A Worcester man has died of injuries suffered Sunday in an industrial accident at a Hilltown steel fabricating plant. 57-year-old Dieu Nguyen of Scheid Way in Worcester was pinned between sheets of heavy steel stock at Haberle Steel on Cherry Lane, just outside of Souderton.  He was pronounced dead Monday at Lehigh Valley Hospital, where he had been flown for treatment.  The official cause of death was to be determined at an autopsy set for Wednesday.  Hilltown Police and the U.S. Occupational Safety and Health Administration are investigating the death.