A plastic mold polishing service restores and refines cavity surfaces after machining, electrical discharge machining and production wear, and it decides whether a finished part ships with a mirror gloss or a matte industrial look. Our toolroom runs diamond polishing, stoning, blasting and texture repair on injection moulds, die-cast dies and compression tools. Every cavity is checked against the SPI mold finish standard, with photos and a surface report, before the tool is released for production.
What a Plastic Mold Polishing Service Covers
- EDM recast removal, including the heat-affected white layer left after spark erosion
- Progressive diamond lapping from 15 um down to 0.25 um paste grades for A-grade gloss
- Paper and stone finishing for B and C semi-gloss or matte grades
- Dry blast and texture matching, including VDI 3400 and Mold-Tech pattern repair
- Weld repair, gate and vent dressing and shut-off lapping after production wear
Finish Grades and What They Cost in Labour
| SPI grade | Method | Typical Ra |
|---|---|---|
| A-1 mirror | #3 diamond buff | 0.012-0.025 um |
| A-3 gloss | #15 diamond buff | 0.05-0.10 um |
| B-2 semi-gloss | 400-grit paper | 0.10-0.15 um |
| C-3 matte | 320-grit stone | 0.63-0.70 um |
| D-3 texture | #24 oxide blast | 3.2-18 um |
Buyers often ask for a polished tool without naming a grade, and that is where quotes drift apart. A-1 mirror work runs on S136 or 420 stainless hardened to about 54 HRC and needs one to three degrees of extra draft for release; B-2 at 400 grit is the common default for cosmetic parts; C-3 stone finish suits hidden structural surfaces; D grades are blast textures used where grip or fingerprint hiding matters. Mold finishing scope should be agreed before the tool enters the toolroom, because the grade sets both the labour hours and the steel choice.
Steel, Draft and Resin Interaction
Not every steel holds a fine polish across a long production run. Aluminium prototype tools cannot hold an A-grade gloss, and glass or mineral filled resins dull a mirror finish faster than an unfilled grade. We confirm the resin family and expected shot count before quoting the finish, and we flag where a gloss callout would expose sink marks and weld lines that a matte grade would hide.
Turnaround and How We Quote
Single-cavity polish and recast removal typically takes three to five working days; multi-cavity A-grade work runs five to ten days depending on access and size. Quotes are per cavity, based on grade, size and access, and include a before-and-after surface report. Browse the plastic mould catalogue for related tooling, read our guides on mould gate design and part design guidelines, or find toolrooms in the supplier directory.
Related product categories
The materials and part types discussed above are grouped in our sourcing directory:
