How Shops Make Custom RTV Silicone Molds | RUUIPON

A custom RTV silicone mold is made in a fixed shop order: freeze the master, build the mold box, weigh platinum (or named tin) A/B, vacuum-degas, pour, cure, pull the master, fit the jacket, then dump a witness. That is the sequence on our Bao'an bench since 2018. Buyers searching "how are custom silicone molds made" often get a steel-tool video; this page is the liquid-rubber path you actually buy from ruuipon.com. It is not a CNC cycle on steel, and it is not LSR through a cold-runner. If you need a molded silicone *part*, stop here and use wydsilicone.com.

CAD lock starts the 3–7 business day prototype clock. Production is MOQ 20 pieces per design after you approve the witness. Simple 3D is USD $50 when we still have to model. Mix is 1:1 or 10:1 by weight. Platinum shrink we compensate on the master is typically 0.1–0.3%. If any of those lines is still open, you are not in mold-making yet — you are in a drawing review.

Does not apply when the "mold" is a compression tool for HCR parts, when you are asking how Amazon reprints a stock bear, or when the master is still a moving logo. Unfrozen art is design, not mold-making. Design desk: mold design service.

Freeze the master before anyone orders a drum

The master is the cavity. CNC aluminum or resin, a fully washed and UV-post-cured SLA with a barrier coat, a machined block, or a physical sample you own. Layer lines print. Sealer blush prints. Undercured SLA inhibits platinum — sticky face, cured jacket, scrap for food.

We write shrink for *this* grade on the 2D, including whether the CAD is already compensated. We note parting, pour direction, and peel direction. Shore is a grade, not a color chip. Food cavities are platinum; we would not spec tin for those. Craft tin is a named exception, not a silent swap.

ISO 3302-1 class (M2 is a common default) belongs on the drawing if you are holding rubber tolerances. It is a class, not a slogan that the pour is "precision."

If the file is a photo, we do not mill from vibes. $50 CAD when that scope applies, you sign millimetres, then the master exists. Printed-master detail: 3D-printed masters.

Box, keys, and the structure call

The flask sets pour height and wall of the rubber. A warped plywood box becomes a tapered block. Release on the master and the box comes before mix.

RUUIPON Mold Structure Decision sits here, not after the first slump:

• Flat back → open-back skin.
• Deep undercuts that still peel → glove.
• If they will not peel → two-part, plug, or core, with registration keys (pips, bushes, CNC bosses) so the halves find themselves every cycle.
• Large wet casting → mother mold / jacket in the same quote.

A shop that says "the flash line will show me" watches the halves drift after a few hot dumps. Inner cores for hollow chocolate or ice spheres need a pull path before we mix. If the core cannot extract, you designed a cut mold.

Weigh, mix, vacuum, pour

A/B by weight at 1:1 or 10:1 per the grade. Mix until the streak is gone. Vacuum degas until the foam collapses. Pour a thin stream, not a dumped cup. Detail coat first on fine logos. Cure on the grade's schedule. Pull the master. Inspect the cavity under raking light.

Skipping the chamber on a logo well is a compromise against trapped air. We would not skip vacuum on a food serif because a hobby video did. Tiny shallow ice trays can sometimes live with a careful stream and vibration; say so, do not make it the default.

Jacket and the witness dump

Soft 10A–20A skins balloon. Loaded food trays sag at the outer row (0.5–1.5 mm is a typical unsupported edge; gummies can drift 3–6% there). The jacket — plaster, resin, fiberglass, or a printed shell — is built with the box, not after the first warped dump.

Then we cast a witness in *your* compound when you send it (pectin, chocolate, PU). An empty cavity photo is not first article. Keep the unsanded master. Recast the skin if letters tear. Sanding the master "to clean it up" is how you lose the brand you approved. Tooling charge still is not unrestricted ownership; write who archives the master on the PO.

What the buyer should watch on mix day (without standing in Bao'an)

You do not need a factory tour for this sequence to be real, but you do need a few proofs you can ask for in email. Weigh tickets or a photo of the A/B cups on a scale. A vacuum chamber with the foam collapsed, not a kitchen mixer "to save time." A raking-light photo of the cavity after pull, especially the logo wells. A jacket that existed before the first wet dump, not a cardboard nest invented after the tray banana-peeled. If the dump is food, the platinum drum lot should match the CoC you were promised — 21 CFR 177.2600 is extraction of the finished article, not a gate sign that says FDA-approved factory.

Food vs craft does not change the order of operations. It changes the chemistry we will put in the cup and the wash/post-cure you run before first contact. We would not spec tin for a food cavity and then "clean it up" with a boil. Craft PU can still need vacuum; bubbles in a resin figurine are on us if we skipped the chamber on a detailed face.

Typical shop values

Caption: typical shop values.

Common mix-up: treating the 3D print as the finished mold

RFQs arrive with an SLA figurine and a request to "start pouring candy tomorrow." In the shop that print is a candidate master: wash, full UV, barrier coat, inhibition check, then box. Production still wants that master finished. Using the print *as* the cavity copies layer lines into every dump.

Worked example (anonymized)

Two-part resin character, 90 mm, undercut arms. We sealed an SLA master, built a keyed box, mixed platinum 10A–20A at 10:1, vacuumed, detail-coated the face, poured, fitted a printed jacket, and dumped a PU witness. CAD lock included the shut the STL lacked ($50). Prototype in the 3–7 business day window after that lock. A later colorway was a recast against the same unsanded master. MOQ 20 of the production skin. Nobody milled steel. Nobody called this LSR.

We would not recommend

We would not recommend pouring on a raw SLA and calling the sticky face "needs more cure."

We would not recommend a one-piece glove on a closed letter that will not peel.

We would not recommend quoting this sequence as a way we make HCR or LSR *parts*.

We would not recommend skipping the witness dump because the cavity "looks sharp in photos."

flowchart LR
  M[Master frozen] --> X[Box + keys + structure]
  X --> Mix[Weigh A/B 1:1 or 10:1]
  Mix --> V[Vacuum degas]
  V --> P[Pour / detail coat]
  P --> C[Cure, pull master]
  C --> J[Jacket]
  J --> W[Witness dump]

What to ask when you're buying

• Master source: CNC, sealed SLA, or physical sample — and who keeps it?
• Vacuum on the mixed A/B, yes or a named skip?
• Open-back, keyed split, or cored, and what is the jacket?
• Platinum or tin, and will the witness be *my* dump?
• If the witness misses, is the next step refinish, recast, or a new CAD?

RFQ copy-pack (how it's made)

To [email protected]:

• STEP or sample; master preference
• Dump material
• Structure: you name it or we run the Decision
• Food docs if the cavity is food
• Prototype after CAD lock, then MOQ 20 / design

Matched next step: send the master source and the dump so we can sequence the pour, not a request for a generic "how it's made" video. Phone +86 135 3006 2969. contact. Sample clock: prototype validation.

FAQ

Is a custom silicone mold milled from a block of rubber? No. We pour liquid RTV around a master. Milling is for the master or for steel part-tools, which we do not quote here.

Do you vacuum every pour? On food and fine resin, yes. A named skip is a compromise we will write down. Silent skips show up as pinholes in the serif.

How long after mix until I can dump? Cure follows the grade. The buyer clock we publish is 3–7 business days after CAD lock for the prototype tool, including the sequence above — not the pot life of the cup.

Can you skip the jacket to save money? On a tiny shallow open-back, sometimes. On a loaded gummy sheet or a 10A glove, the jacket is the tool. We would not delete it after the first slump.

Who owns the master after I pay? A tooling charge is not unrestricted ownership. Put archive and recast rights on the PO. We keep the unsanded master so reorder is a recast.