Meeting Invar 36 Machinability Challenges

Engineers and product designers prize Invar 36 because of its ability to maintain its size and shape over a wide range of temperatures. This makes it a very useful and common material in a variety of engineered products ranging from watch parts to satellites.

If you want to learn more, please visit our website INvar Material.

However, Invar is a tricky material to work with. It can be very difficult to machine and requires special considerations to avoid problems. In this article, we&#;ll discuss Invar 36 machinability challenges and some methods for overcoming them.

What Is Invar 36?

Invar 36 is an iron-nickel alloy containing 36% nickel. This composition is optimized to have an exceptionally low coefficient of thermal expansion&#;one-tenth that of carbon steel at temperatures up to 400°F. This means it doesn&#;t expand or shrink at extreme temperatures nearly as much as other metals do. Invar 36 is also a low-expansion alloy.

Because it&#;s so resistant to thermal expansion, Invar 36 is commonly used for applications that demand high dimensional stability under temperature variation. For example, radio and electronic devices, aircraft controls, optical systems, surveying tape, and clockwork components are resistant to thermal expansion.

Invar 36 Machinability Challenges

Although it looks and feels similar to carbon steel, Invar 36 alloy is much more difficult to machine. It is soft and very ductile, especially in the annealed condition. This can make Invar 36 machinability a challenge.

Cutting tools tend to plow into the material instead of cutting it cleanly. Because of this, Invar 36 produces stringy, gummy chips that tend to &#;bird nest&#; around the cutting tool, interfering with cutting and coolant flow.

Like other nickel alloys, Invar is susceptible to work hardening. Work hardening occurs when the surface of the metal ahead of the cutting tool plastically deforms, forming a hardened layer that is very difficult to penetrate in subsequent passes or operations. This can lead to poor surface finish, part deformation, and broken tools.

Tips for Machining Invar 36

Though it&#;s a challenging material to cut, there are ways to improve Invar 36 machinability, including the following best practices.

Getting good results when milling Invar requires a careful balance of tool diameter, number of teeth, cutting speed, feed, and chip space. Machine power, condition, and setup are also very important to reduce chatter and prevent work hardening.

The gummy chips Invar produces can interfere with the cutting tool if too much accumulates. Use a chip breaker and ensure your tooling is sharp and rigidly supported when machining Invar. High-speed steel and carbide tools both work well on Invar, though with carbide tools, it is important to use a powerful machine and a rigid setup to minimize vibration. Helical tools resist chatter and will generally provide the best surface finish. Descaling the surface before machining can make machining significantly easier.

Prevent work hardening by keeping the tool moving and minimizing heat. Maintain a positive feed rate and avoid dwelling so heat doesn&#;t build up in one area. Machining Invar requires higher feeds and lower speeds than other metals. Ensure you have adequate lubrication volume and pressure to keep the cutting surface cool. When turning Invar 36, use the largest tool possible to provide a large heat sink.

Finally, machining Invar introduces stresses that can change the thermal expansion behavior of the finished product. It may need to be annealed after machining to relieve these stresses and ensure dimensional stability.

We Supply Invar 36 to Machinists and Fabricators

For over two decades,

Industrial Metal Service

has been supplying Invar 36 and other specialty metals to manufacturers, machinists, and fabricators in the San Francisco Bay Area and nationwide. We sell various forms of new and verified remnant metals, including Invar, steel, aluminum, titanium, and

high-temperature alloys

If you are looking for more details, kindly visit Soft Magnetic Alloy.

. Our metal remnants are

verified using x-ray fluorescence analyzers

to ensure our customers know the quality of the metal they&#;re receiving.

Invar 36[1], also known within the industry as Nilo 36[2], is a nickel-iron superalloy known for its low coefficient of thermal expansion. Containing 36% nickel, it maintains nearly constant dimensions as well as good strength and hardness over a wide range of temperatures. Invented in by Swiss physicist, Charles Edouard Guillaume, Invar was created as a low-cost solution to a meter once made of platinum and iridium. Guillaume&#;s work led to the discovery of a fairly inexpensive iron-nickel alloy&#;a steel-like material&#;that expands very little when heated. He named the alloy Invar because it was almost unchanging or "invariable.&#;

Invar 

[3]

 is typically machined, but what many people don&#;t know is that it can be cast. 

Invar 36 Success

One of our customers came to us specifically wanting to use INVAR 36 for a component requiring the near constant dimensions and long-term dimensional stability this alloy is known for. Due to confidentially agreements, we cannot name the customer but what we can tell you, is that like with many other projects, Signicast engineers rose to the challenge to not only cast Invar 36 successfully but completely exceeded the customers&#; expectations&#;all while saving them money. Because after all, isn&#;t that the end goal? Create a quality component at the lowest total cost. 

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Why did our customer need Invar 36? The slightest change in dimension or shape of their component could alter their end product&#;even though they were already in a temperature controlled room. A few degrees could alter the function of the part. They knew they needed to work with a material like Invar 36 but machining it from solid became costly.

How did Signicast help? We had never worked with Invar 36 in the past, but there has never been a challenge our engineers didn&#;t at least try to overcome. With some research and testing we came up with a casting material that actually performed as good or better than wrought and we were able to cast net-shape successfully. Not only did we add savings on final part cost because they didn&#;t have to machine the part, but our final part cost was actually cheaper than their original block of metal&#;prior to machining.

The end result? A very happy customer who saved tenfold and a new material added to our offerings.  

Invar 36 maintains nearly constant dimensions at temperatures below -150 degrees Celsius up to 260 degrees Celsius.

Who Should Use Invar 36?

Customers who are under strict temperature constraints will likely see the advantages of using Invar 36. Unfortunately, those who are currently machining from solid do not realize that casting net-shape is even an option. In today&#;s world, Invar 36 is often used in measuring devices, precision mechanical systems, laser components, thermostat rods, meters and components that transport liquefied gases&#;to name a few.

Invar Industry Applications

Invar can be used in a variety of applications within the aerospace, medical, and consumer electronics industries. But where superalloys with low CTE are really starting to outperform other metals is in technologies within the automotive industry. As autonomous vehicles rise in popularity, sensors, radars, and cameras become increasingly advanced and critical to the function of the car. LiDAR, an acronym for light detection and ranging, uses light waves from a laser to calculate how long it takes for the light to hit an object or surface and reflect back to the scanner&#;determining the distance of surrounding objects. An alloy with near constant dimensions and long-term dimensional stability, such as Invar 36, is extremely important in such intricate devices. Alternative alloys, like Kovar, with low CTE are also viable options for casting LiDAR sensors. Investment casting is a cost-effective solution compared to machining LiDAR parts from solid.

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