Additive processes are an effective tool toward the single-iteration design goal.

In past columns we’ve discussed the benefits of strong focus on design for manufacturability (DfM) and assembly (DfA) in the design phase and poka yoke or “mistake-proofing” in production. As the cost of 3-D printing technology drops, its usefulness in DfM/DfA and poka yoke activities grows. At SigmaTron International, 3-D printers are used in a variety of ways to improve design for assembly and reduce variation. Here we look at ways this technology is used in design, manufacturing and test processes to solve challenges that otherwise add time, cost or defect opportunities.

In SigmaTron’s design process, the goal is a single iteration wherever possible. One way that gets accomplished is through peer review of a physical sample of the product. The peer review process usually involves all engineering disciplines, including software development, PCB layout, mechanical, hardware, test engineering and the production team on both the contract manufacturing and customer teams. While 3-D modeling software can provide a representation of the product, 3-D printed parts allow participants in this type of peer review to more easily test assumptions on assembly order of parts and the way parts move in the physical product. SigmaTron’s design team frequently uses a 3-D printer to demonstrate how housings and covers will work on new products to help the team visualize the manufacturing and user processes involved.

Another product development benefit is minimalized tooling iterations for designs that aren’t fully locked down. In some cases, SigmaTron’s design team 3-D prints small quantities of parts for designs that are likely to have engineering changes that will impact hard tooling. When balanced against tooling costs, the 3-D parts are a cheaper option. This path also enables greater flexibility in adjustments to design for assembly or user-friendliness in the early stages of product release when tight deadlines for initial build quantities are involved, since no tooling is involved.

Test fixture design is another area where 3-D printed parts are becoming valuable in solving test challenges. 3-D printing enables custom fixtures for odd-shaped parts and high-mix product families. SigmaTron’s design team in Illinois routinely develops unique test fixtures that incorporate 3-D printed parts to solve test challenges in its facilities around the world.

For example, a high-volume control was experiencing high failures in test. The root cause was its odd shape, which made alignment in a test fixture difficult. A redesigned test fixture included a 3-D printed clamp, which had the exact shape of the odd-shaped printed circuit board assembly, along with a rotary knob control that permitted the part to be rotated for a potentiometer test. Printing the clamp was less expensive than fabricating it in plexiglass and accommodated a design that included the rotary control knob. The clamp ensured the unit under test made consistent contact with the test fixture, which eliminated the test failure issue. The redesigned fixture reduced test load and unload time, and the rotating control knob shortened the overall time required to test. The improved throughput met the company goal.

In another example, the team designed a template to support the self-test of a handheld unit. The product had multiple buttons on its faceplate, including one capable of resetting the entire unit. The template covered the reset button to eliminate the possibility of the inspector pressing the wrong sequence of buttons to initiate the self-test.

SigmaTron’s team in Tijuana, Mexico, has also been using 3-D printing to poka yoke test challenges. In one case, they had a product with 45 variations that utilized a test where voltage was transferred via a connector during test. Six different connector pair variations were among the product types, and confusion about the appropriate connector socket was causing damage and adding time during test. The team designed a 3-D printed six-connector pair exchangeable socket system that enabled 12 units to undergo test at the same time. The socket system had a quick connect/disconnect to the test, making it easy to support different product variations or replace at the end of its usable life. The cost was substantially below the cost to create unique traditional test fixtures.

In another case, product test was accomplished via a tablet app, which scanned a traveler barcode as part of the test process. The team found the time necessary for operators to raise the tablet and align it properly to scan the barcode was impacting throughput. There was also the possibility of tablet damage if the operator dropped it while trying to initiate the test via the app. To address both issues, they designed a 3-D printed fixture that aligned the tablet camera and barcode automatically. The tablet stayed on the fixture, and the travelers could be easily changed. Throughput goals were achieved, and risk of damage to the tablets through excess handling was eliminated.

Production fixturing is a final area where 3-D printing is helping solve challenges. While it isn’t an option for high-heat processes, it is a good option for odd-form, nonwettable part masking in conformal coating. Printed masking caps and boots are a less expensive option than third-party tooling and require less lead-time. They are also faster to install and remove than other forms of manual masking.

Using 3-D printed parts to sanity-check design assumptions, increase flexibility in product development timelines or address unique challenges in manufacturing or test is often the simplest, fastest and lowest-cost option. In some cases, the ability to configure unique shapes and interfaces adds levels of functionality not possible with traditional fixturing options. In many cases, the ability to fabricate a one-off solution permits levels of customization that are otherwise not cost-effective.

Robert Alvord is director of engineering at SigmaTron in Elgin, IL; Victor Mendez is manufacturing engineer at SigmaTron in Tijuana;

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