Innovative Stainless Steel Applications in transport ... - Euro Inox

3. Lightweight structures and design
Most stainless steel structures in transport vehicles are made of hollow sections.
Examples include bus-body frames and sheet-metal parts, either flat (e.g. bus-body
surface sheets) or formed (e.g. roll-formed profiles in trains or metro cars). A relatively
new technology, of great potential, is the use of all-steel sandwich panels. It offers the
possibility of massive weight reduction. This chapter briefly reviews hollow-section and
sandwich-panel design principles. Further information on the manufacturing of such
structures will be found in Chapter 4, “Manufacturing issues in lightweight structures”.
3.1. Stainless hollow-section structures
This chapter discusses the manufacturing, dimension ranges and properties of stainless
structural hollow sections readily available on the market. Apart from common
“catalogue” or standard dimensions and materials, hollow sections may also be
purchased in other materials and tailored dimensions, depending on the manufacturer´s
capabilities. A more thorough presentation of standard stainless steel hollow sections
and their manufacturing and applications can be found in a recent handbook (Yrjölä
2008).
3.1.1. Manufacture of hollow sections
Structural hollow sections are usually made by cold forming and welding. Cold forming
is carried out either by roll forming or by bending separate hollow sections. Welding
methods used are TIG or plasma arc welding, HF (high frequency induction welding)
and laser welding (Yrjölä 2008).
Roll forming
Roll forming is a continuous manufacturing method, in which steel strip is cold-formed
on the production line using a number of roll-pair stands. The material used is coiled
steel strip, longitudinally cut to the width corresponding to the dimensions of the hollow
section. The steel strip is uncoiled, welded to the previous strip and fed to the rollforming
line. If required, strip-edge quality can be improved by edge trimming before
forming. There are two different forming methods for square and rectangular hollow
sections: round forming or direct forming.
In round forming, steel strip is first formed into a circular hollow section then welded
and formed with profiling rolls into a circle, square or rectangle. Steel strip can also be
directly formed into a rectangle, by bending it from the corner zones and welding the
seam. The latter method is used when manufacturing hollow sections with large outer
dimensions and/or in the case of small quantities.
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