Advances in Titanium Machining
How to Effectively Machine Titanium
Titanium is one of the more abundant metals residing in the earth’s crust, and yet it remains one of the more difficult metals to extract, mill, and machine. It’s specifically because of these challenges that titanium products often have higher costs associated with them.
The benefits of titanium (light weight, impervious to corrosion, etc.) far outweigh these challenges, though, which is why we continue to develop new advancements to more effectively machine this metal. When it’s done effectively, it is possible to start cutting costs and increasing production rates.
Current advances in titanium machining are focused on better and faster metal removal rates while prolonging tool lifespan.
Understanding the Challenges
When you’re machining tough metals like titanium, cutting speeds generally have to be kept low because of the thermal effects on the cutting tools. Titanium, in particular, is a poor thermal conductor, which means that the heat that is generated by the cutting process can’t dissipate through the part or the machine table.
This can lead to surprisingly high temperatures which, in turn, dull the cutting tools. It gets worse when you factor in how much dull cutting tools create more heat, which continues to damage the tools even further. It’s a terrible – and terribly inefficient – cycle.
The elasticity of titanium also presents a certain challenge. This metal has a low modulus of elasticity, which causes it to spring away from cutting tools. This can cause more tool vibration and chatter, which can also lead to a poor surface finish.
Finally, titanium also tends to work harden during normal cutting processes. When that happens, it can cause problems for your tools. If those tools can’t cut through the depth of the hardened material, that will accelerate the hardening process. As this process continues, the cutting speeds that were sufficient at the beginning of the job will no longer work effectively, causing more wear on the tool.
In response to these types of challenges, many tools and techniques have been developed to address them and create more efficient solutions.
Effective use of coolant is critical for machining titanium, especially when you’re trying to work at higher speeds. In any sort of metal cutting, you need coolant, but titanium can build up such high temperatures (up to 2,000 degrees) that it can turn water-based coolants into super-heated steam. The coolant literally vaporizes before it can get where it needs to go, and the steam can contribute to even higher temperatures around the tools.
It’s also important to note, at this point, that titanium can chip as it is cut. The high-chemical reactivity of the titanium alloys under such high temperatures means that the chips can weld straight to the tools if they’re not cleared away fast enough.
The solution is to deliver the right kind of coolant at the right pressure. A high-flow, high-pressure system that produces cooling in the right direction will knock the chips off the cutting tools and help keep the temperatures down.
A secure hold is also critical for effective machining. The elasticity of titanium has to be considered for any project. So when you begin the cut, rigidity is what matters. So in order to do it right, the work must be kept close to the strongest points in the fixture to help avoid potential harmonics.
And, of course, tooling in general continues to advance. This includes everything from tool coatings to variable rake tooling – whatever it takes to handle the heat and stress of machining and milling titanium.
All together, these tools and processes help make milling titanium more cost effective, which, in turn, means more high quality products making it to market.