Tool Steel Selection Guidelines for High Volume Injection Moulding Tooling Baseline Fabrication
High-volume injection moulding baseline tooling demands martensitic stainless or pre-hardened steels matched to polymer abrasiveness and cycle volume.
SPI A1 Polish
Meaning
Optical quality surface finishing represents the highest level of polishing achievable for injection mould cavities. An spi a1 polish is attained using fine diamond powders on a mirror-finish steel substrate. It is reserved for parts requiring extreme clarity or a high-gloss aesthetic.
Surface Roughness
is measured in micrometres to ensure the finish meets the required specification. This level of polishing typically achieves a Ra value of 0.012 to 0.025. Achieving such a smooth surface requires a high-quality, vacuum-degassed tool steel with minimal inclusions.
Optical Performance
is the primary reason for selecting this finish for lenses or light guides. The mirror surface of the mould is replicated on the polymer part, allowing for the undistorted transmission of light. Any imperfection in the polish will result in a visible defect or a loss of optical efficiency.
High-gloss finishes also make the part easier to eject from the cavity.
Polishing Cost
is high due to the manual labour and time required to reach the a1 level. Each step in the sequence must be completed perfectly before moving to a finer diamond grade. Mistakes made early in the process will be visible in the final finish.
This investment is justified for premium consumer products or technical optical components.