Monday 12 October 2020

How to Approximately Access the Weld Line Strength - Rule of Thumb for Plastic Part Design

In this blog post, I present to you another helpful rule of thumb for plastics part design and material selection. 

Plastic part designs may have a weld line due to polymer melt fronts merging together to form one melt front. At the weld lines, glass fibers do not function as reinforcements and as a result reduced mechanical strength occurs in this area. 

Accessing the approximately weld line strength of a polymer compound can be done by checking the tensile strength of the associated base polymer.

In the example below, glass fiber reinforced polyamide (PA 66 GF 50) has a tensile strength of 237 MPa and a weld line strength of 92 MPa. The associated base polyamide has a tensile strength of 85 MPa which is in a similar range as the weld line strength of the PA 66 GF 50 compound. 

Thank you for reading & #findoutaboutplastics


Herwig Juster

Other Rule of Thumb posts: 

How to Reduce Environmental Stress Cracking - Rule of Thumb for Plastic Part Design & Material Selection

If you liked this post, please share and like!

Interested in my monthly blog posts – then subscribe here and receive my high performance polymers knowledge matrix.
New to my Find Out About Plastics Blog – check out the start here section

[1] Gunter Erhard: Designing with Plastics, Hanser, 2006


  1. As a professional welder never compromises with safety. You should use all the safety gear while welding including helmets. Viking 3350 welding helmets are the best welding helmets that you can buy from the Service Welding Supply website.

  2. When selecting the shielding gas to be utilized in a welding operation, it doesn't matter which welding method you're employing. Depending on the application, brass welding may be accomplished using MMA, MIG, or TIG welding gas. It is recommended that anyone interested in learning how to weld brass go to Weld Gearz for their first research.