DETROIT (WKZO) -- Vice President Joe Biden is expected to speak at the American Federation of Teachers convention in Detroit at the end of the month.  The union represents 1.5-million teachers across the nation and will hold its annual convention at Cobo Center July 27th through the 30th.  Biden is tentatively scheduled to speak at the event July 29th in his first visit to the state since a stop in Grand Rapids in February.