Functional periodicity as a concept for the (re-)design to agility of production systems

The complexity of a production system is caused by two factors: by a time-independent poor design that causes low efficiency (system design), and by a time-dependent reduction of system performance due to system deterioration or to market or technology changes (system dynamics). To optimize the efficiency and changeability of a production system, both factors must be considered. Starting from complexity theory, a procedure is presented in this paper that helps not only to design production systems with low or zero time-independent complexity (focus: flexibility and efficiency), but also to prevent the unpredictable influences of the time-dependent combinatorial complexity by transforming it into a periodic review and adaptation of the system’s volume and variant capabilities (focus: agility). With the help of a practical industrial example the validity of the approach is illustrated.     

Modeling Disk Cracks in Rotors by Utilizing Speed Dependent Eccentricity

This paper discusses the feasibility of vibration-based structural health monitoring for detecting disk cracks in rotor systems. The approach of interest assumes that a crack located on a rotating disk causes a minute change in the system’s center of mass due to the centrifugal force induced opening of the crack. The center of mass shift is expected to reveal itself in the vibration vector (i.e., whirl response; plotted as amplitude and phase versus speed) gathered during a spin-up and/or spin-down test. Here, analysis is accomplished by modeling a Jeffcott rotor that is characterized by analytical, numerical, and experimental data. The model, which has speed dependent eccentricity, is employed in order to better understand the sensitivity of the approach. For the experimental set-up emulated here (i.e., a single disk located mid-span on a flexible shaft), it appears that a rather sizable flaw in the form of a through-thickness notch could be detected by monitoring the damage-induced shift in center of mass. Although, identifying actual disk cracks in complex “real world” environments, where noncritical crack lengths are small and excessive mechanical and/or electrical noise are present, would prove to be rather challenging. Further research is needed in this regard.     

Diffusion mass transfer under the conditions of instability of products of electrochemical reaction

Theoretically considering the diffusion-migration mass transfer in binary z ₁–z ₂-electrolytes during anodic dissolution of metals is performed with due allowance for the decomposition of intermediates formed. The components’ concentration and electric potential distributions in the diffusion layer, as well as the system’s current-voltage characteristics are calculated. It is shown that under conditions of the cation slow removal the electrochemical process is slowed down with an increase in the products’ stability constant. Original Russian Text ? A.V. Noskov, S.A. Lilin, 2007, published in Zashchita Metallov, 2007, Vol. 43, No. 2, pp. 117–122.     

Valuation of changeable production systems

The introduction of changeable production systems increases the adaptability of factories in an uncertain environment. This paper analyzes the valuation of the economic efficiency of such systems using the real options theory. The developed approach proposes a structured valuation process for selecting options related to production engineering and factory planning. Based on a classification of possible modifications of a production system, options profiles are derived. Considering the existing uncertainty of a company’s environment these profiles may be utilized to identify real options which ought to be included when valuating a technical production system design.     

Factors of chemical activity of metal surface

In this work, the factors of the chemical activity of the metal surface are studied in terms of their physical nature. The concepts of chemical bonding, e.g., the equalizaton of electronegativities and maximum chemical hardness, are related to the theories of a metal surface response to external electromagnetic excitations. The metal surface is considered in terms of the electronic gas edge model (Kohn and Mattsson). The equations of the Landau-Migdal theory of the electronic Fermi liquid are used to describe the effect of a field’s interactions with electrons. An analysis of the solution of a system of equations showed that the parameters of the metal system’s response to the external electric field (chemical potential of the electron and local and integral density of one-particle electronic levels near the Fermi level) are identical to the main characteristics of its chemical activity according to Yang and Parr (Yang, W., Parr, R.G., “Proc. Natl. Acad. Sci. United States,” 1985, vol. 82, p. 6723): electronegativity, local and global chemical softness. The model under consideration contains no artifacts. The authors believe that the method is promising for further studies of fundamentals of the nature of physicochemical phenomena at interfaces.     

Cartesian compliance model for industrial robots using virtual joints

Industrial robots represent a promising, cost-saving and flexible alternative for machining applications. Due to the kinematics of a vertical articulated robot the system behavior is quite different compared to a conventional machine tool. The robot’s stiffness is not only much smaller but also position dependent in a non-linear way. This article describes the modeling of the robot structure and the identification of its parameters with focus on the analysis of the system’s stiffness. Therefore a method for the calculation of the Cartesian stiffness based on the polar stiffness and the use of the Jacobian matrix is introduced. Furthermore, so called virtual joints are used. With this method it is possible to model each joint of the robot with three degrees of freedom. Beside the gear stiffness the method allows the consideration of the tilting rigidity of the bearing and the link deformations to improve the model accuracy. Based on the results of the parameter identification and the calculation of the Cartesian stiffness the experimental model validation is done.     

A cantilever beam method for evaluating Young’s modulus and Poisson’s ratio of thermal spray coatings

Young’s modulus and Poisson’s ratio for thermal spray coatings are needed to evaluate properties and characteristics of thermal spray coatings such as residual stresses, fracture toughness, and fatigue crack growth rates. It is difficult to evaluate Young’s modulus and Poisson’s ratio of thermal spray coatings be-cause coatings are usually thin and attached to a thicker and much stiffer substrate. Under loading, the substrate restricts the coating from deforming. Since coatings are used while bonded to a substrate, it is desirable to have a procedure to evaluate Young’s modulus and Poisson’s ratio in situ. The cantilever beam method to evaluate the Young’s modulus and Poisson’s ratio of thermal spray coat-ings is presented. The method uses strain gages located on the coating and substrate surfaces. A series of increasing loads is applied to the end of the cantilever beam. The moment at the gaged section is calcu-lated. Using a laminated plate bending theory, the Young’s modulus and Poisson’s ratio are inferred based on a least squares fit of the equilibrium equations. The method is verified by comparing predicted values of Young’s modulus and Poisson’s ratio with reference values from a three-dimensional finite ele-ment analysis of the thermal spray coated cantilever beam. The sensitivity of the method is examined with respect to the accuracy of measured quantities such as strain gage readings, specimen dimensions, ap-plied bending moment, and substrate mechanical properties. The method is applied to evaluate the Young’s modulus and Poisson’s ratio of four thermal spray coatings of industrial importance.     

Modeling linear guide systems with CoFEM: equivalent models for rolling contact

Today’s machine tools are highly complex mechatronic systems capable to exert large translational and rotatory movements. In most cases rolling bearings are used to connect the moving parts to each other. As full FE models of rolling bearings can consume a large amount of degrees of freedom (DOF) efficient methods for reducing the DOF consuming rolling elements to more simple equivalent models are needed. As an example a linear guide system is used. A special feature of the considered linear guide is that the runner block consists of three separate parts, which are hold together only by pretension and friction. FE simulations of such linear guide system were not reported before in the literature. Beside the full FE model three equivalent contact models are presented. The first two equivalent contact models feature novel characteristics. Advantages and disadvantages of the equivalent models are discussed using as reference a slice of the full model and simulation results of static stiffness. The validation of the numerical models is also done using the general analytical solution of Hertz.     

On certain features of the asymptotic calculation of the physical regularities of the implementation of charged drop electrostatic instability

The dispersion equation for the capillary oscillation of a charged spheroidal drop was found within the limits of the analytical asymptotic approach by incomplete decomposition with small parameters with the first order depending on the amplitude of the oscillations and the second order, on the amplitude of the spheroidal deformation. It is shown that the critical conditions of the electrostatic instability for all the modes of a drop’s oscillation decrease at an increase in the spheroidal deformation range.     

Conductivity of aqueous suspensions of alumosilicates

When studying the electrochemical properties of diluted suspensions of natural and modified bentonite, the correlation between the inductive component of the system’s resistance and the temperature has been established. It confirms the hypothesis on the presence of paramagnetic particles in the system, whose solubility decreases with the growth of the temperature. Active forms of oxygen, as generated in the near-electrode space, can be such particles. It is shown that, in model systems, hydrogen peroxide is formed in this space due to the reversible dissociative adsorption of oxygen on platinum in the presence of a suspension electrode with proton conductivity.     

An unconventional Au/TiO2 PROX system for complete removal of CO from non-reformate hydrogen

Au-based catalysts, generally known for high activity in the selective catalytic oxidation of CO to CO₂ at ambient temperatures, can play a significant role in increasing the fuel cell system’s CO tolerance. In this work, an unconventional CO tolerance method, using an Au/TiO₂ “guard bed”, has been investigated. The system is unconventional in the sense that it does operate as a PROX catalyst, but not in a traditional reformer system configuration. Instead, it has been developed to completely remove CO onboard the vehicle over a wide range, ppm to percentage levels, from impure pressurized H₂-rich gas, i.e. from partially enriched H₂ that would be stored in a fuel tank/cylinder but that would have some CO contamination and would essentially be dry. This set up will allow a reduction in the cost and complexity of conventional “off-board” hydrogen enrichment. The system CO tolerance obtained with the Au/TiO₂ system was compared with state of the art PtRu/C and PtMo/C CO tolerant anode technologies. Catalytic effectiveness in the removal of CO has been directly monitored by both direct analytical measurements and by monitoring the operation of a laboratory fuel cell to which the purified hydrogen stream was passed.     

偏心非圆齿轮—曲柄摇杆引纬机构的动力学分析

为了深入研究偏心非圆齿轮-曲柄摇杆引纬机构的动力学特性,建立了偏心非圆齿轮-曲柄摇杆引纬机构的动力学模型,并利用动力学方程序列求解法进行了求解.利用Visual Basic 6.0编写了动力学辅助分析软件,得到了各轮齿啮合点和铰链点的受力变化规律,为机构动力学参数的设计和优化提供了理论基础,同时为机构部件进行强度分析提供了依据.     

Identification of the bulk behavior in the near-contact-surface of steel workpieces

Originally dedicated to the characterization of the material surface properties for processes involving extended workpieces such as tube drawing, the upsetting- sliding test involves a circular cross- section indenter which creates a localized plastic strain by sliding with a given penetration along a generator line of a specimen. The mechanical characteristics of the indenter are the same as those of the tool in the fullscale problem, and the specimen is directly extracted from the workpiece or from the target part of the production plant. An analysis of the upsetting phase of the test is proposed to identify the specimen bulk properties in the near- surface. The stress- strain curve of the specimen is averaged by a Ludwik’s model. A dichotomizing search is involved to compute the most suitable Ludwik’s parameters by minimizing the error made between experimental results and elastoplastic finite element computations. Identifications carried out on a 1522 annealed steel specimen accurately determined the bulk behavior.     

A new approach to determine the wear coefficient for wear prediction of sheet metal forming tools

Accounting for the increase of wear in metal forming tools, it is eminent to have detailed information about the tool lifetime already during the tool design. With the wear simulation tool REDSY—developed at the Institute of Metal Forming and Casting—tool wear can be simulated qualitatively and quantitatively for sheet metal forming processes. The calculations are based on Archard’s wear model, a model using contact mechanics to describe the wear behavior. In this project, a new approach to determine the wear coefficient has been developed using a simple cylindrical cup deep drawing experiment for the wear measurements. Several tool and sheet material combinations were analyzed using a five-stage progressive die tool in a precision automatic punching press in order to achieve a high wear volume in a short period of time. The wear coefficient for the respective material combination could be determined combining the experimental results with simulation. This method is verified by comparing the wear simulation results with actual measurements. This project was funded by Germany’s Bundesministerium für Wirtschaft und Arbeit (BMWA) over Arbeitsgemeinschaft industrieller Forschungsvereinigungen “Otto von Guericke” e.V. (AiF). Project code: AiF14291N.     

System identification during milling via active magnetic bearing

One of the main focuses of recent machine tool development is to increase the machining performance. But the enhancement of the metal removal rate (MRR) is often limited by the stability of the milling process. To prevent unintentional chatter vibrations and to observe changes in the system’s behavior, there is a need to observe the state of the milling process during machining. Beside others, one approach is the development of an adaptronic motor spindle using active magnetic bearings (AMB) combined with conventional roller bearings in a so called “hybrid approach”. The AMB acts as a contact less sensor and actuator, in order to estimate the frequency response function (FRF) of the spindle-tool system during the milling process. The two major dependencies on the FRF are the spindle speed and the cross-sectional area of the chip. Also the closed loop damping can be observed to estimate the stability margin. This paper presents the identification of the varying eigenvalues during the machining.

Applying Simulation and Analytical Models for Logistic Performance Prediction

Different types of models are used to describe the interdependencies between logistic performance measures of production systems in research and practice. The most widely known analytical models in this field are queuing theory models. Simulation, on the other hand, is a widespread technique for the exploration, design and optimisation of complex production systems. Due to the limitations of queuing and simulation models, a mathematical approximation approach developed at the Institute of Production Systems and Logistics is becoming more relevant: the Logistic Operating Curves. The paper introduces the theory of these three modelling methods and compares as well as differentiates them.     

The status of utah coal in global resources

Coal resources have had a historical effect on the development of Utah and a far-reaching influence in the western expansion of the United States. Although Utah’s production is just more than two percent of the total national production, the resource quality is higher than most other coal fields in the United States. Coal production surpassed 25 million tons in 1995 and has increased in recent years. In this article, the specific properties of Utah’s various coal fields are discussed in terms of marketability, mining difficulty, and transport to markets. The broad spectrum of Utah’s coal production—past, present, and potential future growth—is reviewed through distribution and coal usage data spanning a ten-year period. Editor’s Note: Although JOM style dictates the use of metric units of measurement, this article retains U.S. customary units to conveniently reflect the commodities standards employed in the coal industry. F.R. Jahanbani earned his M.S. in business management at Brigham Young University in 1967. He is currently a senior energy specialist at the Department of Natural Resources, State of Utah.     

Cyclic influences within the production resource planning process

Nowadays, manufacturing companies operate in a constantly changing environment. Customer requirements, increasingly stringent environmental laws and the entrance of new competitors into the manufacturer’s market influence the decisions and processes of manufacturing companies. In order to sustain a competitive advantage, a manufacturer needs to anticipate this dynamic environment and offer the right amount of the right products at the right time to the right markets. Therefore, companies need to understand and analyze the different influencing factors. Many of these factors occur at periodical intervals and demonstrate a cyclic behavior. This article proposes a number of models and methodologies for anticipating and managing the different occurring cycles. In this pursuit, various trends in the production industry and the manufacturer’s environment are highlighted. Thereby, different aspects, perspectives and concepts regarding the production process are discussed. Finally, the need for the professional management of cycles is emphasized and the application of the introduced methodologies is demonstrated through a case study of the industrial robot industry.     

Analysis of asymmetrical hot strip rolling by the slab method

Two analytical models based on the slab method are proposed to examine the behavior of sheet at the roll gap during the asymmetrical hot strip rolling process. In model I, the effect of shear stress in vertical plane at the roll gap is considered, whereas this effect is neglected in model II. Neutral points between rolls and strip, rolling pressure distributions along the contact art length of rolls, rolling forces, and rolling torques can be calculated easily by these proposed analytical models. The results including rolling pressure distributions, rolling forces, and rolling torques by both models are compared. The rolling pressure distribution predicted by model I shows that a “pressure well” develops in the cross shear region. On the other hand, no “pressure well” is predicted in model II. Furthermore, the rolling forces predicted by model I are always lower than those measured in the experiment, whereas those predicted by model II are always higher. However, the averages of the values predicted by model I and II are in fairly good agreement with the experimental data. Thus this analytical approach can offer useful knowledge in designing the pass schedules of the asymmetrical hot strip rolling processes.