Barney E. Klamecki

CAD/CAM for dental restorations-some of the curious challenges

The current state of the art for production of dental restorations is reviewed, and DentiCAD, a system being developed by Maryland University and Minnesota University which is capable of producing dental crowns, is described. DentiCAD can produce dental restorations that fit at least as well as those that are cast. Some of the challenges and difficulties that have arisen during development are addressed. Some of the questions that, because of the new technology, can now be addressed and that are presenting new challenges are discussed.<<ETX>>

Wear — an entropy production model

Abstract The universal occurrence of wear has led to consideration of the wear process from a thermodynamic point of view. The intent was to characterize the nature of the wear process and material behavior by defining the thermo-dynamic conditions under which such processes are possible. The sliding of two surfaces, one of which wears at a much greater rate than the other, was idealized as a single body to which heat and work are supplied and from which mass transfer is allowed. The condition that for an isolated system undergoing some process entropy production must be non-negative was used to develop a constraint for allowable wear processes. This constraint relates heat, work, chemical potential and surface energy and limits the processes and material behavior possible in the model system.

Friction measurement apparatus for sheet metal forming

Abstract Friction at the tooling–workpiece interface is very important in sheet metal forming operations. Accurate knowledge of friction at such interfaces is needed for process design and analysis, numerical process simulation and validation and control of forming processes. Two physical models or friction simulators, based on the stretching of a strip around a pin, were developed to characterize sheet metal forming friction. In contrast to other test apparatus which use measurements of strain to infer friction forces, these apparatus use direct measurements of forces. Effects of strain, stretching speed, lubrication, pin radius and wrap angle on coefficient of friction were determined.

A review of wood cutting tool wear literature

The current state of knowledge about wood cutting tool wear is assessed by reviewing the published work in this area. Research concerned with tool wear which deals primarily with the tool material, with the work material and with tool-work interactions is considered.ZusammenfassungAnhand einer Literaturübersicht wird der gegenwärtige Wissensstand über das Gebiet der Abnutzung von Schneidwerkzeugen für Holz festgestellt. Dabei werden solche Untersuchungen berücksichtigt, die sich in erster Linie mit dem Werkzeugmaterial, mit dem zerspanten Material und mit der Wechselwirkung dieser beiden Größen untereinander befassen.

An entropy-based model of plastic deformation energy dissipation in sliding

Abstract In order to study the individual energy dissipation mechanisms which act in plastic deformation in sliding, an entropy production model of the sliding process is constructed. Rather than a physical material body, the system considered is a geometric space in which metallic lattice defects can exist. This system can interact with its environment which is the space of annihilated defects. In this system model energy dissipation through structural changes caused by defect creation and heat generation due to defect annihilation are included. For a behavior in which the defect annihilation rate is exponentially dependent on temperature, the minimum entropy production rate system evolution criterion predicts the existence of two different stationary entropy production rate states. In one state entropy production is dominated by structural changes and in the other by heat generation. Changes from one of these states to the other during sliding may account for the formation of a varying sliding body microstructure along the sliding direction.

A thermodynamic model of friction

Abstract The interaction of two bodies is considered from a thermodynamic point of view. The bodies are assumed to interact in an open system in such a way that a non-equilibrium stationary state develops. It is shown that mechanical frictional interactions must be dissipative processes. In addition, a thermodynamic stability criterion is developed for small fluctuations about the non-equilibrium state.

Acoustic emission monitoring of the wear process

Abstract Acoustic emissions are generated at the sites of the fundamental processes resulting in material wear and so are an attractive possibility for continuously monitoring wear and for basic studies of the wear process. Changes in wear rate and acoustic emission activity were measured across the mild-severe wear transition in the sliding of metals. The intent was to characterize these changes in wear behavior in terms of acoustic emission characteristics and to determine the usefulness of acoustic emission measurements for the study of wear. Experimental results showed that changes in acoustic emission count rates correspond to changing wear rate. Acoustic emission amplitude distributions as well as acoustic emission energy measurements indicated a strong potential for the use of these two parameters in the identification of different modes of failure during the wear process.

Energy dissipation in sliding

Abstract It is expected that the dissipation of energy in bodies which are sliding will alter their properties and hence affect their behavior in further sliding-in application. A description of the energy dissipation distribution in the sliding of one body over another is attempted. It is first demonstrated that the existence of a non-zero relative velocity between the sliding bodies indicates that sliding is a non-equilibrium process. A near-equilibrium analysis of the process using entropy production is then used to show that in sliding energy is dissipated. Limitations inherent in the near-equilibrium analysis make it necessary to study the far-from-equilibrium sliding process by use of energy conservation concepts. A model of the energy dissipation process in sliding as two coupled non-linear equations is developed. The non-linearity of the model makes many kinds of solution behavior possible. Of special interest is the possibility of cyclic energy dissipation behavior in the sliding bodies.

Force Sensors Embedded in Surfaces for Manufacturing and Other Tribological Process Monitoring

The measurement of tooling-workpiece interface forces is needed for process design, process modeling and analysis and process monitoring for control. One approach to measuring local interface loads with minimal disturbance of the surface and process is to embed sensors in the surface below the surface region of interest. Small piezoelectric sensing elements were cast into surfaces and their ability to measure loads applied normal to the surfaces was assessed. Sensor outputs were analyzed in terms of sensor depth below the surface, distance along the surface from the load location to the sensor location and sensor to sensor spacing. A mechanical model of the sensor-surface system was developed which predicted sensor output. The use of this sensing concept and type of sensor was demonstrated in strip drawing tests. Using temperature compensated sensors, workpiece holddown force was measured in tests during which drawbead penetration was varied.

Milling Cutter Wear Monitoring Using Spindle Shaft Vibration

With the intent of continuously monitoring cutting tool condition in intermittent machining operations in a benign manner, a noncontacting measurement system was assembled to measure spindle shaft torsional vibration. Spindle vibration was measured using an optical system and analysis of it in the frequency domain resulted in a measure of spectral power which corresponded to amount of cutter wear.