I thought this was interesting when it was posted in early April, but decided not to pile on to the responses. Every once in a while, the folks at Core77 do step in it and their faithful readers are only too glad to point it out.
Rotational molding! I’d practically forgotten this technique even existed; we see it so rarely, probably because you could accurately describe it as being “expensive, and takes freaking forever.”
For those of us who design products utilizing a wide range of materials and processes, it wasn’t that rotomolding was the chosen process that was notable in his post, it was hipstomp’s apparent surprise that rotomolders weren’t extinct. As many respondents reminded our dear poster, rotational molding is still very much alive and kicking. I have personally worked on several rotomolded products in the last year and know that most molders and mold builders are quite busy indeed.
One of the reasons why you don’t see rotomolding as often as other processes might have something to do with the poor job the rotomolding industry has done promoting its process to the design community. True, rotomolding isn’t appropriate for high-volume applications, but for specific situations requiring the kind of rugged parts this process can produce, there are few other processes that can do the same as cost-effectively. Perhaps watering cans aren’t the best example of that as some observed–perhaps blow molding might have been a better choice (depending on the production volumes), but there would still be a fair amount of scrap generated by that design.
Hipstomp goes on to suggest that RP processes might be more appropriate for the creation of hollow parts. I’m not saying that these products can’t be produced using rapid prototyping methods like Polyjet, but I guess I still question why. As commenter Dave observed:
RP materials and processes are improving, but this is a question that should be posed to people with knowledge of roto-molding and other processes, as well. RP is not a silver bullet, despite what seems like an ID fascination with having a one-size-fits-all answer to manufacturing. As for surface finish, there are RP machines (polyjet) that do pretty high resolution (.0006″ layer thickness). With texture built into the build file, maybe surface finish will eventually not be an issue of “can we make it this way?” “Should we make it this way?” will remain though.
A more fundamental limitation comes into play. RP methods require high precision movements of the RP machine for every part. Roto-molding, like injection molding, blow molding, etc. requires high precision to build the tool, then much lower precision to build the parts.
To be clear, I’m not beating up on hipstomp; I myself am a moderator of the Materials and Processes discussion forum on Core and I’ve re-posted many of his articles on this blog. But it does say something about how we as a design community looks at M&P as the foundation of what we do as industrial designers. True, not all ID’s engage in the development of artifacts, but many of us still do and not all of them are mass-produced to justify infection molding or so custom as to warrant using RP processes regardless of how novel that might be. I think it’s worth taking the time to properly educate our students and continually educate ourselves and our community on the materials and manufacturing technologies (old and new) that are being (still) used today and where each fits in the broad spectrum.
Take a look at the post as well as the comments and let me know what you think.