Tubes for orthopedic applications have to be much “beefier” than those for minimally invasive surgery (MIS) or laparoscopic applications, explains Todd Oehlerking, vice president, sales & marketing for Accu-Tube LLC. “They have to withstand the force of drilling, cutting, and driving screws into bone,” he said.
Gun-drilling has been used to produce seamless stainless-steel tubing for devices like drills and reamers, but it presents challenges. “Gun drilling is a slow, costly process with constrained capacity, and it’s notorious for missing delivery dates,” according to a recent Accu-Tube white paper.
Accu-Tube manufactures custom stainless-steel tubing for the medical device industry, and Oehlerking says it’s one of only a handful of suppliers that has in-house centerless grinding capabilities. “This allows us to achieve the tight tolerances needed to prepare tubes for Swiss machining,” he says. “We also offer burr-free cutting to custom lengths.” Its specialty is processing stainless-steel alloys such as 17-7, 304/304L, and 316/316L.
When Accu-Tube acquired Mercury Tube in February 2020, it gained expertise in manufacturing thick-wall, large-diameter stainless-steel tubing. Coupled with Accu-Tube’s expertise in 17-7 stainless steel, the newly combined operation was able to begin welding and drawing tubing with the strength of 17-4 at a much lower fabrication cost, Oehlerking explained. “Welded-and-drawn tubing has been around for decades and is the most popular type of tubing used in medical device manufacturing,” he said.
“Our acquisition of Mercury Tube—known for supplying stainless-steel tubing for the industrial, aerospace, medical, and thermal management markets—gave us access to larger equipment that enabled us to manufacture tubing with thicker walls and larger outer diameters (ODs) than traditional medical device tubing manufacturers,” he continued. “We use 17-7 stainless steel, a strong and cost-effective material that, in its heat-treated condition, can equal the performance of the popular 17-4 stainless steel. We can now achieve wall thicknesses up to 0.100 inches.”
For comparison, “a thick wall in the MIS world is 0.020-0.035 inch,” Oehlerking said. “That’s just a starting point for ortho because they need thicker walls to withstand the machining needed for high-force applications like drilling and cutting. What’s unique about this tubing is that we’re pushing limits of OD-to-wall ratio to make a much thicker wall in a smaller tube. For example, we can provide 12-foot lengths with an inner diameter (ID) down to 0.049 inch, or half of what some others can.”
There’s a lot of data available to support use of the new tubing because 17-7 is a widely used material in medical device applications, he added. “Testing is highly application specific, so customers would need to determine what testing they need based on their end use. Accu-Tube is open to supporting any testing required,” he said.
In addition, Oehlerking said that the cost savings realized with this tubing would allow customers to evaluate the possibility of transitioning from reusable instrumentation to single-use instrumentation.
Three sizes of the new tubing will be available this fall on Chamfr.com:
- 0.250 x 0.134 in.
- 0.315 x 0.214 in.
- 0.1875 x .049 in.
Accu-Tube expects its efforts to result in much more than just thick-wall tubing in a novel material. “By investing considerable resources, we’ve made a technological leap in developing a process to make thicker walls in smaller tubes. We’re pushing the boundaries of what OD-to-wall ratios are possible to manufacture,” Oehlerking said. “This tubing will become a new tool in the R&D engineer’s toolbox. It’s appropriate for a wide range of orthopedic applications. As we’ve seen with other tubing in the past, innovative engineers will likely dream up ways of using this tubing that we haven’t even thought of.”