Influence of the built-up edge on the stress state in the chip formation zone during orthogonal cutting of AISI1045

In-situ strain measurements with high energy synchrotron radiation during orthogonal cutting of AISI1045 were carried out. Thereby it was possible to determine the stress state in the chip formation zone during the cutting process. As such, observations regarding the formation of built-up edges during the cutting process have been made. The formation of a built-up edge on the cutting tool is a common phenomenon during cutting of mild steel and other ductile materials, in particular at low cutting speeds. This may result in increased tool wear and a decrease in the resulting surface quality. By analyzing the chip roots of the in-situ experiments, it was possible to determine the geometry of the built-up edges on tools with a rake angle of γ = 0° and cutting edge radii of rβ = 30 μm and rβ = 60 μm. Using the obtained data a simulation model which represents the built-up edge could be established with two versions of the built-up edge: a solid one as part of the rigid tool and an elastic one in front of the tool. Using FEM cutting simulations with and without built-up edges, it was possible to show the influence of a built-up edge on the chip formation and the stress state in the chip formation zone. With this data, a comparison of the results of the cutting simulations with those of the in-situ experiments was conducted

Influence of the Built-up Edge on the Stress State in the Chip Formation Zone During Orthogonal Cutting of AISI1045

AbstractIn-situ strain measurements with high energy synchrotron radiation during orthogonal cutting of AISI1045 were carried out. Thereby it was possible to determine the stress state in the chip formation zone during the cutting process. As such, observations regarding the formation of built-up edges during the cutting process have been made. The formation of a built-up edge on the cutting tool is a common phenomenon during cutting of mild steel and other ductile materials, in particular at low cutting speeds. This may result in increased tool wear and a decrease in the resulting surface quality. By analyzing the chip roots of the in-situ experiments, it was possible to determine the geometry of the built-up edges on tools with a rake angle of γ = 0° and cutting edge radii of rβ = 30 μm and rβ = 60 μm. Using the obtained data a simulation model which represents the built-up edge could be established with two versions of the built-up edge: a solid one as part of the rigid tool and an elastic one in front of the tool. Using FEM cutting simulations with and without built-up edges, it was possible to show the influence of a built-up edge on the chip formation and the stress state in the chip formation zone. With this data, a comparison of the results of the cutting simulations with those of the in-situ experiments was conducted

Cutting simulation with consideration of the material hardening in the Shear Zone of AISI1045

By the use of high energy synchrotron X-ray diffraction it was possible to determine the stress state in the chip formation zone during orthogonal cutting of AISI1045. The analysis of the diffractograms showed a hardening of the material during the movement through the shear zone. For this reason nano indentation experiments on prepared chips have been carried out. With these experiments, the material hardening has been confirmed. The nano indentation experiments were reproduced by FEM simulations and it was possible to determine flow curves of the hardened material above the shear zone based on existing flow curves of AISI1045. Thus, cutting simulations have been carried out, which considered the material hardening in the shear zone. The simulation results were then compared with the results of the in-situ strain measurements

IN-SITU CHARACTERIZATION OF SURFACE QUALITY IN γ-TiAl AEROSPACE ALLOY MACHINING

The functional performance of critical aerospace components such as low-pressure turbine blades is highly dependent on both the material property and machining induced surface integrity. Many resources have been invested in developing novel metallic, ceramic, and composite materials, such as gamma-titanium aluminide (γ-TiAl), capable of improved product and process performance. However, while γ-TiAl is known for its excellent performance in high-temperature operating environments, it lacks the manufacturing science necessary to process them efficiently under manufacturing-specific thermomechanical regimes. Current finish machining efforts have resulted in poor surface integrity of the machined component with defects such as surface cracks, deformed lamellae, and strain hardening. This study adopted a novel in-situ high-speed characterization testbed to investigate the finish machining of titanium aluminide alloys under a dry cutting condition to address these challenges. The research findings provided insight into material response, good cutting parameter boundaries, process physics, crack initiation, and crack propagation mechanism. The workpiece sub-surface deformations were observed using a high-speed camera and optical microscope setup, providing insights into chip formation and surface morphology. Post-mortem analysis of the surface cracking modes and fracture depths estimation were recorded with the use of an upright microscope and scanning white light interferometry, In addition, a non-destructive evaluation (NDE) quality monitoring technique based on acoustic emission (AE) signals, wavelet transform, and deep neural networks (DNN) was developed to achieve a real-time total volume crack monitoring capability. This approach showed good classification accuracy of 80.83% using scalogram images, in-situ experimental data, and a VGG-19 pre-trained neural network, thereby establishing the significant potential for real-time quality monitoring in manufacturing processes. The findings from this present study set the tone for creating a digital process twin (DPT) framework capable of obtaining more aggressive yet reliable manufacturing parameters and monitoring techniques for processing turbine alloys and improving industry manufacturing performance and energy efficiency

The Orthogonal In-Situ Machining of Single and Polycrystalline Aluminum and Copper, Volume 1

Metal cutting is a unique deformation process characterized by large strains, exceptionally high strain rates and few constraints to the deformation. These factors, along with the difficulty of directly measuring the shear angle, make chip formation difficult to model and understand. One technique for skirting the difficulty of post mortem chip measurement is to perform a cutting experiment dynamically in a scanning electron microscope. The performance of the in-situ experiment with full instrumentation allows for component force measurement, orientation measurement (on a round single crystal disk) and a timing device, all superimposed below the deformation on the TV monitor and recorded for future viewing. This allows the sher angle to be directly measured for the screen along with the other needed information

Machining as a mechanical property test revisited

There is much need for data on mechanical behavior of metals at high strains and strain rates. This need is dictated by modeling of processes like forming and machining, wherein the material in the deformation zone is subjected to severe deformation conditions atypical of conventional material property tests such as tension and torsion. Accurate flow stress data is an essential input for robust prediction of process outputs. Similar requirements arise from applications in high speed ballistic penetration and design of materials for armor. Since the deformation zone in cutting of metals is characterized by unique and extreme combinations of strain, strain rate and temperature, an opportunity exists for using plane-strain cutting as a mechanical property test for measuring flow properties of metals.^ The feasibility of using plane-strain cutting to measure flow properties of metals is revisited in the light of recent data showing controllability of the deformation conditions in chip formation by systematic variation of process input parameters. A method is outlined as to how the deformation conditions can be varied by changing the process parameters. The method is applied to cutting of commercially pure copper (FCC), iron (BCC) and zinc (HCP). Forces and chip geometries are measured, in conjunction with particle image velocimetry characterization of the deformation using high speed image sequences. The flow stresses are estimated from these measurements.^ The measured flow stress and its dependence on strain are shown to agree well with prior measurements of these parameters using conventional tests, and flow stress inferred from hardness characterization. The method is also demonstrated to be able to measure properties of metals that recrystallize at room temperature (zinc), wherein quasi-static tests predict much lower strength. Sources of variability and uncertainty in the application of this measurement technique are discussed. Future work in the context of further evaluation of this measurement approach is proposed

Study on Ductile Fracture with Anisotropic and Strain Rate Effects in Manufacturing Processes

Ductile fracture is a topic of great importance in automotive and aerospace industries. Prediction of ductile fracture in engineering structures relies on developing robust material models under complex loading conditions. This dissertation addresses the anisotropic and strain rate effects in constitutive and ductile fracture models of lightweight metals. In the present modeling framework, the anisotropic plasticity behavior is modeled by combination of an initial anisotropic yield function and an isotropic hardening correction by Lode dependence. A new all-strain based anisotropic fracture model is proposed based on the approach of linear transformation on plastic strain rate tensor. The strain rate effects in ductile fracture is considered as an extension of the modified Mohr-Coulomb (MMC) fracture model by coupling strain rate with stress state in terms of Lode angle parameter. The rate-dependent MMC model provides a well-bound solution up to the intermediate strain rate range ( \u3c 1000/s) for metal forming and crashworthiness applications. The present modeling framework is calibrated from coupon tests of aluminum alloy and advanced high strength steel (AHSS) sheets using digital image correlation (DIC) technique and validated through correlations by finite element (FE) simulations. This study also demonstrates the applications of ductile fracture modeling in manufacturing processes. The thermo-mechanical FE simulations of orthogonal cutting processes using the Johnson-Cook constitutive and damage models show that the highly damaged regions in zones of material separation form a thin boundary layer at the tool tip. The numerical simulation results explain the success of analytical model with uncoupled component works of plasticity, friction and separation. The FE modeling results of formability and component-level testing suggest that part behavior and material failure is well predicted using calibrated ductile fracture models under different loading conditions

Advances in Design Methodology in Swelling Shale Rock in Southern Ontario

As infrastructure requirements increase in southern Ontario, excavations within swelling rock formations will become more frequent and larger. The objective of this study is to advance design capability for structures in swelling rock through three aspects: i) developing a practical swelling model for design engineers, ii) investigate two crushable/compressible materials for the mitigation of swelling rock effects, and iii) observe and analyze the behaviour of swelling rock to current excavation techniques. A swelling rock constitutive model has been developed. The swelling parameters include the horizontal and vertical free swell potential, threshold stress, and critical stress as well as a “pseudo-Poisson’s ratio” effect that allows the practicing engineer to explore the interaction between orthogonal suppression pressures without the need for advanced testing. The model has been verified through analysis of swell tests and well-documented case studies. Extruded polystyrene foams and light-weight cellular grouts were tested at monotonic low strain rates mimicking the loading behaviour of swelling rock to identify their potential as mitigation materials. Results show low strain rates affect the yield strengths and elastic moduli. Cellular grout test results indicate it behaves as three-phase material in stress and groundwater conditions typical for infrastructure projects. Two case studies were investigated, monitoring, and analyzed. The Zone 1 Water Main project was located in the Halton Region, Ontario and the Billy Bishop Pedestrian Tunnel was located in Toronto, Ontario Results were analyzed to investigate the effect of excavation technique and shape on the elastic and time-dependent deformations of the rock mass