The best way to recreate weld seams on plastic is to weld with plastic.

I take a piece of stretched sprue about 20mm long and 1mm in diameter and chuck it into my motor tool. Then I hold the end of the plastic rod against the surface of the model where I want to add a weld seam and let it spin. As the sprue melts against the surface, I slowly move it in the direction of the seam to create a bead. Adjusting the speed at which I drag the motor tool affects the thickness of the bead – faster is thinner; slower thicker.

If you use a darker color sprue than the surrounding paint you can replicate the burned area commonly seen at weld sites.  With this method, it is possible to join plastic with no glue. Practice on a piece of unused plastic to see how to adjust the width of the cord before attempting to do it on the final project.

And remember to wear safety glasses. Don’t spin the sprue without touching the plastic, or it may fly away.

Tip submitted by:
Isidoro GalindoChihuahua, Mexico