Zenon Ignaszak

Technological aspects of particle-reinforced composites production

Abstract Technological aspects of particle-reinforced composite production together with their geometrical and thermal analysis have been presented in this article. An estimation of metallurgical properties of aluminium alloy matrix composite has been revealed. This study concerns the influence of technological manufacturing parameters on the crystallization, solidification and exploitation features of MMC (metal matrix composite) with aluminium alloy matrix, reinforced with C-graphite, SiC and Al 2 O 3 particles, in the amount up to 5% by weight. The composites here investigated are designed as a material for mechanical parts, which should be characterized by considerable wear resistance, low or high friction coefficient, as well as erosion and corrosive wear resistance.

Problem of Acceptability of Internal Porosity in Semi-Finished Cast Product as New Trend "Tolerance of Damage" Present in Modern Design Office

Discontinuities in cast products, obtained from a liquid state of an alloy, are the result of phenomena occurring during multiphase system crystallization. On the one hand, compacted defects as a shrinkage pipe are relatively easy to eliminate. On the other hand, it is known that presence of fine shrinkage and gas porosity is unavoidable. Detectability of these dispersed discontinuities depends on type of inspection method applied. Structure, including intensity and location of porosity zones, is dependent on the type of the alloy, casting configuration and conception of technological solution, related with control of velocity of the heat extraction to the mould. Thus, mechanical properties in the volume of a casting are not homogenous and are strongly reduced only in the zones of porosity. However, in strength calculations of cast products, this obvious fact is not taken into consideration. The rule of material homogeneity is applied instead, along with drastic increase of factor of safety. The paper indicates benefits of precise determination of limits of porosity zones located in the casting, using the NTD methods (for example, Phased Array ultrasonic tomography). Coordinates of porosity zones in 3D, introduced into CAD geometry and assigned with different properties allow to estimate the actual state of stress and strain of real object using FEM methods (systems like Ansys, Comsol). Load justified by operating conditions and application of tolerance of damage rule, with simultaneous reference to the limited state of stress according to LOV (Loss of Volume) and LEFM (Linear Elastic Fracture Mechanics) methods should find their place in design procedures of cast products, which will allow for better use of material and reduction of weight of the casting. This approach, named Tolerance of damage concerning the castings is the motto of this paper.

Sensitivity Tests of Simulation Models Used in Chosen Calculation Codes on Uncertainty of Thermo-Mechanical Parameters during Virtual Mechanical Stress Estimation for Ferrous Alloy Castings

Simulation systems used for many years in foundry industry such as MAGMASOFT, NovaFlow&Solid and ProCAST, contain thermo-mechanical modules permitting the estimation of mechanical stresses and hot tears appearing in casting during its cooling. It is also known that these modules are rarely used because of the very limited thermo-mechanical database especially for ceramic materials such as foundry sand moulds. These technologies – castings pouring in non-permanent sand moulds, particularly iron alloys are most often applied in foundry. In our study the method of evaluating the algorithms quality applied in thermo-mechanical phenomena models based on parameters sensitivity testing from the proper database of the simulation system was used [1]. The comparative analyses of both experimental and virtual results were realized (by stress estimation). The methodology of experimental research was similar to that described where gray cast iron castings of stress bars (grid) were casted in sand mould bonded by organic resins.

Estimation of Coupled Thermo-Physical and Thermo-Mechanical Properties of Porous Thermolabile Ceramic Material Using Hot Distortion Plus® Test

In the paper the thermo-mechanical phenomena which occur in thermal shocked thermolabile porous ceramic material were described. Such materials are applied in foundry industry for mould making and they are characterized the low thermal stability losing its strength above 400°C. In [3] the usefulness of Hot Distortion Plus® to estimate the thermo-physical parameters (apparent thermal conductivity, heat capacity) was discussed. These parameters are necessary in data base of simulation codes which permit to simulate the phenomena in casting-mould system. The aim of these tests is to predict the mould material phenomena influence on castings quality. Parameters applied in these thermo-mechanical models (Youngs modulus, Poissons ratio, Yield stress) and their variations with temperature are not really known for thermal unstable mould material. There is no adapted method in literature and description of such total investigations of both parameters groups: thermo-physical and thermo-mechanical. The authors method called Hot Distortion Plus® consists in acquisition of temperature curves of heated sample of material and correlation with curves of their dilatation. Following the simulation using inverse solution method to reproduce the measured parameters with experiment was applied. The tests were carried out for the new quartz sand bonded by resin (approx. 1%). The specimens (dimensions 114 × 25 × 6mm) from binder-sand mixture were made using special core-box.

Study on Data Base of Modeling Concerning Casting Phenomena in Cast-Iron-Mould Simulation Systems

In the foundry processes the hard modeling based on physical-mathematical formula is burdened with simplifications resulting from both: knowledge level on description of particular phenomena and level of theirs complexity. Trends observed in modeling of foundry processes and expectations of users compared with creators’ up-grades propositions are discussed. The author presents real possibilities of efficient modeling validation considering that limits of multiphysics/multiscale modeling exist for massive cast-iron castings, including the zones infected by degenerated structure (e.g. chunky graphite, dross inclusions). The model validation demands experimental-simulation studies. In the paper also the stress grid castings made of lamellar cast-iron are presented as an example of experimental model validation including the thermomechanical properties of cast-iron and furan mould and applying special Hot Distortion (HDplus®) tests of this sand. The validation of thermo-mechanical model was carried out with the use of Comsol system and chosen foundry simulation code.

Problems of heat source modeling in iso-exothermic materials used as riser sleeves in foundry

The modeling of heat transfer in materials containing exothermic components must take into consideration the presence of heat sources in the Fourier–Kirchhoff equation. The aim of this investigation was the identification of real and effective thermophysical parameters of the insulating–exothermic materials used as riser sleeves containing these exothermic heat sources. The experiments of steel pouring into the mould, containing different insulating and exothermic sleeves were carried out, using thermocouples measurement systems (thermal analysis of casting–mould system). Then the thermophysical coefficients of these materials were calculated using inverse problem solution. The worked time–dependent formula of exothermic reaction heat (heating yield in W/m3) was called heat source function. The paper presents the basis and the practical expression of heat source by different functions, its justification and the results of simulations using these functions. The numerical system Calcosoft and its Inverse Solution procedure were applied.

Substitute thermal conductivity coefficient for multi-component ceramic materials

Abstract On the example of granular material (as quartz sand bonded by resin, used for mould production in metallic alloy casting—in foundry industry), the phenomenon complexity level in a such porous material during heat transfer, is presented. Accurate modelling of these phenomena (superposition) is of limited meaning, because of incomplete material data bases, that are needed in this case. Practical solution is based on the application of simplified models as for non-porous, homogenous, solid materials. This fact requires the knowledge of the substitute thermal conductivity coefficient ( λ substit ). In the paper, the second practical proposal is justified. The methodology of λ substit determination, by inverse solution related to experiment, is described. The coefficient λ substit depends on the local temperature and on the time of various temperature influences in the same place of material. The effectiveness of λ substit using the computer simulation of heat chock, in described mould material, e.g. during metallic alloy casting, is also proved.

Effective Modelling of Phenomena in Over-Moisture Zone Existing in Porous Sand Mould Subjected to Thermal Shock

The problem concerns the thermo-physical properties of the porous ceramic material called mould to which the liquid metal is poured (in foundry industry). In the foundry processes the sand mould fulfils an auxiliary role only as technological tool, but its physical and technological properties determine the quality of the casting. The study includes the iron plate casting experiments poured in multi-component porous sand mould. The temperature fields in casting and in different zones of the mould were recorded. The determining of the thermo-physical properties of mould sand containing the over-moisture zone using simulation tests by Procast and NovaFlow & Solid foundry systems was the goal of this study. An originality of the related research is an attempt to take into account the effects of the global thermal phenomena occurring in the quartz sand bonded by bentonite-water binder, using the apparent (substitute) thermal coefficients. The majority of foundry simulation systems are not capable to modelling the phase transformation of water into vapour, vapour transport and its condensation in porous media (called green sand moulds). In these cases the application of heat and mass transfer substitute coefficients during modelling/simulation is an interesting effective way.

Sensitivity of Models Applied in Selected Simulation Systems with Respect to Database Quality for Resolving of Casting Problems

This paper highlights permanent development of process virtualization in the mechanical engineering industry, especially in the area of foundry. Virtualization is increasingly developed on the stage of product design and materials technologies optimization. Simultaneously, increasing expectations of design and process engineers regarding the practical effectiveness of applied simulation systems is observed. To enhance the knowledge in the scope of modelling and simulation in the foundry processes, one should be acquainted with the hard modelling based on physical-mathematical formula and also the soft modelling, burdened with simplifications resulting from both knowledge level on description of particular phenomena and level of theirs complexity. The trends observed in modelling of foundry processes and expectations of users compared with creators upgraded propositions new, additional modules based mostly on poorly tested theory are discussed. In such cases, each new module should be tested on sensitivity of additional parameters, which appear in these new modules. If needed and possible, these tests ought to be related to validation of the whole complex model containing such new modules. The purpose is to obtain simulation tools allowing the most possible realistic prognosis of the casting structure, including indication, with the highest possible probability, places in the casting that are endangered with the possibility of a gas and shrinkage porosity formation. These problems with elements of model validation are presented in the paper.

Mechanical Properties Gradient Existing in Real Castings Taken into Account during Design of Cast Components

The problem concerns the structure and properties heterogeneity of cast products, on the example of the Al-Si (A356) alloy. The trends of usage of this knowledge by constructors of that kind of products are described in this paper. It is well known that soundness of cast products is a postulate formulated by designers and users of machines and devices, where castings are among important parts. It is often forgotten though, that perfect soundness (density) of the cast material in ready for use parts simply does not exist. The gas and shrinkage porosities, present in semi-finished casting products, obtained from a liquid state of an alloy is the result of phenomena occurring during multiphase metallic system crystallization. Still, general introduction of the tolerance of damage rule requires knowledge about casting technology, inspection of the state of discontinuity of casting structure. The use of coupled experimental researches (including NDT non-destructive testing and local mechanical properties of castings) and simulation tests (Procast, ANSYS) have shown how the properties gradient influences on the safety factor distribution in the casting subjected by chosen load.