Case Study: Resin Coaster Mold That Tore on Demold 3

An Etsy resin coaster brand hit us on WhatsApp with a photo of a torn silicone lip and three good coasters. Pour 1 looked fine. Pour 2 needed a wiggle. Pour 3 ripped the ear island that held a 1.2 mm undercut on the brand bevel. They had ordered a “flex” tray from a catalog seller and assumed soft Shore would forgive geometry. It did not.

This anonymized resin silicone mold case study is the remake path we ran at RUUIPON (Shenzhen since 2018): measure the tear, cut the undercut, set Shore for epoxy demold, sample in 3–7 days, then MOQ 50. It is not the chocolate logo DFM story (logo chocolate case study) and not the general tear checklist (tear-strength demold failures).

Ears Tore on Demold 3 — Not on Pour Chemistry

They blamed “hot epoxy.” Shop photos showed a clean platinum-looking tray with a knife-edge undercut under the bevel. Soft Shore without draft turns every demold into a peel that loads a thin silicone bridge. Tear strength guides help, but the first fix is geometry.

Weekend staffing made it worse. A new pourer copied a YouTube pry. The torn ear then printed flash lines on every coaster. Returns spiked on “rough edge” reviews. Cash was already in ads.

We build custom silicone resin molds for brand and maker runs — quote ~24h on complete files, prototype after CAD lock usually 3–7 days, production soft tooling at MOQ 50.

What Failed on the First Soft Tool

• Bevel undercut ~1.2 mm deep with almost no draft on the return wall.
• Ear wall thickness under the undercut ~1.5 mm silicone — too thin for repeated flex.
• Shore feel ~A 20–22 (too soft for a sharp undercut; stretched then ripped).
• Cavity count 4; target 90 mm coaster; scrap after day 2 ~22% by their count (tear + flash reprints).

Shore bands for resin: see Shore hardness guide. Undercut rules: resin mold design guide.

DFM Fix: Draft, Fillet, Shore

1. Cut undercut to ~0.4 mm visual bevel (kept brand look in photos; lost the “trap” that tore the ear).
2. Added 1.5–2° draft on the return wall; filleted inside corners.
3. Raised Shore target to A 28 (inside a typical 25–35 resin flex band for shallow coasters).
4. Ear wall ~3.0 mm; kept 4 cavities — output was fine, scrap was not.
5. Sample pour with their epoxy and pigment before MOQ 50.

We refused to “solve” it with more release spray as the main fix. Spray hides bad geometry until the next hire. We also refused a same-week jump to 200 trays before sample — multiplying a tearing tool only multiplies scrap.

Before / After Numbers

Spec	Failed tray	Remake
Undercut / bevel trap	~1.2 mm, no draft	~0.4 mm + 1.5–2° draft
Shore A	~20–22 feel	28 target
Ear wall	~1.5 mm	~3.0 mm
Scrap (tear/flash)	~22%	<4% after re-teach
Demold	Pry + stretch	Flex peel, no tool
Path	Catalog “flex” buy	Sample 5 days, then MOQ 50

Operators needed one note: stop prying the bevel. Soft tooling wins when you peel, not when you treat it like polycarbonate.

Sample Gate Before MOQ 50

Prototype checks we wrote into the approval email:

• No cavity needs a tool on demold.
• No ear tear after 20 pulls on the sample tray.
• Flash under agreed limit; bevel still readable in product photos.
• Shore feel in 26–30 on our check.

Written approval covered undercut, Shore, and scrap target. Production followed in the normal 2–4 week band after sign-off. Process: after you approve the sample.

Copy This Resin Brief

Send STEP/STL or measured photos, epoxy brand + peak exotherm note, target coaster OD/thickness, undercut intent in mm, Shore “recommend for demold,” and quantity (sample then MOQ 50). Tick fields on the RFQ checklist tool. Quote form: custom silicone mold quote.

Factory and founder proof: About RUUIPON. Docs path when food-contact is not the issue but vendor questionnaires still ask: certifications.

FAQ

Will a softer Shore always save undercuts?
No. Too soft on a sharp undercut stretches then tears. Soften only inside a band that still returns — usually with draft and fillets.

Can I keep a deep undercut for photos and a shallow tray for production?
Two tools for one SKU doubles training error. Prefer one demold-safe geometry and shoot the cast.

What is MOQ at RUUIPON?
MOQ 50 mold pieces per design after sample approval. Prototype usually 3–7 days after CAD lock.

How fast is the quote?
Complete RFQs usually within about 24 hours — email [email protected] or WhatsApp +86 135 3006 2969.