Plastic Injection Moulding: Process, Tooling & Costs
What is plastic injection moulding and how does it work?
Injection moulding is a manufacturing process in which molten plastic is forced under pressure into a precision mould cavity, where it cools and solidifies into a finished part. The cycle repeats continuously — typical cycle times run from a few seconds to a couple of minutes depending on wall thickness and material — making the process economical for volumes from the low hundreds into the millions.
The four stages of every injection-moulding cycle are clamping, injection, cooling, and ejection.
What happens at each stage of the cycle?
Clamping. The two halves of the mould — the cavity (A-side) and the core (B-side) — are forced together by the clamping unit of the injection-moulding machine. Clamping force, measured in tonnes, must exceed the separating force created by the injected melt; insufficient clamping causes flash at the parting line.
Injection. Plastic pellets are fed from a hopper into a heated barrel, melted by a reciprocating screw, and then rammed forward under pressure into the mould's sprue, runner system, and gate. Injection pressure typically ranges from 70 to 140 MPa depending on material and part geometry. The screw holds forward pressure — pack and hold pressure — to compensate for volumetric shrinkage as the plastic cools.
Cooling. This is usually the longest phase of the cycle. Cooling channels machined through the mould carry temperature-controlled water (or oil for high-temperature materials), extracting heat from the part. Uniform cooling reduces warpage and sink marks. Cooling time depends on wall thickness: as a rule of thumb, each millimetre of wall requires roughly 2–3 seconds of cooling time for common materials such as ABS or PP.
Ejection. Once the part has solidified sufficiently to be dimensionally stable, the mould opens and ejector pins, sleeves, or a stripper plate push the part clear of the core. The mould then closes and the cycle begins again.
What are the injection-moulding machine and the mould?
The machine is rated by clamping force (typically 50 to 4,000+ tonnes for production presses). A larger, thicker, or higher-pressure part needs a higher-tonnage machine. Shot weight capacity, plasticising rate, and tie-bar spacing are also selection criteria. Machine selection is handled by Nordmould's manufacturing partners and is not a decision the buyer normally makes.
The mould (tool) is the precision component the buyer pays for. It consists of at least two steel or aluminium plates containing the cavity geometry, the runner and gate system that delivers melt to the cavity, cooling channels, and the ejection system. A single-cavity tool produces one part per shot; a multi-cavity tool produces two, four, eight, or more identical parts per shot, reducing piece price at the cost of higher tooling spend.
The mould is a long-life asset. It travels with the buyer's account at Nordmould; if you ever move to higher volumes or change supplier, the tool moves too.
What is the difference between aluminium and hardened-steel tooling?
Tooling choice is one of the most consequential early decisions. The table below sets out the key differences using standard industry values.
| Parameter | Aluminium tooling (Bridge) | Hardened-steel tooling (Production) |
|---|---|---|
| Typical tool life (shots) | 10,000–50,000 | 500,000–1,000,000+ |
| Typical lead time | 2–5 weeks | 6–11 weeks |
| Relative tooling cost | Lower (index: 1×) | Higher (index: 2–5×) |
| Suitable volumes | 100 – ~5,000 pieces | 5,000 pieces and above |
| Cavity finish | Good; limits ultra-high-gloss | Full cosmetic grades available |
| Dimensional precision | Good for most applications | Best; suited to tight tolerances |
| Typical entry price at Nordmould | From €3,000 | Higher; confirmed at DFM stage |
When to choose aluminium (Bridge tooling). You need market-validation quantities, regulatory approval samples, or a pilot batch before committing to full production investment. Aluminium machines faster, costs less, and still produces injection-moulded parts — not 3D prints — with real material properties and surface finish. If your product succeeds, the bridge tool can stay in service or be replaced with a steel tool at scale.
When to choose hardened steel (Production tooling). Your design is frozen, volume forecasts are reliable, and piece-price matters. Hardened steel holds tighter tolerances over millions of cycles, accommodates complex texture and high-gloss finishes, and supports multi-cavity layouts for high-volume efficiency.
Nordmould's Bridge tier exists precisely for the gap that most large moulders ignore: the 100–5,000 piece range where a startup or OEM needs real parts without betting €15,000–30,000 on a production tool before the design is proven.
Why are 100-piece runs economically viable?
Traditional injection moulding economics favour volume: tooling is a fixed cost, so the more pieces you amortise it across, the lower the per-unit cost. A €5,000 aluminium tool across 100 pieces adds €50 per part; across 1,000 pieces it adds €5. The per-unit moulding cost (material plus machine time) is small by comparison.
What makes 100-piece runs viable at Nordmould is aluminium tooling combined with lean tool design. A simple, well-designed part in a single-cavity aluminium tool can be quoted from €3,000 tooling, making the unit economics workable for pre-series, regulatory samples, or spare-parts programmes. The free DFM review is where Nordmould checks that the geometry is simple enough to hit that entry point — and flags any features that would push costs up before you commit.
What materials are available?
| Material | Family | Key properties | Typical applications |
|---|---|---|---|
| ABS | Amorphous | Good impact strength, easy to paint and bond | Enclosures, housings, consumer products |
| PP | Semi-crystalline | Lightweight, chemical-resistant, living-hinge capable | Caps, clips, packaging, automotive interior |
| PC | Amorphous | High clarity, heat-resistant, tough | Lenses, safety covers, structural covers |
| POM (acetal) | Semi-crystalline | Low friction, high stiffness, dimensional stability | Gears, bearings, precision mechanical parts |
| PMMA (acrylic) | Amorphous | Optical clarity, UV-stable | Display covers, lighting diffusers, signage |
| PA (nylon) | Semi-crystalline | High strength, wear-resistant, hygroscopic | Structural components, connectors, gears |
| TPE | Elastomeric | Flexible, recyclable, bonds to PP/ABS | Grips, seals, soft-touch overmoulds |
| TPU | Elastomeric | High abrasion resistance, elastic, chemical-resistant | Wear parts, flexible housings, cable jacketing |
Engineering grades — glass-filled PA, PC/ABS blends, PPS, PEEK — are available on request and confirmed at DFM stage. Material choice affects shrinkage rate, warpage tendency, achievable tolerance, and the surface finish grade the tool needs to deliver.
What are the DFM rules for injection-moulded parts?
Design for Manufacturability (DFM) is the practice of shaping a part so that it can be moulded reliably, at cost, and to tolerance. The most common issues Nordmould's DFM review catches are described below.
Wall thickness. Uniform wall thickness is the single most important DFM principle. Thick sections take longer to cool, create sink marks on the opposite surface, and introduce residual stress. Recommended wall thickness ranges from 1.0 mm for small precision parts to 3.5 mm for larger structural sections, depending on material. Transitions between thick and thin walls should be tapered, not abrupt.
Draft angles. Vertical walls parallel to the direction of mould opening need draft — a slight taper — so the part releases cleanly. A minimum of 1° per side is standard; textured surfaces need 3–5° to avoid the texture tearing on ejection.
Ribs. Ribs add stiffness without thick walls. The rib thickness should be 50–60% of the adjacent wall thickness to avoid sink marks on the show surface. Rib height should not exceed three times the rib thickness without additional support.
Bosses. Cylindrical bosses for screws or inserts need wall thickness at 50–60% of the nominal part wall, and a gusset or rib support at the base to prevent sink. Unsupported tall bosses are a common cause of warpage.
Undercuts. Features that prevent the part from ejecting in the pull direction — side holes, internal threads, clips, recesses — require side-actions or lifters in the tool, which add cost and complexity. When possible, re-orienting or splitting the feature eliminates the undercut. Nordmould's DFM review identifies every undercut and recommends the lowest-cost resolution.
Gating. The gate is the point where melt enters the cavity. Gate location affects weld-line position, surface appearance, and packing efficiency. Edge gates are common for simple parts; submarine and hot-tip gates allow gate marks to be hidden. Gate placement is finalised during DFM and tool design.
What tolerances and surface finishes can injection moulding achieve?
Injection moulding is a precision process, but achievable tolerance depends on material shrinkage, tool construction, and part geometry.
| Condition | Typical achievable tolerance |
|---|---|
| Hardened-steel tool, stable material (POM, PC) | ±0.05 mm on critical dimensions |
| Aluminium tool, stable material | ±0.10–0.15 mm |
| Semi-crystalline high-shrink material (PP, PA) | ±0.15–0.30 mm depending on wall |
| Large part, thin wall, flexible material | ±0.30 mm or wider |
Nordmould confirms achievable tolerances for your specific part in writing at the DFM review stage. GD&T callouts on your drawing are reviewed against these limits before tooling is approved.
Surface finish is determined by the tool cavity surface. Nordmould's standard options are matt, glossy, and high-gloss. Textured surfaces — leather grain, fine stipple, spark eroded — are available and are quoted alongside tooling. High-gloss optical-grade finishes require hardened-steel tooling and extended hand-polishing time, reflected in the tool price.
What are the lead times and what drives cost?
Stage-by-stage lead time:
| Stage | Aluminium (Bridge) | Hardened steel (Production) |
|---|---|---|
| DFM review | 1 business day | 1 business day |
| Tooling manufacture | 2–5 weeks | 6–11 weeks |
| Trial shots and approval | 3–5 business days | 3–5 business days |
| Series production run | 1–3 weeks (volume-dependent) | 1–3 weeks (volume-dependent) |
Cost drivers. Tooling cost is determined by part size, geometric complexity, cavity count, required surface finish, and tool steel grade. Piece price is driven by material weight, cycle time (governed by wall thickness), secondary operations, and annual volume (higher volumes justify multi-cavity tools with lower piece price). The tooling cost is a one-time spend; repeat orders run at piece price only.
The most effective way to reduce total project cost is to minimise wall thickness, eliminate unnecessary undercuts, and standardise on a material already running at the factory. All of these are reviewed during the free DFM process.
What does the Nordmould service look like in practice?
Nordmould acts as a single accountable contact between the buyer and its vetted EU manufacturing partner network. The buyer gets one engineer to talk to, one written quote, one delivery schedule, and one set of documented quality records — rather than managing a direct relationship with a factory where language, time zone, and contractual recourse are all uncertain.
The three service tiers cover the full product journey:
- Rapid — 3D-printed or soft-tool prototypes for design validation and stakeholder samples, before any hard tooling investment.
- Bridge — Aluminium tooling for low-to-mid volumes from 100 pieces. The right tier for market pilots, regulatory submissions, and SME production series.
- Production — Hardened-steel tooling for series manufacture, OEM supply, and certified production runs.
All tiers include the free DFM review. All pricing is issued in writing before a purchase order is raised. Tooling from €3,000. All operations under EU jurisdiction, serving Estonia, Finland, Sweden, Norway, Denmark, Latvia, Lithuania, and Iceland.
Nordmould is built for the buyer who has been told "your volume is too low" by a large moulder, or who has had a bad experience managing a tool on the other side of the world. The service is designed to be technically rigorous without being opaque.
Frequently asked questions
How does plastic injection moulding work? Plastic pellets are melted and injected under pressure into a closed steel or aluminium mould. The melt cools, solidifies, and the mould opens to eject the finished part. Nordmould manages the full cycle — tooling, trial shots, and series production — from a single accountable contact.
What is the difference between aluminium and hardened-steel tooling? Aluminium tools cost less and machine faster (typically 2–5 weeks), making them suitable for 100–5,000 parts. Hardened-steel tools take 6–11 weeks and cost more upfront, but last for hundreds of thousands of shots. Nordmould quotes both options so you can choose based on your volume and budget.
What is the minimum order quantity at Nordmould? Nordmould accepts orders from 100 pieces. Bridge aluminium tooling makes low volumes economically viable; the tooling cost is amortised across your run rather than written off as a prototype expense.
How much does injection mould tooling cost? Tooling at Nordmould starts from €3,000 for simple single-cavity aluminium tools. Complex multi-cavity hardened-steel tools run considerably higher. The exact figure depends on part geometry, cavity count, and required tool life — all confirmed in the free DFM review.
What materials does Nordmould offer for injection moulding? Standard materials are ABS, PP, PC, POM, PMMA, TPE, and TPU. Engineering grades such as PA (nylon), PC/ABS blends, and glass-filled variants are available on request. Material selection is discussed and confirmed as part of the free DFM review.
What draft angle is required for injection-moulded parts? A minimum of 1° of draft per side on vertical walls is standard practice; textured surfaces typically need 3–5°. Insufficient draft causes drag marks, surface damage, and sticking on ejection. Nordmould's DFM review checks every wall face before tooling begins.
What tolerances can injection moulding achieve? With hardened-steel production tooling, tolerances of ±0.05 mm are achievable on critical dimensions for stable engineering materials such as POM or PC. Semi-crystalline and flexible materials hold looser tolerances. Nordmould confirms the achievable tolerance for your specific part at DFM stage.
How long does it take to go from design to first parts? DFM review takes one business day. Aluminium tooling typically completes in 2–5 weeks; hardened-steel tooling in 6–11 weeks. Add one week for trial-shot approval and shipping. Nordmould provides a written schedule at quote stage before any commitment.
Why use a European injection moulder rather than sourcing from Asia? EU-based tooling means no import duties, no IP exposure to foreign jurisdiction, faster prototyping iterations, and direct communication. Nordmould quotes in euros, ships within the Baltic & Nordic region, and operates under EU commercial law.
What is a DFM review and why does it matter? DFM (Design for Manufacturability) is a structured check of your 3D model against the constraints of the injection-moulding process: wall thickness, draft, ribs, undercuts, gate and ejector locations. Nordmould performs this review in writing at no charge before any tooling spend is approved.