Injection molding parts onto a carrier web located between mold halves, each mold half having a cavity, resulting in molded articles having parts on both sides of the carrier web. Polymer flow into the cavities is assisted by application of ultrasonic energy to the mold. After the molding operation, mold halves are separated, and the carrier web is advanced, or indexed, to a next position for another molding sequence. Articles produced include lenses with part of the carrier web between lens halves, and a carrier web bearing an array of molded parts.