How is a cheap plastic Trash Can made?

Is it injection molded? I ask, because I’ve recently redesigned a plastic trash can from my sophomore year of school, and I need to be prepared to answer how the new design would be made in an interview.

Could this be a 4-part injection mold? Blow molded? Is there another process I’m missing? Recently in an interview I was asked why my design didn’t have a lip on top. I truthfully (but horribly) answered that I was still working on the design. I later realized that I should have asked, “why does the top of a trash can need to be rigid?” - of course, unless that lip is required for manufacturing needs.


EDIT: It seems many cheap plastic cans are injection molded. Would injection molding be possible with my current design?

Hi Cameron,

great to see your progress during your studies.

You are right on track. It is most common to do these things as injection molds, as it is the most
cost efficient solution for large series and gives you a range of materials that are available as
recycled granulate as well. Blow Molding gives you thicker walls, is slower and produces uneven results
with differences in wall thickness. These are not easy to controll in process automation.

As far as your final design is concerned, I am afraid it would be difficult to produce on standard machinery
for injection molding. Usually trash cans are made as cylindrical cones. Just imagine the negative form inside
your can. How would you free the inner mold core out of that can?

It is an attractive idea though and I am sure you`ll find a way to work a way around the production obstacles.
I am sorry, I feel that my english is reaching its boundaries here as technical terms are missing…

All the best.

yours mo-i

Larger trash cans are also usually rotationally molded to my knowledge, but smaller ones probably go the injection molding route.

The issue you are going to have with your design is that you wind up with an undercut (an area where you can’t remove the mold) in those little feet you have sticking out on the sides.

You can do side actions in a mold (the mold can pull out from those undercuts) but this winds up adding a lot of complexity and I don’t think this will solve the issue on the bottom of the pail.
Ultimately though adding complexity to the tooling means a more complex molding process (you now have more moving parts which increases the risk of flash, adds a witness line where the tools meet, and will increase the overall part cost.)

What you may be better off doing is thinking of is there a way to get your design intent with two parts, a main bucket and then a base that combine to form your design.

If you want to keep your intent as is you might be able to have the bottom surface of that undercut hollow, so that it’s essentially just a standing wall off the side of your product. You could pull the tool out of the bottom and then potentially have them flex out of the mold. (This may cause surface damage/drag marks to the part during removal).

Just don’t make the designer mistake of saying that it’s a Fiberglass/Carbon fiber trash can that gets hand laid up. I recall a girl in my studio designing a sh*t bucket (literally, a wheelbarrow for moving horse manure) and then saying that it was made out of Carbon fiber so that it would be strong and light. I literally couldn’t stop myself from shouting “So is plastic…and it wouldn’t cost $15k”. Needless to say she never went far!

Don´t want to be a spoil sport the week before christmas, but don´t you think (cyberdemon)
it would be much better for an aspiring student to find the workaround solutions himself?

With a little hint maybe…?

The horse manure container made of carbonfiber made my day, though… :slight_smile:

Thanks for the advice Mo-i, and thanks for the gift Cyberdemon. =) To be honest, that was actually the solution I was thinking of - where the bottom part is hollow, and the floor of the ‘trash chamber’ is around the level of the foot pedals. That puts me greatly at ease to get some validation.

With the taper on all 4 sides of your design, if you have the floor of the “trash chamber” at the same level as the foot pedals in Cyberdemon’s drawing, you will still have an undercut. That undercut will also be on the cavity side of the mold, which makes it even more difficult if it were on the core side of the mold. Also assuming this is a standard 10-12 gallon garbage can, you will need a 100+ ton press. Your tool costs will very high.

If you want a simple 2-part mold, you will need to change the design. I would put the floor of the “trash chamber” on the ground and think of the pedals as add-on “ears”. If x=width, y=depth and z=height, your current “ears” have an undercut only in the y direction. Change that taper from in, as it is now, to out, and the undercut will go away. You won’t have the integrated lines as the original design, but the tooling cost will drop dramatically. Present both as options.

What if the can and feet were separate elements that snapped together after molding? Or were fastened with screws? You could keep some of your aesthetic only having a small line between where the can and feet meet. Pardon my ignorance, but would that solve some of the undercut issues?

There are even more possible solutions if you want to keep your original design. But everyone I could think of
would drive up cost.
on the other side: the original trash can within your presentation does have more than one
part as well. So it doesn’t necessarily have to be a unipart design if you want to be cost competitive.

Does it have to be made of plastic? (no I am not talking of carbon fibre)

Thanks for the advice everyone. For now I’ll stick with my 4-part mold story, and if they’re concerned, I’ll suggest alternatives to show I thought about it. Maybe next portfolio refresh I’ll change the design a bit, not sure yet…