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Print not sticking to platform


#1

Hi all,
As in the enclosed image is how most of my prints have ended thus far. The print sticks more readily to the vat container than the build platform and that’s not how it’s supposed to be.

What I feel that is needed here is some insight. I clean the vat + platform with water/soap first and then with IPA between each attempt. When underexposed, things will stick to the platform but not to the previous layers. When overexposed it will stick to the vat rather than the previous layer/build platform. Is this a correct assumption?


#2

I also thought that delamination and vat sticking was purely an exposure issue, but my experience printing so far has shown that it is not.

I wrote a long post on my experiences experimenting with separation forces. Once of the strongest separation forces I found seemed to be the vacuum force (smooth cured resin surface on smooth vat causing vacuum forces to resist separation) and in my failed prints never found any evidence of chemical or mechanical sticking (which I tested by comparing the effort to pull straight off versus push to the side with a plastic razor scraper - the razor scraper was always very easy, pulling was always very hard).

Rather, breakage seems to be the meeting of two forces: vacuum separation force against the vat against resin adhesion force of the weakest previous layer.

Thus in diagnosing failed prints, I found that the vat remnants didn’t really have much useful data, but what was left on the build plate was quite useful. By measuring the height of what remained on the build plate and then dividing that by the print layer height, I can determine the approximate layer where failure occurred. Often, that coincided with a layer setting change which would point to the layer settings which need adjustment.

The other big factor was shape. I go into more detail in my linked post, but the net is that if layer surface area of the print increases over the duration of the print, then separation forces are increasing relative to the adhesion strength of previous layers. This can lead to warping and then print failure.


#3

Underexposure makes the cured resin less sticky and soft. It is easier to separate from the vat but may fall during printing. Overexposure is the opposite but you will see light bleeding. Round solid pattern has the highest adhesion among all patterns on the Teflon. Apply large area (full area) attachment layers with a total thickness of 0.25mm to increase the adhesion between you model and the platform. If this does not work, please add supports between attachment layers and your model. Hope this will help.


#4

@jkao Yeah. thanks for writing that up. I’ve read through it several times already. I now have my first successful print of the Yoda going. I too had to increase from 5 to 12 sec per layer for anything to solidify.

My first attempt failed, but for once I had something stuck to the build plate and by measuring that with callipers I found that I had to increase the layer time at the failed layer. I “think” it is printing fine now as there is something stuck beneath the platform at least…

@Keymaster It helps, but I need to know more. Do you have a good URL where we can go to learn more about how this works? For someone used to FDM printing, this seems to be simply too many uncontrollable parameters.


#5

@Jensa: Yeah, there are a lot more variables in resin printing than FDM printers. Resin has for more variables and the printing process if far more opaque (literally!) than FDM.

If you want to do more research, here’s where I started:

Resins seem to have 5 major components:

  • Polymer - Makes the liquid into a solid and is the "backbone" of resin. For low/non-VOC resins, which is pretty much all we want to use, this is usually some type of acrylate, like methyl acrylate. I learned a lot by reading through the storage/handling procedures for methyl acrylate which will give you an idea all the things this material can do and the factors relating to polymerization since the most unsafe aspect of acrylate storage is the risk of uncontrolled polymerization, which is the reaction we're most interested in.
  • Photoinitiator - Takes energy from light and initiates a chemical reaction that tips the equilibrium in favor of polymerization
  • Inhibitor - Consumes oxygen and tips the eqilibrium away from polymerization (the safe handling sheets cover inhibitors heavily since they are what make acrylics "safe")
  • Filler - Polymerization results in a volume change, the filler affects the way this occurs somehow, and there are a lot of complicated effects here. There appears to be more written about how fillers apply to epoxy and polyurethane resins but many similar principles seem to apply to all polymers. For instance one area to look at is nucleating agents, like talc, which are commonly used to "improve" characteristics of epoxy and polyurethane resins, as well as PLA filament (the mystery ingredient to make "high temperature" PLA with higher heat deflection temperatures. It's fillers that seem to be used to affect shrinkage properties.
  • Pigment - Lots of discussion in the forums about this, especially from @Vince. Besides affecting overall light transmission, it also affects selective wavelength transmission and may also have filler properties (kind of like how different colors of filament in FDM result in different hardness and material properties).

The printing process is also way more opaque that FDM printing, so you have to observe more deductively since you can’t see what’s going on in the vat under the surface of the resin (both because the resin may be opaque and because when the “action” is going on, it’s just too bright to look at).

The things I’ve learned to observe are:

  • Looking at the vat from underneath after a layer has been exposed, especially during separation - you can see shadows of your structures, especially larger surface areas, and see those shadows change as they separate. You can often see if parts get stuck to the vat or if support structures are breaking based on this. I've sometimes been surprised by what I've seen here, like breaking support structures kind of look like flashes of light or shooting stars appearing across my part during separation. Not sure why this is.
  • Looking at the vat flex, especially in the shape of flex at the points where the part is attached. In particular, getting a feel for the difference in the way flex looks between what is caused by liquid suction (between build plate and resin early in the print when the plate is agitating the resin) and by the part sticking to the vat. For instance, if I have a small part at the flexible end of the vat, I'll see an S-shaped flex pattern early in the build, where there is first an upward curve caused by the liquid suction, then when the curve reaches the part, the slope of the curve is reduced by the sticking of the part
  • Sound - Lots of data here. The biggest thing missing from all those time-lapse Youtube videos. I wish there were more boring multi-hour close-camera videos on YouTube of various different printers just so I could listen to the different lifting sounds at different parts of the print on different types of vats. We may be in a better position to use sound with a single-motor system like the Titan1 compared to printers with motorized tilt (Form1) or sliders (B9Creator) since we don't have additional motors generating noise during separation. You can hear the sound of parts separating from the vat, different than the sound of parts separating from the build plate. You can hear when supports are separating versus larger part surfaces. I can't yet figure out the sound of a mid-part failure and haven't caught any "in the act".
  • Metrology/Forensics - I keep calipers by my printer and measure all my successful and failed prints. Unexpectedly large XY dimensions can mean overexposure. The Z height of some failure feature (delamination, warp, weird flaps hanging off mid-print, anything that seems wrong) can give hints as to the cause (does the height coincide with a change in layer settings, a transition between layers of base supports, some other feature)

There are a lot of material properties in resin printing, but the experimentation process has been somewhat similar to when I started with FDM printing, especially when I was trying to figure out bridging, overhangs, and fitting parts (press fit dowl pin-in-hole type calibration). I had to print a lot of calibration parts to understand what I could print at what speed with what materials, temperatures, cooling, size, and finish quality. FDM did have some additional variables since there are more mechanical components, so you need to figure out whether the results you’re seeing are due to material properties (and thus need to be solved through settings) or because of mechanical problems (belt tightening, resonance, loose screws, etc…).

However, I do find that the difficulty in directly observing the chemistry and the points of curing make it overall more challenging to learn SLA printing.


#6

@Jensa Here are some notes to start with

  1. minimizing the separation forces
    a. avoid vacuum force for hollowed models
    b. minimize the cross sectional exposed area for each slices
    c. avoid symmetric patterns
    d. use low adhesion resins (usually low viscosity)
    e. avoid repeating patterns
    f. use a smaller build platform
    g. lower lifting speed
    h. avoid printing at a region too close to the hinge

  2. avoid model dropping during printing
    a. longer exposure time to make sure the adhesion to the top is larger than the adhesion to the bottom (Teflon)
    b. use low shrinkage resin to avoid warping
    c. minimize bulk shrinkage by hollowing or avoid big solid chunk in the model
    d. use supports to enhance structural strength
    e. if possible, rotate the model so that large area slices are more close to the platform

If you understand how to minimize separation forces, you can print very nice models with details that other 3D printing technology can not achieve.


#7

Great points here! Why not put these two posts straight in the documentation? When I finally got a successful print, the most surprising thing was the sound. Given that this is so important - why not document it?

I was also quite surprised at the strength of pillar based supports. Given the suction applied to the part, I’m amazed that the set of 0.6mm pillars didn’t break. It seems to me that using Pillars are quite crucial?

the hinge

I presume this means “the part of the vat that is closest to where it’s stuck to the platform”?

I posted some images of the last print here. http://jcprojects.tumblr.com/post/108685265614/more-success-much-more-to-learn-though I really need to buy a macro lens now :wink:


#8

i have yet to get any model to work when printing it directly off the print bed, i tried this lil keychain guy like 5 times, eventualy i put him on a creative workshop raft with 3 tiny supports on his feet, and perfect print.


#9

Is there no way to “favorite” a post here? There’s some good stuff in this thread!


#10

@Mark: You can favorite a topic (e.g. whole thread) at the top of the page, but not individual posts.


#11

We use both the sound and observed lifted height to estimate the separation force. In the future, it is possible to develop an algorithm to quantify the force. Adaptive lifting is our long term goal so there is no need to guess the separation force.


#12

I can’t get anything to print at all! I wanted to start a new topic but the forum won’t let me.

NOTHING prints, no failed prints, nothing! I’ve tried several different exposure times, at the completion of each print cycle there is NOTHING. I’ve followed all of the instructions and this is beyond frustrating.


#13

@BrianK I had the same problem initially and it was indeed frustrating. The values given in the examples (at the bottom of this page http://www.kudo3d.com/downloads_manuals/) require that you set the right X/Y size for each example. I set mine to 192x108mm initially. This is 100 microns and there’s no example file for this resolution.

I then set my projector to 37 microns ( 71.1 x 40mm ) by moving it upwards inside the cabinet and things started working. I then moved the projector went back to 100 microns and started multiplying values until I got something to stick. I think the baselayer needed almost two minutes to solidify at this resolution.

I highly recommend checking out the youtube videos that @jkao have posted. They’re long, but full of great info!


#14

hi jkao,

The read your text here and I felt it is relevant to my prints recently done using DSR flexible resin on Titan 2. btw the weblink above is not working could you please send it to me.


I tried printing the part as shown below, but not succeeded even after 3 times. Please review through the printing parameters and part shape and suggest me for getting successful print.

All 3 times, base layer and few layers of supports sticks very well to the build plate and then after it sticks bottom of the resin tank. I have tried varying resin tanks Hard to soft ones but nothing helps.


#15

the lift is too low(1.5), so it haven’t detach from the resin tank when lift, i’d use a 4 or 5 (3 is ok but depend on how tight you get the membrane)
and if you may, extend the exposure to 10 second
last im not sure if the down would make any difference, 150 is just a little scary fast.