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laser cut mild steel

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Dave Halford23/06/2019 17:42:30
556 forum posts
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Hi all

How does laser cutting create a hard skin on ordinary en3 mild steel?

Bill Chugg23/06/2019 20:12:10
973 forum posts
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All down to the laser heat.

Bill

Dave Halford23/06/2019 20:19:06
556 forum posts
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But it's not supposed to heat treatable steel ???????

JasonB23/06/2019 20:23:38
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I think it is due to the use of CO2 or Nitrogen in the cutting process to blow the molten metal away, some of the carbon from the CO2 gets into the metal and raises it's carbon content a bit like case hardening. The Nitrogen has a similar effect to Nitriding.

Dave Halford23/06/2019 20:53:07
556 forum posts
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Thanks Jason, that makes sense.

Bill Chugg23/06/2019 21:17:24
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Most laser cutters use a jet of high pressure gas, many use nitrogen (n2), some use CO2, to help blow the molten metal away from the kerf. in the plasma stream, N2, becomes ionized and becomes atomic Nitrogen. Atomic nitrogen hardens steel as well, not as much as carbon does or as deep. and of course if it is CO2, then that just adds carbon to the molten surface. a micro-hardness survey (either vickers, or my perference for something this small which is Knoop, the indenter for knoop is wider but not as tall so you can stack the indentions closer together vertically which makes surveying something this thin much easier.) of a polished section across a HAZ will show how hard and how deep it is.

Found this on the net which ties in what Jason said.

Paul Lousick23/06/2019 23:49:10
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An alternative to laser cutting is water jet cutting which does not have the problem caused by heating the metal.

Materials are cut using a jet of pressurised water as high as 60,000 pounds per square inch (psi).

To increase cutting ability, abrasives such as garnets and aluminum oxide are often added. The overall process mimics erosion in nature, just at a much higher speed and concentration. Water jets are capable of cutting many industrial materials including stainless steel, titanium, aluminium, tool steel, ceramics, granite, and armour plate.

Paul

Ian McVickers24/06/2019 12:27:21
160 forum posts
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The laser will heat the metal around the cut to above its transformation point and this will create a Heat-affected Zone. The HAZ for laser cutting is quite small and localised near the cutting point. For CO2 lasers Oxygen is mainly used for cutting mild steel but Nitrogen can also be used for high pressure cutting. Nitrogen mainly used for high pressure cutting Aluminium and Stainless Steel. At least that's how we do it.

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