Injection molding with periodic forces to the material in the mold

An injection moulding process for moulding a molten material, containing at least one kind of thermoplastic resin having a heat distortion temperature and a melt processing temperature, in a mould having a mould cavity and at least one channel communicating with the mould cavity, each channel entering the mould at a respective mould inlet, the process comprising:

• heating inner surface areas of the mould to the melt processing temperature of the material prior to supplying the molten material into the mould;
• supplying the molten material into the mould by way of at least one channel and subjecting the molten material to a propelling force, sufficient to propel it through the channel into the mould;
• applying periodic forces to the material in the mould at a plurality of spaced-apart regions, a first and a second of the regions being located on either side of the molten material in the mould cavity, the periodic force being applied with a difference in phase so as to cause shear of the molten material within the mould cavity between the first and second regions;
• allowing the molten material in the mould to solidify by cooling the mould below the heat distortion temperature of the resin while or after applying the periodic force;
• and then
• opening the mould, and removing the moulded article.