The energy in vibration welding
Recently, we’ve been discussing conventional vibration welding and hybrid or ‘clean’ vibration welding. Vibration welding, a linear frictional weld method, you probably know all about. Hybrid – the introduction of an infrared preheat function prior to the conventional vibration weld process, is a relatively new method of welding plastic parts.
A quick review: The intent of the IR preheating prior to the introduction of frictional energy is fairly obvious – elevate the temperature of the weld joint. The anticipated result of this preheating is improved flash (plastic displacement from the joint) control and the potential in certain applications to reduce the necessary amplitude and/or force to achieve the ideal weld performance and assembly appearance.
In the case of vibration welding, amplitude is defined as the movement of the driven platen which is usually the upper tooling surface. This movement is adjustable, the user programs the value. Usually, this value is the distance from the stationary or central position of the driven platen to the extreme or edge of the displacement, or, half of the total movement. Sometimes amplitude is referenced as total movement or peak-to-peak.
"Usually, more is better, right? Not always."
In general terms, the typical 240 Hz linear vibration welder can achieve an approximate maximum amplitude displacement of 0.9 mm (.035”), or 1.8 mm (.071”) peak-to-peak movement. The amplitude of this linear friction energy generates the heat sufficient to soften the plastic to a semi-molten state for welding. Usually, more is better, right?
Not always. Amplitude introduces stress into the weld joint and it can cause real problems with internal walls or rib sections and internal mechanisms or sub-assemblies. Regarding stress, at its most fundamental level, vibration welding is a shear welding process. Shear is necessary to initiate the heating. Shear stresses can be minimized by ‘quick stopping’ activity, but that’s another discussion. Suffice it to say that vibration welding is an aggressive weld process that can be difficult to manage for some applications.
Back to hybrid vibration welding and a preheated weld joint: With the material already in a softened state, the potential to reduce the necessary amplitude to achieve the desired results now exists. Additionally, a reduction in required weld force may be possible. With the hybrid welding approach, the user gets the benefits of preheating with the robustness of the long-proven vibration welding process!
As we’ve stated before, not all applications benefit from hybrid vibration welding. But many do. Extol offers a wide range of CEMAS vibration and hybrid vibration welding equipment. Our application engineers are in place to assist you in making the best process decisions.