The nozzles that atomize fuel are drilled with holes measured in tenths of a millimeter, held to flow targets of a few percent. Both micro-gundrilling and EDM work at this scale — the choice depends on hole count, aspect ratio and surface requirements.
A modern injector nozzle has a central blind feed (the “injector hole” or sac) with 5–10 tiny angled orifices opening into the combustion chamber. Total flow through those orifices — not their individual diameter — is the spec that matters, held to a couple of percent. That forces the process to be repeatable at a scale where a 2 μm variation changes flow noticeably.
| Criteria | Micro gundrilling | Micro EDM |
|---|---|---|
| Diameter | ~Ø0.3–1.0 mm practical | Down to Ø0.05–0.1 mm |
| L/D | Up to ~50:1 | Up to 20–30:1 |
| Hole shape | Round, burr-controlled | Round; taper controllable by EDM settings |
| Surface / recast | Machined, clean | Thin recast layer (often flushed or post-processed) |
| Multi-hole angle | Needs angular indexing | Easy angular indexing |
| Cycle / cost | Fast per hole at larger dia | Slower, higher per-hole cost |
Micro gundrills are delicate — the drill body is thinner than a needle. Parameters are conservative:
Micro-EDM uses a tungsten or carbide electrode smaller than the hole, eroding by spark with deionized water or oil dielectric. For nozzles the electrode is often wire-guided or orbital to control taper. Key variables: gap voltage, on/off time, electrode wear compensation, and dielectric flushing. A recast layer of a few microns forms on the wall — many injector specs require its removal (electropolish, abrasive flow, or wet honing) to avoid flow and durability issues.