Konrad Wegener

Fatigue performance of additive manufactured metallic parts

Purpose – Additive manufacturing technologies such as, for example, selective laser melting (SLM) offer new design possibilities for a wide range of applications and industrial sectors. Whereas many results have been published regarding material options and their static mechanical properties, the knowledge about their dynamic mechanical behaviour is still low. The purpose of this paper is to deal with the measurement of the dynamic mechanical properties of two types of stainless steels.Design/methodology/approach – Specimens for dynamic testing were produced in a vertical orientation using SLM. The specimens were turned to the required end geometry and some of them were polished in order to minimise surface effects. Additionally, some samples were produced in the end geometry (“near net shape”) to investigate the effect of the comparably rough surface quality on the lifetime. The samples were tension‐tested and the results were compared to similar conventional materials.Findings – The SLM‐fabricated stain...

High temperature material properties of IN738LC processed by selective laser melting (SLM) technology

Purpose – Selective laser melting (SLM) is being investigated by Alstom and IWF due to its flexibility, cost‐ and lead‐time reduction potential for reconditioning of hot gas path components used in todays heavy‐duty gas turbines. This paper aims to address this issue.Design/methodology/approach – Tensile tests as well as relaxation and creep tests were carried out to assess SLM processed IN738LC for use in high temperature applications. To evaluate potential anisotropic material behaviour resulting from the layer‐wise build up process, all specimens were built in two directions: parallel and perpendicular to the build direction, respectively. Furthermore, extensive metallurgical investigations were made to analyse the chemical homogeneity as well as the correlation between microstructure and high temperature properties of SLM processed IN738LC.Findings – Tensile tests showed that strength properties superior to cast IN738LC can be achieved by processing this material by SLM alternatively. Due to differen...

An integrated cost‐model for selective laser melting (SLM)

Purpose – The integration of additive manufacturing (AM) processes into a production environment requires a cost‐model that allows the precise estimation of the total cost per part, although the part might be produced in the same build job together with other parts of different sizes, complexities and quantities. Several cost‐models have been proposed in the past, but most of them are not able to calculate the costs for each single part in a mixed build job or are not suitable for Selective Laser Melting (SLM). The purpose of this paper is to develop a cost model, including all pre‐ and post‐processing steps linked to SLM.Design/methodology/approach – Based on collected data and the generic cost model of Alexander et al., an adapted model was developed for the SLM process including all required pre‐ and post‐processes. Each process was analysed and modelled in detail, allowing an evaluation of the influences of the different geometries on the cost of each part.Findings – By simultaneously building up mult...

Understanding error generation in fused deposition modeling

Additive manufacturing offers completely new possibilities for the manufacturing of parts. The advantages of flexibility and convenience of additive manufacturing have had a significant impact on many industries, and optimizing part quality is crucial for expanding its utilization. This research aims to determine the sources of imprecision in fused deposition modeling (FDM). Process errors in terms of surface quality, accuracy and precision are identified and quantified, and an error-budget approach is used to characterize errors of the machine tool. It was determined that accuracy and precision in the y direction (0.08–0.30 mm) are generally greater than in the x direction (0.12–0.62 mm) and the z direction (0.21–0.57 mm). Furthermore, accuracy and precision tend to decrease at increasing axis positions. The results of this work can be used to identify possible process improvements in the design and control of FDM technology.

Processing of metal-diamond-composites using selective laser melting

Purpose – The purpose of this paper is a feasibility study that was performed to investigate the basic processability of a diamond-containing metal matrix. Powder-bed-based additive manufacturing processes such as selective laser melting (SLM) offer a huge degree of freedom, both in terms of part design and material options. In that respect, mixtures of different powders can offer new ways for the manufacture of materials with tailored properties for special applications such as metal-based cutting or grinding tools with incorporated hard phases. Design/methodology/approach – A two-step approach was used to first investigate the basic SLM-processability of a Cu-Sn-Ti-Zr alloy, which is usually used for the active brazing of ceramics and superhard materials. After the identification of a suitable processing window, the processing parameters were then applied to a mixture of this matrix material with 10-20 volume per cent artificial, Ni-coated mono-crystalline diamonds. Findings – Even though the processing...

Machine tool optimization strategies for ecologic and economic efficiency

Optimization activities in manufacturing must be addressed in the multifaceted context that combines economic, social and environmental goals. Research activities of today not only strive to cope with the legislative pressure of the Directive of the European Parliament on Energy Using Products but also strive for economic advantages for the machine tool user by investigating and applying suitable procedures and methods that help to model, forecast and reduce overall energy consumption. A key issue is the reduction of the amount of resources consumed for the same output and the increased machine tool efficiency with the help of selective methods and a minimum investment. A bottom-up approach to identify potential initial points for optimization is given in the presented research work. This article introduces a methodology for detecting and evaluating reasonable investments for retrofit solutions with different approaches. A technical measurement and optimization approach, depending on the actual circumstances, and an economic approach, that is used to detect optimization potentials with the economic evaluation of selected solutions are proposed in this article.

Microstructure and Mechanical Performance of Cu-Sn-Ti-Based Active Braze Alloy Containing In Situ Formed Nano-Sized TiC Particles

A Cu-Sn-Ti-based active brazing filler alloy was in situ reinforced with nanosized TiC particles by adding different amounts of a cellulose nitride-based binder. The TiC particles emanate from a reaction of the Ti within the filler alloy with the carbon from the binder that does not decompose completely during heating. The correlation between the microstructure and mechanical performance was studied. In addition, the effect of different binder amounts on the shear strength and cutting performance of brazed diamond grains was studied in shear tests and single grain cutting tests. The results clearly show that the mechanical performance of the brazed diamond grains can be improved by the formation of TiC particles. This is attributed to particle strengthening of the filler alloy matrix as well as to the decreasing grain size and more homogeneous distribution of the (Cu,Sn)3Ti5 phase with increasing amount of binder.

Picosecond laser fabrication of micro cutting tool geometries on polycrystalline diamond composites using a high-numerical aperture micro scanning system

The generation of microsized components found in LEDs, watches, molds as well as other types of micromechanics and microelectronics require a corresponding micro cutting tool in order to be manufactured, typically by milling or turning. Micro cutting tools are made of cemented tungsten carbide and are conventionally fabricated either by electrical discharge machining (EDM) or by grinding. An alternative method is proposed through a laser-based solution operating in the picosecond pulse duration whereby the beam is deflected using a modified galvanometer-driven micro scanning system exhibiting a high numerical aperture. A micro cutting tool material which cannot be easily processed using conventional methods is investigated, which is a fine grain polycrystalline diamond composite (PCD). The generation of various micro cutting tool relevant geometries, such as chip breakers and cutting edges, are demonstrated. The generated geometries are subsequently evaluated using scanning electron microscopy (SEM) and quality is measured in terms of surface roughness and cutting edge sharpness. Additionally, two processing strategies in which the laser beam processes tangentially and orthogonally are compared in terms of quality.

Simulation of warpage induced by non-isothermal crystallization of co-Polypropylene during the SLS process

Polymer processing using Additive Manufacturing Technologies (AM) has experienced a remarkable growth during the last years. The application range has been expanding rapidly, particularly driven by the so-called consumer 3D printing sector. However, for applications demanding higher requirements in terms of thermo-mechanical properties and dimensional accuracy the long established AM technologies such as Selective Laser Sintering (SLS) do not depict a comparable development. The higher process complexity hinders the number of materials that can be currently processed and the interactions between the different physics involved have not been fully investigated. In case of thermoplastic materials the crystallization kinetics coupled to the shrinkage strain development strongly influences the stability of the process. Thus, the current investigation presents a transient Finite Element simulation of the warpage effect during the SLS process of a new developed polyolefin (co-polypropylene) coupling the thermal,...

Towards Decentralized Production: A Novel Method to Identify Flexibility Potentials in Production Sequences Based on Flexibility Graphs

E-mail: lennart.soeren.bochmann@volkswagen.de ∗2Institute of Machine Tools and Manufacturing, ETH Zurich, Zurich, Switzerland ∗3Chair of Enterprise Logistics, Technical University of Dortmund, Dortmund, Germany ∗4Department of Computer Science VII, Technical University of Dortmund, Dortmund, Germany ∗5F/L/S Fuzzy Logik Systeme GmbH, Dortmund, Germany ∗6Fraunhofer Institute for Material Flow and Logistics, Dortmund, Germany