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I’m curious about why that is. Naively, it seems like printing layer by layer would allow for a lot of inspection. Maybe even photograph each layer as you go?

I’m curious about why that is. Naively, it seems like printing layer by layer would allow for a lot of inspection. Maybe even photograph each layer as you go? And then test and go back to see what kinds of defects were apparent in the photos.

dotnet00 2y ago
It's just that it's very easy for deviations from what the sensors see to occur. In traditional 3d printing, this can be stuff like a sensor switch wearing out, maybe physically moving slightly, being temperature sensitive, maybe the frame has changed shape slightly due to heat, moving the sensor a little, maybe something in the microcontroller happened to cause a slight delay in reading the sensor, or looseness developing in the motion system, or something being slightly out of alignment, or some component in the extrusion system experiencing momentarily higher friction and so on. The layers are really thin, so manually inspecting them would slow down the printing process drastically. Then, ultimately, what even can you do if there's a defect? The layer has been laid already. If material is missing somewhere, you could have the machine go back and add it, but if there's excess material somewhere, or it's in a form that the machine can't fix, there's not a lot to be done, particularly in applications like rocketry, where your structural strength tolerance are very tight.
- metal_am 2y ago
  I know for certain that defects in the powder layer can be fixed in binder jet by redoing the recoater. There has been talk in the research world about being able to fix errors in L-PBF but I’m not sure they’ve gone past the research stage. The big point is that you can know a part might be out of whatever your acceptance criteria might be.
- serf 2y ago
  >It's just that it's very easy for deviations from what the sensors see to occur. right, but this is a problem in any modern precision machining, and it has been (mostly) conquered to a degree that we can produce very precise things in an almost entirely automated fashion. >If material is missing somewhere, you could have the machine go back and add it laser sintering is easier to audit than a normal fdm style print in a lot of ways if you care to take the time to do it. The process can be paused fairly easy with the right machine and right environment, the product can be weighed mid-process, it can have all sorts of vision and laser metrology done to the product midway through production; whatever -- and the mid print failure rate is astronomically lower than extrusion based methods. it doesn't seem that unbelievable to me.
- Iulioh 2y ago
  We aren't talking about deposition 3d printing for metal parts as it needs to get to the oven and precision is...not it's strong part The most common form for metal precision production is powder bed fusion You deposit a whole layer of powder and a laser melts the desired parts
metal_am 2y ago
Peregrine from Oak Ridge National Lab does exactly this. Lots of other research papers about it too.
Ruthalas 2y ago
You are correct, and with the current metal AM techniques (DED, SLM), you can also take thermal imaging of the melt pool throughout. From this you can a pretty accurate picture of the weld quality across the whole volume. I'm not sure that's sufficient to eschew any other non destructive testing, but it is great information.
mywittyname 2y ago
> Maybe even photograph each layer as you go? Differential cooling is an issue, and is one that isn't apparent until the layers have already been printed. If their process actually works, whatever they are doing isn't trivial.

dotnet00 2y ago

It's just that it's very easy for deviations from what the sensors see to occur. In traditional 3d printing, this can be stuff like a sensor switch wearing out, maybe physically moving slightly, being temperature sensitive, maybe the frame has changed shape slightly due to heat, moving the sensor a little, maybe something in the microcontroller happened to cause a slight delay in reading the sensor, or looseness developing in the motion system, or something being slightly out of alignment, or some component in the extrusion system experiencing momentarily higher friction and so on. The layers are really thin, so manually inspecting them would slow down the printing process drastically. Then, ultimately, what even can you do if there's a defect? The layer has been laid already. If material is missing somewhere, you could have the machine go back and add it, but if there's excess material somewhere, or it's in a form that the machine can't fix, there's not a lot to be done, particularly in applications like rocketry, where your structural strength tolerance are very tight.

metal_am 2y ago
I know for certain that defects in the powder layer can be fixed in binder jet by redoing the recoater. There has been talk in the research world about being able to fix errors in L-PBF but I’m not sure they’ve gone past the research stage. The big point is that you can know a part might be out of whatever your acceptance criteria might be.
serf 2y ago
>It's just that it's very easy for deviations from what the sensors see to occur. right, but this is a problem in any modern precision machining, and it has been (mostly) conquered to a degree that we can produce very precise things in an almost entirely automated fashion. >If material is missing somewhere, you could have the machine go back and add it laser sintering is easier to audit than a normal fdm style print in a lot of ways if you care to take the time to do it. The process can be paused fairly easy with the right machine and right environment, the product can be weighed mid-process, it can have all sorts of vision and laser metrology done to the product midway through production; whatever -- and the mid print failure rate is astronomically lower than extrusion based methods. it doesn't seem that unbelievable to me.
Iulioh 2y ago
We aren't talking about deposition 3d printing for metal parts as it needs to get to the oven and precision is...not it's strong part The most common form for metal precision production is powder bed fusion You deposit a whole layer of powder and a laser melts the desired parts

metal_am 2y ago

Peregrine from Oak Ridge National Lab does exactly this. Lots of other research papers about it too.

Ruthalas 2y ago

You are correct, and with the current metal AM techniques (DED, SLM), you can also take thermal imaging of the melt pool throughout. From this you can a pretty accurate picture of the weld quality across the whole volume. I'm not sure that's sufficient to eschew any other non destructive testing, but it is great information.

mywittyname 2y ago

> Maybe even photograph each layer as you go? Differential cooling is an issue, and is one that isn't apparent until the layers have already been printed. If their process actually works, whatever they are doing isn't trivial.