Pressure Required for Green Compact 5

[davyjacob]

Hi guys,

I am going to mix one metal powder and one salt with a suitable binder to form a mixture. Now, I will fill this mixture in a mold and I will compress to get green compact. My doubt here in this case is, upto what pressure I should compress? Is there any formula available to calculate the maximum pressure required to compress the mixture to form green compact?

regards,
Davy

 

[EdStainless]

So these are fine powders, right? Like less than 10 micron particle size?
And your binder will be a wax, say a stearate?
And if the parts have a simple shape,
Based on what I recall from my days in powdered metals I would expect something like 25ksi to do the trick.
Carbide tooling?


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[rodofgod]

I'm interested in this thread, it's way outside my knowledge base and I admit, I had to look up 'Green Comact'!

 

[rodofgod]

Compact even!

 

[davyjacob]

@EdStainless

Yes, the part will be simple like cylindrical piece. You mentioned 25ksi would do the trick. But, how to claim that 25ksi will be enough to do green compact? I did go through powder metallurgy books to find based on what calculation pressure is decided. But there is no explanation given.

 

[kumkumvijay]

Hello
I would like to share my opinion as below:

The compacting pressure must be decided based on the density of metal required in the final part. Also based on the method of pressing, you can change the pressure eg: die pressing, hot isosatic, cold isostatic etc.

If you have decided the final density of the sintered part then you can calculate the desity in green compact and from that you can decide the mixture and pressure.

The link below may help you

https://documents.htracyhall.org/oc....) (Heckler, A.J.) (Heeger, A.J.)-419_OCR.pdf

http://riad.pk.edu.pl/~mnykiel/iim/KTM/MP/DOWNLOAD/pdf/CHAPT04.PDF

http://www.wpi.edu/Images/CMS/MPI-PMRC/ddpowder.pdf

 

[EdStainless]

You need enough pressure to allow them to be handled, and to sinter well.
In reality you will press series of parts at different pressures and then sinter over a range of temps for each pressure.
Then you find the combination that results in the density and properties that you need.
There is no magic compaction pressure.
You could always get yourself a small used isostatic press. You can use higher pressures because you don't have die frictions issues. We would iso press at 40-50ksi with very nice results.

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[davyjacob]

@kumkumvijay

Thanks for the reply. Actually, my ultimate goal is that after through the steps of compacting and sintering, the final component should be with good amount of porosity. So, in this case what compact density I should go for and what pressure I should go for? The method of pressing I am interested is die pressing and for the mixture I will use 60 percent wt of salt and 40 percent wt of metal powder.

 

[EdStainless]

Set up the design of experiments, you have particle size, press pressure (actually green density) and sinter conditions (temp and time).
It will be a bunch of testing but that will be the only way to get there.

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Plymouth Tube

 

[IRstuff]

" what compact density I should go for and what pressure I should go for"

You should have a requirement for that, shouldn't you?

TTFN
faq731-376

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[arunmrao]

davyjacob,

Your requirement of green strength is not adequately defined. Do you need the green strength to eject the compact from the die without breaking and withstand any springback . Or is it that for handling and storing the green compacts, you need the minimum strength. Also,within the same compact the density at the top, body and bottom will vary. The size and distribution of porosity also varies.

 

[kumkumvijay]

Hello davyjacob

I am not sure whether you are doing Selective Inhibition Sintering (SIS) which use salt. what is the prupose of the salt? Are you making ceramic coating over the metal powder or salt will be dissolved in solvent to create porous structure.

In case if you planning to use the slat for making ceramic coating then the amount of pressure can be determined based on the kind of salt and metal powder used.

For ex Aluminum premixes exhibit excellent compressibility and yield high density parts at low compaction and ejection pressures. Premixes can be compacted to 90% density at only 12 tsi and 95% at 25 tsi. Typical green strengths range from 450 to 1500 psi which is sufficiently strong to withstand normal handling without chipping or breaking.

If you are expecting more porous structure, its good enough to compress it at lowest possible pressure which will eject and handle green compact with out breaking.

The green compact pressure will be based on what kind of metal powder and salt is used by you.

Thanks