Danger in 3D printing over a lithium ion battery

Question

So I bought a Lulzbot Mini a couple months ago and finally downloaded Ultimaker's version of Cura... Boy... have I been missing out...

One feature Ultimaker Cura implemented that I've been looking for is a "pause at z-height" feature ("post-processing tool"). I'm building prototypes of an electronics device, and creating two pieces that snap together looks a lot worse than printing a single piece. If I could pause my print, insert my electronics, and continue printing, my device would look a lot more professional (even if it took longer to make).

My one concern is the lithium ion battery. Right now I'm printing in TPU. With a heated bed of 40 degrees Celsius, and a heated extruder at 240 degrees Celsius, there seems to be a significant risk that the lithium ion battery reaches a temperature above 60 degrees Celsius (damaging the cell, causing a potential explosion). Granted, I am not sure what "60 degrees Celsius" actually means. It could mean only one part of the packaging needs to reach this temperature, or it could mean the entire LiPo's internal temperature would need to reach this. In either case, the numbers don't look good.

On the other hand, the heated bed surely doesn't need to remain heated beyond the first few layers? Additionally, I can create a "roof" for the LiIon battery that I can slip it under, providing some insulative TPU before the rest of the device. I think the print would happen safely like this, but obviously, an explosion would be really really bad. Like it would probably burn my house down, and I would be asleep when it happened.

Does anyone have any experience doing this? Is there a way to turn off the heated bed mid-print? I guess I can insert a g-code line during the pause? Will this affect the remainder of the print you think? Am I being paranoid? Can the extruder actually pass heat through a 1–2 mm of insulation and cause an explosion? Anyone know how heat travels from the initial, liquid print material through the rest of the structure?

Any more advice or things I should consider before pursuing this?

A more specific pause type might be helpful, if anyone knows of any.

Answer 1

I would have to see your design to comment more but why not just change your model with the lid or top that can be either fused on later or attached in some other fashion?

It is possible to turn off the heated bed after a certain layer. It looks like there is a discussion here with the G-code: Can Cura Turn Off a Heated Bed Partway Into a Print?

I would personally avoid exposing the battery to the heat generated by the hotend or the build plate. Printers alone can burn your house down. Why combine it with the awesome power of a lithium ion battery?

Answer 2

There is an option to directly insert extra commands at a specific Z height, no need to enter them manually.

That said, it is a bad idea to turn off the heated bed while printing, because this will often detach the object from the bed completely (that's kind of the point of having the heated bed in the first place: better adhesion while printing, and easier removal afterwards).

I wouldn't print over a battery to enclose it, not just because it is likely to damage the battery, but also to keep the battery exchangeable. Enclosing the rest of the design in a case is possible, but normally it is easier to print two separate parts that can be screwed together through a hole in the PCB.

So, experience: it's not worth it usually.

Answer 3

If your heatbed is at 40°C, and it's not dangerous until 60°C, I wouldn't worry.

The heatbed is what heats up the printed object, not the print head. It will obviously heat it up a tiny bit in a small local area when printing, but the heat dissipates rapidly, only affecting the temperature of the object very little.

If you're worried, try getting a laser thermometer, and monitor the surface temperature of the battery during a test print. They're like $10, so it's not a big investment to try it out.

Alternately, maybe you can do a test print with a stand-in for the battery, and embed a temperature probe in the stand-in, and monitor the temperature real-time while printing.

Answer 4

Although the bed may only reach 60°, the extrusion above the battery will be at closer to 200°C. Granted there will be a fairly low heat flux, but it will still cause ageing of the battery. At a minimum, some insulation or packing above the battery would seem like a sensible move. This could be printed material, and you could print over the top if you really want to seal the part.

Also remember that as LiPo cells age, they generate gas (this is designed to be trapped in the pouch) and swell. You should try and avoid any risk of puncture if this happens.

Answer 5

Well. First. If you ever think, hmm this might cause an explosion. DON'T DO IT. SERIOUSLY. Modify the design so you can insert the battery.

That said, most softwares will let you set a heater temp per layer. I have mine set through simplify 3d. I usually use this setting for the hot end, as I like to have the first layer hot. You will have bad results doing this with the bed as you will likely cause the print to expand or shrink enough to pop off. You are better not using the heated bed for the print than to turn it off. Look into rafts as well. That is how makerbot helps mitigate their heatless beds. A fan will also help..

AGAIN do not try anything that can possibly might blow something up. There are a lot of variables you do not know, such as how conductive the plastic is and how much will travel through the hotend to the battery. Or how off the specs are for this battery.

Answer 6

Discharge the battery entirely, then there is no danger of ignition if the membrane breaks. The battery cells are usually protected by Kapton tape (LiPo) or maybe even metal (LiIon). Both will withstand the temperature of 240°C. The downside is that the cells are damaged after a deep discharge. You should discard the battery afterwards.

What I would expect when you do that:

A deeply discharged battery will bloat up because the solvents will gas out. This will also happen if you heat up the battery enough (>>60 degree). The gases themselves can be ignited again but are captured in our air sealed Kapton envelope :) Igniting these gases will be comparable to a short flash with a spray can.

The temperature is not enough to damage the envelope. The solvents will be also not very dangerous in that temperature range. In case of mechanical breakdown of the membrane nothing will happen anymore.

From Solvents and Additives: