A Near-Surface Layer Heat Treatment of Die Casting Dies by Means of Electron-Beam Technology

Increasing the service life of die casting dies is an important goal of the foundry industry. Approaches are either material- or process-related. Despite new material concepts, hot work steels such as H11 are still predominantly used in the uncoated condition for die casting dies. In order to withstand the stresses that occur, this steel is used exclusively in the quenched and tempered condition. Required properties such as high high-temperature strength and high hardness combined with high toughness are, in principle, contradictory and can only be adjusted consistently over the entire die by furnace-based heat treatment. However, the results of various investigations have shown that improvements in the thermal shock resistance and wear resistance of hot work tool steels can be achieved by thermally influencing the microstructure near the surface. Based on these studies and related findings, an approach to surface heat treatment using the electron beam was developed. Due to the particle character of the radiation and the associated possibility of high-frequency beam deflection, the electron beam offers significantly greater flexibility in energy input into the workpiece surface compared with lasers or induction. The overall technological concept envisages replacing furnace-based heat treatment in the production of casting dies by localized and demand-oriented boundary layer heat treatment with the electron beam. The experiments include, on the one hand, the experimental determination of a suitable temperature–time interval with a focus on short-term austenitization. On the other hand, a simulation-based approach of boundary layer heat treatment with validation of a suitable heat source is investigated. Regarding short-term austenitization, the corresponding temperature and time range could be narrowed down more precisely. Some of these parameter combinations seem to be very suitable for practical use. The test specimens show a hard surface layer with a depth of at least up to 6 mm and a very tough buffer layer. Numerical simulation is used to estimate the resulting metallurgical microstructure and the achievable hardness as a function of the temperature–time interval. In addition, the results provided show the possibility of determining and optimizing the material properties by means of a simulation-based approach within the framework of a purely digital process planning and subsequently transferring them into a process planning. In the technical implementation, a temperature control was first established by means of a two-color pyrometer. In the further course of research, the pyrometer will be supplemented by an internally installed infrared camera, which will allow the reproducible setting of specified temperature profiles even for complex, large-area contours in the future

Demokratisierter Leichtbau

Stetig gestiegene Anforderungen hinsichtlich Komfort, Sicherheit und Fahrdynamik haben lange Zeit zu einem ansteigenden Fahrzeuggewicht bei Modellwechseln innerhalb eines Fahrzeugsegments geführt. Dieser Trend konnte erst vor wenigen Jahren durch den intensiven Einsatz von Leichtbauwerkstoffen (Leichtmetalle, höchstfeste Stähle, faserverstärkte Kunststoffe) gestoppt und in eine aktuell stagnierende bzw. leicht abnehmende Gewichtstendenz bei Fahrzeugen mit konventionellen Antrieben überführt werden. Diese Tendenz und der damit verbundene Fokus auf das Forschungsgebiet Leichtbau ist speziell beim Einsatz alternativer Antriebssysteme und vor dem Hintergrund des in der deutschen Automobilindustrie erreichten Standards an Qualität, Ökologie und Wirtschaftlichkeit zu schärfen

Deformation measurement within adhesive bonds of aluminium and CFRP using advanced fibre optic sensors

Monitoring the deformation within an adhesive joint during the curing cycle provides valuable information regarding the build-up of thermal strain and stress. Distributed fibre optic sensors are very useful for spatial continuous measurements of deformation or temperature. Integrated into a hybrid joint, the thermal curing process of the adhesive can be monitored. This detailed insight into the joint helps to understand the deformation and thereby also the resulting stress. Analysing the deformation process establishes the foundation to adapt techniques to reduce the thermally induced deformation and thereby the resulting stress

Investigation on fatigue strength of cut edges produced by various cutting methods for high-strength steels

Due to the interest in effective light steel constructions, high-strength steels have gained importance. Different thermal cutting processes are frequently used in the metal processing industry. Besides the weld seams, free cutting edges gain technical and economic relevance as locations for potential fatigue cracks. In this investigation, fatigue tests were carried out on 8-mm-thick samples of S355M and S690Q steels at a stress ratio of R = 0.1. The cutting methods used were oxygen, plasma, laser, and waterjet cutting. Quality improvement methods, like shot peening, grinding, and cutting speed reduction, were applied for some series. The surface roughness was measured to classify the specimens into quality groups according to ISO 9013. The cut edge condition was also characterized by hardness and residual stress measurements. The investigation shows that all tested series exceed the FAT100 class and can be classified in FAT125. Specimens ranged in quality group 2 of ISO 9013 according to the roughness achieve FAT140 regardless of cutting technology or material. According to the ISO 9013, most of the specimens are classified in the quality group 2 and group 3. Fatigue strength results are significantly different in one quality group. No prediction can be made. ISO 9013 has a weak connection to fatigue strength. Quality improvement methods have a significant influence on the fatigue strength and can increase it. Due to reduced cutting speeds, the roughness decreases also. It results in an increase of the fatigue strength in all tested series in this study. In order to make a prediction of the fatigue performance, the standard has to be specified and the cutting process as well as the steel strength should be considered

Novel form-flexible handling and joining tool for automated preforming

The production rates of carbon fiber reinforced plastic (CFRP) parts are rising constantly which in turn drives research to bring a higher level of automation to the manufacturing processes of CFRP. Resin transfer molding (RTM), which is seen as a production method for high volumes, has been accelerated to a high degree. However, complex net-shape preforms are necessary for this process, which are widely manually manufactured. To face these challenges a new concept for the manufacturing of carbon fiber preforms with a form-flexible gripping, draping and joining end-effector is presented and discussed. Furthermore, this paper investigates the application of this concept, describes the initial build-up of a demonstrator, focusing on material selection and heating technology, and discusses test results with the prototype. This prototype already validates the feasibility of the proposed concept on the basis of a generic preform geometry. After a summary, this paper discusses future in-depth research concerning the concept and its application in more complex geometries. © 2015 by De Gruyter 2015

Linear Elastic FE-Analysis of Porous, Laser Welded, Heat Treatable, Aluminium High Pressure Die Castings based on X-Ray Computed Tomography Data

The welding of aluminium high pressure die castings is a well known and broadly investigated challenge in various fields of industry and research. Prior research in this specific field mainly focused on the optimisation of the welding and the casting process and on the cause of the frequently occurring porosity and incomplete fusion phenomena, whereas the impacts of these defects have hardly been addressed. Therefore, the underlying study presents the investigation of weldments in EN AC-AlSi10MnMg high pressure aluminium die castings by linear elastic finite element analysis based on X-ray computed tomography as a novel approach. Hereby, four laser weldments with differing surfaces and pore contents were investigated by X-ray computed tomography and tensile testing. Based on the voxel datasets of the porous weldments, triangular finite element meshes were generated and a numerical finite element analysis was conducted. Good agreement of the stress–strain curves between the simulations and the experiments was achieve

Form-flexible handling and joining technology (formhand) for the forming and assembly of limp materials

The assembly of limp, elastic or differently shaped objects poses a huge challenge which needs to be met by machine tools and the corresponding processes of handling, forming and joining. These processes are often carried out manually. This technological gap triggered the present work at the Technische Universität Braunschweig. A novel form-flexible handling tool (FormHand) is presented which focuses on the automation of these production steps taking into consideration the material behavior. The combination of the flexibility of both industrial robot and the FormHand end-effector allows for new processes appropriate for these materials. This article investigates the used materials of the granular filler and the cushion textile, the working states of FormHand and the use of online sensors for an automated process application

Geometry and Distortion Prediction of Multiple Layers for Wire Arc Additive Manufacturing with Artificial Neural Networks

Wire arc additive manufacturing (WAAM) is a direct energy deposition (DED) process with high deposition rates, but deformation and distortion can occur due to the high energy input and resulting strains. Despite great efforts, the prediction of distortion and resulting geometry in additive manufacturing processes using WAAM remains challenging. In this work, an artificial neural network (ANN) is established to predict welding distortion and geometric accuracy for multilayer WAAM structures. For demonstration purposes, the ANN creation process is presented on a smaller scale for multilayer beads on plate welds on a thin substrate sheet. Multiple concepts for the creation of ANNs and the handling of outliers are developed, implemented, and compared. Good results have been achieved by applying an enhanced ANN using deformation and geometry from the previously deposited layer. With further adaptions to this method, a prediction of additive welded structures, geometries, and shapes in defined segments is conceivable, which would enable a multitude of applications for ANNs in the WAAM-Process, especially for applications closer to industrial use cases. It would be feasible to use them as preparatory measures for multi-segmented structures as well as an application during the welding process to continuously adapt parameters for a higher resulting component quality