Shear-Zone Size, Compressive Stress, and Shear Strain in Metal-Cutting and Their Effects on Mean Shear-Flow Stress

1960 ◽  
Vol 82 (1) ◽  
pp. 79-86 ◽  
Author(s):  
Dimitri Kececioglu
Keyword(s):  
Flow Stress ◽  
Shear Flow ◽  
Size Effect ◽  
Shear Strain ◽  
Shear Zone ◽  
Compressive Stress ◽  
Metal Cutting ◽  
Zone Size ◽  
Wide Range ◽  
Shear Flow Stress

A relationship for the calculation of the shear-zone size is given. The shear-zone size, when machining SAE 1015, 118-Bhn seamless steel tubing under a wide range of cutting conditions, is found to vary from 0.95 × 10−6 in.3 to 61.5 × 10−6 in.3 The mean shear-flow stress is found to increase significantly with a decrease in the shear-zone size and with an increase in the compressive stress in the shear zone. It is concluded that the only size effect in metal-cutting is the shear-zone size effect, and that no separate depth-of-cut size effect should be sought. An apparent decrease in the shear-flow stress with an increase in the true, mean shear strain in the shear zone is observed, and this behavior is explained.

Effects of Accelerated Tests on Shear Flow Stress in Machining

1987 ◽  
Vol 109 (3) ◽  
pp. 206-212 ◽  
Author(s):  
V. K. Jain ◽  
B. K. Gupta
Keyword(s):  
Flow Stress ◽  
Shear Flow ◽  
Shear Strain ◽  
Tool Material ◽  
Interface Temperature ◽  
Accelerated Tests ◽  
Instantaneous Values ◽  
Longitudinal Turning ◽  
Materials Behavior ◽  
Shear Flow Stress

Facing and taper turning tests (also known as accelerated cutting tests) are commonly used for the evaluation of machinability of materials. Of late, it has been reported that instantaneous values of tool-chip interface temperature, tool wear, shear angle, etc, in longitudinal turning are different from the corresponding values in accelerated cutting. This effect has been attributed to shear strain acceleration phenomenon. Materials behavior during accelerated cutting changes in a manner different than that in longitudinal turning. To test this hypothesis, experiments have been conducted using HSS as tool material and mild steel as work material. It has been concluded that shear flow stress during accelerated cutting is governed by shear strain acceleration and its governing parameters. Shear flow stress value is highest during facing, lowest in taper turning and in between the two during longitudinal turning.

The Effect of Workpiece Hardness and Cutting Speed on the Machinability of AISI H13 Hot Work Die Steel When Using PCBN Tooling

2002 ◽  
Vol 124 (3) ◽  
pp. 588-594 ◽  
Author(s):  
Eu-Gene Ng ◽  
David K. Aspinwall
Keyword(s):  
Flow Stress ◽  
Shear Flow ◽  
Shear Zone ◽  
Cutting Speed ◽  
Chip Morphology ◽  
Die Steel ◽  
Aisi H13 ◽  
Hot Work Die ◽  
Cutting Speeds ◽  
Shear Flow Stress

When machining hardened steel (⩾45 HRC) with polycrystalline cubic boron nitride (PCBN) tooling, the cutting speeds used produce high temperatures in the primary shear zone, which are sufficient to plasticize the workpiece. The paper initially reviews the effect of workpiece hardness and cutting speed on chip formation, workpiece surface integrity and cutting forces. Equations are detailed for determining the primary shear zone temperature, the proportion of heat conducted into the workpiece and the shear flow stress. Following on from this, experimental work is presented involving the orthogonal machining of AISI H13 hot work die steel with PCBN tooling. Tests were carried out over a range of cutting speeds with workpieces of different hardness, in order to provide cutting force, shear angle, chip morphology and primary shear zone thickness data. The shear flow stress decreased with increasing cutting speed and/or workpiece hardness. With the AISI H13 heat treated to 49±1 HRC, the stress magnitude changed more significantly with cutting speed and the proportion of heat conducted away from the workpiece approached 99 percent at 200 m/min. Shear localized chips were produced with white unetched layers due to intense heat generation followed by rapid cooling.

The Effect of Workpiece Hardness and Cutting Speed on the Machinability of AISI H13 Hot Work Die Steel When Using PCBN Tooling

1999 ◽  
Author(s):  
Eu-Gene Ng ◽  
David K. Aspinwall
Keyword(s):  
Flow Stress ◽  
Shear Flow ◽  
Shear Zone ◽  
Cutting Speed ◽  
Chip Morphology ◽  
Die Steel ◽  
Aisi H13 ◽  
Hot Work Die ◽  
Cutting Speeds ◽  
Shear Flow Stress

Abstract When machining hardened steel (≥ 45 HRC) with polycrystalline cubic boron nitride (PCBN) tooling, the cutting speeds used produce high temperatures in the primary shear zone, which are sufficient to plasticise the workpiece. The paper initially reviews the effect of workpiece hardness and cutting speed on chip formation, workpiece surface integrity and cutting forces. Equations are detailed for determining the primary shear zone temperature, the proportion of heat conducted into the workpiece and the shear flow stress. Following on from this, experimental work is presented involving the orthogonal machining of AISI H13 hot work die steel with PCBN tooling. Tests were carried out over a range of cutting speeds with workpieces of different hardness, in order to provide cutting force, shear angle, chip morphology and primary shear zone thickness data. The shear flow stress decreased with increasing cutting speed and/or workpiece hardness. With the AISI H13 heat treated to 49±1 HRC, the stress magnitude changed more significantly with cutting speed and the proportion of heat conducted away from the workpiece approached 99% at 200 m/min. Shear localised chips were produced with white unetched layers due to intense heat generation followed by rapid cooling.

Minimum work as a possible criterion for determining the frictional conditions at the tool/chip interface in machining

1976 ◽  
Vol 282 (1310) ◽  
pp. 565-584 ◽  
Keyword(s):  
Flow Stress ◽  
Shear Flow ◽  
Plastic Zone ◽  
Approximate Theory ◽  
Angle Of Friction ◽  
Average Coefficient ◽  
Average Shear ◽  
Work Done ◽  
Minimum Work ◽  
Shear Flow Stress

An approximate theory of machining is described in which the average shear flow stress in the plastic zone in the chip adjacent to the tool/chip interface, which is allowed to vary with strain rate and temperature, is used as the friction parameter and this is shown to be far more effective than the normally used average coefficient (or angle) of friction. It is proposed that the average thickness of the tool/chip interface plastic zone is determined by a minimum work criterion, its value being such that for given cutting conditions the average shear flow stress within the plastic zone will be minimized, thus minimizing both the frictional and total work done in chip formation. A comparison is made between results predicted by assuming minimum work and experimental results.

A Treatise on the Streamlines and the Stress, Strain, and Strain Rate Distributions, and on Stability in the Primary Shear Zone in Metal Cutting

1972 ◽  
Vol 94 (2) ◽  
pp. 690-696 ◽  
Author(s):  
C. Spaans
Keyword(s):  
Flow Stress ◽  
Hydrostatic Pressure ◽  
Strain Rate ◽  
Shear Zone ◽  
Material Flow ◽  
Metal Cutting ◽  
Rate Increase ◽  
Temperature Distributions ◽  
Strain And Strain Rate ◽  
Strain Rate Increase

It is shown that both the flow stress and the hydrostatic pressure are constant in the greater part of the shear zone. The increase of the temperature with the strain is balanced by a proper strain rate increase, which provides a basis for a model generating the shape and the size of the shear zone, with the streamlines of material flow and the strain, strain rate and temperature distributions. Quick-stop tests make the streamlines visible. There is no reason for instability in the primary shear zone.

Modified Primary Shear Zone Analysis for Identification of Material Mechanical Behavior During Machining Process Using Genetic Algorithm

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
L. Pang ◽  
H. A. Kishawy
Keyword(s):  
Genetic Algorithm ◽  
Boundary Conditions ◽  
Strain Rate ◽  
Shear Strain ◽  
Shear Zone ◽  
Metal Cutting ◽  
Chip Thickness ◽  
Machining Process ◽  
Zone Model ◽  
Shear Strain Rate

In the current work, an inverse analysis on the primary shear zone was introduced to determine the five constants in Johnson–Cook’s material constitutive equation under the conditions of metal cutting. Based on the detailed analysis on the boundary conditions of the velocity and shear strain rate fields, Oxley’s “equidistant parallel-sided” shear zone model was revisited. A more realistic nonlinear shear strain rate distribution has been proposed under the frame of nonequidistant primary shear zone configuration, so that all the boundary conditions can be satisfied. Based on the presented analysis, the shear strain, shear strain rate and temperature at the main shear plane were calculated. In conjugation with the measured cutting forces and chip thickness, a genetic algorithm (GA) based optimization program has been developed for the system identification. In order to verify the effectiveness of the developed algorithm, the obtained material constants were used in a forward analytical simulation. The acceptable agreement with experimental data validates the proposed method.

Mechanics of Metal Cutting for a Material of Variable Flow Stress

1963 ◽  
Vol 85 (4) ◽  
pp. 339-345 ◽  
Author(s):  
P. L. B. Oxley
Keyword(s):  
Flow Stress ◽  
Carbon Tetrachloride ◽  
Cutting Force ◽  
Shear Zone ◽  
Metal Cutting ◽  
Cutting Conditions ◽  
Depth Of Cut ◽  
Variable Depth ◽  
Variable Flow ◽  
Interface Friction

A new analysis is presented in which the variable flow stress property of the work material is taken into account. It is shown that changes in the so-called angle of tool-chip interface friction can result from changes in the shear zone mechanism and, for example, the paradoxical behavior observed when cutting with carbon tetrachloride as a “lubricant” can be accounted for in this way. It is concluded that if actual predictions are to be made about the cutting process, i.e., without first making cutting tests, then the angle of tool-chip interface friction cannot be accepted as given information. The analysis is extended to cutting with a variable depth of cut, and in agreement with experiment it is predicted that, with all other cutting conditions the same, the cutting force will be less for an increasing depth of cut than for a decreasing depth of cut.

scholarly journals In-SEM micro-machining reveals the origins of the size effect in the cutting energy

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Bentejui Medina-Clavijo ◽  
Gorka Ortiz-de-Zarate ◽  
Andres Sela ◽  
Iñaki M. Arrieta ◽  
Aleksandr Fedorets ◽  
...  
Keyword(s):  
Size Effect ◽  
Shear Zone ◽  
Metal Cutting ◽  
Force Measurement ◽  
Shear Zones ◽  
Deep Submicron ◽  
Orientation Measurement ◽  
Cutting Energy ◽  
In Operando ◽  
Geometrical Factors

AbstractHigh-precision metal cutting is increasingly relevant in advanced applications. Such precision normally requires a cutting feed in the micron or even sub-micron dimension scale, which raises questions about applicability of concepts developed in industrial scale machining. To address this challenge, we have developed a device to perform linear cutting with force measurement in the vacuum chamber of an electron microscope, which has been utilised to study the cutting process down to 200 nm of the feed and the tool tip radius. The machining experiments carried out in-operando in SEM have shown that the main classical deformation zones of metal cutting: primary, secondary and tertiary shear zones—were preserved even at sub-micron feeds. In-operando observations and subsequent structural analysis in FIB/SEM revealed a number of microstructural peculiarities, such as: a substantial increase of the cutting force related to the development of the primary shear zone; dependence of the ternary shear zone thickness on the underlaying grain crystal orientation. Measurement of the cutting forces at deep submicron feeds and cutting tool apex radii has been exploited to discriminate different sources for the size effect on the cutting energy (dependence of the energy on the feed and tool radius). It was observed that typical industrial values of feed and tool radius imposes a size effect determined primarily by geometrical factors, while in a sub-micrometre feed range the contribution of the strain hardening in the primary share zone becomes relevant.

On the nominal transverse shear strain to characterize the severity of creasing

TAPPI Journal ◽  
2018 ◽  
Vol 17 (04) ◽  
pp. 231-240
Author(s):  
Douglas Coffin ◽  
Joel Panek
Keyword(s):  
Shear Strain ◽  
Transverse Shear ◽  
Elastic Limit ◽  
Experimental Results ◽  
Transverse Shear Strain ◽  
Maximum Strain ◽  
Machine Direction ◽  
Engineering Approach ◽  
Wide Range ◽  
Analytic Expression

A transverse shear strain was utilized to characterize the severity of creasing for a wide range of tooling configurations. An analytic expression of transverse shear strain, which accounts for tooling geometry, correlated well with relative crease strength and springback as determined from 90° fold tests. The experimental results show a minimum strain (elastic limit) that needs to be exceeded for the relative crease strength to be reduced. The theory predicts a maximum achievable transverse shear strain, which is further limited if the tooling clearance is negative. The elastic limit and maximum strain thus describe the range of interest for effective creasing. In this range, cross direction (CD)-creased samples were more sensitive to creasing than machine direction (MD)-creased samples, but the differences were reduced as the shear strain approached the maximum. The presented development provides the foundation for a quantitative engineering approach to creasing and folding operations.

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