“Top Twelve” criteria of Ti-machining
What makes titanium desirable as a part material-its strength-to weight ratio and temperature resistance- , is what makes it so difficult to machine. However, if all criteria of the machining envelope are optimized, it can be done productively and cost-effectively:
- Low cutting speeds generate low frequencies that are more difficult to absorb and reduce. Axial load is preferred over radial load for less costly spindle bearings.
- The best tool-holder relative to vibration dampening is a hydraulic chuck (fluid).
- High pressure coolant aids in taking the chips out of the cutting area. They might otherwise increase heat build-up. Coolant volume is for reducing heat and note that water is the best coolant and more important than lubricity for milling…
- Good chip load is for heat disposal out of the area. Playing with feed rate varies the tool engagement and with it the temperature and that lowers tool life. Dwelling the cutter leads to work-hardening.
- The best type of clamping is for the fixture to embrace the workpiece. Too much pressure can distort the part…
- The longer the tool protrudes from the spindle the more unstable the cutting and the more difficult it is to achieve good geometric tolerances (the cutting force is proportional to tool length divided by tool diameter and a high cutting force deflects the cutting tool).
- The adaptive control reads the part contours ahead and adjusts speeds and feed rates. Z-type milling secures more axial load on the machine spindle.
- Variable helixes offset frequencies and forces during cutting.
- Positive tool geometries aid in shearing the material (they are more in the cut) and are, therefore less “forceful” on tool and spindle.
- The larger the radius on the tool the more tool pressure during cutting but the longer the tool life and the worse the surface finish.
- The multi-coating mentioned offers more coating density and thus longer coating life, more heat resistance plus better oxidation during cutting (smoother chip flow).
- Ti 5553 is stronger with even less ductility and is, as a result, even more difficult to machine (typically even less tool life). As I said the HPR series give acceptable tool life in spite…
Dr. Bert Erdel, December 2017