Plastics joining ultrasonic

Ultrasonic Welding, Chap. 5, Handbook of Plastics Joining, Plastics Design Library, Norwich, NY, 1997. 

Plastics Joining Technology, supplier marketing literature, Branson Ultrasonics Corp., 1994. 

PRINCIPALS FOR DESIGNING MEDICAL PARTS FOR PLASTIC JOINING Presented by Arthur Summo, Branson Ultrasonics, Danbury, CT 1/3/07... 

Ultrasonic head forming and welding is a fast assembly technique. It is a very rapid operation of about 2 seconds or less and lends itself to full automation. In this process high-frequency vibrations and pressure are applied to the products to be joined, heat is generated at the plastic causing it to flow, and, when the vibrations cease, the melt solidifies. The heart of the ultrasonic system is the horn, which is made of a metal that can be carefully tuned to the frequency of the system. The manufacture of the horn and its shape is normally developed by the manufacturer of the equipment. The results from this operation are not only economical, but also most satisfactory from a quality control standpoint. 

In pressure welding, the parts to be joined are locally heated at the place where the joint is to be formed. The parts are then pressed together in the plastic state so that they are joined. Usually no filler is employed. Cold pressure welding makes use of high pressure, without the aid of heat, to unite parts. Ultrasonic and explosion welding are variations of this technique. 

Welding methods are listed in Table 7.1. Ultrasonic welding is one of the most efficient methods of joining plastic parts, and different materials can be welded so long as they have a common monomer. While particularly useful for hard rigid materials, it may generate particles. 

In ultrasonic welding the molecules of the plastic to be welded are sufficiently disturbed by the application of ultrahigh-frequency mechanical energy to create frictional heat, thereby causing the plastics to melt and join quickly and firmly. 

The part assembly design addresses the ability to join/assemble the component parts. Where the components are assembled with adhesives, it is important to know the compatibility and strength of adhesion to dissimilar substrates, in addition to the chemical compatibility of the plastic with the specific adhesive and its constituents. If melt bonding methods, like ultrasonic, vibration, or spin-welding processes, are employed, thermal compatibility aspects have to be taken into account. The broad possibilities of mechanical assembly methods include snap fits, press fits, bolts, and threads. The material properties needed for each of these design calculations are listed in Table 11.9. 

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