What are the SPI mould classes 101 to 105?

SPI classes grade injection moulds by production life: Class 101 exceeds one million cycles in hardened steel, Class 102 up to one million, Class 103 up to 500,000 in pre-hardened steel, Class 104 up to 100,000 in soft steel or aluminium, and Class 105 under 500 cycles for prototypes.

How long does an injection mould last?

Prototype aluminium tools manage hundreds to a few thousand shots; bridge aluminium tools 5,000-25,000+; pre-hardened P20 steel tools several hundred thousand; hardened H13/S136 tools one million or more with maintenance. Resin abrasiveness matters — glass-filled grades can halve tool life.

Aluminium or steel mould — which should I choose?

Aluminium for prototypes and low volumes: roughly 30-50% cheaper and faster to machine, good thermal conductivity, limited life. Steel for production: P20/718 pre-hardened for mid volumes, hardened H13/S136 for high volumes, abrasive resins and mirror polishes. Nordmould's Bridge tier uses aluminium; Production tier uses steel.

What is the difference between single, multi-cavity and family moulds?

A single-cavity mould makes one part per cycle; a multi-cavity mould makes several identical parts per cycle, cutting unit cost; a family mould makes different parts of one assembly in the same shot. Family tools save tooling cost but need balanced filling and matched part volumes.

Who owns the injection mould — buyer or moulder?

Industry convention is that the buyer who paid for the tool owns it, with the moulder storing and maintaining it. Ownership, storage fees, maintenance responsibility and transfer rights should be written into the agreement. Nordmould registers customer tooling to the customer's order with documented transfer terms.

What maintenance does an injection mould need?

Routine care includes cleaning and vent inspection per run, lubrication of moving parts, periodic parting-line checks, and scheduled refurbishment of wear items like ejector pins and O-rings. Glass-filled resins demand more frequent attention. Skipped maintenance shows up as flash, burns and drifting dimensions.

Injection Mould Tool Types: SPI Classes 101-105, Steels, Cavities & Lifespan

Updated: 2026-10-23

The mould is the largest single investment in most injection-moulding projects, and its specification — class, steel, cavities, mechanisms — decides both the upfront price and the per-part economics for years. This guide explains the standard tool classes, the steels behind them, cavity strategy, and the ownership and maintenance questions buyers should settle in writing.

What are the SPI mould classes?

The SPI (now PLASTICS) classification grades tools by intended production life. It is the common language of tooling quotes.

Class	Life (cycles)	Construction	Typical use
101	1,000,000+	Hardened steel (≥48 HRC), hardened wear items, full cooling	High-volume production, medical, automotive
102	Up to ~1,000,000	High-hardness steel, quality wear items	High volume, less abrasive duty
103	Up to ~500,000	Pre-hardened steel (P20/718, ~30-36 HRC)	Medium volume — the production workhorse
104	Up to ~100,000	Soft steel or aluminium	Low volume, bridge production
105	Under ~500	Aluminium or soft materials	Prototypes, design validation

Nordmould's three tiers map onto this scale: Rapid ≈ Class 105, Bridge ≈ Class 104 (aluminium), Production ≈ Class 101-103 (steel, sized to your volume).

Which tool steel for which job?

Aluminium (typically 7075/QC-10) machines 30-50% faster and cheaper than steel and conducts heat superbly, giving fast cycles — but it wears, dents and cannot hold a mirror polish long. It is the right answer for prototypes and low volumes, and wrong for abrasive glass-filled production.

P20/718 pre-hardened steel (30-36 HRC) is the standard production steel: tough, polishable, weldable, good for hundreds of thousands of cycles. H13 (through-hardened ~48-52 HRC) handles abrasive resins and long runs. S136/Stavax stainless (48-52 HRC) is the choice for corrosive resins like PVC, medical tools and true SPI A1 mirror polishes. Stainless costs more and machines slower — specify it where corrosion or optical polish demands it.

How many cavities should a mould have?

Cavitation divides the tooling cost across volume and multiplies output per cycle. The trade-offs:

Layout	Tooling cost	Unit cost	When it wins
Single cavity	Lowest	Highest	Low volume, large parts, uncertain demand
2-8 cavities	+30-80%	Drops steeply	Proven demand, small-medium parts
16+ cavities	High	Lowest	Commodity volumes, small parts
Family (different parts per shot)	One tool instead of several	Good for matched sets	Assemblies with equal volumes per part

Two cautions. Multi-cavity tools demand fill balance — cavity-to-cavity variation is a quality risk that needs good runner design or valve gating. Family tools lock the parts' volumes together; if one part of the assembly sells twice as fast, you mould scrap of the other. The break-even arithmetic sits in the cost-per-part guide.

Before choosing tool construction and cavity count, compare tooling investment and break-even. Keep one-off charges, repeat-batch costs and realistic demand separate when assessing the alternatives.

What mechanisms drive tool complexity and price?

A straight-pull two-plate tool is the cheapest that will make a given part. Every departure adds money: side actions (sliders) and lifters for undercuts — commonly from €1,000-5,000+ per direction; three-plate construction for pin gating; hot-runner systems from a few thousand euros upward; unscrewing mechanisms for threads; collapsible cores for internal undercuts.

This is why DFM pays: eliminating one undercut in CAD removes a mechanism from the quote. The 14 checks in the DFM rules guide are ordered roughly by how much tooling money each one saves.

What should the ownership and maintenance agreement say?

Convention: the buyer who pays for the tool owns it. Put four clauses in writing: ownership and marking (tool tagged to the customer), storage terms and any annual fee, maintenance responsibility and what happens to wear parts, and transfer rights — the ability to move the tool to another moulder on notice. Customer-owned tooling is portable by design at Nordmould: it is registered to your order and released on agreed notice.

Maintenance is not optional overhead. A production tool needs cleaning and vent checks per run, lubrication of slides and ejectors, and scheduled refurbishment. Abrasive glass-filled resins accelerate wear on gates, parting lines and ejector pins — budget for it, and expect flash and drifting dimensions as the early warning that a tool needs attention.