Ultrasonic staking, or riveting, is an assembly procedure used to join dissimilar materials, usually plastic to metal or dissimilar plastics. A hole in the metal part receives the plastic rivet, or stud, and a specially contoured horn contacts the stud. The stud melts and reforms to create a locking head over the metal.

As in any process involving localized heating by the dissipation of ultrasonic vibrations, an efficient system is necessary. The designer must control where and how fast a temperature rise will occur. Geometry plays an important role in determining the location of high strain which results in desirable localized heating, so an energy director is used in designs employing the ultrasonic staking technique. That is, the cross sectional area / height ratio of the material at the location where the initial dissipation is to occur is drastically reduced as compared to the adjacent segments which in this case are the body of the horn and the piece part containing the stud.

Two common designs are used to produce the needed geometry. The first Flat Stud, makes use of a point or line type contact incorporating the joint design in the tip (or base) of the horn itself. The second technique Pointed Stud, calls for the energy director to be designed into the stud.

To see examples and advantages of each variation and to determine the most appropriate design for your project click on the Product Details weblink on the right. You will see drawings and formulas for the correct stud heights.