Machining titanium is not like machining other metals; significant differences make titanium difficult to machine. Despite these difficulties, this metal is gaining popularity for end-use parts.
Different industries such as defense, aerospace, and medical are adopting titanium because it is stronger and lighter in weight than other metals, such as steel. The properties of this metal make it ideal for structural applications, especially for aerial components.
Additionally, various alloys of titanium can be heat-, corrosion-, and creep-resistant. These attributes have led titanium to be used for such critical load-bearing applications as fasteners, disks, and blisks in gas turbines, landing gear, heat exchangers, storage tanks, and so on. Titanium is also biocompatible, enabling its use in medical implants, such as screws, plates, and joints.
The many benefits and applications of titanium make this metal a valuable option for manufacturers, though it is more expensive than some other materials. As usage continues to grow, it’s important for machinists to know how to reliably machine titanium.
Differences and Considerations When Machining Titanium
According to Alex Minich, global product manager and senior applications engineer at Greenleaf Corp., “machinists need to consider the differences between titanium and other metals to achieve sustainable productivity.”
1. Low Thermal Conductivity
One important difference is that titanium has an incredibly low thermal conductivity. “Plasticization in the machining process relies on thermal conductivity, with some of the heat generated in the shear zone transferring to adjacent parts of the workpiece to make the material easier to cut,” Minich explains. “That doesn’t happen with titanium; all of the heat generated through the shear zone stays in the chip and doesn’t get transferred to the workpiece.”
As a result of the low thermal conductivity, the heat in the chip gets transferred to the cutting tool, affecting the efficacy of the tool. This is why it’s important to select the right types of tooling when machining this metal. The only cutting tools capable of working with titanium are tungsten carbide and PCD.
2. Highly Reactive
Another consideration is that titanium is very reactive. It forms very stable bonds with many elements found in cutting tool coatings, causing chemical wear and erosion to the tooling. To avoid this chemical disintegration, Minich recommends using a coating that already contains titanium.
3. Extremely Ductile
Titanium is also extremely ductile. Minich likened machining it to “machining a wet sponge”. “Even if you have a continuous cut, even if you're just turning, it will always have that micro-vibration,” he says. “Through each chip that forms and separates, it'll compress, it'll spring back. So, that places unique demands on the cutting tools.”
To combat this micro-vibration, the machining environment should be extremely rigid and well damped. Additionally, Minich advises machinists to use a strong insert shape, such as an RCMT round insert, to ensure a smoother process when turning titanium-based alloys.
Methods to Extending Tool Life
Due to titanium’s unique properties, wear is generally more aggressive in tooling used to machine it. Even a tool optimized to turn titanium would not last as long machining titanium compared to working with other materials. However, there are methods to help extend tool life.
1. Tool Selection – Pick the Right Coating
Minich stresses how important tool selection is, saying that machinists must choose a grade and coating appropriate for machining titanium. He reiterates that it’s important for the tool’s coating to include titanium, which helps minimize the chemical degeneration caused by machining this metal. A low coefficient of friction is also important for the coating to avoid overheating.
2. Use Ultra High-Pressure Coolant
Cutting tools will reach much higher temperatures when machining titanium compared to other materials. The increased temperature is another reason that these tools wear faster. To combat this, Minich suggests using high-pressure coolant. Appropriately delivered, it helps prevent too much heat from getting trapped and protects tooling from adverse chemical interactions and accelerated mechanical abrasion.
3. Ensure Cutting Edge is Very Sharp
Additional methods to protect the cutting tool during the machining process include ensuring the cutting edge is very sharp to produce higher shear, using a positive insert with flank clearance, and applying a high-feed approach with a high lead angle.
Reliable Processes for Machining Titanium
Machinists need to approach working with titanium differently than they would with any other material. Minich recommends doing some research before turning titanium for the first time. Doing due diligence to understand the right tools and processes to use will help set machinists up for success.
This includes learning how to mitigate tool wear but also noticing as soon as wear starts to develop. With titanium it’s important to measure wear, especially when setting up the tooling for the first time, so machinists can correctly track wear and replace tooling on time.
As wear develops on the cutting tool more heat will be generated. This will in turn cause the insert to wear even faster, disintegrating the coating, and can lead to tool failure.
Another required consideration is the application of coolant. Ultra high-pressure coolants help combat tool wear, but can also help improve cutting conditions, according to Minich. This allows machinists to increase machining speeds significantly, which reduces cycle time.
The “under coolant” method of applying coolant directly at the cutting tool's cutting edge is useful for certain processes when machining titanium. The stream of coolant coming from under the insert helps reduce friction between the flank of the insert and the workpiece. Less friction means less heat, and to reliably machine this metal, machinists must prevent the cutting tool from overheating.
“If you’re trying to machine titanium the way you would steel, your tooling is not going to last. You’ll run the cost of tooling significantly higher than expected,” Minich explains. “So, tool selection, tracking wear, and having the appropriate programming and cutting conditions are all very important to reliably machining this metal.”
As for cutting conditions, Minich advises focusing on achieving the correct speed. Optimizing speed is the most important variable when machining titanium. Then machinists can work on feed and depth of cut.
“You can’t go too fast, because you’ll generate too much heat, causing degradation of the cutting tool,” says Minich. “For the other variables, you benefit more from increasing the feed rather than depth of cut, due to the material’s low thermal conductivity. A high-feed approach limits heat transfer and helps prevent notching.”
The Future of Titanium in Manufacturing
Demands from the aerospace and defense industry have mostly driven the rise in titanium usage for end-use parts. These parts improve product performance and increase efficiency — benefits that will continue to drive demand for this material.
In recent years, manufacturers have made progress in the process of machining titanium. Improvements include an increased ability to formulate titanium-based alloys, advancements in coating technologies, and improved chip form development. “These developments have allowed manufacturers to machine titanium faster and improve tool life,” Minich says.
Minich believes that demand for titanium alloys will stay steady for years to come, with the process continuing to be refined due to the popularity of this material. Titanium has a higher specific strength than other metals and is lightweight, offering improved efficiency when used for aerospace products. Titanium usage is also growing in medical applications, especially as the average age of the population continues to increase.
“Manufacturers are always looking for efficiency gains, no matter the industry,” explains Minich. “So, it’s important for machinists to know all the particulars for successfully working with this metal.”
Manufacturers and machinists looking to learn more about titanium turning and machining setups can explore Greenleaf Corp.’s tooling offerings. And to discover even more innovative manufacturing technologies that can improve your operations, attend a Manufacturing Technology Series event.
Biography
Alex Minich
Global Product Manager & Sr. Applications Engineer
Greenleaf Europe B.V.
Mr. Minich holds an aerospace engineering degree from TU Delft and started his career at Greenleaf as an applications engineer in 2014. He’s since been responsible for sales, technical support, project and product development, and knowledge management. In his current role, Mr. Minich drives product development and product management, and supports key applications globally.