Structural applications of steel have long made use of elongated beams with carefully designed profiles, whose geometry gives them specific mechanical properties. Nowadays, the variety of cutting and joining techniques are available which means increasingly intricate steel sections can be produced to meet a growing set of applications.
This article summarizes some of the main cutting and joining techniques used in the production of customized steel sections.
Structural Applications
Towards the end of the 19th century, the engineer Benjamin Baker made a bold decision: To construct the world’s longest single-cantilever bridge out of steel. Formerly untrialled in any applications of this scale, Baker knew that the malleability and strength of steel made it the perfect material for load-bearing applications in engineering.
The Forth bridge is still regarded as an engineering marvel. At the time it made an undeniable statement of steel’s potential. Ever since, the role that steel plays in modern-day construction and engineering would be difficult to overstate. Structural steel is a vital part of any engineer’s toolkit, and without it the skyline of the modern world would be drastically different (not to mention much lower).
Steel is now one of the most frequently used engineering materials, due to its versatility.1 The highly tuneable nature of steel both in alloying and manufacturing lends it to a wide range of applications.
Steel production starts at the chemical level, where a host of alloying elements in trace quantities can impart desirable properties. Carbon often defines the purpose of a steel, controlling strength and ductility.
Corrosion resistance is added by elements such as copper, chromium and nickel,, making alloys suited to applications such as highway bridges.2 Increasing the mass fraction of chromium to 10.5% yields stainless steel, whose famed corrosion resistance has earned it use in surgical and laboratory equipment worldwide.3
The material properties of steel are also determined by geometry. The ubiquitous I-beam is a key example: often most economical for conventional structural applications, the I-beam can efficiently handle bending or shear loads in one direction.
It is also easily manufactured, along with several other cross-sections, by rolling from a single piece of metal. However, while rolled sections suffice for many applications, a far greater range of properties can be achieved by using cutting and welding techniques to fabricate custom sections.
Different Cutting Processes for Steel Sections
Steel can be cut in a number of ways:
Flame cutting is a simple yet effective technique that has been used for over a century to cut carbon and high-strength low-alloy (HSLA) steels.4 A mixture of oxygen with propane or acetylene is burned to produce a hot flame which is able to cutt steel ranging from 6 mm sheets to several-inch-thick pieces.
A clean and accurate cut face is produced by flame cutting, but can, for some applications, require the use of additional machining due to the creation of a heat-affected zone (HAZ) around the cut edges. This creates a problem for very thin materials, which can be cut more precisely using other methods.
Plasma cutting was developed in the 1950s as an alternative to flame cutting that can cut high-alloy steels such as stainless steel. It uses an arc of plasma (ionized gas) to apply heat to the steel.
The focused plasma jet has thermal and kinetic energy that melts the steel and expels material from the kerf. As well as being highly efficient and accurate, boasting a typical tolerance of 0.5mm, plasma cutting can be used to cut any metal. 5 6
The most precise steel cutting process is laser cutting, which uses heat in a very precisely controlled area. Depending on the steel being cut, the heat can ignite an oxygen burning process (as in flame cutting) which completely evaporates the steel, or will be sufficient to melt the steel, in which case high-pressure nitrogen is used to blow the molten material away.
While it is not suitable for cutting reflective metals, the highly focused laser beam enables huge reduction of the HAZ and can achieve very high tolerances – typically 0.1-0.8mm dependent on the sheet thickness. 7
The most versatile option for cutting steel is water cutting. A high-pressure water jet carrying abrasive particles can cut through steel with no heat damage to the workpiece, and with a surprisingly low tolerance of around 0.5mm.8
Water cutting is an extremely adaptable and exact cutting process for practically any material, however the costs are relatively high.
Welding Steel Sections Together
Steel sections are usually joined by welding, once cut. Since the invention of electric arc welding in the late 19th century, a multitude of welding processes have been developed for numerous applications, most of which use an electric arc to supply sufficient energy to melt the base metal and facilitate fusion.
Recent improvements in “energy beam” welding techniques such as electron beam welding and laser welding offer vast improvements in speed and accuracy in comparison to electric-arc-based techniques. The strength and low distortion of laser weld seams lends itself to high-performance technological applications such as the International Thermonuclear Experimental Reactor presently under construction in France.9 However, the high cost of equipment needed has limited use of these techniques.10
Laser Cutting and Welding Services from Masteel
Masteel UK is one company putting the advantages of laser welding to use. In conjunction with flame, laser, plasma and water cutting techniques, Masteel uses laser welding to produce stainless steel profile sections with very small weld seams.
This high precision enables quick and reliable joining of intricately cut profiles. The process is automated and efficiently scalable, making small-volume projects and one-off prototypes economical as well as large-scale manufacturing runs.
References and Further Reading
- Principles of Structural Design – W.F. Chen, E.M. Lui, Imprint CRC Press, 2005
- Design of Steel Structures – MIT Department of Civil and Environmental Engineering Spring Semester, 1999
- http://www.worldstainless.org/Files/issf/non-image-files/PDF/TheStainlessSteelFamily.pdf
- What is flame cutting? – http://www.esabna.com/us/en/education/blog/what-is-flame-cutting.cfm
- Waterjet Cutting Process Basics – http://www.esab.co.uk/gb/en/education/blog/waterjet-cutting-process-basics.cfm
- Standard metal cutting processes: laser cutting vs. plasma cutting – http://www.teskolaser.com
- Laser Cutting Tolerances – http://www.daysteel.co.uk
- Waterjet Machining Tolerances – https://waterjets.org/archive/getting-the-most/tips/waterjet-machining-tolerances/
- Review of candidate welding processes of RAFM steels for ITER test blanket modules and DEMO - P. Aubert et al, Journal of Nuclear Materials, 2011
- Laser Beam Welding - http://www.esab.co.uk/gb/en/automation/lbw/index.cfm
This information has been sourced, reviewed and adapted from materials provided by Masteel UK Ltd.
For more information on this source, please visit Masteel UK Ltd