Research On Surface Integrity Of Titanium Alloy Ti-6Al-4V In Helical Milling Process

Titanium alloys find increasing applications in aerospace industries due to theirexcellent properties. However, the machining of the titanium alloy has posed a greatchallenge for engineering practice owing to several undesirable properties. Helicalmilling is an ideal solution for hole-making of hard-to-machine materials. Surfaceintegrity is a technical indicator for the description, assessment, and control of allkinds of potential damages to the workpiece’s surface/subsurface and their influenceson the workpiece performance. Nevertheless, information retrieval revealed that thereis very limited, if any, information about the influence of helical milling on surfaceintegrity. Therefore, experimental study on helical milling of Ti-6Al-4V wasconducted to fulfill this purpose. The main contents are summarized as follows:Cutting forces are important indicators for study on cutting process, itsmagnitude and fluctuation will affect the workpiece surface integrity, tool wear andtool life, and machining stability. The experiment results demonstrated that the helicalmilling of Ti-6Al-4V undergone much smaller thrust force (25%of that in drilling).This small thrust cutting force enables the ideal surface integrity to be obtained.Surface roughness, micro-hardness, residual stress distribution andmicro-structure alternation are the main aspects in surface integrity. Experimentalinvestigation on surface integrity in helical milling of Ti-6Al-4V was conducted tounderstand the influence of cutting parameters on the roughness, micro-hardnessdistribution, residual stress distribution and micro-structure alternation. The resultsrevealed that desired surface roughness, moderate work hardening, compressiveresidual stress can be obtained without the undesirable white layer. Therefore,surface integrity can be greatly improved by applying the helical milling technology.Finally, based on an improved Z-map model, a3D surface topography simulationmodel was established to simulate and predict the surface finish profile generated byhelical milling. The surface topography simulation model incorporates the effects ofthe relative motion between the cutting tool and the workpiece, and the roughnessparameters are deduced from the surface topography simulation model. Theexperimental results showed that the proposed simulation algorithm can predict wellthe surface roughness in a helical milling operation.