𝐓𝐨𝐝𝐚𝐲'𝐬 𝐊𝐍𝐎𝐖𝐋𝐄𝐃𝐆𝐄 𝐒𝐡𝐚𝐫𝐞 : 𝐄𝐯𝐞𝐫𝐲 𝐢𝐧𝐣𝐞𝐜𝐭𝐢𝐨𝐧-𝐦𝐨𝐥𝐝𝐞𝐝 𝐩𝐚𝐫𝐭 𝐠𝐞𝐭𝐬 𝐞𝐣𝐞𝐜𝐭𝐞𝐝. 𝐌𝐨𝐬𝐭 𝐩𝐚𝐫𝐭𝐬 𝐜𝐚𝐫𝐫𝐲 𝐭𝐡𝐞 𝐞𝐯𝐢𝐝𝐞𝐧𝐜𝐞.

𝐓𝐨𝐝𝐚𝐲'𝐬 𝐊𝐍𝐎𝐖𝐋𝐄𝐃𝐆𝐄 𝐒𝐡𝐚𝐫𝐞

𝐄𝐯𝐞𝐫𝐲 𝐢𝐧𝐣𝐞𝐜𝐭𝐢𝐨𝐧-𝐦𝐨𝐥𝐝𝐞𝐝 𝐩𝐚𝐫𝐭 𝐠𝐞𝐭𝐬 𝐞𝐣𝐞𝐜𝐭𝐞𝐝.

𝐌𝐨𝐬𝐭 𝐩𝐚𝐫𝐭𝐬 𝐜𝐚𝐫𝐫𝐲 𝐭𝐡𝐞 𝐞𝐯𝐢𝐝𝐞𝐧𝐜𝐞.

Those small circular impressions on the B-side of an automotive trim part?

They are ejector pin marks — created when the ejector system pushes the part out of the mold.

On the B-side, they're usually acceptable.

On the A-surface, they're an immediate cosmetic rejection.

Why do they happen?

When the mold opens, ejector pins push the part off the core.

If there are too few pins, each carries more force.

If the pins are too small, the pressure increases.

If the part is ejected too early, the hot plastic deforms.

Poor pin placement can also leave visible impressions or cause distortion.

Every ejector pin mark tells the story of the force, timing, and pin location.

Four common causes:

① Too few ejector pins

② Pins too small in diameter

③ Premature ejection

④ Incorrect pin placement

𝐇𝐨𝐰 𝐭𝐨 𝐩𝐫𝐞𝐯𝐞𝐧𝐭 𝐭𝐡𝐞𝐦:

✓ 𝐈𝐧𝐜𝐫𝐞𝐚𝐬𝐞 𝐭𝐡𝐞 𝐧𝐮𝐦𝐛𝐞𝐫 𝐨𝐟 𝐞𝐣𝐞𝐜𝐭𝐨𝐫 𝐩𝐢𝐧𝐬

✓ 𝐈𝐧𝐜𝐫𝐞𝐚𝐬𝐞 𝐩𝐢𝐧 𝐝𝐢𝐚𝐦𝐞𝐭𝐞𝐫

✓ 𝐄𝐱𝐭𝐞𝐧𝐝 𝐜𝐨𝐨𝐥𝐢𝐧𝐠 𝐭𝐢𝐦𝐞 𝐛𝐞𝐟𝐨𝐫𝐞 𝐞𝐣𝐞𝐜𝐭𝐢𝐨𝐧

✓ 𝐏𝐨𝐬𝐢𝐭𝐢𝐨𝐧 𝐩𝐢𝐧𝐬 𝐨𝐯𝐞𝐫 𝐫𝐢𝐛𝐬 𝐚𝐧𝐝 𝐬𝐮𝐩𝐩𝐨𝐫𝐭 𝐚𝐫𝐞𝐚𝐬

✓ 𝐔𝐬𝐞 𝐬𝐥𝐞𝐞𝐯𝐞 𝐨𝐫 𝐛𝐥𝐚𝐝𝐞 𝐞𝐣𝐞𝐜𝐭𝐨𝐫𝐬 𝐰𝐡𝐞𝐫𝐞 𝐫𝐞𝐪𝐮𝐢𝐫𝐞𝐝

Ejector pin marks are not just a tooling issue.

They are the result of design, tooling, and process decisions.

Distribute the force.

Place the pins correctly.

Eject at the right time.

💬 Have you ever seen ejector pin marks read through to the A-surface on an automotive trim part?

What change solved the problem?

Share your experience below.

source : IM Technologies

#InjectionMolding #EjectorPinMarks #PlasticDesign #DFM #MoldDesign #AutomotiveEngineering