Showing papers by "Mohamed Elbestawi published in 2005"

Effect of coolant strategy on tool performance, chip morphology and surface quality during high-speed machining of A356 aluminum alloy

Abstract: This paper describes the results of application of different coolant strategies to high-speed milling of aluminum alloy A356 for automotive industry. The paper investigates the effect of flood coolant, dry cutting, and minimum quantity of lubricant (MQL) technologies on tool wear, surface roughness and cutting forces. The cutting speed range was up to 5225 m/min. The feed rate used was up to 20 m/min. The result of MQL application is compared with dry milling and milling with flood coolant application. It was found that the MQL technology could be a viable alternative to the flood coolant application. The adhesive tool wear mechanism and adhesion activated surface quality deterioration are revealed and the role of lubricant in their reduction is defined.

Finite element modeling of erosive wear

Abstract: Material damage caused by the attack of particles entrained in a fluid system impacting a surface at high speed is called ‘Erosion’. Erosion is a phenomenon that takes place in several engineering applications. It also can be used in several manufacturing process such as abrasive waterjet machining. Erosion is a complex process dependent on particle speed, size, angle of attack as well as the behavior of the eroded material. Extensive experimental results have been reported in the literature on the erosion of different materials. Simulating the erosion process through finite element enables the prediction of erosion behavior of materials under different conditions, which will substitute the need of experimentation, and will enable the identification of constants required for existing analytical models. In this paper, an elasto-plastic finite element (FE) model is presented to simulate the erosion process in 3D configuration. The FE model takes into account numerical and material damping, thermal elastic–plastic material behavior and the effect of multiple particle impacts as well as material removal. The workpiece material modeled was Ti–6Al–4V. The effects of strain hardening, strain rate and temperature were considered in the non-linear material model. Comparison against results reported in literature and erosion models by Finnie, Bitter and Hashish are made. It is shown that the predicted results are in agreement with published results obtained experimentally and from analytical erosion models.

Design and control of a dual-stage feed drive

Abstract: High precision positioning over a large workspace is a fundamental feature of a precision machine. Connecting coarse (large stroke) and fine (high resolution) drive stages, in series, to form a dual-stage feed drive (DSFD) system can provide the desired performance. The DSFD concept has applications that include fast tool servos for the creation of asymmetric surfaces or online chatter suppression, and micro–macro robots for high precision assembly. This paper studies the design of DSFDs for machine tools. The design issues are discussed with special considerations for the dynamics and control of the two drive stages. Two DSFDs, single-axis and two-axis, are designed with piezoelectric actuators (PAs) for the fine stages and linear motors (LMs) for the coarse stages. Both feature flexures for frictionless precision motion that are designed to meet the static and dynamic requirements of a milling process. A model-based control algorithm ensures that the stages work together in a complementary fashion. The single-axis DSFD reduced the tracking error by about 75% in comparison to a similarly controlled LM drive. A second DSFD was built for milling experiments. In sinusoidal profile cutting the maximum tracking error was reduced by 83% and the average magnitude of the error was reduced by 63%. In sharp corner cutting the DSFD reduced the maximum tracking error by 38% and the average magnitude of the error by 39%.

On the FE Modeling of Closed-cell Aluminum Foam

Abstract: This investigation is concerned with the development of a multi-unit-cell which enables the modeling of the mechanical response of metallic foams subject to oblique loadings. The geometry of the cell was derived from careful observation of the foam morphology. The new closed unit cell is formed by the use of ellipsoids which are interconnected through a truncated pyramid. In this approach, we represent the morphology of closed-cell aluminum foams through the use of corresponding average uniform geometrical and mechanical properties. Extensive multi-unit-cell finite element analyses were conducted to examine the effect of key geometric parameters on the collapse load, normalized crush force versus deformation characteristics as well as the corresponding energy absorption. The numerical simulations were compared with crush test experiments involving different oblique loads. In spite of showing an initial stiff response, which is typical in idealized numerical models, the results revealed that the developed multi-unit-cell is able to simulate the crush behavior of closed-cell foams.

Experimental determination of the friction coefficient on the workpiece-fixture contact surface in workholding applications

Abstract: Surface flatness, geometric integrity and micro-surface finish characteristics are crucial for automotive industry to properly seal joints, reduce leakage and consequently increasing engines efficiency and reducing emissions. Optimum fixture layout is a key element in achieving this goal. Machining of flexible parts impose further challenges to the selection of a proper fixture scenario. Workpiece motion arising from localized elastic deformation at the workpiece/fixture contacts due to machining and clamping forces significantly affect the workpiece location accuracy and hence the machined part quality. The tangential friction force plays an important role in fixture configuration design as it can be utilized to reduce the number of fixture components, thereby the workpiece features accessibility to machining operations and providing a damping mechanism to dissipate input energy from machining forces out of the workpiece/fixture system. Although the literature is full of research on friction and its application, it lacks research that relates to the contact found in workpiece/fixture systems. This paper presents the results of an experimental investigation of the workpiece/fixture contact characteristics.

Evaluation of Tool Wear Suppressive Ability of Lubricants Usein in Minimum Quantity Lubrication Application in High Speed Machining of Cast Aluminum Alloys

Abstract: The disadvantages of conventional metalworking fluids such as disposal problems, health problems and economic factors have led to the development of strategies to reduce their amount in metalworking. Recently, Minimum Quantity Lubrication (MQL) technology was developed and it seems to be a suitable alternative for economically and environmentally compatible production. It combines the functionality of lubrication with an extremely low consumption of lubricant and has a potential to replace metalworking fluids application in machining operations. The MQL lubricants are formulated with two major groups of additives; anti-wear (AW) additives and extreme pressure (EP) additives. When such lubricants are applied to the cutting zone, protective layers are formed on the interacting surfaces of the workpiece and the cutting tool. These layers prevent direct contact between the tool and chip surfaces, and, therefore reduce friction forces and tool wear. In order to utilize MQL to its full potential, it is essential to select appropriate lubricant composition for particular work material and machining parameters. The experimental study of different compositions of MQL lubricants is reported. The effectiveness of the lubricants are determined in terms of their ability to protect the cutting tool in high speed machining of cast aluminum alloys, which are widely used in automotive industry. The main objective of this research is to quantitatively evaluate the ability of lubricant’s additive composition to reduce the tool wear. This is reached through the comparison between the tool wear rate measured during the machining of aluminum cast alloy with the application of MQL, and the tool wear rate obtained in dry machining of the same alloy. Two kinds of the lubricants are evaluated; vegetable and synthetic. The content of AW and EP additives in each kind of lubricant was varied on three levels in order to capture the effect of the lubricant’s composition on tool wear. The result of the MQL lubricants evaluation is discussed and the recommendations for optimal lubricant composition are made.Copyright © 2005 by ASME