What counts as micro injection moulding?

Parts with a moulded weight below about 1 gram, features below roughly 100 microns, or tolerances measured in single-digit microns. The strictest definition covers parts of a few milligrams, such as micro gears, microfluidic features and medical micro-components.

What tolerances can micro injection moulding hold?

Well-engineered micro tools with controlled processes routinely hold ±0.005-0.01 mm on critical dimensions, and ±0.002-0.005 mm is achievable on the best-controlled features. At this scale, steel temperature and measurement method matter as much as the machine.

Why is shot weight control difficult in micro moulding?

A micro part may weigh 10 mg while the smallest conventional machine shot is several grams. Micro machines use dedicated small screws or plunger units with shot capacities of a few grams, because a large screw cannot meter a few milligrams repeatably.

Which materials can be micro moulded?

Most engineering thermoplastics including POM, PC, PA, PEEK, LCP and medical grades, plus COC and PMMA for optics. Very high-viscosity materials struggle in micro channels; LCP is favoured for micro electrical parts precisely because it flows exceptionally well.

How much does micro injection moulding tooling cost?

Micro moulds typically cost €8,000-30,000 for single-impression tools despite the small part size, because precision machining, wire EDM and metrology dominate the price. The part is small but the toolmaking hours are not.

Micro Injection Moulding: Capabilities, Design Rules and Applications

Micro injection moulding produces parts you can lose on your fingertip: gears the size of a grain of rice, medical dosing features measured in microns, connector pins with walls thinner than a human hair. It is one of the fastest-growing niches in plastics, driven by medical devices, microfluidics, wearables and micro-electronics. It is also one of the least forgiving. This guide covers what counts as micro, what is achievable, and what it takes to succeed.

What counts as a micro part?

Three overlapping definitions are in use:

Micro-weight parts: total moulded weight below about 1 g, with serious micro work starting below 100 mg
Micro-featured parts: features below roughly 100 µm (pins, walls, holes, channels), even if the part itself is larger
Micro-tolerance parts: tolerances in the low single-digit microns, whatever the size

A part can be any one of these or all three. A microfluidic chip, for example, is a gram-scale part carrying 50 µm channels: micro-featured rather than micro-weight.

Why does scale change the process?

Three effects dominate at micro scale. Metering: a part weighing 20 mg cannot be dosed by a standard screw whose smallest repeatable shot is grams, so micro machines use small-diameter screws or two-stage screw-and-plunger units with shot capacities of 1-5 g. Freezing: a 100 µm feature freezes almost instantly, so filling must be extremely fast and mould temperatures run high, often 30-50 °C above conventional settings, sometimes with variotherm heating for the fill phase. Surface area: the sprue and runner for a micro part can outweigh the parts ten to one, which is why runnerless or micro-runner tool design matters so much.

What tolerances are realistic?

Standard micro features: ±0.01-0.02 mm is comfortably achievable
Controlled critical dimensions: ±0.005-0.01 mm with good steel, temperature control and process discipline
Best-case features: ±0.002-0.005 mm on short dimensions with premium tooling, variotherm control and 100% measurement feedback

At these levels the limiting factors stop being the moulding machine and become steel thermal expansion (roughly 11 µm per metre per °C), measurement uncertainty, and material batch variation. CMMs give way to optical and CT measurement, which is one reason our quality and tolerances page treats micro parts as a special measurement case.

What are the design rules for micro parts?

Wall thickness: 0.1-0.5 mm is the working range; below 0.1 mm only with high-flow materials and short flow lengths
Aspect ratio: features deeper than about 5:1 (depth to width) become ejection and filling risks
Draft: still required; at micro scale even 0.5° matters because ejection forces per area are high and features are fragile
Corners and edges: radii of 20-50 µm are typical machining limits and should be called out explicitly, not assumed
Gates: pinpoint and micro-edge gates of 0.1-0.3 mm; gate vestige must be specified because it is a visible fraction of the part
Handling: design for automation from the start; micro parts are separated, oriented and packed by machine, not by hand

The general rules in our design for injection moulding guide still apply; they just get tighter and the consequences of ignoring them arrive faster.

Which materials work at micro scale?

Material	Why it is used in micro parts
POM	Low friction, precise, the classic micro-gear material
LCP	Exceptional flow into thin micro channels; electrical micro-connectors
PC	Tough, clear, dimensionally stable optical and medical parts
PA	Micro mechanical parts; control moisture tightly
PEEK	High-temperature and implantable medical micro parts
COC / COP	Microfluidics and diagnostics: clear, low water uptake, DNA-compatible
PMMA	Micro-optics and light guides

Very viscous materials and heavily filled grades (above ~30% glass) struggle below about 0.2 mm features; unfilled or lightly filled grades are the safe default. See our materials guide for the broader selection logic.

What does the tooling look like?

Micro moulds are conventional moulds built to watchmaker standards. Cavity work is done by micro-milling, sinker and wire EDM, and sometimes laser ablation or LIGA-derived inserts for sub-50 µm features. Ejection uses micro-pins down to 0.3 mm diameter or air ejection for fragile parts. Tool temperature control is tighter than ±1 °C. Single-impression and low-cavitation tools dominate because cavity-to-cavity consistency at micron level is the hard constraint, and mould flow simulation is often run on the runner system alone to keep fills balanced.

Nordmould evaluates micro part enquiries with our toolmaking partners before quoting, because at this scale the honest answer to "can you mould it" depends on feature-by-feature toolmaking feasibility, not just machine capability.

Where is micro moulding used?

Medical: dosing components, catheter features, drug-delivery parts, surgical micro-instruments
Microfluidics and diagnostics: lab-on-chip channels, well plates, assay features
Electronics: micro-connectors, fibre-optic ferrules, sensor housings
Watchmaking and precision mechanics: gears, escapements, bearings
Automotive: micro-optics, sensor components, micro-actuator parts

What does it cost?

Micro parts invert the usual cost logic. Tooling of €8,000-30,000 for a single-impression tool is normal because precision machining and metrology dominate; piece prices are often €0.05-0.50 despite the tiny size, because cycle times are modest, inspection is intensive and shot weights make material cost irrelevant. The commercial case rests on value per gram, not cost per kilo: micro parts are among the most valuable plastic parts made.

How to start a micro part project

Start with the feature list, not the part: identify the smallest features, the tightest tolerances and the material, then get a toolmaker feasibility view before the design freezes. A mould flow simulation and a DFM review against our tolerance guide are the two cheapest risk-reducers available. Nordmould can review micro part drawings and give you a straight answer on feasibility, tooling cost and realistic tolerances.

Related guides

Developing a micro part? Send Nordmould your feature list and drawings for a feasibility and tooling review.