Introduction: How to Form Memory Wire Nitinol

Memory wire, a.k.a. Nitinol, a.k.a. Muscle Wire, a.k.a. Flexinol, is a nifty metal alloy (mixture) of Nickel (NI) and Titanium (TI). The NOL stands for Naval Ordinance Laboratory, where the memory properties were discovered by William J. Buehler and Fredrick Wang. If you are interested in buying Nitinol or the history and its many uses, check out these links:
http://www.robotshop.com/flexinol-en.html
http://www.musclewires.com
http://en.wikipedia.org/wiki/Nickel_titanium

Step 1: Material List

Read all instructions first!
Materials needed:
Metal tweezers or clamps of some sort
Flame
Water and container
Rod for a spiral, anything else you would need for different shapes
Body heat or battery holder pack
Nitinol wire, ($20 to $30 per meter)

Step 2: Annealing Explination

  Nitinol, the non-brand-specific name, comes in an as-drawn form, which is what a Maker would want, because it allows one to set the memory. As-drawn refers to the drawing (not picture drawing) process, which is how a bar of alloy is continually pulled through reduced sized openings until it is a wire. When I received the Muscle Wire, it was very springy and difficult to bend. This is because the drawing down process presses the atoms in the metal closer and closer together. To make the wire easier to form, it has to be annealed.

  Annealing the wire is the same type of annealing that is used for all other metals, as well as glass. The material is brought to a temperature that allows the atoms to relax and rearrange, but not too hot as to deform or melt. A way to anneal wire is to heat it to a dull red glow along the entire length, and then quench it by putting it into water. It would be a good idea to find a container that will fit your metal, I used a bread pan. It is also possible to anneal the wire while it is looped, although it will try to straighten out at first. It is not necessary to use a pickle, for you jewelry smiths out there, although it would help to clean the wire. I chose not to, simply because I do not have the setup for that.

Step 3: Annealing

I am not responsible for anything that you do with these instructions (including burning down your house or your neighbor’s house), so now that we have that out of the way, I used two large tweezers to hold the wire in front of my flame. I am using a glass melting torch that burns oxygen and propane, but you can use any type of flame, as long as it can get the wire to a dull glow, i.e. propane, acetylene, oxy-acetylene, your gas stove top, etc., etc. Be careful as to not burn yourself, bystanders, things in your kitchen, or melt the wire (Which is pretty easy, remember, only heat up to a dull red glow). Once every section has been brought up to a dull red glow at least for a couple of seconds, quench the entire wire in water to cool it off. You can also quench the ends of the tweezers, as they tend to get hot enough to burn the unwary.

Step 4: Don't Burn Through the Wire!

This is what happens when you get the wire too hot. I now have a shorter wire to work with.

Step 5: Annealed and Bendy

Now the wire is easy to bend, because the atoms have been relaxed. The problem with this is that whatever shape you bend it into, once heated to a lower heat than the flame, it will return to the straight shape. The goal here is to have it return to a shape that you set. Somehow for whatever shape you are trying to set, it has to be able to be held while it is heated to approximately 950 degrees.

Step 6: Wrap Wire

To make a spring, I wrapped the wire around a small metal rod. I have used brass and tungsten, steel should be fine, but aluminum has such a low melting point that it would probably be a bad idea. I used small clamps to hold the wire onto the rod. Be aware that the wire will try to straighten on you in the lower heat ranges. Try using steel needles in a kiln brick to wrap the wire around if you want to make a different shape or words. Just remember to clamp the ends so the wire can't escape. It may be possible to bend the section and hold the bend while you heat/cool to set the shape.

Step 7: Set Spring Shape

Heat the wire in the shape that you have bent and clamped it into. Quench it before handling. I do not know if it is necessary to quench while it is still very hot, but since I am impatient and do not feel like waiting 5+ minutes for it to cool down enough to handle, that is what I do. Although it looks like I am torching the handles on the clips, they are not actually in the flame. My flame is set very low with minimal oxygen to make it easier to not burn the wire up. I would use pure propane, but it is a dirty gas and will clog the ports on my burner, not to  mention getting soot all over.

Step 8: Set Shape

Your wire is now set to your shape, and still soft enough to easily bend. Bend it, mash it, etc. into a different shape. You can apply heat with your hands or use hot water to get it to move back to your set shape. Or you can use electricity to heat the wire up until it moves. The resistance of the wire to the electricity causes it to heat up. Do this with a battery holder and two alligator clip leads. I used a 4 AA battery holder, which provided 6 volts (1.5volts per battery x 4 batteries). You can also use a 9 volt battery. Either way, don't leave it connected too long, or it will reset your hard earned efforts, and possibly burn out the Nitinol. Connect one wire to one side of the wire, and connect the other live wire to the other side of the Nitinol wire. It will spark and get hot, but it will also move back into your shape. It would probably be a good idea to attach this setup to a resistor and a momentary switch (button) to close the circuit till you release the button (momentary part).

In these 3 pictures, the first is the set shape, second I have stretched it out, and third it has gone back to the set shape (mostly) after slightly heating it.

Step 9: Movie

Step 10: Tips

  If you are using Nitinol for a project where you need it to move something, it can pull some serious weight with the shrinkage of the straight wire. I have read variously 2 to 10 pounds. The wire has to be pulled back long, and if you are using this as a design element, you should buy Flexinol, which has been cycled through the increase/shrink cycle enough times that it will consistently shrink by 10%, which is quite enough to pull a lever to increase the movement potential. A project that I made with the Muscle Wire brand uses a spring to pull the wire back into the stretched out shape before the heat/electricity was applied. Also, the wire will cool slowly once the heat is removed, and will gradually pull back out of the set shape if it is under tension.

Soldering this wire takes a little bit of extra work. Because of the movement of the wire, it will quickly break any solder joins. the wire will first need to be crimped, and then the crimp can be soldered. For more information on that, click on the Makezine blog link in the next section.

  I hope this is helpful to anyone who wishes to experiment with the fascinating properties of Nitinol, and if you have any comments or suggestions, please write them up below. This information is to the best of my knowledge, and some things may be a little hazy or incorrect so helpful input is always appreciated.

Step 11: Helpful Links

Comments

author
AmarnathT2 (author)2016-02-24

https://www.youtube.com/watch?v=FBaIdvgbBAM మాంత్రికులు, బాబాలు చేసే ట్రిక్కులలో ఇది కూడా ఒకటి నైటినాల్ తీగ ను వంచి వేడి నీటిలో వేస్తె అది యదా రూపం సంతరించుకుంటుంది

author
KelloggsResearchLabs (author)2015-01-06

Required heat treatment can vary dramatically based on how they make the wire, diameter and transition temperature of the wire. They vary from supplier to suppliers too. It can be very difficult and frustrating if you don't know the material you purchased.

Check www.KelloggsResearchLabs.com, we can make whatever shape you want for you. If you really want to create your own shape, our raw wire starts from $4.99 per 5 feet.

author

I'm going to give you a try. It could save me from spending $55 at an online magic store for 2" of wire. :)

author
Grafx4Life (author)Grafx4Life2015-09-04

Maybe I should have bought the 5 feet of wire. The $22 I paid for a peice of wire that may function as a paperclip, certainly doesn't look like a paperclip. But nice to have I suppose. Lesson learned. Could have it's uses.

nitinol paperclip.jpg
author
jdillon6 (author)2015-03-12

I always prefer USA based manufacturers because I know what unemployment is like. However Alibaba has a huge variety of "shape memory" type Nitinol at very affordable prices for kilogram bulk material, wire, rods, bars etc. See link at: http://www.alibaba.com/trade/search?fsb=y&IndexArea=product_en&CatId=&SearchText=nitinol%2C+memory+wire+or+bar

author
RobertD6 (author)2014-09-22

"Step 2: Annealing Explination" is misspelled; it should be changed to Explanation.

author
pride156 (author)2014-07-16

You know the transformation can be triggered with electricity too! I guess the internal resistance creates the heat needed to flip phase, but... it can be done that way too $.02

author
KemikalzAreFun (author)2013-05-01

Where would I go about getting the wire I need?

author
adam 101 (author)KemikalzAreFun2013-05-02

click on the links the author left on the intro step

author
pride156 (author)adam 1012014-07-16

Fort Wayne Metals, Memry, NDC, Johnson-Matthey- in that order

author
codeandpixels (author)2014-03-11

Hey, nice Instructable.

I bought some nitinol wire, after contacting them to see if what they sell is comparable to Flexinol and will contract when heated, and they said it would if I train it that way. Unfortunately, "As drawn", it seems to work opposite of what I would like, increasing in length when heated. can find lots of info about training the wire to a shape, but I can't find anything about training it to contract.

Since you mentioned an increase/shrink cycle that is used to make Flexinol, I was wondering if you have any more info about that process.

author
pride156 (author)codeandpixels2014-07-16

"Constrain it—it has to be under load. Then you heat treat it at 500 degrees Celsius and water quench or fast-cool it."

author

From what I remember, the cycling that is used to produce Flexinol is so that the end product stays the same contraction rate instead of getting longer over time. Unfortunately this was quite a while ago, and I no longer have the websites that I got the information from if they are not listed in the Instructable.

author

Thanks! My attempts to train it by heating it (I used a candle flame) and letting it cool several times under tension haven't worked, so I may have to call it a loss and shell out for the pre-trained muscle wire.

author
Phoenix17 (author)2013-05-20

I am not an expert, but quenching is more for tempering or hardening, depending on the initial temperature.

Does this wire have different or unusual properties? in my experience and general knowledge suggests to anneal a metal to make it as plyable as possible, you want to give it the maximum amount of time to cool (ie cool as slowly as possible).

I have made a number of knives in the past and I prefer something like 1080 steel, raised to not quite white hot, then oil quenched until cool; then raise to approximately purple and oil quench again. This hardens and then tempers the worked steel.

author
Doulos3 (author)Phoenix172013-11-30

Nitinol does have some unusual properties. Nitinol can recover to its set shape from 8-10% strain when activated at its transition temperature. In relation to this instructable, Nitinol's transition temperature can also be raised when above about 500 degrees Celsius. At that high of a temperature, the Nitinol recrystallizes and will be "set" into a shape after quenching. So it is a kind of tempering per say. This stuff is pretty cool though, I've seen and heard of this thing being used in artificial arteries, temperature dependent shades, actuators, and even 1 kW motors. Some differences between Nitinol and other SMAs include a lower frequency response and a higher force imparted with Nitinol. It is a pretty cool metal though.

author
Kinnishian (author)2013-05-09

You are annealing it when you heat it and gradually cool, but some of the language seems to ambiguously refer to the quenching as part of the annealing, when it is quite the opposite (the quick cooling forces the atoms into a stressed formation.)

Cool instructable!

author
nicko0 (author)2013-05-06

hey ! your a lamp worker! ? are u using memory wire and glass in jewelry or something?

author
Edgar (author)2013-05-06

Gizmo makers around the World will thank you for this...
Went to my Blog:
http://faz-voce-mesmo.blogspot.pt/2013/05/a-newsletter-da-cncking-e-carradas-de.html

author
Treknology (author)2013-05-05

The temperatures quoted should be double-checked when you order your wire. Activation and Programming temperatures vary depending on the alloy-mix.

If you're able to use strong enough means to shape your wire initially, I also recommend by-passing the annealing steps. As shown, the author ended up with a shorter piece of wire than originally intended so, it should only be considered if really necessary.

author
dfields1 (author)2013-05-02

Nice movie! Elegant the way the wire moves.

author
KemikalzAreFun (author)2013-05-02

oops, must have missed that. Thank you!

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