Meaning
Surface roughness changes occur at contact interfaces when microscopic peaks undergo elastic or plastic compression under contact loading. Localized micro asperity deformation alters cavity surface friction during plastic part ejection and tool locking. Polymer process engineers monitor surface polishing to control release forces and prevent drag marks on molded parts.
Permanent deformation stops when contact stresses remain below the yield strength of the mold material or polymer skin layer.
Interface Contact
Pressure applied at parting lines flattens tiny machining marks on steel surfaces over millions of clamp cycles. Plastic deformation increases real contact area between core and cavity faces, which alters heat transfer rates across the interface.
Friction Development
Interlocking surface peaks resist sliding motion until high shearing forces flatten microscopic irregularities. Smooth polished cavities exhibit higher contact area, increasing van der Waals attraction and release drag. Controlling micro asperity deformation through texturing maintains controlled air release and consistent part ejection.
Ejection Force
High ejection forces occur when soft polymer skins press tightly into cavity micro-roughness during cooling. Excessive holding pressure forces molten plastic into microscopic steel crevices, escalating drag during ejection. Managing micro asperity deformation with suitable mold coatings reduces pin push-through defects and lowers required knockout force.
