a method for suppression of weld line weakening by virtually eliminating weld lines is disclosed . the process involves the near explosive injection of a metered amount of foamed thermoplastic molding material into an enclosing compartment formed by partly closing a compression type mold followed immediately by compression molding of the well mixed foamed material . the process finds particular utility in the manufacture of very long fiber reinforced parts . variations on mold design and clamping cycles yield a variety of parts having foamed regions surrounded by more dense un - foamed regions . the method is particularly well adapted to the manufacture of large , very long fiber reinforced , foam - centered , hard surfaced , light weight , rigid parts .