Wednesday, November 21, 2018

Interesting 3D Printer Failures

I recently experienced a couple failures and almost failures that might be interesting to people who build 3D printers.

The first one was discovered when I started to rebuild the Y axis in Son of MegaMax (blog post will be made when the work is done), my bed flinger printer that lives at the Milwaukee Makerspace.  I took the bed plate off because I was going to make a new bed plate and convert the ball screw drive to belt drive.

Here's the bed plate about a year after it was put into use on the machine.  It has a self-adhesive 450W kapton heater.  I don't know what type of adhesive it had on it.


And this is what it looks like today, after 5 or 6 years of temperature cycling:


Notice the brown spots- there are air bubbles that formed between the heater and the bed plate under them.  Air is a great thermal insulator, so the aluminum bed can't take the heat away from the heater where there is a bubble and the result is hot spots.  It's probably safe to assume that almost any self-adhesive material is going to eventually let go this way, and the heater will eventually burn itself up.

The Keenovo silicone/fiberglass heaters, and probably a lot of others, come with 3M 468MP adhesive transfer sheet on them.  UMMD has had such a heater on it for a little over 2 years.  I recently noticed that the heater was starting to peel off the underside of the print bed.  Right now I have a piece of silicone foam wedged under it to keep the heater pressed against the bed plate, but sooner or later (probably sooner) the rest of it is going to start peeling off.  This is why it's a good idea to mount TCOs on the heater, as I should have done, instead of on the bed plate, as I did.  If the heater comes off the plate, having the TCO on the plate won't keep the heater from burning itself up, and maybe other things too.

Silicone foam used to keep the heater pressed against the bed when the adhesive started letting go, a little over 2 years after it was installed.

Finally, again on UMMD, the PEI print surface was mounted on the bed using 2" wide tape labeled 3M 200MP.  The standard stuff people use these days is 3M 468MP adhesive transfer tape, and if you look closely at the label on it, it says "200MP Adhesive" on it, so the two seem to be the same thing.

468MP adhesive transfer sheet commonly used to hold PEI and heaters on aluminum bed plates.

The 468MP transfer sheet that uses 200MP adhesive was letting go of the heater on the underside of UMMD's bed plate.  Then another odd thing happened just a couple days ago.  I started a largish ABS print on UMMD and went away and after an hour or so, the print failed.  It looked strange.  Like the edges of the print lifted, but closer inspection revealed that the PEI lifted up off the bed plate- the ABS was still stuck to the PEI.

Here's the print that failed.  Look at the edges of the bed plate and PEI...
Here it is from a lower angle.  The tape that was used to stick the PEI to the plate remains stuck to the plate, and is no longer sticky on the top side.  
The central area of the PEI was still stuck to the bed plate.  I removed the print from the PEI and found that the PEI laid back down flat on the bed surface and you'd never know anything was wrong just by looking at it.

A couple years ago, when I noticed the PEI starting to lift at the edges of the bed on SoM, I removed it and retaped it to the bed plate.  One of several things that recently prompted me to start a rework of SoM's Y axis was that the PEI was starting to lift at the edges for the second time in about 5 years.

I think there are a few things to learn from this:

  1. 468MP adhesive transfer tape using 200MP adhesive has a limited life span when it is heat cycled regularly.  I've been getting about 2 years of use, but I print a lot of ABS.  If you print PLA or other lower temperature materials, you might get more than 2 years from it.  
  2. It's a good idea to inspect the bed frequently and pay special attention to the heater to avoid disasters.  When you're inspecting it, try lifting the edges of the PEI and the heater away from the plate to verify that the adhesive is still working.
  3. When you're assembling parts with 468MP/200MP, follow directions on 3M's web site to get maximum bond strength and lifetime.


5 comments:

  1. I had the same thing happen on my build plate that uses Mic6 as well and I found that hitting the surface of the aluminum with some 200 grit sand paper has greatly helped with the adhesion between the plate and the PEI sheet.

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    1. In my case the adhesive let go of the PEI, not the aluminum plate. I had to use paint stripper to get the adhesive off the plate when I replaced the PEI surface. I originally stuck the shiny side of the PEI to the bed plate. When I replaced it I tried sticking the dull side to the plate. We'll know in about 2 years if that works any better.

      I haven't looked at the heater closely yet to see if the adhesive is stuck to the plate or the heater. When I reattach the heater I'll probably use high temperature silicone.

      Delete
  2. When I was assembling my bed (similar in design to yours) I was researching the 3M adhesive sheets and from what I read on the 3M site you linked convinced me that it wasn't suitable for attaching the silicone heater. In the end I went for RTV silicone to bond the heater to the plate. I am surprised that the PEI lifted like that. I don't print much ABS though. I'll definitely be checking the PEI. I had the rough side of the PEI down on the adhesive. Maybe that helps. Thanks for sharing your findings.

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    1. I used the 468MP sheet to attach the heater because it came on the heater. I'll be cleaning it off and using high temperature silicone to reattach it. I will also move the TCO to the heater and attach it with the same high temperature silicone.

      I previously put the shiny side of the PEI down on its adhesive sheet. This time I tried it with the dull side down. We'll see if it lasts any longer.

      Delete
  3. I'm using silicone heaters and pei with the same adhesive 468mp on a 30x30cm printer and i often print PC(polycarbonate) or nylon with carbon fiber in it. PC works great at 160c to 180c bed temp and nylon sticks excelent to PEI at 130c 150c bed temp. First problem with those temps is that the adhesive starts to smell horible after 15 or so minutes and as a matter of fact after about an hour you cannot stay in the say room. It even makes your eyes hurt. I contacted 3M and told them about the temps I use and the smell it emmits on those temps and they said it's nothing to worry about. I don't actually believe them. That said, at those temps the adhesive usually last 3-5 months before everything start to peel off. And with AC beds is a bit dangerous if something shorts. Always have ground on those. I just changed everything before reading this unfortunatly, but next time i guess i will use RTV silicone or a silicone rubber i have for fixing coolers on electronics that i have already tested at 220c (some cheap thing from ebay that i cannot recall how i found it). Thats my experience and thanks for the info

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