A reader recently used the “Ask an Expert” feature of our Titanium Machining Zone to ask the following question.
We make a family of medical implants from Ti6Al4V. We currently average 2.88 cubic inches per minute from a carbide four-flute, AlTiN-coated coarse-tooth rougher. I run it on a VMC at 160 sfm and 0.001 fpt. I'm looking for some tooling recommendation to increase tool life and reduce cycle time.
Response from Mark Larson, manager of titanium process development for Makino
Your 2.88 rate is very good compared to many shops we talk with.
What affects tool life the most, based on our studies and observations, is speed. You aren't very high in terms of sfm, but how high you can go really go depends on your cooling solution.
For better tool life, try to use through-spindle coolant (if you aren’t already) in order to get the coolant as close to the cutting edge/material interface as possible. Higher pressure is good, but higher coolant flow is also important.
There are many new coolants for titanium. I realize that in the medical field you may be limited on what coolants are acceptable, but at least check into new coolants from Blaser Swisslube and Hangsterfer's that are specifically for titanium.
As far as tool-specific ideas, coatings can help, but they tend to wear away quickly in titanium. Check with your current supplier on new “nano,” “micro” or “multi-layer” coatings. Many tool suppliers have these now. In addition, chip evacuation up the flutes can be improved with some coatings that reduce the amount of friction allowing the chips to “slide” up and away from the cutting area easier. Given that you are on a vertical, add air lines—or even use operator intervention—but find a way to keep from re-cutting chips that might be left laying on or around the part. Or, if one is available, move to a horizontal.
The right choices in tooling and technique can optimize the thread turning process.
Fast CNC processing and high-pressure coolant contribute to removing metal at dramatic rates. But what should a shop know about cutting tools in high speed machining?
One of the most common methods of tapping in use today on CNC machines is 'rigid tapping' or 'synchronous feed tapping.' A rigid tapping cycle synchronizes the machine spindle rotation and feed to match a specific thread pitch. Since the feed into the hole is synchronized, in theory a solid holder without any tension-compression can be used.