Custom RTV Silicone Mold Project Workflow, Gate by Gate

If you're running a custom RTV silicone mold project, the workflow is a sequence of gates: RFQ inputs, master DFM, pattern cut or print, pour, first dump, correction, freeze, then production dumps. Skipping a gate doesn't save time. It moves the argument onto the depositing table. Distance only makes missing gates more expensive.

Name the chemistry at the first gate: platinum or tin RTV, split or glove, jacket type, dump compound. A workflow that says “silicone project” without that name is already late. LSR injection and HCR compression are a different quotation for molded *parts*, not this RTV mold — don't copy a steel Gantt onto a poured tool and then ask why there's a master.

RFQ inputs that prevent a second quote cycle

Send, as a set:

• STEP plus a 2D with tolerances, measurement state for the *dump*, and finish/texture chips called by name.
• Annual dumps, lot quantity, color count of the dump, and whether a year-two exists.
• RTV family or performance window (Shore, food files).
• Flash spec at the split, cosmetic standard, inner-core BOM if hollow.
• Tooling commercial terms: ownership of master and jacket, recast, who pays the correction pour if the CAD moves.

If any of those are “TBD,” the quote is a guess. Two shops guessing differently isn't a competitive bid. It's two different jobs.

Master first, then pour, then dump

DFM on RTV is draft, splits, keys, pour gates in the box, shrink method for the *cast* article, and whether the geometry belongs in a glove, a keyed split, or a cored mold. Do this before CNC or SLA. Compound selection in parallel is fine; freezing a random print as the master is not.

CAD-safe stock on critical logos belongs in DFM, not as a prayer at first dump. Sign a design freeze. Informal “we might round that corner” is an open ECO. Pattern shops will either wait or cut the old file.

Useful gates, with artifacts:

• DFM sign-off: marked 3D, shrink note for the dump, split/key sketch, platinum or tin.
• Design freeze / kickoff: file revision, master process (CNC vs SLA), cavity count, jacket type.
• Master buyoff: finish, barrier coat if printed, photos versus chips.
• First-dump pack: mix sheet, cavity IDs, dimensions at 23 °C after wait X, hardness of the skin, photos of keys.
• Correction / freeze: same pack, ECO closed, recast terms issued.
• SOP dumps: traveler, storage rules, spare-skin plan.

Video with cavity numbers in frame beats a polished factory clip. Time-zone lag is real; put gate dates on the PO as calendar language (“first-dump pack due,” not “ASAP”).

Common mix-up: treating first dumps as a design studio

A lot of RFQs treat the first chocolate as a styling review. In the shop that usually means you're designing in the rubber. After the master exists, every geometry, logo, texture, and shrink change is an ECO with cost and time. If the CAD wasn't ready, you bought a prototype mold and should have said so.

RTV lot changes after first dump (new grade, new supplier) are also ECOs. They can move size and certificates (FDA 21 CFR 177.2600, LFGB). Don't bury them in a packing list.

The pour-shop freeze isn't SOP. Production needs the traveler: mix recipe, dump recipe, flash limit sample, retain dump, storage rules. A mold that only the original technician can pour isn't handed off. If the factory splits pattern-making and pouring (common in the Chinese cluster), write which entity owns the first-dump sign-off. A perfect cavity delivered to a dump house that then “adds clamp” on a warped jacket is how keys die in week one.

What to ask when you're buying

• When is the file revision frozen, and who's the named signer?
• Master process and finish gate before anyone mixes A/B?
• What's in the first-dump pack, and how many working days for buyer review?
• Who pays the correction pour if the CAD moves after freeze?
• Recast and storage on the same PO as the first skin?
• Roles: buyer engineer, buyer quality, shop pattern maker, shop pour lead — who owns which gate?

Unowned gates stall. Dual-owned gates stall twice. For hollow chocolates, add the mandrel as a gated input; late cores are a silicone delay even when the master is ready.

Worked example

A 10-cavity logo soap, 70 × 50 × 25 mm, two-piece keyed platinum RTV, resin jacket, about 800 dumps in season. Workflow was DFM on the split and leather-grain keep-out, CNC master freeze, pour, first-dump pack (all cavities, mix sheet, chip photos), one ECO to deepen the grain at the split, then freeze plus a recast clause. Daily WeChat without a revision was ignored. The cheapest hour was the hour they didn't mill the old pocket.

Keep the workflow boring. Roles on the kickoff sheet, one written status per gate, file revision in the subject line. If the shop can't point to the frozen file hash or revision at master buyoff, stop cutting. Packaging, labeling, and retain storage are part of SOP handoff: bag by cavity if required, lot on the carton, a retain dump that will still exist when the second season ships. A workflow that ends at a pretty first-dump photo hasn't ended.

Risk registers belong even on candy: unstable CAD, pigment lead time for the dump, texture-house queue, certificate testing requested as if it were a free PDF. Put them on the same calendar as CNC hours.

When this gate list is the wrong Gantt

LSR/HCR part tools skip the master and start at steel — don't copy this rubber workflow onto that RFQ. A one-day tin glove off a finished sample can collapse DFM and first dump if you write the waiver. Unfrozen marketing CAD with seven "ASAP" gates isn't a production workflow; reclassify it as prototype. Geometry can override calendar: finishing an SLA master (wash, UV, barrier) can be the long pole even when CNC hours look short.

Related: development timeline, engineering before the pour, what tooling means.

Gate list to paste on the PO

• Frozen file revision and named signer
• Master process + finish buyoff before A/B mix
• First-dump pack contents and buyer review days
• Who pays the correction pour if CAD moves after freeze
• Recast and storage on the same PO as the first skin
• Roles: buyer engineer, buyer quality, pattern, pour lead

Send the STEP, dump material, and the freeze date you'll actually honor. We'll return a gate calendar (master → pour → first dump → recast terms), not an ASAP wish.

We would not recommend treating first dumps as a design studio

We would not recommend milling an unfrozen logo, overlapping two unofficial CAD revisions, or using “ASAP” as a gate date. We would not bury an RTV lot-family change in a packing list. We would not copy a steel Gantt onto a poured tool and then ask why there is a master. After the master exists, geometry changes are ECOs.

RUUIPON Mold Structure Decision: DFM names glove vs keyed split vs core *before* CNC or SLA. Soft Shore 10A–20A or wet dump? jacket is a gated input, not an accessory. Hollow chocolate? mandrel is a gated input; late cores are a silicone delay.

flowchart TD
  A[RFQ set] --> B["DFM: split, keys, dump shrink, Pt vs tin"]
  B --> C[Design freeze / named signer]
  C --> D["Master buyoff: finish, barrier, chip"]
  D --> E[Pour + first-dump pack]
  E --> F{ECO?}
  F -->|CAD still moving| G[Reclassify as prototype]
  F -->|window holds| H[Freeze + SOP traveler + recast terms]

Typical shop values

Caption these as typical shop values, not a named lot.

| Item | Typical shop value | | --- | --- | | Mix | Platinum 1:1 or 10:1 by grade; vacuum degas until the foam collapses | | Cavity Shore | 10A–20A skin with a rigid jacket | | Platinum shrink after full cure | About 0.1–0.3% — coupon the dump, CAD-safe logos until first dump | | Typical first food tray | 8–12 cavities is a common kickoff band | | RTV skin wall | Often 8–15 mm | | Loaded-tray edge sag if jacket is gated late | About 0.5–1.5 mm | | Outer-row gummy vs center if the tray sags | Edge often 3–6% heavy |

FAQ

When should the RTV grade be frozen in the workflow? Before first dump if size, color of the dump, or certificates matter. You can DFM and even cut the master CAD-safe on a planning shrink band, but first dump must use production-intent gum and bake. A substitute grade postpones the real sample. Write that postponement if you accept it.

Can DFM and master machining overlap? They can overlap in calendar time if the same revision is under change control. They can't overlap as two unofficial files. One revision in the vault. Overlap without control is how the polisher textures an old pocket.

Who chairs the first-dump review if the buyer can't fly? The pour shop presents the pack; the buyer signs against the drawing and the chips. A local inspector can walk the keys at master buyoff. Don't skip the sign-off because the video looked fine. Sign the pack or list the open items. Silence isn't approval.

How many ECOs are normal after first dump? Zero if the drawing was frozen. One or two if CAD-safe stock is being taken to size. A long ECO string means the product was still being designed in the rubber. That's a prototype program. Reclassify it and stop pretending it's production workflow.

Does SOP need a separate gate from the correction pour? Yes. The correction pour says the mold and recipe can make the dump. SOP says production shift, packaging, lot identity, and recast spares are ready. Shipping sample dumps as launch stock without a traveler is a common way to mix “sample” and “sale” in the same carton.