Weld Cones & Tack-Offs
By designing the mold to close in specific locations to a distance that is less than the combined thickness of inner and outer walls, a weld is formed. The amount of compression determines the strength of the weld. Mold locations with a separation that is close to the combined thickness of the inner and outer walls will have a light tack-off that will support compression forces, but may allow separation. By reducing the distance between mold halves to between 60% and 80% of the combined thickness of inner and outer walls, the weld can resist both compression and separation forces. Compression to less than 50% of the combined thickness of inner and outer walls can result in weakening of the perimeter of the weld and lead to cracking when stressed.

The location of welds within a part will determine the stiffness and ability to support loads. Designers must remember to pay attention to blow ratios between welds.