Abstract
M.Ing.
During all manufacturing processes it is crucial to use certain design
criteria and guidelines. Special care should be exercised when the final
product of a manufacturing process is used in the automotive industry,
because the failure of such a component may have tragic consequences.
The failure of a bus chassis in the public transport sector is an example of
a case where the failure of a product can have serious consequences. In
recent years it has become common practice to use corrosion-resisting
steel in the manufacture of these vehicles. The reason for this is the
corrosion caused by a prolonged service life and adverse conditions such
as salted road surfaces (The salt is used to melt the ice that forms on
roads, particularly in European countries).
These bus structures consist of tubes of varying size and geometry, and
the manufacturing process of these tubes is considered in the present
investigation. In a tube manufacturing process the design criteria may
consist of such properties as the tube size and geometry, the thickness of
the sheet that is used and the radius of the corners of the tube. Design
criterion is also dependent upon the material that is used. The change in
mechanical properties of the material during a manufacturing process is
an important consideration during the establishment of design guidelines. The purpose of this investigation is to study the effects of particularly the
cold forming manufacturing process on the mechanical properties of the
material. The material used is 3CR12 corrosion resisting steel, a
proprietary alloy also known as Type 1.4003, that was developed by
Columbus joint venture as a cheaper alternative to stainless steels.
3CR12 is not a substitute for stainless steel but it is an alternative to
treated mild steel, providing a cost-effective solution to corrosion.
An experimental investigation is conducted into the forming of 40mm
3CR12 square tubes and normal plate bending of 3CR12. Various
different wall thicknesses and bend radiuses are considered.
A numerical investigation consisted of simulating the above-mentioned
manufacturing processes using non-linear finite element analysis and then
comparing its results to the experimental investigation. The experimental investigation showed that substantial work hardening
occurred in the corner regions of the tube during forming. A loss of up to
70% of 3CR12's ductility may result in the corner regions. The work
hardening at the inside of the tube was found to be higher than at the
outside. A region of very little work hardening near the middle of the
tube wall thickness was also identified (neutral axis). This neutral axis
also seems to shift slightly more to the inside of the tube with thicker
wall sections.
The numerical analysis confirmed the experimental observations. An
excellent correlation between the experimental and numerical results was
achieved.