Tolerances tighter than they need to be
Very tight tolerances on features that don't need them add cost with no benefit. We suggest relaxing them where the assembly will accept it.
DFM guide for OEM designers
Designing a part for volume from the start.
Most silicone parts are designed by someone who's designed one before. If this is your first, or if the last one taught you nothing you'd want to repeat, here's what to think about while the design is still on the screen.
The premise
Silicone is forgiving in the tool and unforgiving at scale.
A flexible silicone tool can produce almost any shape you can draw. That's why prototype silicone parts often look great — the tool bent, stretched, or was manipulated by hand to release the part.
At volume, none of that is available. A production tool releases the part with a defined ejection mechanism, on cycle time, without human intervention. Features that were fine in prototype start to cost money in labour, reject rate, or tool wear.
Designing a silicone part with volume in mind from the start doesn't restrict what you can make — it means the same design works at prototype and at production without redesign. That's what this guide is about.
Geometry basics
The four features that determine whether a part releases cleanly.
Silicone releases best from tools designed with release in mind. Small changes here save more cost than any other DFM detail.
Include draft on any vertical wall
Even a couple of degrees of taper on every wall parallel to the pull direction makes release dramatically cleaner. Straight walls drag on every cycle.
Design undercuts out where you can
An undercut requires the tool to split at that feature. Every additional split line adds tool cost and adds a witness line on the part.
Radius all internal corners
Sharp internal corners concentrate stress in the silicone and trap material during release. A small radius costs nothing and prevents tears.
Consider ejector locations early
Where the ejector pins land will leave marks. Route the ejectors to a face you don't care about, ideally before the tool is drawn.
Cross-section
How wall thickness drives cycle time and cost.
Keep walls as even as possible
Even walls cure uniformly. Thick sections cure last and control cycle time — a small thick section can double the cycle for the whole part.
Avoid thin-to-thick transitions
Where thin meets thick, the material will flash across the thin section during cure. Design the transition to be gradual or move the parting line.
Ribs are better than solid mass
Where a stiff feature is needed, ribs and gussets stiffen the part without adding curing time or material cost.
Where flash lands
The four tool-side details that show on your part.
These decisions are made once, in the tool design, and travel with every part for the tool's lifetime. Worth getting right.
Parting line off any face that matters
Cosmetic, sealing, skin-contact — none of these should have the parting line running across them. Move the parting line to a face you don't care about.
Gate location on a hidden face
The gate leaves a mark. Locate it on the underside of the part, or on a feature that will be hidden in assembly.
Vents where air will get trapped
Air pockets prevent complete fill. Design vents into the tool at any high point of the cavity. Vents leave small witnesses — put them where you can accept them.
Flash groove around the cavity
For compression especially, cut a defined flash groove so surplus material lands somewhere predictable rather than feathering across the part.
Our process
Four things we flag on almost every new design.
Features that will trap air
Cavities with a single high point that isn't vented will fill inconsistently. Easier to fix in CAD than to work around in the tool.
Wall thickness variation
Anywhere thick meets thin sharply, we flag it. Small design changes prevent flash and reduce cycle time.
Assembly-side detail that's actually optional
Features designed for one assembly method that add moulding cost. We check what the assembly team actually needs before locking the tool in.
Keep reading
More guides from the workshop.
Post-processing silicone — what happens after the press opens
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Read the guideColour matching and batch consistency
For anything a customer will see, colour is one of the two things they judge (feel is the other). Getting the colour right is…
Read the guideMoving from prototype tooling to production
Your product is real. You've made prototypes, maybe pilot runs. The design is stable and the volume forecast is starting to be…
Read the guideDesigned and developed in the UK. UK moulding capability, with some higher-volume production placed with trusted partners where that's the right commercial answer.
At a glance
The idea in a picture.
Which route suits your quantity
Swipe to see the whole diagram
Get in touch
Tell us the part, the volume, and the timeline.
Rough annual volume, target unit price, and any deadlines. That's enough to work out whether compression, LSR injection or something else is the right tool.
Real people, a real workshop
You deal with the people who make it.
No call centre and no middlemen. When you contact TCI Products, you speak to the team who design, build and check your mould.
- A real Warwickshire workshopUnit 15, Waterloo Park, Bidford-on-Avon, Alcester B50 4JG.
- Real people on the phoneCall the team on 01789 224228, Monday to Friday.
- The same team on every jobDesign, production and aftercare come from the people you see here.
- Part of TCI GroupFive specialist brands, one engineering team. Visit TCI Group.
Thomas LaneManaging Director
George PrestonDesign & Project Manager
Kelly BallingerHead of Partnerships
Jim AndertonProduction Manager
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