Voilà les messages du spécialiste qui a répondu sur le forum officiel si ça peut éclairer un peu.
C'est sorti du contexte, mais ce sont principalement des explications, donc les réponses sont autosuffisantes.
C'est sorti du contexte, mais ce sont principalement des explications, donc les réponses sont autosuffisantes.
Citation :Thank you for clarifying the exact polymer is polyamide. I have a PhD in Materials Engineering, and my specialty is thermoplastic polymers and composites, so for the benefit of the rest of the readers I can provide some general background on polyamide and why it works well for this application:
Polyamide comes in a number of different types (PA6, PA6,6, PA12, etc). Each grade has slightly different properties, though they all have similar behavior in general.
When injection molding, polyamide has a viscosity similar to water. This is much better than something like PVC or ABS as it allows the polyamide to fill fine details in the mold (as evidenced by the comparison between metal master and the injection molded part Koni provided)
Depending on the polyamide grade, the melt temperature of the material is similar to that of ABS. Softening and bending parts is doable, though polyamide will be a bit stickier than an ABS model when hot.
One thing to note is that polyamide is more hydrophilic (likes water) than ABS or PVC. This means that polyamide must be dried prior to molding, and the "dry as molded" part that comes out of the mold will be quite rigid (it helps that CB is apparently using polyurethane or silicone molds to demold), but as the part absorbs a small amount of water from the atmosphere it will soften a little and gain durability (to Bostrias comment that you can bend thin pieces and they will rebound to their original position. The other advantage of hydrophilic material is the way it takes paint. Acrylic paint should bond very well to the surface and for those who want to try something different - you can even dye it! You will still want to prime it first to seal the model and achieve a smooth surface finish.
Regular "plastic cements" won't work on polyamides due to the chemical structure (as mentioned by other previously) but cyanoacrylate glue should work well.
I am quite pleased by this announcement. The material selected should provide excellent performance, durability, and paintability. Using this for large models also dramatically reduces weight (and therefore cost) as volume increases dramatically as you scale up size. I also think plastic models such as this are much easier to cut and repose/swap.
Citation :Polyamide is often used in metal replacement applications in automotive, so I think you will be surprised by the performance. Bendable does not mean soft - it just means its not brittle and won't snap (looking at you, Djanbazan sniper barrel that keeps falling off).
Citation :Depends on the exact grade of polyamide they are using, I suspect nylon 6 since its the least expensive but nylon 12 is also pretty common in applications where durability is a concern. Either polyamide should be stiffer and stronger than GW's high impact polystyrene (HIPS), potentially as much as double in both categories. Nylon in general is also abrasion resistant, which is why Bostria recommends against filing. The amount of deformation before nylon yields and breaks is also higher that HIPS, so it should be more resistant to being dropped on the floor or knocked off a table (ie. less likely to permanently bend or snap something).
Citation :I think it would do CB well to market this as "high performance polyamide/nylon plastic". I remember the disaster that was the GW finecast release and I think plenty of people have that kind of knee-jerk response whenever they hear that a metal mini is being replaced by plastic.
If I remember correctly, finecast was a 2 part, cast polyurethane. Casting allows for fine features, similar to why metal cast models have so much detail, but it is very prone to bubbles due to the mixing process and the fact that it gels fairly fast - so if you didn't get the bubbles out fast enough they end up trapped in features of the mold. Polyurethane is also chemically attacked by acetone and isopropanol, so quite hard to strip I imagine (never had any of them myself).
According to this chart, nylon should resist acetone, but its probably not a good idea to use isopropanol. Interestingly though, it resists ethyl alcohol (vodka :p) as well as methyl alcohol (denatured alcohol/methylated spirits).
Citation :The issues you point out are more to do with the silicone mold that the polymer, especially when it comes to the small "bridging" between features that you point out. As mentioned, the polyamide flows very well, which means if the mold doesn't seal perfectly then the injection pressure will cause some polymer to escape. Luckily, since these are plastic, you just need a small pair of wire cutters or your hobby knife to clean them up. Silicone molds enable significantly more feature complexity, such as undercuts and other features that would lock a part in a metal mold, but at the cost of reduced tolerances and small leaks. Assuming this is early days for CB with this process, I expect they will improve as they tune their clamping and injection pressures, as well as develop design standards for molded features to reduce leak paths.
Citation :Of all of the issues, the only ones that really concern me are the ragged holes on both sides. This looks almost like flow freeze, as if the mold gating and flow path was not optimized correctly. There also appears to be slight mold misalignment in a few of the shots as well. I anticipate that this kind of issue will be prevalent in the 1st gen of molded plastics, but hopefully CB implements a stricter QC policy on the initial production to catch these kind of issues and then learns how to refine their mold designs for the next generation.
Citation :Polymer's with "watery" viscosity are more likely to have flashing issues (since they want to flow into gaps, but I don't think they would cause the other issues we see here. The bubble and detail issues are more likely mold design related - bubbling is usually caused by a lack of proper venting (nowhere for the air to go when the injection happens). Silicone molds are also hard to temperature control (in a metal mold you will usually have water piping or build in electric heaters to maintain a specific mold temp. This can make the polymer more likely to freeze when its injected through a tight joint in the model or if the polymer is trying to fill a detailed feature that is far from the gate (and therefore colder). Unlike some cheaper plastics, polyamide starts to degrade if it is more than about 20 degrees C above its melt temp, so you can't just overheat it to give yourself some buffer.
Citation :Yep, mold freeze is a huge consideration in mold design and is probably something that CB didn't have to worry about as much with metal casting since the metal has a higher thermal mass. Cast/injection materials always cool from the outside in, so areas where flow is restricted have the effect of cooling faster and also causing a drop in packing pressure as the entrance to a cavity can freeze before its fully filled. To fix it, you either need to have the part multi-gated so that there are no major restrictions between the gate and the cavities or you change your design rules to mandate minimum opening sizes that are large enough not to freeze until the cavity is fully packed.
Citation :This is correct, nylon is already below its glass transition temperature at room temperature so further cooling it (short of liquid nitrogen) will not produce a meaningful change in properties. The rough filed surface is not due to the plastic melting - rather it is due to the high abrasion resistance of nylon polymers. As CB recommended, cutting and fine sandpaper will yield a much better surface finish. A wet sanding technique is ideal to reduce surface scratches.