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yellowshark

How to prevent/reduce post print PLA delamination

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Hi I have been producing a number of prototypes to attach a motion sensor to various parts of the human body. I have been told that one of these is suffering delamination.

Put simply, it is a wrist bracelet; quite wide at 42.5mm with the bracelet depth being 3.2mm. It is elliptical in shape not circular and not fully enclosed. I.E. there is a gap between the two ends of the bracelet of 20mm.

We were just playing with a design so when printed it was not intended as a prototype but our client really liked it and wanted to take it to a seminar in Milan. Where it currently resides so I have not seen the delamination.

It was printed at .3 layer width, 60m/s and 220c extruder temp and 60c bed temp; layer width might have been .2 but I am sure we would have used .3 as we were just playing. I am guessing normal average fan settings would have been used.

The only forces applied to the unit will be pushing the two ends of the bracelet apart to slip it over the wrist. My understanding is that the delamination is at the edges of the bracelet, not in the middle.

So my question is what, fundamentally, changes could/should be made to print settings of a PLA part to try and stop this happening?

The question might be simply rephrased as “to improve layer adhesion” but I am surprised it is occurring just at the edges rather than in the middle so without sight of the part I am not sure quite what is failing.

 

 

 

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What is the nozzle diameter on your printer? I'd make sure that the layer height is smaller in proportion to the nozzle diameter, so that the plastic is spread onto the layer below, rather than being dropped onto it. Perhaps printing hotter would help - 0.3mm layers at 60mm/s is quite a high volume per second - perhaps the plastic is not heating fully before it is extruded, further reducing the adhesion between layers?

But, it will be easier to tell whats going on when you have pictures. :-)

 

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Thinner layers should help. Or alternatively consider reheating the ends after you are done. You could point a heat gun at the end of the bracelet where it delaminated until it remelts and smooths out to keep it from catching a layer on some clothing.

Or you could dip the ends in boiling hot water for 20 seconds then pull it out and smooth it with something smooth and hard like a counter top or the hot glass of a UM2 set to 80C.

I'm guessing that the issue is more about the surface not being smooth enough such that it catches in clothing. You should ask them to take a photo with a cell phone and text it. Cell phones tend to be very good at macro photography.

 

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I agree with the thinner layers. In my (albeit a bit limited with this sort of thing) experience thinner layered parts are stronger.

As for why it only happens on the edges. I would assume because that's where the wear and tear is happening. They're probably grabbing the bracelet with one hand for each side and then prying it apart. If they only use one finger that's likely putting a twisting force on the bracelet. Kinda sorta like wringing out a rag, only not quite so violent. I'm finding it a bit hard to describe what I mean...

 

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Thanks to my two favourite guys for coming back so quickly :). It is a .4mm nozzle. Layer dim. for me has the greatest affect on unit cost but I do think we will push to use .2 instead of .3. Also for production we will use 30 m/s as the interface to the sensor module is quite intricate, using a series of "feet" that slot in then slide to lock the two parts together; tolerance is quite small so I think faster than 30m/s would be risky plus the other parts were done at 30 m/s and connect seamlessly.

Also we have been asked to fillet the edges as they are sharp and this unit sits on the skin.

So all in all this all fits with what you are both saying and may well, neh, will get rid of the problem - although I have always wanted a heat gun :)

Unfortunately I am a cell phone luddite, disliking its intrusion into my privacy so yes I should have requested a picture, doh.

I will post one when received.

 

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Just a tip on the fillets. I find that fillets on a surface that sits directly on the print platform comes out kind of crappy due to the severe overhang it creates on the lowest part of the fillet. I like to put a 45o chamfer on the bottom instead and then a fillet on the upper edge of that chamfer. Other edges can of course be filleted like usual.

 

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Thanks for that Robert, a smart idea. I will be printing it tomorrow with the changes noted above and I was wondering how the bottom section (print oriented with the bracelet set vertically) with the fillet would come out. It is narrower than stated above, at 1.6mm, so I am not sure how it will come out. I will keep the chamfer in hand and update you on what happens

 

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Hi Robert, we in fact went straight to your technique for the fillets. They turned out real nice, so many thanks for that

The latest report today is that they are suffering delam across the Clip not just on the edge (admitting it has taken some abuse). Clearly the major stress is pulling the two ends apart to fit it over the wrist, which follows the direction of greatest tensile strength but it must be putting stress on the layer bonds too.

So now printing another for them at 30m/s and .2 layer depth.

Plan B will be to increase the width of the strap are from 1.6mm to 3.2 mm to double the surface area in contact. This though will make the strap stiffer I am sure and may make it functionally unacceptable.

Plan C will be to go back to nylon although I am a couple of weeks away from getting my new Taulman filament. This will provide the flexibility needed if 3.2mm is too stiff and I think I have read in various places that nylon gives stronger layer bonding.

 

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