Optimization of Set-up Conditions for Stability of The Centerless Grinding Process

The stability of the centerless grinding process is very sensitive to the set-up conditions due to the uniqueness of the work-holding system. Centerless grinding produces precision components with high productivity only when the set-up condition is optimally chosen. This paper describes the effect of set-up conditions on three stability criteria of the centerless grinding system. It also presents guidelines for determining proper set-up conditions to avoid spinners, chatter vibration and roundness problems. Finally, an algorithm for providing the optimum set-up condition based on process aims is proposed and the simulation results are discussed.     

Hepatotoxicity of anticholesterol, cardiovascular, and endocrine drugs and hormonal agents

Drugs in these categories may have effects on several organs in addition to the liver. For example, amiodarone may produce thyroid and corneal injury apart from or in addition to the phospholipidosis seen in the liver. Oral contraceptive steroids remain a rare but important concern for developing hepatic adenomas and possibly hepatocellular carcinoma, as well as a risk factor for developing Budd-Chiari syndrome in long-term users. Among the antihyperlipidemic agents, nicotinic acid, especially the sustained release formulations, may produce severe of even fatal hepatic injury. Increasing numbers of reports of hepatotoxicity from newer beta blockers and angiotensin-converting enzyme inhibitors require ongoing vigilance in patients receiving these medications.     

Dynamic imaging of the pancreas using real-time endoscopic ultrasonography with secretin stimulation

BACKGROUND: Tissue factor (TF) is a transmembrane glycoprotein that, after binding to factor VII/VIIa, initiates the extrinsic coagulation pathway, resulting in thrombin generation and its sequelae. Thrombin has been shown to induce TF mRNA in endothelium, monocytes, and smooth muscle cells, further perpetuating the thrombogenic cycle. This study was designed to determine the effect of specific inhibition of thrombin by recombinant hirudin (r-hirudin) on TF distribution after balloon angioplasty in the cholesterol-fed rabbit femoral artery and porcine coronary artery models. METHODS AND RESULTS: Thirty-five femoral arteries from 32 cholesterol-fed New Zealand White rabbits and 84 coronary arteries from 55 Yorkshire-Albino swine were studied by use of a recently developed in situ method of TF localization based on digoxigenin labeling of recombinant factor VIIa (Dig-VIIa), with correlative studies of TF immunoreactivity by use of anti-rabbit (AP-1) or anti-human (sTF) antibodies. At sites of balloon angioplasty in rabbit femoral or pig coronary arteries (double or single injury), TF-antibody and Dig-VIIa staining were noted in association with endothelial cells, smooth muscle cells, and foam cells and within the fibrous tissue matrix primarily of the adventitia and neointima. Staining was significantly greater after balloon angioplasty than in vessels that had not undergone angioplasty but was similar after single and double balloon injury. Animals treated with r-hirudin (rabbits, 1 mg/kg bolus plus 2-hour infusion; pigs, 1 mg/kg bolus plus 0.7 mg x kg(-1) x d(-1) infusion for 14 days with implantable pump) had diminished TF-antibody and Dig-VIIa staining 28 days after balloon angioplasty compared with controls (bolus heparin only). This effect was more prominent on the neointima and was more striking in the porcine than the rabbit model. CONCLUSIONS: TF expression, persistent 1 month after balloon angioplasty in rabbit femoral arteries and porcine coronary arteries, is attenuated by specific thrombin inhibition with hirudin. These results suggest that thrombin inhibition, in addition to its effect on acute thrombus formation and its effect on luminal narrowing by plaque in experimental animals, may result in a prolonged reduction in thrombogenicity of the restenotic plaque through this effect on TF expression.     

The occurrence of shear bands in nonisothermal,hot forging of Ti-6AI-2Sn-4Zr-2Mo-0.1Si

The occurrence of shear bands in nonisothermal, hot forging of Ti-6Al-2Sn-4Zr-2Mo-0. ISi (Ti-6242) was investigated in order to establish the material properties and process parameters which generally lead to shear bands and shear cracks in conventional hot forging of metals. Upset compression tests on cylindrical samples and lateral sidepressing tests on long, round bars were performed to determine the modes by which flow localizes in deformation states ranging from axisymmetric to plane strain. In axisymmetric deformation, it was found that nonisothermal, hot compression leads to chill zones and bands of intense deformation separating the chill zones from the deforming bulk. For plane strain deformation, shear bands were found to initiate along zero extension directions and subsequently localize flow in a manner analogous to the formation and propagation of shear bands in isothermal, hot forging. For both deformation states, it was found that material properties, such as the flow stress dependence on temperature, and process parameters, such as forging speed and die temperature which strongly influence the amount of heat transfer, play critical roles in the flow localization process. A simple model quantifying these effects was developed to predict the occurrence and severity of the shear bands observed in the Ti-6242 alloy hot forged at various temperatures and rates. In addition, the occurrence of shear cracking under certain forging conditions was rationalized in terms of the chilling brought about by nonisothermal, hot forging conditions and the inferior workability of Ti-6242 at temperatures far below the transus temperature.     

Severe plastic deformation (SPD) processes for metals

Processes of severe plastic deformation (SPD) are defined as metal forming processes in which a very large plastic strain is imposed on a bulk process in order to make an ultra-fine grained metal. The objective of the SPD processes for creating ultra-fine grained metal is to produce lightweight parts by using high strength metal for the safety and reliability of micro-parts and for environmental harmony. In this keynote paper, the fabrication process of equal channel angular pressing (ECAP), accumulative roll-bonding (ARB), high pressure torsion (HPT), and others are introduced, and the properties of metals processed by the SPD processes are shown. Moreover, the combined processes developed recently are also explained. Finally, the applications of the ultra-fine grained (UFG) metals are discussed.     

Deformation and unstable flow in hot forging of Ti-6Ai-2Sn-4Zr-2Mo-0.1Si

The stable and unstable plastic flow of Ti-6Al-2Sn-4Zr-2Mo-0.1Si (Ti-6242) has been investigated at temperatures from 816 to 1010 °C (1500 to 1850 °F) and at strain rates from 0.001 to 10 s^-1 in order to establish its hot forging characteristics. In hot, isothermal compression, Ti-6242 with an equiaxed a structure deforms stably and has a flow stress which decreases with straining due to adiabatic heating. With a transformed-β microstructure, unstable flow in hot compression is observed and concluded to arise from large degrees of flow softening caused by microstructural modification during deformation and, to a small extent, by adiabatic heating. Both microstructures have a sharp dependence of flow stress on temperature. Using the concepts of thermally-activated processes, it was shown analytically that this dependence is related to the large strain-rate sensitivity of the flow stress exhibited by the alloy. From lateral sidepressing results, the large dependence of flow stress on temperature was surmised to be a major factor leading to the shear bands occurring in nonisothermal forging of the alloy. Shear bands were also observed in isothermal forging. A model was developed to define the effect of material properties such as flow softening rate and strain-rate sensitivity on shear band development and was applied successfully to predict the occurrence of shear bands in isothermal forging.     

The effect of shear bands on service properties of ti-6ai-2sn-4zr-2mo-0.1si forgings

The effect of shear bands on the elevated temperature tensile, creep, and fatigue properties of Ti-6Al-2Sn-4Zr-2Mo-0. ISi (Ti-6242) forgings has been established. Evaluations on forgings containing and not containing shear bands demonstrated that the effect is very small if not negligible in tensile and fatigue loading. For these types of loading, observations were explainable on the basis of the fact that the shear bands are regions of somewhat higher hardness than the remainder of the forging, and, thus, failure tended to nucleate away from the shear bands. In contrast, shear bands had a noticeable effect on stress-rupture properties. The deleterious effects under this type of loading were ascribed to microscopic processes such as enhanced diffusion along shear bands. Formerly Senior Research Scientist, Metalworking Section, Battelle’s Columbus Laboratories     

Laser-assisted microgrinding of ceramics

Creating three-dimensional micro scale features in hard ceramics is challenging. This paper presents the results of an experimental study of a two-step laser-assisted microgrinding process that has the potential to meet this challenge. The process works by locally weakening the ceramic material via laser irradiation and subsequently microgrinding the weakened material to create a finished micro scale feature. The paper presents the results for laser-assisted microgrinding of silicon nitride. In particular, the differences in grinding force, surface finish, tool condition, and material removal rate obtained with and without laser assist are compared and discussed. Physically based explanations for the experimental observations are given.