Thermoplastic injection moulding
Molten material is injected at high pressure into a steel or aluminium mould. The process reproduces precise parts at high speed, from a few grams to several kilos.
Expertise
Plastics processing and moulding subcontracting
Plastic injection moulding, thermoforming, silicone moulding, vacuum casting: compare quotes from plastics processors, tooling included.
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Plastics processing brings together the trades that turn plastic materials into parts: injection moulding, thermoforming, extrusion, blow moulding, rotational moulding, silicone and polyurethane casting. Each process suits different volumes, sizes and shapes, and most require tooling, a mould, whose cost and lead time weigh as much as the price of the part itself.
When you look for small-batch plastic injection moulding, the first question is profitability: from what quantity does an injection mould become more attractive than 3D printing or machining? The answer depends on the size of the part, the material, the complexity of the mould and the number of cavities. For a few dozen copies, vacuum casting in a silicone mould is a serious option; for a few hundred large parts, thermoforming may beat injection.
Plastics processors work at several levels: mould design, manufacture or subcontracting of the tooling, moulding, finishing (decoration, pad printing, ultrasonic welding, assembly) and inspection. This page details the processes, materials, the design points that change everything, and how to request a quote whose figures are comparable.
Common services
Overmoulding, two-shot moulding and inserts
A part can be overmoulded onto a metal insert or combine two materials (rigid and soft, two colours) to integrate seals, grips or reinforcements.
Thermoforming
A heated plastic sheet is drawn onto a mould by vacuum. Tooling costs far less than for injection: covers, trays, shells and large housings in low volumes.
Vacuum casting and silicone moulding
From a master pattern, a silicone mould lets you cast around twenty replicas in polyurethane resin imitating ABS, polypropylene or rubber.
Rotational and blow moulding
Rotational moulding makes large hollow parts (tanks, bins, containers), blow moulding makes hollow bodies (bottles, cans) in large volumes.
Extrusion
Profiles, seals, sleeves and tubes are produced continuously by pushing the material through a die; the die is the tooling specific to your cross-section.
Mould design and manufacture
A mould maker designs and machines the tooling, including cooling channels and ejection systems. They also look after maintenance, rework and storage.
Materials worked
Polypropylene (PP) and polyethylene (PE)ABS, PC and PC/ABS blendsPolyamides PA6 and PA66, with or without glass fibrePOM (acetal), PBT and PMMATPE, TPU and elastomersLiquid silicone rubber (LSR) and casting siliconePolyurethane casting resinsRecycled, flame-retardant or food-grade materials
Common applications
- Housings and covers for electronic devices and instrumentation
- Technical parts for automotive, rail and marine
- Components for medical and laboratory devices
- Technical packaging, trays and reusable crates
- Pre-series parts for market tests
- Sports goods, toys, furniture and consumer products
- Seals, bellows, plugs and soft parts
- Machine covers and casings in low volumes
What affects the price
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1
The mould
This is the first investment. The cost ranges from simple aluminium tooling to a multi-cavity steel mould, which is considerably more expensive. It is amortised over the number of parts produced.
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2
Material
The price of the resin, the weight of the part and the waste (sprue, runners) enter into the cost. Engineering or filled materials cost more than standard plastics.
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3
Cycle time and output rate
Injection and cooling time determines the number of parts per hour: a thick wall slows the cycle and increases cost.
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4
Number of cavities
A multi-cavity mould produces several parts per cycle and lowers the unit cost, but costs more to make. The choice depends on annual volume.
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5
Finishing operations
Deburring, decoration, pad printing, ultrasonic welding, insert fitting, assembly and inspection add steps to be quoted. They can be entrusted to another workshop.
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6
Quantity and launch
Press set-up, mould change and start-up impose a minimum batch. Below that, the unit price rises sharply.
Tips for a successful request
Post a request- Send a 3D model (STEP) and a drawing with the material, the colour (RAL or Pantone reference) and the surface appearance you want.
- State the quantity per run, the target annual volume and the expected product life: they determine the type of mould.
- Specify regulatory requirements: food contact, biocompatibility, fire behaviour, resistance to UV or chemicals.
- State who will own the mould, who will maintain it and where it will be stored; fix this in the quote.
- Mention the functional dimensions, bearing surfaces and cosmetic areas to guide the choice of gate locations.
- Specify ancillary operations (assembly, marking, packing) and delivery constraints.
Designing an injectable part: the rules that avoid nasty surprises
A part well designed for injection is easier to mould, cheaper and more consistent. Several principles come up in every design review.
- Uniform wall thickness: differences in thickness cause sink marks (depressions), distortion and uneven cooling. A rib is generally about half the thickness of the wall it reinforces.
- Draft angles: walls must be slightly inclined in the direction of ejection, often by at least one degree, more on textured surfaces, so that the part comes out without scratching.
- Radii and fillets: rounded corners help material flow and limit stress concentrations.
- Shrinkage: every material contracts on cooling, in the order of a percent depending on the resin. The mould maker compensates for this shrinkage in the tooling; a part with tight tolerances therefore requires trials.
- Gate location and weld lines: the feed point leaves a mark, and flow fronts that meet form lines that are best kept away from load-bearing or cosmetic areas.
These rules are discussed with the plastics processor before the mould is frozen. If you do not yet have the skills in-house, a design office can adapt your design for injection; to validate the shape before investing, first print a few copies by 3D printing.
Mould, tooling and ownership: what to clarify before ordering
An injection mould is an investment ranging from a few thousand euros for a simple aluminium part to several tens of thousands for multi-cavity steel tooling, depending on size, complexity and the target number of cycles. Manufacturing lead time is generally counted in weeks, even months for complex tooling, before validation trials and then possible rework.
An aluminium mould suits pre-series and small runs, for a few hundred to a few thousand parts: it is machined faster, costs less and has a more limited life. A hardened steel mould is intended for large runs and abrasive filled materials. For a few dozen parts of near-production quality, silicone moulding and vacuum casting avoid metal tooling altogether.
Before placing an order, clarify in the quote the ownership of the tooling (client or plastics processor), maintenance, storage, insurance, the tool-life guarantee and the possibility of transferring the mould to another moulder. Also fix the number of trial parts, the acceptance criterion for the first samples and the inspection requirements, for example a first-article dimensional report produced by a dimensional inspection specialist.
For a product that is likely to evolve, discuss the modularity of the mould: interchangeable inserts allow a detail to be changed without remaking the whole tool.
Injection, thermoforming or casting: choosing by quantity
There is no universal threshold, but orders of magnitude guide your thinking. For a few copies, 3D printing or vacuum casting is the obvious choice. For a few dozen to a few hundred large parts or parts of simple shape, thermoforming is often the most economical. As soon as volumes rise, injection takes the lead thanks to its speed and very low unit price once the tooling has been amortised.
Also take precision and appearance into account. Injection offers the best tolerances and the widest range of surface finishes (textured, polished). Thermoforming only controls one face of the part and requires trimming; resin casting gives an appearance close to production but with mechanical properties sometimes different from those of the final material.
This reasoning follows the approach of the guide from prototype to series. A tip for your Meaflow request: ask for prices for several quantity scenarios (for example 50, 500 and 5,000 parts), with the tooling quoted separately. The quotes you receive let you spot the tipping point between processes. Detail your project with your 3D files and your material constraints.
Guides to go further
From prototype to series production: the stages of industrialisation
Mock-up, functional prototype, pre-series, tooling, qualification: how to structure the move from a single unit to repeatable production, and choose the right processes for your volumes.
3D printing or CNC machining: which should you choose for your parts?
3D printing or CNC machining? Seven selection criteria, FDM, SLA, SLS, MJF and metal technologies, a comparison table and cases where combining both processes makes sense.
How to Write a Subcontracting Quote That Stands Out
Read the brief, set out a credible price and lead time, include the right details and stand out from other workshops: a step-by-step method.
Related expertise
3D printing
FDM, SLA, SLS, metal, prototypes and small runs
Prototyping
Functional prototypes, pre-series, models
Design office & CAD
Design, drawings, 3D modelling, calculations
Inspection & metrology
Dimensional inspection, NDT, reports
Frequently asked questions
A question not answered here? Visit the help centre or write to us.
How much does a plastic injection mould cost?
The cost depends on the size of the part, its complexity, the number of cavities and the mould material. Simple aluminium tooling stays in the order of a few thousand euros, while a multi-cavity steel mould can represent several tens of thousands. Only a quote based on your 3D model can give a precise figure.
From how many parts is plastic injection cost-effective?
There is no universal threshold: it depends on the size of the part, the material and the cost of the mould. As a general rule, injection becomes attractive once the volume justifies amortising the tooling, often from a few hundred or thousand parts. Below that, compare with 3D printing, vacuum casting or thermoforming.
What is the lead time to make a mould and then the parts?
A mould takes from a few weeks to several months depending on its complexity, plus trials and possible rework before the samples are approved. Production then starts according to the plastics processor’s workload. To get parts faster, vacuum casting produces copies without a metal mould. These times are indicative and vary from one project to another.
Can I have a small run of plastic parts made?
Yes, with an aluminium mould for a few hundred to a few thousand parts, or by thermoforming or vacuum casting for smaller quantities. State the quantity, the target material and the appearance you want in your request: plastics processors will propose the most suitable process, with the cost of the tooling clearly identified.
Who owns the mould?
This is negotiated and must appear in the quote. Often the client pays for the tooling and becomes its owner, while the plastics processor keeps it for production. Also specify maintenance, storage, the tool-life guarantee and the possibility of taking the mould back to hand it to another workshop.
What should I give the plastics processor to get a quote for an injected part?
A 3D model in STEP format and a drawing with the material, colour, surface appearance and functional dimensions. Add the quantity per run, the annual volume, the standards to be met (food, fire, medical) and, if possible, an existing sample. The plastics processor will check feasibility and suggest design changes.
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