Glass Filled Polymer Injection Tool Wear Mechanisms
Glass filled polymer injection tool wear stems from fiber micro-ploughing and matrix erosion, requiring hard powder metallurgy steels or duplex PVD coatings.
Subgate Wear
Meaning
Localized erosion of the secondary injection port below the parting line facilitates the production of parts without visible gate marks on primary surfaces. This subgate wear typically occurs in molds producing small, aesthetically sensitive components like buttons or light pipes for smart home devices. As the metal wears away, the gate becomes larger, which can lead to difficulties in the automatic degating of the part.
It often appears as a slight protrusion or tail on the hidden surface of the component.
Erosion Mechanism
High injection pressures force abrasive resin through a narrow, curved channel at great speed. This subgate wear is accelerated by the sharp transition angles required to route the plastic from the runner to the underside of the part. Over time, the edge of the subgate loses its crispness and begins to round over.
Process Impact
Variations in the gate geometry alter the pressure profile during the filling of the cavity. If subgate wear is significant, it can cause the part to stick in the mold or break during the ejection process. This leads to increased scrap rates and the potential for plastic debris to jam the tool.
Corrective Measure
Use of replaceable subgate inserts allows for the restoration of the gate geometry without extensive machining of the entire cavity. Hardened steels or specialized coatings can prolong the life of these inserts. Regular inspection of the gate vestige on the finished part provides an early warning of excessive wear.