Tempering laser cut parts

[Kevan ShawParticipant @kevanshaw32462]

I just received a batch of parts from Model Engineers Laser. These are all steel and come with a notice that there is likely to be hardening along the cut faces. The option of heating to 400°C to temper is mentioned, I don’t have a tempering oven so asking how I can best achieve this. My principle heating kit is a plumbers blowtorch, can I use this if so what colour should I be looking for?

The parts concerned are coupling and connecting rods and some smaller valve gear parts so maintaining straightness and flatness is a concern but so is good even machinability. Any thoughts?

 

[Dave SParticipant @daves59043]

Are they a hardenable steel?

I’d check them with a file and go from there.

i didn’t have any problems with the HAZ on the laser cut parts for my CNC build

Dave

[SillyOldDufferModerator @sillyoldduffer]

Tempering requires a long soak, hours, at relatively low temperature, so a quick blast with a hot blowtorch isn’t right.

I’ve an article where LBSC mentions leaving parts overnight on top of a dying coke brazier.   Likewise, forum members who work with chilled cast-iron sometimes recommend leaving hard castings overnight on the remains of a coal fire.   I don’t have a brazier or fireplace!

Anyone tried a barbecue kit?  The simple type consisting of a bed of charcoal in a small tin tray.   In principle, set fire to one in the garden and wait for the charcoal to glow.  Then put the items on top of the charcoal and cover to smother the fire. Leave until cool, overnight.  The cover should be an insulator to slow down the cooling.  Maybe a metal dustbin lid with an old towel on top.  Dredging my unreliable memory, I think LBSC also suggested whitewashing delicate parts to protect them from oxidisation and dirt.   The modern equivalent would be a stationery correcting fluid like Tippex.

The best way is an oven! Clean, with accurate temperature control.   Making an electric oven from Nichrome wire, glass-wool, and insulating fire brick isn’t rocket science, but surely too much bother and expense for a one-off job.

Silver-steel can be tempered in a domestic oven, but that’s a special virtue.  Most steels need higher temperatures.  May be the warning is just in case the laser cutter unluckily causes severe hardening, when mostly it’s not a problem. Dunno, I’ve no experience of laser cut metal.  Be interesting to see what others suggest.

Dave

 

 

[JasonBModerator @jasonb]

Not sure why you would want to temper them. Some laser cutters do leave a bit of a hard edge which is best dealt with by annealing or normalising the steel.

Heat to red and hold there for 5mins if it is just thin steel and then allow to cool slowly

Depending what the steel was it may also have a thin layer of mill scale which is best removed by 20-30mins in pickle, Brisk Cleaner is what I use. This will also remove any blackening left by your heating efforts.

[not done it yetParticipant @notdoneityet]

Why would a domestic oven not be sufficient to lower the hardness of any edges to a reasonable value?  Doesn’t need to fully soften those edges, only make them less brittle, if that is important.

[Richard SimpsonParticipant @richardsimpson88330]

Just a question gents, I’m asking because I don’t know, not because I’m suggesting anything. So, not to be controversial but, why bother?  Why is having a hardened edge a problem?  I assume any bearings will be fitted with bushes so there are no running surfaces involved so what would be the problem of leaving them as they are?

Only think I could possibly think of might be surface cracking, is that the reason?

[JasonBModerator @jasonb]

 flatness is a concern but so is good even machinability

NDIY Reason enough for me to normalise, particularly if any of that machining may be on only one side of the parts

[JasonBModerator @jasonb]

Richard the hole for those bushes may not be a good enough fit if laser cut and need finishing, laser cut holes may need tapping,edges may be too rough and need machining or draw-filing, cross holes may need drilling for pins or oil points, etc all reasons why you may not want to work a hard surface.

[noel shelleyParticipant @noelshelley55608]

A domestic oven at a pinch or a home made oven using a couple of oven elements and a stat wound up to 400c is the thing you need. A K type thermocouple and a kiln controller would be the ideal or even a secondhand pottery kiln. There’s a few ideas as to how to do it WHY is up to the OP ! Noel

[Nigel Graham 2Participant @nigelgraham2]

Outside surface such as the edges of plates may yield to careful use of a small disc grinder or a linisher. A tungsten-carbide drill might help with the holes, enlarging them enough for finishing to fit or tapping diameter.

[JasonB]

On JasonB Said:

Richard the hole for those bushes may not be a good enough fit if laser cut and need finishing, laser cut holes may need tapping,edges may be too rough and need machining or draw-filing, cross holes may need drilling for pins or oil points, etc all reasons why you may not want to work a hard surface.

OK, thanks Jason.

[BazyleParticipant @bazyle]

I’ve never used laser cut parts but given they know what the parts are for and the finishing required I would have thought they would offer the appropriate annealing as standard, with an option for no post treatment at a discount.

[bernard towersParticipant @bernardtowers37738]

Amazing how the laser hardens low and ultra low carbon steels when we in the workshop have to add something to it to do that!!

[JasonBModerator @jasonb]

The CO2 lasers are more prone to creating a larger HAZ than fibre lasers, there is a clue in the CO2 as to why.

Any dirt, scale or oil on the surface such as you may find on annealed, pickled and oil sheet can also get burnt and the tiny amount of carbon produced alloys with the cut surface.

[Martin KyteParticipant @martinkyte99762]

Not sure I follow you regarding the CO2 lasers Jason. That’s just the lasing medium surely which just dictates the wavelength of the photons in the beam. No CO2 at the target.

[JasonBModerator @jasonb]

Yes, sorry I was getting mixed up with the gases used to clear the cut. I think Nitrogen leave it cleaner where oxygen can leave an oxide scale

[FulmenParticipant @fulmen]

Correct. Oxygen is more effective (carbon steel) but at the cost of more slag. Nitrogen will give a cleaner cut.

The reason why even mild steel can take a harden has to do with cooling rate. Even low carbon steel can be hardened (to a degree) with very rapid cooling. The rapid heating of the laser allows the heat to flow very quickly to the cold surrounding material, similar to welding. But it shouldn’t be too bad on mild steel, it won’t be anywhere as hard as high carbon steel.

Annealing can’t hurt, heating to a dull grey should do the trick if you want to cover your bases. Dull red (in darkness) is probably around 500C and would be overkill. Anything above 250C will help.

 

[jaCK HobsonParticipant @jackhobson50760]

Depends on steel. But… generally the heat affected zone should be shallow so you should not need long tempering times. Just get to temp and you done.

You don’t have to worry about getting too much above 400C so long as you don’t go to austentite @ 770C which will be glowing red. So just heat with your gas torch as much as you can but stop if you see any sign of a glow. If going by tempering colour, then go beyond blue and into grey.

depending on the steel, you probably don’ even have to worry about going over 770.

if it is  oil hardening tool steel e.g. O1 then it might be more tricky.

If air hardening (A1, HSS) then much more tricky.

 

[FulmenParticipant @fulmen]

Looking at their website they don’t deliver anything beyond S355 in the mild steel category.

[Kevan ShawParticipant @kevanshaw32462]

Thanks for the reply’s I have a set of coupling rods I am working on that need machining to all faces. I have tried the punisher approach to start with and will start machining soon to see what happens. I bought a 3rd blank to make mistakes in🤣

[JAParticipant @ja]

I have bought items from Model Engineers Laser and have yet to find any hardened edges. I think this is a notice just to cover themselves.

The first thing to do is to try to find any hard edges with a file as Dave S posted 11 days ago.

JA

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