Thixoforming : Semi-solid Metal Processing

10
Thixoforging and Rheoforging of Steel and Aluminium Alloys
Gerhard Hirt, Rene Baadjou, Frederik Knauf, Ingold Seidl, Hideki Shimahara, Dirk Abel,
Reiner Kopp, Rainer Gasper, and Alexander Sch€onbohm
10.1
Introduction
Thixoforging is closely related to the drop forging process. In contrast to the
thixocasting process, the semi-solid material is inserted into the lower half of
horizontally sectioned dies. On closing the dies, the material is deformed until the
die cavity is completely filled in one step. The force transmission for the forming and
densification step is applied across the whole surface of the die so that the component
is compressed during the complete solidification of the material [1–3].
The thixo lateral extrusion process involves charging the semi-solid material
through an aperture into already closed dies (Figure 10.1). As opposed to thixocasting,
the plunger reaches into the die cavity and regulates the densification pressure
directly in the dies. Furthermore, the injected material equals the weight of the
finished component as in thixoforging, because of the abolition of an ingate as used
in thixocasting processes [3].
The modification of the tools and dies for thixoforging and thixo lateral extrusion
by inserting additional components makes it possible to produce composite parts.
The flowing material surrounds inlays, which act like additional tools. In contrast to
the compound casting process, there is the possibility that alloys with a comparable
melting point are applicable without destroying the geometry by melting [4].
Figure 10.1 shows a schematic view of thixoforging and thixo lateral extrusion,
which enable similar components to be obtained by different tool concepts.
Specific advantages of this process compared with thixocasting are shorter flow
lengths for the complete filling of the dies and a higher compression during the
solidification that minimizes pores, which are caused by shrinking. For example, in
the case of thin-walled components made of aluminium, the gas inclusion is very low
so that a weldable microstructure can be produced even for filigree parts as used in
the automotive industry. The process also has disadvantages compared with
A List of Symbols and Abbreviations can be
found at the end of this chapter.
j369