Recently a major medical device manufacturer was getting some discouraging feedback from surgeons-their surgical scissors were difficult to control. It seems the screw and small nut used in the hinge mechanism, although secure and reliable, was either too loose or too tight to allow pinpoint operation accuracy.
Endoscopy surgical scissors need a consistent "feel" so that opening and closing of the blades is sensed the same way every time. It was evident to the surgeons during delicate procedures that although they visually positioned the scissors and cut by sight, of equal and critical importance was the minimal friction experienced when adjusting the blades.
In an effort to make medical surgical operations go smoother the scissor manufacturing engineers sought out a new method to fasten and assemble the blades together. With help from the Orbitform Group's Application Lab engineers all aspects of the scissor making processes were carefully analyzed.
Screws: Even with the most precise methods of process control the screw and nuts weren't holding with a consistent tension, because of small thickness variations within the blade halves.
Riveting: Since the blades needed to be "firm yet flexible" simply riveting them together to an exact stop point was not an option as this wouldn't allow for needed flexibility.
Orbital Forming: The Orbitform Applications Lab Engineers determined the best way was to orbitally form the scissor parts to a clamp load which eliminated the part variations as a factor.
Key to Success, Process Intelligence
By utilizing multiple load cells on an Orbitform Model 125 benchtop orbital forming machine, a form-to-force process control solution was created which allowed the torque on the scissor joint to correspond to a pre-determined load, thus eliminating part size as a quality factor.
This unique orbital forming machine used a specially designed spindle, slide, and servo motor arrangement. This provided very accurate control of the .058 inch diameter pivot joints and permitted the forming machine to dwell at a position instead of a positive stop. Most importantly, extensive testing by the scissor manufacturing engineers verified that each pair of medical scissors was able to repeat the opening and closing well within the desired force range.
The new orbital work station featured Watchdawg process control digital readouts for orbital and anvil positioning and exact force monitoring. Also, a custom fixture for positioning the assembly helped increase the throughput and decrease the fastening time.
Orbitform's Applications Lab and Orbital Product Team brought this project from analysis to solution within budget and ahead of schedule. The resulting application specific machine is now running these surgical scissors 24/7. And thankfully for surgeons, and their patients, the cuts have never been better.
The Orbitform Group includes Orbitform, Milford, Adtech, Marathon Weld, Arbor Automation, Rollerform, and Watchdawg Process Intelligence.
For further information please call 517-787-9447 or visit www.orbitform.com.