Exposure parameters reference/documentation

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rapidmanufactory
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Exposure parameters reference/documentation

Post#1 » Mon Sep 15, 2014 2:23 am

Hello,
This forum, the questions and the abundance of answers and advices are really being helpful in the quest to complete our 1rst print.
However I'm finding it impossible to locate the exposures parameters reference (material catalog), could someone please point out a comprehensive documentation of those parameters (software v. 1.7.2)?

Thank you all, :)
Chady

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tim.yoshi
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Exposure parameters reference/documentation

Post#2 » Mon Sep 15, 2014 2:47 am

There is no such a documentation other than wiki, or question/answer everywhere here on forum. Ask what you'd like to know more precisely.
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Robert Howle
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Exposure parameters reference/documentation

Post#3 » Mon Sep 15, 2014 4:48 am

You will need to state your chosen xy and z and the resin u intend to use.
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akgold
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Exposure parameters reference/documentation

Post#4 » Mon Sep 15, 2014 7:07 am

Quote from rapidmanufactory on September 15, 2014, 08:23
Hello,
This forum, the questions and the abundance of answers and advices are really being helpful in the quest to complete our 1rst print.
However I'm finding it impossible to locate the exposures parameters reference (material catalog), could someone please point out a comprehensive documentation of those parameters (software v. 1.7.2)?

Thank you all, :)
Chady


Without knowing your progress of printing I would say to you to start with using the software's default settings for which ever resin you are using in what ever XY,Z printing your choosing to use.
As Robert has stated many time over to get help on a problem we first must know which printer your using vers. 1.1 or 1.2HD.
then What size are you printing in per machine. or better yet what do you intend to print as that will determine the range of settings available because it varies widely between 30 XY and 70 (HD) or 50 XY to 100XY version one B9.
I'm so far behind I think I'm First !!

rapidmanufactory
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Exposure parameters reference/documentation

Post#5 » Mon Sep 15, 2014 9:30 pm

Hello,
thank you all for your answers, however we are not looking for parameters specific to the materials we are using (we may need that later), but for now we would like to understand how it work: ie. logic and relations between the parameters (multipliers) that would allow us to reason about it ourselves and maybe help the community back later on.
A small lexicon of the parameters' names would be handy.

We are using a b9 1.2HD.

Here's our first print with it using Spot-HT (partly successful: Some parts broke):

[IMG]http://i62.tinypic.com/vdjx9s.jpg[/IMG]
[IMG]http://i59.tinypic.com/14bm5hd.jpg[/IMG]
[IMG]http://i59.tinypic.com/25jjb5j.jpg[/IMG]

attachment layers: 10 layers, 20 sec
print layers: 6.5 sec (as an example we had no idea where this number came from, we had configured the print to use 1.02 sec).

Thanks,
Chady

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mikej
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Exposure parameters reference/documentation

Post#6 » Tue Sep 16, 2014 12:37 am

Sorry this is so long in coming, we're still focused on software at the moment.

To create your own material settings that work on all machines at all settings you need to know the following info. It's best if you do your testing at the lowest XY resolution because the energy per area is lowest and that's where things are the most sensitive.

So, set up your machine at 70 XY (v1.2) or 100 XY (v1.1).

Experimentally determine your minimum and maximum Slice Thickness (ST). Note that pigmentation (or dye) will determine your Depth of Cure (DOC) limits. For a given pigmentation, you should be able to achieve a DOC that is thick enough to attach to the previous layer but not so thick as too "blur" in the Z direction, that is your minimum ST. Your Maximum ST would be the DOC after an extended exposure time. These two times will be used in the "Factor Tool..." later.

Go to the Materials Catalog and create a Duplicate of one of the existing materials giving it a Name, Description and entering your Minimum Slice Thickness and Maximum Slice Thickness.
I'll talk about the Exposure Factor and DOC Rate Factor at the end of this post.

The Over Cure Multiplier is applied to "edge" pixels. Because of light bleed in the XY plane, a pixel surround by other active pixels receives more energy than one that is not. So we "Over Cure" these perimeter type pixels by some small amount. If you have a lot of pigment (low light bleed) then the Over Cure Multiplier should be very small, less pigment, it may need to be a bit larger (see Cherry vs Red).

Determine your desired Attach Multiplier and Attach Layers. Attach Layers is the number of initial layers that get over exposed in an attempt to get better adhesion to the build table. The first layer may be thicker than normal, as there can be variations in the gap between the pdms and the metal build table. Most times, you will only need 1 or 2 Attach Layers. The Attach Layer Multiplier is used to determine the exposure length as a multiple of the calculated normal exposure times. Something like 1.5-2.5 is a typical value. Too low and you will have attach failures, too high and your first layers will stick to the pdms and the release cycle will jam.

The Shrinkage Multiplier is for compensating for post print shrinkage. If you print a test part on a perfectly calibrate machine that is supposed to be 1.0 wide and the actual, post cured, object is .98 wide, the you would use a Shrinkage Multiplier of .98. In practice, this will cause the printed ("green") object to be printed larger, such that when it post cures and shrinks, it should be the correct size.

Finally, The Exposure Factor and DOC Rate Factor are determined using the "Factor Tool..." button. You set up the factor tool with specifics of the machine you are using to experiment and enter your experimentally determined Minimum ST and Maximum ST exposure times. The tool then calculates the Exposure Factor and the DOC Rate Factor for you.

Printer inputs are:
MDM - "Model Differences Multiplier", aka "Projector Multiplier" This value is 1.0 for v1.0-v1.1 model printers and 0.5 for v1.2 model printers. This compensates for different projector model outputs beyond simple lamp wattage.

PPM - "Projector Power Multiplier" is calculated as 240 watts / the projectors power (240 watts for v1.0-v1.1 and 280 watts for v1.2). This compensates for different lamp sizes.

IAM - "Image Area Multiplier" is calculated as the X resolution * Y resolution * the pixel size / 1966.08. IAM will equal 1.0 for v1.1 machine calibrated to 50 microns.

MSM - "Machine Specific Multiplier" is from the experimenter's printer's settings, when the testing was done.

LFM - "Lamp Factor Multiplier" compensates for the experimenters current lamp age when the testing was done. Both the D535 and the D912 have rated lamp lives of 3000 hours, which means, if they have not failed, they put out about 1/2 power after 3000 hours.

You must enter all the above info based on the printer you used to do your experimental testing. Then enter the experimentally determined exposure times for min & max Slice Thickness and the Factor Tool will calculate the Exposure Factor and DOC Rate Factor for you.

Once these factors are set, you have a "new material" in the catalog that should work the same on any other printer at any other calibration. You can export this material and share it with others that can import it into their catalog.


To see an example of the above explanation for Red, go to the Materials Catalog, make a Duplicate of Red, observe the various fields and click the "Factor Tool..." button to see the info that goes into computing the Exposure Factor and DOC Rate Factor and Overcure Multiplier. You can also hover over a field to see a brief description or use the "?" button and click on a field for a more detailed description.
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rapidmanufactory
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Exposure parameters reference/documentation

Post#7 » Wed Sep 17, 2014 2:20 am

Hello mike,
thank you for taking the time to post this, we're still assimilating it and will get back with questions if any or our results for Spot-HT and Spot-E.

Thanks again,
Chady

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panastation
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Exposure parameters reference/documentation

Post#8 » Wed Sep 17, 2014 3:02 pm

thanks mike

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Exposure parameters reference/documentation

Post#9 » Thu Sep 18, 2014 2:22 am

Thanks for posting this Mike, you lost me already about paragraph 4! :-) but I'll have another read through when I'm not so sleepy, I do want to understand this!
ZLab3d, printing with B9Creator 1.1 & 1.2 since 2013

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ROSITAGIOIELLI
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Exposure parameters reference/documentation

Post#10 » Wed Oct 08, 2014 5:23 am

Hey Mike, for someone you post the parameters bible! Now I begun to understand some thing! I suggest to write that also in the user manual
Thanks Sergio

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Archimedes
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Re: Exposure parameters reference/documentation

Post#11 » Fri Dec 19, 2014 10:29 pm

mikej wrote:For a given pigmentation, you should be able to achieve a DOC that is thick enough to attach to the previous layer but not so thick as too "blur" in the Z direction, that is your minimum ST. Your Maximum ST would be the DOC after an extended exposure time.


Mike, thanks for putting this together. I understand from the quote above how to determine minimum ST, but how do you measure the actual depth of cure for the maximum ST? Am I missing something obvious?

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brumbaer
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Re: Exposure parameters reference/documentation

Post#12 » Sat Dec 20, 2014 3:15 am

Depth of Cure is not measured, it's calculated.
See it as a material constant.
What you do to get the values for any resin is,
    Choose the minimum and maximum thickness. Basically you set those values to the range you want to use and hope (or know) that the resin will be usable in this range.
    Determine the correct exposure times at min and max thickness by doing some test prints.
    Open the calculator and set the parameters according to your machine and what you determined and the DOC and normalizedMinExpTime are calculated.
When setting up a print the software will use DOC, min thickness, normalizedMinExpTime and the parameters of the printer to be used (MFM, LFM etc.) to calculate the base exposure time for the selected thickness on this machine.
It's something like this:

Code: Select all

base = exp(DOC * (targetThickness - MinThickness) / MinThickness) * normalizedMinExpTime * IAM * PPM* LFM * MSM * MDM;

exp(x) is e raised to the power of x
The max Thickness is a not needed for this, but is needed to recalculate DOC in case of changes, so it is also a material parameter.

The additional parameters for overcure and attach exposure times layer are straight forward multipliers, you will have to determine experimentally or make an educated guess for.

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Archimedes
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Re: Exposure parameters reference/documentation

Post#13 » Sat Dec 20, 2014 9:38 am

brumbaer wrote:What you do to get the values for any resin is,
    Choose the minimum and maximum thickness. Basically you set those values to the range you want to use and hope (or know) that the resin will be usable in this range.
    Determine the correct exposure times at min and max thickness by doing some test prints.
    Open the calculator and set the parameters according to your machine and what you determined and the DOC and normalizedMinExpTime are calculated.

Thanks for this. I am presently working with Spot-HT using the 30μ xy / 25μ slice settings you posted previously, but I am encountering some z-bleed on unsupported areas. I am contemplating adding additional pigment to solve this problem, so I want to understand the process for experimentally determining the new material parameters. When selecting correct exposure times at the target minimum and maximum thicknesses, what should I look for in a test print other than z-bleed?

It's something like this:

Code: Select all

base = exp(DOC * (targetThickness - MinThickness) / MinThickness) * normalizedMinExpTime * IAM * PPM* LFM * MSM * MDM;

This is the equation that the factor tool in the materials catalog uses to calculate the exposure time at minimum slice thickness, so “DOC” = “DOC Rate Factor” and “normalizedMinExpTime” = “exposure factor”, correct?

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brumbaer
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Re: Exposure parameters reference/documentation

Post#14 » Sat Dec 20, 2014 2:35 pm

I do not know the B9 sources, but the formula I gave, gives the same results, so the B9 software will use that formula or something very close to it.

In the 1.6 software you had to enter the exposure values for each combination of thickness and resolution. With two printer models, you would have to double the number of combinations. You would end up with something like (25 - 70) / 5 = 9 That's 10 thickness values * 3 resolutions * 2 printers = 60 values per resin.
The 1.7 just asks for two values and interpolates the exposure for other 58 thicknesses/resolutions/models combination.
This is interpolation, it is a mathematical model. The real world does not have to agree with it :)

Also this formula expects all parameters to be correct. Reading the forum you might have come across posts in which changes had to be made to the MDM value - a case where the parameters were not correct.

Using a material should usually give decent results, but it is not guaranteed. The results will be the better, the closer you are to one of the two value/combinations used for computing the materials doc/exposure value, provided your machine and the "material creator's" machine are close to the "theoretical machine" described by the parameters.

Anyway, if you want to have "perfect" settings, use the exposure times given (read calculated for your machine and model) as a start and experiment with the values in the print dialog until the results are what you want and than feed those values into the material editor/calculator creating a new material especially for this thickness.
Alternatively you can try different MDM values on the material in question.

Note: I'm not saying that this is necessary at all times, you might get very good results with preset materials: But it is also possible that you get better results, by modifying MDM or even creating your own material.

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Metalcaster
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Re: Exposure parameters reference/documentation

Post#15 » Sat Dec 20, 2014 3:58 pm

It might be a good Idea if we could save the MSM values we assign to a new material when it ends up working>>> currently you can only save other values(correct me if i am wrong on that).
I am running 2 different materials that I use a different msm values on. When i come up with these changes, I have to write them down instead of being able to save them with the specific material

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Stephen Attaway
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Re: Exposure parameters reference/documentation

Post#16 » Sun Dec 21, 2014 9:06 am

Hello, B9 team,

I assembled my B9 the day after Thanksgiving and have been learning to use it for making detailed jewelry parts. I really like this machine.

I find the B9 forum very useful. Just after assembling the unit and getting my first print, I had to travel for a week. During the time I was trapped in an airport terminal for hours between flights, I spent time reading the posts on the forum. Each night at the hotel, I read the posts on the forum. I read the manual, the wiki, and fully explored the software. An unexpected bonus of the B9 and the forum is that Mike reads and comments on nearly every post. What a joy it was to explore the history and see the development of the B9 unfold.

In an effort to better understand the red, cheery, and 1:1 mix, I performed a set of tests to help me understand how my projector was exposing the material and how sensitive the material is to changes in exposure. Shown below is a plot of the depth of cure as a function of lamp exposure time. When the exposure time is plotted with a log scale, the exposure curve presents a straight line. This means the depth of cure is an exponential function of the exposure.

b9 thickness vs time.jpg


If you want to better understand the reason that the depth cure follows an exponential of the exposure, the following link may help: (http://en.wikipedia.org/wiki/Beer%E2%80%93Lambert_law)
The Beer–Lambert law relates the attenuation of light to the properties of the material through which the light is traveling. The two sentence explanation of the Beer-Lambert law is: “Divide an attenuating sample into thin slices that are perpendicular to the beam of light. The light that emerges from a slice is slightly less intense than the light that entered because some of the photons have run into molecules in the sample and did not make it to the other side.” The exponential nature of light absorption means that not only will the total thickness vary non-linearly with exposure, but the degree of cure within the layer will not be uniform.

To make the measurements, I followed these steps:
1) Insure that there is sufficient material in the vat to cover the exposure area with about 2 mm of resin.
2) Remove the build platform from the B9. Leave the sweeper in place.
3) Load a job to print with a nice size base layer.
4) Override the exposure for the attached layer to define an exposure time (t=2.5,5,7.5,or 10 sec).
5) Start the print and press the pause button as the exposure begins. The pause will allow the print to complete.
6) Retrieve the exposed layer. If the sweeper is in place, then the base layer will either be pushed to the side or still be attached to the PDMS. I recommend rubber gloves with lots of paper towels on hand for this somewhat messy operation.
7) Abort the print, change the exposure time, and repeat with the next exposure time.

After a carful drying of the samples with a paper towel, I fully cured the parts with a UV LED flashlight. I measured the thickness of the parts with a “digital readout outside micrometer” (available on eBay for $17).

I used Excel for fitting the data from the measurement using a log format for the time axis. I used the equation from the Excel fit to compute the cure layer based the exposure time set by the default settings from the print menu. The default exposure time for the 1:1 mix was 1.77 seconds. The computed thickness for the 1:1 mix was 0.24 mm. The computed thickness was much greater than I expected, since the layer thickness is only 0.03 mm.

I understand that the cure thickness must be greater than the layer thickness to insure a good bond to the next layer, but I was not expecting an 8x ratio between the layer thickness and exposure thickness.

One interesting thing I learned during this process is just how much the strength of the resin is affected by the exposure time. The thick layers (0.4 mm) were plenty strong, but the thinner layers (0.27 mm) were very flexible and almost like a wet noodle. When I exposed them with the UV flashlight, they instantly became hard and rigid. Clearly, the degree of monomer conversion for a lightly exposed layer is much less than 100%. Given the Beer-Lambert law, each layer will have an exponential exposure gradient through the thickness. Setting the exposure time to produce a layer thickness of only 0.03 mm would likely produce too week of a part to allow full bonding with the above layers. In addition, the part would likely be too week to survive the shearing from the PDMS. Other factors like shrinkage with full curing would also likely limit the layer thickness. While the exposure curves cannot be used to compute the minimum exposure time for 0.03 mm layer thickness, they offer insight into how layers are formed and the relative rates of cure for different resins.

The great thing about the B9 is that the software is open, allowing about every factor of the printing process to be changed. The prints are not costly, and they are fast. The resin can take some time to clean when a part fails, but that is not a big problem. All resin based-machines have exposure problems that differ from part to part. The ability to adjust the prints and experiments until the exposure is just at the edge of what is printable is a great feature.

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Metalcaster
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Re: Exposure parameters reference/documentation

Post#17 » Sun Dec 21, 2014 12:26 pm

Great info. Thank you. Do you think that with this info, it would be possible to calculate the cure time of a finished pieces at various thicknesses? Thick parts can have problems curing enough to cast... specially when there is no related formula to determine time .

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Robert Howle
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Re: Exposure parameters reference/documentation

Post#18 » Sun Dec 21, 2014 12:37 pm

Yes, a post print, curing formula (to determinge time needed based on thickness, etc.) would be great.

Then I guess such things and UV source, total wattage, etc.

Maybe only way to formulate a post cure solution would involve heat (oven curing) where temp and time and object thickness, are the primary variables.

Robert Howle
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Metalcaster
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Re: Exposure parameters reference/documentation

Post#19 » Sun Dec 21, 2014 1:02 pm

Heat curing on thick parts definitely needs exploring, but UV light cure is also an important area... specially for those of us ex
perimenting with different materials for different purposes. Casting has the most need for curing properly.
I use both methods and still have some curing / casting issues occasionally.
This is really good info !

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Robert Howle
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Re: Exposure parameters reference/documentation

Post#20 » Sun Dec 21, 2014 2:14 pm

I for one, am beginning to think that curing properly is one of the major issues with casting problems. Assuming u burnout correctly, sprue, air flow, etc.
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