Context: This is regarding the first real main milestone that had happened. We had been building up for this meeting the whole time. And it was all about meeting with him so that we could go and manufacture Carbon Fibre components. This was because of the fact that we wanted to go and make it in-house. This would allow for greater customisability, as well as better tailoring of our parts for our particular purposes. But it actually went reasonably well.
Personnel: Hook, Alexander Aveline, Charles Ting, Jayden
What happened:
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Main discussion Points
- Moulds are a significant issue
- Nosecone manufacture is a great problem
- Body Tubes are of too great a diameter.
- Material has to be paid for.
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Moulds
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Gary Senior, told us that we have to go and manufacture an aluminium mould (ideally) to go and make the body tubes, nose cones, body tube panels. etc
- The primary motivation behind making an aluminium mould is that it would go and expand and contract by like 4/1000 of a millimetre which would therefore mean that the tubes would release more easily.
- The second motivation behind using an aluminium mould is the fact that it conducts heat really well and this would therefore allow the heat to conduct really easily and therefore this would lessen cure times and also allow for a quick and efficient curing of the material.
- Aluminium also goes and gives a very good inner surface finish, But then again the inner surface finish isn't entirely important because of the fact that it is on the inside. However, of course making an mould the other way i.e. negative means that it would be gigantic and thus cause us more problems.
- However, the downsides with making an aluminium mould include the fact that it would be massive! The recovery body tube, the biggest and largest part that we have to manufacture would need to be 500 cm long, which is massive, which raises issues with the fact that it has to be put inside of the autoclave and it wouldn't really fit.
- It would also as a result of the size be completely expensive, and basically impossible to obtain for the price, we'd either have to go and get the Aero department to manufacture it in a CNC machine, or we would go and get an outside company to do it. We could use pipe and we thought about that, but getting a 6 inch pipe is difficult but the main issue that comes up with it is the fact that it wouldn't be thick enough, and if an aluminium pipe isn't thick enough it does mean that it would bend and thigns, there were problems using a 1 cm thick plate and that bending as well and causing more problems, so that's that.
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Gary Senior also suggested that we could go and use a hardwood mould like teak or mahogany.
- There is a problem with teak and mahogany in the fact that they are both hardwoods and must be sourced in sufficiently large pieces, he explicitly said that you couldn't substitute with MDF because that is full of resin and this means that we won't be able to go and make a mould from that. Well, this adds cost esepcaily if you want to get ahold of a massive piece of wood and then try and cut it.
- It also must be coated in resins and things which isn't ideal. Also there is no filler that could go adn cope witht eh temperature at which curing woudl occurs, and as a result of that. you'd almost certainely get grains at the bottom, and that wouldn't be great for aesthetic purposes but that is that.
- Talk to Alan D Smith ( Faculty of Engineering , Department of Aeronautics ). He is the primary wood working guy.
- The manufacture of the wood moulds would be basically the same as if you made it out of aluminium the only advantage might be cost savings, but that is about it.
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Gary Senior also suggested using Steel moulds, they have done it before but a very long time ago.
- The issue with steel moulds is the fact that it doesn't conduct heat as well as aluminium so therefore it would have to be heated up slower in the autoclave so as to prevent it from curing poorly, which is rather unfortunate.
- The other issue is the fact that it is a lot harder to go and polish and make a nice surface finish on a steel mould in order to obtain a carbon fibre which is sufficiently smooth for our purposes as compared to Aluminium.
- But then again it should be sufficiently cheaper to manufacture than an Aluminium thing.
- But it also still has the same issues that exist for Aluminium moulds and things like that.
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Gary Senior was also rather dubious towards a 3D printed mould
- However, he said that if it can cover with the curing temperature it might be alright.
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Foam moulds
- Jon Cole went and said that we could go and use foam moulds, which is in contrast to what was said by Gary Senior. He didn't specify any specific foam, but he said that it was a possibility.
- It is quite hard, and it can be CNC-ed, slowly. You can then sand it. " Maybe Renshape "
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Treatment of moulds
- The mould should be covered in a release agent so that it can then be separated properly.
- He also said something about a release foam
- He mentioned the fact that they had experimented with using some foil on the outside to go and create a very smooth finish
- He also said that they had put a peel ply on the top to try and get a better surface finish on the non-mould facing size.
- They also mentioned that they have to put some sort of a breathable layer on top so that the air can escape.
- Tape was put in places to go and hold in ther resin to try and get a better aesthetic appeal.
- He also mentioned that it was then vacuum bagged and then it was then put inside of an autoclave. However he said somethign abotu adding bungs on the end, to then go and vacuum around it, which is pretty schnazzy.
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Gary Senior, told us that we have to go and manufacture an aluminium mould (ideally) to go and make the body tubes, nose cones, body tube panels. etc
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Body Tube Panel
- He recommended using a mould for the aluminium panels and cutting the sheets down to the correct shape and then laying them out, and then just trimming them down to the side using sand paper
- He recommended not using cutting because the tools that they have were incapable of cutting to the appropriate dimensions and well cuts. However, the issue with the inappropriate cutting is the fact that they would still match together like a good jigsaw puzzle.
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Body Tubes
- The moulds would have to be too large
- So perhaps we should go and make smaller sections. and not the large 500 cm sections, so maybe including more skeletal airframes inside fo the recovery section but, that's just me.
- For the body tube, it is also worth mentioning that given the fact that the prepreg sheets are cut as one layer at a time, that does mean that when they are brought altogether it forms a seam at the edges which is dubious and can't really be gotten rid of.
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Fins
- The fins were highly makable
- However, it was acknowledged that the plates would have to be made, adn that they don't the any just lying about, so either we have to go to a composites supplier and purchase carbon fibre plates, or they would lay it up for us, however, in that case it would mean that they woudl go and provide us with the material, but it would take most of the time to cure it and thing.
- They can be easily water jet cut. If oyu give them the plates they can have it cut by next day.
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Nose Cone
- The nose cone however was the sort of thing that went and caused the most issues with the entire process, that is for a great many reasons
- He mentioned that the mould would most definitely have to be a split mould, which is fortunately what we were intending on manfacturing right from the very beginning.
- He mentioned that it would be very difficult to go and layer up the sheets of carbon fibre into the moulds,
- It is also something hat goes and stays outside of the realm of what they are normally in charge of i.e. Plates and Curved plates.
- The mould would once again have to be made from Aluminium.
- How to connect the 2 parts together, he sounded a bit dubious about the whole idea of having a flange on then outside and then gluing the pieces together before sanding it down.
- He also seemed dubious to the gluing of ABS to a nose cone, since it was made from carbon fibre and things like that.
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Processes
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Materials
- If we were to use materials from the department, they would have to deduct the charge for the fibres. However that being said they were more than happy to go and do the curing and the vacuuming and other things for free.
- A single sheet of woven fibre, that could then be laid up in a quasi-isotropic way would cost about £40 per square metre, which is rather pricy.
- He said that to order materials, you should go and calculate the exact amount that you needed and then add 10% becuase things do go wrong.
- He also said that the mixing ratio would be more like 60:40 (Fibre:Resin).
- That being said, they did have a roll of carbon fibre that was expired and we were allowed to use, we coulnd't really go and use a lot of it. It is expired, but that being said it is still good for another year. He said that we probably have enough to go and make the 4 panels as well as the nose cone.
- All of the material inside of the workshop is prepreg and they won't really do any wet lay up for us, and that is generally the area where most of the teams that we had encountered had went and done there stuff from. And also there are a lot of safety concerns, which hinders progress significantly.
- They can't do fibreglass really.
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He recommended the following sources
- Easy Composites
- Marine Ware
- SHD composites
- 0.25 mm thickness for some of the thicker sheets.
- To drill he said to use a dagger drill bit which is spiky and has this motion in which it scrapes the sides of the hole and that prevents delimitation and things like that.
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Curing
- He said that there were a wide range of composites that they could go and use for their manufacture.
- He said that they had this higher temperature curing material which was (170ºC 100 PSI)
- He said that there was also this lower temperature curing material which was (60ºC ? PSI)
- The higher temperature curing material was better, because of the fact that it can then be taken out from the freezer and handled at room temperature without any risk of curing, this would be easier to go and make the nose cone.
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Materials
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Where to go from here?
- Research into companies that are willing to manufacture moulds for us.
- research prices for carbon fibre plates etc.
- Contact Hack Space, to go and find out if they go and make composites, because it would probably be more advanced and they might have a greater chance of manufacturing what we need?
- Is it feasible to go and manufacture the tubes and thigns in a wet lay up? RAFT notwithstanding?
- Contact Company that ART and Rohit Singh looked at to get their tubes made? We wanted in house, but that is teh best we can do?
- Use skeletal airframe in recovery tube? It does lower the amount of loads int aht tube and therefore less material is required.
- "Carbon Fibre centring rings or rods?"