The Effect of Vacuum Seal Drawing in SLA/DLP/LCD 3D Printing

 


 

In the last article, we shared Obtain the Parameters of Photosensitive Resin in SLA/DLP/LCD 3D Printing (Ⅰ): Exposure Value. Using the method shared in the last article, we have tested the optimal exposure value of an ABS-like resin is 3s on a frequently-used machine. In the following measurement, we printed a tolerance matching bottle and cap, but the verification effects are quite different from our expectations. During the gradual investigation, we found that the most influential factor to the measurement was vacuum seal drawing.

 

 

Follow us to measure the impact of vacuum seal drawing in SLA/DLP/LCD 3D printing. First, we used the recommended default lift speed and retract speed of 40 mm/min and 50 mm/min to start the first measurement.

 

 

Test 1

 

Exposure Time: 3s

Lift Speed: 40mm/min

Retract Speed: 50mm/min

Print Time: 3h25min

 

In the first test, both bottoms of the bottle and cap were attached to the vat. Considering that the lifting speed was too fast which led to excessive drawing force, the model was directly pulled off the build plate. Therefore, in test 2, the lifting speed has been excessively reduced to 10mm/min, so as to determine whether it is the speed factor.

 

 

Test 2

 

Exposure Time: 3s

Lift Speed: 10mm/min

Retract Speed: 50mm/min

Print Time: 5h17min

 

It could be clearly seen that after lowering the lifting speed, the printing time had extended a lot. Though the printing was successful after lowering the speed, there were too many uncured residues on the surface. After cleaning, the surface quality of the model was very poor due to the residues. And breaches were obvious in some parts.

 

 

During the cleaning process, brushing the surface of the model with a banister brush can remove a lot of uncured suspended residues. And filtering the alcohol after cleaning with a paper funnel, it left a lot of impurities in the filter.

 

 

To sum up, considering whether it is underexposed, the exposure value has been increased to 4s in test 3.

 

Test 3

 

Exposure Time: 4s

Lift Speed: 10mm/min

Retract Speed: 50mm/min

Print Time: 5h29min

 

After the exposure value was increased to 4s, the uncured residues on the surface were not significantly reduced. The surface quality after cleaning was slightly improved compared with the second test, but there were still breaches. Considering that the resin was not totally new which had been repeatedly added and used for more than a week. In order to judge whether the resin deterioration has affected the surface quality, the new resin has been replaced in test 4.

 

 

Test 4

 

Exposure Time: 4s

Lift Speed: 10mm/min

Retract Speed: 50mm/min

Print Time: 5h31min

 

After replacing the resin, there were still uncured residues on the surface especially the bottle body part which could be scraped with a scraper. After cleaning, there would be a significant improvement for the surface quality compared to the first few tests. But breaches were still existed.

 

 

As a result, it is still necessary to continue to verify whether the exposure is insufficient. So the exposure value is excessively adjusted to 6s for test 5.

 

Test 5

 

Exposure Time: 6s

Lift Speed: 10mm/min

Retract Speed: 50mm/min

Print Time: 5h53min

 

The first thing you could see was that adjusting the exposure also had an effect on the print time, but much less than the speed. After the exposure value was adjusted to 6s, there was no breach on the model. And uncured surface seemed to be improving but it was still obvious. After cleaning, the surface quality was better. But compared with the previous tests, it was closer to the tight fit.

 

 

When the exposure value was adjusted to 6s, it showed a tight fit state, indicating that over-exposure had happened. But the phenomenon of uncuring had not been significantly improved. Considering whether the angle placement has an impact on the uncured condition, we replace the sticking bottom printing with an angle placement test.

 

Test 6

 

Exposure Time: 6s

Lift Speed: 10mm/min

Retract Speed: 50mm/min

Print Time: 9h32min

 

 

The test found that when the bottle and cap were placed at an angle of 60°, the uncured condition was still obvious. At the same time, an obvious horizontal dividing line was found on the cap. During the printing process, the dividing line happened to be formed from the vacuum state to the non-vacuum state. In order to judge whether this line will change with the placement angle, we print the cap separately and place it at 45°.

 

 

Test 7

 

Exposure Time: 6s

Lift Speed: 10mm/min

Retract Speed: 50mm/min

Print Time: 5h53min

 

After placed at 45°, the position of the dividing line did move correspondingly, which still occurred in the transition position from vacuum state to non-vacuum state. And the uncured condition was improved compared to 60°. In addition to this dividing line, another dividing line also appeared above. In order to eliminate this vacuum seal state and improve the uncured phenomenon, we make holes at the bottom of the cap.

 

 

Test 8

 

Exposure Time: 6s

Lift Speed: 20mm/min

Retract Speed: 50mm/min

Print Time: 5h19min

 

We printed a set of two caps with a 5mm hole for one cap and two 3mm holes for another. Also, the lifting speed was increased to 20mm/min due to the disappearance of the vacuum environment. There was no obvious difference between the two caps. The dividing line still existed, but uncured phenomenon had disappeared basically.

 

 

Conclusion

 

The reason for the repeated verifications is that many factors affect the quality of 3D print. Among all the factors, vacuum seal drawing has a great influence on printing:

 

  1. Excessive drawing force causes the model to be pulled off the build plate.

 

  1. Excessive drawing force leads to unstable resin liquid level, resulting in serious uncured condition on the surface.

 

  1. At the junction of the largest cross section changes, the drawing force leads to the instability of z-axis and obvious dividing line appears.

 

Also, you can consider placing the model upside down to avoid the problem of vacuum sealing, as shown on the right of the figure below. Aslo a proper angel should be taken into consideration to avoid adding supports to the screw on the cap.

 

 

You may notice that some of the prints still have some problems, as shown in the figure below. Due to limited space, we will continue to share with you in the next article why these lines occur and how to avoid them.

 

 

Model Source:

https://www.thingiverse.com/thing:384578