Vibration welding is a friction welding process; in order to melt
plastic, the parts must be made to move relative to one another.
Branson offers two types of vibration welding: linear vibration and
orbital vibration. Linear vibration welding uses transverse,
reciprocating motion; the vibration occurs in only one axis. Orbital
vibration welding uses constant velocity motion, a non-rotating offset
circular motion in all directions. The vibration motion occurs equally
in both the x and y axes and all axes in between.
The vibration welding process eliminates the need for solvents,
adhesives, mechanical fasteners, and other consumables. Additional
advantages and benefits of the vibration welding process include:
Fast, clean, energy efficient
Suitable for large parts (up to 20" x 60") and irregularly-shaped parts
No need for elaborate ventilation systems to remove fumes or heat
High productivity with lower cost than many alternate assembly methods
Ease of interface with automated assembly line production
Can weld multiple smaller parts at one time.
The following points need to be addressed when designing parts for vibration welding:
There must be enough clearance between the two parts for the
vibration motion (0.080" [2.0mm] total, ± 0.040" [1.0 mm] off
centerline).
The weld bead or tongue should be equal to the nominal wall
thickness for unfilled materials, and at least 1.25X the nominal wall
thickness for filled materials, depending on weld strength requirements.
The part walls must be stiff enough to prevent flexure or bending during welding. In many cases this may require adding flanges.
The amount of relative motion and the design features required to
prevent wall flexure during the process vary depending upon the polymer
being welded and the type of weld required. Several typical joint and
part design details are listed below:
Butt Joint
The simplest joint design, the butt joint can be used on short walls or
walls that are parallel to the vibration motion. No flash containment
is included in this design.
Butt Joint with Grip Tab Detail
This design also uses a flange with a grip tab or reverse flange detail
to eliminate wall flexure and part warpage. It allows the clamp force
to be applied directly over the weld area on parts that have tall walls.
Tongue and Groove with Grip Tabs
This joint provides pre-welding part alignment and also incorporates a
design which will contain and hide the weld flash. This joint design
will produces the “cleanest” finished appearance.
Virtually all thermoplastic polymers can be welded to themselves utilizing the vibration welding technique. Vibration welding also offers the largest range of welding of dissimilar materials, as well as the ability to weld different molding grades (injection molded, extruded, etc.) to each other. Since it uses mechanical friction to weld, the process puts as much energy as required at the interface to melt the plastic. As long as the parts are able to be vibrated relative to each other in the plane of the joint, the process may be used.
This method of assembly, when compared with ultrasonic assembly, is particularly advantageous for semi-crystalline resins such as acetal, nylon, thermoplastic polyester, polyethylene, and polypropylene, as well as PVC, cellulosics, thermoplastic rubber, and elastomers, filled and reinforced resins, and those exhibiting hygroscopic properties. Fillers such as glass, minerals, talc, and mica do not present a problem for the process, as long as the percentage is kept under 40%. Different grades of a material can be welded to each other.
Vibration welding replaces ultrasonic welding in many troublesome applications, since the ultrasonic process relies on transmitting energy through the part to the joint interface. For example, the ability to transmit weld energy is dependent upon the grade of material, as well as part shape and size, the percentage of regrind, the heat history of the plastic, as well as the color additives, melt flow index and filler content. Vibration welding is not subject to the same constraints, since energy is not transmitted through the part, but rather it is generated directly at the interface.
Vibration welding is a friction welding process; in order to melt
plastic, the parts must be made to move relative to one another. 
The simplest joint design, the butt joint can be used on short walls or
walls that are parallel to the vibration motion. No flash containment
is included in this design.
This design also uses a flange with a grip tab or reverse flange detail
to eliminate wall flexure and part warpage. It allows the clamp force
to be applied directly over the weld area on parts that have tall walls.
This joint provides pre-welding part alignment and also incorporates a
design which will contain and hide the weld flash. This joint design
will produces the “cleanest” finished appearance. 
