Influence of laser parameter on weld bead shape and process stability of laser welded steel sheets

in Proceedings of 10th Conference on Photonic Technologies LANE 2018 (2018)

Laser butt-welding of dissimilar heat sensitive materials is one of the most challenging tasks. Significant differences in melting and transition temperatures are typical and occur frequently. Therefore ... [more ▼]

Laser butt-welding of dissimilar heat sensitive materials is one of the most challenging tasks. Significant differences in melting and transition temperatures are typical and occur frequently. Therefore, accurate control of the temperature profile at the interface of the weld is essential. In this paper, the influence of the laser parameter power and velocity, as well as laser spot diameter on the laser process were investigated. It is shown that the beam diameter has a significant impact on the weld bead formation. Further variation of the type of shielding gas showed an effect on the bead geometry depending on the used laser spot diameter. Spectroscopic process observations showed a significant impact of the spot diameter and shielding gas on the energy input and the efficiency of the laser process. A homogeneous damping effect of the laser radiation was obtained by using the larger fiber diameter accompanied with a higher overall intensity of process radiation. [less ▲]

Standardisierte unternehmensübergreifende Wertstrommethode (StreaM)

Doctoral thesis (2018)

In the course of globalization, complex corporate networks arise in which diverse players are involved in the value-added process. Particularly at the interfaces of the value chain, there are challenges ... [more ▼]

In the course of globalization, complex corporate networks arise in which diverse players are involved in the value-added process. Particularly at the interfaces of the value chain, there are challenges in terms of communication and cooperation, since so far no uniform procedure for the visualization, analysis and continuous improvement of product and information flows is used. These difficulties occur both within organizations and especially across company boundaries. In particular, no internationally recognized value stream standard exists at present, which is inter alia a result of a low cooperativeness of organizations due to a lack of trust, inadequate knowledge and insufficient incentives. The inconsistent use of Value Stream Management (VSM) affects many economic sectors worldwide. These inconsistent VSM approaches lead to inefficiencies, such as rework and coordination difficulties in the case of value stream audits, which represent an avoidable waste of time, natural and financial resources. In the scientific literature, a large number of fundamental VSM approaches, modifications and further developments are available that serve as a basis for the present work. The existing VSM approaches include provisions, e.g. in terms of symbols, data boxes, associated process variables and their calculation, which are each extensive, diverse and in some cases process-specific. In contrast, complex, globally distributed value chain structures require a holistic approach for the modeling of value streams. In the context of this dissertation, a VSM draft standard will be generated by means of a comparison of existing VSM approaches. Based on four different value stream levels, a multi-stage approach for the visualization, analysis and continuous improvement of cross-company product and information flows will be developed. The present thesis thus provides the methodological basis on the way towards an internationally recognized VSM standard and demonstrates in addition the potential of efficient and targeted application of VSM in value networks. On the one hand, standardizing the VSM method will enable an improved communication and cooperation along value chains in different economic sectors. On the other hand, the holistic approach helps to identify, show and implement improvement measures across company borders and ultimately leads to a reduction or ideally to the elimination of waste from an end customer perspective. The developed approach allows organizations worldwide to assess internal as well as cross-company value streams in a structured manner, to design them flexibly and to implement them effectively in practice. [less ▲]

CILAP-Architecture for Simultaneous Position- and Force-Control in Constrained Manufacturing Tasks

in ICINCO 2018 Proceedings of the 15th International Conference on Informatics in Control, Automation and Robotics Volume 2 (2018, July)

This paper presents a parallel control concept for automated constrained manufacturing tasks, i.e. for simultaneous position- and force-control of industrial robotic manipulators. The manipulator’s ... [more ▼]

This paper presents a parallel control concept for automated constrained manufacturing tasks, i.e. for simultaneous position- and force-control of industrial robotic manipulators. The manipulator’s interaction with its environment results in a constrained non-linear switched system. In combination with internal and external uncertainties and in the presence of friction, the stable system performance is impaired. The aim is to mimic a human worker’s behaviour encoded as lists of successive desired positions and forces obtained from the records of a human performing the considered task operating the lightweight robot arm in gravity compensation mode. The suggested parallel control concept combines a model-free position- and a model-free torque-controller. These separate controllers combine conventional PID- and PI-control with adaptive neuro-inspired algorithms. The latter use concepts of a reward-like incentive, a learning system and an actuator-inhibitor-interplay. The elements Conventional controller, Incentive, Learning system and Actuator-Preventer interaction form the CILAP-concept. The main contribution of this work is a biologically inspired parallel control architecture for simultaneous position- and force-control of continuous in contrast to discrete manufacturing tasks without having recourse to visual inputs. The proposed control-method is validated on a surface finishing process-simulation. It is shown that it outperforms a conventional combination of PID- and PI-controllers. [less ▲]

Application of Value Stream Management to enhance product and information flows in supply chain networks - based on the example of web-based automotive retail business

in Management and Production Engineering Review (2018), 9(2), 13-19

Due to globalized business operations, companies in different economic sectors are part of complex supply chain networks. Their value-added processes comprise product and information flows, e.g. with a ... [more ▼]

Due to globalized business operations, companies in different economic sectors are part of complex supply chain networks. Their value-added processes comprise product and information flows, e.g. with a focus on manufacturing, service or trade. Until the final product is delivered to the end customer, it needs to pass many different processes in cooperating organizations. As a result, there a lot of business-to-business (B2B) interactions with cross-enterprise transactions, often including cross-border communications and sometimes even cross-industry trades with technological and often cultural implications. Especially the interfaces of supply chain networks are prone to inefficiencies, misunderstandings and delays due to a lack of standardized B2B transactions, which leads to waste in form of rework, errors and mistakes. In addition, new customers are hard to find for the manufacturing or trading company, since potential customers are so far limited to a regional network. The advantages of extending the customer base still need to be explored by many organizations. This paper discusses the opportunities by streamlining the communication along supply chain networks in a general fashion and then describes the application in a B2B automotive retail business. A concept of a web-based trading platform, which provides a seamless service for all steps of a convenient and efficient used vehicle remarketing business, is developed. It includes all phases, like offering and price finding in a comprehensive online platform, which also covers further activities, such as logistic services, financial transactions, and a mandatory feedback loop. The suggested B2B vehicle-trading platform enables a quick turnover of each transaction, which is analyzed and optimized based on the application of cross-enterprise Value Stream Management. [less ▲]

Optimierung und Charakterisierung einer mittels Laserstrahl gefügten Verbindung zwischen Aluminium und Polyamid 6.6

Doctoral thesis (2018)

The creation of strong joints between dissimilar materials and in particular between polymers and metals is one of the most often discussed topics in the fields of automotive, aerospace and transportation ... [more ▼]

The creation of strong joints between dissimilar materials and in particular between polymers and metals is one of the most often discussed topics in the fields of automotive, aerospace and transportation. Especially the combination of polyamide and aluminum is of highest interest, due to their market share as construction materials. New joining concepts are anticipated to deliver strong, durable and resource efficient structural components that are ideally suited for lightweight designs. However, current research activities have shown that the highly distinct material properties of these materials pose enormous challenges on the creation of hybrid structures. The cause that potentially enables the connection between the aluminum surface and the polymer is still not fully understood. The research objective of the presented work, therefore is, on the one hand, to create an optimal joint between aluminum and polyamide 6.6 using a laser beam to reach high shear strength for an industrial application. On the other hand, the presented work seeks to deliver a substantial contribution to furtherly understand the interaction between the polymer and the metal surface during the thermal joining. A laser-based joining method was developed that enables the researchers to overcome limitations of conventional processes, that is minimizing space requirements, making the application of additional gaskets obsolete, reaching high strength, saving weight and reducing processing time. The effectiveness of different surface pre-treatments has been studied, and the described optimization of this method has lead to an increase of the shear strength of the joints by more than 100 %. Laser ablation and the hydrothermal treatment of the metallic surface, before the joining operation, lead to the highest joint strength. The surface pre-treatment method of laser ablation delivered to transfer the gathered insights and experience from the laboratory to the industrial scale, due to its repeatability and reproducibility. The experiment mentioned above includes the use of production materials, such as aluminum with a higher sheet thickness of up to 1.48 mm and glass fiber reinforced polymer. Shear strength of 40 MPa was reached in quasi-static single lap shear tests. During dynamic testing, samples maintained 63 % of static breaking load after one million cycles. The hydrothermal treatment of the aluminum surface leads to a lower surface roughness of Ra = 1.58 µm in average as opposed to 4.90 µm after laser ablation. Due to the lower roughness values, the first-mentioned method was chosen to study the interaction. An XPS-analysis revealed a strong influence of the surface pre-treatment method on the chemical composition of the metal surface, which becomes noticeable by hydroxylation of the surface layer and is expressed by the oxide ratio (O/Al) and hydroxide ratio (OH/O). A high O/Al ratio of 2.36 and an OH/O ratio of 0.63 after the hydrothermal treatment is showing a strong increase of the amount of hydroxide in direct comparison to values of 35 % and 36 % of OH/O ratio after ethanol and hexane cleaning respectively. The question, as to which extent the presence of such hydroxide structures at the boundary layer of the aluminum influence the interaction between the metal surface and the polymer, was a subject matter of an additional FT-IR analysis. In case of the infrared spectra from thin polymer films on the hydrothermally treated surface, clear indications of interaction are visible. In direct comparison to the infrared spectra from polymer films on either ethanol or hexane cleaned surfaces, this interaction seems to increase nearby of the interface further. The interaction mentioned above appears at the carbonyl band and amine band as a shift of 4 cm-1 and 8 cm-1 and an increase of the full width at half maximum by 35 % respectively 40 %. Additional strong differences are visible at the molecule vibrations below 1,200 cm-1, which are typically assigned to both crystalline phases and amorphous phases of the polyamide. In case of the hydrothermal treatment, collected data indicates a polymorphous state inside the polymer films, which seems to become increasingly disordered close to the interface. On the contrary, spectra from the polymer films on ethanol and hexane pre-treated substrates show only marginal changes. Methods are proposed to build upon the results described in this work and refine distinct signs of the interaction. [less ▲]

Aluminum pretreatment by a laser ablation process: influence of processing parameters on the joint strength of laser welded aluminum – polyamide assemblies

in Procedia CIRP (2018)

Laser welding of metal – polymer assemblies is an innovative bonding process. It was already demonstrated that laser surface pretreatments of aluminum (Al), prior to laser welding with a polymer, impacts ... [more ▼]

Laser welding of metal – polymer assemblies is an innovative bonding process. It was already demonstrated that laser surface pretreatments of aluminum (Al), prior to laser welding with a polymer, impacts joints strength. This work adopts a design of experiments (DoE) approach to investigate the influence of several Al laser ablation parameters on joint strength of laser welded Al – polyamide (PA6.6) assemblies. Significant parameters were highlighted, process window was outlined, and optimal parameters were identified. After assembly failure, the joint area was evaluated using optical microscopy. Depending on the laser ablation parameters, the joint area can be enhanced resulting in a significant increase in the corresponding bearable shear load. [less ▲]

Recent Progress Toward Intelligent Robot Assistants for Non-Destructive Disassembly

in Müller, Rainer; Plapper, Peter; Brüls, Olivier (Eds.) et al Robotix-Academy Conference for Industrial Robotics (RACIR) 2018 (2018)

One key to successful and fluent human-robot collaboration in disassembly processes is equipping the robot systems with greater autonomy and intelligence. In this paper, we present our progress in ... [more ▼]

One key to successful and fluent human-robot collaboration in disassembly processes is equipping the robot systems with greater autonomy and intelligence. In this paper, we present our progress in developing such an intelligent robot assistant system. We present the multi-agent control architecture we developed and describe its technical implementation. Our control approach relies on two types of knowledge models: product and process models. The product model describes the structure of the product to be dismantled through a description of the parts involved and the connections between them. A connection type-related process model describes which agents and objects participate in the disassembly process and which methods of human-robot cooperation or collaboration are most useful. When supplied with a product model and a goal definition, our robotic assistant can automatically generate a partially ordered disassembly task sequence. For each disassembly task, the user can choose one of the divisions of labor defined in the process model. Using the process model, through perception and deliberation, the control system can both execute actions and coordinate and synchronize the actions of human and machine. This approach allows the system to be more autonomous when providing assistance to human coworkers in complex and one-piece disassembly processes. [less ▲]

Continuous Improvement of complex process flows by means of StreaM

Presentation (2017, December 11)

In numerous sectors and industries worldwide, there is a trend towards an intercompany and often international division of value creation and related work tasks. To overcome the challenges of complex ... [more ▼]

In numerous sectors and industries worldwide, there is a trend towards an intercompany and often international division of value creation and related work tasks. To overcome the challenges of complex cross-enterprise supply chain networks, innovative approaches to visualize, assess and enhance value streams are sought. The StreaM method, which is described in this paper, enables a comprehensive analysis, design and planning of cross-company product and information flows on different levels of value stream detail. At the same time, the entire methodology is based on a common understanding of key symbols, parameters and calculation procedures. In addition, the use of the developed StreaM method and the associated model in a case study proves its practical applicability in an industrial setting. In further validation projects, the transfer of the “Standardized cross-enterprise Value Stream Management Method” to other industry sectors is envisaged to continuously improve energy, trade or service processes. [less ▲]

Continuous Improvement of Complex Process Flows by Means of StreaM as the “Standardized Cross-Enterprise Value Stream Management Method”

in Proceedings of 2017 IEEE International Conference on Industrial Engineering and Engineering Management (IEEM) (2017, December)

In numerous sectors and industries worldwide, there is a trend towards an intercompany and often international division of value creation and related work tasks. To overcome the challenges of complex ... [more ▼]

In numerous sectors and industries worldwide, there is a trend towards an intercompany and often international division of value creation and related work tasks. To overcome the challenges of complex cross-enterprise supply chain networks, innovative approaches to visualize, assess and enhance value streams are sought. The StreaM method, which is described in this paper, enables a comprehensive analysis, design and planning of cross-company product and information flows on different levels of value stream detail. At the same time, the entire methodology is based on a common understanding of key symbols, parameters and calculation procedures. In addition, the use of the developed StreaM method and the associated model in a case study proves its practical applicability in an industrial setting. In further validation projects, the transfer of the “Standardized cross-enterprise Value Stream Management Method” to other industry sectors is envisaged to continuously improve energy, trade or service processes. [less ▲]

Influence of laser ablation and plasma surface treatment on the joint strength of laser welded aluminum-polyamide assemblies

Scientific Conference (2017, September 14)

Laser assembly of a metal with a polymer is an innovative process for the development of hybrid lightweight structures. It was already demonstrated that surface treatment of aluminum prior to laser ... [more ▼]

Laser assembly of a metal with a polymer is an innovative process for the development of hybrid lightweight structures. It was already demonstrated that surface treatment of aluminum prior to laser joining has a critical influence on joint strength of laser assembly with polyamide. In this work, further investigation of the influence of surface treatment prior to laser assembly is carried out. In particular, two kind of surface modification pretreatments of aluminum, laser ablation and plasma surface modification, in combination with plasma surface pretreatment of polyamide, were investigated. Surface properties of aluminum and polyamide after pretreatment are compared to their untreated state. More precisely, surface chemistry, surface energy and roughness characteristics are evaluated by X-ray photoelectron spectroscopy (XPS), sessile drop tests and 3D profilometry, respectively. Joint strength of laser assembly of treated aluminum and polyamide is reported. The more influential surface characteristics for the improvement of joint strength are determined, paving the way to significant advances in metal-polymer laser assembly technology. [less ▲]