A worker tack welds a ventilation duct as it is assembled at Giese Manufacturing Co. in Dubuque, Iowa. Photographer: Daniel Acker/BloombergManufacturing in the U.S. expanded at the fastest pace in more than two years as orders and production jumped, indicating more factories were growing optimistic about the second half of the year.The Institute for Supply Management's factory indexincreased to 55.4, the strongest since June 2011 and exceeding the highest projection in a Bloomberg survey of economists, after 50.9 in the prior month, the Tempe, Arizona-based group's report showed today. Readings above 50 indicate expansion, and the median forecast of 84 economists surveyed by Bloomberg called for an advance to 52.Sustained demand for automobiles and for materials tied to the recovery in housing are keeping assembly lines busy even as global markets struggle to improve. Manufacturing, which accounts for about 12 percent of the economy, may also find relief in the second half of the year as the headwinds associated with cuts in the fede