Engineering Insight

The jaw housing of the Aragon Surgical laparoscopic device.

The jaw housing is one of the most expensive parts of a laparoscopic surgical instrument developed by Aragon Surgical (Palo Alto, CA, USA; www.aragonsurgical.com). Consequently, it was a tempting target in a cost-reduction exercise spearheaded by Connecticut Spring & Stamping (CSS; Farmington, CT, USA; www.ctspring.com). Fully machining the part was driving up production costs, but Aragon Surgical did not think it had any alternatives: the part had to be produced in a specific circular shape to function properly.

During an initial contact with Aragon Surgical, CSS engineers began brainstorming efficient ways in which the housing might be stamped instead of machined from solid material. CSS has extensive metal stamping expertise in the medical device arena, which includes prototyping and high-speed progressive die stamping, in-die tapping, reel-to-reel processes, modular systems and short run stamping. The engineers applied these skills to the puzzle at hand.

Door of perception
The solution came in the form of a lock barrel made by CSS for a high-end commercial door lock. The barrel was similar in many ways to the jaw housing. When CSS showed the part to Brandon Loudermilk, Aragon Surgical’s Senior Research and Development Engineer, and explained how it was manufactured, he started considering the option to stamp the part.

“Aragon Surgical became interested in it from a cost standpoint. Like any company, they are under tremendous pressure to lower costs. There is only so much you can do with machinining. This was a complete change,” says Lou Morelli, Tooling Engineer at CSS. By stamping the part, time and labour were slashed, thus dramatically reducing cost. The tooling costs were significant, but the high per-part savings offset the investment.

According to Steve Dicke, Vice President of sales and marketing, machining produces 10 pieces an hour, whereas the initial stamping of the part produces 4000 pieces an hour.

CSS engineers went over the Aragon Surgical part print with a fine-toothed comb, adjusting the 3-D CAD model and marking up the original drawing with their ideas. The groups discussed the tight dimensions and stepped through each feature to see if they could hold the tolerances. They determined the critical features of the mating parts, studied their interaction and discussed how the features could be machined out.

Stamping the part
“We worked with them to come up with a part. We redrew the part for them,” says Morelli. “There was some give and take in the process . . . some tolerances that we could hold, and some others that we couldn’t,” he explains, adding that all required tolerances were held.

Ultimately, consensus was reached and CSS began to work on production tooling.

A unique rotary head is required to mill the portion of the stamped part that is machined to achieve a particular surface finish and accuracy after it has been stamped. When the part was fully machined from solid material, it was held to a tolerance of ±0.001 in. By stamping the part, a tolerance of ±0.002 in. can be attained. Even though the tolerance is higher, the part is fully functional in the design at significant savings. “It has all the same specifications,” says Morelli. “It didn’t have any loss of torque.”

A startup company, Aragon Surgical is conservative with its capital, and the two companies ultimately agreed to amortise tooling costs. The initial run was about 20 to 30% cheaper than the machined version; after tooling costs, the new stamped jaw housing is 50 to 60% less expensive to manufacture and yet fulfills all the design specifications.