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An investigation is reported on the wear of single-layer electroplated cubic boron nitride (CBN) grinding wheels and how the wear process affects the wheel topography and grinding behavior. Internal cylindrical and straight surface grinding experiments were conducted over a wide range of conditions on hardened bearing steel with wheels conraining different abrasive grain sizes. The radial wheel wear was characterized in each case by an initial transient at a progressively decreasing rate to a steady-state wear regime at a nearly constant rate until the end of the wheel life. Wheel wear during the initial transient was found to be mainly due to pullout of the most protruding weakly held grains, and the radial wheel wear in the steady-state regime was dominated by grain fracture. The wear rate in the steady-state regime for various grinding conditions and grain sizes was found to be directly related to the undeformed chip thickness. Dulling of the grain tips by attrition and fragmentation caused an increase in the grinding power. Wheel wear was accompanied by a progressive increase in the active grain density and a corresponding decrease in surface roughness. The surface roughness was found to depend mainly on the active grain density and is insensitive to the operating parameters. [DOI: 10.1115/1.2122987]

An investigation is reported on the thermal aspects of grinding with single layer electroplated CBN wheels. The topography of these wheels is not periodically restored by dressing or truing, so the grinding behavior progressively changes as the wheel wears down. Straight surface grinding experiments were conducted to determine the effect of wheel wear and fluid flow on the grinding temperatures and energy partition. Low energy partition values of 3%-8% were obtained at temperatures below the fluid burnout limit. The energy partition results were analyzed in terms of a topographical analysis of the wheel surface and a thermal model which accounts for the removal of heat at the grinding zone by conduction to the abrasive grains and to the grinding fluid. [DOI: 10.1115/1.1644547]

This is the second in a series of two papers concerned with high speed grinding of silicon nitride with electroplated diamond wheels. In the first article (ASME J. Manuf. Sci. Eng., 122, pp. 32-41), it was shown that grinding of silicon nitride is accompanied by dulling of the abrasive grains and a significant increase in the grinding forces and power. High wheel speed caused more wheel wear, which was attributed to a longer accumulated sliding length between the abrasive grains and the workpiece. This second paper is concerned with the progressive change in wheel topography during grinding and how it affects the grinding process. A statistical model is developed to characterize the wheel topography during grinding in terms of active cutting grains and wear flat area. According to this model, continued grinding is accompanied by an increase in both the number of active grains and the wear flat area on the wheel surface as the wheel wears down. The measured increase in grinding forces and power was found to be proportional to the wear flat area, which implies a constant average contact pressure and friction coefficient between the wear flats and the workpiece. Increasing the wheel speed from 85 to 149 m/s significantly reduced the contact pressure, which may be attributed to a reduction of the interference angle, but had almost no effect on the attritious wear rate of the diamond abrasive. Therefore, more rapid wear of the diamond wheel at higher wheel speeds due to a longer sliding length may be offset by reduced contact pressures and lower grinding forces.

Modeling uncertainty in machining, caused by modeling inaccuracy, noise and process time-variability due to tool wear, hinders application of traditional optimization to minimize cost or production time. Process time-variability can be overcome by adaptive control optimization (ACO) to improve machine settings in reference to process feedback so as to satisfy constraints associated with part quality and machine capability. However, ACO systems rely on process models to define the optimal conditions, so they are still affected by modeling inaccuracy and noise. This paper presents the method of Recursive Constraint Bounding (RC[B.sub.2]) which is designed to cope with modeling uncertainty as well as process time-variability. RC[B.sub.2] uses a model, similar to other ACO methods. However, it considers confidence levels and noise buffers to account for degrees of inaccuracy and randomness associated with each modeled constraint. RC[B.sub.2] assesses optimality by measuring the slack in individual constraints after each part is completed (cycle), and then redefines the constraints to yield more aggressive machine settings for the next cycle. The application of RC[B.sub.2] is demonstrated here in reducing cycle-time for internal cylindrical plunge grinding.

Distributions of the heat flux to the workpiece and the convection heat transfer coefficient on the workpiece surface during straight surface grinding are estimated from measured temperatures in the workpiece subsurface using inverse heat transfer methods developed in Part 1. The results indicate that the heat flux to the workpiece is distributed approximately linearly (triangular heat source) along the grinding zone with. about 70 to 75 percent of the total energy transported as heat to the workpiece for grinding of steels with a conventional aluminum oxide wheel and only about 20 percent with CBN superabrasive wheels. The wheel-workpiece contact length corresponding to the region of positive heat flux to the workpiece is found to be generally close to but slightly longer than the theoretical geometric contact length. The convection heat transfer coefficient for cooling by the applied grinding fluid is greatest just behind the trailing edge of the grinding zone where fluid is directly applied, and negligible ahead of the grinding zone.

Thermal analyses of the grinding process generally require assumptions concerning the distributions of the heat flux to the workpiece within the grinding zone and convective cooling outside the grinding zone. The present work is concerned with the use of inverse heat transfer methods to estimate the heat flux and convection heat transfer coefficient distributions on the workpiece surface during straight surface grinding from temperature measurements within the workpiece. In the present paper, three inverse heat transfer methods are developed: temperature matching, integral and sequential methods. Each method is evaluated for accuracy and stability using simulated temperature data. The selection of the sampling frequency of the temperature measurements and location of the temperature sensor are found to be critical for both estimation accuracy and stability. In a second paper, these inverse heat transfer methods are applied to estimate the distributions of the heat flux and convection heat transfer coefficients on the workpiece surface for grinding of steels with aluminum oxide and CBN abrasive wheels.

Temperatures generated in the workpiece during straight surface plunge grinding follow a transient behavior as the grinding wheel engages with and disengages from the workpiece, and throughout the entire grinding pass for workpieces which are shorter than needed to reach a quasi-steady state condition. In the present paper, a thermal model is developed for the transient temperature distribution under regular and creep-feed grinding conditions. Numerical results obtained using a finite difference method indicate that the workpiece temperature rises rapidly during initial wheel-workpiece engagement (cut in), subsequently reaches a quasi-steady state value if the workpiece is sufficiently long, and increases still further during final wheel-workpiece disengagement (cut out) as workpiece material is suddenly unavailable to dissipate heat. Cooling by a nozzle directed at the end face of the workpiece should significantly reduce the temperature rise during cut out.

An experimental investigation is reported of the energy partition to the workpiece for grinding of steels with aluminum oxide and cubic boron nitride (CBN) abrasive wheels. The energy input to the workpiece was obtained by measuring the temperature distribution in the workpiece using an embedded thermocouple technique and matching the results with analytically computed values. It was found that 60-75 percent of the grinding energy is transported to the workpiece as heat with an aluminum oxide abrasive wheel, as compared to only about 20 percent with CBN wheels. An analysis of the results indicates that the much lower energy partition to the workpiece with CBN can be attributed to its very high thermal conductivity whereby a significant portion of the grinding heat is transported to the abrasive instead of to the workpiece. The much lower energy partition to the workpiece with CBN wheels results in much lower grinding temperatures and a greatly reduced tendency for thermal damage to the workpiece.

An analysis is presented for the fraction of the energy transported as heat to the workpiece during grinding. The abrasive grains and grinding fluid in the wheel pores are considered as a thermal composite which moves relative to the grinding zone at the wheel speed. The energy partition fraction to the workpiece is modeled by setting the temperature of the workpiece surface equal to that of the composite surface at every point along the grinding zone, which allows variation of the energy partition along the grinding zone. Analytical results indicate that the energy partition fraction to the workpiece is approximately constant along the grinding zone for regular down grinding, but varies greatly along the grinding zone for regular up grinding and both up and down creep-feed grinding. The resulting temperature distributions have important implications for selecting up versus down grinding especially for creep-feed operations.

A fundamental investigation is reported on the mechanics of the bore honing process. An experimental test rig was developed consisting of a honing machine instrumented with sensors to measure spindle power, expansion pressure, and honing head displacement and interfaced to a computer for data acquisition and analysis. Experimental results are presented, which show the effects of applied normal force and grit size on the power, removal rate, specific energy, stone wear, honing ratio, and surface roughness for honing of cast iron bores with silicon carbide abrasive stones. Considerable variability in honing behavior was observed due to stone inconsistency and differences in stone properties from different manufacturers, but the results are reasonably consistent when cross-plotted versus removal rate rather than applied normal force. Slower removal rates, obtained with smaller applied normal forces and effectively harder stones, resulted in relatively less stone wear and smoother surfaces, and finer abrasive grit sizes led to relatively more stone wear and smoother surfaces. An analysis of the results indicates that the forces and specific energy associated with the process can be separated into chip formation, plowing, and sliding components, which is similar to what is found for grinding processes.

A theoretical model of fluid flow in grinding has been developed by an analysis of fluid flow through a porous medium. Fluid tangential velocity, radial velocity, depth of penetration into the wheel, and the useful flow rate through the grinding zone are predicted by using this model. The analysis indicates that the nozzle position, nozzle velocity (or flow rate), and the effective wheel porosity are the three main factors which most significantly influence the useful flow rate through the grinding zone. A dimensionless effective wheel porosity parameter is introduced which is the ratio of the effective wheel porosity to its bulk porosity. By fitting the theoretical analysis to available experimental results, creep feed wheels were found to have much bigger dimensionless effective porosities than conventional wheels, which enhances their ability to more effectively pump fluid through the grinding zone.

An improved model for force transients in turning is introduced to incorporate the geometry of the cut, as well as plowing at the cutting edge and rubbing of the flank wear land against the workpiece surface. This model is compared experimentally with the existing force models and is shown to provide an accurate representation of the force transients.

Robert Gerald Jan Moes,1 Eline L Huisman,1 Samuel JP Malkin,2 Barnaby Hunt2 1Novo Nordisk BV, Alphen aan den Rijn, Netherlands; 2Ossian Health Economics and Communications, Basel, SwitzerlandCorrespondence: Barnaby Hunt, Ossian Health Economics and Communications GmbH, Bäumleingasse 20, Basel, 4051, Switzerland, Tel +41 61 271 6214, Email hunt@ossianconsulting.comIntroduction: Achieving and maintaining glycemic control is the cornerstone of type 1 diabetes management, with the aim of reducing the incidence of diabetes-related complications over the long term. However, many individuals fail to reach glycemic targets. The present study evaluated the clinical and economic burden associated with poor glycemic control in people with type 1 diabetes in the Netherlands, and the improvements in outcomes that can be achieved by improving treatment.Methods: Immediate glycemic control, defined as achieving a glycated hemoglobin (HbA1c) target of 7.0% at the start of the analysis, was compared with delays in achieving control of 1, 3 and 7 years, with outcomes projected using the IQVIA CORE Diabetes Model. Projections of life expectancy, quality-adjusted life expectancy, and direct and indirect costs (expressed in 2021 euros [EUR]) were made at a patient level and extrapolated to the population level.Results: Improving HbA1c from 8.0% to 7.0% and 9.0% to 7.0% resulted in gains of up to 0.66 and 1.37 quality-adjusted life years (QALYs) per patient over a lifetime, respectively. At a population level, achieving immediate glycemic control was associated with gains of 9438, 27,171 and 72,717 QALYs and cost savings of up to EUR 224 million, EUR 556 million and EUR 1.3 billion compared with remaining in poor control for 1, 3 and 7 years, respectively.Conclusion: The clinical and economic burden of poor glycemic control in people with type 1 diabetes in the Netherlands was projected to be substantial, but considerable gains in quality-adjusted life expectancy and cost savings could be achieved through early and effective treatment.Keywords: diabetes complications, glycemic control, health economics, Netherlands, type 1 diabetes