Study Of Surface Integrity And Fatigue Life Of Titanium Alloy Hole-making Process

Titanium alloy is widely used in aviation field due to its excellent performance.But titanium alloy is a difficult-cut material because of high chemical activity, low thermal conductivity, and low elastic modulus. So it is difficult to guarantee the surface quality during machining. In this work, case studies deploying traditional drilling and helical milling technologies were carried out to investigate the tool life and hole surface integrity. Then, explored the method to improve the hole quality and extend the fatigue life of titanium hole.Firstly, the tool life of drilling and helical milling on titanium alloy was studied.Analyzed the tool damage form and wear mechanisms. Hole-making process of titanium alloy was analyzed under the two processes, monitoring changes of cutting force, the influence of tool wear on the cutting forces was studied.Secondly, the influence of hole-making process and tool wear on microstructure,microhardness and residual stress distribution was studied. Artificial neural network was used to study the correlation of surface roughness and cutting force; Results show that, a slightly soften region was always present on the drilled surface, "thermal softening" and brittle "white layer" were observed. However helical milling process was reversed in contrast.Finally, fatigue life prediction models was established based on Manson-Coffin formula and combined with stress work equivalence method. Fatigue tests were carried out and experimentally verify the reliability of the model. Through macroscopic and microscopic morphology of fatigue fracture analysis, explored the changes of microstructure and residual stress on fatigue life.This paper studies titanium surface integrity and fatigue life of helical milling and drilling process, provides a reference in the field of aviation manufacturing.