Know Your Metals: How to Machine Titanium
Machining best practices look very different from one material to the next. Titanium is notorious in this industry as a high maintenance metal. In this article, we’ll cover the challenges of working with titanium and offer valuable tips and resources to overcome them. If you work with titanium or are interested in doing so, make your life easier and familiarize yourself with the characteristics of this alloy. Each element of the machining process should be analyzed and optimized when working with titanium, or the final result could be compromised.
Why is titanium becoming more and more popular?
Titanium is a hot commodity due to its low density, high strength, and resistance to corrosion.
- Titanium is 2x as strong as aluminum: For high-stress applications that require strong metals, titanium answers those needs. Although frequently compared to steel, titanium is 30% stronger and almost 50% lighter.
- Naturally resistant to corrosion: When titanium is exposed to oxygen, it develops a protective layer of oxide that works against corrosion.
- High melting point: Titanium must reach 3,034 degrees Fahrenheit to melt. For reference, aluminum melts at 1,221 degrees Fahrenheit and Tungsten’s melting point is at a whopping 6,192 degrees Fahrenheit.
- Connects well with bone: The key quality that makes this metal so great for medical implants.
Titanium centric industries
- Aerospace: The #1 market for titanium parts. Jet engines, airframe components and spacecrafts are the leading dependents of titanium components. Resistance to corrosion, ability to withstand high temperatures and its light weight make titanium the perfect metal for aerospace manufacturing.
- Automotive: Mostly used for engine valves, exhaust systems and suspension springs. Using titanium components in automotive applications can lead to increased horsepower and torque and improved fuel economy. And believe it or not, titanium reduces the material weight so significantly that industrial markets can actually make advances in production technology with steep cost reductions.
- Medical: As mentioned above, titanium has the unique ability to bind with not only bone but with living tissue as well. That makes it the ideal material for orthopedic implants.
- Shipbuilding: It wasn’t until the 1960s – when the cost of titanium significantly dropped – that the alloy became an option for manufacturing ships and submarines. Titanium is able to resist corrosion even from sea water.
Fun facts about titanium
- It doesn’t occur naturally: Titanium is found in minerals. After the minerals are harvested, then titanium can be extracted.
- Only 0.57% of Earth’s crust is titanium: Though it is the ninth most abundant element in the Earth’s crust, titanium is still quite rare. That’s why it is so expensive to harvest in comparison to other metals.
Challenges of working with titanium
Despite the benefits of titanium, there are some valid reasons that manufacturers turn away from working with titanium. For example, titanium is a poor heat conductor. This means that it creates more heat than other metals during machining applications. Here are a couple things that can happen:
- With titanium, very little of the generated heat is able to eject with the chip. Instead, that heat goes into the cutting tool. Exposing the cutting edge to high temperatures in combination with high pressure cutting can cause the titanium to smear (weld itself onto the insert). This results in premature tool wear.
- Due to the stickiness of the alloy, long chips are commonly formed during turning and drilling applications. Those chips easily become entangled, thus impeding the application and damaging the surface of the part or in a worst-case scenario, stopping the machine altogether.
Some of the properties that make titanium such a challenging metal to work with are the same very reasons the material is so desirable. Here are some practical tips to make sure your titanium applications run smoothly and successfully.
5 tips to increase your productivity when machining titanium
1. Enter titanium with an “arc in”: With other materials, it’s OK to directly feed into the stock. Not with titanium. You have to glide in softly and in order to do this, you will need to create a tool path that arcs the tool into the material as opposed to entering via a straight line. This arc allows for a gradual increase in cutting force.
2. End on a chamfer edge: Avoiding abrupt stops are key. Creating a chamfer edge before running the application is a preventative measure you can take that will allow the transition to stop to be less sudden. This will allow the tool to gradually decline in its radial depth of cut.
3. Optimize axial cuts: There are a couple things you can do to improve your axial cuts.
- Oxidation and chemical reaction can occur at the depth of cut. This is dangerous because this damaged area can result in work hardening and damage the part. This can be prevented by safeguarding the tool which can be done by changing the axial depth of cut for each pass. By doing this, the problem area is distributed to different points along the flute.
- It is common for deflection of pocket walls to occur. Instead of milling these walls to the entire wall depth with just one pass of an end mill, mill these walls in axial stages. Each step of the axial cut should not be greater than eight times the thickness of the wall that was just milled. Keep these increments at an 8:1 ratio. If the wall is 0.1-inches-thick, the axial depth of cut should be no more than 0.8 inches. Simply take lighter passes until the walls are machined down to their final dimension.
4. Use generous amounts of coolant: This will help carry the heat away from the cutting tool and wash away chips to help reduce cutting forces.
5. Low cutting speed and high feed rate: Since temperature is not affected by feed rate nearly as much as it is by speed, you should maintain the highest feed rates consistent with your machining best practices. The tool tip is more affected by cutting than any other variable. For example, increasing the SFPM with carbide tools from 20 to 150 will change the temperature from 800 to 1700 degrees Fahrenheit.
If you’re interested in further tips regarding machining titanium, check out this article from Modern Machine Shop here: 10 Tips for Titanium.
Here’s a list of books and guides that can help you dive deeper into all things titanium.
A must-have for anyone who works with titanium. Consider this book the official titanium manual. Expect many different examples to help you understand the covered topics.
In this book, you’ll learn about the recent advancements in the machining of titanium alloys. It includes explicit solutions to enhance the machinability of titanium-based alloys to help you deal with those qualities that make titanium difficult to work with.
This book discusses the challenges that are presented when cutting materials with superior mechanical and chemical characteristics, like titanium. The author offers guidance on the appropriate cutting tools to use with titanium.
This 2nd edition text by Matthew J. Donachie is a complete introduction to titanium alloys. This book is recommended for any level of experience and offers both technical information along with an executive summary on the different uses of titanium.
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