AIA: Press Meets Lamp Assembly Tolerance
Dazor Manufacturing Corp. (St. Louis) manufactures task lighting and magnifier products used in commercial, professional, industrial, educational, medical and residential applications. Dazor's most popular line of task lights is the Classic series, featuring precision-balanced "floating-arm" technology, which allows positioning of the lamp's swing arm with a touch of the finger.
Originally, when manufacturing the six models that comprise the series, Dazor pressed together the socket swivel and the shade, which covers either two or three light tubes, using a conventional mechanical press and die. With this approach, however, it was impossible to maintain a consistent pressing force. Variations in the assemblies caused Dazor to miss its internal quality control standards. Faulty assemblies had to be either reworked or scrapped entirely, including the shade.
"The cost was staggering in man-hours and raw materials," says Dazor manufacturing engineer Jeff DeProw. "We estimated that an average of four out of 10 shades would need to be reworked, including stripping the paint, repainting and refinishing. One of 10 would also be scrapped. These numbers were unacceptable, and we had to find a solution."
To achieve a proper fit between the socket swivel and the shade, the components have to be joined to a tolerance of ±0.002 inch, which requires the proper amount of force applied in a highly controlled manner. Otherwise the assembly will be either too tight, causing the paint to chip off, or too loose, compromising performance.
To solve the problem, Dazor installed a direct-acting air press from Schmidt Technology Corp. (Pittsburgh). The press generates up to 2,750 pounds of force throughout the entire ram stroke. Ram stroke is adjustable from 1.18 to 3.94 inches in 0.0008-inch increments and guided via Teflon-lined bushings.
Dazor's tool and die shop modified its existing die to accommodate the new press, and installed a PressControl PC50, two-hand control system, to operate the press. This system features an optoelectronic cycle initiation device, electronic stroke position interface, digital cycle control and a digital display with an adjustable complete-stroke cycle counter and reset button. The return stroke of the ram is initiated upon reaching a stroke completion sensor, which ensures the assembly tolerance is met on all six models. This latter feature eliminates the possibility of variations in the stroke length as a result of fluctuations in the air pressure supplied to the press. Although not a significant issue at Dazor, this is a common problem in manufacturing facilities with marginal air supplies.
Because of its increased control, the new press system reduced the defect rate on Dazor's Classic series line to the point where the scrap rate is almost zero and reworks have been virtually eliminated.
For more on air presses, call 800-959-1218 or visit www.handpresses.com.