What thermoplastic materials can be bonded by ultrasonic plastic welders? Can I weld dissimilar thermoplastics?

Weldable thermoplastic resins can be categorized as amorphous or crystalline.

Weldable AMORPHOUS resins include:  polycarbonate, polyphenylene oxide, polystyrene, ABS, polyetherimide, acrylic, and polysulfone. Weldable CRYSTALLINE materials include:  thermoplastic polyester, nylon, acetal, polyethylene, polyphenylene sulfide, and polypropylene.

Yes, a limited number of dissimilar, amorphous thermoplastics can be welded together (e.g., ABS and polycarbonate). Melt temperature difference for dissimilar materials can't be greater than 50° F.

Will my plastic material still bond ultrasonically if it has a fire retardant treatment?

Flame retardants can affect the weld by reducing the strength of the bond.  In such cases, "overwelding" can sometimes be the solution.  This involves utilizing a higher amplitude machine or a slightly longer weld time to create a sufficiently strong bond.

What is an acceptable amount of glass content for ultrasonic welding of plastics?

Up to 20% is preferred.  However, adequate welds can sometimes be achieved with up to 30% glass filler.

What are the common joint designs for plastic welding?

The so-called "energy director" approach is used for many joints.  This requires a triangular projection be used on one of the pieces being joined and placed where the melting initiates.  For leak-tight joints and some semi-crystalline parts, a shear joint is recommended. A shear joint requires some interference between the parts to be welded. As the parts are ultrasonically heated and compressed, one part "shears" softened plastic from the other.