Redundant Ultrasonic Welds

[jevoltin]

We are currently reviewing a design that uses an ultrasonic weld and a rubber gasket to produce a water tight seal for a small ABS plastic enclosure. The enclosure is tested to a water depth of 10 feet. In order to simplify the assembly process, it has been suggested that we eliminate the rubber gasket and add a second ultrasonic weld inside the first weld. In other words, there would be two rows of ultrasonic welds around the entire perimeter of the seam.

I understand that this could be done using three pieces. The current design has two pieces. With three pieces of ABS plastic, you would perform the inner weld between the first two pieces, add the third piece, and then perform a second weld. The result would be two complete welds providing redundancy and a higher probability of maintaining a seal during pressure testing.

Could a design using two pieces achieve two welds that provide a meaningful increase in seal reliability? I'm concerned that the two welds would be formed simultaneously and share similar defects, weaknesses, etc. Additionally, the process of forming two welds simultaneously could significantly alter the welding process by yielding unpredictable vibrations.

Any experience or thoughts in this area would be greatly appreciated.

- John

 

[dwightdixon]

Ultrasonic weld configurations can be shear or energy director types. Having two areas that are designed to melt and fuse might improve the reliability. I have never seen it in the practical world. Have the design reviewed by Branson or one of the other big suppliers is your best course of action. They know more about the process than any one user of the process.