Surface Kurtosis Sku

Height Distribution

The shape of the height distribution curve provides a detailed look at the nature of the surface texture beyond simple average roughness. When a tool has a high surface kurtosis sku, it means that the surface is dominated by extreme height values that may act as points of high stress. These sharp features can pierce the polymer skin or cause localized areas of high friction during ejection.

Conversely, a surface with a low Sku value is more uniform and may provide better support for the part. This parameter is particularly sensitive to the presence of outliers such as deep scratches or high burrs. By analyzing the Sku, a moulder can understand whether the tool has been properly finished or if there are remaining machining marks.

This information helps in selecting the appropriate polishing or texturing techniques to achieve the desired functional properties.

Process Variation

Tracking the changes in the distribution shape over the life of a tool provides insights into the wear mechanisms at play. As the sharp peaks are worn down by the abrasive action of the resin, the surface kurtosis sku will typically decrease towards a value of three or less. This shift indicates that the surface is becoming more rounded and uniform.

However, if the tool is subject to pitting or chemical corrosion, the Sku may increase as new deep valleys are formed. Regular measurement of this parameter helps to identify these changes before they significantly affect the quality of the moulded parts. It provides a more nuanced view of tool degradation than height measurements alone.

This data is used to optimize the maintenance schedule and ensure that the tool remains within its functional limits.

Release Performance

The interaction between the polymer and the tool surface is heavily influenced by the distribution of the peaks. A tool with a low surface kurtosis sku often provides more consistent release properties because the contact area is more evenly distributed. This can lead to lower ejection forces and a reduced risk of part deformation.

In applications where a specific tactile feel or optical property is required, controlling the Sku is essential for achieving a repeatable result. Metrology systems provide the data needed to verify that the tool manufacturer has achieved the correct surface characteristics. Comparing the Sku across different areas of the mould ensures that the part will have uniform properties.

This level of detail is necessary for high performance applications where surface texture is a critical design element.