Micro molding is not simply injection molding done smaller. Below a certain part size, several things stop scaling and start behaving differently, and equipment configured for conventional molding produces poor results regardless of operator skill.<\/p>\n\n\n\n
The shift happens gradually rather than at a defined threshold, but parts weighing well under a gram, or with features measured in tens of microns, are firmly in micro molding territory. Medical device components, electronic connectors, optical parts, and microfluidic devices are the usual applications.<\/p>\n\n\n\n
This guide covers what actually changes, what it means for design, and what to ask a supplier.<\/p>\n\n\n\n
Why Small Parts Need Different Equipment<\/strong><\/p>\n\n\n\n Shot Size and Machine Sizing<\/strong><\/p>\n\n\n\n A conventional molding machine is sized around its shot capacity. Using a large machine for a tiny part means the material sits in the barrel far longer than intended, which for many engineering polymers means thermal degradation.<\/p>\n\n\n\n Residence time is the practical issue. A machine sized for a 100 gram shot running a 0.05 gram part cycles the same material through the barrel repeatedly. Heat-sensitive polymers degrade, and the degradation is not always visible in the part but shows up in properties.<\/p>\n\n\n\n Micro molding machines use much smaller injection units, often with different metering arrangements than a conventional reciprocating screw, specifically to control shot size accurately at these volumes and limit residence time.<\/p>\n\n\n\n Injection Control Resolution<\/strong><\/p>\n\n\n\n Injecting a fraction of a gram accurately requires resolution that conventional machines do not have. Small variations that would be negligible on a large part represent a large proportion of a micro shot.<\/p>\n\n\n\n Micro molding equipment is built for that control, with finer position and pressure resolution.<\/p>\n\n\n\n Runner to Part Ratio<\/strong><\/p>\n\n\n\n On a micro part, the runner often weighs considerably more than the part itself. Sometimes many times more.<\/p>\n\n\n\n This has two consequences. Material waste becomes significant relative to part weight, and the thermal history of the material is dominated by the runner rather than the part. Micro molding tooling frequently uses miniature hot runners or carefully designed micro runner systems to manage this.<\/p>\n\n\n\n Tooling Differences<\/strong><\/p>\n\n\n\n Tolerances on the tool are tighter.<\/strong> If a part feature is 100 microns and needs holding within a few percent, the tool must be made to a fraction of that. This pushes tooling into precision machining, wire EDM<\/a> and sometimes micro EDM territory.<\/p>\n\n\n\n Venting becomes critical.<\/strong> Air must escape as the cavity fills, but vents sized conventionally would flash on a micro part. Vent depths measured in a few microns are common, which requires precise machining and careful maintenance since they block easily.<\/p>\n\n\n\n Ejection is harder.<\/strong> Ejector pins on a very small part may be comparable in size to features, and the part may be too delicate to push. Alternative ejection strategies, including air, stripper arrangements or careful gate design, become necessary.<\/p>\n\n\n\n Handling and packing.<\/strong> Parts too small to pick up individually need automated handling, and packaging must prevent loss and damage. This sounds trivial and is not, since a part that cannot be reliably transferred from mold to package is not manufacturable at volume.<\/p>\n\n\n\n Tol\u00e9rances<\/strong><\/p>\n\n\n\n Micro molded parts can hold tight absolute tolerances, but the relationship between tolerance and part size behaves differently than intuition suggests.<\/p>\n\n\n\n Achievable tolerance does not scale down proportionally with part size. A tolerance that is routine as a percentage on a large part becomes very demanding on a small one, because the absolute value approaches the limits of tooling precision, shrinkage predictability and measurement capability.<\/p>\n\n\n\n Three factors set the limit:<\/p>\n\n\n\n Tool precision.<\/strong> The cavity cannot be made more accurately than the machining process allows.<\/p>\n\n\n\n Shrinkage predictability.<\/strong> Polymers shrink as they cool, and while shrinkage is compensated in tool design, its variation is not perfectly uniform. On a small part, small absolute shrinkage variations represent a larger share of the tolerance band.<\/p>\n\n\n\n Measurement.<\/strong> Which leads to a point that surprises many buyers.<\/p>\n\n\n\n Inspection Is a Distinct Problem<\/strong><\/p>\n\n\n\n Measuring micro parts requires different methods. Contact measurement may deform the part. Standard coordinate measuring machines may lack the resolution required, and their probe may be larger than the feature.<\/p>\n\n\n\n Optical and vision measurement systems, and in some cases computed tomography scanning for internal features, are the usual routes.<\/p>\n\n\n\n This matters commercially for two reasons. First, a supplier claiming tight micro tolerances must be able to demonstrate how they measure them, and “we have a CMM” is not sufficient at this scale. Second, measurement uncertainty consumes part of your tolerance band. If your tolerance is 10 microns and the measurement system carries meaningful uncertainty, less than 10 microns of that band is actually available to the process.<\/p>\n\n\n\n Ask specifically what equipment is used, what its resolution is, and how measurement uncertainty is accounted for.<\/p>\n\n\n\n Mat\u00e9riaux<\/strong><\/p>\n\n\n\n Most engineering thermoplastics can be micro molded, but material selection is constrained more than at conventional scale.<\/p>\n\n\n\n Filler size matters.<\/strong> Glass fibres sized for conventional parts may be comparable in length to micro part features, which causes filling problems and inconsistent properties. Unfilled grades or those with fine fillers are generally preferred.<\/p>\n\n\n\n Flow characteristics matter more.<\/strong> Filling a very small cavity through a very small gate demands good flow. High-viscosity grades that fill conventional parts adequately may not fill micro cavities.<\/p>\n\n\n\n Thermal stability matters more.<\/strong> Because of residence time and the runner-to-part ratio, heat-sensitive materials suffer more thermal exposure per unit of part weight than at conventional scale.<\/p>\n\n\n\n Common micro molding materials<\/strong> include PEEK, LCP, POM, PC, PP, nylon grades and various medical-grade polymers. Where a specific grade is required, confirm micro molding suitability with both the material supplier and the molder.<\/p>\n\n\n\n Consid\u00e9rations relatives \u00e0 la conception<\/strong><\/p>\n\n\n\n Many conventional design rules still apply, and some apply more strictly.<\/p>\n\n\n\n Uniform wall thickness<\/strong> remains important, and the consequences of violating it are the same: differential shrinkage, warpage and sink.<\/p>\n\n\n\n Draft angles<\/strong> remain necessary. Very small parts are more susceptible to ejection damage, so adequate draft matters more, not less.<\/p>\n\n\n\n Gate location<\/strong> becomes more constrained. The gate is large relative to the part, so its position and the vestige it leaves are significant design considerations rather than details.<\/p>\n\n\n\n Radii at corners<\/strong> help filling and reduce stress, and at micro scale sharp corners are also harder to machine into the tool accurately.<\/p>\n\n\n\n Aspect ratios<\/strong> need care. Very deep, very thin features are difficult to fill and difficult to eject, and the tool steel forming them is fragile.<\/p>\n\n\n\n Tolerances should be specified only where function requires.<\/strong> As at any scale, but the cost penalty is steeper here.<\/p>\n\n\n\n Volume and Cost<\/strong><\/p>\n\n\n\n Micro molding tooling costs more than conventional tooling of comparable cavitation, because the precision required is higher and the machining more demanding.<\/p>\n\n\n\n Against that, cycle times are typically short, since small parts cool quickly, and multi-cavity tooling is common. Once tooling exists, unit costs at volume can be very low.<\/p>\n\n\n\n The implication is a higher break-even volume than conventional molding. Micro molding suits established high-volume programmes rather than exploratory low-volume work. For validation quantities, machined or 3D printed parts, or prototype tooling<\/a> at reduced cavitation, are usually the sensible route before committing production tooling.<\/p>\n\n\n\n Applications<\/strong><\/p>\n\n\n\n Dispositifs m\u00e9dicaux<\/strong> are the largest application area: catheter components, drug delivery parts, surgical device components, diagnostic consumables. Cleanroom molding and full traceability are common requirements.<\/p>\n\n\n\n Electronics and connectors<\/strong> need small precise parts in materials with specific electrical and thermal properties, often LCP for its flow and temperature characteristics.<\/p>\n\n\n\n Optics<\/strong> requires surface quality and dimensional precision that push tooling and process control hard.<\/p>\n\n\n\n Microfluidics<\/strong> needs very fine channel geometry with consistent cross-section, which combines tight tolerance with challenging filling.<\/p>\n\n\n\n What to Ask a Micro Molding Supplier<\/strong><\/p>\n\n\n\n The measurement questions are the most useful filter. A supplier who has thought carefully about metrology at this scale is a supplier who understands micro molding. One who answers with conventional inspection equipment is likely applying conventional molding practice to small parts, which is the core problem this article describes.<\/p>\n\n\n\n\n