The dead of the printing of large objects and the effect of hot plates

The dead of the printing of large objects and the effect of hot plates

Source: Http://goo.gl/088nW

Much of this article is mainly about the continuation of the original author's previous "Warping fundamentals" to think. In particular, to think about the speed of printing, the size of the printed object, and the type of plastic, these are the factors that cause the object to curl. There are also some obvious and easy points to note that the use of the him will reduce the phenomenon of warping.

More a same ' out loud ' thinking on the issue of warping in this post to follow on from the Last post on warping Funda Mentals. In particular, thinking on the speed of a print, the size of an object and they type of plastic all effect warping. Also some other obvious points on why a heated print bed helps reduce warping.

and then we're going to talk about the speed of printing, the size of the objects, and the impact of plastic species on the curl.
The effects of printing speed, object size and plastic types on warping.

By accelerating the printing of small objects, it seems that this way can control the extent of the curl. This may also be due to the short period of time when the outer part of the contour is not cold, so the whole object is held in a more uniform temperature state under a shorter print time, resulting in the results.

By printing small objects quickly it seems your can limit the amount of warping that takes place. This is due to the limited time, the outside of the object have to cool and so results in the whole object being of A more even temperature through the short duration of the print.

[Object above] represents a larger or slower printing object. [The object below] represents a smaller or faster-to-print object The left side is the cut-off slice of the object (right). Red represents a schematic map of the temperature distribution of the object. Top of image:a large object or an object which is printed at A slow speed. Bottom of image:a quickly printed or smaller object. The left hand side are a cut away of the solid object on the right.

In the same way, the picture shown above is used to illustrate two objects at the same printing speed, and the larger object is the smaller object below. Because large objects have to be printed for a longer period of time, it also means that the circumference of this object has a longer time to be cooled, which leads to the result of the dead song.

Again, the image above also applies if the top object is larger than the bottom and both were printed at the same speed. The larger object would take longer to print and so would have a more time for the sides of the object to cool and possibly re Sulting in less warping.

Or, when different plastics are used, the above objects can be seen as high-temperature hot-formed plastics (e.g. HDPE HDPE, which is the family milk bottle we often see), and the following objects are low-temperature hot-formed plastics (e.g., starch powder, raw plastic pla). In contrast to the room temperature, when we heat up the plastic and start printing, for example, HDPE and PLA, we compare two objects with the lower edge temperature (relative to the center temperature of the object), the former is the winner.

The image above also applies if different plastics is used, with the top object being a high temperature Tg plastic (Eg: HDPE) While the lower image being a low temperature Tg plastic (EG:PLA). The higher temperatures relative to ambient (often 25oC) required to print HDPE would result in the outside edges falling I n temperature considerably faster with respect to the centre than compared to PLA.

This image contains information about two objects/temperature/location Differentiate between HDPE and PLA, the size of the printed object is 50mm 0 represents one side of the object, 25 is the center position, and 50 is the other edge of the object. Fictional temperature profiles through the centre of a 50mm Wide object during printing. Zero mm is one side of the object, 25mm is its centre and 50mm are the other side of the object.

Although the temperature of the edges of the HDPE objects is even higher than the temperature of the center of the PLA objects, they have a large distance from the temperature of the center of the HDPE object, but it is the transformation that immersed in this temperature that has led to the dead's phenomenon. The expansion of different plastics (expansion coefficient) is also a key environment.

Although the sides of the HDPE object is hotter than the core of a PLA object, they is still relatively a lot cooler tha n the core of the HDPE object. It's This steeper temperature gradient, leads to warping. Differences in the expansion coefficient between the different types of plastic of a-also play a part.

Hot plate and dead curved image
Heated beds and warping.

The hot plate is obvious and easy to see, is a large object cold, or high temperature heat-forming plastic, such as one of the solutions. The application of the hot plate is widely admired because of the impact of the use of this device.

Heated beds is the obvious solution to the problem of cool off on big objects or high Tg plastics. The wide spread adoption of heated beds are a tribute to their effectiveness.

The temperature of the hot plate (right) and the working panel under the room temperature (left) are displayed. The direction and size of the arrows represent the internal forces that crowded to the hot core as a result of an external bulge. A heated bed (in red) was on the right and a of the temperature bed on the left. The direction of the arrows and their size represent internal stresses caused By contraction of the hot core after the exterior have already become ridged.

Unfortunately, even with the use of hot plates, its effectiveness is limited. When an object is printed, the heat of the hot plate will decline at a high level. I guess the effects of this heat effect, from the block above the object, are nothing to do with the hot plate. These are the inner forces that act on the upper layers of the layer, although they do not cause the lower layers (or other non-stressed layers) to curl at the edges, but are sufficient to reduce the strength of the object to hold a fixed shape.

Unfortunately it seems even a heated print bed has its limits. As an object is printed the warming effects of the heated bed would diminish with height. I Imagine this and leads to the same warping effect in the top sections of the the object that's present in objects printed W ith out a heated bed. These internal stresses that build in the top layer would weaken the object even if it's not enough to cause the lower, s Tress free layers, to curl up at the edges.

This problem can be improved from the following method, and from above continues with the hot air blowing to the object. A warm working space or an environment with a red outer light bulb (infrared globe) on the top shelf. However, if the general commercial printer can not use the soluble (dissolvable) support material (RepRap series is testing), the original author's understanding and imagination, the use of the present line with such a temperature environment has its limitations, such as the fragile sowing pick part, And sticking out of the part of the outside like the snot. One way to resolve these drops is to use a large number of fan fans, but this will return to the problem of dead for the loss of temperature * (note).

This problem could is solved by streams of the hot air blowing from above, a heated build chamber or even an infrared globe AB Ove the print bed. However, with out the dissolvable support material used in commercial printers (work in progress for RepRap ' s) I imagine T His would also has its limits as slight overhangs or teardrop through holes the begin to slump on larger objects. A simple solution to slumping are to strap on a lot of fans, and then you would being back in square one with the warping prob lem* ...

* Note: If there is a way to analyze a 3D object and point out which side is most likely to be the most prone to this kind of drop, it is really wonderful; we can pin this riskier to the print block, and we control the air flow by controlling the fan side of the jet. This will also combine a warm working block, and avoid high temperatures to drop the plastic. But it's just a matter of thinking ~

* Just as a side note:what would be really nice are if there was a-to-analyse a 3d object and determine where slumping is most likely to occur. Then throughout the print a fine jet of the class temperature air aimed at the print nozzle could is turned on or off as the PR int head Prints the layers above these ' high slump risk zones '. You might is able to get away with a elevated build chamber temperature and reduce slump at the same time. Just a thought.

A slow-control way to reduce temperature is also a way to significantly reduce the dead of a large object when it is printed. In contrast to the full heat of the hot plate, to completely stop the heat and replace it with a gradually decreasing temperature (for example, to reduce the 2-3 degrees per minute, until the temperature is reduced to the chamber). The purpose of doing this may be to reduce the number of scrolls, but the original author says he has not yet tried it. (Small editor: This is really effective!) ）

It may also is possible to greatly reduce warping by have a slow controlled cool down such as used when casting large OB Jects. So instead of the heated bed switching from "full on" to "full off" there could be a gradual decline of 2 or 3 degrees per Minutes until temperature is reached. This might aid in reducing warping but have not been tested as far as I ' m aware.

It should be noted that the hot plate should be able to provide strong adhesion, especially its surface and plastic bottom of the first layer of the touch. The reason why I am concerned is that in high temperature, the interaction between chemical molecules is more intense (surface tension of low temperature hot melt plastic); During long periods of time, the plastic heat melts on the surface and then into a liquid-like coating and extension. (For more information please refer to this article, the original author wrote the article mentioned "plastic is like glue water")

It should also be noted this heated print bed seems to also allow for greater adhesion between the print bed surface a nd the first layer of plastic. From what I can gather this is due to a increase in intermolecular contact brought on by the higher temperatures (Lowe R molten plastic surface tension) and the longer time frame were the plastic is molten at the surface and so can spread (w ET) more. More info.

In any way, I hope this information will help the new members of the RepRap community. If I omit what part or part is wrong, please let me know. (The original author is a guest of the atmosphere)

Anyway, I hope those new to the RepRap community find this helpful. If I missed a few things or something doesn ' t seem quite right, by all means, let me know.

About the original author Richard , is a PhD student in Australia's reading materials engineering. The first response under his text is that there are many argued and supplements to the above text, and the points raised are interesting and hand-flipped.

I really think that this kind of theoretical analysis is important for solving the problem of dead. I wrote a short analysis (should also be makes a few more details). As I write this response, I think more deeply about the factors that cause dead, and obviously my analysis is different from yours, so I get a different conclusion, so I think it's important to leave this message here.

I really think this kind of theoretical analysis are important to solve the warping problem. I wrote my own short analysis in the thread:http://forums.reprap.org/read.php?1,55300 but I might does a more detailed WRI Te up as well. Writing that post made me consider in more detail the causes of warping. My analysis differs in important ways from yours, though, which leads me to different conclusions. So I feel it's important to comment here.

I think both of us know that the key to dead Kephason is the narrowing of the temperature (thermal contraction). In a calculated way, we can imagine that no matter how small any segment is, it has two different lengths, high temperature length (Lh) and low temperature (Lc), and each plastic is LH>LC.

It's clear to both of us that the key factor if it comes to warping is the thermal contraction of layers. For a qualitative analysis, we can imagine that any short segment of filament have both lengths:the length when hot (Lh), a nd the length when cold (LC), where Lh > Lc for any particular filament.

Any time you want to print a hot plastic on a cold plastic, you have to think about four changes in length. The first is the printed plastic (L1H), the second is the length of the plastic cold (l1c), and the third is the length of the old plastic (L2H) when it was printed, and the length (L2C) of the old plastic cold.

Any time your print a hot filament on a cold one, and you had four lengths to consider:the length of the hot new filament whe n Freshly printed (l1h), the length of the new filament after it had cooled (l1c), the length of the old filament when it was freshly printed (L2H), and the length of the old filament when it had cooled (L2C).

We know l1h > l1c and l2h > l2c, according to the temperature of the shrinkage.
Due to thermal contraction, we know that:l1h > l1cl2h > L2C

We also know that hot plastic is printed on cold plastic, so this means that the two sides are equal in length: l1h = l2c
But we also know this new, hot filament was printed on the old, cold filament. This forces their lengths to be equal:l1h = L2C

This is the Xiaozheng that causes the problem to be produced. When the object is cold, the object scrolls because of l1c < L2C. uneven cooling is not the cause of dead, and it doesn't matter which part of the print is cold first. It is important that the printed plastic is stacked on top of the cold plastic. A slow cold does not have to have any difference with the quick cold.

That ' s where the trouble happens. When the object is cools, l1c < L2C, so the object warps. Uneven cooling does not leads to warping; It doesn ' t matter which part of the printed part cools first. What matters is the hot filament is deposited onto cold plastic. A slow cool down shouldn ' t is any different than a rapid quench.

If you take an object that has no dead at all, and then increase the temperature of a particular change (at any rate of increase, such as a changing high temperature difference), the object will be curved. But when you let the object return to the uniform temperature (regardless of the rate of temperature), it will return to the original form. The problem now is that the object being printed is an unfinished state (because it is shaped in an uneven state); when it is brought into a homogeneous environment, it will dead, and it is not important to change it fast or slow. "-------- The exception to this is that if the temperature change is large enough to cause phase changes, the internal structure will change after this process, in this case.

If a Un-warped object at a uniform temperature, and impose a temperature gradient on it, it would Warp. If you return the it back to uniform temperature, it'll return to its original shape. The trouble is, a reprapped part was an un-warped object at a nonuniform temperature. When it was brought to a uniform temperature, it warps. It shouldn ' t matter how quickly the transition happens. The exception is if the temperature change was high enough to cause a phase change, in which case the internal structure WI ll be different before and after the process.

Now think about the impact of print speed and object size on dead. The difference between LH and Lc is a proportional relationship to the temperature change (LH = LC + a DT). To make a very fast or very small print, all the plastic is stacked in a rapid manner (no time to cold), so this time the DT = 0, and there is no dead of the phenomenon. Conversely, in a very large or very slow printing state, the first impression of plastic is always before the new plastic printing stack, cold to room temperature, this time the DT = max (the maximum value of material heat).

Now to consider the effect for print speed and object size on warping. The difference between LH and LC are proportional to the temperature change (Lh = LC + A DT). For a infinitely fast or small print, all the filament'll be a deposited instantaneously with no time to cool between lay ERs, so DT = 0, and no warping occurs. For a infinitely large or slow print, the old filament have always cooled to the ambient temperature by the time the new F Ilament is laid down, so DT = max.

A printing routine is neither very fast nor very slow, so there are two key factors to think about; The object is cold from the surface (heat and heat irradiating), as well as the heat spread (heat). The heat is produced by a new stack of plastic, which is transferred from the new plastic to the cold surface of the old plastic.

For a print that ' s neither infinitely fast nor infinitely slow, there ' s II important factors to consider (that I can thin K of). There ' s cooling from the surface of the part (convection and radiation) and thermal diffusion inside the part (conduction) . Heat is added from the surface, with the form of freshly deposited filament, and then conducts through the body of the Toward the cold surface.

This is not a drastic change in the temperature of the dead. The heterogeneity temperature mentioned here refers to the edge region of the object, where hot plastic is printed on a cold surface, but in the center of the heated plate, the warm plastic is printed on warm plastic. This appears to imply that the part of the boundary will have the greatest force, and that the interior of the object is the least-sold, because DT is the smallest in the center. However, even if the object does not have a temperature gradient (for example, if it is a consistent cold, such as a slow-print state), the dead will happen (because the newly printed plastic is hot). This is only a purely consideration, but the dead of the song will even consistent the whole part.

It isn't the steepness of the temperature gradient that leads to warping. What's this non-uniform temperature means was that at the edges, hot filament was printed on cold plastic, whereas at the cent Er, hot filament are printed on warm plastic. That means, the warping stresses would be a highest at the edges, and less at the center, because Delta T was less at the Center. However, even if there were no temperature gradient in the object (ie, if it were uniformly cold, as in the case of the SL ow print), warping would happen because the fresh filament is hot. It's just that's the case, the warping stresses'll be even throughout the part.

Sexually speaking, there is no big difference between the two. The accesses than either is a balanced roll (so it may be the cause of a parabolic change in the bottom), and the other is an unbalanced roll (perhaps a dead that is closer to the four-curvature line, with a drop in the edge), and, in any of these, the dead of the object.

Qualitatively, there ' s not a big difference between these, cases; One warps evenly (so it would probably form a parabolic shape in the bottom) and one warps unevenly (so it might is more O f a quartic curve, with the steepest bend at the edges). But they ' d both warp.

In my imagination and understanding, an object can be printed to a very high degree, as long as the hog before the effect of the hot plate is declining. Hot plates are usually more forgiving than the object itself, and the increase in heat and temperature increases from the edges of objects, while the cooling effect of reducing the flow is also. If this phenomenon becomes a disturbance, then, when the print is pushed up to a certain height (this is the basis for the entire structure change), simply raise the temperature of the hot plate, so that the upper surface can hold a constant temperature of a fixed degree of warmth. However, this may require some very sophisticated software.

An object would has to be very tall before the effect of the heated bed could really wear off, I imagine. Because the heated bed is generally wider than the object, there should be warm convection currents rising and warming the Sides of the object, reducing convective cooling. If it became a problem, then up to a certain point (the point where the base of the part would undergo a phase change), th e temperature of the heated bed can be increased as the object gets taller, so as to maintain a constant temperature at th e Upper surface. That's would probably take some sophisticated software, though.

Jacob

The dead of the printing of large objects and the effect of hot plates