I'm getting some plastic parts (made with HDPE) CNC machined. A few of these parts require the addition of threaded inserts. I've printed the parts myself using a 3d printer and when I add the threaded insert, it's impossible to insert it perfectly in the plastic part (perfectly straight in the hole) since I'm using a soldering iron (not very professional) to heat up the insert.
I know threaded inserts are used in professionally manufactured plastic products, so I'm wondering how they make sure the threaded insert is perfectly inserted into the plastic part. Which tool do they use to add the insert? What type of inserts are used?
Thanks everyone for the help.