Is there a limit of the percentage of Glass fiber that can be added into plastic for a good ultrasonic welding ?
The addition of fillers to polymers affects the weld strength. Generally, increasing filler (such as glass fibers) content in a polymer matrix reduces the weld strength. This decrease in weld strength with an increase in filler content is believed to be due to the lower polymer volume fraction available at the weld interface. As more filler is added, less polymer volume exists at the joining surfaces for bonding.
Answering the question of the percentage limit of glass fiber that can be added in a polymer for good welding, is not straight forward. Many factors need to be considered including but not limited to: Glass fiber dimensions (diameter, length), aspect ratio, glass fiber orientation, polymer matrix, surface treatment of glass fibers (e.g. with silanes), processing history, degree of dispersion of glass fibers, etc.
In fact, for the exact same glass fiber content (30 wt%) in a polycarbonate matrix, the tensile strength of a weld decreased with increasing fiber orientation angle to the weld line (see attached publication).
Agree with Ali's remark that weld strength decreases with increasing filler content and the factors which would affect. However in discussion of fiber orientation, you should note that the attached publication is about "mold-in" weld which is created during the mold-filling process. On the other hand the ultrasonic welding is done with 2 already molded parts. In this case fiber orientation is normally parallel to the surface but of course dependent of the design of the molded part.
Regarding the limit of the fiber content, you can try any high fiber-content material which is commercially available, which I believe is up to around 50 weight %. However when good weld-strength is needed, 30 - 35 % grade would be normally recommended.
@Hajime Thanks a lot for the answer, what you described is close to what i'm looking for.Do you have further documents regarding this topic , i mean the influence of additive and glass fiber in the ultra sonic welding results ?
Thanks for your feedback :-)
@Marouene; Good to hear it helped. Actually it is a general view based on my experience. So I am afraid I do not have further document.
When you try to find literature youreself, you can also search with "vibration welding". It is different process, precisely speaking, but it is widely used in industry and would be helpful to understand mechanism of welding
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