It seems we are getting very close to where 3D prints are as good as injection molding. Maybe another 5 years tops?
In some ways 3D printing is better than injection molding at this present time. (1) No relief is needed, so parts can be truly square, truly round, truly vertical. (2) No complicated/expensive injection tool is required, so parts are directly created within hours or minutes of receiving your new 3D resin printer, instead of having to wait months. (3) No need for CAD/CAM knowledge...just need to know how to create 3D models. (4) 3D printers are ideal for small parts...such as those required for N-scale and smaller. (5) 3D printers that will print just about everything you'll need for N-scale will fit on a counter top or table top. (6) Parts can be created that actually nest inside each other, such as actual chain, hinged parts that don't require assembly, complicated interiors of buildings, railroad cars, engine cabs etc. (7) 3D printers that will do everything you need for N-scale (and smaller) cost less than $1,000 for a complete setup...or much lower if your needs are more basic and smaller. ( 8 ) You can print with resins that offer strength, flexibility, clarity, opacity, detail retention, speed or combinations of these qualities...all from the same 3D resin printer. (9) You can make incremental adjustments to the parts/products you're printing if they're not "right" or what you want the first time they come off the build plate in a matter of minutes instead of having to cut a new injection tool that may take days, weeks or months....and much more.
The main problem with 3D resin printing at this time is basically the resin choices that are available. These problems are at least twofold (1) Resin is toxic, smells bad, has a shelf life before curing, and requires control of the work environment's ambient temperature, ventilation, and physical protection of the human operator. Excessive exposure to either fumes or physical exposure can be dangerous for the operator if proper precautions are not made and adhered to. (2) Present day UV resins will get you various combinations of (a.) fine details (b.) tensile strength (c.) flexibility (d.) clarity (e.) surface integrity. If you want a crystal-clear part, such as window panes, or canopy, or dome windows, or vehicle windows that you insert into a body shell, resins will yellow after time, and because of the layer-printing process, not be perfectly smooth...unless you invoke anti-aliasing/blur, which then degrades detail sharpness. If you want a flexible part, such as tires, or passenger car diaphragms, you can print them, but they won't be highly detailed. If you want to print integral stand-off details on your model such as tiny N-scale grab irons, you can print them, but they will be brittle enough to not be durable (extremely fragile). Because of the increasing precision of higher end 3D resin printers, you can get some prints that offer near flawless surface integrity (no layer lines), but curved surfaces are still a problem and require a compromise between retaining details and blurring layer lines for surface smoothness.
Frankly, from a mechanical aspect, we are just about at the point where the printer itself will print surfaces where the layer lines are so small that a coat of paint will obscure them, especially if a bit of anti-aliasing/blur is applied. Printer resolutions vary from the X-Y axes to the Z-axis, with maximum resolution on the X-Y axes being right at 22 microns...which is equal to an N-scale measurement of a little over 1/8". Z-axis accuracy on my Anycubic Mono 3 Premium 8K printer is 0.005mm or 0.00019685" or 5 microns or pretty close to 1/32 of an N-scale inch (4.9609375 microns/0.0001953125")
Get out your tape measure and see how small 1/32" is. That, today, is the the best Z-axis accuracy of a consumer-grade 3D resin printer.
Now, if we could get the X-Y axes accuracy to be even close to that, then we'd be set...maybe.
The question being, will UV resins for 3D resin printers be capable of defining a resolution of 5 microns? 1/32 of an N-scale inch? I don't know. Do injection molded models have a surface accuracy of less than 5 microns? I'm not sure exactly how to measure that, but I would guess the answer is "yes".
The real problem with present-day 3D resin printers' X-Y accuracy...with those that use LCD screens...is that the actual point of focus for collimated light (not coherent LASER light) after going through the LCD, through a screen protector, through an FEP membrane on the bottom of the resin vat, get blurred...a lot. Effective actual horizontal pixel size on the resin side of the FEP film comes in at around 50 to 55 microns...that's 0.0019685" to 0.0216535" or around an N-scale 5/16"...so just the LED technology is a problem.
There is a technology, and a couple of consumer-grade printers out there that sort of "solve" this blurring problem since they don't use an LCD, but project coherent LASER light (after bouncing the beam off thousands of minuscule movable mirrors) through an optical-grade glass window, then through the FEP membrane to the resin in the resin vat. These are DLP printers, but present-day technology limits the LASER dot to right at 51 microns, about the same "effective pixel size" as a top-end 8K/12K LCD printer...but, without blurry edges. This is problematic, making for sharp edges, but much more evident layer lines...so this sharpness has to be mitigated by an effective anti-aliasing algorithm, which the latest DLP printers from Elegoo and Anycubic seem to have done...making them, from a print quality/sharpness aspect, about the same as LCD machines...except with only basic features and a much smaller print envelope for the price.
Soooo...the main advantage nowadays that injection molding has over 3D resin printing is the surface quality, and production speed/volume. However, the costs associated with injection molding a finished kit/part far exceed the costs of buying and using a consumer-level high-end 3D resin printer, and 3D printed parts can be much more accurate dimensionally, and much more complex...even if the surface accuracy may not be quite as good as with injection molding.
In my own experience, with my Anycubic Photon Mono 3 Premier 8K printer with its 28.5 micron X-Y resolution and a 10" build plate...I get parts that I find to be completely acceptable for my N-scale needs...and I am very picky. If I have a problem with layer lines, it's always been something I can correct with print angle, exposure times, etc., and my anti-aliasing/blur functions allow near completely smooth complex curved surfaces, such as roofs, domes etc.
Also, new resins are starting to address the durability problems of resins available only a couple of years ago, as well as specialized resins for transparent, flexible, or extra strong prints, while still retaining good to excellent details.
Finally, water washable resins are becoming more common also. This makes cleanup much less costly/inconvenient/dangerous, even though uncured resins of any sort are toxic until they are cured.
From an industrial standpoint, we are seeing more and more parts of injection molded or etched kits and models being incorporated into the finished product, such as passenger car interiors, or small details that allow easy customization of engines and cars to represent specific prototypes, such as detail parts on Kato's Kobo versions of their E9's representing the modern day excursion service engines that pull UP's excursion/business trains.
There are some 3D technologies that are still verrrry expensive, such as 3D color printing, making painting a model a thing of the past...but, that is still in its late infancy, but is something that injection molding can only do in a very gross way, injecting various sprues of kit parts with different colors of plastic...all of which need to be repainted anyway to look decent.
So, I'm pretty sure that 3D printing is "there" right now for the modeler who isn't interested in producing thousands of kits or finished models, to print his/her own cars, engine bodies, detail parts, people, vehicles, animals, structures, scenic elements...with more accuracy and better looks than injection molded parts...but, ya gotta do the research, learn the techniques, educate yourself how to use a decent 3D modeling program, buy the right machine and resins, and be patient when something fails...to get consistent, most excellent N-scale models out of your desktop 3D resin printers.
Cheerio!
Bob Gilmore
