This white spots issue happened on a high gloss product in black color, which was not found on tryouts, but on mass production after injection molding about 50 shots.
The mold with banana gate inserts, so when the white spots appeared at the first time, we thought that there might be some oil inside the gate inserts cause the issue. So we disassembled the mold and clean the inserts and re-started the sampling, white spot did not show again until about 50 shots.
The issue happened after about 50 shots sampling, the mold was going to warm up, so temperature might be one root cause, but the white spots only showed up around the gate. And because the cosmetic surface is high gloss which need high mold temperature and high pressure to pack the part to have shining and without sink marks.
From the info above, we thought that the resin might have been degraded as the high shearing stress flowed through the gate when mold temperature went up, then white spot happened. So low down the injection pressure, melt temperature and mold temperature might be helpful.
We tried many different molding set up parameters to fix the issue, but it did not work. So enlarging gate size was the last option, and the issue was fixed.
Hope this case what we experienced can be a minnow to catch a whale. Please advise if you have any good idea.
