Maximum precision applications — fuel injection nozzles, film cooling holes, high-aspect-ratio micro-holes.
Method Comparison
| Criterion | Percussion | Trepanning | Helical |
|---|---|---|---|
| Speed | Fastest | Moderate | Slowest |
| Depth capability | Deepest (< 20 mm) | Moderate (< 10 mm) | Limited (< 2 mm) |
| Hole quality | Lowest | Good | Highest |
| Diameter range | 50–700 μm | 0.3–10 mm | 10–200 μm |
| Taper control | Limited | Good | Excellent |
| Recast layer | Moderate | Low | Minimal |
Laser Types for Drilling
Pulse Duration Comparison
| Laser Type | Pulse Duration | Peak Power | Ablation Mechanism | Best For |
|---|---|---|---|---|
| Nanosecond (ns) | 1–100 ns | Moderate | Melt ejection | General industrial drilling |
| Picosecond (ps) | 1–100 ps | High | Vapourisation + melt | Precision drilling, metals |
| Femtosecond (fs) | 100–1,000 fs | Very high | Cold ablation (vapourisation) | Highest quality, minimal HAZ |
Pulse Duration Effect on Hole Quality
| Feature | Nanosecond | Picosecond | Femtosecond |
|---|---|---|---|
| Heat-affected zone | 10–100 μm | 1–10 μm | < 1 μm |
| Recast layer thickness | 5–50 μm | 1–10 μm | < 1 μm |
| Micro-cracking | Possible | Minimal | None |
| Taper | Highest | Moderate | Lowest |
| Material removal rate | Highest | Moderate | Lowest |
Key Laser Sources
| Laser Type | Wavelength | Average Power | Pulse Energy | Repetition Rate |
|---|---|---|---|---|
| Nd:YAG (ns) | 1,064 nm | 50–500 W | 1–50 J | 1–50 Hz |
| Fibre laser (ns) | 1,064 nm | 20–200 W | 0.5–10 mJ | 20–200 kHz |
| Picosecond | 1,064 / 532 nm | 10–100 W | 10–500 μJ | 200 kHz–1 MHz |
| Femtosecond | 800 / 1,030 nm | 5–100 W | 5–500 μJ | 1 kHz–1 MHz |
Process Parameters for High Aspect Ratio
Key Parameters
| Parameter | Effect on Drilling | Typical Range |
|---|---|---|
| Pulse energy | Higher = faster removal, more taper, larger HAZ | 0.1–50 mJ |
| Pulse duration | Shorter = less HAZ, less taper | 500 fs–100 ns |
| Repetition rate | Higher = faster, more heat accumulation | 1 kHz–1 MHz |
| Number of pulses | More = deeper hole (to saturation) | 100–10,000+ |
| Wavelength | Shorter = better absorption in metals | UV to IR |
| Focus position | Determines hole entry size and taper | Surface to below surface |
| Assist gas | Oxygen enhances removal; inert reduces recast | Air, O₂, Ar, N₂ |
Aspect Ratio Achievable by Regime
| Material | Laser Regime | Max Aspect Ratio | Depth |
|---|---|---|---|
| Soda-lime glass | fs GHz-burst (1.28 GHz) | 150:1 | 3.7 mm |
| Silicon | fs GHz-burst | 27:1–30:1 | 1 mm |
| Diamond | ns rotary | ~66:1 | > 1.6 mm |
| Stainless steel | fs trepanning | 7:1 | 0.58 mm |
| Metals (general) | ns percussion | 20:1–50:1 | 1–10 mm |
GHz-Burst Mode
Recent advances in femtosecond laser drilling use GHz-burst mode — packets of pulses at 1–2 GHz intra-burst repetition rate:
| Parameter | Benefit |
|---|---|
| Ablation efficiency | 2–5× higher than single pulses |
| Aspect ratio | 150:1 demonstrated in glass |
| Hole quality | Smooth walls, minimal taper |
| Material | Best results in transparent materials (glass, silicon) |
TIP
GHz-burst mode is currently the most promising laser drilling technique for extreme aspect ratios. The rapid succession of pulses within each burst maintains a vapour layer at the hole bottom, allowing subsequent pulses to couple energy deeper into the hole rather than being absorbed at the entrance.
Hole Quality Characteristics
Common Defects
| Defect | Cause | Mitigation |
|---|---|---|
| Taper (wider entry, narrower exit) | Beam divergence, energy loss down hole | Reduce pulse energy, increase pulses, use helical drilling |
| Recast layer | Molten material resolidifies on hole wall | Use shorter pulses, increase assist gas pressure |
| Heat-affected zone | Thermal diffusion from pulse energy | Switch to fs laser, reduce pulse energy |
| Micro-cracking | Thermal stress in brittle materials | Preheating, reduce energy per pulse |
| Spatter | Expelled material deposited around entry | Improve gas flow, use protective coating |
| Hole circularity error | Beam profile asymmetry | Improve beam quality, use trepanning |
Typical Quality Metrics
| Metric | ns Percussion | fs Percussion | fs Helical | Gun Drilling |
|---|---|---|---|---|
| Diameter tolerance | ±0.02–0.10 mm | ±0.005–0.020 mm | ±0.002–0.010 mm | ±0.005–0.025 mm |
| Taper angle | 1–10° | 0.5–5° | < 1° | < 0.1° |
| Surface finish Ra | 1.0–5.0 μm | 0.5–2.0 μm | 0.2–1.0 μm | 0.4–1.6 μm |
| Recast layer | 10–100 μm | 1–10 μm | < 1 μm | None |
| HAZ thickness | 20–200 μm | 2–20 μm | < 2 μm | None |
Laser Drilling vs. EDM vs. Gun Drilling
Comparison by Application
| Requirement | Best Method | Why |
|---|---|---|
| Highest aspect ratio | Laser (fs GHz-burst) | 150:1 demonstrated in glass |
| Smallest hole diameter | Laser | Down to 5 μm |
| Best surface integrity | Gun drilling or ECM | No HAZ, no recast |
| Hardest materials | Laser or EDM | No cutting forces |
| Fastest cycle time | Gun drilling | 10–100× faster |
| Lowest cost per hole | Gun drilling | Established process, low consumables |
| Burr-free | Laser or EDM | No mechanical burr |
| Non-conductive materials | Laser only | EDM requires conductivity |
Process Comparison Table
| Factor | Laser | EDM | Gun Drilling |
|---|---|---|---|
| Aspect ratio | 150:1 (max) | 200:1 | 200:1 |
| Min diameter | 0.005 mm | 0.05 mm | 0.5 mm |
| Tool wear | None | High | Moderate |
| Cutting forces | None | None | Present |
| Surface integrity | HAZ + recast | Recast layer | Good (machined) |
| Material restriction | None (all materials) | Conductive only | < 45 HRC practical |
| Cycle time | Moderate–Slow | Slow | Fast |
| Equipment cost | High | Moderate | Moderate |
| Operating cost | Moderate | Low–Moderate | Moderate |
FAQ
Q: What is the highest aspect ratio achievable with laser drilling? Femtosecond GHz-burst laser drilling has achieved 150:1 in soda-lime glass and 30:1 in silicon. For metals, practical aspect ratios are typically 10:1–50:1 with conventional nanosecond lasers.
Q: What is the difference between percussion, trepanning, and helical drilling? Percussion applies pulses to one spot (fastest, lowest quality). Trepanning cuts a circular path (larger diameters, good quality). Helical drilling combines rotation with downward focus movement (highest quality, slowest, shallowest).
Q: Does laser drilling produce a heat-affected zone? Yes. The HAZ thickness depends on pulse duration: nanosecond lasers produce 10–100 μm, picosecond 1–10 μm, and femtosecond < 1 μm.
Q: Can laser drill non-conductive materials? Yes — this is a key advantage. Laser drilling works on metals, ceramics, glass, diamond, composites, and polymers. EDM requires conductive materials.
Q: How does laser drilling compare to gun drilling for accuracy? Gun drilling produces straighter holes with less taper and better surface finish. Laser drilling has higher positional accuracy (±0.5 μm) and can produce much smaller holes, but the holes are tapered and have a recast layer.
Q: What is GHz-burst mode laser drilling? A technique where each pulse train contains 50–400 sub-pulses at 1–2 GHz repetition rate. This maintains a vapour layer at the hole bottom, improving energy coupling and enabling extreme aspect ratios.
Q: What is the cost per hole for laser drilling vs. gun drilling? Laser drilling is typically 3–10× more expensive than gun drilling due to slower cycle time and higher equipment cost. The gap narrows for very hard or brittle materials where gun drills wear rapidly.
Q: What is the minimum hole diameter achievable with laser drilling? Holes as small as 5 μm can be reliably produced. Research has demonstrated holes below 1 μm using specialised optics.
Q: What causes taper in laser-drilled holes? Taper is caused by beam divergence, energy loss as the hole deepens, and material ejection from the entrance region. Helical drilling and optimised focus strategies reduce taper.
Q: When should I choose laser drilling over gun drilling? Choose laser when the hole diameter is below 0.5 mm, material hardness exceeds gun drilling capability, the material is non-conductive, burr-free holes are required, or the part cannot withstand cutting forces.