19×19 0.5mm tungsten cable with plasma-welded ends [Photo courtesy Carl Stahl Sava Industries]
Tungsten cable is the perfect strength, flexibility, and diameter for surgical robots.
Connor Chiuchiolo and Scott Dailey, Carl Stahl Sava Industries
When manufacturing tungsten mechanical cable for surgical robotics, the tungsten itself presents enormous mechanical upside, including extraordinary tensile strength captured within astonishingly small diameters.
What’s more, tungsten stranded into ultrafine mechanical cable possesses a remarkable malleability unseen in stainless steel alternatives.
Combined, tungsten’s strength and flexibility make it the material of choice for surgical robot makers. But tungsten (also called wolfram) is brittle as a pure metal, which makes it a challenging material for cable design engineers to work with.
Take, for instance, a 19×19 tungsten cable comprising 361 wires. Imagine the cable design engineer solved a bird caging issue that emerged on each side of a pressed ball fitting. In this case, an industrial press applied too much pressure to the fitting, which subsequently crushed, separated or even severed the brittle filaments of the cable’s strand. while the fitting would hold to the cable, the overage of pressure applied to the fitting damaged the assembly’s strength, durability and perhaps even shortened its length.
A typical hazard present in the manufacture of tungsten cable is that solving one challenge often presents others. Experienced tungsten cable design engineers expect such eventualities and prepare for them.
If bird caging issues emerge as a result of an industrial press applying too much force to mating fittings, tensile strength and even the length of the cable could be compromised. So when such unwanted damage to the cable filaments is resolved, it cannot be at the expense of other qualities inherent in tungsten cable. Thus, cable design engineers must continue altering manufacturing processes until all issues are eliminated.
Because the fittings used to manufacture tungsten cable assemblies are not worlds apart from those used to serve other markets, experienced cable design engineers producing tungsten surgical robotics cable draw on decades of experience mating temperamental alloys with components like a ball, until the perfect and delicate balance of strength, longevity and geometry are perfected. Thus, applying requisite pressure to the ball fitting is an exercise in formulaically altering the characteristics and settings of the cable and respectively, the machinery producing it.
The right study of pressure, dimensional tolerances, and the often miniscule adjustments to poundage ensure unharmed tungsten strands, as well as an attached ball fitting that satisfies strength ratings and meets lifecycle testing expectations.
Tungsten cable is behaviorally limp, as shown in this 7×37 0.021in. tungsten cable. [Photo courtesy Carl Stahl Sava Industries]
Lean cable manufacturing practices
Reducing the number of variations in the manufacturing process is one of the chief ways tungsten cable design engineers mitigate the risk that one solved manufacturing problem introduces another. As simple as it may seem, reducing handling is among the easiest ways to reduce variation.
But how does a cable design engineer create sophisticated cables that help a surgical robot reduce hospital stays and complications, if they’re avoiding handling the cable while producing it? The answer is simple: engineers must produce lean manufacturing processes that limit the frequency and degree of tungsten cable handling during production.
As discussed, tungsten cable possesses incredible strength once installed in a surgical robot. Yet for all of wolfram’s tensile benefits, taken outside its application environment, tungsten mechanical cable is highly susceptible to damage when handled. Simply running one’s thumb and index fingers along its length can cause immediate separation of the filaments and render the cable assembly useless.
The helical filaments of tungsten cable are so easily separated that even excessive handling from a manufacturing cell to packaging and ultimately to shipping can cause irreversible damage to these sophisticated assemblies.
For these reasons, tungsten cable for surgical robotics must be handled no more or less than is absolutely necessary to produce the assembly itself. What’s more, even the packaging, shipping and delivery of tungsten cables must undergo as little stress as possible.
Engineers experienced in the manufacture of tungsten cable must therefore also ensure lean manufacturing processes account for the transportation of the completed product at a mass scale between production departments, as well as couriers and other potentially harmful touch points.
Tungsten cable is the right material for a complex job
As a mechanical cable material, tungsten is a niche solution. While it has a long history of supporting the crystal-growing industry due to its natural tolerance to high temperatures, it has few other practical mechanical cable applications today.
Supporting the pitch and yaw functionality of an explosive surgical robot market has quickly made tungsten the go-to alloy for the industry today. But its unique and unparalleled benefits as an actuator of motion in tight spaces are also related to its manufacturing and engineering challenges.
This paradoxical material therefore represents an elegant, reliable and impressive solution to surgical robotics designers, while representing a groundbreaking wealth of manufacturing achievements that make tungsten cable the rarified engineering wonder for which is it deserves to be known.
This article was written by Carl Stahl Sava Industries Associate Design Engineer Connor Chiuchiolo and VP of Marketing Scott Dailey. For more information about Riverdale, New Jersey-based Carl Stahl Sava Industries, visit www.savacable.com.
The opinions expressed in this blog post are the author’s only and do not necessarily reflect those of MedicalDesignandOutsourcing.com or its employees.
