Method for processing workpieces by ultrasonic energy

A method of welding two thermoplastic workpieces together during a weld cycle utilizing a high frequency vibration sonic or ultrasonic apparatus, said apparatus comprising an electroacoustic transducer which transmits such vibrations to a horn which is dimensioned to be resonant and which is in forced engagement with at least one of the workpieces to be welded, said method comprising the steps of:

• establishing forceful contact between said horn and workpieces such that said workpieces are in engagement with one another at least along areas constituting a weld line to be formed;
• energizing said electroacoustic transducer so as to resonate said horn with a desired motional amplitude;
• maintaining said forceful contact between said horn and said one workpiece throughout said work cycle;
• and
• varying said motional amplitude of said horn during said weld cycle in accordance with a desired motional amplitude profile.

A method of ultrasonically welding two thermoplastic workpieces together along a predetermined weld line during a weld cycle so as to reduce the formation of particulate weld material which may contaminate a product made from said workpieces or contained within said workpieces, one of said workpieces having an energy director on one of its surfaces to be welded to said other workpiece along said weld line, said method comprising the steps of:

• bringing said workpieces together with said energy director bearing against said other workpiece along said weld line to be formed;
• providing an ultrasonic electroacoustic transducer for applying ultrasonic power to said one workpieces;
• energizing said electroacoustic transducer for a first portion of said weld cycle at a first motional amplitude sufficient to preheat said energy director thereby to minimize shattering of said energy director;
• and
• then energizing said electroacoustic transducer for the remainder of said weld cycle at another motional amplitude for the remainder of said weld cycle for heating said thermoplastic material of both of said workpieces along said weld line to a temperature sufficient to effect welding of said workpieces to one another.