The story behind the #PIRANHACLAMP
I (@carlf from the Kunststoffschmiede) will share with you the process of how we got to our final mould. It took us nearly 9 months and a team of mainly 4 people.
Don’t even think that we were full time on this clamp, but be sure: Product development takes some time…
So here it is:
The way from an idea to a functioning mould.
As well as the first clothes peg, we made our first prototypes in plexiglas/acrylic glas (You want to know how it works? Watch the turorial on youtube: https://www.youtube.com/watch?v=24ECE3VL13k)
We tested it and it worked. Yes it worked:) Such a good feeling!
But we also had to notice that plexiglas isn’t the right material for the mould. Not in the long run. Because in the current design of the #piranhaclamp we have this tiny bridge from the inner circle to the outside. This bridge is too weak, so it easy breaks when you demould your clamp.
At first we had a working mould and a bad design. Now we had a bad mould and a good design. It did not feel like failure, but we still had not achieved our goal…
All in all I’m pretty happy with the results, the clamps look good and they work!
First they milled a positiv of the clamp out of copper. This copper electrode was used to burn (EDM technique) the form of the clamp into the metal mould. Here are some pictures of the production.
In summer of 2017 we finished building the injection machine, and made the first tests. One of these first test was the clothes peg.
We tried an old design from DDR. We replaced the metal spring with a plastic spring, but it didn’t worked out very well. The spring fractured quite often:( So sad…
Nevertheless it was a success, because we learned a lot about plastic, made an undercut injection mould and presented the first try with many other fancy community creations at the DDW’17.
By using a spanner to tighten the wing nuts (kind of defeats the point) I was able to minimise the flashing.
In the meantime, we have been able to establish contact with an injection molding company. The Schicktanz GmbH: 70km away from our workspace and very supportive.
They have their own workshop to build high-end moulds.
It ended up that they made the mould for the #piranhaclamp for free. Thank you!
Even if the mould was for free, it was a huge charge on our team to supply the right files. It is quite different if you make a testmould with plexiglas or give something in order, which is worth several thousand euros.
We made the last prototypes with the 3D printer.
And after a few hours of discussion we decided us for one design and made all files ready for Schicktanz GmbH.
Here some specs:
parting line: central
draft angle: 3%
engraving depth: about 0,5mm
curves: 0,5mm radius
So our main advise in product development: Failure is essential.
We made the spring thicker, thinner, shapeless and even, but it did not help. She was still breaking. So we came to the realization that we need a completely different design.
Anna made a research about clamps. There’re so many way’s of clamping your laundry. We never would have thought that:)
We wanted to have a clothes peg with just one part and Anna found a design on thingiverse:) https://www.thingiverse.com/thing:339768
When everythin is nice and smooth we are about 30 clamps during one hour. But we are using a car jack to press the mould against the nozzle. That’s a lot faster then threat. and we have less waste because our sprue shorter.
Wow! Good Work!
Do you have any daft angel? When the mould gets warm, the clamp is easy to get out.
The red clamps are polypropylene. I then tried HDPE. It didn’t work too well. I wasn’t able to fully fill the mould and I noticed I had to apply a lot more pressure on the handle of the injection machine. I think I made the gate too small for HDPE, even so I think this shape is better suited to polypropylene.
I’m not overly impressed with the toggle clamps. I usually use socket head set screws in each corner which provide much better clamping, only need an allen key to undo them and really only take a few more seconds to remove. I ended up with quite a lot of flashing on the part on my first attempt, as the mould was not clamped together tightly enough.
Yes we will share the drawings. Licensed under a CC BY-SA 4.0
These are the files we used. pick what you need.
I’m not planning on selling the clamps themselves, just the moulds so people can make their own. I don’t think it really makes sense to sell plastic products in the Bazar, it adds a lot of unnecessary shipping when we should be focusing on tackling plastic waste at a local level. I don’t know if @kunststoffschmiede sell the clamps somewhere, perhaps they do, they would be closer to you than I am.
And here is the listing on the Bazar.
First results, the first thing I noticed is that the mould is quite hard to open and extract the part, due to the relatively long circumference of the part. I added some ‘prising slots’ to the mould. I should have done this first of all but I wanted to see what it was like without.
Ok, here’s my first go at making this mould. Made one small Ooops, set the machine origin in the wrong place on the first half! But not a disaster, was able to recover it. I moved the injection point to where I prefer it, added a gate, and threaded it M10. I haven’t used the toggle clamp system before, I’ll see how it works out. I made the whole mould a bit smaller to save material (kept the same dimensions of the Piranhaclamp obviously).
Now to test it!
thanks a million kunststoffschmiede for sharing and caring !
I’ve modeled the CAM operations so far and from what i see now :
– 25 Euro for 6600 Aluminium
– around 14 hours (+/-5h) machining time (because of the narrow slots with a 2 mm ball end-mill) = 140 Euro (incl. electricity, end-mills, labor)
– 20 Euro Shipping
not sure where to place channel for the plastic entry yet, nor i don’t know this can be done actually with Dave’s default injection/extrusion machine but i will try my best to get it working for both. I know there is a tool to simulate injection molding…. anyone has suggestions ?
ps: finally pp got it’s first nice open-source mold
Hey, sorry to all of you! The past month I was travalling through Kenya without internet…
I have just arrived… for these two points i need some time 😉
1. I’ll have to check what I can share with you. I’m sure we will upload the files. But Kunststoffschmiede is a group of a few people and I have to check if the majority agrees with it.
2. Translate the technical drawings into english
Awesome work, thanks for sharing
inspiring topic! Going to use this one as an example for proper documentation 🙏well done
Hey @carlf this is a fantastic topic. Thanks for sharing. So much knowledge ❤️.
I think this topic needs the space it deserves. Would you like to write (copy and paste 😀) a guest post for our news section?
Also, this needs to be on our Bazar, yes or yes 😇
Keep up the great work.
Great news coming soon
Hey @kunststoffschmiede !
Thanks for the sharing of tall that work; very interesting to follow the “walls” you encountered in the whole process !
So if I am correct; you decided to use PP for your Piranhaclamp?
Is there any reason why the molding may not be able with other types ?
Also; i am curious how you operate the cooling on the molded product; do you let it cool naturally or do you force it with fresh water cooling?
Does your product warp much after cooling ?
Looking forward to read more about this project;
The last steps we have to make is the engraving of the plastic type (we purposely left it out to test if PP is the right plastic) and to find the fastest way to open and close the mould
I hope I could explain it to you well! Feel free to write every question or remark in this topic;-)
Besides we are testing all use cases we can imagine;-)
What comes next?
I probably won’t make enough of them myself to sell, but I may give them away locally and use them as an example of a useful product that can be made from plastic waste with low-tech equipment.
Ok, here’s version 2. I made a few small changes. I went back to cap screws to close the mould, more secure and really doesn’t take much longer to open (I actually think they are less fiddly and faster to tighten as well).
I made this mould with a draft angle on all the edges except the actual teeth which are parallel. I made it slightly more than 3° and the part is much easier to extract from the mould. I used PP again for these tests (shredded flowerpots).
Thanks for sharing the design! I’m going to make a mould based your cad files, if it turns out well I might even offer it in the Bazaar so people can make their own Piranhaclamps locally (makes more sense than shipping the actual clamps around the world). If I do, I will of course give you the proper attribution you deserve for coming up with this.
well yes, we didn’t test other types:) but for all we know, pp is one of the most flexible types of plastic.
maybe we will use an external tool to brand. currently we are testing the dremel versa tip. in this case we would be free to try other types. but for every clamp it’s another step.
we don’t cool or preheat the mould. all natural:)
in the beginning the clamp shrinks a lot and it’s a little bit difficult to demould it. after some injections the mould is a little bit cozy, then it’s very easy to demould the clamp.
as a generel rule you can work with 2-3% of shrinking. it also depends on how much pressure you give.
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