M. Ramulu

A study on the drilling of composite and titanium stacks

Abstract An experimental study on drilling of graphite/bismaleimide (Gr/Bi) titanium (Ti) stacks was conducted by using different cutter materials with a standard geometry to understand and characterize the process. The tool materials used were high-speed steel (HSS), high-speed cobalt (HSS-Co), and carbide. It was observed that at the interface of Gr/Bi–Ti, high temperatures induced material damage near and around the hole region. Dissimilar mechanical and thermal properties affected the tool life and allowed for increased matrix degradation and burr formation in Ti, regardless of the cutting tool material. As a result, fewer holes were produced when high spindle speeds and slow feeds were used. It was also found that carbide drills outperformed all other tools in terms of tool life, minimal surface damage, and heat induced damage on both workpiece materials.

Drilling process optimization for graphite/bismaleimide-titanium alloy stacks

Abstract In this study, the drilling process of graphite/bismaleimide-titanium alloy (Gr/Bi–Ti) stacks was optimized in terms of machined hole quality and machining cost. The drilling experiments were conducted by using two different cutter materials, HSS-Co and carbide. Drilled hole quality parameters include surface texture, titanium burrs, hole diameter, cylindricity, and roundness deviation. Machining cost was estimated through drill wear experimentations. A multiple objective linear program was used to optimize drilling feed and speed not only to maximize each hole quality parameter to the greatest extent possible but also to minimize machining cost. Optimum process conditions for achieving desired hole quality and process cost were found to be a combination of low feed and low speed when using carbide drills, and high feed and low speed in drilling with HSS-Co drills. The sensitivity of weighting factors on the feasible process conditions depends on the optimal point position and distribution of each objective.

Orthogonal cutting of fiber-reinforced composites : A finite element analysis

Abstract Orthogonal cutting of unidirectional fiber-reinforced polymer composites was analyzed using the finite element method. A dual fracture process was used to simulate chip formation incorporating both the maximum stress and Tsai—Hill failure criteria. All aspects of the cutting tool geometry are considered in the model including the tool rake and clearance angles, nose radius and wear land, as well as friction between the tool and work material. Predictions for the cutting forces from numerical simulations are verified with experimental measurements for orthogonal trimming of unidirectional graphite/epoxy. The principal cutting force predictions agree very well with those obtained from experiments. The influence of fiber orientation and tool geometry on the fracture stress are highlighted and their effects on the material removal process in orthogonal trimming of reinforced polymers are discussed.

Electron Beam Additive Manufacturing of Titanium Components: Properties and Performance

This research evaluates the fatigue properties of Ti-6Al-4V specimens and componentsproduced by Electron Beam additive manufacturing. It was found that the fatigue per-formance of specimens produced by additive manufacturing is significantly lower thanthat of wrought material due to defects such as porosity and surface roughness. However,evaluation of an actual component subjected to design fatigue loads did not result in pre-mature failure as anticipated by specimen testing. Metallography, residual stress, staticstrength and elongation, fracture toughness, crack growth, and the effect of post process-ing operations such as machining and peening on fatigue performance were alsoevaluated. [DOI: 10.1115/1.4025773]Keywords: additive manufacturing, electron beam, titanium, fatigue, fracture

State of the Art of Research and Development in Abrasive Waterjet Machining

Thermodynamic analysis of material removal mechanisms indicates that an ideal tool for shaping of materials is a high energy beam, having infinitely small cross-section, precisely controlled depth, and direction of penetration, and does not cause any detrimental effects on the generated surface. The production of the beam should be relatively inexpensive and environmentally sound while the material removal rate should be reasonably high for the process to be viable. A narrow stream of high energy water mixed with abrasive particles comes close to meeting these requirements because abrasive waterjet machining has become one of the leading manufacturing technologies in a relatively short period of time. This paper gives an overview of the basic research and development activities in the area of abrasive waterjet machining in the 1990s in the United States.

Chip formation in orthogonal trimming of graphite/epoxy composite

The mechanisms of chip formation in edge trimming of graphite/epoxy laminates with polycrystalline diamond tools were studied. Characteristics of chip formation were found to be primarily dependent on fibre orientation, with only secondary effects from tool geometry and operating conditions. Although discontinuous chips were noted with all tool/material combinations, variation in the chip geometry depicted a change in chip formation mechanisms with fibre orientation. Spectral analysis of the cutting force signatures and machined surface profiles were used to distinguish changes in chip geometry with fibre orientation and tool geometry. An increase in the rake angle of the cutting tool insert was found to localize the extent of fracture from the tool nose, resulting in smaller discontinuous chips and giving rise to a higher machined surface quality.

The influence of abrasive waterjet cutting conditions on the surface quality of graphite/epoxy laminates

Abstract An experimental investigation was conducted to determine the influence of cutting parameters on the surface roughness and kerf taper of an abrasive waterjet machined graphite/epoxy laminate. Experimental design was used to systematically measure the influence of cutting parameters on the surface roughness and kerf taper of laminate specimens. Stylus prolifometry was used to measure the surface roughness and a visual inspection including scanning electron microscopy (SEM) was conducted. Profilometry measurements supplemented with microscopy analysis suggests that three regions of surface topography are evident on the machined surface of the laminate specimens. ANOVA techniques indicate that the influence of cutting parameters on the surface roughness changes as a function of cutting depth. Mathematical models were developed to predict the surface roughness and kerf taper in terms of the cutting parameters of a graphite/epoxy laminate to cutting depths of 16 mm.

Effect of fibre direction on surface roughness measurements of machined graphite/epoxy composite

Abstract Machined graphite/epoxy composite surfaces were studied using surface profilometry and scanning electron microscopy to determine suitable surface-describing parameter(s) for machined fibrous composite surfaces. It was found that the microgeometrical variations in terms of roughness parameters Ry and Rz are better descriptors of the machined surface than the commonly used roughness parameters Ra and Rq. The surface roughness and profile are found to be highly dependent on the fibre orientation and the measurement direction. The power spectral density function is shown to be capable of identifying the wavelength distribution of the machining damage that corresponds to the spatial distribution of the valleys in the profiles. Surface profiles of machined unidirectional composite laminates are found to be Gaussian and periodic in the direction of machining, and Gaussian and random perpendicular to the cutting direction. While edge-trimmed cross-ply laminate surfaces are Gaussian and random for profiles measured along the tool movement direction, they are periodic and non-Gaussian in the direction perpendicular to the tool movement.

Material removal in abrasive waterjet machining of metals. Surface integrity and texture

An experimental study was conducted to determine the influence of material properties on the surface integrity and texture that results from abrasive waterjet (AWJ) machining of metals. A microstructure analysis, microhardness measurements, and profilometry were used in determining the depth of plastic deformation and surface texture that result from material removal. Models now available for dry abrasive erosion were adopted and found useful in understanding the influence of material properties on the hydrodynamic erosion process. It was found that the depth of subsurface plastic deformation is inversely proportional to a metals strength coefficient and extends the greatest depth near jet entry in the initial damage region (IDR). Furthermore, surface skewness in AWJ machining of metals increases with ductility and the corresponding critical strain for lip formation.

Water jet and abrasive water jet cutting of unidirectional graphite/epoxy composite

Abstract Unidirectional graphite/epoxy composite material has been machined by water jet and abrasive water jet cutting processes. Topography and morphology of the machined surfaces were evaluated with surface profilometry and scanning electron microscopy. The surface characteristics in terms of roughness and the micromechanisms of material removal for both processes were analysed and compared. Abrasive water jet surface characteristics of graphite/epoxy were found to be significantly different from those of the water jet cutting process and micromechanical behaviour of material removal was strongly dependent on the fibre orientation.