Optical Profilometry Metrology Protocols for Indirect Tool Cavity Topography Verification
Calibrated silicone replicas combined with optical profilometry yield sub-micron tool cavity topography metrics without destructive sectioning.
Steep Slope Angle
Meaning
The inclination of a surface relative to the horizontal plane of the tool determines the ease with which a part can be ejected. A steep slope angle refers to vertical or near vertical walls in a mould cavity that require significant force to release. Without sufficient draft, the shrinking plastic will grip the tool steel and cause damage during the ejection stroke.
These angles are a critical consideration during the design phase to prevent production delays and part defects.
Ejection Stress
Friction between the mould and the cooling polymer increases as the material contracts around a core. When the steep slope angle is too close to zero degrees, the ejector pins must push harder to overcome this resistance. This often leads to pin push marks or visible deformation on the floor of the part.
Adding a few degrees of draft transforms the vertical contact into a clearance as soon as the part moves a fraction of a millimeter.
Surface Scuffing
Textured surfaces require even larger angles to ensure that the peaks of the grain can clear the valleys of the tool without dragging. A steep slope angle on a leather grain texture will cause the pattern to smear or appear shiny in certain areas.
Material Selection
Highly crystalline polymers like nylon or acetal shrink more than amorphous resins and are therefore more sensitive to these geometric constraints. A designer must account for the specific shrinkage rate of the grade being used when setting the minimum allowable slope. If a part must have a perfectly vertical wall, the tool might require expensive side actions or collapsible cores to allow for safe removal without damaging the finish.