Research activities at the Institute of electrotechnology in the field of metallurgical melting processes

A wide range of industrial metallurgical melting processes are carried out using electrothermal and electromagnetic technologies. The application of electrotechnologies offers many advantages from technological, ecological and economical point of view. Although the technology level of the electromagnetic melting installations and processes used in the industry today is very high, there are still potentials for improvement and optimization. In this paper recent applications and future development trends for efficient use of electromagnetic processing technologies in metallurgical melting processes are described along selected examples which are part of the research activities of the Institute of Electrotechnology of the Leibniz University of Hannover

Numerical Models for Induction Hardening of Gears

I modelli numerici permettono ai progettisti di evitare un approccio trial and error, lungo e costoso, nello stabilire i parametri di tempra. Questa Tesi pertanto affronta uno studio sull’influenza dei parametri di macchina sullo strato temprato di una ruota dentata temprata ad induzione tramite (FEM). Successivamente è stato proposto un confronto tra i risultati di misure sperimentali di temperatura su un processo di tempra e i risultati delle simulazioni numeriche dello stesso processo

Design improvements for increasing lifetime of single-shot coils applied at rotating workpieces

In the industry, induction hardening of rotationally symmetrical workpieces by a single-shot process is a widespread method. Due to only partial superimposition of the workpiece areas to be heated by the coil, high power densities are often needed there. These lead to local hot spots, amounting to an intensive material stress and often result in a short lifetime of the inductor. In this paper, some numerically investigated models will be presented, revealing approaches, how to reduce mechanical stress in the single-shot coil and thus, enabling an increase of service life

Tailored Forming of Hybrid Bevel Gears with Integrated Heat Treatment

“In recent years, multi-material designs of technical components have been gaining in importance. When combining different materials in a single component, it is possible to achieve high performance and extended functionality while simultaneously saving cost-intensive or rare materials. One promising approach to manufacture hybrid parts such as bi-metal gears is the utilization of the technology of tailored forming. This technology includes three main process steps: producing of bi-metal workpieces, forming and finishing. At the example of bevel gears, bi-metal preforms were produced by laser cladding of the martensitic steel X45CrSi9-3 on a cylindrical substrate made of the carbon steel C22.8 and formed to the final gear geometry by means of hot die forging. Subsequently, the hot bevel gears were directly quenched from hot-forming temperature by an air-water spray and self-tempered using the residual heat. To analyse the effect of each process step on the microstructure, specimens were extracted from cladded, forged and heat treated components and investigated by means of metallographic analysis and hardness measurements. The results demonstrate that cladded workpieces were successfully formed to complex toothed parts without any defects. The hot forming process has a positive impact on the welded layer and the interface zone by grain refinement and the associated improved mechanical properties. The required hardness values at the tooth flanks were achieved by the integrated heat treatment"

Microstructural evolution and mechanical properties of hybrid bevel gears manufactured by tailored forming

The production of multi-metal bulk components requires suitable manufacturing technologies. On the example of hybrid bevel gears featuring two different steels at the outer surface and on the inside, the applicability of the novel manufacturing technology of Tailored Forming was investigated. In a first processing step, a semi-finished compound was manufactured by cladding a substrate using a plasma transferred arc welding or a laser hotwire process. The resulting semi-finished workpieces with a metallurgical bond were subsequently near-net shape forged to bevel gears. Using the residual heat after the forging process, a process-integrated heat treatment was carried out directly after forming. For the investigations, the material combinations of 41Cr4 with C22.8 (AISI 5140/AISI 1022M) and X45CrSi9-3 with C22.8 (AISI HNV3/AISI 1022M) were applied. To reveal the influence of the single processing steps on the resulting interface, metallographic examinations, hardness measurements and micro tensile tests were carried out after cladding, forging and process-integrated heat treatment. Due to forging and heat-treatment, recrystallization and grain refinement at the interface and an increase in both, hardness and tensile strength, were observed. © 2020 by the authors. Licensee MDPI, Basel, Switzerland

Control of Thermal Distribution in Additive Manufacturing

Additive Manufacturing is a rapidly growing industry. However, the defects generally occurring in parts built through Additive Manufacturing have hindered its way towards a reliable technology for mass production. Most of these defects generally occur through residual stresses building up in the parts during the process. Complex machinery is available which ensures defect free parts but it comes with a trade-off for cost. The aim of this study is to provide a potential cost-effective solution to address the defects and issues arising due to uneven thermal distribution in the AM built parts. A detailed study about the basic understanding of the consolidation mechanism of the Powder Bed based Additive Manufacturing processes and Induction is discussed. The use of induction to selectively control the thermal distribution in these manufacturing process is proposed. Preliminary stage simulations and experiments are carried out to validate the proposal and its scope of application is discussedMaster of Science in EngineeringAutomotive Systems Engineering, College of Engineering & Computer ScienceUniversity of Michiganhttps://deepblue.lib.umich.edu/bitstream/2027.42/145492/1/Master's Thesis Copy Formatted (2).pdfDescription of Master's Thesis Copy Formatted (2).pdf : Thesi

Computer-aided analysis and design of the shape rolling process for producing turbine engine airfoils

Mild steel (AISI 1018) was selected as model cold rolling material and Ti-6A1-4V and Inconel 718 were selected as typical hot rolling and cold rolling alloys, respectively. The flow stress and workability of these alloys were characterized and friction factor at the roll/workpiece interface was determined at their respective working conditions by conducting ring tests. Computer-aided mathematical models for predicting metal flow and stresses, and for simulating the shape rolling process were developed. These models utilized the upper bound and the slab methods of analysis, and were capable of predicting the lateral spread, roll separating force, roll torque, and local stresses, strains and strain rates. This computer-aided design system was also capable of simulating the actual rolling process, and thereby designing the roll pass schedule in rolling of an airfoil or a similar shape

Challenges in the Forging of Steel-Aluminum Bearing Bushings

The current study introduces a method for manufacturing steel–aluminum bearing bush-ings by compound forging. To study the process, cylindrical bimetal workpieces consisting of steel AISI 4820 (1.7147, 20MnCr5) in the internal diameter and aluminum 6082 (3.2315, AlSi1MgMn) in the external diameter were used. The forming of compounds consisting of dissimilar materials is challenging due to their different thermophysical and mechanical properties. The specific heating concept discussed in this article was developed in order to achieve sufficient formability for both materials simultaneously. By means of tailored heating, the bimetal workpieces were successfully formed to a bearing bushing geometry using two different strategies with different heating durations. A metallurgical bond without any forging defects, e.g., gaps and cracks, was observed in areas of high deformation. The steel–aluminum interface was subsequently examined by optical microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). It was found that the examined forming process, which utilized steel–aluminum workpieces having no metallurgical bond prior to forming, led to the formation of insular intermetallic phases along the joining zone with a maximum thickness of approximately 5–7 µm. The results of the EDS analysis indicated a prevailing Fex Aly phase in the resulting intermetallic layer

Numerical simulation of inductive heating processes

For product optimization regarding weight reduction, material properties have to be adapted efficiently. To achieve this, new compositions of materials can be created or the manufacturing process can be changed in a way that heterogeneous distributions of material properties are enabled. An example for such an improved process chain is the production of thermo-mechanically graded structures like shafts. The manufacturing method mainly consists of three stages. The first one is characterized by a local temperature increase of the workpiece due to inductive heating. In the second phase the workpiece is deformed and simultaneously cooled throughout the contact with the forming die. In the last step, however, a high pressured air stream is applied, leading to a partial cooling of the workpiece. The inductive heating step is controlled by an alternating current inducing a high frequency magnetic field, which causes a temperature increase due to the resulting eddy currents. To analyse this process, the coupling between the electric and the magnetic field is described by the fully coupled Maxwell equations. Moreover the heat conduction equation is considered to describe thermal effects. To solve this multifield the equations are in the first step decoupled using an additional time differentiation. In the second step an axisymmetric case is considered, motivated by the fact that the inductive heating process of a cylindrical shaft is analysed. Afterwards the resulting equations are spatially discretized by the Galerkin finite element method. The temporal discretization is carried out via the Newmark method so that afterwards the electrical source distribution can be achieved. As a consequence the temperature evolution is determined in a postprocessing step

FE analysis in time domain of Simultaneous Double Frequency induction hardening

In questo lavoro è stata effettuata una simulazione nel dominio del tempo del processo di tempra ad induzione in doppia frequenza, sia per il problema elettromagnetico che per quello termico. Il modello considerato tiene conto di tutte le non linearità del materialeope