Manufacturing method for hollow article

An invention of manufacturing method for hollow article and its mold structure comprising with a multi-frame mold assembly to clip and enclose a hollow plastic material so as to derive a multi-stage pressure from the inside of said enclosed plastic material; the first pressure is derived by the first mold frame which enclosed an extruded hollow plastic material and force the surface of said enclosed material to extend between the inside of said first mold frame and at lease a baby mold embraced by the first mold frame. The pre-expansion inside the baby mold will avoid an over expansion while making complex hollow article. The second pressure is derived by a further squeezing action of said baby mold which will finally forms a complex hollow article with more uniform thickness.