Guide complet du moulage par micro-injection

Votre client en dispositifs médicaux vient d'envoyer un dessin pour un boîtier d'aide auditive avec une languette à encliquetage de 0,3 mm de large. Votre standard fournisseur de moulage par injection l'ont examiné et ont dit qu'ils ne peuvent pas l'outiller. Si vous essayez de déterminer si moulage par injection can produce parts this small — reliably, in production volumes — this guide gives you the straight answer from the factory floor.

What Is Micro Injection Molding and How Does It Work?

Micro injection molding is a specialized manufacturing process for producing plastic parts weighing less than 1 gram with features smaller than 1 mm. It uses dedicated plunger-injection machines with injection molding shot volumes of 0.001 to 5 cc — roughly 1,000 times smaller than a standard injection molding machine. The process is not simply “regular molding at a smaller scale.” The equipment, tooling, and process parameters are fundamentally different.

A standard injection molding machine uses a reciprocating screw to meter and inject material. At sub-gram part weights, the screw can’t control shot volume accurately enough. Micro molding machines replace the screw with a plunger system that meters material in a separate chamber, then injects it with positional accuracy of plus or minus 0.0001 cc. This separation of melting and injection is what makes consistent micro-part production possible.

The mold itself is also different. Cavity features under 0.5 mm can’t be machined with standard CNC tools. They require electrical discharge machining and wire cutting to create sub-millimeter geometries in hardened tool steel. Mold surface finish matters more too — at the micro scale, a 0.5 micrometer Ra surface finish difference directly affects part ejection and dimensional consistency.

How Does Micro Injection Molding Compare to Other Micro Manufacturing Methods?

For high-volume production of complex plastic geometries under 1 gram, micro injection molding is the clear choice. Here is how it compares to the alternatives we’ve seen clients evaluate before committing to a process.

The break-even between micro molding and micro CNC typically falls around 500 to 1,000 parts. Below that volume, CNC is cheaper because there’s no mold investment. Above 1,000 parts, the per-part cost advantage of molding becomes overwhelming. A 0.05 g POM gear that costs $8 to CNC machine drops below $0.10 per part at 10,000 molded units. The mold runs $8,000 to $15,000, so payback is fast.

SLA 3D printing is useful for prototypes and design validation, but the material properties don’t match injection molded thermoplastics — especially for medical and aerospace applications requiring biocompatibility or flame ratings. We recommend SLA for early-stage prototypes, then transitioning to micro molding for production.

What Materials Work Best for Micro Injection Molding?

Cette section traite des matériaux les mieux adaptés au micro-moulage par injection et de leur impact sur le coût, la qualité, les délais ou les risques d'approvisionnement. Tous les thermoplastiques ne fonctionnent pas à l'échelle micro. Le matériau doit remplir des caractéristiques aussi fines que 0,1 mm sans se figer, et il doit le faire de manière constante sur des milliers de cycles. Voici les matériaux que nous utilisons réellement en production pour les micro-pièces, et pourquoi.

LCP in injection molding (Liquid Crystal Polymer) is the go-to for thin-wall micro parts. Its melt viscosity is roughly one-tenth that of standard engineering resins, which means it can fill features that other materials can’t reach. Wall thicknesses down to 0.1 mm are achievable with LCP at mold temperatures of 120 to 150 degrees C and injection speeds above 800 mm/s. It’s the standard choice for electronic connectors with pitches below 0.3 mm.

PEEK dominates medical and aerospace micro applications. It handles continuous temperatures up to 250 degrees C, passes USP Class VI biocompatibility testing, and resists chemical attack from sterilization processes. Processing requires barrel temperatures of 370 to 400 degrees C and mold temperatures of 160 to 200 degrees C. Temperature control within plus or minus 2 degrees C is critical — a 5 degree drift can cause 30 percent dimensional variation in a micro PEEK part.

POM (acetal) is the workhorse for mechanical micro parts like gears, bushings, and snap fits. It machines well in the mold, has low friction, and holds tolerances consistently. Medical-grade ABS rounds out the common choices for housings and enclosures where biocompatibility is required but extreme temperature or chemical resistance is not.

How to Select the Right Material for Micro Parts

Choosing the right material also depends on secondary operations. If the micro part requires ultrasonic welding, only certain grades of ABS and PMMA bond reliably at the joint interface. For laser welding, the material pair must have different absorption characteristics — typically a carbon-loaded base with a natural-color lid. These constraints are often overlooked in the design phase and can force a material change late in development.

Processing windows for micro molding materials are significantly narrower than for standard molding. A typical POM gear might tolerate plus or minus 10 degrees C barrel temperature variation at normal scale, but the same material in a micro part requires control within plus or minus 3 degrees C. Dedicated micro molding machines feature multiple barrel temperature zones with independent PID controllers and thermocouple feedback every 50 mm along the barrel length.

What Are the Key Design Rules for Micro Molded Parts?

Designing for micro molding is not the same as scaling down a standard part design. The physics change at sub-millimeter dimensions, and rules that work at normal scale break down. Here are the guidelines that actually matter in production.

Wall thickness is the most critical parameter. Below 0.5 mm, freeze-off becomes your primary defect risk. The material solidifies on contact with the cavity wall before it can fill the feature completely. To counter this, you need mold temperatures above 80 degrees C (higher for crystalline materials), injection speeds above 500 mm/s, and gate placement within 2 mm of the thinnest section. At 0.1 mm wall thickness with LCP, you’re running at the absolute edge of what the process can do.

Draft angles matter more at micro scale, not less. A 0.5 degree draft on a 5 mm deep feature seems negligible, but on a micro part with a 0.2 mm wall, that draft determines whether the part ejects cleanly or deforms. As discussed in our injection mold guide, we recommend a minimum of 1 degree draft on all vertical surfaces for micro parts, and 2 degrees for features deeper than 3 mm.

Radii should be at least 0.05 mm on all internal corners. Sharp internal corners create stress concentrations that cause cracking during ejection or in service. At micro scale, even a 0.02 mm radius makes a measurable difference in part strength. Gate design is equally important — for parts under 0.5 g, a single edge gate with a maximum land length of 0.5 mm is usually the best choice.

How Is a Micro Injection Mold Different from a Standard Mold?

The fundamental difference is how the cavity is created. Standard molds use CNC milling for most cavity features, with EDM³ reserved for sharp corners and deep ribs. Micro molds reverse this ratio — EDM and wire cutting handle the majority of cavity features because CNC can’t create geometries below about 0.3 mm reliably.

Mold temperature control is also more demanding. A standard mold might run at 40 to 60 degrees C with simple water channels. A micro mold running PEEK needs 160 to 200 degrees C with cartridge heaters and thermocouple feedback in each cavity insert. Temperature uniformity across the cavity affects fill, shrinkage, and warpage at least 10 times more at micro scale than at normal scale.

Ejection is the third major difference. Standard molds use ejector pins and plates. On a micro part with a 0.3 mm wall, a standard 2 mm ejector pin covers the entire wall surface — you’ll punch through the part. Micro molds use specialized micro-ejector pins (0.2 to 0.5 mm diameter), air ejection, or robot-assisted part removal. Some micro molds don’t eject at all — they use a robot to pull the part from the cavity with vacuum pickup.

Production micro molds typically last 200,000 to 500,000 cycles before cavity refurbishment, depending on material abrasiveness and feature complexity. Molds running glass-filled materials may need rework at 100,000 cycles. For ultra-tight tolerances, plan to re-measure critical dimensions every 20,000 cycles.

What Industries Depend on Micro Injection Molding?

Cette section traite des industries qui dépendent du micro-moulage par injection et de son impact sur le coût, la qualité, les délais ou les risques d'approvisionnement. Les dispositifs médicaux représentent environ 40 % de toutes les pièces micro-moulées produites dans le monde. Les composants d'aides auditives, les embouts d'instruments chirurgicaux, les mécanismes d'administration de médicaments et les cartouches de tests de diagnostic reposent tous sur des pièces plastiques de moins d'un gramme avec des détails invisibles à l'œil nu. Les exigences réglementaires (ISO 13485, USP Classe VI) rendent la validation des processus plus exigeante, mais les volumes justifient l'investissement — une seule conception de stylo d'injection peut atteindre 5 millions d'unités par an.

Electronics is the second-largest sector. Every smartphone contains 10 to 20 micro molded connectors, switches, and lens elements. Wearable devices and IoT sensors are pushing connector pitches below 0.3 mm — requiring mold features that didn’t exist five years ago. The miniaturization trend shows no sign of slowing.

Automotive micro molding is growing fast, driven by sensor proliferation. A modern vehicle contains 50 to 100 micro molded sensor housings, connector seals, and valve components. These parts need to survive under-hood temperatures up to 150 degrees C while maintaining dimensional stability over a 15-year service life.

What Does Micro Injection Molding Actually Cost?

Cette section traite du coût réel du micro-moulage par injection et de son impact sur le coût, la qualité, les délais ou les risques d'approvisionnement. Le coût des outillages de micro-moules varie entre 5 000 et 25 000 dollars, en fonction de la complexité de la pièce, du nombre d'empreintes et de la finition de surface requise. Les moules prototypes à une empreinte pour des géométries simples commencent autour de 5 000 dollars. Les moules de production multi-empreintes avec des tolérances serrées et des surfaces de cavité polis coûtent entre 15 000 et 25 000 dollars.

Per-part costs range from $0.02 to $0.50 at volumes above 10,000 units. At 100,000 units, most micro molded parts fall between $0.02 and $0.10 each. The economics improve dramatically with volume because the fixed tooling cost amortizes quickly on a small, fast-cycle part. A micro part with a 5-second cycle time in a 16-cavity mold produces nearly 100,000 parts per day on a single machine.

Don’t forget ancillary costs: part handling (micro parts often need robot pickup, not gravity drop), inspection equipment (optical measurement systems run $30,000 to $80,000), and packaging (static-free containers for parts that weigh less than a paperclip). These add 20 to 40 percent to the total project cost beyond tooling and molding.

How Do You Ensure Quality in Micro Injection Molding?

Cette section traite de l'assurance qualité dans le micro-moulage par injection et de son impact sur le coût, la qualité, les délais ou les risques d'approvisionnement. Le contrôle qualité à l'échelle micro nécessite des méthodes d'inspection totalement différentes du moulage standard. On ne peut pas utiliser de pieds à coulisse sur une caractéristique de 0,3 mm. Les systèmes de mesure optique (machines à mesurer tridimensionnelles par vision) avec un grossissement de 10x à 200x sont la norme pour la vérification dimensionnelle. Ces systèmes mesurent la taille, la position et la géométrie des caractéristiques à partir d'images agrandies avec une résolution allant jusqu'à 0,5 micromètres.

Process monitoring is more important than inspection at micro scale. Because you can’t economically measure every dimension on every part, you rely on statistical process control tied to machine parameters. Monitoring injection pressure, screw position, mold temperature, and cycle time gives you real-time indication of process stability.

Our tooling workshop includes EDM machines, wire cutters, precision engravers, and CMM inspection equipment — all necessary for creating and verifying the sub-millimeter features that define micro molded parts. With 8 senior engineers averaging over 10 years of experience, we’ve handled micro molding projects across medical, electronics, and automotive applications.

Frequently Asked Questions About Micro Injection Molding

What is the minimum part size for micro injection molding?

The practical minimum is approximately 0.5 cubic mm in volume, or parts weighing as little as 0.001 g. Achieving this requires plunger-style injection systems with precision metering chambers accurate to 0.0001 cc and mold temperatures maintained above 100 degrees C throughout the entire injection cycle. At these extremely small dimensions, even a 0.0005 cc variation in shot volume produces a visible quality defect, so process control must be exceptionally tight and validated over thousands of consecutive cycles before full production release.

How much does a micro injection mold cost?

Micro mold tooling costs between $5,000 and $25,000 depending on part complexity, cavity count, and surface finish requirements. Single-cavity prototype molds for simple geometries start around $5,000, while multi-cavity production molds with tight tolerances and polished cavity surfaces run $15,000 to $25,000. The higher cost reflects the specialized EDM and wire cutting processes needed to create sub-millimeter cavity features that conventional CNC milling simply cannot achieve, regardless of the quality of the cutting tools or the skill of the machinist operating the equipment.

What tolerance can micro injection molding achieve?

Standard micro molding tolerances range from plus or minus 0.01 to 0.05 mm depending on the specific material being molded, the geometry of the part, and the aspect ratio of its critical features. Flat surfaces under 5 mm span in low-shrinkage materials like POM can consistently achieve plus or minus 0.008 mm in production. Deep holes with aspect ratios above 5:1 typically hold plus or minus 0.03 mm due to core pin deflection and uneven shrinkage around long steel features in the mold cavity.

What is the minimum wall thickness for micro injection molding?

Wall thicknesses down to 0.1 mm are achievable with low-viscosity materials like LCP, provided the mold is heated to 120 to 150 degrees C and injection speed exceeds 800 mm/s to prevent premature freeze-off during cavity filling. Below 0.1 mm, cavity fill becomes extremely difficult because material solidifies on contact with the cavity wall almost instantly. Consistent wall variation under plus or minus 0.02 mm requires optimized gate placement within 2 mm of thin sections and rigorous process monitoring throughout the production run.

How long does a micro injection mold last?

Production micro molds typically last 200,000 to 500,000 cycles before cavity refurbishment, depending on the abrasiveness of the molding material and the feature complexity of the part design being produced. Molds running glass-filled or carbon-fiber reinforced materials may need rework at 100,000 cycles due to accelerated wear on fine cavity features. For ultra-tight tolerances, we strongly recommend re-measuring critical dimensions every 20,000 cycles and budgeting for cavity re-polishing or core replacement as routine preventive maintenance to avoid unexpected dimensional quality drift in production.

Can you micro mold PEEK?

Yes, PEEK micro molding is widely used for medical implants and aerospace applications requiring biocompatibility and continuous temperature resistance up to 250 degrees C. Processing requires barrel temperatures of 370 to 400 degrees C, mold temperatures of 160 to 200 degrees C, and injection speeds above 500 mm/s. Barrel temperature control within plus or minus 2 degrees C is critical — a 5 degree C drift can cause 30 percent dimensional variation in a micro PEEK part, making precise thermal management essential for consistent production quality and dimensional repeatability.

What is the difference between micro molding and small part molding?

Micro molding specifically refers to parts under 1 gram with critical features below 1 mm, requiring dedicated plunger-injection machines with shot volumes of 0.001 to 5 cc and EDM-fabricated molds with sub-millimeter cavity details. Small part molding produces 1 to 10 gram parts on standard reciprocating-screw machines with conventional CNC-milled steel molds. These represent fundamentally different equipment categories, tooling approaches, and process control parameters, despite both processes ultimately producing relatively small plastic components for similar end-use applications across multiple industries.

1. shot volumes: Shot volume is the amount of molten plastic injected into the mold cavity per cycle, measured in cubic centimeters. Micro molding shot volumes range from 0.001 to 5 cc. ↩

2. LCP: LCP refers to high-performance thermoplastic with exceptional flow characteristics for thin-wall micro parts, commonly used in electronic connector applications. ↩

3. EDM : EDM refers to precision manufacturing process that removes material using electrical sparks, capable of creating features under 0.1 mm in hardened tool steel. ↩