Meaning
Process of eliminating the thin zone of re-solidified metal left on a tool surface after electrical discharge machining. Recast layer removal is necessary because this layer is often brittle and contains micro-cracks. The removal ensures that the base metal properties are restored to the cavity surface.
Mechanical Polishing
Using abrasive stones or diamond pastes physically grinds away the white layer until the parent steel is reached. Recast layer removal must be thorough to prevent the brittle material from flaking off during injection. This step also prepares the surface for a specific texture or high-gloss finish.
Chemical Etching
Acid baths are used to dissolve the damaged layer without affecting the bulk of the tool. This method for recast layer removal is effective for complex geometries where manual polishing is difficult. It provides a uniform surface that is free of the stresses induced by the spark erosion process.
Surface Longevity
Eliminating the brittle zone prevents the initiation of fatigue cracks during the high-pressure cycles of moulding. A tool that has undergone proper recast layer removal will last for more cycles than one left in its as-machined state. This maintenance step is a requirement for high-volume production tooling.
The structural integrity of the steel is maintained by the removal of the heat-damaged skin.
