Manufacturing process challenges when machining superalloys

The implementation of advanced manufacturing systems with high process capability is an essential requirement for the high value manufacturing industries. To ensure high process capability, industry needs to deal with the requirement for tight tolerances and the unavoidable variations in materials, and manufacturing and inspection processes. In the case of machining superalloys, such variations result in the need to change the machine parameters for producing different batches of materials from different suppliers. This is required in order to get the process under control and reduce waste and defects, leading to better competitiveness. This papers discuss the variability in materials and the corresponding process requirements when machining superalloys, and highlights the impact of metrology in achieving manufacturing process improvement.

Visual field defects in Alzheimer's disease patients may reflect differential pathology in the primary visual cortex

The aim of this study was to test the hypothesis that differences in density of senile plaques (SP) and neurofibrillary tangles (NFT) in the cuneal and lingual gyri of area V1 of the visual cortex could explain the predominantly inferior visual field defects seen in patients with Alzheimer's disease (AD). The density of SP and NFT was measured in the cuneal and lingual gyri of 18 AD patients. In 7/18 (39%) patients, the density of SP and/or NFT was significantly greater in the cuneal compared with the lingual gyri. In 3/18 (17%) patients, densities were greater in the lingual than the cuneal gyri and in 8/18 (44%) patients there were no significant differences among gyri. The data suggest that pathological differences between cuneal and lingual gyri could contribute to the reported visual field defects in some AD patients.

Defects in steel investment castings

A general investigation was performed, in an industrial environment, of the major types of defect specific to investment castings in steel. As a result of this work three types of metallurgical defect were selected for further study. In the first of these, defects in austenitic stainless steel castings were found to result from deoxidation by-products. As a result of metallographic investigation and the statistical analysis of experimental data, evidence was found to support the hypothesis that the other two classes of defects - in martensite stainless and low alloy steels -both resulted from internal or grain boundary oxidation of the chromium alloy constituent This was often found to be followed by reaction between the metal oxides and the ceramic mould material. On the basis of this study, proposals are made for a more fundamental investigation of the mechanisms involved and interim suggestions are given for methods of ameliorating the effect in an industrial situation.

The Kinematics of interference mechanisms in certain machining operations

The mechanism of "Helical Interference" in milled slots is examined and a coherent theory for the geometry of such surfaces is presented. An examination of the relevant literature shows a fragmented approach to the problem owing to its normally destructive nature, so a complete analysis is developed for slots of constant lead, thus giving a united and exact theory for many different setting parameters and a range of cutter shapes. For the first time, a theory is developed to explain the "Interference Surface" generated in variable lead slots for cylindrical work and attention is drawn to other practical surfaces, such as cones, where variable leads are encountered. Although generally outside the scope of this work, an introductory analysis of these cases is considered in order to develop the cylindrical theory. Special emphasis is laid upon practical areas where the interference mechanism can be used constructively and its application as the rake face of a cutting tool is discussed. A theory of rake angle for such cutting tools is given for commonly used planes, and relative variations in calculated rake angle between planes is examined. Practical tests are conducted to validate both constant lead and variable lead theories and some design improvements to the conventional dividing head are suggested in order to manufacture variable lead workpieces, by use of a "superposed" rotation. A prototype machine is manufactured and its kinematic principle given for both linear and non-linearly varying superposed rotations. Practical workpieces of the former type are manufactured and compared with analytical predictions,while theoretical curves are generated for non-linear workpieces and then compared with those of linear geometry. Finally suggestions are made for the application of these principles to the manufacture of spiral bevel gears, using the "Interference Surface" along a cone as the tooth form.

Fatigue crack initiation and propagation from defects in aluminium welds

Fatigue crack initiation and propagation in aluminium butt welds has been investigated. It is shown that the initiation of cracks from both buried defects and. from the weld reinforcement may be quantified by predictive laws based on either linear elastic fracture mechanics, or on Neuber's rule of stress and strain ooncentrations. The former is preferable on the grounds of theoretical models of crack tip plasticity, although either may be used as the basis of an effeotive design criteria against crack initiation. Fatigue lives fol1owing initiation were found to follow predictions based on the integration of a Paris type power law. The effect of residual stresses from the welding operation on both initiation and propagation was accounted for by a Forman type equation. This incorporated the notional stress ratio produced by the residual stresses after various heat treatments. A fracture mechanics analysis was found to be useful in describing the fatigue behaviour of the weldments at increased temperatures up to 300°C. It is pointed out, however, that the complex interaction of residual stresses, frequency, and changes in fracture mode necessitate great caution in the application of any general design criteria against crack initiation and growth at elevated. temperatures.

Investigation into visual defects attributed to Vigabatrin

Vigabatrin (VGB) is a transaminase inhibitor that elicits its anitepileptic effect by increasing GABA concentrations in the brain and retina. - Assess whether certain factors predispose patients to develop severe visual field loss. - Develop a sensitive algorithm for investigating the progression of visual field loss. - Determine the most sensitive clinical regimen for diagnosing VGB-attributed visual field loss. - Investigate whether the reports of central retinal sparing are accurate. The investigations have resulted in a number of significant findings: - The anatomical evidence in combination with the pattern of visual field loss suggests that the damage induced by VGB therapy occurs at retinal level, and is most likely a toxic effect. - The quantitative algorithm, designed within the course of this investigation, provided increased sensitivity in determining the severity of visual field loss. - Maximum VGB dose predisposes patients to develop severe visual field loss. - The SITA Standard algorithm was found to be as sensitive and significantly faster, in diagnosing visual field defects attributed to VGB, when compared to the Full Threshold algorithm. The Full Threshold was found to be the most repeatable between visits. - The normal SWAP 10-2 database provided an effective method of differentiating SWAP defects. - SWAP, FDT and the mfERG have increased sensitivity in detecting visual field loss attributed to VGB. The pattern of visual field loss from these investigations suggests that VGB produces a diffuse effect across the retina including subtle central abnormalities and more severe peripheral defects. - Abnormalities detected using the mfERG have suggested that VGB adversely affects the photoreceptors Müller, amacrine and ganglion cells in the retina. An urgent review of the manufacturers recommended maximum dose for VGB is required.

The development of an expert system for the identification anodic coating process defects as a contribution to the dissemination of anodizing technology

Initially this thesis examines the various mechanisms by which technology is acquired within anodizing plants. In so doing the history of the evolution of anodizing technology is recorded, with particular reference to the growth of major markets and to the contribution of the marketing efforts of the aluminium industry. The business economics of various types of anodizing plants are analyzed. Consideration is also given to the impact of developments in anodizing technology on production economics and market growth. The economic costs associated with work rejected for process defects are considered. Recent changes in the industry have created conditions whereby information technology has a potentially important role to play in retaining existing knowledge. One such contribution is exemplified by the expert system which has been developed for the identification of anodizing process defects. Instead of using a "rule-based" expert system, a commercial neural networks program has been adapted for the task. The advantages of neural networks over 'rule-based' systems is that they are better suited to production problems, since the actual conditions prevailing when the defect was produced are often not known with certainty. In using the expert system, the user first identifies the process stage at which the defect probably occurred and is then directed to a file enabling the actual defects to be identified. After making this identification, the user can consult a database which gives a more detailed description of the defect, advises on remedial action and provides a bibliography of papers relating to the defect. The database uses a proprietary hypertext program, which also provides rapid cross-referencing to similar types of defect. Additionally, a graphics file can be accessed which (where appropriate) will display a graphic of the defect on screen. A total of 117 defects are included, together with 221 literature references, supplemented by 48 cross-reference hyperlinks. The main text of the thesis contains 179 literature references. (DX186565)

Pulse oximetry screening for congenital heart defects in newborn infants:an evaluation of acceptability to mothers

Background: Introducing neonatal screening procedures may not be readily accepted by parents and may increase anxiety. The acceptability of pulse oximetry screening to parents has not been previously reported. Objective: To assess maternal acceptability of pulse oximetry screening for congenital heart defects and to identify factors predictive of participation in screening. Design and setting: A questionnaire was completed by a cross-sectional sample of mothers whose babies were recruited into the PulseOx Study which investigated the test accuracy of pulse oximetry screening. Participants: A total of 119 mothers of babies with false-positive (FP) results, 15 with true-positive and 679 with true-negative results following screening. Main outcome measures: Questionnaires included measures of satisfaction with screening, anxiety, depression and perceptions of test results. Results: Participants were predominantly satisfied with screening. The anxiety of mothers given FP results was not significantly higher than that of mothers given true-negative results (median score 32.7 vs 30.0, p=0.09). White British/Irish mothers were more likely to participate in screening, with a decline rate of 5%; other ethnic groups were more likely to decline with the largest increase in declining being for Black African mothers (21%, OR 4.6, 95% CI 3.8 to 5.5). White British mothers were also less anxious (p<0.001) and more satisfied (p<0.001) than those of other ethnicities Conclusions: Pulse oximetry screening was acceptable to mothers and FP results were not found to increase anxiety. Factors leading to differences in participation and satisfaction across ethnic groups need to be identified so that staff can support parents appropriately.

Pulse oximetry as a screening test for congenital heart defects in newborn infants: a test accuracy study with evaluation of acceptability and cost-effectiveness

Background: Screening for congenital heart defects (CHDs) relies on antenatal ultrasound and postnatal clinical examination; however, life-threatening defects often go undetected. Objective: To determine the accuracy, acceptability and cost-effectiveness of pulse oximetry as a screening test for CHDs in newborn infants. Design: A test accuracy study determined the accuracy of pulse oximetry. Acceptability of testing to parents was evaluated through a questionnaire, and to staff through focus groups. A decision-analytic model was constructed to assess cost-effectiveness. Setting: Six UK maternity units. Participants: These were 20,055 asymptomatic newborns at = 35 weeks’ gestation, their mothers and health-care staff. Interventions: Pulse oximetry was performed prior to discharge from hospital and the results of this index test were compared with a composite reference standard (echocardiography, clinical follow-up and follow-up through interrogation of clinical databases). Main outcome measures: Detection of major CHDs – defined as causing death or requiring invasive intervention up to 12 months of age (subdivided into critical CHDs causing death or intervention before 28 days, and serious CHDs causing death or intervention between 1 and 12 months of age); acceptability of testing to parents and staff; and the cost-effectiveness in terms of cost per timely diagnosis. Results: Fifty-three of the 20,055 babies screened had a major CHD (24 critical and 29 serious), a prevalence of 2.6 per 1000 live births. Pulse oximetry had a sensitivity of 75.0% [95% confidence interval (CI) 53.3% to 90.2%] for critical cases and 49.1% (95% CI 35.1% to 63.2%) for all major CHDs. When 23 cases were excluded, in which a CHD was already suspected following antenatal ultrasound, pulse oximetry had a sensitivity of 58.3% (95% CI 27.7% to 84.8%) for critical cases (12 babies) and 28.6% (95% CI 14.6% to 46.3%) for all major CHDs (35 babies). False-positive (FP) results occurred in 1 in 119 babies (0.84%) without major CHDs (specificity 99.2%, 95% CI 99.0% to 99.3%). However, of the 169 FPs, there were six cases of significant but not major CHDs and 40 cases of respiratory or infective illness requiring medical intervention. The prevalence of major CHDs in babies with normal pulse oximetry was 1.4 (95% CI 0.9 to 2.0) per 1000 live births, as 27 babies with major CHDs (6 critical and 21 serious) were missed. Parent and staff participants were predominantly satisfied with screening, perceiving it as an important test to detect ill babies. There was no evidence that mothers given FP results were more anxious after participating than those given true-negative results, although they were less satisfied with the test. White British/Irish mothers were more likely to participate in the study, and were less anxious and more satisfied than those of other ethnicities. The incremental cost-effectiveness ratio of pulse oximetry plus clinical examination compared with examination alone is approximately £24,900 per timely diagnosis in a population in which antenatal screening for CHDs already exists. Conclusions: Pulse oximetry is a simple, safe, feasible test that is acceptable to parents and staff and adds value to existing screening. It is likely to identify cases of critical CHDs that would otherwise go undetected. It is also likely to be cost-effective given current acceptable thresholds. The detection of other pathologies, such as significant CHDs and respiratory and infective illnesses, is an additional advantage. Other pulse oximetry techniques, such as perfusion index, may enhance detection of aortic obstructive lesions.

Celiac disease patient IgA antibodies induce endothelial adhesion and cell polarization defects via extracellular transglutaminase 2

We have recently found that celiac disease patient serum-derived autoantibodies targeted against transglutaminase 2 interfere with several steps of angiogenesis, including endothelial sprouting and migration, though the mechanism involved remained to be fully characterized. This study now investigated the processes underlying the antiangiogenic effects exerted by celiac disease patient antibodies on endothelial cells, with particular regard to the adhesion, migration, and polarization signaling pathway. We observed that celiac IgA reduced endothelial cell numbers by affecting adhesion without increasing apoptosis. Endothelial cells in the presence of celiac IgA showed weak attachment, a high susceptibility to detach from fibronectin, and a disorganized extracellular matrix due to a reduction of protein cross-links. Furthermore, celiac patient IgA led to secretion of active transglutaminase 2 from endothelial cells into the culture supernatants. Additionally, cell surface transglutaminase 2 mediated integrin clustering in the presence of celiac IgA was coupled to augmented expression of ß1-integrin. We also observed that celiac patient IgA-treated endothelial cells had migratory defects and a less polarized phenotype when compared to control groups, and this was associated with the RhoA signaling pathway. These biological effects mediated by celiac IgA on endothelial cells were partially influenced but not completely abolished by R281, an irreversible extracellular transglutaminase 2 enzymatic activity inhibitor. Taken together, our results imply that celiac patient IgA antibodies disturb the extracellular protein cross-linking function of transglutaminase 2, thus altering cell-extracellular matrix interactions and thereby affecting endothelial cell adhesion, polarization, and motility. © 2013 Springer Basel.