A molding method, comprising: providing an injection mold having a first mold member and at least one movable mold member that can move toward and away from the first mold member to close the mold, wherein a mold cavity is formed in at least one of the first or movable mold members, the cavity having at least one gate therein, and further wherein a source of ultrasonic energy (214; 218) is positioned to apply ultrasonic energy to the cavity; closing the mold, whereby the at least one gate is fluidly connected to a source of molten (co)polymer; heating the mold to a mold temperature measured adjacent to the cavity of from 104°C to 116°C; thereafter injecting the molten (co)polymer into the cavity through the at least one gate of the closed mold to substantially fill the cavity and the gate with the molten (co)polymer; allowing the closed mold to cool until the molten (co)polymer within the gate has solidified; applying ultrasonic energy from the source of ultrasonic energy to the molten (co)polymer in the cavity of the closed mold without remelting the solidified (co)polymer within the gate until the mold temperature has increased to between about 116°C and 122°C, thereby substantially relieving any flow induced stresses in the molten (co)polymer; thereafter cooling the closed mold until the mold temperature has decreased to about 101°C and 107°C; thereafter heating the closed mold until the mold temperature has increased to between about 116°C and 122°C, thereby substantially relieving any thermally induced stresses in the molten (co)polymer; and thereafter allowing the mold to cool until the molten (co)polymer has solidified within the mold, thereby forming an injection molded article. providing an injection mold having a first mold member and at least one movable mold member that can move toward and away from the first mold member to close the mold, wherein a mold cavity is formed in at least one of the first or movable mold members, the cavity having at least one gate therein, and further wherein a source of ultrasonic energy (214; 218) is positioned to apply ultrasonic energy to the cavity; closing the mold, whereby the at least one gate is fluidly connected to a source of molten (co)polymer; heating the mold to a mold temperature measured adjacent to the cavity of from 104°C to 116°C; thereafter injecting the molten (co)polymer into the cavity through the at least one gate of the closed mold to substantially fill the cavity and the gate with the molten (co)polymer; allowing the closed mold to cool until the molten (co)polymer within the gate has solidified; applying ultrasonic energy from the source of ultrasonic energy to the molten (co)polymer in the cavity of the closed mold without remelting the solidified (co)polymer within the gate until the mold temperature has increased to between about 116°C and 122°C, thereby substantially relieving any flow induced stresses in the molten (co)polymer; thereafter cooling the closed mold until the mold temperature has decreased to about 101°C and 107°C; thereafter heating the closed mold until the mold temperature has increased to between about 116°C and 122°C, thereby substantially relieving any thermally induced stresses in the molten (co)polymer; and thereafter allowing the mold to cool until the molten (co)polymer has solidified within the mold, thereby forming an injection molded article.