There are different designs to use. The parts being welded together should be of the same material and of the same process (both injection molded, both blow molded, etc..). Some materials weld together with different results, so don't expect the same air/water tight or mechanical bond for every material. Typically, generally speaking, a weld design is of a "male" type on one part which will have interference to the other part which doesn't have any, or may have very slight "female" type design to it. This interference prevents the 2 parts from assembling fully until it's welded and the 2 parts melt together at the area the interference is located at.
Generally speaking the weld line would be the "nub" in the following photo, also called an "Energy Director", the vibration from the ultra sonic welder vibrates the two parts while pushing them together, until that nub get's hot enough to melt and bonds the two pieces together, with the correct parameters the bond can be nearly invisible and as strong as the surrounding material, as well as water tight.
Different materials require different parameters and can require a lot of trial and error before good welds can be produced.
A few parameters that are generally used for good welds are:
Force - pressure pushing the two parts together
Weld Time - time the vibration is active
Hold Time - time after vibrating to hold the parts till the material cools
Frequency - speed of vibration
Amplitude - distance of each vibrating stroke
Velocity - speed the parts are pressed together
Ramp Speed - how long it takes to get the weld "horn" up to operating frequency
Collapse distance - usually set after a trigger point of when the parts contact to when the tooling has dropped lower due to the energy director melting
Collapse Time - time it takes to reach collapse distance, this usually has to do with bond strength, like tempering you don't want the weld to be hot for too long or too short
I've spent a lot of time working with, building, and modifying ultra sonic welders so let me know if there's any more questions that arise from this.
Thank you. I went with adding a male end and no female. The files have been sent to the mold maker for review. As soon as I get a responce I will post it and hit a correct answer. Again thank you, this one had me stumped.
Any manufacturer of the welders I've dealt with have also been really good about reviewing designs, as well as testing and finding good parameters for use. Be sure to check with them too since each welder can cost around $60,000 they're usually pretty good about helping.