The applicability of the standard DIN EN ISO 3690 for the analysis of diffusible hydrogen content in underwater wet welding

The European standard ISO 3690 regulates the measurement of diffusible hydrogen in arc-welded metal. It was designed for different welding methods performed in dry atmosphere (20% humidity). Some details of the standard are not applicable for wet underwater welding. The objective of this study was to extend the applicability of DIN EN ISO 3690:2018-12 to underwater wet-shielded metal arc welding (SMAW). Four different aspects regulated within the standard were accounted for: (1) sample dimensions and number of samples taken simultaneously; (2) time limitations defined by the standard regarding the welding and the cleaning process; (3) time, temperature, and method defined for analysis of the diffusible hydrogen content; (4) normalization of the hydrogen concentration measured. Underwater wet welding was performed using an automated, arc voltage-controlled welding machine. The results are discussed in light of standard DIN EN ISO 3690, and recommendations are provided for the analysis of diffusible hydrogen content upon underwater wet welding. © 2020 by the authors

Development of a Generic Framework to Assess Asset Management Maturity within Organisations

With the comprehensive Lean Smart Maintenance philosophy and its associated maturity model, organisations were given a tool to reach asset and maintenance excellence. This paper discusses the approach used to transfer the scientifically based methods and concepts of the Lean Smart Maintenance Maturity Model into an assessment structure to generate a generic tool to collect the complete and correct information necessary to determine an organisation\u27s maturity level. Research results show that a standardised assessment process combined with continuous improvement cycles, a more accurate assessment of the company\u27s maturity is possible. A well-structured MM assessment supports less experienced assessors whereby experienced assessors will not need a full questionnaire but only a well-structured list of items and their maturity levels

Validation of a Lean Smart Maintenance Maturity Model

Rising complexity in industrial asset and maintenance management due to more volatile business environments and megatrends like Industry 4.0 has led to the need for a new perspective on these management domains. The Lean Smart Maintenance (LSM) philosophy, which focuses on both the efficient (lean) and the learning (smart) organization was introduced during the past few years, and a corresponding maturity model (MM) has been developed to guide organizations on their way to asset and maintenance excellence. This paper discusses use cases, in which the usability and the generic aspect of the LSM MM are validated by using data from three different asset management assessment projects in organizations with different types of production. Research results show that the LSM MM can be used as a basis for management system improvement, independent of production types such as one-of-a-kind industry, mass production and continuous production

Evolution of a Lean Smart Maintenance Maturity Model towards the new Age of Industry 4.0

Over the last few years, the complexity of asset and maintenance management of industrial plants and machinery in the producing industry has risen due to higher competition and volatile environments. Smart factories, Internet of Things (IoT) and the underlying digitisation of a significant number of processes are changing the way we have to think and work in terms of asset management. Existing Lean Smart Maintenance (LSM) philosophy, which focuses on the cost-efficient (lean) and the learning organisation (smart) perspectives enables a value-oriented, dynamic, and smart maintenance/asset management. The associated LSM maturity model is the evaluation tool that contains the normative, strategic, and operational aspects of industrial asset management, based on which numerous reorganisation projects have already been carried out in industrial companies. However, due to the ever-increasing development of Industry 4.0 (I4.0), it is necessary to extend the model by selected aspects of digitisation and digitalisation. Based on a structured literature review (SLR) of state of the art I4.0 maturity models, we were able to investigate the essential maturity items for I4.0. To restructure and expand the existing LSM maturity model, the principle of design science research (DSR) was used. The architecture of the LSM maturity model was based on the structure of the Capability Maturity Model Integration (CMMI). Further development of a Lean Smart Maintenance maturity model thus covers the future requirements of I4.0 and data science. It was possible to enhance existing categories with new artefacts from the I4.0 range to represent the influence of cyber-physical systems (CPS), (big) data and information management, condition monitoring (CM) and more. Furthermore, the originally defined LSM-Model was restructured for a more simplified application in industrial use cases

Welding characteristics and microstructure of an industrially processed Fe-Mn-Al-Ni shape memory alloy joined by tungsten inert gas welding

Iron-based shape memory alloys have recently attracted increased attention due to their low material costs combined with good workability and high transformation strains. They show excellent welding properties, as shown by several studies and compared to non-iron-based shape memory alloys, and are potential candidate materials for large-scale application as damping elements in building structures. Since subsequent heat treatment is only possible to a limited extent for large-scale components, it is necessary to minimize the effects of processing and welding operations on the shape memory properties. Therefore, a suitable microstructure must be established in the heat-affected zone and the fusion zone during the welding process. Thus, industrially processed polycrystalline Fe-Mn-Al-Ni was joined by tungsten inert gas welding with matching filler material. The phases formed upon welding with different parameters were investigated using optical microscopy, scanning electron microscopy and X-ray diffraction. Shielding gas composition as well as mean arc linear energy have a huge impact on the γ-phase precipitation. Intercrystalline cracking can be supressed by increasing the γ content. Further, the α-fraction and grain size in the fusion zone can be controlled by the welding parameters. Ultimately, a hardness value of the fusion zone equal to heat-treated material was achieved which suggests that the fusion zone may be able to transfer the stress required for martensitic transformation

Detection of the contact tube to working distance in wire and arc additive manufacturing

Currently, wire and arc additive manufacturing (WAAM) is mainly done by planning the torch movements layer wise. The height step between the layers is derived from preliminary experiments. Small deviation in the determination of the height step can accumulate over the layers and lead to improper shielding gas conditions or a collision the between torch and the work piece. This makes continuous process monitoring necessary. To overcome these problems, a closed-loop layer height control strategy is beneficial. For the development of a closed-loop height control strategy, it is necessary to have knowledge of the effective height step between the layers during manufacturing. The present study focuses on the development of a sensing method, which allows users to detect the contact tube to working distance (CTWD) in WAAM. The system was developed for short circuit mode of gas-metal arc welding WAAM. The system can also provide information on whether the torch passes over weld beads crossing the weld track or other geometric irregularities existing in the z-direction. Several characteristic values of the process were detected and were matched to the actual CTWD. The accuracy of the sensing method was evaluated, and based on the measured correlation and standard deviation, the electrical resistance during short circuit monitored the CTWD best

Microstructural Investigation of a FeMnAlNi Shape Memory Alloy Processed by Tungsten Inert Gas Wire and Arc Additive Manufacturing

In the present study, tungsten inert gas wire and arc additive manufacturing was used to process an iron-based FeMnAlNi shape memory alloy. By a layer-by-layer method, a wall structure with a length of 60 mm and a height of 40 mm was generated. Bidirectional welding ensured grain growth parallel to the building direction. To maintain a nearly constant temperature–time path upon cooling, the structure was fully cooled after each weld to room temperature (298 K). With this approach, an anisotropic microstructure with a grain length of up to 8 mm (major axis) could be established. The grain morphology and formed phases were investigated by optical microscopy and scanning electron microscopy. The images revealed a difference in the orientation with respect to the building direction of the primarily formed γ grains along the grain boundaries and the secondarily formed γ grains in the heat-affected zones. Subgrains in the α matrix were observed also by scanning electron microscopy. With X-ray diffraction, the preferred orientation of the α grains with respect to the building direction was found to be near ⟨100⟩. Overall, an anisotropic polycrystalline material with a columnar texture could be produced, with a preferred grain orientation promising high values of transformation strains

Development and evaluation of a closed-loop z-axis control strategy for wire-and-arc-additive manufacturing using the process signal

Wire-and-arc-additive manufacturing (WAAM) is an additive manufacturing technology with a high deposition rate. WAAM usually employs a layer wise build-up strategy. This makes it necessary to know the height of each deposited layer to determine the height the z-axis has to travel after each layer. Current bead geometry models (BGM) lead to variations, which can gradually accumulate over the layers. The present study focuses on the development of a closed-loop control system capable of keeping the contact tube working distance (CTWD) constant during short-circuit gas metal arc welding (GMAW) based WAAM. The algorithm calculates the CTWD based on the resistance during the short circuit. The closed-loop strategy is compared to an open-loop control strategy, which moves along a predefined height step after each layer. Using the proposed control strategy, WAAM becomes a fully automated process without the need for preliminary experiments to determine the height step. Only a short calibration slope is necessary for a complete closed-loop additive build-up. To study the influence of the control strategy on the workpiece the energy input, mechanical strength, microhardness, porosity, and microstructure were analyzed. It is shown that the CTWD of the open-loop deposited component increases slowly. Due to the novel control approach, this is prevented by the closed-loop control, while the mechanical strength and microhardness remain

An Experimental and Numerical Study of Damage Due to Particle Impact on Sapphire Orifices Used in High-Pressure Water Jet Cutting

In the present study, the damage mechanisms that cause premature failure of sapphire water jet orifices were analyzed using a combined experimental and finite element modeling (FEM) approach. Depending on the operating behavior and local conditions, the service life of orifices for high-pressure water jet cutting often deviates considerably from the manufacturer’s specifications. Literature states a typical service life of 50 to 100 h, while in some cases, premature failure after a few hours or even minutes of operation can be observed. The focus of this paper is on the interaction of particles that impact the orifice surface but also the effect of faulty orifice assembly is taken into account. To estimate the risk of failure, the stress distribution in critical parts of the orifice were calculated via FEM, which is fed with experimental data. The modified Mohr failure criterion was then used to evaluate the stress distributions with respect to the possible failure of the orifice jewel. The results revealed that the risk of damage caused by excessive assembly preload forces is marginal. The stress caused by the impact of particles of different sizes is up to four orders of magnitude higher than the stress caused by assembly forces and is therefore identified as the main risk for orifices to fail prematurely. Experimental data shows mainly particles of calcium carbonate and iron–aluminum silicates, which are compounds that originate from the process water itself. It is demonstrated that particles are more critical than formerly assumed in the literature. This paper identifies particles with a diameter of more than 10 µm as critical when there are no other loads present. In operation, even particles as small as 2 µm in diameter can cause damage to the orifice jewel. To prevent premature orifice failure due to foreign particles, water filtration with a 2 µm mesh is recommended, while future research needs to focus on the interior cutting head design to prevent precipitation from the process water

Corrosion Behavior of an Additively Manufactured Functionally Graded Material

Dissimilar metal welds (DMW) combine the high strength and cost benefits of ferritic stainless steels with the high corrosion resistance of austenitic steels, and are thus commonly used in different types of power plants. However, due to the abrupt change in properties, these joints are susceptible to premature failure. Work pieces with a smooth transition in composition and/or properties are referred to as "functionally graded materials" (FGM). When used as transition joints, FGM can enhance the lifetime of certain components. In the present study, the FGM were manufactured by using wire arc additive manufacturing employing cold-wire gas metal arc welding. Since the corrosion resistance of such FGM are still unknown, the corrosion properties of the FGM work piece were compared to those of a DMW work piece by means of electrochemical analysis using potentiodynamic polarization and a salt spray test. The FGM showed a 24 % lower average corrosion rate compared to the reference piece and no signs of pitting or galvanic corrosion. This shows the potential of FGM and further research should be carried out