Grinding performance and workpiece integrity when superabrasive edge routing carbon fibre reinforced plastic (CFRP) composites

Data is presented for wheel wear, cutting forces and workpiece integrity when high speed routing 10 mm thick CFRP laminates using single layer electroplated diamond and CBN grinding points as opposed to standard end milling tools. A 60,000 rpm retrofit spindle was utilised to accommodate the 10 mm diameter wheels having grit sizes of 76, 151 and 252 μm employed under either roughing or finishing parameters. Wear of CBN points exhibited a near two-fold increase over diamond with a similar ratio for cutting forces. Despite use of flood cooling, point geometry when roughing compromised life and integrity due to excessive clogging.     

Profiled Superabrasive Grinding Wheels for the Machining of a Nickel Based Superalloy

Machining data are presented for small diameter, profiled (fir tree root form), single layer/electroplated CBN (B46, B76 and 91) and diamond (D46) grinding wheels, when cutting Udimet 720. Spindles operating at 60,000 and 90,000 rpm were employed, with a synthetic polyalphaolefine (PAO) oil based fluid in a down grinding mode on single sided specimens. Operating parameters were selected to reflect finishing conditions. Measured tool wear was lower for CBN grit as compared to diamond however workpiece roughness was lower with Ra approaching 0.75 μm when using D46 wheels. Higher rotational speed produced lower grinding wheel wear. No workpiece burning was observed irrespective of grit type at the conditions tested.     

Creep feed grinding of gamma titanium aluminide and burn resistant titanium alloys using SiC abrasive

Following a brief introduction to titanium alloys and their machinability, the cutting performance of a gamma titanium aluminide intermetallic (γ-TiAl) alloy: Ti–45Al–8Nb–0.2C wt% and a burn resistant titanium (BuRTi) alloy: Ti–25V–15Cr–2Al–0.2C wt%, is compared with creep feed grinding using SiC abrasive. The work utilised 2 separate L9 Taguchi fractional factorial arrays. Typically G-ratios were a factor of 10× greater for γ-TiAl than BuRTi, with on average 10% lower maximum power and 25% lower maximum specific energy for the γ-TiAl alloy. A combination of a moderately high wheel speed: 35 m/s, low depth of cut: 1.25 mm and low feed rate: 150 mm/min, produced the lowest average workpiece surface roughness (Ra1.4 μm). Workpiece surface integrity evaluation indicated that with lower operating parameter levels, in particular a wheel speed of 15 m/s, surfaces free of burn and cracks could be produced, while at higher wheel speeds: 35 m/s, extensive workpiece surface burn was evident, with the γ-TiAl alloy suffering extensive cracking. Microhardness measurements showed in some instances slightly increased workpiece surface hardness of around 50–60HK_0.025 for the BuRTi alloy and 200HK_0.025 for the γ-TiAl material over respective bulk hardness values of 375HK_0.025 and 400HK_0.025.     

Workpiece surface roughness and integrity after WEDM of Ti-6Al-4V and Inconel 718 using minimum damage generator technology

Following a brief review of EDM and its use on advanced aerospace alloys including workpiece integrity constraints, data are presented after machining Ti-6Al-4V and Inconel 718. Roughing and finishing (multiple trim cut) strategies were employed on two high specification machines with pulse generators designed to provide minimum workpiece integrity damage. Results include productivity, 3D topographic maps of workpiece surfaces, microstructural and microhardness depth profile data. Average recast thickness was <11 μm, several trim passes showing no apparent recast or damage. Similarly, no significant change in workpiece microhardness variation was observed with cracking confined to the recast layer.     

Machinability and surface integrity of RR1000 nickel based superalloy

Alloy development for gas turbine components has produced materials able to maintain strength and integrity at operating temperatures up to ∼1050 °C. Next-generation RR1000 nickel-based superalloy reflects this philosophy, albeit at the expense of machinability. Experimental data for drilling showed flank wear when operating at 45 m/min to be <100 μm for a distance cut of 1800 mm (150 holes). Thrust forces measured 1600–1800 N. Re-deposited material on hole surfaces and drag/distortion was evident on cross-sectional micrographs. Roughness of end-milled specimens was <0.8 μm Ra with minimal damage using new tools, however significant burring/increased microhardness (∼150 HK_0.05) and white layer formation occurred when employing worn tools.     

Workpiece surface integrity when slot milling γ-TiAl intermetallic alloy

Slot milling is presented as a potential manufacturing route for aerospace component feature production when machining γ-TiAl intermetallic alloy Ti–45Al–2Mn–2Nb + 0.8 vol.% TiB₂XD using 2 mm diameter AlTiN coated WC ball nose end milling cutters. When operating with flood cutting fluid at v = 88 m/min, f = 0.05 mm/tooth, d = 0.2 mm, maximum flank wear was ∼65 μm after 25 min. SEM micrographs of slot surfaces show re-deposited/adhered and smeared workpiece material to a length of ∼50 μm. Brittle fracture of the slot edges was restricted to <10 μm with sporadic top burr formation observed up to ∼20 μm. Cross sectional micrographs of the slot sidewalls showed bending of the lamellae limited to within 5 μm.     

Hole quality assessment following drilling of metallic-composite stacks

The use of material stacks comprising titanium, carbon fibre reinforced plastics (CFRPs) and aluminium is expanding for structural aerospace applications, especially where high mechanical loads exist such as for aircraft wing and tail-plane components. Here, the production of bolt/fixation holes is essential to the manufacturing process in order to facilitate part assembly. The paper outlines an analysis of hole quality/integrity following drilling of titanium/CFRP/aluminium stacks under flood cutting fluid and spray mist environments. Uncoated and coated (CVD diamond and hardmetal) tungsten carbide drill performance is evaluated against key response measures including hole size, out of roundness, cylindricity, burr height, hole edge quality, average surface roughness (R_a), microhardness (of the metallic elements) and swarf morphology. Burr height (up to 0.5 mm) was observed to be greater at the hole exit (aluminium) compared to hole entry (titanium) while delamination was significantly reduced when machining CFRP in the stack configuration as opposed to a standalone arrangement. Spiral shaped continuous aluminium swarf was prevalent while both short and long helical chips were found with the titanium material when cutting wet. In contrast, the CFRP layer typically produced dusty black composite particles suspended in the soluble oil of the coolant emulsion.     

Modeling cognitive adaptation: A longitudinal investigation of the impact of individual differences and coping on college adjustment and performance.

Drawing on cognitive adaptation theory, optimism, psychological control, and self-esteem were explored as longitudinal predictors of adjustment to college in a sample of 672 freshmen. Although a direct effect of optimism on adjustment was found, most of the predicted effects were mediated by coping methods. Controlling for initial positive and negative mood, the beneficial effects of optimism, control, and self-esteem on adjustment were mediated by the nonuse of avoidance coping, greater use of active coping, and greater seeking of social support. Alternative models of the causal relations among these variables did not fit the data as well as the a priori mediational model. The results of a 2-yr follow-up indicated that self-esteem and control predicted greater motivation and higher grades, controlling for college entrance exam scores. Implications for cognitive adaptation theory and for interventions with populations under stress are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Detection of secretion from single pancreatic beta-cells using extracellular fluorogenic reactions and confocal fluorescence microscopy

Confocal microscopy with Zinquin, a fluorogenic Zn(2+)-specific indicator, was used for spatially and temporally resolved measurement of Zn2+ efflux from single pancreatic beta-cells. When cells were incubated in buffer containing Zinquin, application of insulin secretagogues evoked an increase in fluorescence around the surface of the cell, indicative of detection of Zn2+ efflux from the cell. The fluorescence increases corresponded spatially and temporally with measurements of exocytosis obtained simultaneously by amperometry. When images were taken at 266-ms intervals, the detection limit for Zn2+ was approximately 0.5 microM. With this image frequency, it was possible to observe bursts of fluorescence which were interpreted as fluctuations of Zn2+ level due to exocytosis. The average intensity of these fluorescence bursts corresponded to a Zn2+ concentration of approximately 7 microM. Since insulin is co-stored with Zn2+ in secretory vesicles, it was concluded that the Zn2+ efflux corresponded to exocytosis of insulin/Zn(2+)-containing granules from the beta-cell. Exocytosis sites identified by this technique were frequently localized to one portion of the cell, indicative of active areas of release.