Week 13 - Composites

This week covers how to produce a composite. It is related to molding and casting except there are going to be fewer steps. This should be good fun provided I choose wisely about what I design.

Assignment:

design and make a 3D mold (~ft2), and produce a fiber composite part in it


  

23rd April 2015 - Skateboard?

During the lecture Neil showcased some of Fablab Barcelona's work with composites. They have done extensive work in making skateboards using this composites module. I would also like to give this a go. It will be functional afterwards and I can be very creative with what design I choose to put on the board.


25th April 2015 - Change of plan

I found out that it is preffered that we do not use thin layers of wood for this assignment and stick to more forgiving things like textiles. Hence, I have decided to design a mudguard. It means I can design a nice shape and maybe work out how to fix it to a bike later on.

**A FEW HOURS LATER**

I came up with the following design:



Here is the design file.

Next step is to mill out the design in foam. This will be done tomorrow.


23rd April 2015 - Milling the design

Once again the fablab was kindly opened on a sunday for us so I took the oppotunity to get my design milled. Setting up the job was similar to the 2D milling soft ware.

To make the tool paths, you upload your design to the software "pathworks 3D". Then you tell the software (among other things) what cutting tool to use for the roughing and finishing job. You can then preview and save the toolpaths for the shopbot. After that the work flow is identical to the previous assignment involving the shopbot.

I cut my foam block to size and attatched it to a sacrificial layer using double sided tape. I set the origin for the job on the corner of the block and ran the roughing and finishing job with the same 10mm milling bit (much less hassle inbetween jobs!). Also, to ensure that the collet of the shopbot wouldn't interfere, I drew it's dimensions on rhino and moved it around the design.



Below you can see me working with the machine. Yes! Another time lapse! (It's rather short because my phone fell out of position but it's better than nothing.



Prying the foam from the sacrifical layer took a lot of force and some of the corners became scuffed. So I stuck it to a scrap piece of wood with more double sided tape and used plastercine to smooth the boundary between the wood and the foam.



The last step for making the mold was to coat the mold with a layer of gesso to make the foam less porous. This was a quick and easy step:



Underneath you can see the vacuum bag that I would be using for the cast.

The last thing I need to do is prepare the material that I will use to make the composite. I "unrolled" the shape of the fender in rhino so that I can laser cut the shape I need in cardboard. Then I can use the cardboard template to cut out the material. I will use three layers of linen and a top layer of denim to make it look more appealing.

Below is the unrolled piece and the pieces of fabric I cut:







Next thing I did was cover the mold in vaseline. This will make it easier to free the composite later.

The resin we used was the super sap 100/1000 combination. This requires a ratio of 2:1 (resin:hardener) and a couple minutes of mixing. Then using a roller I saturated three layers of jute (cloth-bag) and one layer of denim. Once the layers were in place I put it all inside the vacuum bag and sucked the air out.



One step I forgot to do was cover the top layer in cling foil. This is meant to stop the composite sticking to the inside of the bag so I will have to wait and see how it turns out.


29th April 2015 - De-molding!

This morning I returned to the vacuum bag and took out the composite and mold. There were a few creases where the denim could not stetch enough but I was still pleased!



Next step was to remove the composite from the mold. I had to break the mold (pardon the pun!) in order to release the composite but it was finally out! The top surface had a very unique finish but the inside wasn't quite as appealing.




I tidied up the edges so that it looked more like the shape I originally designed. The found a downside to composites here which was that the surface can't be sanded down. Hence, it is important to remove creases in the layers before the resin sets. Unfortunately the denim I used couldn't stretch enough on this occasion. But the final piece is very rigid, light weight and has a certain aesthetic appeal about it.



That concludes my work on my assignment for composites! All I need to add to this is a method of atatching the mudguard to the bike.