Stainless steel sections form the basis of constructional and manufacturing projects. While the majority of structural steel members are hot rolled, smaller and more precise sections may be cold drawn or machined.
Cold drawn or machined sections offer a huge increase in dimensional accuracy. This happens usually at a premium cost. Carried out at room temperature, lubricated steel billets are pulled through a die for this. So the workers produce a finished shape of high dimensional accuracy and good physical properties. As well as creating an accurately-sized section, cold forming also imparts a highly polished surface finish and a strength-enhancing. This is due to alignment of the grain structure. While round bar and other simple shapes can be drawn fairly readily, more complex shapes usually require multi-pass working to create the final size and shape characteristics.
If further accuracy is required, the physical machining of larger material sections may also be needed. Able to produce pieces of very high dimensional accuracy – to as fine as micron tolerances – sectional machining is the choice. Traditionally carried out using slab or end-milling processes, the machining of steel or stainless steel sections is popular in high technology industries. These include aerospace and high performance machines where accuracy trumps cost. For this, a cost saving method is the combination of both technologies. But nonetheless, a cold drawn shape is used for further precision machining.
Sectional machining is becoming enhanced by newer technologies such as ultra-high tolerance CNC machining, laser cutting, and chemical machining.
Machining will never impart the same structural properties that cold drawing can produce. But parts made by this process also do not generally require annealing or further working to make them usable in many applications. The choice between the two processes becomes a trade-off between the required strength, the accuracy of the section and the overall amount or length of material that is required. Cold drawn section can be quickly produced in long sections whereas the machining of a similar section is impractical or prohibitively expensive.
Both technologies offer significant advantages over hot-rolling material but the final application and the practicalities of processing become the driving factor in selecting the appropriate process.