12/16/2023
When designing any part, a common challenge is striking a balance between aesthetic quality and ease of manufacturing. When parts feature design aspects that cannot easily be ejected from basic injection molds (known as "undercuts"), the molds get more complex and costly.
On slide 1, circled in orange, we see what are known as "witness lines". These visible features occur in injection molded parts where plastic flows over a joint of two or more steel mold parts. The blue circle outlines where plastic is injected into the mold.
In this exact situation, these witness lines are likely formed from moving mold parts commonly referred to as "lifters". The lifters are required to allow this part to be ejected from its mold. With the current part geometry (seen on slide 2), the retainer arm tabs of this part would be stuck in the mold without a special ejection mechanism to allow the part to be freed.
To remove this undercut, the aesthetic quality of the part face would be impacted by creating a hole for a "pass through core". This pass through core would allow the part to be ejected easier, at the expense of a perfectly flat part face.