Omar Fergani

Microstructure Effects on Cutting Forces and Flow Stress in Ultra-Precision Machining of Polycrystalline Brittle Materials

This paper presents a physics-based analysis to quantitatively describe the effects of grain size, grain boundaries, and crystallographic orientation on the flow stress of the polycrystalline material and thereby on the cutting and thrust forces. The model has been experimentally validated, in terms of the force intensities and sensitivities to microstructure attributes such as the grain size and the misorientation by comparing the forces to measured data in micromachining of polycrystalline silicon carbide (p-SiC). Molecular dynamics (MD) simulations are performed to explore the effects of grain boundaries and misorientation and to validate the modeling analysis in the context of resulting force ratios. [DOI: 10.1115/1.4029648]

Prediction of Residual Stress Induced Distortions in Micro-Milling of Al7050 Thin Plate

In this paper, a new analytical model based on a mechanistic force prediction and elastoplastic relaxation procedure predicting the deflections induced by the residual stresses in a milled micro part is proposed. The force model defines the Hertzian type distribution applied by the tool on the part. The proposed deflection model is valid for thin rectangular parts typically produced only using a micro-milling process. The deflection and the force model were analytically developed and experimentally tested on thin Al 7050 micro plates. The force model was validated using micro dynamometer and the deflection profile was verified using the white light interferometer. The proposed model showed that it has a reasonable ability to predict the residual stress induced deflection in the context of stress gradient and intensity.

Analysis of residual stress-induced distortions of thin sheet structures in multi-step milling

In high-precision product industries, controlling residual stress-induced distortions in large, thin-walled components is critical in order to produce high-quality light-weight components. Understanding the residual stress history is key to deal with this problem. In this study, the residual stress history from start to end of multi-step machining is measured and investigated in order to better understand the influence of machining strategies on the part distortions. The multi-step machining process is utilized to investigate the relation between residual stress history, the machining-induced residual stress and the part distortion. An analytical model is used for reference and comparison with experiments. The experimental work is performed using multi-step milling process as experimental set-up, X-Ray diffraction to measure residual stresses, and CMM to measure the profile and the distortion of the thin structure.

Additive-manufactured sandwich lattice structures: A numerical and experimental investigation

The utilization of additive-manufactured lattice structures in engineered products is becoming more and more common as the competitiveness of AM as a production technology has increased during the past several years. Lattice structures may enable important weight reductions as well as open opportunities to build products with customized functional properties, thanks to the flexibility of AM for producing complex geometrical configurations. One of the most critical aspects related to taking AM into new application areas—such as safety critical products—is currently the limited understanding of the mechanical behavior of sandwich-based lattice structure mechanical under static and dynamic loading. In this study, we evaluate manufacturability of lattice structures and the impact of AM processing parameters on the structural behavior of this type of sandwich structures. For this purpose, we conducted static compression testing for a variety of geometry and manufacturing parameters. Further, the study discusse...

Prediction of Residual Stress in Multi-Step Orthogonal Cutting

The effect of residual stresses on the fatigue behavior as well as the dimensional stability of high precision part is very important. Machining operation consists generally multi-step operations from roughing to finishing. It is therefore critical to predict residual stresses under such configuration. In this paper, an analytical algorithm is proposed to predict the final residual stresses induced by a multi-step machining operation capturing the change of stress state of the workpiece as well as material hardening behavior during the multi-step orthogonal cutting. The model predictions were compared to other work’s finite element method (FEM) predictions.Copyright