Lessons Learned in Converting Machined Parts to Stamped Parts
During the process of converting fully machined parts to stamped parts with machined features, the lessons learned by medical device manufacturers Aragon Surgical and Avantis Medical Systems and firearms manufacturer Smith & Wesson show how each step plays an important role in moving a part from concept to completion at the blazing speeds now considered normal at Connecticut Spring & Stamping.
Posted: July 25, 2012
One interesting aspect of the early conversations was that CSS engineers showed Aragon another piece they make, a lock barrel for a high end commercial door lock that was similar in many ways to the jaw housing. “When I saw how they could produce that part, how round it was and how good the finish was, it made me consider talking to them more about stamping this part.”
Once they started talking, CSS engineers went over the part print with a fine-toothed comb, adjusting the 3D CAD model and marking up the original drawing with their initial ideas. The groups discussed the tight dimensions, stepping through each feature to see if they could hold the tolerances, looking at the mating parts to see what the critical features were and how the mating parts interacted, discussing which features were critical and agreeing on which other features could be machined out, and how the part would have to be aligned. Many emails, redlined drawings, web meetings later, the agreement was made. And that was just the first phase!
The tooling costs were significant, but the high per part savings made the investment worth it. When the part was made as part of a tube, it was held to a tolerance of plus or minus 1/1000th of an inch. The stamped part is capable of plus or minus 2/1000th of an inch. Even though the tolerance is 1/1000th more, the part is fully functional in the design, at a significant savings.
The startup firm is conservative with its capital, and went through numerous discussions to arrive at an agreement, which included amortizing the tool costs used to stamp the part. “We paid up front for a certain quantity of parts, with the additional cost going towards paying for the tool costs. This enables us to get cheaper parts quickly, without putting out our capital up front. After the initial run was consumed, the tooling comes out of the piece price, making it that much more attractive and profitable.”
Loudermilk estimates that the initial run was 20 to 30 percent cheaper; when the tooling costs come out the new stamped jaw housing is 50 to 60 percent cheaper than the machined version, while still meeting all the design specifications.
PROTOTYPING: IF AT FIRST YOU DON’T SUCCEED, KEEP TRYING
One fact of life in the metal stamping and springs industry is that metal components are often the last to be sourced. Since plastic parts cannot be changed without significant mold costs and very long lead times, stamped metal parts and springs frequently need to adjust to other parts’ restrictions. This makes prototyping a very important part of the design development process.
Is raw material cost a main concern, or is tooling cost the biggest issue? Getting this information up front is essential to develop a prototype or series of prototypes to meet their needs. With a brand new product, enough detail is needed to work out the best material to make a prototype that can be manufactured in a production scenario.
Tony Morefield, director of manufacturing and engineering services for Sunnyvale, CA-based Avantis Medical Systems, used the prototyping phase to great advantage to develop a cost effective spring for a catheter, which is fitted on the end to lock the part into the working channel of a scope. Avantis had experienced quality issues with its original supplier and was looking for a spring that would perform well in the instrument. Spring tolerances were key; there were tight angles Avantis needed to be held for the spring to perform properly. As part of the research and development process for the part, CSS went through about four revisions where they tested slightly different angles and dimensions on the spring.
“Actually, it’s interesting, but at first I didn’t even realize we were prototyping,” says Morefield. “We received feedback from the original drawings that the engineers were not comfortable they could manufacture the part as designed. We revised the drawings live on conference calls and discussed the design to see where we had leeway as far as changing tolerances. This method was great for coming to an agreement quickly on what the next revision would look like.”
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