We do a lot of nitinol projects here at Modern Grinding. If there is one material which keeps me up at night and gives me grey hairs, it is grinding nitinol. The biggest difficulty is the abrasive nature of nitinol. It can kill a standard grinding wheel in a single pass. We recently had a part which was one inch long and .024″ in diameter and it ended up taking us an entire day to complete 7 pieces in spec.
If you are building a medical device using nitinol here are some considerations that you should make.
Outside Diameter Vs. Minor Diameter
In order to grind nitinol, we start with a single wire and grind away material. If your outer diameter is .125″ and your minor diameter is .050″, your manufacturer is going to be in a world of hurt. Removing that amount of material is going to hurt any profile that is dressed into the grinding wheel. If you have a large difference between your outside diameter and your inner diameter, and if there are secondary ways to fabricate the wire after grinding the wire look into these while also talking to your grinder.
If you have room to increase your thread diameter tolerance, let the manufacturer know this. The most difficult dimension to keep is going to be your minor diameter of your thread.
Standard Nitinol Sizes
Nitinol is much more expensive than stainless steel. Commonly wire manufacturers won’t stock uncommon nitinol sizes. Check with your manufacturer if they have a size close to what you have designed if you have room to play with on your wire. This comes into play during nitinol prototype phase. If you need small quantities of an off size wire it can be costly. The manufacturer will need to order raw materials and the minimum purchase cost may be a lot more wire than your product requires
Not trying to scare anyone, we welcome any and all nitinol grinding challenges and we will try to provide the most competitive pricing on any and all projects.