Printing issues - missing powder with large ojects

[rudschul]

In general my printer works fine. Right know i have a problem with printing large objects. I want to print an area of 10cm * 10 cm. It is not possible to rotate the object. The first 3 layer are fine, but then from the middle left there is powder missing. The next 7 layer each layer is missing more and more powder. If the area is getting smaller the missing powder is filled again. But the print is not useable.
If i rezise the object to 8cm * 8cm the print is fine with no problem. All dimension bigger than 8cm*8cm have the same problem. As bigger the object as bigger the problem.
Does someone know a solution to rise the amount of powder to get from the powder reservoir to the printing area?

[Mike Francies]

Hi Rudschul - I assume the layers are solid and because the sintering melts the powder into a smaller volume there is not enough powder in the next layer to fill that volume. I think you are right in thinking you need to increase the lift of the reservoir. I don't know how quickly the Sintratec software development is but it should be relatively easy to equate the lift with the area being sintered, shouldn't it?

I am surprised you are not experiencing warping with that area of solid infill. I am still getting some warping in the front left corner of my build area and I try not to use that part until I find a solution to the uneven heating.

Edit: Just a thought - can you not tilt it at a very small angle, just enough so it does not print the whole surface at any time?

[rudschul]

Hi Rudschul - I assume the layers are solid and because the sintering melts the powder into a smaller volume there is not enough powder in the next layer to fill that volume. I think you are right in thinking you need to increase the lift of the reservoir. I don't know how quickly the Sintratec software development is but it should be relatively easy to equate the lift with the area being sintered, shouldn't it?

Yes, you are completly right. You are able to see, that you will need more and more powder. As Sintratec told me i am able to see that sintered area is brighter than the not sintered area after a new prepared layer. As brighter you are able to see these areas as more energy was stored. In conclusion the powder ist not sintered anymore it is melting :-) For me that very good :-) But you will need more powder but it is more stable.

I am surprised you are not experiencing warping with that area of solid infill. I am still getting some warping in the front left corner of my build area and I try not to use that part until I find a solution to the uneven heating.

My warping zone is front right. This regeon is a little bit colder with my printer. I was playing with laser speed and surfage temperatur.

Edit: Just a thought - can you not tilt it at a very small angle, just enough so it does not print the whole surface at any time?

No that is no solution. When i am thinking about the kit i ask Sintratek about the max printing size. They told my that 11*11*11 might be possible. A lot of my parts i want to print are abotut this dimension. So i have first to fix this problem to go further on.
For me it is very importend to know what dimension i am able to print with no problems.

[Mike Francies]

Another thought - last night I printed some calibration cubes and when I put the powder into the reservoir I accidentally knocked the machine. What I noticed was that the powder settled down quite a lot so I knocked the machine a few more times and the powder settled even more. If you were to do this it would allow more powder for each layer as the powder density would be higher. Just a thought.

[rudschul]

ok very interesting. I will try.

[rudschul]

I tried you proposal. Yes it make a diference of the packing dense. Do you have sometimes warping issues which cause the print will destroyed? I print with following parameter:

Chamber temperature : 150
Surface temperature : 171, 7
Speed 550

After about 2 cm my object starts warping at 2 pillars

[Mike Francies]

Hi rudschul,

I too had warping issues until I raised the powder surface temperature to 174.2C and lowered the speed to 550mm/s. What I had noticed was that at startup, the chamber temperature and the surface temperatures were not the same and there was a difference of some 6 degrees C. They ought to read the same and both should have been at room temperature. I reasoned that this was why I needed to raise the surface temperature as this was reading low. You may have the same problem.

If I am printing a few parts at the same time I drop the surface temperature to 173.7C otherwise the powder 'cake' of the un-sintered powder seems to be too hard so I figured the laser was raising the surface temperature just that little bit more that took it past the optimum.

I still suffer from warping if I try to print within 20mm of the edges.

I also have another problem that Sintratec assure me they are working on and that is that objects printed in the far third of the print area (away from the window) are all stretched in the Y axis. So much so that a 20mm square ends up 20 x 21mm. Everywhere else seems to be within reasonable limits.

Hope this helps.

[rudschul]

In conclusion you think it was a good idea to lower the temperature or to raise the speed?

I agree to your scaling issues. I have the same problem, but it is not so importent for my to solve it. But if you have a solution please post it.

My main problem is to print big part (9*9*9) with constant quality. I alway run in trouble. (Warping, defect endstopper, loose nut, less powder).

It is very frustrating that i have no support access anymore and there is no realy active community who share there problems and there solutions.

[Mike Francies]

I think you need to raise the surface temperature to cure the warping problem. If the surface temperature is very close to the melting temperature, the part has no chance to cool down and therefore warp.

What is your problem with the endstopper and powder?

I don't have a solution to the scaling problem but Sintratec have said they are aware of it and are working on a solution.

[rudschul]

Ok i will raise the temperatur a little bit more and try again....

The enstopper will not work because some powder or polymere get into the endstop and work like an isolator.
Do you see a little white film outside you printer? These ploymere in compination with the powder come into the endstopp.