Assembly Considerations
| Vibration |
Vibration welding is a frictional welding technique in which the surfaces being welded are rubbed together under 200 to 240 psi pressure to produce sufficient frictional and shear heat to soften them. When the melt film is sufficiently deep, the vibrating action is stopped and the components are held clamped in the desired final position until the melt solidifies and the assembly is sufficiently cool to withstand handling. Component alignment is determined by the final resting position of the vibrating platen.
The rubbing frequency range is usually from 120 to 300 Hz and the amplitude from 0.030 to 0.200 inches. Displaced material ranges from 0.015 to 0.030 inches depending on the configuration of the components being welded. If the surfaces being welded are uneven or warped, more material has to be displaced and the cycle times become longer.
Vibration welding complements the ultrasonic welding technique in being able to weld parts that are considered too large for ultrasonic welding. It is ideally suited for parts having flat surfaces to be welded. Multi-plane surfaces can also be welded with this technique as long as the vibratory motion is not hampered by them.
Parts with internal features like ribs or compartment dividers can also be welded as long as they are able to reach the welding plane. Also, additional parts can be captured between the two components being welded, if they do not interfere with welding and are not too sensitive to the vibratory motion. Vibration welding process, however, can produce unacceptable noise and may require sound-deadening enclosures.
Components for vibration welding are generally designed with flanges as wide as two to three times the wall thickness. Flanges add rigidity to the wall and provide a larger surface for welding. They also provide a better grip for the clamp and permit the application of pressure closer to the joint. Figure 1 shows typical flanged joint designs. With displaced material ranging from 0.015 to 0.030 inches, a considerable amount of flash can be generated at the welding surface. Flash traps or melt recesses can be designed as shown in figure 2 to capture the excess molten material.
