Effect Of Tool Edge Radius Research Articles

Numerical and experimental analysis of the tool edge radius effect in micromachining of ferrous materials

The tool edge radius effect in micromachining of ferrous materials was investigated extensively using advanced numerical and experimental approaches. The results revealed that the best surface finishing could be obtained at a critical combination of undeformed chip thickness and tool edge radius where material is removed through severe plastic deformation associated with an effective negative rake angle. The chip formation exhibits an extrusion-like behaviour as driven by intense deviatoric and hydrostatic stresses that are highly localised around the deformation zone. The changes in the chip formation behaviour over the range of a/r = 0.05-2.0 are indicated by four stages of machining force distributions. It is worth noting that the tool edge radius effect has a great influence on material deformations and contact interaction in tool-based micromachining. Thus, an analytical contact length model for tool-based micromachining is proposed.

Predictive modeling of transition undeformed chip thickness in ductile-regime micro-machining of single crystal brittle materials

This paper proposes a predictive model to determine the undeformed chip thickness in micro-machining of single crystal brittle materials, where the mode of chip formation transitions from the ductile to the brittle regime. The comprehensive model includes a force model considering the rounded tool edge radius effect and ploughing. Irwin's model for computing the stress intensity factor is adopted here as it gives a relation between the stress intensity and applied normal stress including effects of crack size and crack inclination. The occurrence of plastic deformation is built upon the condition that the shear stress in the chip formation region must be greater than the critical shear stress for chip formation and the stress intensity factor must be less than the fracture toughness of the material. The point of transition takes place when the fracture toughness is equal to the stress intensity factor. The above conditions form the theoretical basis for the proposed model in determining the transition undeformed chip thickness. End-turning experiments have been conducted using a single crystal diamond cutting tool on (1 1 1) single crystal silicon, and the results compared to the model predictions for validation. The proposed model would support the determination of the cutting conditions for the micro-machining of a brittle material in ductile manner without resorting to trial and error.

The effect of tool edge radius on the contact phenomenon of tool-based micromachining

The contact phenomenon during micromachining is complicated due to the tool edge radius. This paper presents investigation of the effects of tool edge radius on the frictional contact and flow stagnation phenomenon, the stick–slide behavior and contact stress distributions, the evolutions of contact length, and the relationship between material deformation and total contact length. Through the arbitrary Lagrangian–Eulerian FE modeling approach, our findings revealed that the flow stagnation during material separations could be attributed to the counterbalance of shear contact components and it appeared to be insensitive to machining magnitude where a constant stagnation point angle of 58.5±0.5° was determined for a wide range of undeformed chip thicknesses. Three distinctive sticking and sliding regions associated with the flow stagnation phenomenon on the cutting tool were discovered following the identification of two stress criteria for sticking, τ f =0 and/or τ f = k f . In addition, the influence of tool edge radius on contact length and material deformation was determined and a theoretical model for the contact length of tool-based micromachining was proposed. It was also observed that tool–chip contact evolved in two successive stages through a series of intermittent sticking and sliding interactions as governed by the undeformed chip thickness and the transition of effective rake angle. An ultraprecision machining setup coupled with a high-speed and small field-of-view photography technique was proposed for experimental substantiation of the numerical results.

A Study of Exit-Burr Formation Mechanism Using the Finite Element Method in Micro-Cutting of Aluminum Alloy

A burr formation process in micro-cutting of Al7075-T7451 was analyzed. Three stages of burr formation including steady-state cutting stage, pivoting stage, and burr formation stage are investigated. And the effects of uncut chip thickness, cutting speed and tool edge radius on the burr formation are studied. The simulation results show that the generation of negative shear zone is one of the prime reasons for burr formation. Uncut chip thickness has a significant effect on burr height; however, the cutting speed effect is minor. Unlike in conventional cutting, in micro-cutting the effect of tool edge radius on the burr geometry can no longer be neglected.

Investigations of tool edge radius effect in micromachining: A FEM simulation approach

Abstract Predictive models that are developed based on the assumption of perfectly sharp cutting tools yield reasonable accurate results for conventional machining. But the same assumption is not valid for micromachining as the undeformed chip thickness a in microscale approaches the tool edge radius r of several microns. In this study, finite element analysis (FEA) of micromachining using the arbitrary Lagrangian–Eulerian (ALE) method showed that chip is formed through material extrusion under a critical a/r

Model-Based Analysis of the Surface Generation in Microendmilling—Part I: Model Development

This paper presents the development of models that describe the surface-generation process for microendmilling. The surface-generation models for the sidewall and floor surfaces consist of deterministic and stochastic models. In the sidewall surface-generation model, the deterministic model characterizes the surface topography generated from the relative motion between the major cutting edge and the workpiece material. The model includes the effects of the process kinematics, dynamics, tool edge serration, and process faults (e.g., tool tip runout). The stochastic model predicts the increased surface roughness generated from ploughing due to the significant tool edge radius effect. In the floor surface-generation model, the deterministic model characterizes the three-dimensional surface topography over the entire floor surface and considers the effects of the minimum chip thickness, the elastic recovery, and the transverse vibration. The variation of the ploughing amount across the swept arc of the cutter due to the varying chip load conditions is considered in the stochastic model.

Modelling the effects of tool-edge radius on residual stresses when orthogonal cutting AISI 316L

Tool-edge geometry has significant effects on the cutting process, as it affects cutting forces, stresses, temperatures, deformation zone, and surface integrity. An Arbitrary-Lagrangian–Eulerian (A.L.E.) finite element model is presented here to simulate the effects of cutting-edge radius on residual stresses (R.S.) when orthogonal dry cutting austenitic stainless steel AISI 316L with continuous chip formation. Four radii were simulated starting with a sharp edge, with a finite radius, and up to a value equal to the uncut chip thickness. Residual stress profiles started with surface tensile stresses then turned to be compressive at about 140 μm from the surface; the same trend was found experimentally. Larger edge radius induced higher R.S. in both the tensile and compressive regions, while it had almost no effect on the thickness of tensile layer and pushed the maximum compressive stresses deeper into the workpiece. A stagnation zone was clearly observed when using non-sharp tools and its size increased with edge radius. The distance between the stagnation-zone tip and the machined surface increased with edge radius, which explained the increase in material plastic deformation, and compressive R.S. when using larger edge radius. Workpiece temperatures increased with edge radius; this is attributed to the increase in friction heat generation as the contact area between the tool edge and workpiece increases. Consequently, higher tensile R.S. were induced in the near-surface layer. The low thermal conductivity of AISI 316L restricted the effect of friction heat to the near-surface layer; therefore, the thickness of tensile layer was not affected.

Molecular dynamics simulation of the effect of tool edge radius on cutting forces and cutting region in nanoscale ductile cutting of silicon

Unlike in conventional cutting processes, where the undeformed chip thickness is significant compared to the cutting tool edge radius, in nanoscale cutting processes, the undeformed chip thickness is very small, on the nanoscales. Therefore, the tool edge radius can not been ignored. It has been found that there is a brittle-ductile transition in cutting of brittle materials when the cutting tool edge radius is reduced to nanoscale and the undeformed chip thickness is smaller than the tool edge radius. In order to better understand the mechanism of the transition, a molecular dynamics (MD) method, which is different from continuous linear mechanics, is employed to model and simulate the nanoscale ductile mode cutting process of monocrystalline silicon wafer. The simulated variation of the cutting forces with the tool cutting edge radius is compared with the results of the cutting force from experimental cutting tests and they show a good agreement. In the simulated results, it can be seen that the thrust force is much larger than the cutting force in cutting. The simulated results also denote that the resultant force in the cutting process is not uniformly distributed along the cutting tool edge. In the simulation, the elastic springback of small thickness is observed on the machined workpiece surface.