Abdel E. Bayoumi

A study on shear banding in chip formation of orthogonal machining

A simplified theory of instability of plastic flow is applied in this paper to analyze the formation of shear localized chips in orthogonal machining. A flow localization parameter is expressed in terms of associated cutting conditions and properties of the workpiece material. The analysis is used to investigate the effect of cutting conditions on the onset of shear localization and the formation of adiabatic shear banding in metal cutting. Comparisons are made between the analysis and experiments in which the flow localization parameter is obtained for several workpiece materials. The results of this investigation are thought to lend a strong justification for the analysis and its potential benefits in analyzing and/or remedying problems associated with chip formation and temperature generated in metal cutting.

Tool wear modeling through an analytic mechanistic model of milling processes

Abstract Very few attempts have been made to simulate the cutting forces for 2D cutting processes with sharp cutting tools and even fewer attempts with the use of worn cutting tools. This paper presents an approach to model tool flank wear effects through a previously developed analytic mechanistic model for milling operations. This expansion of the model can be used to predict cutting forces acting on the flank and rake surfaces of a milling cutter as a function of the cutter geometry, cutting conditions, tool wear and a set of process parameters. This is a new and important capability in milling processes for control purposes and for predicting tool wear in real-time applications. The mechanistic flank wear model is developed in a similar manner to that for sharp tools, in which a mechanistic approach and force equilibrium expressions of the normal and friction loads acting on the flank surface of the tool were used. An appropriate set of transformations is developed to transform the set of equilibrium force equations that act on the flank surface to a fixed coordinate system attached to the cutting tool. The measured flank forces are experimentally obtained and used with the flank force equations to solve for the flank friction and pressure parameters. The results show the effect of feed rate, spindle speed and flank wear on the process parameters. The predicted cutting forces compare well with the measured cutting forces.

Interfacial shear strength and durability improvement by silanes in single-filament composite specimens of basalt fiber in brittle phenolic and isocyanate resins

In connection with a study of the fiber reinforcement of wood, a number of silane coupling agents were evaluated in the bonding of basalt fibers to phenolic and isocyanate resins most commonly used in wood bonding. Interfacial shear strength improvement before and after 1 h boiling in water was determined, utilizing a modified single-filament composite specimen in which the fiber was first coated by a thin layer of brittle phenolic or isocyanate resin before being embedded in a flexible epoxy resin matrix. In the case of the phenolic resin, the most improvement was obtained with 3-(4-methoxyphenyl)propylmethyldichlorosilane, which provides more reactive aromatic sites for substitution than phenethyltrimethoxysilane. Similarly, for the isocyanate resin, 3-aminopropyltriethoxysilane gave the best results. In this case, the reaction of the amino group with the isocyanate resin through successive formation of carbamic acid and urea bonds was confirmed by FT-IR spectral data. Monitoring of acoustic emission du...

A parametric study of improving tool life by electrospark deposition

Abstract Electrospark alloying (ESA) is a pulsed microwelding surfacing process for alloying a hard wear resistant electrode with a metallic substrate. This process was evaluated as a means of increasing metal cutting tool life in machining operations. A number of ESA electrode material parameters were first screened with a crossed cylinder wear testing machine (ASTM G-83). Full hard high speed steel (HSS) cylinders were run against an ESA-coated stationary HSS cylinder. Three superior coatings from these tests were then applied to the flank and face surfaces of high speed steel tools. Machining test results showed that the dominant wear mode of crater wear was significantly reduced by ESA coating. ESA coating of the tool face only was shown to increase wear resistance significantly more than coating both face and flank surfaces. In addition, programming the electrode motion from side to side rather than front to back over the tool face increased tool life. Comparisons are made with uncoated HSS and TiN-coated (PVD technique) HSS tools. The TiN-coated tool has a similar tool life to failure. The best ESA coated tool had a life better than the HSS tool by roughly 2000%.

Determination of process parameters through a mechanistic force model of milling operations

Abstract Mechanistic process parameters for the end milling operation are determined for 11L17 free machining steel, 2024 aluminum and 62-35-3 free machining brass by analyzing the measured cutting force data and using a mechanistic force model. It has been found that pressure and friction acting on the cutter-chip interface decrease with the increase of feed rate, while the cutting speed has a negligible effect on some of the material-dependent parameters. Process parameters are summarized into empirical equations as functions of feed rate and tool rotation angle for each workpiece material. The use of sampled force data in the computation of the process parameters reduces the amount of testing greatly compared to those methods that utilize only average force data.

Comparison of the wear resistance of selected steels and cemented carbide cutting tool materials in machining wood

Abstract An experimental investigation is described where specimens of selected steels and cemented carbides are tested to simulate cutting green wood and cured wood. Extensive results are presented that show quantitatively the progressive wear of several Stellites, steels and cemented carbides as a function of time for sliding under wet and dry conditions. A simple theoretical analysis of tool wear that applies to cutting green wood with cemented carbide tools is described. The analysis, which indicates the important parameters in the wear process, is used to predict the effect of carbide particle size on wear rate. Comparisons are made between the predicted and experimentally determined wear rates for two groups of cemented carbide materials. Good agreement is found between experimental measurements and theoretical predictions. It is shown that wear depends on carbide particle size. Superior wear resistance of cemented carbides is attributed to the high hardness and low chemical reactivity of the carbide phase. The improved wear resistance of the Stellites is attributed to the low reactivity of the matrix.

On tool wear and its effect on machined surface integrity

This paper presents the results of an investigation of induced residual stress, induced strain, and induced subsurface energy in machined surfaces due to the machining process. The influence of tool wear on residual stress, strain, and energy is also reported. The exact elasticity solution for a split ring was extended and used to calculate the residual stress in the machined surface by using ring dimension changes caused by the electrochemical removal of a thin layer of residually stressed surface. The strain distribution beneath the machined surface was determined by using the grid technique. The subsurface energy stored in the machined surface was then obtained from the data of residual stress and strain. For the materials studied, this investigation showed that such energy could not be neglected when establishing the total energy needed for machining a unit volume of material.Tool coatings having different surface roughness and tools having various magnitudes of flank wear were investigated. The experimental results show that tool wear is a dominant factor affecting the values of induced residual stress, strain, subsurface energy, and the quality of the machined surface. The increase of tool wear caused an increase of residual stress and strain beneath the machined surface. It was also found that the overall energy stored in the machined subsurface increases as the tool wear increases and as the tool surface gets rougher. When the cutting tool is severely worn, the machined surface not only becomes very rough, but also contains many partially fractured laps or cracks. This makes tool wear a key factor in controlling the quality of the machined surface.

The effect of donor-acceptor interactions on the mechanical properties of wood

This paper explores the empirical correlations between the mechanical properties of solvent-treated wood and solvent parameters. Wood beams (10 inch x 0.7 inch x 0.4 inch) of lauan, birch, and Douglas fir were soaked in five solvents (benzene, dioxane, methanol, dimethyl sulfoxide, and distilled water) for 4 months at room temperature (23°C) and then mechanically tested in bending. The acoustic emission (AE) energy (related to failure energy), the modulus of rupture (MOR), and the modulus of elasticity (MOE) of the specimens were determined. It was found that all of these properties of the specimens decreased with the solvent strength parameter which was related to acceptor number (AN), donor number (DN) and molecular volume (MV ). The linear correlation of the AE energy of the specimens with the solvent parameter (AN + DN)1/2 was verified. Alternative relationships between the AE energy, MOR or NIOE of the specimens and the modified solvent strength parameters, 2.5 DN + AN or DN/MV1/3, were explored. The...

A statistical wear model for certain tool materials with applications to machining

Abstract The stochastic nature of tool life is explored using wear data from experimental tests on selected cutting tool materials. The theoretical predictions of the progressive wear of these materials as a function of time, for sliding under both wet and dry conditions, are compared with the experimental results. A statistical wear model, encompassing three stages of wear, is developed and the Birnbaum-Saunders cumulative damage distribution is used to describe the stochastic variability. The distribution of wear-out time is thereby determined.

Automated tool-wear monitoring and tool changing using intelligent supervisory control†

Process performance is very dependent upon the unique characteristics of the process equipment and the work/tooling interactions. To address this problem, research has been conducted to explore the feasibility of using an intelligent supervisory controller to build a local process database and provide control for the process. The research concerns the milling process as used in a machining centre. This paper will report on the data analysis, proposed control approaches, and how these results relate to the intelligent supervisory controller