Artificial Heart Valves

These are heart rings that have been used as a prosthetic and also as the valves in an artificial heart.

This part also presented Grindley with some unique challenges.

This part is made from a material that is very similar to stellite. It is very hard and abrasive. When the customer first came to us they needed to have a ring made of this material. They wanted to have a full radius formed on the ID of the part and a groove with edges having a full radius. (Much like the ring that you see to the left.) In the Mid-70’s, when we were making this part, there was nothing commercially available to cut this material. The first step that we did was to make our own drills. We would slot a piece of steel and silver solder a piece of carbide into it. The carbide would be ground to give us our drill. We tried to drill it on our Wadell chucker, a hydraulically driven machine, but the material was so tough that we couldn’t get enough feed to prevent work hardening. It was then that we put it on a #2 Brown & Sharpe automatic with hardened cams that we were able to push through the material. It worked very well. We formed the ID with a form tool and the first challenge was overcome. The customer then asked us if we could make the center strut an integral part of the ring. This obviously required us the rethink the way we were making the part. After doing some research it was decided that we could use Electro Chemical Machining (ECM). We had neither equipment nor expertise, but that didn’t stop us. The machine that we procured was a huge machine that took up about ¼ of our building. Bob then set about designing the tooling for this new venture. After several tries we were able to successfully form the strut as an integral part of the ring. We also designed and built tooling to form the ID radius. Because of its size, the ECM machine was difficult to work with such a relatively small part. Not to mention that it was taking up a lot of real estate to make such a small part. So Bob set about to design a much smaller ECM that would do all that we needed. He designed a small vertical (the first ECM machine was horizontal) machine that was easier to use and had better electrolyte flow. With all of that accomplished the customer asked us for one more modification. They wanted the strut AND the hook to be integral to the ring. Again this required us the rethink the way we manufactured the part. But this modification required a little bit more innovation. There were dimensions that we just could not machine with our existing equipment. So Bob went back to his drafting board to design and build special machines that would fabricate the underside of the hook and the top of the strut. As you can see the efforts were successful. With all of the innovation to make the ID of the ring the apparently simple OD profile also required some attention. When we first approached the problem we thought that we could cut it with a form tool. There are some radii that would be difficult to hold otherwise. But we couldn’t get the finish that was required. We thought that we would use the best of both worlds. Using a crush grinding wheel to grind the OD we were able to easily  regulate the small radii that were required.