A proprietary process that stamps tubing on a progressive die allows adding features such as slots and holes at no additional cost. “We got the idea when a medical manufacturer asked us to develop a cost-effective, disposable cauterizing device for minimally invasive surgeries,” says Frank Jankoski, director of technical services, Micro Medical Technologies, Somerset, N.J., (micromedicaltech.com).

Jankoski says companies typically purchase pieces of drawn metal tubing at a cost of about $1.50 each, and then perform several secondary operations to add additional features. The problem: every time an operator handles a part, it tacks on about $0.30 to the part's cost.

The rolled tubing process, in contrast, feeds a coil of flat, stainless-steel stock 17-in. wide and 0.022-in. thick into a progressive die on a conventional stamping press. Stations in the die then progressively form or roll the 0.2-in. diameter tube. Each quadrant of the diameter is formed at a different station.

“Adding features costs no extra just by nature of the process,” says Jankoski. “For example, it's the same price to stamp one or ten holes in a part. Our process lets us take what was a $5.00 part and make it for $1.00. The number of features we can add is only limited by the space in the press. Up to 20 features are currently possible.”

Jankoski says the company recently developed a new flat feature. “Many endoscopic instruments are rotating, meaning surgeons can spin them around 360°. The surgeon grips a handle and then twirls a knob on the instrument to rotate it,” he says. “Drawn tubing would require pinching tube sides together in a secondary operation that costs about $0.50 per piece. The rolled-tube method, on the other hand, adds the identical feature at no addition cost.”

Jankowski says a transition feature is in development. “Many endoscopic instruments have plastic handles that surgeons like because it fits their hands well,” he says. “But there is always a push for smaller instruments that make the smallest possible openings in the body. A problem is that smaller tools are difficult to attach to plastic handles. To address this problem, we are producing tubing that has a 0.219-in. diameter and a cone or transition to a 0.309-in. diameter, and then, an inch further down, another larger diameter. These transitions allow keeping the plastic handles while making it easy to attach to smaller instruments.”

A straight tube is also in development. “Occasionally, straightness is critical. For instance, friction can be a problem when one tube slides inside another. We are testing straightening tubes in the stamping die. Another idea is to slightly bow the tubing a certain amount in the die and let later laser welding compensate. This would work because welding adds stress to only one side of the tube and operations can be engineered to bend the opposite direction from the initial bow.”

The company recently added in-house YAG laser welding for jobs that require airtight seams. “In most endoscopic surgeries, the body cavity is inflated with CO₂ so surgeons have room to work. So a body cavity is under a little pressure, which tends to push bodily fluids up the instrument tubing or shaft. To prevent leakage, we place a 0.020-in.-wide weld along the length of the tubing seam,” says Jankoski.