Abstract: This paper presents the focus of research and the structure of the Collaborative Research
Centre SFB 675 “Creation of High-Strength Structures and Joints by setting up local material
properties” funded in 2006 by the German Research Foundation (DFG).
Abstract: The industrial application of stainless steels is of high importance because of their high
corrosion resistance and forming behaviour. The evolution of martensite during the deep drawing
processes leads to an increasing strain hardening of the material. In the collaborative research centre
675 “Erzeugung hochfester metallischer Strukturen und Verbindungen durch gezieltes Einstellen
lokaler Eigenschaften” (Creation of high strength metallic structures and joints by setting up scaled
local material properties), metal forming processes is being researched. Emphasis on this part of the
project is the stress-induced formation of martensite in sheet metal and bulk metal components in
metastable austenitic steel. The aim of the investigations is to develop partial structure fields of
martensite in sheet metal components in order to construct a lightweight structure. Therefore,
components are divided into stretched and non-stretched parts. This leads to a defined buckling of
components, for example in case of a crash. Furthermore, the effect of the transformation induced
formation of martensite in metastable austenitic steel should be utilised on bulk metal forming
components. Thereby special load adapted components with locally optimized properties are
producible, like austenitic ductile regions and martensitic high-strength areas.
Abstract: Within subproject A2 processes leading to local Bake Hardening (BH) effects in
multiphase steels will be investigated. The characteristic values which integrally describe the Bake
Hardening effect depend on the deformation path and the degree of preforming, as well as on
temperature and duration of the subsequent heat treatment. The thermal stability of the induced
strengthening is also determined, in order to specify the boundary conditions for thermal
assembling. Thus, they can be qualified for the assembly of locally strengthened structural
Abstract: The subproject A3 deals with the production and manufacturing and the subsequent
treatment of partially strengthened, three layered, symmetrical Sandwich Structures. With this type
of strengthening, complex material properties can be developed, e.g. high strength with high
stiffness, good thermal joining properties at the place of strengthening, as well as an improved
strength and strength absorbing ability. The forming behaviour is still widely unknown.
Abstract: The investigation of the basic principles for the production of foamed out sections using
magnesium foam for support structures by including the foaming process into the cold forming of
sections to produce indiviually locally strengthened components is the subject of this research project.
To absorb tensile stress, the metal foam will be strengthened with three-dimensional branched
struts of high-tensile materials. The quantification of the influence of locally introduced foaming
elements on e.g. stiffness alterations and the influence of the resonance frequency of the total structure
will be effected by destructive but particularly also by nondestructive tests.
Abstract: In subproject B1, local physical and geometrical effects which have only been observed so
far as side effects in the laser joining process, are to be used purposefully, in order to achieve
graded strength properties and to improve the component rigidity significantly. One aim of the work
in the first requested period is the investigation of effects of laser-based joining connections on the
structure rigidity for simplified sample geometries. A defined local strength increase will first be
done on blind seams and later on seams with suitable seam geometries. In the context of SFB 675,
laser joining processes are to be developed further so that the final assembly can take place with
and other methods to increase strength for semi-finished products without considerably changing
the local material characteristics. Beyond that, general rigidity effects of the connections are to be
used purposefully for rigidity improvement.
Abstract: High strength aluminium wrought alloys as well as powder metallurgical aluminium
alloys are limited regarding massive formability. The formability at room temperature can be
significantly affected by superimposing hydrostatic pressure. Depending on the process control, cold
forming enables locally induced strain hardening effects, whereby increased hardness or hardness
gradients can be regulated. Simultaneously, the necessity of mechanical post processing is reduced
by a metal forming fabrication of joint and connection elements at room temperature.
By splitting the component in strengthened and not strengthened regions, specially adapted
property profiles can be adjusted to the application. Thus, specially load adapted components with
locally optimised property profiles e.g. ductile or high strength, brittle areas can be manufactured. A
defined buckling or folding of a component in case of a crash can thereby be achieved.
In this project innovative tool principles for superimposed cold solid forming will be developed.
They will be used to manufacture high strength and complex aluminium structure components with
specific adjustment of local strain hardening. A tool technique is to be created in order to generate
locally hardened areas within massive structures by metal forming. Furthermore, the task is to
determine the procedures limits for superimposed cold massive forming with specifically adjusted
strain hardening of aluminium alloys.
For the realisation of these aims fundamental research has to be made, by which the coherences
between specific process parameters and the increased formability are determined. Furthermore, the
cold hardening effects are to be adjusted by cold massive forming with superimposed hydrostatic
pressure and displayed with the help of FEA.
In the long term, the analysis aims at the development of pressure superimposed forming that is
technically utilisable as a near net shape manufacturing process for high complex aluminium
structure components with selective adjustment of local properties.
Abstract: Novel manufacturing technologies for high-strength structure components of aluminium
allow a local modification of material properties to respond to operational demands. Machining and
finishing processes for changing material properties like deep rolling or rubbing are to be combined
to a single process step. Intention is the controlled modification of the component’s properties by
manipulation of its subsurface. For that purpose the essential understanding of interaction
mechanisms of the basic processes turning, deep rolling and rubbing is necessary. Influences of tool
geometry as well as process parameters on material properties are investigated. The results are to be
extended by parameter studies, done by numerical simulation. Combined processes like “turnrolling”
or “turn-rub-rolling” will be developed.
Abstract: The subproject B5 examines the welding technological processing of locally hardened
materials to produce structures and knots by means of high-freqency welding (HFW). The aim of
B5 is a defined intervention in process and plant technology to control current voltage, temperature
and compressive stress distribution of the entire weld seam. Particularly the effects on locally
hardened areas have to be measured and optimized. Also the process specific advantages of HFW
(e.g. plastic deformations and the application of an in situ heat treatment) have to be examined and
optimized to improve structural strength.