Have you seen injection moulding parts below 1 gram?
Three thresholds define the category. A part crossing any one of them is likely to need micro-specific process capability.
Part mass. Micro moulding generally describes shots below roughly a gram, and the demanding end of the category runs into milligrams. At those masses the moulded part frequently weighs less than the sprue and runner feeding it, sometimes by an order of magnitude. That inversion is the clearest sign you have left conventional territory, and it is why material waste ratios in micro moulding look nothing like those in standard production.
Feature size. Sub-millimetre wall sections, and functional features measured in tens or hundreds of microns. Once a wall thins past a certain point, flow behaviour stops being intuitive: the polymer freezes off before the cavity fills unless the process is built around the geometry rather than adapted to it.
Tolerance band. Conventional moulding works comfortably in tenths of a millimetre. Micro moulding routinely calls for single-digit microns on critical dimensions. At that resolution, shrinkage variation, tool wear and ambient temperature stop being background noise and become primary process variables.
The most persistent misconception is that micro moulding is defined by clamp tonnage. It is not. It is defined by the injection unit.
A small press fitted with a conventional screw cannot reliably dose a very small shot. The required volume is a tiny fraction of what the barrel holds, which creates two failures simultaneously. Dosing repeatability collapses, because the screw is metering at the very bottom of its usable stroke where small positional errors translate into large proportional volume errors. And residence time rises, because material sits in a heated barrel far longer than the process intends. For thermally sensitive polymers, that second problem presents as degradation: discolouration, embrittlement, or loss of mechanical properties that no amount of parameter adjustment will recover.
Genuine micro moulding equipment addresses this with a shot-size-matched injection unit: a plunger system or a micro-screw, typically single-digit millimetres in diameter, dosing volumes appropriate to the part rather than to the machine. That specification is the one that matters. When assessing a supplier’s micro capability, ask about the injection unit, not the tonnage.
A part that clears none of these three thresholds is small-precision work rather than micro. It will tool faster, cost less per part and scale into multi-cavity production more easily on a conventional press. Specifying micro moulding for a part that does not require it converts a routine programme into a specialist one and prices it accordingly.
Micro moulding cost is not concentrated in press time. Cycle times are frequently short, and the machines themselves have a small footprint and modest energy draw. The cost sits in three other places.
Tooling. Micro cavities are typically produced by micro-milling, micro-EDM, or a combination of both, in tool steels selected for polish and wear resistance rather than machinability. Cavity counts are usually low, because balancing fill across many micro cavities is difficult and because the value of the parts rarely justifies the tool complexity. Venting deserves particular attention: air trapped in a micro cavity cannot escape through conventionally sized vents, so vacuum-assisted moulds are common. Every one of these decisions raises tool cost above a comparable conventional mould. Our guide to injection moulding cost factors covers the underlying economics in more depth.
Metrology. Callipers are irrelevant at this scale. Dimensional verification moves to optical measurement systems, vision inspection, and in some cases X-ray or CT scanning where internal features, voids or assembled fit need to be confirmed without destroying the part. Inspection stops being a checkpoint and becomes a cost line in its own right and for regulated work, a documentation obligation.
Handling and automation. Parts of this size do not eject and drop into a bin. They stick to tooling, they are lost to static, and they are almost impossible to sort manually without damage. Reliable micro production depends on controlled demoulding, vacuum or robotic part removal, and packaging designed to keep individual parts traceable and undamaged designed in from the outset, not bolted on once parts start appearing.
Five questions separate real capability from optimistic marketing.
Material selection sits alongside these questions. Liquid crystal polymer, PEEK, POM and medical-grade polycarbonate recur in micro applications because they combine flow performance in thin sections with the mechanical or biocompatibility properties the end use demands. Material and geometry have to be resolved together and early, which is why design input ahead of tooling commitment usually pays for itself.
Allied Hori runs micro injection moulding on its 10T–30T presses, within a wider injection moulding capability spanning 10T to 350T, so a programme that begins as a micro component and grows into a larger assembly does not need to change supplier. Tooling is designed and fabricated in-house, and in-house X-ray and CT scanning support dimensional and internal-feature verification where optical measurement alone is insufficient.
Shot weights below one gram are within standard production capability.
The quality system is certified to ISO 9001, ISO 14001, IATF 16949 and ISO 13485: the last of which governs work for medical device customers, where micro components are most concentrated, alongside sensor, connector and IoT applications.
If you have a component you believe requires micro moulding — or you are not certain whether it does — send us the drawing. Establishing which side of the line a part falls on is a short conversation, and it is considerably cheaper than discovering the answer after a tool is cut.
