Guest Article: The Damaged Pins By Clifford Stover, P. E.

Sep 1, 2012 by

A large electronics corporation was getting ready for final production of a new state-of-the art automated teller machine for use by numerous banks and grocery stores.  This particular company had an overseas engineering group which designed the bulk of the internal electronics and had already produced a good number of the required microprocessors in-house. One of the most important and expensive processors had come out of manufacturing with over 30 percent of the units having 3 or 4 bent leads on each of the chips.

 

 

These processors were not compatible on the production line, and attempting to have technicians hand-straighten these was near impossible. The cost of re-engineering the tooling to fix the mistake in the production process was too costly on both the front and back end, as the units were already finished, the tooling had been changed out, and the time was extremely prohibitive as the ATM units were scheduled for delivery in a short time.

 

 

Called in by an old colleague, I was asked to assess the situation and propose a solution if possible. My background started in the tool die industry, progressed to being a competent mold maker, and on into design and development engineering. Having spent over a decade attending engineering school part time with a full time job in these industries helps a great deal with different problem solving tasks.

After carefully assessing the situation, it was obvious the solution was not in the remanufacture of the units, but in designing some type of fixture or press application that would accurately locate the microprocessor, hold it in place, and gently re-align and straighten all the leads so it could be re-introduced into the production process

In order to accurately locate the microprocessor, hold it in place without damaging the circuitry, and bend the leads back in place where they could be run through the production process, the tolerances on the active or moving portions of the tooling and the hold-down section needed to be designed to within 0.0005” to be effective.

(Editor’s note: for comparison purposes, a human hair is typically .007” to .002” in diameter, so the correction needed was roughly a quarter to a fifteenth the diameter of a human hair).

After looking at the actual physical dimensions, rigidity, and the fragile nature of the processor, the tooling was designed with an upper male half which incorporated a spring-loaded hold down mechanism that would gently locate the processor while the tooling compressed. The female portion, or bottom half, was designed with proper draft angle to pull in the bent leads and sufficient clamping force and angle to eliminate spring-back past the specified angle of the finished lead and result in a set of leads or pins that could be run through the robotic assembly line.

Some of the issues with tooling of this type are 1) in  preventing galling by utilizing dissimilar materials at sliding points, 2) to use materials that are hard and rigid to prevent any type of distortion during the process, and 3) to set up the tool to be operator friendly, safe, and easy to use.

The working parts of the tool were designed and manufactured out of S7 and H13 tool steels, which are soft in the untreated state and can be hardened and finish ground for durability and life. The remaining tool was made of 4140 steel with leader pins, die springs, and a toggle clamp to be used by the operator to clamp the tooling together.

What could have cost the company weeks or months of downtime, many thousands of dollars in tooling and reproduction cost, was solved by a professionally engineered, competently designed, and quickly built tool that was no bigger than a kitchen blender. The cost of the tooling was around the price of a new VW or Toyota. The cost saved was likely that of a new Lamborghini, or two.

 

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