𝐓𝐨𝐝𝐚𝐲'𝐬 𝐊𝐍𝐎𝐖𝐋𝐄𝐃𝐆𝐄 𝐒𝐡𝐚𝐫𝐞 : 𝐒𝐢𝐧𝐤 𝐌𝐚𝐫𝐤𝐬 — 𝐓𝐡𝐞 𝐌𝐨𝐬𝐭 𝐂𝐨𝐦𝐦𝐨𝐧 𝐂𝐨𝐦𝐩𝐥𝐚𝐢𝐧𝐭 𝐖𝐞 𝐇𝐞𝐚𝐫 (𝐚𝐧𝐝 𝐖𝐡𝐲 𝐈𝐭'𝐬 𝐑𝐚𝐫𝐞𝐥𝐲 𝐭𝐡𝐞 𝐌𝐚𝐭𝐞𝐫𝐢𝐚𝐥'𝐬 𝐅𝐚𝐮𝐥𝐭)

 𝐓𝐨𝐝𝐚𝐲'𝐬 𝐊𝐍𝐎𝐖𝐋𝐄𝐃𝐆𝐄 𝐒𝐡𝐚𝐫𝐞

 🔹 𝐒𝐢𝐧𝐤 𝐌𝐚𝐫𝐤𝐬 — 𝐓𝐡𝐞 𝐌𝐨𝐬𝐭 𝐂𝐨𝐦𝐦𝐨𝐧 𝐂𝐨𝐦𝐩𝐥𝐚𝐢𝐧𝐭 𝐖𝐞 𝐇𝐞𝐚𝐫 (𝐚𝐧𝐝 𝐖𝐡𝐲 𝐈𝐭'𝐬 𝐑𝐚𝐫𝐞𝐥𝐲 𝐭𝐡𝐞 𝐌𝐚𝐭𝐞𝐫𝐢𝐚𝐥'𝐬 𝐅𝐚𝐮𝐥𝐭)

"Can you just switch resin?" is usually the first question we get when a customer spots a dimple on their part. Most of the time, the resin isn't the problem — the wall thickness is.

Here's what's actually happening:

🧊 Uneven cooling — thick sections (bosses, ribs, thick walls) stay hot and keep shrinking long after the surrounding thin walls have solidified. That continued shrinkage pulls the surface inward — that's your sink mark.

📏 The rule of thumb: ribs and bosses should stay at 50–60% of the nominal wall thickness. Go thicker "for strength," and you're almost guaranteed a visible sink on the opposite face.

🌡️ It's not just geometry — packing pressure, hold time, and gate location all affect how much material is fed into that thick section before it freezes off. Same part, same mold, different process settings = different sink depth.

🔍 Why it shows up late — sink marks often pass a first-article inspection (cooled slowly, under control) but appear in full production once cycle times tighten up. That's why we test at production-intent cycle times, not just sample conditions.

✅ SCSplastic , sink risk gets flagged in DFM review — before tooling — by checking rib/boss ratios and simulating packing behavior across the part. Cheaper to redesign a rib in CAD than to chase it on the molding floor.

📐 A 0.1mm sink might be cosmetic. On a sealing or mating surface, it's a reject.

source : #SCSplastic

#InjectionMolding #SinkMarks #DFM #WallThickness #PlasticDesigne