Sink marks are a common manufacturing flaw found in injection moulded parts. Here is how to identify them, and avoid them. How injection moulding works. Understanding why sink marks show up in parts requires a little knowledge of the process of injection moulding. Put simply, plastic is heated until it melts into a liquid. Then it … Continue reading That Sinking Feeling – Sink Marks In Injection Moulded Parts & How To Avoid Them