Injection Molding
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ABS injection sink mark
Problem Phenomenon
Surface dents on the back of rib positions, boss positions, or thick-wall areas, especially obvious on high-gloss surfaces, affecting appearance and assembly.
Cause Analysis
The intersection of ribs/bosses and the wall is locally thick, cools slowly, and shrinks greatly; when holding compensation is insufficient, the surface is pulled concave; insufficient holding pressure/time or premature gate freeze-off is the direct cause, and an excessive rib thickness ratio is the structural inducement.
Solution
①Control the rib thickness to 40%~60% of the wall thickness; ②increase the holding pressure and extend holding until gate freeze-off; ③reduce material at thick-wall areas (core pulling); ④strengthen the cooling of this area; ⑤arrange the gate near the thick wall.
Key Takeaway
For ABS sink marks, 'first manage the structural wall thickness, then manage the holding compensation': rib thickness and thick walls are the root, holding and freeze-off are the technique; only piling holding pressure on the machine without touching the structure easily introduces internal stress and flash.
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