Ductile Fracture due to Adiabatic Shear during the Serrated Chip Formation in High Speed Cutting: a Microscopic Investigation

2011 ◽  
Vol 467-469 ◽  
pp. 181-185 ◽  
Author(s):  
Chun Zheng Duan ◽  
Liang Chi Zhang ◽  
Hong Hua Li ◽  
Min Jie Wang
Keyword(s):  
Ductile Fracture ◽  
Chip Formation ◽  
High Speed ◽  
Shear Zones ◽  
Adiabatic Shear ◽  
Shear Direction ◽  
Serrated Chip ◽  
High Speed Cutting ◽  
Serrated Chip Formation ◽  
1045 Steel

A deep understanding of adiabatic shear fracture (ASF) during serrated chip formation is essential to explore the material removal mechanism of high speed cutting (HSC). This paper aims to reveal the microscopic details of ASF in serrated chips. The material to investigate was AISI 1045 steel of different hardness grades, and the micro-structural analysis was conducted using optical and scanning electronic microscopes. The investigation showed that at the hardness of HRC50, most fractured surfaces were covered by a large number of dimples elongated along the shear direction, indicating that the fundamental cause of the serrated chip generation is the deformation localization of the adiabatic shear followed by ductile damage fracture in primary shear zones. The higher the material hardness is, the easier the adiabatic shear and ductile fracture take place. A new model was then proposed to interpret the ductile fracture due to adiabatic shear governed by the nucleation, growth and coalescence of micro-voids during serrated chip formation.

Mechanism of Material Softening in Primary Shear Zone during Serrated Chip Formation in High Speed Machining of High Strength Steel

2009 ◽  
Vol 407-408 ◽  
pp. 504-508
Author(s):  
Chun Zheng Duan ◽  
Min Jie Wang ◽  
Yu Jun Cai
Keyword(s):  
Shear Zone ◽  
Chip Formation ◽  
High Speed ◽  
High Strength ◽  
Shear Zones ◽  
Adiabatic Shear ◽  
Microstructural Development ◽  
High Speed Machining ◽  
Serrated Chip ◽  
Serrated Chip Formation

The metallurgical observations of microstructure characteristics of the adiabatic shear bands(ASB) within the primary shear zones of the serrated chips produced during high speed machining high strength steel have been performed by using optical microscope, SEM and TEM. The observations showed that the microstructure between the matrix and the center of the ASB gradually was changed, the fine equiaxed grains appeared with size of about 0.4～0.6μm in the center of the adiabatic shear band. The serrated chip formation was likely due to material softening that occurred in the primary shear zones. The microstructural development of dynamic recovery and rotational dynamic recrystallization is the dominant metallurgical process leading to material softening in primary shear zone during high speed machining. A model of microstructural development in primary shear zone during serrated chip formation in high speed machining was suggested by analyzing material softening mechanism.

Finite Element Investigation of the Influence of Thermophysical Parameters on Segmented Chip Formation during High Speed Cutting

2011 ◽  
Vol 130-134 ◽  
pp. 2817-2821
Author(s):  
You Xi Lin ◽  
Cong Ming Yan
Keyword(s):  
Thermal Conductivity ◽  
Finite Element ◽  
Specific Heat ◽  
Chip Formation ◽  
High Speed ◽  
Element Model ◽  
Serrated Chip ◽  
High Speed Cutting ◽  
Thermophysical Parameters ◽  
Serrated Chip Formation

A 2D fully thermal mechanical coupled finite element model is applied to study the influence of material parameters on serrate chip formation during high speed cutting process. The serrated chip formation during high speed machining was predicted. Of interests are the effects of thermal conductivity, specific heat and density. Results showed significant influence of these thermophysical parameters on the serrated chip phenomena, especially in the case of the density. Increasing thermal conductivity specific heat and density lead to a decreasing degree of segmentation. The influence of the thermal conductivity on the cutting force and the specific heat on maximum temperatures in the shear band is also discussed.

Research on Adiabatic Shear during Serrated Chip Formation of High Speed Turning of Hardened Steel

2010 ◽  
Vol 139-141 ◽  
pp. 743-747
Author(s):  
Chun Zheng Duan ◽  
Hai Yang Yu ◽  
Min Jie Wang ◽  
Bing Yan ◽  
Yu Jun Cai
Keyword(s):  
Chip Formation ◽  
Cutting Forces ◽  
High Speed ◽  
Cutting Speed ◽  
Chip Morphology ◽  
Rake Angle ◽  
Adiabatic Shear ◽  
Cutting Condition ◽  
Serrated Chip ◽  
Serrated Chip Formation

The development of chip morphology, critical cutting condition of adiabatic shear during serrated chip formation and cutting forces were observed and measured by high speed turning experiment for 30CrNi3MoV hardened steel. Results show that the cutting speed and rake angle are leading factors to influence chip morphology and cutting forces. With the increase of cutting speed, the continuous band chip transforms into serrated chip at a certain critical value. As the rake angle is changed from positive to negative, the critical cutting speed of adiabatic shear significantly decreases, the cutting forces abruptly reduces when the serrated chip forms. The results from predicting critical cutting speed using the critical cutting condition criterion of adiabatic shear in metal cutting process show that the leading reason of serrated chip formation is that the adiabatic shear fracture repeatedly occurs in the primary shear zone.

Investigation of Chip Morphology in High-Speed Milling of Nickel-Based Superalloy GH706

2014 ◽  
Vol 800-801 ◽  
pp. 113-118
Author(s):  
Sheng Lei Xiao ◽  
Xian Li Liu ◽  
Yu Wang ◽  
Kai Li
Keyword(s):  
Chip Formation ◽  
High Speed ◽  
Cutting Speed ◽  
Chip Morphology ◽  
Adiabatic Shear ◽  
Shear Instability ◽  
Serrated Chip ◽  
High Speed Milling ◽  
Nickel Based Superalloy ◽  
Serrated Chip Formation

This paper analyzed the serrated chip formation process and mechanism in high-speed milling of nickel-based superalloy GH706. Firstly, analyzed two theories of serrated chip formation: cyclical fracture theory and adiabatic shear theory. Secondly, used the simulation of chip formation in high-speed milling of GH706 process, and concluded that the two major theories have achieved dialectical unity when machining for such difficult machining materials. Finally experiments for serrated chip, when cutting speed exceeded 200/min, serrated chips became more obvious. Research has shown that for nickel-based superalloy, adiabatic shear instability of the unstable thermoplastic in the first deformation zoon become the leader of formation of serrated chip, followed as the speed increases, fracture aggravate the degree of serrated chip.

Prediction of Chip Morphology and Formation in High Speed Milling of Hardened Steels

2015 ◽  
Vol 1120-1121 ◽  
pp. 1145-1152
Author(s):  
Jun Zhong Pang ◽  
Xiao Bin Huang ◽  
Dou Dou Chang ◽  
Jie Pan
Keyword(s):  
Chip Formation ◽  
High Speed ◽  
Shear Banding ◽  
Chip Morphology ◽  
Material Model ◽  
Adiabatic Shear ◽  
Serrated Chip ◽  
Adiabatic Shear Banding ◽  
Serrated Chip Formation ◽  
Material Constitutive Equation

A P20 steel are machined in the milling speed range of 200 to 942m/min. The morphology and formation of the chips are investigated at various speeds. The serrated chips with adiabatic shear band are observed at a high milling speed. The transition from continuous to serrated chip formation is favored by the increase in work material hardness and milling speed. The study assumes that the chip segmentation is only induced by adiabatic shear banding, without material failure in the primary shear zone. Based on adiabatic shear theory, using the JC and the power material constitutive equation, the modified material model which takes into a strain softening is developed for prediction of the serrated chip formation. Experimental measurements are compared with the simulation results.

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