Leveraging additive manufacturing technology to mistake-proof production.

One thing OEMs universally agree on is that none of them likes non-recurring engineering (NRE) charges. Implemented as part of new product introduction (NPI), however, custom tooling, fixtures and jigs can eliminate defect opportunities by minimizing process variation that could otherwise occur when those issues can’t be resolved through product design changes. They are also a good tool when a production team identifies the need for a poka-yoke, or mistake-proofing solution, later in a product’s lifecycle.

The concept of poka-yoke was developed by Shigeo Shingo as part of the Toyota Production System (TPS). When applied, the resulting process improvement eliminates a specific defect. Its focus on simplicity is its strength, in that simple fixes are often the best solution for small variances in the manufacturing process. Simple fixes are also easy to rapidly implement and encourage production operator involvement in the pursuit of product perfection. That said, when fixtures are procured through third parties, the cost may exceed the benefit.

The Lean Six Sigma team at SigmaTron International’s facility in Tijuana, Mexico, decided to investigate ways to reduce tooling-related NRE costs by developing in-house 3-D printing and computer numerically controlled (CNC) machining capability. In 2022, they initiated a DMAIC (define, measure, analyze, improve and control) effort to determine necessary equipment and the likely return on investment if the capability was added.

The facility now has two 3-D printers, two CNC-controlled routers and the software tools necessary to design and fabricate a range of fixtures. In the first seven months of 2023, designing and fabricating fixtures internally has generated cost savings of almost 200% over the costs had the fixtures been purchased from external suppliers.

In addition to lowering tooling-related NRE costs as programs are ramping up, the lower cost of this in-house capability has made it possible to expand use of specialized tooling for poka-yokes identified in Kaizen events. Improvement opportunities are identified by Lean Six Sigma-trained personnel in regular Gemba walks through the production area. The facility’s Industry 4.0 AOI inspection capability, which covers both SMT and secondary assembly operations, is also helping rapidly identify quality trends where a poka-yoke fixture solution would eliminate a defect opportunity.

In one case, an overlay was created to cover an unused plugged via on a printed circuit board assembly (PCBA) used in a harness assembly. Production operators soldering the harness to PCBA were confused by the via because it looked similar to pads for the harness attachment and was in the same area of the PCB. Once the overlay covered the via, yield improved from 95% to 100% on the product. The annual return on investment exceeded the cost of the overlay by over $3,000.

In another case, wave soldering had become a production bottleneck due to a shortage of fixtures used to stabilize a capacitor on PCBA. Lower cost in-house fixturing capability enabled the team to add 20 additional fixtures. Waiting takt time per assembly dropped to 1 min from 10 min. The annual return on investment exceeded the total cost of the fixtures by nearly $1,500.

In a different example, a manually inserted connector needed to be pressed into a socket on the PCBA. Manual pressure increased the risk of damage and had a 5 min. takt time. Internally designed and fabricated small press tools controlled the pressure, eliminating the damage risk. Takt time on the operation dropped to 30 sec. The annual return on investment exceeded the cost of the presses by over $2,500.

In addition to quality, cost and efficiency improvements, moving to an in-house fabrication option has given the team better control of the tooling design and reduced tooling fabrication lead time. The fixtures are utilized in a variety of operations including manual insertion, wave solder, AOI, SMT, test, secondary assembly and box-build.

The Lean Six Sigma team is now evaluating ways to better automate the tooling fabrication process, to further shrink lead time and cost.

Filemon Sagrero is continuous improvement engineer at SigmaTron International (sigmatronintl.com) and a Six Sigma Black Belt; filemon.sagrero@sigmatronintl.com.

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