Effect of laser cutting on hardness
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    Default Effect of laser cutting on hardness

    I'm interested in the use of a gantry laser to cut steel and aluminum up to size for machining but would like to know what the consequence is as far as heat hardening on the cut edge. How deep does the hardening go and how much does it effect tool life when cutting to clean the laser cut edge?


    Brian

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    Quote Originally Posted by Raptorman0909 View Post
    I'm interested in the use of a gantry laser to cut steel and aluminum up to size for machining but would like to know what the consequence is as far as heat hardening on the cut edge. How deep does the hardening go and how much does it effect tool life when cutting to clean the laser cut edge?


    Brian
    "Steel and Aluminum"

    Well, that narrows it right down now eh ?

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    Hardening only goes so far and tooling is affected to a certain amount.
    I don't know why Digger did not say that. LMAO

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    Steel and alu in the same post ?

    Ask for a 10 cm square sample from your nearest very big laser cutter.
    Chop it up with your favourite end mill or face mill.

    A:
    Mostly insignificant.
    Hard inclusions and bad material are harder than the small haz edges on mild steel of little thickness.
    Alu cuts like butter.

    A:
    A 18 m yacht of 8-10 mm mild steel might take 2 hours for 20 sheets of steel to cut.
    The edges haz could have 1% of effect on tool life.

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    All I run on laser is stainless.... it does harden the edge on holes that are cut and dulls the countersink quicker than a punched/drilled hole. We had one vendor in particular for some reason had a much more significant problem with this.... but, I think the newer technology with Fiber Laser minimizes the heat effected zone. Our current vendor runs fiber lasers while some of our previous vendors had CO2 units. The fiber laser is 4-5 times faster.....

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    Yeah, I included Aluminum not because I was expecting a hardening issue but because it's a material I plan to cut with the laser. I could have gone down a list of different steel types but how long would that list be? What I wanted was a sense as to the effect and I appreciate the replies even if some are more snarky than informative. It does appear that fiber lasers are beginning to dominate over CO2 and speed of cut would be a good indicator of the amount of heating so if fiber is that much faster it stands to reason there should be less heating and thus less hardening. Having an idea on the depth of the hardening might inform a better choice for dealing with it -- perhaps grinding would be a good option.


    Brian

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    Quote Originally Posted by digger doug View Post
    "Steel and Aluminum"

    Well, that narrows it right down now eh ?
    There are a lot of steel formulation -- should I have listed all of them? There will no doubt be variations from one type to another but a ballpark answer at this stage would be sufficient.


    Brian

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    Quote Originally Posted by Raptorman0909 View Post
    There are a lot of steel formulation -- should I have listed all of them? There will no doubt be variations from one type to another but a ballpark answer at this stage would be sufficient.


    Brian
    If you want a good answer on the hardening affect … Yes

    There is NO ballpark answer, just like there is NO ballpark steel.

    Have you cracked a book lately listing the various kinds of steels ?

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    Simply put, the hardness of the steel edge will mostly depend on the carbon points of the steel. < 20 (like 1018) not much effect, >30 and you will get significant hardening. Most alloys are similar, like XX20, XX40 . Tool steel will harden, no matter what kind.

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    Quote Originally Posted by Red James View Post
    Simply put, the hardness of the steel edge will mostly depend on the carbon points of the steel. < 20 (like 1018) not much effect, >30 and you will get significant hardening. Most alloys are similar, like XX20, XX40 . Tool steel will harden, no matter what kind.
    Thank you Red James, it makes sense that carbon content would be a major factor in determining the effect. As to depth of hardening logically the speed of the cut would seem to be the major factor in that a slow cut would tend to heat more than a fast cut -- that would argue in favor of high power lasers and lasers of the right wavelength and focusing. A more powerful laser would be more expensive, but the payoff would be reduced cutting time and greater throughput as well as reduce work hardening that could lower tooling costs by reducing the wear on the tooling in downstream machining.

    As an aside from the hardening issue, while it might appear aluminum would be easier to cut by laser, my understanding is that for any given laser power the cutting rate for steel is about 2X that of aluminum.


    Brian

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    Quote Originally Posted by digger doug View Post
    If you want a good answer on the hardening affect … Yes

    There is NO ballpark answer, just like there is NO ballpark steel.

    Have you cracked a book lately listing the various kinds of steels ?
    Well if the carbon content is the major factor that determines the hardening effect then we could argue the ballpark begins with very low carbon steel and ends with very high carbon steel and that that range effects hardening to a given depth based on cut rate. I have not seen any references that detail this which is why I asked here in the first place.

    Oh, according to the World Steel Association there are about 3500 different grades of steel -- did you want me to list all of them? I don't quite understand the need to turn a straight forward question into 3D chess!


    Brian

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    IF the steel is "air hardening", expect hardening after laser cutting.

    If the material is NOT air hardening, don't expect hardening in the HAZ after laser fabrication.

    It's not rocket science, but you need to do you own home work!

    By the way, What is HARD? And "heat hardening" is too vague to consider. HEAT softens metals!

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    Quote Originally Posted by CalG View Post
    IF the steel is "air hardening", expect hardening after laser cutting.

    If the material is NOT air hardening, don't expect hardening in the HAZ after laser fabrication.

    It's not rocket science, but you need to do you own home work!

    By the way, What is HARD? And "heat hardening" is too vague to consider. HEAT softens metals!
    You harden steel by first heating it then cooling it quickly so heat is most definitely required. In the case of a laser the heat from the laser and the melted steel transfers heat to the edge and as the laser move beyond the heat sink of the rest of the steel cools the edge very quickly -- hence the hardening. Heat no more softens than hardens as both require the proper cooling to do there job.


    Brian

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    No one mentions the type of laser to be used.
    Some will do nothing to the hardness, others...massive.
    Unfortunately the ones that cut "cold" are very expensive.
    Bob

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    Quote Originally Posted by Raptorman0909 View Post
    You harden steel by first heating it then cooling it quickly so heat is most definitely required. In the case of a laser the heat from the laser and the melted steel transfers heat to the edge and as the laser move beyond the heat sink of the rest of the steel cools the edge very quickly -- hence the hardening. Heat no more softens than hardens as both require the proper cooling to do there job.


    Brian
    You are Jabbering like a kid.

    Heat never hardened any metal. Not even Flame Hardened cast iron lathe beds. It's always the cooling that does the hardening. IIRC the term is "heat treating" to get the desired results. " Heat hardening" is too vague a term to be meaningful.

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    from experience with mild steel and CO2 laser, basically no effect on hardness, there is however a "film" on the cut edge that should me removed (mechanically) prior to electrolytic zinc plating, I had a batch of parts where the zinc would peel off of a laser cut edge, rest of the part wasn't affected, it was a hot rolled sheet 5mm thick, so had some scale on the flats, and the galvanizing shop pretreatment was good enough to handle that, but zinc on the laser cut edge still peeled

    I've also sent out some parts to be cut from a material very similar to 4130 (2mm thick sheet, same laser), and the laser cut edge was very hard, a file would skate on it, but the hard crust depth was very shallow, I didn't measure, maybe 0.02~0.04mm (~0.001")

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    Quote Originally Posted by CalG View Post
    You are Jabbering like a kid.

    Heat never hardened any metal. Not even Flame Hardened cast iron lathe beds. It's always the cooling that does the hardening. IIRC the term is "heat treating" to get the desired results. " Heat hardening" is too vague a term to be meaningful.
    Well actually you're doing the jabbering -- go ahead, plunge a room temp piece of high carbon steel into water and tell me how much harder it got. Go ahead.

    Its require the heat first. Other than that you're spot on.


    Brian

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    Quote Originally Posted by jz79 View Post
    from experience with mild steel and CO2 laser, basically no effect on hardness, there is however a "film" on the cut edge that should me removed (mechanically) prior to electrolytic zinc plating, I had a batch of parts where the zinc would peel off of a laser cut edge, rest of the part wasn't affected, it was a hot rolled sheet 5mm thick, so had some scale on the flats, and the galvanizing shop pretreatment was good enough to handle that, but zinc on the laser cut edge still peeled

    I've also sent out some parts to be cut from a material very similar to 4130 (2mm thick sheet, same laser), and the laser cut edge was very hard, a file would skate on it, but the hard crust depth was very shallow, I didn't measure, maybe 0.02~0.04mm (~0.001")
    Thanks, that was the kind of feedback I was hoping for. Did you have to finish machine the laser cut edge of the 4130 and if so what was the effect on tool life?


    Thanks,

    Brian

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    AFAIR round holes I drew up 1mm per side under, hss drilled them after to be reamed to final size, as I said, the hard crust is very thin, so dont baby it when drilling, it was couple dozen parts with few holes, I think one drill handled all of them, cleaned up outside perimeter with zirconia flap disk on a die grinder or angle grinder before welding

    I just wanted to point out that hardening does happen, I remember scratching brake press dies with first parts before noticed this

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    Cutting with Oxy as an assist gas will give very different results than cutting with Nitrogen in steels.


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