Basic Polishing Procedure for Plastic Molds To achieve high-quality polishing results, it is essential to have high-quality polishing tools and accessories, including oilstones, sandpaper, and diamond polishing paste.
The general polishing process for plastic molds is as follows:
Fine Polishing Fine polishing primarily uses diamond polishing paste. If using a polishing wheel mixed with diamond polishing powder or paste, the typical polishing sequence is 9μm (#1800) ~ 6μm (#3000) ~ 3μm (#8000). 9μm diamond polishing paste and a polishing wheel can be used to remove hairline scratches left by #1200 and #1500 sandpaper. Next, polishing is performed using felt and diamond polishing paste, in the sequence of 1μm (#14000) ~ 1/2μm (#60000) ~ 1/4μm (#100000). Polishing processes requiring a precision of 1μm or higher can be performed in a clean polishing chamber within the mold processing workshop. For more precise polishing, an absolutely clean environment is essential. Dust, smoke, dandruff, and saliva can all ruin a high-precision polished surface achieved after hours of work.
Rough Polishing: Surfaces after milling, EDM, and grinding can be polished using a rotary surface polisher or ultrasonic grinder with a speed of 35,000–40,000 rpm. A common method is to use a Φ3mm diameter, WA #400 wheel to remove the white EDM layer. This is followed by hand oilstone polishing, using a strip of oilstone with kerosene as a lubricant or coolant. The general order of application is #180 ~ #240 ~ #320 ~ #400 ~ #600 ~ #800 ~ #1000. Many mold manufacturers choose to start with #400 to save time.
Semi-Fine Polishing: Semi-fine polishing mainly uses sandpaper and kerosene. The grit numbers for sandpaper are as follows: #400 ~ #600 ~ #800 ~ #1000 ~ #1200 ~ #1500. In practice, #1500 sandpaper is only suitable for hardened die steel (52HRC and above), and not for pre-hardened steel, as it may cause surface burns on pre-hardened steel parts.
Fine Polishing: Fine polishing with polishing compound at 8000 or 10000 grit will achieve a mirror finish.
