Key Engineering Materials Vols. 651-653

Abstract: Double angle drills have recently been used to improve the surface finish in drilling. The double angle drill consists of lower edges at a large wedge angle and upper edges at a small wedge angle on the lips. The paper discusses the cutting processes of the double angle drill in analysis and experiment. A force model is applied to simulate the cutting force and the chip flow direction. The cutting tests are conducted to verify the force model in drilling of carbon fiber reinforced plastic (CFRP) and aluminum alloy (A7075) with a single and a double angle drills. The double angle drill is effective in control of delamination in drilling of CFRP due to reduction of the thrust force. Meanwhile, in drilling of A7075, the small wedge angle of the upper edges on the double angle drill is not effective in reduction of the thrust forces. The curved edge at the end of the lip, in turn, promotes burr formation in drilling of A7075. The effectiveness of the double angle drill depends on the workpiece material.

Abstract: This paper presents an improvement of the approach for increasing automation level of CNC machines by using a supervising controller that, for a given toolpath, tool geometry, and workpiece material, calculates the optimal sequence of controls. The developed system, based on three steps: process simulation, solution of the optimal control problem (OCP), and state reconstruction with state learning, is improved while reformulating the OCP by taking into account the surface roughness.

Abstract: In numerical approaches for high speed machining, the rheological behavior of machined materials is usually described by a Johnson Cook law. However, studies have shown that dynamic recrystallization phenomena appear during machining in the tool/chip interface. The Johnson Cook constitutive law does not include such phenomena. Thus, specific rheological models based on metallurgy are introduced to consider these dynamic recrystallization phenomena. Two empirical models proposed by Kim et al. (2003) and Lurdos (2008) are investigated in machining modeling. A two-dimensional finite element model of orthogonal cutting, using an Arbitrary Lagrangian-Eulerian (ALE) formulation, is developed with the Abaqus/explicit software. Specific rheological models are implemented in the calculation code thanks to a subroutine. This finite element model can then predict chip formation, interfacial temperatures, chip-tool contact length, cutting forces and chip thickness with also and especially the recrystallized area. New specific experiments on an orthogonal cutting test bench are conducted on AISI 1045 steel specimens with an uncoated carbide tool. Many tests are performed and results are focused on total chip thicknesses and recrystallized chip thicknesses. Finally, compared to numerical results got with a Johnson Cook law, numerical results obtained using specific rheological models to take into account dynamic recrystallization phenomena are very close to experimental results. This work shows also the influence of rheological behavior laws on predicted results in the modeling of high speed modeling.

Abstract: The microstructure of materials has a significant influence on tool life, however most of the research in modelling to date considers the material as homogeneous. This research aims to develop a microstructure-based Finite Element Model in order to qualitatively analyze the influence of the scale of the microstructure on the generated tool wear. In particular, this paper is focused on the orthogonal cutting process of a ferrite-pearlite dual-phase steel using uncoated carbide tools. Based on individual mechanical properties of these phases, a 3D coupled Eulerian Lagrangian heterogeneous model was developed. An empirical tool wear rate prediction model was implemented by a user subroutine in both models (heterogeneous and homogeneous) to predict wear and wear rate values. A comparison between the microstructure-base model (heterogeneous) and the homogeneous model considering wear and wear rate values was made. The results demonstrate the validity of microstructure-based Finite Element Model for an improved prediction of the wear phenomena.

Abstract: The objective of the present paper is to analyse the dynamic recrystallization process occurring during the hot cutting of spheroidal graphite iron. In the first instance, hot cutting tests are performed with an orthogonal cutting test bench. The emergence of dynamic recrystallization is highlighted thanks to microstructural observations. Then, a finite element model of the hot cutting operation is introduced. The material behaviour is modelled with a specific constitutive model considering the influence of dynamic recrystallization on the plastic flow stress. Finally, the predictive response of this model is compared to the experimental observations.

Abstract: The workpiece distortion that occurs during machining, can lead to a large increase in the number of the scrap parts. Residual stresses are the main cause of these distortions and they are generally present in both forging and casting products. In order to obtain the desired microstructure and mechanical properties, the workpiece is subjected to heat treatment before being worked. Quenching produces residual stresses that exist throughout a large percentage of the casting or forging part. Distortion occurs as a result of removing stressed material from the workpiece. The component will re-equilibrate and distort as each layer of stressed material is machined away. This paper describes a procedure development for distortions numerical analysis on a SAF2507 casting bulk workpiece. A solubilization heat treatment has been simulated, in order to predict the bulk residual stresses distribution. Different metal cutting processes have been considered to measure the numerical distortions induced in the workpiece.

Abstract: Forces and temperatures in specific orthogonal cutting conditions and calculated by finite element analysis, have been evaluated taking into account the uncertainty of some process conditions. A traditional deterministic approach, in machining simulations, is not able to explain the uncertain physical variations related to material characteristics (yield and tensile strenght, hardness, etc.) and tool/chip/workpiece interface conditions (friction and tool wear). During machining operations many different sources of non-controllable process variations usually display their effect leading to a degree of uncertainty in the final parts quality. Statistical tools and methods are increasingly being used in combination with FE numerical simulation, in order to take in account of the variability of the process. Then, if one of the purposes of process design is to study and model robustness or reliability of a given process in aleatory conditions, a CAE study might become a feasible way to do it. Today, the evaluation of the performances of a metal cutting process is possible using several commercial FEA packages. These software tools automatically allow the preventive evaluation of the robustness of technological decisions. In this work the authors, by means the integration between stochastic simulation tools and machining FE codes, have evaluated the process sensitivity to a random variation of uncontrollable parameters or conditions. Furthermore, a specific experimental and numerical activity has been performed in order to better understand the technical capabilities in terms of process simulation in stochastic conditions.

Abstract: Finite element analysis of cutting processes of difficult-to-cut alloys is attracting more and more interest among the scientific community thanks to the change of predicting difficult to measure parameters as cutting forces, specific cutting pressures, cutting temperatures and the chip morphology. Aiming at calibrating and validating an FE numerical model, the predicted variables have to be compared with experimental results. Nowadays, Additive Manufactured Titanium alloys are being increasingly employed in the production of surgical implants and aero engine parts, but their peculiar fine acicular microstructure have to be taken into account dealing with their thermo-mechanical behavior as during machining operations. Based on the lack of literature works concerning experimental investigations on the machinability of Additive Manufactured Titanium alloys, this paper is aimed at investigating the cutting forces and temperatures arising during orthogonal cutting of an Electron Beam Melted (EBM) Ti6Al4V alloy.

Abstract: The formability requirements of high-strength steels are increasing as a result of progressive lightweight construction. An innovative two-stage shear cutting process has been developed in order to meet these requirements. It significantly reduces the edge crack sensitivity of the material in the cutting zone. Studying the effect of worn tool elements on process safety is a key focus for the ongoing improvement of this production process. A production-based tool condition was simulated by creating different cutting edge radii on the active tool elements. Collaring tests showed a reduction of residual formability through wear of up to 65% for high-strength heavy plates (plate thickness > 3 mm).

Abstract: Near-net shape austempered ductile iron (ADI) castings can be considered as a significant economic advantage to the increasing industrial demand for cost and weight efficient materials. However, due to microstructure induced inherent properties, ADI is considered as hard to machine material. The present paper thus investigates the interaction between the microstructural characteristics of ADI and wear mechanisms of PVD-coated carbide tools. The inherent properties of ADI materials are the function of its microstructural characteristics (retained austenite volume content and its carbon content, ferritic cell size, etc.) which can be controlled by the austempering parameters. Experimental studies of dry drilling of different ADI materials with the PVD-coated carbide tools were carried out at a cutting speed of 60 m/min and at a feed of 0.15 mm/rev. The wear mechanisms of the cutting tools were studied by using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis techniques. The obtain results revealed the evolution of crater wear as the main wear mode. In addition, it provides the key findings aims to correlating the machining characteristics of ADI with its microstructure and production conditions.