Proc IMechE Part B: J Engineering Manufacture
2014, Vol. 228(2) 181–190

Serrated chipformation mechanism based on mixed mode of ductile fracture and adiabatic shear

Bing Wang and Zhanqiang Liu

[Abstract] Serrated chip is the frequent chip morphology duringhigh-speed machining of ductile materials, while the mechanism of serrated chipformation still remains some ambiguous aspects. This article presents theinvestigation of chip morphology from the viewpoint of chip free surface andcross section. Experiments of orthogonal cutting hardened AISI 1045 steel and7050-T7451 aluminum alloy were carried out. The cutting speed of AISI 1045steel was varied from 100 to 1000 m/min, while 7050-T7451 aluminum alloy was machined at thecutting speed of 100–2500 m/min.The feed rate per tooth was varied from 0.025 to 0.20 mm/z corresponding to each experimental cuttingspeed. The research shows that the microstructure of chip free surface evolvesfrom lamellae to folds and then to dimples. According to the experimental results,a new model of serrated chip formation based on mixed mode of ductile fractureand adiabatic shear is proposed. For the ‘‘ductile fracture–adiabatic shear’’serrated chips, two distinct zones of ductile fracture and dimples were observedon the slide surface of serrated segments. Through studying chip morphologyevolution under  different combinations ofcutting speed and feed rate, it is found that the degree of chip segmentationhas positive correlation with the two parameters. The concept of ‘‘criticalcutting load’’ is then proposed to illustrate the conditions under whichserrated chips may occur. And the critical cutting load of AISI 1045 steel and7050-T7451 aluminum alloy is determined by experiments as 0.024 and 0.10 m2/(minz), respectively.

Keywords: Serrated chip, ductile fracture, adiabaticshear, degree of chip segmentation, critical cutting load

2014-Serrated chip formation mechanism-10.1177_0954405413497941.pdf