Surface integrity when machining age hardened Inconel 718 with coated carbide cutting tools

Considerable attention has been given to the use of ceramic cutting tools for improving productivity in the machining of heat resistant super alloys (HRSA). However, because of their negative influence on the surface integrity, ceramic tools are generally avoided particularly for finishing applications. As a result the main high end manufacturers are more or less dependent on carbide cutting tools for finishing operations. Still the improper use of carbide cutting tools can also result in poor surface integrity. The objective of this investigation is to develop a set of guidelines, which will assist the selection of the appropriate cutting tools and conditions for generating favorable compressive residual stresses. This paper specifically deals with residual stresses and surface finish components of surface integrity when machining (facing) age hardened Inconel 718 using two grades of coated carbide cutting tools specifically developed for machining HRSAs. The cutting conditions were obtained from investigations based on optimum tool performance. The effect of insert shape, cutting edge preparation, type and nose radius on both residual stresses and surface finish was studied at this optimum cutting condition. This investigation, suggested that coated carbide cutting tool inserts of round shape, chamfered cutting edge preparation, negative type and small nose radius (0.8 mm) and coolant will generate primarily compressive residual stresses.     

Planar nanogrinding of a fine grained WC-Co composite for an optical surface finish

Nanogrinding of a fine-grained WC-Co composite was developed to achieve an optical quality surface without further polishing. Direct planar grinding was conducted with a CNC grinding machine using a metal-bond diamond wheel of grit size of 15 μm, under the nanogrinding conditions selected. The ground planar surfaces were examined using laser and optical interferometry, atomic force microscopy, and scanning electron microscopy to measure flatness, surface roughness, and surface integrity as a function of grinding conditions. Damage-free, planar mirror surfaces with a flatness (peak-to-valley, PV) at the submicron scale and surface roughness <5 nm R_a were obtained.     

Selective toxic effects of tamoxifen on osteoclasts: comparison with the effects of oestrogen

BACKGROUND: Studies in animals with short bowel syndrome (SBS) suggest that up-regulation of nutrient transporter activity occurs as an adaptive response to the loss of absorptive area. It is unclear, however, whether nutrient transport is altered at the cell membrane in SBS. The purpose of this study is to clarify amino acid and glucose transport in small intestinal luminal mucosa after 70% small bowel resection in rabbits. METHODS: New Zealand white rabbits underwent 70% jejunoileal resection (n = 27) or a sham operation (n = 19). Brush border membrane vesicles were prepared from small intestinal mucosa at 1 week, 1 month, and 3 months by magnesium aggregation-differential centrifugation. Transport of L-glutamine, L-alanine, L-leucine, L-arginine, and D-glucose was assayed by a rapid mixing-filtration technique. RESULTS: We observed no difference in uptake of all amino acids and glucose at 1 week. The uptake of amino acids and glucose was decreased by 20% to 80% in animals with SBS at 1 month. By 3 months all uptake values except that of glucose returned to normal. Kinetic studies of the system B transporter for glutamine indicate that the decrease in uptake at 1 month was caused by a reduction in the Vmax (1575 +/- 146 versus 2366 +/- 235, p < 0.05) consistent with a decrease in the number of functional carriers on the brush border membrane. CONCLUSIONS: In addition to the anatomic loss of absorptive area after massive bowel resection, alterations in enterocyte transport function may be responsible for malabsorption in patients with SBS.     

Development of characterisation methodologies for macroporous materials

The exceptional property sets of macroporous materials are leading to an increasing number of applications, particularly in the biomedical sector. Apart from the underlying material properties, it is the characteristics of the porous structure that dictate the properties of fabricated devices. Conventional methods of examining the pore structure have a number of inherent disadvantages such as low sampling volume, laborious and frequently destructive sample preparation, tedious and subjective image analysis. Recently, industrial microtomographic methods have become important tools for interrogating porous materials. However, one of the limitations of micro-CT methods is the non-specific nature of commercially available image analysis software coupled with the complicated nature of the key parameters. This paper presents some progress towards the development of a novel analysis tool that aims to characterise specific parameters over a wide range of macroporous materials. This paper focuses on aspects directly relevant to the characterisation of Hydroxyapatite macroporous (HA) foams and demonstrates the capability to obtain statistically meaningful parameters essential for process development and pre-implantation quality assurance.     

Residual stress and surface roughness when facing age hardened Inconel 718 with CBN and ceramic cutting tools

The demand for increasing productivity when machining heat resistant super alloys has resulted in the use of advanced cutting tools such as ceramics and cubic boron nitride (CBN). However, the effects of these tools on the surface integrity, especially the residual stresses created, in the high speed facing operation of Inconel 718 has not been dealt with. In this paper, the residual stresses and the surface roughness when facing age hardened Inconel 718 using CBN and mixed ceramic cutting tools at their respective optimum performance based on productivity has been investigated. The residual stress and surface finish generated during facing with CBN cutting tools have been investigated as a function of speed, depth of cut, coolant, tool geometry and nature of the tool coating. In addition, mixed ceramic cutting tools have been investigated for comparison. The results show that mixed ceramic cutting tools induce tensile residual stresses with a much higher magnitude than CBN cutting tools. The residual stresses and the surface roughness generated by CBN cutting tools are more sensitive to cutting speeds than depth of cut. The use of coolant results in either compressive residual stresses or lowers the magnitude of the tensile residual stresses, whereas dry cutting always resulted in tensile residual stresses. From this investigation, it is suggested that round CBN cutting tools should be used at slow cutting speeds (150 m/min) and small depths of cut (0.05 mm) and with the use of coolant to achieve compressive or minimal tensile residual stresses and good surface finish.     

An Upper Bound on the Error Probability for Differential Phase-Shift Keying in the Presence of Additive Gaussian White Noise and Peak-Limited Interference

A new upper bound on the error probability for differential phase-shift keyed transmission in the presence of additive Gaussian white noise (AGWN) and peak-limited interference is estimated using numerical techniques. An error probability expression is evaluated for various interference angles and the maximum value found is chosen as the upper bound. A simple approximation is presented and found to be close to the upper bound. This upper bound is shown to be a realistic bound, hence it could be useful for practical design purposes.     

Characterization of Nanoprecipitation Mechanisms During Isochronal Aging of a Pseudo-binary Al-8.7?at.?pct Li Alloy

The addition of lithium to aluminium alloys is known to afford the dual advantages of increasing mechanical performance while lowering density. These characteristics make Al-Li alloys particularly desirable for aerospace applications. However, the complex precipitation pathways and extensive nanometer-sized decomposition products, termed “nanoprecipitates,” make characterization difficult and thus limits optimization of the property sets of commercial alloys. This investigation uses thermal analysis and electrical resistivity methods to further understanding of the evolution of the various nanoprecipitates during isochronal aging of an Al-8.7 at. pct Li alloy. The results indicate decomposition via the following pathway: Spinodal-Ordering → Congruent Ordering + Spinodal Decomposition + Dissolution of Small Spinodally ordered regions → Growth of δ′ → Dissolution of δ′ → Nucleation and Growth followed by Dissolution of the δ phase.     

Integrated models for public policy analysis: An example of the practical use of simulation models in health care planning

This paper argues that the time may be ripe for a further promotion of analytic methods in urban and regional planning. It describes the contributtion of an integrated modelling approach to the analysis of health care provision in an English District Health Authority. The purpose is to demonstrate that if models can provide the right kind of information for the planning problem at hand then their use may actually be encouraged and support given for their development. Despite the emphasis that is given to an application in one particular authority, it is felt that some of the lessons learnt will be of wider applicability.     

Influence of microstructure on ultraprecision grinding of cemented carbides

The influence of microstructure on the ultraprecision grinding response of a series of cemented carbides for spherical mirrors was characterized by means of optical and laser interferometry, atomic force microscopy, scanning electron microscopy and X-ray diffraction. Surface roughness, form accuracy, grinding-induced residual stress and material removal behaviors were studied as a function of tungsten carbide (WC) grain size. In connection with the removal mechanisms in ultraprecision grinding, microindentations performed on each material showed similar deformation patterns, all in the plastic regime. The microstructure of WC-Co materials was found to have little influence on the nanometre surface roughness and submicron form accuracy. However, the X-ray stress measurements indicated that the microstructure of carbide materials had a significant influence on the grinding-induced residual stresses; i.e. an increase in grinding-induced residual compressive stress with an decrease in WC grain size. No grinding-induced cracks were observed in the ground cemented carbide surfaces. The material removal in ultraprecision grinding was considered to occur within the ductile regime. The formation of microgrooves and plastic flow regions via slip bands of WC grains along the cobalt binder without visible resultant microfracturing of WC grains were the dominant removal mechanisms.