M. Horváth

Process planning with genetic algorithms on results of knowledge-based reasoning

The paper presents a new approach to solving even unusually complex problems of computer-aided process planning (CAPP). Main principles are based on the analysis of the roles and relations of CAPP in advanced manufacturing systems. Planning is carried out in several stages, by using both domain-specific knowledge and domain-independent, general methods. First, by knowledge-based reasoning, repertoires of plan elements and technological constraints are created that the final solutions must meet. Then, a global plan merging process generates plan variants so as to meet the given optimization objective. Among the various plan merging methods, one using genetic algorithms stands preeminent by its performance and robustness. Domain-specific knowledge, methods of reasoning and plan merging are described in detail.

On a Novel Tool Life Relation for Precision Cutting Tools

When using new, very expensive superhard tool materials (diamond or CBN) for precision and ultraprecision machining of parts made, very often, from expensive materials, exact knowledge of the tool wear process (considering, of-course, its stochastic character) is absolutely necessary. It means, that we need new tool-life equations for these new tools. In the present paper, a new tool life relation is proposed based on machining experiments. It reflects the two-extremum form of tool life curves and is valid for a wide range of cutting conditions.

A bound for ratios of eigenvalues of Schrödinger operators with single-well potentials

For Schrodinger operators with nonnegative single-well potentials ratios of eigenvalues are extremal only in the case of zero potential. To prove this, we investigate some monotonicity properties of Prufer-type variables.

Modifications of Surface Integrity during the Cutting of Copper

Abstract The required extreme surface quality of metallic parts made necessary investigation of different features of surface formed crystallites in polycrystalline materials. Every surface crystallite has different crystal plane orientation, so its reaction to the machine tool during cutting differs from that of other crystallites. These differences are reflected in the features of surface finish, especially when the surface is mirror like. The reason is that orientation of the crystallite determines the plastic and elastic deformation both of the machined surface and the chip. Elastic deformation perpendicular to the surface depends on the perpendicular compressive stress caused by the tool and Youngs modulus, perpendicular to surface. After the passage of the tool, the elastic deformation disappears and its former values result in different levels of crystallite surfaces. Differences are determined by the orientation dependence of the Youngs modulus. The ratio of highest to lowest modulus for copper is about 3, whereas for tungsten it is 1. The most important features of crystal structure and the reasons that cause deviations in surface finish in the machining of copper are reported.

Effect of cutting tools and cut materials on integrity of mirror surfaces

Abstract The thermodynamic features of cutting tools and the cut materials change during cutting owing to their interactions and are considered in the present paper. The temperature of both increases, but, while the temperature and load on the cutting tool, during continuous cutting, may be considered as constant; the temperature of the machined material, in regions close to the cut surface, change both in time and space. When the crystal structure of the machined material is sensitive to changes in temperature, phase transitions, hardening or softening can occur in the surface layer. In particular the phase transition to a martensitic material involves hardening of a soft material. These transitions are of great importance, especially, in the case of ultra precision machining of mirror like surfaces. Similar changes of surface roughness are caused by the anisotropy of the modulus of elasticity. The component of Young’s modulus, perpendicular to a cut surface, mainly depends on crystal orientation and therefore, elastic deformations change from individual crystallite to crystallite.

Effect of Microstructure on the Mirror-Like Surface Quality of FCC and BCC Metals

The microstructure of machined metals changes near the tool-affected zone. This paper presents some new results concerning mirror-like surface cutting of aluminum, copper and tungsten. The microstructure of aluminum and copper represents polycrystalline mild metals with face centered cubic (FCC) crystal structure. Examination of a mirror-like surface by optical microscopy, scanning electron microscopy (SEM), electron backscattered diffraction and atomic force microscopy revealed that grain boundaries and twin boundaries were present, which separates two domains for different crystal orientation. The Youngs modulus that depends on orientation can change considerably on these boundaries and, consequently, the value of elastic deformation of the layer under the machined surface. This effect modified the roughness. Ultraprecision machining of tungsten, which is a body centered cubic (BCC) metal, proved useless using diamond and/or boron-nitride tools. Since tungsten is a very brittle metal at room temperature, its ductile to brittle transition temperature is much higher. Therefore, in contrast to normal cutting, the material that is incapable of plastic deformation will cause brittle fracture of the chip and bad surface quality.

Effect of Crystal Orientation on Surface Integrity

Anisotropy of materials mechanical properties is one of the main factors, determining surface finish of machined surfaces. In the interaction between the cutting tool and the cut material both plastic and elastic deformations appear. Effect of crystallites in the machined surface on the workpiece surface finish depends on crystal direction perpendicular to the surface. Value of elastic deformation is determined by the ratio of applied stress and the determinant modulus of elasticity in given direction. Since E modulus depends on crystal direction, surface roughness changes from one crystallite to other one. The rates of these changes depend on the deviations of Young modulus in different crystal directions. In the paper the changes of surface finish in different materials are shown, as functions of cutting conditions and those of deviations in modulus of elasticity, in different crystallite orientations.

Cooperation Via Conflicts In Manufacturing Systems

The paper discusses how conflicts that emerge necessarily between various agents in a manufacturing system can be exploited in favour of the whole system. Experience related to conflict situations and their resolutions constitutes the core of the system’s social knowledge. A mechanism for co-operative problem formulation and solution is suggested; this mechanism is based on the use of the recollections of previous conflict cases. As a vehicle for capturing this social knowledge and transferring it to the actual control of manufacturing systems, case-based reasoning is proposed, because it is able to handle incomplete, inconsistent and unformatted information, and can support incremental learning.