Core Competences

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Design and Charakterization of Moulding Materials

Motivation

Due to ever increasing regulations targeting health and environment friendly production, light-metal foundaries use more and more inorganically bound cores. Their use reduces harmful emissions considerably, when compared to organically bound cores. Those advantages come with new technical challenges nevertheless. For one, removing the core from the cast part gets more laborous and hence stresses within the part increase. In addition gas-developement and hot-deformation while casting differ considerably from current models.

A glimpse at current projects:

  • correlation between core-blowing parameters and core characteristics
  • simulating inorganically bound moulding material on a micro scale
  • design of a fracture model

Objective

Prediction of moulding material and process properties based on physical and statistical models.

Competences of the Chair

>> moulding material characterization (also refer to "Material-Characterization in Founding")

  • fracture sress
  • elongation at fracture
  • gas permeability
  • casting defect

>> core blowing experiments and influence analysis using different binder-sand combinations

>> moulding material qualification considering hot-deformation

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Material Characterization in Founding

Characterizing metals and moulding materials is an important aspect of founding research. Two routes are of particular interest:

Optimizing Production Processes

  • optimizing the heat treatment process energetically depending on the alloy
  • identifiying process windows by simulation and trial

Material Design

  • tuning micro-structural conditions by heat treatment
  • micro-structural development, modelling and simulation

Motivation

Technical challenges in production reach the limits of experience based solutions, due to increasing complexity and ever narrowing process windows. Therefore an increasing depth of knowledge is essential about the processes taking place within the material along the whole production chain. Two examples are the integration of sensors into cast parts and opening new fields of application by adapting alloy compositions.

A glimpse at current projects:

  • optimizing the heat treatment of cast iron energetically
  • adapting cast irons micro-structure to better fit hydraulic requirements
  • integrating sensors in the parts while casting
  • simulating micro-structure

Objective

Quantifying phase changes and consideration for process control

Competences of the Chair

>> residual stress analysis

  • borehole method
  • cutting free
  • integrated sensors (FBG)
  • nano-indentation

>> electrical measurement

  • DMS measurement
  • temperature measurement

>> optical measurement

>> metallography and fracture surface characterization

  • LOM
  • REM with EDX
  • preparation and etching methods

>> characterizing moulding materials

  • fracture sress
  • elongation at fracture
  • gas permeability
  • casting defect

In Cooperation with Partners:

>> diffraktion methods (FRM II)

  • neutron diffraction
  • X-ray diffractometry

>> atom probe tomography (KIT)

>> synchroton (ESRF)

Analyzed Subject Areas

  • quantitative in-situ phase analysis
  • moulding material analysis
  • bimetall-composite characterization

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Shear Cutting

In addition to general research work in the field of forming technology, the chair has specialised in the field of shear cutting for many years and can draw on a wealth of experience.

With the experimental technology available at the chair and the know-how built up, the following processes are possible:

  • Production of shear-cut samples of various geometries with sheet thicknesses from 0.1 to 10 mm, varying process parameters such as die clearance or cutting edge geometry
  • Various process variants such as fineblanking or two-stage shear cutting possible
  • Cutting of electrical sheet, steel, aluminium, copper, bronze, hybrid and plastic sheets
  • Wear investigations with variation of lubrication, sheet material, tool stiffness, thermal current, active element material and coating
  • Preparation of samples for the identification of the fatigue strength of shear cut edges
  • Investigation of embossing, clinching and bending operations, also in combination with shearing operations.
  • Experimental determination of the edge crack sensitivity of shear-cut samples

Established evaluation methods at the chair:
Determination of required values for the evaluation of the cut surface characteristics, the wear behaviour and the behaviour of shear-cut edges in subsequent operations or in application cases:

  • Quantification of active element wear, adhesion and sliver formation
  • Measurement of process forces
  • Measurement of cut-surface characteristics
  • Macro and micro hardness testing
  • Identification of characteristics for the consideration of the edge crack behavior in the simulation
  • Identification of the electromagnetic properties of shear-cut electrical sheets


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Manufacturing efficient electrical machines

The Chair of Metal Forming and Casting investigates blanking of electrical steel within the DFG projects “Manufacturing of Electromagnetic Components from Non-grain Oriented Electrical Steels” and "Focused Use of Residual Stress in Electrical Steel as Means of Improving the Energy Efficiency". The analysis of optimized production processes aim at increasing electrical drive efficiency.

In order to convert electric into kinetic energy in electrical drives, magnetic fields must be generated. Therefore, the magnetic properties of the electrical drive’s main component, the so-called electrical steel, are decisive for its efficiency. It has been shown, that the manufacturing process of the electrical sheet metal has an influence on its magnetic properties. This is mainly due to residual stress induced in each processing step. On the one hand, residual stress due to shear cutting of electrical steel decreases an electrical drive’s efficiency. On the other hand, the targeted use of embossing induced residual stress allows precise guidance of magnetic flux to enhance the magnetic properties of motor cores.

Focusing on shear cutting of electrical steel, process parameters have a significant impact on the magnetic properties. Using optimized parameters – small cutting clearances and sharp tools – decreases losses and electricity demand of an electrical drive. Tool wear was identified as the main source of magnetic property deteriorations due to the production process. The target of the research project is providing optimized production parameters for our industry.

Embossed flux barriers demonstrate the positive effect of residual stress in electrical steel. Conventional designed as cutouts, flux barriers allow precise guidance of magnetic flux but reduce the mechanical strength of a rotor construction. To operate electrical drives at higher rotational speed, an alternative flux barrier design is investigated. As residual stress deteriorates the magnetic material behavior, locally induced residual stress by embossing works as a flux barrier. Different embossing geometries are analyzed to create a construction guideline for embossed flux barriers to achieve a maximum energy efficiency for particular electrical drives.

Continuous and Compound Casting

Continuous and compound casting compose one of the main research activities of the chair. Those processes promise significant advancement in founding. Therefore a scientific approach is highly interesting.

The following aspects are the main reasons for research activities:

>> material combinations, that facilitate loadcases and promote light weight constructions

  • hybride structures
  • complex properties
  • cost optimized material usage

>> shortening of production chains

  • integrating joining procedures into casting
  • omitting process steps like chemical cleaning and heat treatment

>> resource efficiency

>> using thermal and latent heat for forming compounds

  • material efficiency
  • time saving by process route shortening

>> potential of substance joining for compound formation

>> freedome of design and change

Competences of the Chair

>> process investigation by simulation and trial

  • continuous casting
  • compound casting
  • incremental casting

>> analysis of compound formation

  • remelting and cristallization
  • diffusion
  • wetting
  • micro-formfit

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