Abstract: A method for forming structural injection molded parts includes the steps of positioning a closed-loop cutting blade in surrounding relation to one of a male and female mold which together define a mold cavity corresponding to the shape of a part to be molded, positioning reinforcing material over the female mold, moving the male mold into the female mold to position the reinforcing material in the mold cavity, thereafter moving the cutting blade independently of the mold which it surrounds to trim the reinforcing material, and injecting resin into the mold cavity to produce a structural injection molded part. The cutting blade and the mold which it surrounds are part of and movable with a common die set assembly having a lost motion drive connection between the mold and the cutting blade, such that the trimming step is accomplished by lost motion movement between the mold and the cutting blade after the male and female molds have been mated.