Multi-Cavity Injection Mold Design
Cavity count is a cost decision, not a default. We balance runners and cooling for 2, 4, 8, 16 and 32 cavity tools so every cavity fills at the same rate, holds the same tolerance and wears at the same speed, with steel tooling in 4 to 6 weeks.
Free Consultation24h
Rapid Quote
2 to 32
Tooling Cavity Count
±0.05mm
Cavity-to-Cavity Tolerance
250k shots
Tool Life
Materials
| Grade | Properties | Typical Applications |
|---|---|---|
| P20 Pre-Hardened Mould Steel | 28 to 34 HRC through section, uniform hardness, good polishability and machinability without further heat treatment, economical for medium volume | Prototype and low volume tools, cavity inserts, 4 to 8 cavity production tools |
| 1.2344 (H13) Tool Steel | Hot work grade, 48 to 52 HRC after quench and temper, high hot hardness and thermal fatigue resistance, the standard choice for hardened cavity cores | Production tools for engineering plastics, hot runner tools, high cav tools, long-life cavities |
| 1.2316 (420) Stainless Mould Steel | Pre-hardened to 30 to 36 HRC, corrosion resistant, takes a high polish, good for transparent and optical parts | Optical and clear part cavities, cosmetic tools, food contact moulds, medical device tools |
| 1.2083 (420 Modified) Stainless | Pre-hardened to 48 to 52 HRC, corrosion resistant and hard, suited to transparent parts that need both polish and wear resistance | High gloss clear housings, optical lens tools, cosmetic injection tools |
| S136 (1.2083 Pre-Hardened) Corrosion Resistant | Holds 48 to 52 HRC, excellent polish retention, resists the corrosive by-products of glass filled and halogenated resins | Glass filled PA and PBT tools, halogenated flame retardant applications, medical moulds |
| Copper and Aluminium Mould Inserts | Copper alloy for fast heat transfer in hot runner tips, aluminium for conformal cooling in high cav tools, both used as inserts rather than whole tools | Hot runner nozzles, conformal cooling channels, high cav tools needing uniform cooling |
Process Parameters
| Parameter | Standard Range |
|---|---|
| Available Cavity Counts | 1, 2, 4, 8, 16, 32, up to 64 for simple geometries |
| Tool Lead Time (Steel, 4 to 32 cavities) | 4 - 6 weeks |
| Tool Lead Time (Aluminium Soft Tooling) | 2 - 3 weeks |
| Cavity-to-Cavity Weight Variation | within 1.5% of nominal shot weight |
| Cavity-to-Cavity Dimensional Variation | ±0.05 mm, tighter on request |
| Part Weight per Shot | up to 2.5 kg, larger on request |
| Runner Type | Hot runner, valve gate, insulated hot runner, cold runner with runnerless layout |
| Mould Dimensions | up to 1200 x 900 x 800 mm and 35 tonnes |
| Clamp Force Required | up to 2500 kN |
| Tool Life Expectation | 250,000 to 500,000 shots depending on resin and fill |
Surface Finishes
VDI 3400 Texture (Grained Surface)
Chemically etched cavity steel producing a fine matte grain that transfers to the part. This is the standard cosmetic finish for visible housings, and the grain depth is specified as 0.025 mm for every degree of draft angle required, so the draft and the texture are designed together rather than separately.
Gloss Polishing
Multi-step diamond polishing of the cavity to a mirror finish for transparent and high gloss parts. The polish is applied before any texturing if both are needed, and the cavity layout review flags the areas where the polish will be lost inside a textured zone.
Spray Texturing and Bead Blasting
Bead blasting with glass or ceramic media produces a uniform satin surface that hides tool witness marks and gives a consistent grip. Textures in this family have no draft angle requirement, which makes them a practical choice for walls that would otherwise need extra draft to carry a grain.
Electro-polishing and Cavity Cleaning
Electrochemical polishing removes micro peaks from the cavity surface and reduces the risk of a polished part showing flow lines. A final cleaning cycle removes residual polish compound before the first shots, which is the usual origin of contamination marks on clear parts.
Hot Runner and Valve Gate Finishing
Hot runner manifolds, drop tips and valve gate components are finished and dimensionally verified before installation in the tool. Gate tips are matched to the resin so the melt temperature at the drop stays above the degradation limit for the full cycle time.
Ejector and Cavity Surface Treatment
Ejector pins, sleeve ejectors and lifter surfaces are polished and coated where a cosmetic part would otherwise show a witness mark. The cavity is inspected under raking light before the trial shots so that parting line flash and witness marks are found on the tool, not on the part.
Design for Manufacturing (DFM)
- Pick the cavity count from the annual volume and the number of distinct part numbers, not from the lowest piece price quote, because a 16 cavity tool for a part that runs 20,000 pieces a year sits idle and ties up capital
- Balance the runner so every cavity receives the same melt volume at the same temperature, because an unbalanced runner makes the last cavity fill cold and short
- Keep the runner length symmetric, and use a runnerless layout for round parts where the gate can enter the part directly and eliminate the runner entirely
- Verify the machine tonnage before the layout is fixed, since a 16 cavity layout on a part with a 400 gram shot needs a press the project may not have available
- Consider a family tool for near-identical parts, which shares cavities across part numbers and pays off when several parts share geometry and material
- Use valve gates on cosmetic visible surfaces, because the gate vestige is hidden inside the part instead of being sanded off
- Plan cooling for the thickest section, and add conformal cooling in high cav tools where a drilled channel cannot reach the centre of the cavity
- Leave access for the ejector and for the tool to be serviced, because a high cav tool that cannot be opened without damage will cost more in maintenance than it saved in resin
- Specify the hot runner only when the volume justifies it, since hot runner tooling costs more and the savings come from cycle time and runner scrap, not from the parts themselves
- Upload STEP, IGES or DXF files and get a free cavity count study within 24h with runner balance, cycle time estimate and annual cost comparison
Tooling & Capacity
| Type | Lead Time | Suitable For |
|---|---|---|
| Aluminium Soft Tooling | 2 - 3 weeks | Pilot runs of 25 to 500 pieces, market validation, cavity count testing before committing to steel |
| Cold Runner Steel Tool | 4 - 6 weeks | Volume programs where runner scrap is a small share of total cost, typically up to 100,000 pieces per year |
| Hot Runner Steel Tool | 5 - 7 weeks | High volume programs above 100,000 pieces per year where cycle time and runner scrap dominate the unit cost |
| Family Tool (Multi Part Number) | 5 - 7 weeks | Several near-identical part numbers sharing cavities, cutting the tooling cost per part number |
Quality Assurance
- Cavity count and cavity balance confirmed on the first shot article, with per cavity weight and dimension recorded
- First Article Inspection report on the first cavity, with the remaining cavities verified by weight and critical dimensions
- Cavity-to-cavity weight variation measured and reported against the 1.5% target
- Tool steel mill certificate and the heat treatment report archived with the tool at delivery
- Short shot and full shot trials run at production settings to confirm the fill and the venting are correct
- Mould trial report issued with the tool showing cavity pressure, cycle time and part weight
- Gate vestige and cosmetic surfaces checked on the first shot against the approved sample
- Independent SGS, Bureau Veritas or TUV inspection is available at any stage on request for the multi-cavity tool and moulding
- Tooling maintenance and polish intervals documented in the handover package
- Each multi-cavity lot ships with a dimensional report, material certificate and Certificate of Origin
Applications
- Consumer electronics housings and bezels in volume
- Automotive interior and exterior trim modules
- Packaging closures and container families
- Appliance internal frames and control housings
- LED housings and heat sink bodies
- Connector and terminal block families
- Toy and accessory part families
- Medical consumable components
- Furniture fittings and hardware modules
Why Choose FHY Precision
Cavity count decided on your annual volume and part number mix, with the piece price and the tooling cost shown together
Balanced runner and cooling design so every cavity fills at the same rate and holds the same tolerance, verified on the first shot
Cavity-to-cavity variation held within 1.5% of nominal weight and ±0.05mm on dimensions, measured and reported
Free cavity count study within 24h covering runner layout, cycle time estimate and annual cost comparison
Tool steel mill certificate and heat treatment report archived with the tool at delivery
The quality system is documented and controlled, and third-party inspection with EN 10204 3.1 material certificates is available on request
Tooling and moulding under one roof in China, quoted factory-direct
One purchase order handles analysis, tooling, trials and production parts
FAQ
1. How do I choose the right cavity count for my part?
Start from annual volume divided by the number of part numbers, then work backwards from cycle time. A single cavity tool is usually right below about 20,000 pieces a year for one part number. Beyond that, cavities start to pay for themselves, and the practical ceilings are set by shot weight against machine tonnage and by the cooling time for the thickest wall in the part. The study we provide shows piece price against cavity count with the tooling cost amortised, which is the comparison that actually decides it.
2. What is the real cost difference between 4 and 16 cavities?
Piece price falls roughly in proportion to the number of cavities for the same cycle, but not exactly, because cycle time per shot rises slightly as the runner network grows and as the press has to fill a larger shot. The tooling cost rises with cavity count, so the crossover depends on volume and on how many months you expect to run the program. For a part that runs 200,000 pieces a year the difference is substantial, and for a part that runs 15,000 pieces a year the 16 cavity tool rarely justifies itself.
3. Will all 16 cavities produce identical parts?
Within a defined band, yes. We hold cavity-to-cavity weight variation within 1.5% of nominal and dimensional variation within ±0.05mm on the first shot article, and we report the actual per cavity measurements. The identical-looking result comes from a balanced runner and a symmetric cooling layout rather than from the cavity count itself, and cavities at the end of a badly balanced runner will run cold and give visibly lighter parts.
4. When is a hot runner worth the extra cost?
When the annual volume is high enough that cycle time and runner scrap dominate the unit cost, which in practice means above roughly 100,000 pieces a year for a typical housing. A hot runner removes the runner, so the material in the runner becomes part of the part, and it removes the cooling time for the runner itself, which shortens the cycle. Against that, the hot runner hardware costs more, the tool takes longer to build, and it adds a maintenance item. We model both options in the cavity count study so the comparison is on your numbers.
5. What is a family tool and when does it make sense?
A family tool uses the same cavity for several part numbers, with the differences handled by interchangeable inserts in the tool rather than by a separate cavity each. It works when the parts are geometrically close, for example a series of the same housing in different lengths, or the same bracket with different hole patterns. The tooling cost then covers several part numbers at once instead of one tool each. It is worth evaluating when you have three or more near-identical parts, and it is not worth it when the parts differ substantially.
6. How long does a multi cavity tool take to build?
Aluminium soft tooling runs 2 to 3 weeks and is the right choice for pilot volumes and for testing a cavity count before committing to steel. Steel production tooling runs 4 to 6 weeks for a 4 to 32 cavity tool, and a hot runner tool takes 5 to 7 weeks. Trial shots and the first article inspection are included in those figures, and the clock starts from the point where the design is frozen and the fill result is approved.
7. What happens to the cavity count if my volume changes?
Plan for it in the tool. A good practice is to build the 8 cavity tool in a layout that can accept a further 8 cavities later, so the press side is ready when volume justifies the investment, and only the additional cavity inserts and runner balance need to be added. This is called a future-proof or expandable layout, it costs very little at the outset, and it avoids a second tooling investment later.
8. How is the tool steel chosen for my resin?
P20 pre-hardened steel suits prototype and medium volume tools because it needs no heat treatment and saves tooling cost. Hardened H13 at 48 to 52 HRC is the standard for production cavities. For transparent and optical parts, corrosion resistant 1.2316 or 1.2083 steel gives the polish retention those parts need. For glass filled resins, corrosion resistant steel is required because the sulphur released during the run attacks unprotected tool steel over time.
9. Do you provide the tool drawings and the maintenance plan?
Yes. The handover package includes the cavity layout, the runner and cooling layout, the tool steel and heat treatment records, the gate positions, the ejection layout, the maintenance and polish intervals, and the recommended shot settings from the trial. That package is what lets your own maintenance team look after the tool, and it is the difference between a tool that runs for 400,000 shots and one that has to be rebuilt at 150,000.
10. Can you run production on the tool after delivery?
Yes, and for most customers that is the simpler arrangement. One purchase order can cover the analysis, the tool, the trial shots and the production parts, and the per piece cost is settled once the tool is amortised. Alternatively the tool can be delivered to you for your own presses, in which case the handover package includes the trial settings so your operators start from a known good process.
11. What information do you need to quote a multi cavity tool?
A 3D model in STEP or IGES, a 2D drawing with tolerances and cosmetic callouts, the resin grade and fibre content, the annual volume, the number of distinct part numbers, and the target cost per part if you have one. If the resin is not decided, tell us the operating environment and the mechanical expectations and we will run two candidate grades. The cavity count study comes back within 24 hours on working days.
12. How do you guarantee the same part comes out of every cavity?
Three things do the work. A symmetric runner layout gives every cavity the same melt volume and temperature. Identical cavity inserts, not cavity plugs in a worn base, keep the geometry the same across the tool. And a defined cooling layout means every cavity cools at the same rate, which is what keeps the dimensions from drifting between cavities over the life of the tool. We verify with per cavity weight on the first shot and report the spread, and the target is within 1.5% of nominal.
13. What is the maximum cavity count you can build?
We build up to 32 cavities for a conventional layout, and up to 64 for simple round geometries with a runnerless arrangement. Beyond that the limit is rarely the tool, it is the press, because a high cavity shot needs enough clamping force for the projected area and enough plastic volume for a consistent shot weight. The cavity count study works out the tonnage and the shot weight against your machine list before the layout is drawn, so the number on the drawing is a number you can actually run.
14. Do you build the tool for one part number or several?
Either. A single part number tool is the straightforward case. A family tool uses interchangeable inserts in a shared cavity to cover several geometrically similar part numbers, which spreads the tooling cost across all of them. We can also build a dedicated tool for one part and later add a second cavity block, and the cavity count study shows the cost of each route so you can decide with the numbers in front of you.
15. Do you offer third-party inspection?
Yes. We arrange inspection by SGS, Bureau Veritas or TUV at any stage you specify, from incoming material verification of the tool steel to the pre-shipment dimensional and functional checks on the moulded parts. You receive a neutral report from an inspector you did not appoint, which is often what an end customer requires before accepting a first lot from a new supplier.
16. What is the minimum order quantity?
One set of parts is the minimum, because the tool is a one-time investment and the parts come off it. For aluminium soft tooling the practical minimum is 25 to 500 pieces, which is the volume that justifies soft tooling rather than machining the parts. For steel tooling the volume that makes sense starts around 20,000 pieces per year for a single part number, and the cavity count study quantifies exactly where the economics sit for your specific part.