Do we need mold release agent in 3D printing mold? If it is not used, what effect will it have on the product?
It seems I misread your question.
3D Printed Mold
You were asking about (or the question now states) use of a mold release compound to prevent a molded part from sticking to a 3d print mold.
Yes. It is always beneficial for the molded part to not stick to the mold. Easy separation and part removal is important for the life of the mold and for the surface finish of the part.
There are two molding situations that seem important.
Flexible Mold or Object
In the first, either the part of the mold is elastic, so the actual sliding of one surface on the other isn't important. Here, a mold release agent would help by preventing the cast object from binding to the mold material.
Stiff Mold and Object
The second case is where both the mold and the object are stiff, and the object must slide out of the mold. Here the layer lines should be considered, since there may, locally, be reverse draft angles where the larger part can not slip past an obstructing filament line. Using a process that doesn't leave filament lines, or using the thinnest possible filament layers, or smoothing the mold internal surfaces, or possibly filling the spaces between the ridges with another material may eliminate the problem. A "mold release agent" would still be used to reduce the attachment of the object to the mold, although one may be able to use ample release agent both to fill the groves in the mold and prevent adhesion.
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Used in Casting
A mold release agent is commonly used when a part is cast. The release agent is placed on the inside of the mold before the liquid object is added. As the object becomes solid, the release agent prevents the object from adhering to the mold. As a result, the objects are easier to pop out of the mold, and in some processes, the mold can be reused.
3D Printing is Different
A mold release agent is used to allow the desired part to be separated from the mold. In FDM (thin plastic extrusions bonding together into objects) 3D printing, the object is surrounded by air, except for the bottom where the object contacts the print bed.
For most materials, getting the bottom of the object to stick firmly enough is the problem faced, rather than making it easy to remove. In many cases, a compound is placed on the top of the bed to help the plastic stick to the bed. It is a "mode adhesion agent" rather than a release agent.
For some combinations of materials, the bed material and the plastic have a particularly strong adhesion, such that it can be difficult to remove the object without damaging the bed surface. Notably, this occurs with a PEI bed and PETG plastic. In this and similar cases, the mold adhesion agents can be used on the bed. This slightly separates the plastic from the bed material, and we can avoid bed damage.
With multimaterial printers becoming more common, there are cases where two parts which might touch and stich during printing should be isolated during the printing process. A second (or third) material can be used to isolate the parts. If the isolation material is sufficiently different from the desired objects, it can be removed by a solvent.
This approach is limited to cases where the objects should be separated by at least one printer thickness of the soluble material.
This question lead to an idea of using some "release agent" as anti-stick remedy between support and the printing part.
Basically the main purpose of mold release agent is to prevent sticking. So if the 3d printer will have extra nozzle to dispense agent on top of printed support and before next layers then yes this will be perfect for 3d printing. Support will do role of supporting but not stick to the printed part and as result could be easily removed.
But I am sure almost any oil will do the trick.
My experience with molds in 3d printing: I used 3d printed PLA molds with "oven backing clay" which I believe is mostly vinyl mixed with some organic compounds. With some thinning liquid from the same manufacturer I was able to make clay flow and be injected into mold. I used oil to make clay release from molds easily. After been released parts baked in oven for 30 minutes under 110C. Then they left for some time to cool down and polymerize. The final parts look like plastic but much stronger and obviously heat resistant. This technique could be used to design and test molds that finally will be metal and to be used in real injection molding process. This is what was my original target.