ΒΆ Fiberglass Heat Welding
Fiberglass heat welding is a technique documented by IvanTheTroll. It involves melting the plastic on a frame with a soldering iron just enough to embed fiberglass cloth into it, at which point it re-solidifies as one.
Re-melting the plastic by itself will strengthen many parts (see: Annealing) and the embedded fiberglass both adds to the strength and helps ensure future failures will not be catastrophic. The value is greatest on cheap plastics and on parts that are naturally thin, such as an AR-15's buffer tower.
You can read the guide here: https://ivanthetroll.keybase.pub/Fiberglass Heat-Welding Tutorial.pdf