Molds & Tooling
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PPO Thick-Wall Sink Marks
Problem Phenomenon
Sink marks appear on the back of ribs of PPO thick-walled parts; increasing holding pressure improves it but internal stress rises, and sink marks and stress are difficult to balance.
Cause Analysis
PPO shrinkage is small, but concentrated local shrinkage in thick walls still forms sink marks; holding pressure feeding and stress freezing are trade-offs; gate position and size affect the feeding channel.
Solution
①Set the gate at the thick wall and enlarge it appropriately; ②optimize holding pressure and time to the minimum value that eliminates sink marks; ③thin or hollow out the wall thickness design; ④weigh the priority of sink marks versus stress.
Key Takeaway
PPO sink mark treatment is constrained by the short holding pressure process orientation; structural design thickness reduction is the optimal solution; gate position determines feeding efficiency.; After confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence
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