Titanium Machining: The Effect of the Cutting Parameters

Titanium having a density only about 60% of steel has a far greater strength than many steel alloys. However, titanium has many difficulties in machining. It has a low conductivity and therefore heat due to cutting does not dissipate quickly. This results in concentration of heat on the cutting edge and hence greatly limits the machinability of this material. 


In titanium machining tool life is greatly affected by the following cutting parameters listed in the order of decreasing effect, i.e., the least influential one for tool life is the one at the bottom of the list:

• surface cutting speed
• radial depth of cut
• feed per tooth (chip thickness)
• axial depth of cut

For roughing, the cutting speed is normally limited to 60 m/min where as finishing speeds can reach up to 250 m/min due to small radial depth and tools with rather smaller diameters. 

Although high radial depth of cut increases material removal rate, heat generated due to cutting remains in the cutting zone because the time each flute spends in the air during one revolution decreases so does the cooling effect. Approximately 35% percent of the tool diameter is generally recommended as radial depth of cut for optimum tool life.

Chip thickness is greatly affected by insert shape. For heavier cuts, round inserts or inserts with low approach angle (eg., 45 or 60 degrees) are recommended due to their resistant to higher loads and chip thinning effect. 

Axial depth of cut has almost no effect on too life; however, low speed, heavy machining with large diameter tools puts a demand on the torque delivery of the spindle so one has to be careful with cutting parameters in order to not stall the spindle.