José Outeiro

Evaluation of Present Numerical Models for Predicting Metal Cutting Performance And Residual Stresses

Efforts on numerical modeling and simulation of metal cutting operations continue to increase due to the growing need for predicting the machining performance. A significant number of numerical methods, especially the Finite Element (FE) and the Mesh-free methods, are being developed and used to simulate the machining operations. However, the effectiveness of the numerical models to predict the machining performance depends on how accurately these models can represent the actual metal cutting process in terms of the input conditions and the quality and accuracy of the input data used in such models. This article presents results from a recently conducted comprehensive benchmark study, which involved the evaluation of various numerical predictive models for metal cutting. This study had a major objective to evaluate the effectiveness of the current numerical predictive models for machining performance. Five representative work materials were carefully selected for this study from a range of most commonly used work materials, along with a wide range of cutting conditions usually found in the published literature. The differences between the predicted results obtained from the various numerical models using different FE and Mesh-free codes are evaluated and compared with those obtained experimentally.

Influence of tool sharpness on the thermal and mechanical phenomena generated during machining operations

Although the definition of the cutting tool edge radius is self-evident, its influence on the cutting process is ambiguous. Therefore, a certain qualitative assessment criterion should be developed to classify the cutting edge as to be sharp or rounded in the modelling of the cutting process. It is particularly important because carbide insert manufacturers supply the same product with different radii of the cutting edge. This paper quantifies the importance of the cutting edge radius. It considers the ratio of the cutting edge radius and the uncut chip thickness as the Relative Tool Sharpness (RTS) of the cutting edge. The influence of RTS on the cutting process was analysed analytically and experimentally. This paper discusses the influence of RTS on the energy flows in the metal cutting system and the energy balance of this system.

Thermo-mechanical effects in drilling using metal working fluids and cryogenic cooling and their impact in tool performance

Cryogenic machining opens up new industrial perspectives in difficult-to-cut materials like nickel-based alloys. In particular, drilling is an operation that generates high thermal and mechanical loading to the drill. Therefore, tool performance, hole geometry and surface integrity can be highly affected. The objective of this study is to analyse tool performance during drilling of IN718 using conventional metal working fluids (MWF) and cryogenic cooling conditions, and correlate it with the thermo-mechanical phenomena. This study is conducted with standard coated cemented carbide twist drills, designed to work with MWF. The results show that drill performance under cryogenic cooling is strongly affected by its geometry. The axial force, drilling torque and tool wear/failure are higher under cryogenic cooling when compared to conventional MWF. Therefore, in order to take advantage of the cryogenic machining, new drill design is required, which currently is not available on the market.

Surface integrity predictions and optimisation of machining conditions in the turning of AISI H13 tool steel

Surface integrity (SI) plays a very important role in functional performance. It is dependent on a large number of machining parameters. The major concern of industry is to know which combination of machining parameters provides the best SI of machined components. Traditionally, surface roughness is considered to be the principal parameter to assess the SI of a machined part. However, residual stresses also become an important parameter because they control the lifetime of components (moulds, dies, etc.) and their abilities to withstand severe thermal and mechanical cyclic loadings (fatigue) during service. Therefore, significant improvements in the quality of the mould/die can be achieved with the control of residual stresses and surface roughness, both induced by machining. This paper examines both residual stresses and surface roughness induced by the dry turning of AISI H13 tool steel with different hardnesses. SI parameters were evaluated experimentally with respect to tool geometry, cutting speed, feed and depth of cut. A modelling and optimisation procedure based on artificial neural network (ANN), response surface methodology (RSM) and genetic algorithm (GA) approaches was developed and applied to identify the optimum combination of cutting parameters, leading to the best SI for machined components.

Residual Stresses in Machining of AISI 52100 Steel under Dry and Cryogenic Conditions: A Brief Summary

Residual stress is one of the most important surface integrity parameter that can significantly affect the service performance of a mechanical component, such as: contact fatigue, corrosion resistance and part distortion. For this reason the mechanical state of both the machined surface and subsurface needs to be investigated. Residual stress induced by dry and cryogenic machining of hardened AISI 52100 steel was determined by using the X-ray diffraction technique. The objective was to evaluate the influence of the tool cutting edge geometry, workpiece hardness, cutting speed, microstructural changes and cooling conditions on the distribution of the residual stresses in the machined surface layers. The results are analysed in function of the thermal and mechanical phenomena generated during machining and their consequences on the white layer formation.