Casting Study: Top and bottom sensor plate – dollar bill changer

A dollar bill changer incorporated top and bottom sensor plates fabricated from welded stamped components. The weldments could not hold tolerances greater than +/- 0.020 in. In an effort to resolve dimensional instability and fit problems, the manufacturer, working with a die caster, redesigned the two components as zinc die castings. Die casting the plates results in dimensional stability and precise dimensional tolerance of +/- 0.005 in. This eliminated the previous fit problems. The die cast bottom plate includes bosses, mounting areas, windows, and holes. The only machining needed is hole tapping. The rejection rate fell from 30 percent to less than one percent. Weight is also reduced without loss of strength. Cast walls with zero draft and an overall tolerance of +/-0.005 in. ensured a tight fit with a mating circuit board box. The close fit guides dollar bills through the assembly without jamming or slipping out. The tight enclosure also keeps out dirt and dust, which can interfere with bill guidance and sensing.