As someone who supports 3D printing as an amazing tool with vast applications across nearly every industry, I also find that its use as a buzzword has not been entirely beneficial the public and new designers. Working with inventors and startups quite a bit over my career I’ve seen the shift of people from saying “I need a prototype” to “I need a 3D print” and it doesn’t always fit the project. Even in school I saw a shift that was moving almost all prototyping to 3D printing. As always we see the bright shiny thing and drop everything else for it rather than seeing it as just a single tool in a large tool box. With that in mind, I wanted to put together a few times that 3D printing isn’t the best way to prototype.
Large mostly flat components. I’ve had clients try to tell me we should just 3D print a flat part that has maybe a couple features on it cut out or added that would fill some of the larger print beds. I’ve done it and it’s either super expensive or there are warping issues that make the part less than idea. In my experience, if you can make it out of wood or sheet plastic (requires less tools than working with metal), then it’s probably easier than 3D printing.
Organic materials, and others. While I highly recommend using 3D printing for fit checks any time you can, if you are looking to have working prototypes that might be made out materials besides metals and plastics, prototyping in those materials is often better. Things like wood, leather, and paper come to mind especially.
Softgoods. Prototyping any kind of softgoods, whether a bag or clothing, requires textiles, not 3D printing. Even the flexible 3D printing does not adequately provide the material needed to even prototype with. It does, however, work great for custom hardware and components that can be used with softgoods.
A side note on hardware and other off shelf components. This one might be obvious, which is why it’s just a side note, but since I’ve had clients ask me to 3D print components that would be cheaper to buy off the shelf, I have to put this here. Sometimes it isn’t the 3D printing that makes it more expensive, but the design time to create the 3D model and then 3D print. If it takes a couple hours of design time, plus time getting the full specs from a vendor, then getting it 3D printed, the cost can start getting high relative to the use. For this reason, I almost always use off-shelf components when prototyping.
This list is short, there are very few applications where 3D printing can’t prototype mechanical designs for fit, function, or aesthetics. The technology is ever changing and I’m sure one day we’ll see the ability to 3D print everything. For now though, there are a few remaining ones you can’t 3D print.