Some design for manufacturing risks seem impossible to detect early in the product design process. Clarifying those target risks, helps the engineers perform a faster and more thorough review of the design for manufacturing. Over the years, we have boiled those target risks down to a simple checklist. (If you are interested in the power of the checklist, we highly recommend The Checklist Manifesto by Atul Gawande.)
The design for manufacturing checklist includes both design for injection molding and design for assembly. One item on the checklist deals with the risk that two parts will join in an incorrect way.
During the review of the design for manufacturing, you want to consider misalignment risk. If components were to join in the wrong orientation, the product might no longer function. In the worst-case scenario, that improper assembly might not be noticed until the end-user needs the product and could result in death or injury.
Even in a less serious situation, the team has spent precious resources just to produce a defect. That initial miss while reviewing the design for manufacturing hurts quality, risk, and cost.
These problems tend to emerge only after design transfer. They more likely reveal themselves during manufacturing. By then the cost to fix them has already escalated. Detecting and addressing these risks during design for manufacturing presents the best-case scenario. An example illustrates the point.
A diagnostics customer had designed a nine-component custom housing for a lateral flow test. A bottom housing used pins to form a compression fit with the top housing. If the parts were rotated 180̊ , they risked joining or seeming to join one another. If this were to happen, the final product would not work.
The client wanted to plan for annual production in the millions of devices, so assembly automation would prove critical. Initial parts would be manually assembled. The program would develop the automated assembly in parallel. Manual assembly would introduce human error risk. Automated assembly would allow for more consistency if potential errors have been identified and addressed during design for manufacturing.
Communication risks played a factor. The client used separate sources for the industrial design, component manufacture, and assembly. Collaborating on the design for manufacturing across vendors proved critical for the long-term success of the program.
The team considered altering the design for manufacturing to make detection of misaligned components easier. However, adding an inspection check to make sure the parts were not misaligned would still waste resources on scrap or rework.
Whenever possible, allowing for the misalignment so the product could still function would simplify the manufacturing process. In this case, the components would only work in one orientation.
Instead, the team focused on not allowing the misalignment in the first place. To improve the readiness of the design for manufacturing the team wanted to make correct alignment easier prior to assembly.
The team updated the design to misalign the pins in an asymmetrical orientation. This meant the two components would not achieve a compression fit when rotated incorrectly.
The two parts could still press fully against one another. The pins just would not engage with the pin holes. Instead they would float in space. A human operator might know the parts did not engage, but an automated machine might not. Sure, the components would fall apart because they lack any true joining, but on an automated assembly line that would not be obvious.
The designers heightened ribs on the bottom housing to rise above the plane of the lip that met the top housing. These high ribs provided enough interference to keep the two parts at a distance. Another solution would be to create additional interference features that press against the pins during misalignment. This prevented the two parts from fully meeting.
When the two parts misaligned relative to each other, the two parts could not meet, close, or shut. This ensured that any attempt to assemble the two parts in the wrong orientation will fail in an easily detectable method. Your design for assembly goal is to make the correct alignment of components relative to one another as easy as possible and to make misalignment as difficult and as obvious as possible.
Budgeting the resources to envision improper assembly during design for manufacturing saves valuable resources during new product development. Not every potential manufacturing error can be remembered during the design process. Using a checklist provides a practical means to conduct a thorough design for manufacturing. Ultimately, you want to move into production knowing you have a solid design for manufacturing and for assembly of the final product.
For a free preliminary review of your design for manufacturing readiness, schedule time with a Natech engineer.