Reactive manufacturing control using the ant colony approach

As a reaction to the volatile market demands with regards to the number and variants of products offered, ever more complex procedures for manufacturing control are being developed. Most recently, self-organising procedures, which often mimic the behaviour of natural systems, have arisen. The method of ant colony optimisation (ACO), which was inspired by ants, can provide the necessary fundamentals in order to realise self-organising manufacturing control. In this context, the ifab-Institute has developed the AntControl tool for self-organising manufacturing control based on ACO. In order to investigate the potential of ACO, several concepts have been developed and integrated into the existing OSim simulation tool to create the new OSim-Ant tool. An exemplary simulation study within a manufacturing system has been carried out to evaluate the behaviour of AntControl. This paper presents this tool as well as the results of the simulation study.     

Mechanical properties and adhesion strength of TiN and Al coatings on HSS, steel, aluminium and copper characterized by four testing Methods

TiN and Al coatings on substrates of high-speed steel, steel, aluminium and copper have been used to study mechanical properties of coating systems, especially the adhesion of the coating. The quantities measured are internal stress of the coating, determined by X-ray diffraction, the critical load of the scratch test, the microhardness obtained by the indenter technique, and the interface fracture energy, determined by a three-point bend test developed recently by the authors. The fracture energy, G_c, is a measure for the adhesion strength of a coating system. The effect of bias voltage, sputter cleaning and contamination of the substrates on the adhesion strength and other mechanical properties are investigated with the four methods mentioned. Each of the testing methods reveal only specific aspects of the behaviour of the coating systems. The data obtained depend on bulk properties of the film and the substrate material and on properties of the interface. Variation of the bias voltage can change them in quite different ways. In addition, the inter-relations between the adhesion strength of the coating and the failure behaviour of the three-point bend test samples are discussed.     

Hydraulic transport of solids in pipes: a simple method for the prediction of pressure drop

Suspensions such as grouting slurries, concrete and dredge muds exhibit a complex flow behaviour in pipes which is not fully understood. This flow in cement systems is often complicated by the time-dependent behaviour of the material and the apparent slippage at the wall of the pipe. Most of the methods which have been developed to predict the flow behaviour of thick suspensions are very complex and are frequently inaccurate. In this paper a simple method is discussed which can be used to predict the pressure drop in pipes for time-dependent or time-independent materials with a yield stress. The method is based on the assumption that the sheared layer in the pipe can be simulated by a similar layer in the coasial cylinder viscometer, and the properties of the layer are only dependent on plug speed in both systems. The implication of this assumption is that the shear stresses at the surface of the pipe and at the surface of the inner cylinder of the coaxial viscometer are independent of the pipe diameter and the diameter of the cylinders. The method was tested against the authors’ own data and by other data from the literature.     

Analysis of Interfacial Coating Effect on Thermal Stress in Composites

A preliminary model for the analysis of thermo-mechanical behaviour of interfacial coatings on thefibers in unidirectional composites have been developed on the solution of thermo-elastic mechan-ics. Thermal stress would be introduced into the composite during cooling because of the mismatchof thermo-mechanical properties among their components. The low modulus coating can effectivelyreduce the interracial stress caused by different thermal expansion coefficient between fibers and ma-trix, no matter how high or low the expansion coefficients of coatings are in CF/Al and SiC/Ticomposite systems, however, high modulus coating can decrease the interfacial compressive stress,only when the thermal expansion coefficient of coating is lower.     

Determination of material constants in creep continuum damage constitutive equations

Experimental creep and creep rupture data are presented for copper at 150, 200 and 250°C and for 0.5Cr0.5Mo0.25V steel at 640°C. Creep continuum damage constitutive equations have been shown to be capable of accurately representing the creep behaviour of both materials. A six variable optimisation program, which was developed to efficiently obtain the material constants, is described.     

Nonlinear numerical modelling of FRP reinforced glued laminated timber

Fibre-reinforced polymers (FRPs) are effective in the flexural stiffening and strengthening of structural members. Such systems can be optimised if accurate numerical models are developed. At present, limited information is available in the literature on numerical models that can predict with good accuracy the nonlinear behaviour of FRP reinforced low-grade glued laminated timber beams. This paper discusses the development of a finite element model, which incorporates nonlinear material modelling and nonlinear geometry to predict the load–deflection behaviour, stiffness, ultimate moment capacity and strain distribution of FRP plate reinforced glued laminated timber beams manufactured from mechanically stress graded spruce. Beams with and without sacrificial laminations are modelled and their performance is compared to unreinforced glued laminated timber beams. The model employed anisotropic plasticity theory for the timber in compression. The failure model used was the maximum stress criterion. Strong agreement was obtained between the predicted behaviour and the associated experimental findings. It was deduced from comparing the results from the numerical model with experimental findings that the FRP plate succeeds in increasing the performance of the adjacent timber significantly. The model is a useful tool for examination of the effect of reinforcement percentage and will be used for optimisation of the hybrid beam.     

Resorbable Antibiotic Coatings for Bone Substitutes and Implantable Devices

Antibiotic delivery systems based on biodegradable coatings have found considerable interest for the prophylaxis and local therapy of biomaterial‐related infections. In this study sparingly water‐soluble gentamicin salts have been prepared and tested as biodegradable antibiotic‐releasing coating systems. Using the coating systems, homogeneous, well adhering films can be produced on various implant materials, like ceramics, glasses or metals surfaces, with different surface morphologies. The in vitro release profiles of the antibiotic coating systems were characterized by an initial burst release followed by a sustained release of small antibiotic amounts up to several weeks. It was found that the in vitro release, especially in the initial phase, can be modulated by the ratio between highly water‐soluble gentamicin salts and sparingly soluble ones in the coating. Coating systems of the same type as described for gentamicin are available from a wide range of antibiotics differing in structure and mechanism of antibacterial action. Based on these results, the developed antibiotic coatings offer new perspectives to prevent and treat biomaterial‐related infections.     

Optimal joint selective imperfect maintenance and multiple repairpersons assignment strategy for complex multicomponent systems

This paper addresses the joint selective maintenance and repairperson assignment problem (JSM–RAP) for complex multicomponent systems. The systems perform consecutive missions separated by scheduled finite duration breaks and are imperfectly maintained during the breaks. Current selective maintenance (SM) models usually assume that only one repair channel is available or that the repairperson assignment optimisation can be done at a subsequent stage. Using a generalised reliability function for k-out-of-n systems, we formulate the JSM–RAP for multicomponent systems more complex than the series-parallel systems commonly used in previous SM models. Two nonlinear formulations and their corresponding binary integer programming models are then proposed and optimally solved. Numerical experiments show the added value of the proposed approach and highlight the benefit of jointly carrying out the selection of the components to be maintained, the maintenance level to be performed and the assignment of the maintenance tasks to repairpersons. It is also shown that the flexibility provided by mixed skill cohorts of repairpersons over uniform cohorts can yield higher performance levels when the skillsets are significantly different.     

A simulation approach for evaluation and improvement of organisational planning in collaborative product development projects

Human behaviour and organisational structure impact collaborative product development outcome on a large scale. Therefore, companies are continuously seeking new opportunities to increase the efficiency, effectiveness and predictability of their collaborative product development projects, and to develop innovative principles for organisational design and management such as multi-functional teams. However, there are many factors which have to be considered and assessed to systematically optimise organisational planning in respect of team configuration, structure organisation, and human behaviour. This paper proposes an agent-based simulation methodology to evaluate and improve the organisational planning in complex product development projects. An agent-based integrated simulation model is formulated which can explicitly represent human behaviour, organisational interactions, and tasks networks. Based on the model, the design agent structure and behaviour protocols are studied in detail, and a simulation platform is developed. Finally, the methodology is evaluated in a collaborative roadway design project, and several management insights are established, which are proven to be effective for the organisational optimisation. The results of the case study also show that the methodology can effectively support the evaluation and improvement of organisational planning.     

Optimal design of sandwich panels made of wood veneer hollow cores

In response to the growing interest in replenishable, lightweight, stiff and strong materials, a novel sandwich panel with a hollow core has been manufactured using commercially produced 3-ply veneer. In this paper, the out-of-plane shear behaviour of the novel hollow core is analysed and the expressions for the failure loads are developed. A strength-based optimisation problem is formulated for predicting the optimum values of the panel dimensions that would produce minimum panel weight when subjected to bending. It has been found that the minimum weight, as predicted by the full four-parameter optimisation, is slightly lower than that obtained by using the closed form expressions derived on the basis of simplified three-parameter optimisation. Relationships between the active failure modes are explored. Design maps are shown for a wide range of loading that can be used to calculate the minimum panel weight and the corresponding values of the geometric parameters. The approach developed is general and is equally applicable for sandwich panels with similar hollow cores made of other materials.     

Detonationsflammspritzen hartstoffhaltiger Funktionsschichten

Detonation flamespraying of functional surfaces Thermal spraying is well known for its possibilities to improve the surface of tools. Depending on the purpose advanced properties can be achieved by the coating. Electrical and thermal isolation, wear resistance and corrosion protection are typical applications. The assignment to develop composite coatings for grinding stone and concrete is a new field of investigation. Compared to complex and restrictive sintering and brazing processes the production of grinding tools based on thermal spraying can be an alternative option. With high geometric variability and lower process costs it has a high economic potential. In order to create high performance tools in future, fundamentals of process optimisation are evaluated in this research work. Based on the detonation flamespraying process for embedding large superabrasive particles into a copper‐based matrix has been studied. Bonding quality, coating morphology and hard particle allocation have been examined regarding to the profile requested. In addition the influence of process and substrate temperatures on the properties of the MMC‐compound have been analysed.     

Gamma distribution parameter estimation for field reliability data with missing failure times

Maximum likelihood estimators have been developed for the gamma distribution when there is missing time-to-failure information. Data sets with missing time-to-failure data can arise from field data collection systems that rely on recorded observations of the system by the operators and maintenance personnel. In many regards, this type of data is highly desirable because it implicitly accounts for all actual usage and environmental stresses. Unfortunately the component times-to-failure are not always recorded for fielded systems because of a lack of elapsed time meters, unsatisfactory data reporting requirements, or incomplete or lost information. When only data of this type is available, it creates a non-standard form of da'ta censoring and it has generally not been possible to fit most common time-to-failure distributions. Reliability practitioners have sometimes made unsubstantiated simplifying assumptions so the data can be used. In this paper, a more rigorous approach is presented. Maximum likelihood estimators are derived and demonstrated for the gamma distribution based on merged data records where the individual failure times have not been recorded. These results are important because the gamma distribution can model diverse time-to-failure behavior. This provides a particularly useful tool for data sets that may otherwise not be satisfactorily analyzed.     

A coatings and high temperature corrosion computerized database

Computer-aided structural analyses of high temperature coatings requires use of a computerized database covering the structural aspects of available coatings. A wide variety of corrosion-resistant coatings have been developed to deal with the lack of high temperature surface stability of metals and alloys used in hot components of energy conversion systems or turboengines. These coatings are applied by a number of different manufacturing processes. Each coating has been developed for specific conditions of temperature, corrosion, erosion, and wear.

Because of the multitude of coatings, application methods, and operating conditions, and the importance of their microstructure, the user must have easy access to all of the required data. The Coatings and High Temperature Corrosion Data Bank was created to collect background information on coating characteristics, high temperature corrosion behavior, service data, and field experience. This article describes the history, objectives, and software of the database with emphasis on the scope of the corrosion metadata, data collection, and evaluation.     

Organic photovoltaic films

Organic electronic materials are of interest for future applications in solar cells. Although results for single layer organic materials have been disappointing, high photocurrent quantum efficiencies can be achieved in composite systems including both electron donating and electron accepting components. Efficiencies of over 2% have now been reported in four different types of organic solar cell. Performance is limited by the low red absorption of organic materials, poor charge transport, and low stability. These problems are being tackled by the synthesis of new materials, the use of new material combinations, and optimisation of molecular design, self assembly and processing conditions to control morphology. Power conversion efficiencies of over 5% are within reach, but the fundamental physics of organic donor–acceptor solar cells remains poorly understood. Within the last 18 months, power conversion efficiencies of over 2% have been achieved in four different types of organic solar cells. All are composite systems including electron donating and electron accepting components. Performance is limited by weak absorption in the red, poor charge transport, and low stability, but improvements are available through optimisation of materials and device structures.     

Maßgeschneiderte Innenbeschichtung von Bauteilen mittels Puls Laser Deposition

As the requirements on technical systems are growing in terms of durability and efficiency, coating of the inner walls of highly charged parts becomes more and more important. Well known examples are the protection of combustion chambers or exhaust systems against heat and oxidation as well as wear protection of friction loaded parts like shock‐absorber tubes or casting moulds. The methods available for internal coating are often limited in the inner diameter of the systems to be coated and it has proven to be very difficult to deposit films homogeneously over a wide range. We present a method for coating of complex internal geometries with diameters down to several millimeters. The combination of classic Pulsed Laser Deposition (PLD) and laser evaporation enables synthesis of tailored film systems in terms of microstructure and distribution of single layer thickness. An example for the application of this method is given by means of the preparation of thermal barrier coatings in rocket combustion chambers.     

Optimum part deposition orientation for multiple objectives in SL and SLS prototyping

In the present work an attempt has been made to achieve minimum average part surface roughness (best overall surface quality), minimum build time and support structure for stereolithography (SL) and selective laser sintering (SLS) processed parts by determining optimum part deposition orientation. A conventional optimisation algorithm based on a trust region method (available with MATLAB-7 optimisation tool box) has been used to solve the multi-objective optimisation problem. It is observed that the problem is highly multi-modal in nature and a suitable initial guess, which is used as an input to execute the optimisation module, is important to achieve a global optimum. A simple methodology has been proposed to find out the initial guess so that global minimum is obtained. Finally the surface roughness simulation is carried out with optimum part deposition orientation to have an idea of surface roughness variation over the entire part's surface before depositing the part. Case studies are presented to demonstrate the capabilities of the developed system. The major achievements of this work are consideration of multiple objectives for the two rapid prototyping processes, successful use of conventional optimisation algorithm available with MATLAB to handle multiple objectives and development of graphical user interface-based system.     

Bilevel joint optimisation for product family architecting considering make-or-buy decisions

Product family architecting (PFA) aims at identification of common modules and selective modules to enable product family configuration for mass customisation. Due to nowadays manufacturers moving more towards assembly-to-order production throughout a distributed supply chain, the common practice of outsourcing of certain modules entails make-or-buy (MOB) decisions that must be taken into account in PFA. While the PFA and MOB decisions are enacted for different concerns of the manufacturer and the suppliers, it is important to deal with joint optimisation of the PFA and MOB problems. The prevailing decision models for joint optimisation are mainly originated from an ‘all-in-one’ approach that assumes both PFA and MOB decisions can be integrated into one single-level optimisation problem. Such an assumption neglects the complex trade-offs underlying two different decision-making problems and fails to reveal the inherent coupling of PFA and MOB decisions. This paper proposes to formulate joint optimisation of the PFA and MOB problems as a Stackelberg game, in which a bilevel decision mechanism model is deployed to reveal the inherent coupling and hierarchical relationships between PFA and MOB decisions. A nonlinear bilevel optimisation model is developed with the PFA problem acting as the leader and each MOB problem performing as a follower. A nested genetic algorithm is developed to solve the bilevel optimisation model. A case study of power transformer PFA subject to MOB considerations is presented to illustrate the feasibility and effectiveness of bilevel joint optimisation.     

Optimal traffic data archive scheme

An optimal traffic data archive scheme where the maximum information of the original data can be preserved using less storage space has been described. Compared with traditional equal-width methods where compact data are obtained by aggregating source data at fixed intervals, the optimal scheme uses varying intervals to aggregate data at different levels based on the variations within the source data. The resultant scheme is optimal in terms of information conservation, that is, the errors between the source data and the optimal compact data are the smallest. Operational traffic data have been used to test three proposed optimisation schemes: single-variable, multi-variable and heuristic schemes. It was found that, compared with traditional equal-width schemes, the size of the archived data can be reduced by six times if the single-variable optimisation scheme, or by three times if the multi-variable optimisation scheme is employed. The heuristic scheme using a combination of single-variable and multi-variable optimisations can then reduce storage space by three to six times     

Identification of complex sound sources produced by gear units

Noise source visualisation represents an important tool for technical acoustics. Many techniques of noise source visualisation have been developed, based on a specific noise source in a specific type of acoustic environment. A new visualisation method of complex noise sources is presented, using an acoustic camera and a new algorithm. Different transient acoustical phenomena can be noted. Additionally, a new family of biorthogonal wavelets is applied to determine fault in gears. The new wavelets are a generalisation of biorthogonal wavelet systems. Smoothness is controlled independently in the analysis. For the optimisation of the synthesis bank, discrete finite variation is used. Differentiability is measured, for which a large number of vanishing wavelet moments is necessary, in favour of a smoothness measure based on the fact that a finite depth of the filter bank tree is in most case related to practical applications.     

Microstructure of zirconia-yttria plasma-sprayed thermal barrier coatings

The objective of this paper is to report on the characterization of the highly complex microstructure of zirconia coatings, which arise as a result of the plasma-spraying process. The fine structure has been observed to change through the thickness of the coating, behaviour which has been related to the cooling rate and crystallization of the deposited material. Microstructural features such as an amorphous bond coat/ceramic interfacial film and a grain-boundary glassy phase, which are believed to have a significant effect upon coating properties such as adhesion and compliance, have been shown to be present.