Multi-Cavity and Family Injection Moulding

Maximise each shot with multiples of the same or different parts from a single mould

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What is Family and Multi-Cavity Moulding?

Family moulding and multi-cavity moulding are techniques used to produce multiple parts from a single mould. Rather than producing a single part with each cycle, multiple parts can be produced with a single shot. Multi-cavity moulding describes a tool with the same cavity designed to produce multiples of the same parts. While family moulding describes a tool with various cavity designs such as a left and right components that mate together.

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Definitive Guide to Injection Moulding

This complete reference guide walks you through everything from quoting, design analysis, and shipment to best practices that ensure your model is optimised for moulding.

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Family and Multi-Cavity Moulding Capabilities

Our basic guidelines for multi-cavity and family injection moulding include important design considerations to help improve part mouldability, enhance cosmetic appearance, and reduce overall production time.

General Design Guidelines
Maximum Part Size
Maximum Part Volume
Maximum Number of Cavities
Maximum Surface Area
Lead Times

General Design Guidelines

Maximum of 12,000 psi (82.74 MPa) for the entire assembled family tool
Maximum clamp tonnage of 500 tons (453,592 kg)
Brand model cavities must fill within 2,000 psi (13.79 MPa) of each other

Maximum Part Size

Maximum part size is a function of mould size and part complexity. The largest size we can support with plastic injection moulding is 480mm by 751mm by 203mm.

Maximum Part Volume

Maximum is 1.499 mm. Specs below exclude tiny parts less than 1.27 mm. Between two parts, if volume is:

If part size is:	Maximum Difference in Part Volume
< 50.8 mm	20%
50.8 mm to < 127 mm	15%
127 mm to < 254 mm	10%
254 mm to 1499 mm	5%

Maximum Number of Cavities

The number of possible cavities can be 2, 4, or 8 per mould. This ultimately is dependent on part complexity and size.

Maximum Surface Area

Maximum is 175 in. (4,445mm), each cavity added together. Between two parts, if surface area is:

If part size is:	Maximum Difference in Part Surface Area
< 127 mm	20%
127 mm to < 254 mm	15%
254 mm to < 508 mm	10%
508 mm to < 1499 mm	5%

Lead Times for Multi-Cavity and Family Tools

Fundamentally, lead times are based on the complexity and size of your mold and can vary from 1 to 20 days, based on those attributes. Below is a rough idea of what you can expect in terms of turnaround for your parts.

If maximum part size is:	Design Specs	Lead time is:
69.85 mm by 63.5 mm by 25.4 mm	No side-pulls, hot-tip gates, contoured ejectors, steel core pins, family and multi-cavity moulds	1 business day
381 mm by 229 mm by 101.6 mm; depending on gate type, maximum part size could be smaller	Does not contain more than two side-pulls; no pick-out cams; family and multi-cavity moulds may include only two simple parts.	5 business days
381 mm by 229 mm by 101.6 mm; depending on gate type, maximum part size could be smaller	Does not contain more than two side-pulls; no pick-out cams; family and multi-cavity moulds may include only two simple parts	7 business days

General Design Guidelines

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Maximum Part Size

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Maximum Part Volume

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Maximum Number of Cavities

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Maximum Surface Area

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Lead Times

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Tolerances: Typically, Protolabs can maintain a machining tolerance of +/- 0.08 mm with an included resin tolerance that can be greater than but no less than +/- 0.002 mm/mm.

Injection Moulding Materials

Nylon 6/6
PBT
PC
PEEK
PEI
PP Homopolymer
PP Impact Copolymer

PP Random Copolymer
PPS
PS (GPPS)
Silicone
TPC-ET
TPE
TPU

Surface Finish Options

Finish	Description
PM-F0	non-cosmetic, finish to Protolabs' discretion
PM-F1	low-cosmetic, most toolmarks removed
PM-F2	non-cosmetic, EDM permissible
SPI-C1	600 grit stone
PM-T1	SPI-C1 + light bead blast
PM-T2	SPI-C1 + medium bead blast
SPI-B1	600 grit paper
SPI-A2	grade #2 diamond buff

How Does Multi-Cavity or Family Moulding Work?

Multi-cavity moulds enable the production of multiple versions of the same part in a single shot. You can take this process to the next logical step when you include many different parts on the same mould, creating a family mould. If you have ever built a plastic model, you’ve probably worked with parts made in a family mould. The runners between each part are left intact, forcing you to break each part off the whole.

Advantages

High Production Volume: Significantly increases the number of parts produced per hour compared to a single-cavity mould
Efficiency: Maximises machine utilisation
Lower Per-part Cost: While the mould itself is more expensive initially, the cost per individual part drops dramatically due to the increased output rate and reduced cycle time per part

Challenges

Mould Complexity and Cost: It costs more to design and build a balanced multi-cavity mould due to the added complexity and time it takes to cut the mould, but you might make up for that with a lower piece-part price
Balancing: Ensure that all cavities fill evenly and at the same rate for consistent part quality. Careful runner system design is critical

Applications for Multi-Cavity and Family Moulding

Automotive

For high-volume fasteners, connectors, sub-assembly components, interior trim sets, and small standard parts

Construction

Commodity items like fittings, fasteners, connectors, and closures

Consumer Electronics

Standardised components used across many units, housings, and internal components for specific devices

Medical Devices

Particularly for disposable items and casings for handheld diagnostic tools or kits

Packaging

Especially beverage, food, cosmetic, and pharmaceutical packaging

Appliances

Housings and components for smaller appliances

Types of Parts	Function
Electronic device housings	Front/back casings, battery doors, button sets for a specific remote control, phone, or gadget
Buttons and keys	Keyboards, control panels, remote controls
Caps and closures	Bottle caps, jar lids, flip-tops, spray nozzle components (huge volumes needed)
Connectors	Electrical connectors, terminal housings, fibre optic connectors (standardised, high quantity)
Fasteners	Plastic clips, rivets, screw anchors, cable ties (commodity, high volume)
Medical disposables and casings	Syringe barrels/plungers, pipette tips, test tubes, vial caps, parts for IV sets, sample cups. Two halves of a glucose meter casing, parts for a specific diagnostic test kit (high volume, consistency crucial)
Small ears, bushings, washers	Standardised mechanical components
Small pipe fittings	Elbows, T-connectors, caps for plumbing/irrigation