Doctoral theses

Due to their diverse properties and versatile aesthetics, natural stones are used as construction materials, i.e. for floor coverings, stair steps and as facade cladding. The production of slabs and tiles made of natural stone is mainly performed with rotating diamond cutting discs. In the production of slabs and tiles the cutting rate is more than 60%, leading to a loss of raw material as well as high energy consumption, and tool costs. By using thin cutting discs the width of the cutting kerf can be reduced and the efficiency of the abrasive cutting process can be increased. However, the reduced stiffness of the thin cutting disc may lead to higher tool deflection and reduced cut quality. The objective of this work is to investigate a closed loop control for an abrasive cutting process using thin cutting discs. The used diamond cutting disc is 40% thinner than normally used tools in the industry. For the implementation of a closed loop control a monitoring system is being developed. It allows monitoring the axial tool vibrations throughout the grinding process. Integrating piezoelectric elements in the grinding tool, the vibrations can be detected directly at their source. This ensures a high accuracy of the detecting process. Based on studies, a closed loop cut-off control is being developed and studied. The closed loop control varies the feed rate depending on the axial tool vibrations. Through the developed closed loop control further information on the vibration characteristics of a cutting disc during a process are obtained. Furthermore, approaches to increase the cutting quality of thin cutting discs by a closed loop control are presented.

cut-off grinding, natural stone, process monitoring, process control

Disruptions in productions with negative impact on the objectives of production logistics need to be indentified and resolved. Enterprises often lack of sufficient qualified employee who know how to control the controllable logistic relations in production and thus to realize a targeted improvement of a logistic process. Moreover, a profound knowledge about the compley relations between logistic objectives and measures against interferences in production is often missing. An approach for a model-based diagnose of disruptions in production logistics will be developed in this thesis. It will be exemplified how to implement the approach in an assistance system. Staff will get assistance in detection of deviations, finding causes and deriving reommendations for measures.

production logistics, diagnostics, assistance system, model based rules, web of causes and effects

The performance of humans is subject to fluctuations throughout the day. As criticism of a method developed by Graf power curve is an example the lack of differentiation of people according to biorhythms (morning and evening type) call. In addition, the study looked no spiritual component. An analysis of circadian fluctuations in performance of the people in industrial assembly has not yet explicitly examined. With the present study this gap is closed. On the basis of an appropriate industrial work system performance circadian variations in manual assembly activities depending on different factors (e.g. "Sex", "Age", "biorhythm") are initially recorded and analyzed. The relationship between power fluctuations and the factors determined is statistically backed up by data analytical methods. Finally, are areas of application (e.g. As shift work, timing adjustment) recognized for harnessing the proven power fluctuations and demonstrated potential to account.

performance efficiency fluctuation, assembly, industrial work system, data analysis method

Companies in which the typical tool cycle is used for their production tools and be found with reclamation and reuse are, seek to reduce the average delay deployment of ready tools. To improve the availability of production the number of tools in the circuit or the tool life of the tools can be increased. However, this in turn leads to higher cost. Thus, the achievement of an objective goes to the expense of another. The central part of the work presents the modeling of a typical tool cycle is in a simulation model. Thus, the basic relationship between the indicators and default provisioning tool inventory and their controllability by organizational and technological measures within the framework of simulation studies have shown.

tool allocation delay, tool logistics, tool stock, tool supply, material flow simulation

Sheet metal parts for fastening often require pin-shaped joining elements. In case of high requirements on the tightness or the electrical contact arc stud welding processes are favored. Arc stud welding processes up to now are executed on separate welding stations. For it handling operations and storage of parts are necessary. To shorten the process chain solutions for integrating the arc stud welding in sheet metal working tools are required. In this thesis a solution for capacitor discharge (CD) arc stud welding with tip ignition in sheet metal working tools is presented. The developed welding module is automated in a tool using a metal strip conveyor system. In experiments the attainable joining quality, the interaction between tool and welding process and the process stability by automatic line operation are analyzed. On the basis of practice-orientated disturbances the robustness of the integrated welding process is examined.

sheet metal, capacitor discharge arc stud welding, cd arc stud welding, tip ignition, follow-on tool

Producing companies have to face an increasing number of phase-outs due to shortening product life cycles. Phase-outs show a high potential of cost saving in terms of avoiding remaining inventory after the phase-out. Although this potential is well known an efficient management of phase-outs does not take place. Methods, models or key performance indicators for an efficient phase-out management do not exist. An additional challenge is the collaboration of various companies to produce a defined product. The coordination and collaboration of these companies additionally exacerbate the efficient conduction of a phase-out. This work presents a methodical support for a phase-out management in production networks.

production planning, supply chain management, phase-out management

The flexible customisation of production and logistic processes is an increasing challenge for companies in order to save their entrepreneurial success. This entails requirements concerning production control, which have to be contemplated and interpreted holistocally not at last due to an increasing importance of assembly for the overall manufacturing and assembling processes. The cost effective and timely supply of the assembly with in-house and an increasing amount of external material hasn´t been explored much to date from a scientific point of view. This logistic challenge can be supported by a concept of an assembly synchronous job control. The synchronisation approach focuses on the compensation of assembly disturbances as well as on the enhancement of flexibility in workflow changes. On the basis of an holistic approach of synchronisation between the manufacture of parts and assembly (horizontal synchronisation) the developed concept of a forward-looking prevention of missing parts and an holistic, assembly oriented synchronisation of material supply processes for assembly (vertical synchronisation) wll be expanded by aiming at on-time-delivery improvements of partner orders.

production logistics, production management, production control, assembly, synchronisation

In the dissertation the basics of capacity related external processing will be described. Different approaches to selecting the amount of production to be moved to external production will be analyzed. Additionally approaches to the evaluation of external processing scenarios are discussed. The different approaches will then be checked according to the requirements for viable solutions. The objective of this dissertation is the development of a methodology for triggering a capacity related external processing between press shops. The structure of the methodology will be explained by describing its single steps and the analyzed elements of the production process. Furthermore, the procedures and applications of the steps will be delineated. The functionality and the practicability of the methodology will be shown within a realistic cooperation scenario.

press shop, sheet metal part production, capacity related external processing, cooperation

This paper elaborates the open scientific question with practical relevance to producing enterprises at which service level an article of a production warehouse should be provided to production. The objective of this paper is to develop a decision supporting logistic model calculating the service level of an article which should be achieved when considering the follow-up costs of a stockout situation (stockout costs) on the one hand and the costs of the logistic organization on the other hand (i. e. warehousing). The new logistic model’s elaborative work is based on known stock out cost types (i. e. by REICHMANN) as well as on the characteristic curves for the service level and the delivery delay developed by WIENDAHL and NYHUIS.

characteristic curves, delivery delay, logistic costs, production, service level, stock, stockout co

Considerably, flashless precision forging offers the potential for material saving. To secure form filling, in conventional forging in open dies, e. g. of crankshafts, a surplus of mass of about 50 percent is used. Compared to conventional forging with flash, the economical potential of flashless precision forging is based on smaller tolerance classes and the shortening of the process chain. The newly developed forging sequence of a two cylinder crankshaft for flashless precision forging consists of four stages. The pre-forming takes place in two lateral extrusion processes, with an innovative multi-directional forging tool being used. The final flashless precision forging produces the final geometrie of the crankshaft. To achive the required tolerances of IT 7 to IT 9, a newly developed method for the compensation of the shrinkage behaviour is implemented. This method uses not only a homogeneous gauge but considers the inhomogeneous tension and temperature profiles in the forged parts.

flashless precision forging, crankshaft, shrinkage compensation, FEA

Defects like folds can arise using forging for the production of long flat pieces made of aluminium. A special defect is the formation of inner folds. These can be seen in the grain flow. Inner folds have a negative effect on the dynamic properties of the forged part. As a production process, forging can be divided into single-directional and multi-directional forging. The formation of inner folds was observed at the single-directional forging. By using the multi-directional forging, a forming operation working from different directions, the forming can be set variably. Thus the development of folds can be prevented. A newly developed method can help in the selection of the forming process and in determining an appropriate tool geometry. Here especially the area is adapted, where the development of inner folds occur. Therefore a calculation model was developed. It integrates a computer-aided identification of the inner folds. Using this model, a correction of the parametrically constructed forging tool is possible.

multidirectional-forging, long flat pieces, aluminium, fibre orientation

Cyclically interlinked production systems are commonly used production facilities. In the bidding phase manufacturers of these systems define their capability and operating efficiency to the customers despite of numerous insecurities. Up to now, no planning approach exists to assure these planning results. On this account a method to choose a configuration of these systems in the bidding phase was developed and is presented in this paper. Data mining models are built to predict performance figures of production systems. To predict the operating efficiency of a system configuration, characteristic curves are used. On this basis the planner decides, whether an offer is generated or the system configuration is changed. This paper shows that the newly developed method is suitable to assess configurations of cyclically interlinked production systems in terms of performance and cost effectiveness. It allows the identification of better configurations in respect of the objective criteria. Furthermore, the presentation and discussion of test results in terms of quality and the limitations of the method are discussed. The method is validated on the basis of two practical examples.

interlinked production systems, planning, characteristic curves, data mining

Customer demands for innovative and individual products force manufacturers to push and to accelerate their innovation activities. This leads to a higher variety of products with shorter product life cycles and, consequently, to a more frequent production ramp-up: the stage between development and serial production. The significant commercial relevance of this stage of the product life cycle has been proven several times. However, a considerable number of production ramp-ups are still missing the technical and the economical targets. The reasons for that are manifold. One aspect, which hasn’t been sufficiently considered so far, is the high number of involved parties. This is due to a previous outsourcing of various development and production tasks as well as to the global distribution of plants. Therefore, today’s production ramp-up projects affect the supply chain substantially. Within this thesis, the acting parties, the main tasks and the instruments of a crosscompany production ramp-up are presented. Furthermore, previous attempts at planning and execution of ramp-up projects as well as their priorities and deficits are shown. The analysis of an empirical study helps to identify the relevant success factors of the cross-company production ramp-up and leads to the concept of an internet based ramp-up platform. As an integrated part of it, the regression analysis enables the estimation of a risk of a delay – at an early stage of the production ramp-up. Thus, the experience of accomplished production ramp-up projects can be used as a guideline for forthcoming ones. Additionally, a set of rules which allow a simple and effective monitoring of the production ramp-up along the supply chain is created.

production ramp-up, supply chain, time scheduling, project monitoring, risk management, regression a

Production processes of the forging industry are defined by a multitude of factors. While in the past, technological product quality has been the major goal of improvement efforts, to an increasing degree it is sided with a high logistical performance. However, in the utilisation planning of heaters, a sub-process of heat treatment, there still is often only a markedly insufficient technological-logistical process quality achieved. Relevant problems in this context are – amongst others – the changing of order sequences, the multitude of technological restrictions and the deficient knowledge about technological and logistical interdependencies. For a well-balanced positioning between the compliance with technological restrictions and logistical aims, a method for an automated selection and combination of the evaluated orders into charges and utilization programs is needed. Within this book, such a solution concept for supporting the utilisation planning of heat treatment systems is described. The developed methods of order selection, charge combination and heaters assignment, which are based on the fuzzy-logic, represent the interdependencies between technical and logistical objectives of the utilisation planning, choose suitable orders for the heat treatment, support the combination of charges and assignment programs and offer the saving of specific planning knowledge.

forging industry, heaters utilisation planning, fuzzy-logic, order selection, charge combination

In the context of increasing economic networking more and more companies shift production volumes to foreign locations. However, high return displacement rates show that many companies fail here. The design of the product has a causal influence on the production and therefore on the success of this internationalization. In the present work a method to design internationalization driven product structures will be described. Aims are low product complexity and a customized distribution of know-how. To implement these aims design guidelines are defined, which are assessable using a performance measurement system. An integrated product model and a catalog of options for action assist in the analysis and design. This product structures can be created in an iterative process, which form a basis for successful internationalization.

product structuring, product design, product model, globalization, internationalization

Warm forming of steel is for a limited range of work piece geometries an economic and ecologic alternative to the conventional hot and cold forging technology. Up to now warm forming is predominantly common for rotation symmetric parts. Within the scope of this paper a process chain for closed-die warm forming of long flat pieces has been derived and investigated on the basis of the forming stages of a steering link. The experiments have been performed on a conventional hot forging press. Only a graphite coating machine has been used additionally. It has been verified that long flat pieces made of steel can be warm forged using a preforming operation by bending or drawing out in the die. A material utilisation of 80 % and IT-tolerances lower than IT 12 for width and length have been achieved. Based on FE-simulations it has been shown that, using two preforming operations by bending or drawing out in the die, preforms with a straight, in one plane bent and in two planes bent longitudinal axis can be produced.

bulk metal forming, warm forming, long parts

Various companies implement lean production systems to realize hidden technological and economical potentials. Due to the extensive and long-lasting acquisition of production system knowledge, the implementation of an individualized production system requires comprehensive human and financial resources. In contrary to huge enterprises, respective means are not at the disposal of small and medium sized companies e. g. of the die and mold making industry. This article presents an innovative approach to formalize production system knowledge in an expert system. The system is designed to fit the needs of the die and mold making industry and consists of an ontology for knowledge representation as well as an industry-sector-specific knowledge base. Furthermore, rules for automated knowledge base adaptation are derived using data mining algorithms. Case studies show that the expert system is applicable for systematic and company specific lean-method identification and implementation.

production system, lean production, expert system, knowledge management, data mining

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