Cooler for welding application

[Metallurgyman]

Hi everyone,

As part of my job as a research engineer, I have to come up with novel manufacturing routes and process optimisations for laser welding. One of the routes I am looking into is building a vapour change cooler to greatly reduce the temperature of the workpiece in order to obtain a large temperature gradient between the molten pool and the rest of the material, this would create ideal conditions for a particular type of metal crystal growth, but I won't go into that...

The laser power is around 2000 Watts, with nearly 100% absorption into the workpiece, and the questions I have are:

• Is this safe?
• What power compressor would I need to draw away that amount of heat?
• What type of refridgerant to use?
• Could you reccomend any sources where I could read up on refridgeration design?

Any advice you could offer would be greatly appreciated.

Thanks

[frank]

M....man

it is quite easy to build a 2kW cooling unit.

The problem I see is how do you get the cooling process into the work piece to be welded.

Just putting the work piece into a freezer at -18C prior to welding would help but I'm sure this is not practical.

have you considered how such an instant heat input generated by a welding process directly into a refrigerant liquid/gas mixture would affect system pressures?

I think a little more research needs to be done before we can recommend something useful

[SteinarN]

I suppose the cooling is to take place simultaneously with the welding process. Could it be possible to spray a controlled amount of liquid co2 onto the workpiece? Liquid co2 has a temperature of -79C I think. Is this too cold?

[Plank!]

I suppose the cooling is to take place simultaneously with the welding process. Could it be possible to spray a controlled amount of liquid co2 onto the workpiece? Liquid co2 has a temperature of -79C I think. Is this too cold?

Liquid CO2 will freeze into dry ice when it hits atmospheric pressure, it will make things harder to control, and has the effect of blocking the spray nozzle.

Dry ice in itself, applied around the weld may work, tho the CO2 vapour produced may be a little dense for the laser to focus properly.

Liquid nitrogen might work, small ammounts sprayed near the work piece, air is 74% nitrogen so the vapour should not reduce laser efficiency.

Would nitrogen affect the crystalization process?

CO2 reaches -74.8°c at atmospheric pressure, Liquid Nitrogen -196°c would this cause problems to the structure of the material surrounding the weld?

just a thought, would ammonia be suitable?

[taz24]

Hi everyone,

As part of my job as a research engineer, I have to come up with novel manufacturing routes and process optimisations for laser welding. One of the routes I am looking into is building a vapour change cooler to greatly reduce the temperature of the workpiece in order to obtain a large temperature gradient between the molten pool and the rest of the material, this would create ideal conditions for a particular type of metal crystal growth, but I won't go into that...

The laser power is around 2000 Watts, with nearly 100% absorption into the workpiece, and the questions I have are:

• Is this safe?
• What power compressor would I need to draw away that amount of heat?
• What type of refridgerant to use?
• Could you reccomend any sources where I could read up on refridgeration design?

Any advice you could offer would be greatly appreciated.

Thanks

Not knowing the specifics of laser welding I would consider a few points.

Would the laser weld in a fluid eg chilled water ?

Would liquid C02 poured onto the joint prior to welding work?

Would the stress of a cold metal with a hot weld running through it distort or weaken the metal?

Cheers taz.

.

[Plank!]

Would liquid C02 poured onto the joint prior to welding work?

Liquid CO2 cannot exist at atmospheric pressure.

[SteinarN]

Liquid CO2 cannot exist at atmospheric pressure.

What if the welding process is taking place inside a sealed compartment with higher pressure so the liquid co2 can exists?

[nike123]

Liquid CO2 cannot exist at atmospheric pressure.

That cannot be further from true.
Liquid or gas state of mater depend on pressure/temperature ratio and that fact should be well known to someone who is refrigeration engineer.

[SteinarN]

That cannot be further from true.
Liquid or gas state of mater depend on pressure/temperature ratio and that fact should be well known to someone who is refrigeration engineer.

I think Plank is correct here. If my memory serves me right the triple point for co2 is at a pressure above atmospheric pressure. Liquid canot exist at a pressure belov the triple point, only gas and ice can exists there.

[nike123]

I think Plank is correct here. If my memory serves me right the triple point for co2 is at a pressure above atmospheric pressure. Liquid canot exist at a pressure belov the triple point, only gas and ice can exists there.

Yep, you are right. I was foolishly thinking that liquid nitrogen and liquid CO2 are behave similar and did not checked data for CO2.
Another prove that assumption is mother of all f***ups.
My sincere apologies to Plank!

[Plank!]

That cannot be further from true.

Oh, really?

Liquid or gas state of mater depend on pressure/temperature ratio and that fact should be well known to someone who is refrigeration engineer.

Yep, I'm a refrigeration engineer that works on CO2 systems

[nike123]

Hi everyone,

As part of my job as a research engineer, I have to come up with novel manufacturing routes and process optimisations for laser welding. One of the routes I am looking into is building a vapour change cooler to greatly reduce the temperature of the workpiece in order to obtain a large temperature gradient between the molten pool and the rest of the material, this would create ideal conditions for a particular type of metal crystal growth, but I won't go into that...

The laser power is around 2000 Watts, with nearly 100% absorption into the workpiece, and the questions I have are:

• Is this safe?
• What power compressor would I need to draw away that amount of heat?
• What type of refridgerant to use?
• Could you reccomend any sources where I could read up on refridgeration design?

Any advice you could offer would be greatly appreciated.

Thanks

What is shape of welded piece. If it is pipe, it could be cooled by freezers for pipe work like this:
http://www.cryostop.com/

[nike123]

Oh, really?



Yep, I'm a refrigeration engineer that works on CO2 systems

As I said, my sincere apologies!

[Plank!]

As I said, my sincere apologies!

Hence the smile

[Metallurgyman]

Thank you for all of the input, it has been very helpful.

The application is the repair of gas turbine blade tips from the hot section of a Rolls Royce engine. These are made of titanium and have a convex and concave faces, as well as a twist along the length. Because titanium has a poor heat conductivity the heat builds up around the weld pool and causes undesirable microstructural changes.

I had toyed with the idea of casting a solid copper heatsink, through which I would pass liquid nitrogen, but ideally I would prefer a system where I can control the temperature to some degree.

I thought perhaps I could fabricate an evaporator with an integrated thermocouple to clamp just below the end of the blade, though would this mean I have any control over the temperature? Would varying the compressor speed (and refrigerant pressure) allow temperature control or is the temperature reached determined purely by the type of refridgerant used?

Thanks for all the help so far, refrigeration engineering is not my forte as you can probably guess

[Metallurgyman]

No can do I'm afraid, the pressure around the work can't really exceed atmospheric as I use compressed argon to blow filler metal powder into the weld to build up material.

I would be wary about introducing either nitrogen or carbon dioxide, as these tend to get absorbed into the liquid metal and cause all manners of problems.

Thanks

[Plank!]

ok, that clears things up a bit.

Size is the problem now, those blades are not all that big, so you'll need a fair sized chunk of metal for the evaporator.

Yes you can control the temperature, but it sounds like you are thinking cap tube. Forget that idea with the nature of the heat load you'll need a bit more control, maybe a TEV or EEV.

Try this http://ra.danfoss.com/TechnicalInfo/...1/Rs8cS302.pdf
with this (AKV10)
http://rc.danfoss.com/TechnicalInfo/...(2)%20indd.pdf

You can still use the thermocouple control temp.

[Metallurgyman]

That's great, thank you.

Any idea roughly how much those would cost?

[Gary]

Wouldn't cooling the weld too rapidly make it brittle?

[US Iceman]

Because titanium has a poor heat conductivity the heat builds up around the weld pool and causes undesirable microstructural changes.

I had toyed with the idea of casting a solid copper heatsink...

If you know what the conductivity of the metal is (and the mass) you would have an idea of how much heat you need to transfer from the weld to the blade to the heat sink. If you can determine the temperature required at the heat sink to produce the required cooling (taking into account the metal conductivity and blade mass) to control the weld zone temperature you have a reasonable starting point.

From a simple viewpoint: Q=M X cp X Delta T

Therefore, by knowing the blade mass and specific heat of the titanium you can determine the required Delta T to provide the cooling effect.

From a heat transfer perspective you need the conductivity to find out how fast the heat transfer occurs by conduction from the weld zone to the heat sink location.

If you use a refrigerant you can very easily control the heat sink temperature by using a simple refrigeration system. If you control the evaporating temperature of the refrigerant in the heat sink, you control the heat sink temperature.

Upon further inspection you might find it easier to place the heat sink at the turbine hub and control that temperature. This might be easier than trying to individually control the turbine blades much further away from the weld zones.

Just some random thoughts for your consideration...

[Break7]

Some companies are currently using co2 for cooling during machining. Liquid co2 is sprayed on the cutter and the part during cutting.