Magazine Articles
The articles below are from the Winter 2008 Issue of the AILU Magazine
Energy input from oxidation in laser-oxygen cutting of mild steel
One of the mainstays of modern industry involves the use of a laser in conjunction with an oxygen jet to profile mild or carbon steel. The laser-oxygen cutting process was invented in 1967 in the UK by Peter Houldcroft and is nowadays used to profile mild steel up to 25 mm thick.
This paper provides a description of the chemical and physical phenomena which take place during laser/oxygen cutting, highlights some poplar misconceptions and provides guidelines for use in future theoretical models of the process.Since the early 1970’s researchers have been trying to develop physical and mathematical models of laser-oxygen cutting of mild steel with varying levels of success. Most theoretical models estimate maximum temperatures in excess of 3000K (approximately the boiling point of mild steel) and conclude that the melt inside the cut zone will boil.
This paper corrects many of these erroneous assumptions and its conclusions provide a number of essential guidelines for future models of laser-oxygen cutting of mild steel.
John Powell, Dirk Petring, Vasant Kumar, Saeed Al-Mashikhi, Alexander Kaplan, Katy Voisey
IMAGE: A cross-section of laser-oxygen cut mild steel showing hte brittle oxide layer on the cut edge
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Additive manufacturing of small metallic components
Rapid manufacturing techniques have reduced the time to market of complex parts. IREPA LASER is experienced in this field; it has a patented coaxial powder cladding nozzle and has developed tools for rapid manufacturing of large metallic parts. This study describes the adaption of the process for the freeform manufacture of small structures and components.
Over the last few years, rapid manufacturing techniques (RMT) based on coaxial laser cladding process have been studied. As they use simpler tooling and allow the production of complex shapes, they can provide a good alternative to machining or casting.
There are a number of commercial laserbased metal deposition processes (e.g. DMD™, LENS™), but for micro cladding the approach taken by IREPA LASER has been to adapt its own patented nozzle design to create CLAD® (Construction Laser Additive Directe) - a new form of metal deposition process.
A process for manufacturing small parts has been successfully developed and validated. The patented coaxial nozzle has been optimised for low powder feed rate and tested during a manufacturing phase with a low power single mode fibre laser. Thin shell components and small parts (wall width ≥ 500 µm) have been produced free of critical porosity and cracks and with a powder catchment efficiency of more than 50%. The process allows the building of sound parts, and provides, in certain cases, an alternative to machining. This additive process can be completed directly from a CAD models, allowing the construction of whole parts without a mould or tools and also the addition of features to machined/cast parts.
Simon Sankaré and Didier Boisselier
IREPA LASER, France
IMAGE: An example of the process shows a metal flange modified by adding tubes (AISI 316L SS)
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