TECHNICAL UNIVERSITY OF CLUJ NAPOCA FACULTY OF MACHINE BUILDING. Department for Fabrication Engineering. Eng. Bogdan MOCAN.

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1 TECHNICAL UNIVERSITY OF CLUJ NAPOCA FACULTY OF MACHINE BUILDING Department for Fabrication Engineering Eng. Bogdan MOCAN PhD THESIS Research and contributions on the oriented design and the performance improvement of the robotic arc welding Scientific coordinator Prof. Eng. Petru BERCE, PhD 2011

2 CONTENTS Introduction v Outlining the research area... vi Research interrogations and the research strategies... vi Thesis structure vii Research projects which sustain the thesis... ix Comments x List of figures... xi List of tables xv Definitions and abbreviations... xix List of scientific publications and research contracts... xxiii Part I The context and the state of the art in the field of robotic gas metal arc welding (MIG/MAG) 1. Aspects related robotic GMAW Introduction Aspects regarding the GMAW process Technological parameters of GMAW process Aspects regarding the robotic GMAW Planning trajectories and programming industrial robots implemented GMAW State of the art in robotic GMAW The most recent developments in the modelation and the control of the GMAW process aiming to increase the quality and the productivity of the process The most recent developments in the influence of the robots on the productivity and quality of the GMAW process Conclusions Defining the research area of the thesis Outlining the research field of the thesis The research objective Part II Theoretical contributions to the development of the oriented design and the improvement of robotic gas metal arc welding 4. Substantiating the methodology ROBOTIC-INN-WELD Creating the framework for the development of the methodology for the oriented design and the performance improvement of the robotic GMAW Most recent developments in the design process of assemblies using GMAW process Methodology for the oriented design and the improvement of robotic GMAW : Robotic-Inn- Weld The author s considerations on the Robotic-Inn-Weld methodology Articles published by the author of this thesis which sustain the claims in this chapter Considerations on the oriented design and performance improvement of the robotic GMAW Researches and contributions regarding oriented design and the development of robotic GMAW Identifying the needed capabilities of GMAW to weld a product in optimal conditions Planning the performance of robotic GMAW Conclusions drawn on the planning of the performance of robotic GMAW and solutions to potential conflicts using TRIZ

3 The process oriented design of the robotic GMAW Conclusions drawn on the process oriented design of robotic GMAW The process oriented design of the clamping devices used in robotic GMAW Conclusions on the process oriented design of the clamping devices used in robotic GMAW Designing and planning the GMAW process and preparing the product for welding Integrating the final robotic solution Planning and scheduling the trajectories of the robotic GMAW Implementing the robotic GMAW Conclusions Articles published by the author which sustain the claims of this chapter Part III Practical contributions to the oriented design and the improvement of the robotic GMAW 6. Contributions to the performance improvement of the robotic GMAW case studies Evaluating the welding needs and performing the welding tests of the KB product case study Increasing the robotic welding system performance in welding the head strut case study Designing a robotic welding system for assembling a car body case study Increasing the productivity level and the usability of the IRB1400 robotic GMAW system of the I-Valo industrial lamps case study Discussing the case studies Part IV Conclusions, compendium of the original contributions, the perspectives of this research in the field of robotic GMAW and bibliographical references 7. Conclusions, contributions and further research trends The initial context in substantiating the methodology Robotic-Inn-Weld Conclusions Compendium of original contributions Limitations Further research trends Bibliography

4 SUMMARY Introduction The GMAW currently represents a widespread welding procedure, which applies to several industrial fields. This is due to the advantages presented by this welding procedure (high productivity, high quality link, various opportunities for its mechanization or turning it robotic), high accessibility and easy to automatize/robotize. Traditionally, the studies dealing with the robotic gas metal arc welding (GMAW) focus on the correlations between the technological parameters, regarded as input values and the characteristics of the arc welding, represented by the output or quality parameters. Such approaches look at the final product in terms of the geometry of the welding bead and the mechanical properties of the welded joint only from the point of view of correlating the technological parameters of the welding regime without taking into account the system as a whole (for example, the robotic system, the clamping and fixing devices, planning the trajectory of the robot, designing the edges of the welded elements, etc.) on the final result. This is because it is difficult to understand the influence of the component parts on the quality and the productivity of the process and, at the same time, due to the complexity of the design of such a robotic welding system. With this PhD thesis, the author intended to create an original approach to the way in which robotic GMAW are designed and improved; the Robotic-Inn-Weld, which gravitates around the idea of systematically introducing INNOVATIONS in the solutions, the design and improvement process being directed towards the needs of the stakeholders and those of the process. Outlining the research field This thesis will analyze the design stages of a welded product as well as a robotic GMAW system so that the quality, the productivity and the usability of the robotic system are directed towards an optimal level. Practically, the research will take into account all interested parties and will highlight the functional requirements of the product, of the clamping devices and the robotic system. The novelty is in the way in which the instruments of analysis, planning, evaluation and innovation are used in designing and improving the performance of the robotic GMAW. The thesis will not provide details regarding the modelation of the MIG/MAG welding process, the mass transfer, and the geometric or thermal stability of the welding bead. Research interrogations and the research strategies In the context of what has been mentioned above, the main interrogation investigated by this thesis is the following:

5 Is it possible that, by means of a process oriented design of the GMAW robotic system, the desired level of productivity, quality and usability of those are reached? What are the conditions that have to be met in order for the productivity, quality and usability of these are maintained throughout their entire lifespan? Following the same line as the central interrogation, part of this research is fundamental and explicative, bringing knowledge elements in relation to principles associated to the science of robotic gas metal arc welding. Another part of the research is applicative and it is focused on the developing and validation of practical instruments used in the extended design, improvement and evaluation of the robotic welding. Starting from the central interrogation, the research endeavors have been centered on three major research interrogations: Q1. To what extent is the integrated design approach justified, as well as the improvement of robotic welding, in order for their increase in quality and productivity, setting aside aspects related to the modelation of the GMAW system and the choice of a robot which could satisfy the handling and precision needs of the process? Q2. To what extent, by means of an approach also using specific instruments for planning and innovating, we could reach a more mature solution much quicker in the case of the GMAW robotic which could satisfy the quality and productivity requirements? Q3. What are the main vectors which intervene in the design, improvement and implementation of GMAW and which maximize the quality of the welded products, the productivity and flexibility of such in connection to the ideal paradigms and the convergence of such with the technical ones? Using an integrated approach for the design, implementation and usage of robotic GMAW, small and medium size enterprises (SMEs) could gain a higher quality and productivity, thus gaining better profit. The structure of the thesis The specific scientific aspects in connection to the research of this thesis are structured in an introduction, six chapters of analysis and personal contributions, a glossary of terms, the list of scientific papers sustaining the claims of this thesis and a chapter with conclusions, further research and bibliographical references. The thesis is structured in four parts: Part I: The context and the actual stage of research in the field of robotic gas metal arc welding (MIG/MAG). This first part contains three chapters and presents a synthetic overview created by the author on the actual development stage of the robotic GMAW, with an emphasis on the influence of the introduction of robots in the welding process and the clear outlining of the research areas. Chapter 1: Starting from the definition of the gas metal arc welding process, this chapter describes its characteristics, emphasizing the influence of robotics on the productivity, quality and costs of the MIG/MAG welding procedures.

6 Chapter 2: This chapter performs a systematic analysis of the studies dealing with robotic GMAW. The researches in the field of gas metal arc welding, the constant improvement attempts and especially the introduction of robots in this field are performed in connection to the desire of the companies to increase their competitiveness and their aim to continuously cut the losses and to better meet the needs of their customers in a shorter amount of time. Chapter 3: In this chapter the author clearly outlines the research areas of the thesis and highlights the motivation behind this thesis, the global objective, the specific objectives and the interrogations that will be answered by this thesis. Part II: Theoretical contributions to the development of the oriented design and the improvement of robotic GMAW. The second part of the thesis contains the chapters which highlight the researches and contributions made in the development of design and evaluation methods of robotic gas metal arc welding. Chapter 4: This chapter developed the design and improvement methodologies of robotic gas metal arc welding so that they are better integrated and comprehended by the SMEs. Chapter 5: Taking into account the three objectives of the beneficiary, the scientific research comprised in this chapter brings contributions to the planning and current development of the four elements which are contained by the innovative design of the robotic welded : 1. the structured design of the MIG/MAG welding process; 2. process oriented design of the robotic system; 3. process oriented design of the fixture devices; 4. planning the trajectories of the movement of the robot and the design of the geometry of the joint edges. Part III: Practical contributions to the oriented design and improvement of robotic GMAW Chapter 6: Provides details of four case studies, which certify the relevance of the Robotic-Inn- Weld methodology. The case studies are developed for various products that, at the time of the implementation of the method, were meant to be robotic welded. Each of the analyzed had problems in what the quality and the productivity was concerned. Part IV: Conclusions, compendium of original contributions, further research in the field of robotic GMAW and bibliographical references. Chapter 7: The last part of the thesis contains a corollary of the results and conclusions drawn from the research performed in the thesis, as well as a list of bibliographical references, which substantiated the research. In addition, as a result of the research of this thesis, the last part of the thesis outlines a series of research topics which could be developed in the future. With respect to the bibliographical references, these contain 202 references, out of which 114 are recent (the past 5 years) and 83 are found in the main flux of publications. The compendium of original contributions The main advantages of the approach suggested by the thesis are the algorithm for the systematic determination of the functional capabilities of a gas metal arc welding, the

7 concurrent and structural development of the parts of the robotic welding system and the superior management of the information with the aid of planning and solving without compromising technical conflicts. The thesis brings a series of personal contributions, which can be structured on the following sets: PC 1 an original perspective on the design and improvement of robotic gas metal arc welding in order to increase its performance and to outline the research areas PC 2 constructing a theoretical foundation of a methodology for the design and/or improvement of the robotic gas metal arc welding PC 3 the testing and validation of the component steps of the Robotic-Inn-Weld methodology With reference to PC 1 - an original perspective on the design and improvement of MIG/MAG robotic gas metal arc welding in order to increase its performance and to outline the research areas, the original contributions are: PC 1.1 information regarding the current trends dealing with the increase of the quality and productivity of robotic welding collected both from the research community as well as from the professionals in the field PC 1.2 outlining the research area regarding the quality and the productivity of the robotic gas metal arc welding PC 1.3 identifying the performance parameters of the robotic gas metal arc welding which have a direct influence on the quality and the productivity of the process PC 1.4 the development of a new identification method of the optimal level of capability of a gas metal arc welding system PC 1.5 a totally new approach in the way manual and robotic welding are classified, based on the system capacity to produce high quality welds at an imposed productivity level PC 1.6 information related to the current approaches regarding the design in the welding technology PC 1.7 information regarding the innovative approach in the design of robotic welding PC 1.8 information related to various approaches regarding the design of the fixture devices PC 1.9 information regarding the planning and evaluation of the trajectories followed by the industrial robots PC 1.10 information related to various programming methods of industrial robots With reference to PC 2 - constructing a theoretical foundation of a methodology for the design and/or improvement of the robotic gas metal arc welding, the original contributions are: PC 2.1 the substantiation of a workflow for the current development of robotic gas

8 metal arc welding PC 2.2 the systematization of the concepts integrated in the Robotic-Inn-Weld methodology PC 2.3 identifying the requirements related to the planning of the performance (from a point of view of the quality and productivity) of the robotic gas metal arc welding PC 2.4 the identification of the key performance characteristics of the MIG/MAG welding system PC 2.5 the identification of the key performance characteristics of the robotic welding system PC 2.6 the identification of key design factors of the fixture devices used in robotic welding PC 2.7 the identification of the critical elements in planning the trajectories followed by the robot PC 2.8 formulating four sets of technical conflicts (set 1 - planning the quality of the MIG/MAG welding process [5 conflicts]; set 2 planning the quality of the cell of the robotic weld [5 conflicts]; set 3 planning the quality of the clamping and fixing devices [6 conflicts]; set 4 planning the quality of the trajectory of the robots and the geometry of the edges of the joint [3 conflicts]) which have to be solved by the suggested methodology PC 2.9 generalizing the design logic of the four parts of the robotic welding system and the correlation of the interdependencies between the intermediary stages PC 2.10 the generation of 28 innovative directions for solving the technical conflicts occurring during the design and the development of the robotic gas metal arc welding PC 2.11 the integration and interlinking the design methods of the parts of the Robotic- Inn-Weld methodology PC 2.12 the development of a function which evaluates the performance level of the solution found, from the perspective of the information availability, of the maturity of the solution and their functional aspects With regards to PC3 the testing and validation of the component steps of the Robotic-Inn-Weld methodology, the original contributions are: PC 3.1 the validation of the MICSS instrument by means of four case studies presenting various complexity and capability levels PC 3.2 the validation of the identification activities of the critical aspects when designing the robotic gas metal arc welding from the point of view of reaching a certain imposed quality and productivity level PC 3.3 the validation of the innovative directions of solving technical conflicts occurred during the design and development of the MIG/MAG robotic gas metal arc welding by analyzing four case studies

9 PC 3.4 the validation of the design stages of the robotic system, of the fixture devices, of the planning of the trajectory of the robots and of the design of the welding technology PC 3.5 the validation of the Robotic-Inn-Weld methodology on four case studies from the perspective of the versatility and adaptability to any technical field and any level of complexity of the solution The three sets sum up a total of 27 original contributions offered by this thesis in the field of robotic arc welding. These contributions have already been published in 11 articles in reviews (of which 6 are B+ category and 5 SCOPUS indexed) and 16 articles presented at international conferences (one SCOPUS indexed, 2 ISI Web of Knowledge indexed and IEEE Xplore and one at a very prestigious conference CIRP - LCE). Conclusions The general conclusion of the thesis is that oriented and integrated design of a robotic welding system is a key factor in reaching the desired performance level (quality and productivity). Thus, the design of a robotic arc welding system must be dealt with from a holistic perspective, which takes into account all the four basic characteristics of the robotic welding system (the MIG/MAG arc welding process, the robotic system, the fixture devices and the planning of the trajectory of the robots).