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See detailPre and post-treatments to improve weldability and mechanical properties of Aluminum-Polyamide laser welded specimens
Amne Elahi, Mahdi UL; Koch, Marcus; Heck, Mike et al

in Procedia CIRP (2020), 94

The laser polishing surface treatment is a prerequisite for enhanced weldability that is enabled by superior adhesion between the weldments. The paper describes the laser polishing process of the aluminum ... [more ▼]

The laser polishing surface treatment is a prerequisite for enhanced weldability that is enabled by superior adhesion between the weldments. The paper describes the laser polishing process of the aluminum surface to develop a relatively thick and porous artificial aluminum oxide layer. Microscopic observation shows the laser polishing process significantly improves the adhesion of molten polyamide to the aluminum surface. Besides, the shear load of the pretreated joints is much higher than that of as-received ones. However, for the majority of the welded samples, the failure happens at the polyamide near the interface of aluminum/polyamide due to the thermal effect and structural changes of polyamide during the welding process. By applying the post-treatment of the welded specimens with different cycles, the mentioned failure mechanism is not observed anymore. Therefore, the mechanical properties of the joint will be improved and reach to the limits of the base materials. [less ▲]

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See detailDigitizing of Research and Teaching
Plapper, Peter UL

Scientific Conference (2020, September 05)

The current Covid-19 crisis impacts all manufacturing areas and new processes are sought. This presentation provides the audience with three examples related to assembly work instructions, logistics data ... [more ▼]

The current Covid-19 crisis impacts all manufacturing areas and new processes are sought. This presentation provides the audience with three examples related to assembly work instructions, logistics data handling and manufacturing education, for which innovative ways to obtain access to context sensitive data based on digital tools are investigated. Augmented Reality (AR) and Virtual Reality (VR) facilitate access to relevant manufacturing information. In order to provide logistic warehouse workers with immediate access to shipping documents, to avoid paper print-outs, and to eliminate error-prone typing of information, critical information should be handled digitally and hands-free. To support logistic workers to efficiently document, register and trace receipt, storage or delivery of goods, the presented solution is built on hands-free digital tools with AR technology in commercially available smart glasses. Similarly, workers who execute complex assembly operations frequently require either assistance or support for the next assembly step. Depending on the context, relevant assembly process information is automatically displayed together with the environment in the AR smart glass. Thus, the operator is supported by the presented hands-free-tool to complete the next challenging tasks. Currently, teaching is being transferred from physical class-room teaching to remote or hybrid education. For this purpose, Virtual Reality (VR) provides a very welcome opportunity to complement in-presence teaching with exposure to examples of real manufacturing operations captured in videos of industrial case studies. Students apply learnings from theoretical classes to manufacturing case studies by identifying best practices and also recognizing waste. The presentation shares experience in teaching of lean methods based on AR technology to graduate engineering students. [less ▲]

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See detailHighlighting chemical bonding between nylon-6.6 and the native oxide from an aluminum sheet assembled by laser welding
Hirchenhahn,, Pierre; Alsayyad, Adham Ayman Amin UL; Bardon, Julien et al

in ACS Applied Polymer Materials (2020)

Polymer/metal hybrid assemblies are well suited for automotive and biomedical applications because of their ability to create lightweight structures with a wide range of design possibilities. Laser ... [more ▼]

Polymer/metal hybrid assemblies are well suited for automotive and biomedical applications because of their ability to create lightweight structures with a wide range of design possibilities. Laser welding is a promising technique for joining dissimilar materials thanks to its quickness, freedom of design and absence of adhesives. Still, the fundamental causes of adhesion in hybrid laser welding remain not well understood. Therefore the present work aims at highlighting a chemical bonding between a polymer, nylon-6.6 and a metal, aluminum. To access the interface information, the samples were first broken, leaving a residue on the surface, which was dissolved afterwards. The chemical reactive sites of nylon molecule able to react with aluminum surface were suggested and the feasibility of these reactions was analyzed in the light of the results obtained by means of X-ray photoelectron spectroscopy (XPS) and Time of flight secondary electron microscopy (ToF-SIMS). [less ▲]

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See detailAgent-based, hybrid control architecture for optimized and flexible production scheduling and control in remanufacturing
Groß, Sebastian UL; Gerke, Wolfgang; Plapper, Peter UL

in Journal of Remanufacturing (2020), (2020),

Introduction: Motivated by high ecological and economical potentials and driven by new laws, remanufacturing is receiving increasing attention as a process that puts used products into “as good as new or ... [more ▼]

Introduction: Motivated by high ecological and economical potentials and driven by new laws, remanufacturing is receiving increasing attention as a process that puts used products into “as good as new or better” condition. Within this process, there are many challenges, which are unseen in manufacturing, such as the uncertainties resulting from unknown conditions of the used products. This places special demands on the control of the remanufacturing system (RS). Methodology: To handle these uncertainties an agent-based hybrid control architecture comprising centralized and decentralized components is presented. In the former, the scheduling takes place including the consideration of the use of automated guided vehicles (AGV) to realize flexible material handling within the RS. The scheduling of machines and AGVs is thereby considered simultaneously and not separately, as it is the case in currently available control systems. For the optimization of the simultaneous scheduling Constraint Programming (CP) is used. In the decentralized component, all participants within the RS will be networked as a cyber-physical system and controlled by respective agents. These agents can communicate with each other in order to find solutions. The architecture is implemented as a multi-agent system. Results: Simulation results, using benchmark instances, show that simultaneous scheduling results in a 19.7% reduction of the makespan. Furthermore, the CP-based approach delivers the best results, compared to other approaches for simultaneous scheduling, which are also achieved in a significantly shorter computing time. [less ▲]

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See detailAgentenbasierte, hybride Steuerungsarchitektur für cyberphysische Refabrikationssysteme
Groß, Sebastian UL; Gerke, Wolfgang; Plapper, Peter UL

in Jäkel, Jens; Thiel, Robert (Eds.) Tagungsband AALE 2020 Automatisierung und Mensch-Technik-Interaktion (2020, March 05)

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See detailMensch-Roboter-Kollaboration in der Domäne Refabrikation – State-of-the-Art und Ausblick
Groß, Sebastian UL; Gerke, Wolfgang; Plapper, Peter UL

in Jäkel, Jens; Thiel, Robert (Eds.) Tagungsband AALE 2020 Automatisierung und Mensch-Technik-Interaktion (2020, March 05)

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See detailUNTERSUCHUNG DER METALLURGISCHEN PHASENBILDUNG UND DEREN EINFLUSS AUF DIE VERBINDUNGSEIGENSCHAFTEN SOWIE AUF DIE VERSAGENSURSACHEN VON LASERGESCHWEIßTEN HARTMETALL-STAHL-VERBUNDEN
Schiry, Marc UL

Doctoral thesis (2020)

Laser beam welding of hard metal to steel offers multiple advantages regarding resource saving, mechanical strength of the joint and automation capability. The present work focuses on the fundamental ... [more ▼]

Laser beam welding of hard metal to steel offers multiple advantages regarding resource saving, mechanical strength of the joint and automation capability. The present work focuses on the fundamental research and development of the laser based welding process of tungsten carbide-cobalt hard metals with a tempering steel. Metallurgical analysis of the welding process showed that the formation of intermetallic and/or intermediate phases has a significant influence on the properties and mechanical strength of the dissimilar joint. The amount of molten hard metal in the steel melt bath plays a key role for the formation of the different phases. Therefore, a new parameter dy was defined, which correlates with the hard metal content in the melt pool. It is shown that for hard metals with 12 wt.% of cobalt binder, the phase transformation in the weld seam starts with a relative hard metal content of 10 vol.%. This threshold is dependent on the relative cobalt concentration in the hard metal. The tungsten carbide grain size has a low influence on the phase transformation in the weld seam. Steel melt pools with hard metal content lower than 10 vol.% show under metallographic observation a martensitic/bainitic microstructure. Simulation of the stress formation in the joint showed that due to the volume expansion of martensite during the transformation, tensile stress in the hard metal part was formed. Under shear load, these tensile stresses compensate with the induced compressive stresses and results an almost stress free interface. High shear strengths of the dissimilar joints are possible. A higher percentage of hard metal melting during the welding process increases the carbon and tungsten content in the melt bath. Consequently, the martensite start temperature decreases significantly. When the initiating temperature for martensite transformation falls under room temperature, the weld seam transforms into an austenitic microstructure. Because of the missing volume expansion during cooling of the weld seam volume, low stresses in the hard metal are generated. Under shear load of the joint area, high tensile stresses appear in the sintered part. These stress concentration decreases the shear strength of the weld and lead to premature failure. For the industrial use case, high mechanical strength and a robust manufacturing process is needed. Therefore, the laser welding process of hard metal to steel was optimized. The joint properties strongly depend on the weld bead geometry. Weld seams with x- or v-shaped profiles enable local concentrated metallurgical bonding of the sintered part to the steel sheet. Reduction of the horizontal focal distance of the laser beam to the interface increases the bonding ratio, but also intensifies the melting of the hard metal part and lead to the metallurgical transformation. By tilting a v-shape weld seam, it was possible to optimize the bonding behavior and to minimize the amount of liquefied hard metal in the melt bath. Hard metal with low amounts of binder showed a high temperature sensitivity. After laser welding of these grades, hot cracks were found in the sinter material. These cracks were formed due to the high stresses, which are generate during cooling of the dissimilar joint. Therefore, a laser based heat treatment process was developed and applied. With a defined pre- and post-heating of the joint area, the cooling rate was reduced significantly and the stresses in the hard metal part minimized. High shear strengths were the result. [less ▲]

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See detailNew opportunities by laser joining of dissimilar materials
Plapper, Peter UL

Scientific Conference (2020, February 13)

The presentation gives an overview about research projects at UL related to laser welding of dissimilar materials. Literature reference at the end enables the reader to dig deeper in case some specific ... [more ▼]

The presentation gives an overview about research projects at UL related to laser welding of dissimilar materials. Literature reference at the end enables the reader to dig deeper in case some specific projects are of interest. [less ▲]

Detailed reference viewed: 112 (5 UL)
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See detailRobotix-Academy Conference for Industrial Robotics (RACIR) 2019
Müller, Rainer; Plapper, Peter UL; Brüls, Olivier et al

Book published by Shaker - 3 (2020)

Robotix-Academy Conference for Industrial Robotics (RACIR) is held in University of Liège, Belgium, during June 05, 2019. The topics concerned by RACIR are: robot design, robot kinematics/dynamics/control ... [more ▼]

Robotix-Academy Conference for Industrial Robotics (RACIR) is held in University of Liège, Belgium, during June 05, 2019. The topics concerned by RACIR are: robot design, robot kinematics/dynamics/control, system integration, sensor/ actuator networks, distributed and cloud robotics, bio-inspired systems, service robots, robotics in automation, biomedical applications, autonomous vehicles (land, sea and air), robot perception, manipulation with multi-finger hands, micro/nano systems, sensor information, robot vision, multimodal interface and human-robot interaction. [less ▲]

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See detailLaser joining of titanium alloy to polyamide: influence of process parameters on the joint strength and quality
Alsayyad, Adham Ayman Amin UL; Lama, Prashant; Bardon, Julien et al

in International Journal of Advanced Manufacturing Technology (2020)

Laser-assisted metal–polymer joining (LAMP) is a novel assembly process for the development ofminiaturized joints in hybrid lightweight products. This work adopts a design of experiments (DoE) approach to ... [more ▼]

Laser-assisted metal–polymer joining (LAMP) is a novel assembly process for the development ofminiaturized joints in hybrid lightweight products. This work adopts a design of experiments (DoE) approach to investigate the influence of several laser welding parameters on the strength and quality of titanium alloy (Ti-6Al-4V)–polyamide (PA6.6) assembly. Significant param- eters were highlighted using the Plackett Burmann design, and process window was outlined using the Response Surface Method (RSM). A statistically reliable mathematical model was generated to describe the relation between highlighted welding param- eters and joint strength. The analysis ofvariance (ANOVA) method was implemented to identify significant parametric interac- tions. Results show the prominence offocal position and laser power, as well as significant interaction between laser power and beam speed, on the joint strength. The evolution ofweld defects (bubbles, excessive penetration, flashing, titaniumcoloring, weld pool cavities, and welding-induced deflection) along the process windowwas investigated using optical microscopy. The resulted deflection in titaniumwas quantified, and its relationship with welding parameters was mathematically modeled. Robust process window was outlined to maintain insignificant deflection in the welded joints. Results showed that the growth ofweld defects correlates with a decline in joint strength. Optimal parameters demonstrated a defect-free joint, maximizing joint strength. [less ▲]

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See detailCreation of an ISO Standard at the Example of Value Stream Management Method
Plapper, Peter UL; Mangers, ; Minoufekr, Meysam UL et al

in Jakobs, Kai (Ed.) Shaping the Future Through Standardization (2020)

The main objectives of this chapter are to elucidate the necessity of a standardized Value Stream Management (VSM) and to clarify how this standard can effectively increase corporate performance within ... [more ▼]

The main objectives of this chapter are to elucidate the necessity of a standardized Value Stream Management (VSM) and to clarify how this standard can effectively increase corporate performance within cross-enterprise supply chain networks (SCNs). VSM is an effective tool to collect, evaluate and continuously improve product and information flows within companies in a common and standardized manner. The findings of this chapter are not only valid for consistent product and information flows, but are representative for the relevance of standards in general. In a globalized economy, standards need to be generally accepted and valid for all countries. Thus, corporate or national standards, only have limited impact. The International Standardization Organization (ISO) provides the means to develop, negotiate and communicate standards, which are globally binding. This chapter shares the experience of ISO 22468 standard development within ISO/TC 154 WG7 and proves its applicability by an administrative use case. [less ▲]

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See detailInfluence of Aluminum Laser Ablation on Interfacial Thermal Transfer and Joint Quality of Laser Welded Aluminum–Polyamide Assemblies
Al Sayyad, Adham UL; Bardon, Julien; Hirchenhahn, Pierre et al

in Coatings (2019), 9(11),

Laser assisted metal–polymer joining (LAMP) is a novel assembly process for the development of hybrid lightweight products with customized properties. It was already demonstrated that laser ablation of ... [more ▼]

Laser assisted metal–polymer joining (LAMP) is a novel assembly process for the development of hybrid lightweight products with customized properties. It was already demonstrated that laser ablation of aluminum alloy Al1050 (Al) prior to joining with polyamide 6.6 (PA) has significant influence on the joint quality, manifested in the joint area. However, profound understanding of the factors affecting the joint quality was missing. This work investigates the effects of laser ablation on the surface properties of Al, discusses their corresponding impact on the interfacial thermal transfer between the joining partners, and evaluates their effects on the joint quality. Samples ablated with different parameters, resulting in a range from low- to high-quality joints, were selected, and their surface properties were analyzed by using 2D profilometry, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and energy-dispersive X-ray spectroscopy (EDX). In order to analyze the effects of laser ablation parameters on the interfacial thermal transfer between metal and polymer, a model two-layered system was analyzed, using laser flash analysis (LFA), and the thermal contact resistance (TCR) was quantified. Results indicate a strong influence of laser-ablation parameters on the surface structural and morphological properties, influencing the thermal transfer during the laser welding process, thus affecting the joint quality and its resistance to shear load. [less ▲]

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See detailOptimized and flexible scheduling of AGVs and process machines in Re- manufacturing 4 .0 Systems using multi-agent technology and simultaneous scheduling
Groß, Sebastian UL; Gerke, Wolfgang; Plapper, Peter UL

in Ramírez Fernández, Francisco Javier; Honrubia Escribano, Andrés (Eds.) Abstracts III International Workshop on Autonomous Remanufacturing 2019 (2019, October 02)

In remanufacturing processes the condition of the used products is unknown. This leads to many challenges which are special to the domain of remanufacturing and not known from manufacturing. One of these ... [more ▼]

In remanufacturing processes the condition of the used products is unknown. This leads to many challenges which are special to the domain of remanufacturing and not known from manufacturing. One of these challenges is the stochastic routing of products based on the unknown product conditions. This problem in particular requires a flexible scheduling and control system for the remanufacturing system as well as the intralogistics. The aim of this research is to optimize the scheduling and control of remanufacturing systems considering the flexible material transport by AGVs. Therefore the networking of all resources is organized as an embedded system treating the remanufacturing system as a cyber-physical system in the context of industry 4.0. The scheduling and control of the remanufacturing system will be achieved by a combination of multi-agent technology to deal with unexpected events and the optimization of the schedule by simultaneous scheduling of machines and AGVs. Machine scheduling and transport scheduling have been vastly studied by many researchers, but most of the works address both problems separately. However, these two problems are closely linked and influence each other. By looking at them together, it is possible to achieve an improvement in the overall schedule. In the first step of the research work, the simultaneous scheduling of machines and AGVs has been compared with the currently used sequential scheduling within a simulation study. For this purpose, benchmark instances known in the literature were used. The simulation results show the superiority of the simultaneous scheduling of machines and AGVs. [less ▲]

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See detailRobotic Trajectory Tracking: Position- and Force-Control
Klecker, Sophie UL

Doctoral thesis (2019)

This thesis employs a bottom-up approach to develop robust and adaptive learning algorithms for trajectory tracking: position and torque control. In a first phase, the focus is put on the following of a ... [more ▼]

This thesis employs a bottom-up approach to develop robust and adaptive learning algorithms for trajectory tracking: position and torque control. In a first phase, the focus is put on the following of a freeform surface in a discontinuous manner. Next to resulting switching constraints, disturbances and uncertainties, the case of unknown robot models is addressed. In a second phase, once contact has been established between surface and end effector and the freeform path is followed, a desired force is applied. In order to react to changing circumstances, the manipulator needs to show the features of an intelligent agent, i.e. it needs to learn and adapt its behaviour based on a combination of a constant interaction with its environment and preprogramed goals or preferences. The robotic manipulator mimics the human behaviour based on bio-inspired algorithms. In this way it is taken advantage of the know-how and experience of human operators as their knowledge is translated in robot skills. A selection of promising concepts is explored, developed and combined to extend the application areas of robotic manipulators from monotonous, basic tasks in stiff environments to complex constrained processes. Conventional concepts (Sliding Mode Control, PID) are combined with bio-inspired learning (BELBIC, reinforcement based learning) for robust and adaptive control. Independence of robot parameters is guaranteed through approximated robot functions using a Neural Network with online update laws and model-free algorithms. The performance of the concepts is evaluated through simulations and experiments. In complex freeform trajectory tracking applications, excellent absolute mean position errors (<0.3 rad) are achieved. Position and torque control are combined in a parallel concept with minimized absolute mean torque errors (<0.1 Nm). [less ▲]

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See detailLaser polishing of Aluminum and Polyamide for dissimilar laser welded assemblies
Amne Elahi, Mahdi UL; Koch, Marcus; Plapper, Peter UL

Scientific Conference (2019, June 27)

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See detailLaser overlap joining from copper to aluminum and analysis of failure zone
Mathivanan, Karthik UL; Plapper, Peter UL

Scientific Conference (2019, June 26)

Joining of copper and aluminum sheets are very crucial for battery application. When joining from copper sheet, keyhole mode of welding is essential to overcome the reflectivity and melting threshold of ... [more ▼]

Joining of copper and aluminum sheets are very crucial for battery application. When joining from copper sheet, keyhole mode of welding is essential to overcome the reflectivity and melting threshold of copper. However, in dissimilar material interaction the resulting intermetallic (IMC) phases are brittle, which result in reduced performance.This paper analyses the joint with laser beam irradiated from the copper side (Cu on top). The idea is to distribute the intermetallic compounds inside the joint to obtain a ductile behavior. The zones of failure and the distribution of the intermetallic phase is studied. The microstructural analysis of the fusion zone and mechanical strength of the joint are presented. [less ▲]

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See detailSimulation-based optimization using multi-agent technology for efficient and flexible production planning and control in remanufacturing
Groß, Sebastian UL; Gerke, Wolfgang; Plapper, Peter UL

in International Conference on Remanufacturing (ICoR) 2019 (2019, June 25)

Remanufacturing is a process for used products to make them “as good as new or better”. A remanufacturing system typically consists of the processes disassembly, cleaning, inspection, reconditioning ... [more ▼]

Remanufacturing is a process for used products to make them “as good as new or better”. A remanufacturing system typically consists of the processes disassembly, cleaning, inspection, reconditioning reassembly and testing. Due to unknown condition of the used products many challenges occur which are special to the domain of remanufacturing and not know from manufacturing. The resulting stochastic routing of products and material in particular places special demands on the flexibility of the production planning and control (PPC) in remanufacturing systems. In order to enable stochastic routing, Automated Guided Vehicles (AGVs) are used, which also contributes to increasing the complexity of the PPC. Especially the simultaneous scheduling of machines and AGVs has to be addressed in order to enable an optimal remanufacturing process. This paper provides an overview about current research activities in the field of PPC in remanufacturing and scheduling approaches for AGVs. Furthermore, a promising approach to enable the required flexibility of the remanufacturing system and to control the dynamics contained therein is the use of a multi-agent technology. The proposed approach consists of an optimization of the PPC using a multi-agent based simulation. The multi agent-based simulation consists of intelligent agents that negotiate with each other in order to find an optimal solution and achieve high flexibility. [less ▲]

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See detailDeriving essential components of lean and industry 4.0 assessment model for manufacturing SMEs
Kolla, Sri Sudha Vijay Keshav UL; Minoufekr, Meysam UL; Plapper, Peter UL

in 52nd CIRP Conference on Manufacturing Systems (CMS) (2019), 81

Quantifying lean and ICT architecture related to Industry 4.0 is a new challenge in Small and Medium Scale Enterprises (SMEs) that needs to be addressed by both research as well as enterprises themselves ... [more ▼]

Quantifying lean and ICT architecture related to Industry 4.0 is a new challenge in Small and Medium Scale Enterprises (SMEs) that needs to be addressed by both research as well as enterprises themselves. Especially in the manufacturing sector, SMEs need to transform themselves into emerging trends such as industry 4.0 while practicing existing manufacturing philosophies such as Lean Production Systems (LPS) to be competitive in global markets. The major concern is that there are many assessment models available to measure the status of an enterprise related to either LPS or Industry 4.0. Often, these models are complex and don’t fulfill the requirements of manufacturing SMEs. On the other hand, most of the models only consider either lean or industry 4.0 elements. The outcomes of this research help to develop a hybrid model including both lean and industry 4.0 features suitable for manufacturing SMEs. The main objective of this research is to provide state of the art literature on existing assessment models and consequently map lean and industry 4.0 components to the specific characteristics of manufacturing SMEs. The paper concludes with a summary and outlook for our future research. [less ▲]

Detailed reference viewed: 187 (9 UL)