Investigation of White Layers Formed in Conventional and Cryogenic Hard Turning of Steels

Manufacturing ◽  
2003 ◽  
Author(s):  
Zbigniew Zurecki ◽  
Ranajit Ghosh ◽  
John H. Frey
Keyword(s):  
Residual Stress ◽  
Hard Turning ◽  
Stress Measurement ◽  
White Layer ◽  
Spray Cooling ◽  
Cryogenic Liquid ◽  
Machined Surface ◽  
Machining Speed ◽  
The Impact

Although hard turning of steels has become an accepted industrial practice reducing the extent of grinding, many surface integrity aspects of hard turning require clarification. The striking result of hard turning is the tendency for forming white (non-etching) and dark (overtempered) layers at machined surface. White layers are often associated with residual tensile stresses leading to reduced fatigue strength and poor wear resistance. It has been reported that certain steel compositions, machining conditions, and tools enhance white layers, but no consensus was reached on the nature of white layer and the role of environmental factors. This study examines the impact of cryogenic, liquid nitrogen spray cooling, tool and work materials, as well as machining speed on white layer formation. Results are evaluated using XRD, SEM, EDS, AES, residual stress measurement and microhardness profiling. It is concluded that white layers are a purely thermomechanical phenomenon involving dissolution of low-alloy carbides into austenitic matrix, and catastrophic flow of that 1-phase material resulting in its nano-scale refinement. The depth and extent of the refinement are controlled by cooling, with the cryogenic nitrogen reducing white layer thickness, loss of hardness, and improving residual stress distribution.

Characteristics of Residual Stress Profiles in Hard Turned Versus Ground Surfaces With and Without a White Layer

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
A. W. Warren ◽  
Y. B. Guo
Keyword(s):  
Residual Stress ◽  
Compressive Residual Stress ◽  
Hard Turning ◽  
Cutting Tool ◽  
Stress Measurement ◽  
White Layer ◽  
Machining Process ◽  
Tensile Residual Stress ◽  
Stress Profile ◽  
Stress Profiles

Hard turning and grinding are precision processes in many cases for manufacturing various mechanical products. Product performance is highly dependent on the process induced residual stress. However, the basic differences in residual stress profiles generated by hard turning and grinding with and without the presence of a thermal white layer have not been well understood. This study aims to compare basic characteristics of the residual stress profiles using an extensive residual stress measurement for five surface types: hard turned fresh, hard turned with a white layer, ground fresh, ground with a white layer, and as heat treated. The X-ray diffraction data revealed distinct differences in the residual stress profiles for the five surface types. Hard turning with a sharp cutting tool generates a unique “hook” shaped residual stress profile characterized by compressive residual stress at the surface and maximum compressive residual stress in the subsurface, while “gentle” grinding only generates maximum compressive residual stress at the surface. The depth of compressive residual stress in the subsurface by hard turning is much larger than that by grinding. The high hertz pressure induced by the cutting tool in turning is the determining factor for the differences in residual stress. High tensile residual stress associates with the existence of a turned or a ground white layer. The coupled effects of high hertz pressure and rapid temperature change induced by tool wear play an important role in the resultant tensile residual stress. In addition, residual stress by grinding is more scattered than that by turning. Compared with the deterministic influence of machining process on the magnitudes and profiles of residual stress, the effect of heat treatment is minor.

Role of Tool Flank Wear and Machining Speed in Developing of Residual Stress in Machined Surface During High Speed Machining of Titanium Alloys

2015 ◽  
Author(s):  
Xueping Zhang ◽  
Rajiv Shivpuri ◽  
Anil K. Srivastava
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
High Speed ◽  
Flank Wear ◽  
Tool Geometry ◽  
High Speed Machining ◽  
Machined Surface ◽  
Tool Flank Wear ◽  
Machining Speed

Residual stresses generated from finish machining have a significant impact on the fatigue life of mechanical components by controlling crack initiation and propagation processes in their near subsurface. As governing variables, tool geometry, tool wear, machining parameter, work material property, and lubrication conditions have been widely studied to determine their effects on residual stress pattern in machined surface and subsurface. Among those parameters, tool flank wear was seldom fully investigated although tool flank wear, as well as machining speed, has been identified as the most important contributor to residual stress. Especially, tool flank wear becomes more significant due to the poor work thermal property during the high speed machining of titanium Ti-6Al-4V alloy. This study aims to investigate the combined role of tool flank wear and machining speed in developing residual stress in the machining of titanium alloy using finite element method. A microstructure sensitive material model based on Self Consistent Method (SCM) is adopted to incorporate the phase state and its transformations during machining cycle. Critical flank wear land and corresponding machining speeds are identified, beyond which compressive residual stresses are transferred into tensile residual stresses. High machining speeds demonstrate a distinct influence on residual stresses by means of promoting tool flank wear rate. The numerical simulation results are validated by empirical data provided in previous research.

Characteristics of Residual Stress Profiles in Hard Turned Versus Ground Surfaces With and Without a White Layer

2008 ◽  
Author(s):  
A. W. Warren ◽  
Y. B. Guo
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Compressive Residual Stress ◽  
Hard Turning ◽  
Stress Measurement ◽  
White Layer ◽  
Stress Profile ◽  
Residual Stress Profile ◽  
Mechanical Products ◽  
Stress Profiles

Hard turning and grinding are competitive processes in many cases for manufacturing various mechanical products. Product performance is highly dependent on the process induced residual stresses. However, there exist some inconsistence regarding the true residual stress profiles generated by hard turning and grinding with and without the presence of a white layer. This study aims to clarify the pressing issues via an extensive residual stress measurement for five surface types: hard turned fresh (HTF), hard turned with a white layer (HTWL), ground fresh (GF), ground with a white layer (GWL), and as heat treated. The x-ray diffraction data revealed distinct differences in the residual stress profiles between the turned and ground surfaces. Specifically, the key findings are: (i) HTF surfaces generate a “hook” shaped residual stress profile characterized by surface compressive residual stress and maximum compressive residual stress in the subsurface, while GF surfaces only generate maximum compressive residual stress at the surface; (ii) HTWL surfaces generate a high tensile stress in the white layer, but has highly compressive residual stress in the deeper subsurface than the HTF surface; (iii) GWL surfaces only shift the residual stress to more tensile but does not affect the basic shape of the profile; (iv) Tensile residual stress in the HTWL surface is higher than that for the GWL one. However, the residual stress for the ground white layer does not become compressive and remains tensile in the subsurface; (v) Elliptical curve fitting is necessary for measuring residual stress for the HTWL surface due to the presence of shear stress induced severe Ψ splitting; (vi) Residual stresses by grinding show more scattering than those by hard turning; and (vii) Machining is the deterministic factor for the resulting residual stress magnitudes and profiles compared with the minor influence of initial residual stress by heat treatment.

Residual Stress Measurement of Sealing Glass Based on Optical Fiber Sensing Technology

2018 ◽  
Author(s):  
Li Mingze ◽  
Fan Zhichun ◽  
Diao Xingzhong ◽  
Yan He
Keyword(s):  
Residual Stress ◽  
Optical Fiber ◽  
Stress Measurement ◽  
Pressure Vessels ◽  
Residual Stress Measurement ◽  
Initial Residual Stress ◽  
Fiber Sensing ◽  
Optical Fiber Sensing ◽  
The Impact ◽  
Sealing Glass

Metal-to-glass electrical penetration assemblies (EPA) are highly sophisticated equipment and have been used for electrical connection in containment structures or pressure vessels in nuclear plants because of their high temperature resistance and good hermeticity. One important factor to keep hermeticity and reliability can be attributed to the initial residual stress in sealing glass of metal-to-glass EPA. If the residual stress is too high, small defects easily take place in the sealing materials. An insufficient prestress also cannot meet the requirement of high pressure application. To study the influence of residual stress on hermeticity, we developed a novel method of residual stress measurement in metal-glass sealing based on an embedded optical fiber sensor. The fiber Bragg grating (FBG) sensor was embedded in the glass material during the EPA manufacturing, and the residual stress along the grating could be retrieved via optical fiber sensing technique. Basing on our existing metal-glass sealing technique, the initial residual stress could be modulated by changing the sealing process, then the change of different initial residual stress was measured by the embedded FBG, through which the impact of residual stress on metal-glass sealing hermeticity could be finally revealed. A finite element model was established basing on linear elastic theory, then the localized stress along the FBG and the global stress distribution had been investigated theoretically. Taking the stress measuring by FBG as a breakthrough point, the effect of initial residual stress on sealing hermeticity was studied experimentally. The results showed that the residual stress should be an important assessment indicator to metal-to-glass sealing. This research also provided a new approach to optimize EPA manufacture.

The Role of Residual Stress Measurement in the Development of Laser Peening *

2003 ◽  
Vol 11 (4) ◽  
pp. 195-200 ◽  
Author(s):  
Michael R. Hill ◽  
Adrian T. DeWald ◽  
Jon E. Rankin ◽  
Matthew J. Lee
Keyword(s):  
Residual Stress ◽  
Stress Measurement ◽  
Residual Stress Measurement ◽  
Laser Peening

scholarly journals Analysis of AISI D2 Steel by using SEM Images

2020 ◽  
Vol 8 (6S) ◽  
pp. 148-155
Keyword(s):  
Hard Turning ◽  
Manufacturing Industry ◽  
White Layer ◽  
Chip Morphology ◽  
Cutting Parameters ◽  
Cutting Condition ◽  
Machined Surface ◽  
Sem Images ◽  
Aisi D2 ◽  
D2 Steel

Hard turning is a new emerging technique in manufacturing industry which involves turning of hard steel having hardness more than 60 HRC. Here in the present work, the objective of the study is steel type ENX160CrMo having hardness 62 HRC. Hard turning were carried out at different cutting parameters and chip hardness and micro- chip SEM images were observed. Micro- machined surface images, observed at different cutting condition to know the relation between chip morphology and micro-structure of the machined surface. White layer formation indicates the reduction in fatigue life was also studied.

On Predicting Residual Stress and Chip Morphology in Pre-Stressed Hard Turning

2010 ◽  
Author(s):  
Heping Wang ◽  
Shenfeng Wu ◽  
Xueping Zhang ◽  
C. Richard Liu
Keyword(s):  
Residual Stress ◽  
Temperature Distribution ◽  
Plastic Strain ◽  
Strain Distribution ◽  
Compressive Residual Stress ◽  
Hard Turning ◽  
Chip Morphology ◽  
Stress Conditions ◽  
Machined Surface ◽  
Plastic Strain Distribution

To analyze AISI 52100 steel response in hard turning under pre-stressed conditions, an explicit dynamic thermo-mechanical finite element model (FEM) has been developed. The FEM adopts Johnson-Cook constitutive model to describe the workpiece material property; and Johnson-Cook failure model as chip separation criterion; a modified coulomb’s friction law determines the friction behavior at the tool/chip interface. 500MPa of tensile and compressive pre-stress are imposed on the workpiece to simulate the pre-tension-stress and pre-compression-stress conditions respectively in hard turning. The effect of pre-stress on hard turning is determined by analyzing and comparing the simulation results under the three different pr-stress conditions, in terms of saw-tooth chip morphology, cutting forces, plastic strain distribution and temperature distribution on chip, plastic strain distribution and temperature distribution in machined surface, and especially the residual stress in machined surface. It identifies hard cutting under pretension-stress condition is an effective approach to generate a beneficial compressive residual stress profile in hard turning characterized by a bigger value of compressive residual stress and a deeper penetration depth into the hard turned surface which are helpful to enhance the fatigue life of machined components.

Nickel Superalloy Components Surface Integrity Control through Numerical Optimization

2014 ◽  
Vol 611-612 ◽  
pp. 1396-1403 ◽  
Author(s):  
Antonio del Prete ◽  
Rodolfo Franchi ◽  
Emilia Mariano
Keyword(s):  
Residual Stress ◽  
Surface Integrity ◽  
Removal Rate ◽  
White Layer ◽  
Optimization Procedure ◽  
Tool Geometry ◽  
Stress Profile ◽  
Machined Surface ◽  
Residual Stress Profile ◽  
Target Profile

Different parameters are used to evaluate the machined surface quality; roughness, residual stress and white layer are the most common factors that affect the surface integrity. Residual stress, in addition, are one of the main factors that influence the component fatigue life. Superficial residual stresses depend on different factors, such as cutting parameters and tool geometry. This article describes the development of an automated optimization procedure that allows the matching of a residual stress Target Profile by varying process parameters and tool geometry for a typical aeronautic superalloy, such as Waspaloy, for which a reliable numerical model has been developed for comparison to experimental data. The objective of this procedure is to maximize the Material Removal Rate under physical constraints represented by appropriate limits assigned to: Cutting Force, Thrust Force, Tool Rake Temperature and residual stress Target Profile. The developed optimization procedure has shown its effectiveness to match a given residual stress profile in accordance to process responses numerically evaluated.

Experimental Study on the Impact of Cutting Speed on Surface Integrity of Ti-10V-2Fe-3Al

2014 ◽  
Vol 852 ◽  
pp. 476-480
Author(s):  
Hou Chuan Yang ◽  
Zhi Tong Chen ◽  
Ming Hua Chen
Keyword(s):  
Surface Integrity ◽  
White Layer ◽  
Aerospace Industry ◽  
Cutting Speed ◽  
Cnc Machining ◽  
Machined Surface ◽  
Workpiece Surface ◽  
Speed Increase ◽  
The Impact ◽  
Machined Surface Integrity

Titanium Alloy Ti-1023 is widely utilized in aerospace industry; the integrity of the parts machining surfaces is of critical importance for aerospace industry. Surface roughness, microstructure and microhardness variations were investigated on a CNC machining at different cutting speeds. Experiments results showed machined surface integrity of Ti-1023was sensitive to cutting speed. The roughness of machined surface raised with increase of the cutting speed from 40 m/min to 100 m/min, but decreased while the cutting speed increase from 100 m/min to 300 m/min. It can also draw the conclusion that no significant phase transformation, no obvious deformation and no white layer on subsurface microstructure can be observed. As for microhardness, it can also be seen that the machined workpiece surface was not seriously hardened, less than 35μm depth of work hardening at different cutting speed.

Investigation of Residual Stresses in Case of Hard Turning of Case Hardened 16MnCr5 Steel

2013 ◽  
Vol 581 ◽  
pp. 501-504 ◽  
Author(s):  
Gergely Szabó ◽  
János Kundrák
Keyword(s):  
Finite Element Method ◽  
Residual Stress ◽  
Finite Element ◽  
Surface Layer ◽  
Residual Stresses ◽  
Hard Turning ◽  
Finite Element Method Simulation ◽  
Rake Angle ◽  
Machined Surface ◽  
Chip Removal

In this paper the residual stresses are investigated emerging in the machined layer during hard turning in case of chip removal done by different tool rake angles. By means of finite element method simulation we examined what rake angle is best to complete cutting so that favourable residual stress values are gained in the machined surface layer.

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