The design of titanium alloy components often requires the use of the so-called nontraditional machining methods. Among these electrochemical machining (ECM), chemical milling (CHM), and laser beam torch (LBT) are probably the most widely used. Technical information on procedures and techniques is generally proprietary, however.
Chemical and electrochemical methods of metal removal are expected to be used increasingly in years to come, because of their many favorable features. They are particularly useful for rapid removal of metal from the surface of formed or complex-shaped parts, from thin sections, and from large areas down to shallow depths. These processes have no damaging effect on the mechanical properties of the metal. (See the earlier comments about fatigue properties of stress-free surfaces.) There is no hydrogen entry into the metal to cause embrittlement or loss of ductility.
ECM is the removal of electrically conductive material by anodic dissolution in a rapidly flowing electrolyte which separates the workpiece from a shaped electrode. ECM can generate difficult contours and provide distortion-free, high quality surfaces. For ECM of titanium alloys, a very common electrolyte is sodium chloride used at concentrations of about 1 lb/gal.
CHM is the controlled dissolution of a workpiece material by contact with a strong chemical reagent. The part being processed is cleaned thoroughly and covered with a strippable, chemically-resistant mask. Areas where chemical action is desired are stripped off the mask, and then the part is submerged in the chemical reagent to dissolve the exposed material.
Another operation usable in the processing of titanium alloys is the LBT method. In this process, material is removed by focusing a laser beam and a gas stream on a workpiece. The laser energy causes localized melting, and an oxygen gas stream promotes an exothermic reaction and purges the molten material from the cut. Titanium alloys are cut at very rapid rates using a continuous wave CO2 laser with oxygen assist.