Thesis (M.S.)--University of Wisconsin--Madison, 1982. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 211-221).

Thesis (M.S.)--University of Wisconsin--Madison, 1969. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

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The competitiveness of conventional press & sinter technology mainly depends on the ability to obtain tight tolerance on sintered products. In order to maintain this strategic advantage in spite of the rapid global market changes, a continuous improvement in the dimensional accuracy of the products has to be pursued. One of the major limits in the dimensional precision of sintered products regards the anisotropic dimensional change occurring on sintering. Despite this problem is well known, an effective design procedure accounting for the anisotropic behavior of dimensional variations is far to be reached. The main reasons concern the multiphysical mechanisms involved and the effect of material, geometry and process condition on the final results. This work aims at developing a design methodology accounting for the anisotropy of dimensional changes on sintering. This study has been performed considering both the fundamental principles and the industrial application, aiming at proposing: - a solid theory considering the mechanisms which determine the anisotropic dimensional changes; - a practical and effective design tool for the industrial application. The role of uniaxial compaction on the origin of anisotropic dimensional change was firstly investigated. AISI 316L ring shaped samples were compacted at different geometries, and four different particle sizes. During single action compaction, forces acting on the tooling and powder column, and related displacements, were recorded by the press in order to derive the compaction mechanics of the powder mixes. Further, the dimensions of the samples were measured before and after sintering. A linear trend was observed correlating the deviatoric stresses occurring in compaction to the anisotropic dimensional variations on sintering. This result offers a new perspective in the prediction of the anisotropic dimensional change, and could lay the foundation of a solid model. Aiming at developing an effective design tool to predict dimensional change on sintering, the analytical design procedure previously developed by the research group at the University of Trento was validated on real parts. A Club Project was promoted by EPMA, collecting the University of Trento and five qualified industrial partners. These companies provided five different real parts characterized by different materials and geometries, whose dimensions were measured before and after sintering. The comparison of the measured and the predicted sintered dimensions demonstrated that this design approach can be an effective tool for designers. Further work could implement the promising results obtained investigating the compaction mechanics in the design procedure, aiming at defining a powerful tool to design PM parts accounting for anisotropic dimensional changes.

The present study focuses on the physical and chemical mechanisms of lubricant removal during the first step of the sintering process during powder metallurgy (P/M) processing of ferrous systems. Previous works on the kinetics of delubrication made it possible to develop an empirical model which accounts for the typical weight loss profile observed upon heating of green compacts. It has been established that the rate at which the parts are heated dictates the overall process kinetics, and fitting curve methods yield two parameters which contain the corresponding information: (i) TMAX is the temperature of 50% lubricant removal, and (ii) b is representative of the slope of the curve during weight loss stage. Phase I of this study aims at determining the dependencies of these two parameters with respect to a series of physical variables: green density of the compacts; presence of an alloying element potentially catalytic for the reaction of lubricant pyrolysis; and procedure of compaction and geometry of the compacts. Also, it is suggested that the two parameters obtained from the fitting curve methods can be related to the main two mechanisms of delubrication: evaporation of the lubricant and conversion of the lubricant molecules into smaller hydrocarbons, assuming that these two mechanisms are the kinetically limiting mechanisms. Furthermore, recent studies of the delubrication process have been opening the way to the potential development of gas sensors, which could eventually allow the direct monitoring of the emissions of gaseous species. Several key features have been reported in the literature, including a peak emission of hydrocarbons at the delubrication temperature, as well as strong emissions of CO and CO2 at temperatures above 700°C. The scope of Phase II of this project was thus to verify that these features were retained under various processing conditions, so that the development of a sensor suitable for various sintering environments is viable. Variations in the emission profiles of gaseous species were observed as the processing conditions were changed, and when possible, potential justifications for these changes have been proposed.

No description available.

We focus on single punch compaction of powder metals in hollow cylindrical geometries, and pay special attention to the effects of non-uniform initial density distribution on final green densities, the effects of density-dependent powder properties and pressure dependent coefficients of friction on the evolution of the pressure and density profiles during compaction, and the time variations of the force required for ejection after the compaction pressure is removed. In studying the effects of non-uniform initial density distribution, we extend the work of Richman and Gaboriault [1999] to allow for fill densities that vary with initial location in the die. The process is modeled using equations of equilibrium in the axial and radial directions, a constitutive relation that relates the axial pressure to the radial pressure at any point in the specimen, and a plausible equation of state that relates local density to the local pressure. Coulomb friction is assumed to act at the interfaces between the specimen and both the die wall and core rod. In this manner, we determine the axial and radial variations of the final density, the axial, radial and tangential pressures, and the shear stress. Of special interest are the inverse problems, in which we find the required non-uniform initial density distribution that, in principle, will yield no variation in the final green density. For incorporating the effect of pressure and density dependent powder properties, we employ a one-dimensional model that predicts the axial variations of the pressure and density. In this model, however, we incorporate the density dependence of the radial-to-axial pressure ratio, as well as the pressure-dependence of the coefficients of friction at the die wall and core rod. The density-dependence of the pressure ratio is based on the experimental measurements of Trassoras [1998], and the pressure dependence of the friction coefficients is based on the measurements of Sinka [2000] and Solimanjad et. al [2001]. In the course of this study, we focus attention on a Distalloy AE powder, and establish the relation between its compressibility and its radial-to-axial pressure ratio. Finally, we employ linear elasticity theory to model the ejection of the green compact. In the first phase, we model relaxation of the compact after removal of the compaction pressure as a misfit of three cylinders, representing the core rod, the compact and the die wall. The known input is radial pressure distribution at the conclusion of compaction, and the output is the corresponding radial pressure distributions that prevail after the compaction pressures are removed. In the second phase, we determine the variations with punch displacement of the ejection forces required to overcome friction at the core rod and die wall. The model includes additions to the friction forces due to the radial expansion (i.e. the Poisson effect) that occurs during ejection. Predictions of the model compare well to the experimental results of Gethin et.al. [1994].