Author Topic: F9 Block 5 Updates, Discussions, and Speculations  (Read 80589 times)

Offline Rabidpanda

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Re: F9 Block 5 Updates, Discussions, and Speculations
« Reply #360 on: 11/29/2017 05:53 AM »
It seems more likely that Elon just misspoke. Forging that shape seems extremely unrealistic, unless he is just talking about machining it from a forged billet (which would certainly be possible but would result in a lot of wasted material). Is there any evidence other than that second hand quote that they are forged and not cast?

Offline john smith 19

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Re: F9 Block 5 Updates, Discussions, and Speculations
« Reply #361 on: 11/30/2017 08:23 PM »
The other option is that SX expected to need a forged fin but had a cast/cut one set made up in order to get flight data.

However if the cast/cut set design performed well enough they might have decided "actually a cast/cut design is good enough. The weights OK and quality looks good, and they got them to our door fast"

Historically Forging has been the way to make highly stressed high quality parts but modern casting quality has got a great deal better. The key parameter is the "casting factor," the allowance you have to make in weight for a cast part to have the same strength and rigidity properties of a machined or forged part.

The gear box casing on the Black Arrow LV had a CF of 1.7 IOW it was 1.7x heavier (Aluminum)than a machined or forged version (but a very great deal cheaper).

By the 00's Airbus were accepting (smallish) Titanium cast parts with CF's of 1.0-1.1.

It's been a decades long process but precision casting methods can do high precision casting in highly reactive metals (and molten Titanium is highly reactive) using die casting or lost wax/plastic methods, usually using vacuum melting and vacuum casting to eliminate dissolved gases and ceramic bag dross filters to eliminate inclusions.

Which is good because Ti is a PITA to machine.  :(

So it could just be the SX mfg team were being cautious and the rapid prototyping process has become the new baseline.



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Offline Coastal Ron

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Re: F9 Block 5 Updates, Discussions, and Speculations
« Reply #362 on: 11/30/2017 08:53 PM »
It seems more likely that Elon just misspoke. Forging that shape seems extremely unrealistic, unless he is just talking about machining it from a forged billet (which would certainly be possible but would result in a lot of wasted material).

Musk knows about metal working, so I think it's unlikely he misspoke.

And it's a rare stamped or forged part that doesn't need some clean up, and Musk never said no secondary machining wouldn't be required.

Also, keep in mind that a forging doesn't have to be done in one press. It can be done with a number of successive (i.e. progressive) dies, with the final one being close to the net part.

For example, a grid fin looks similar to a waffle, so there could be a number of successive dies that take a flat plate of titanium and progressively thin out the areas that are the holes, and shape the rest of the material into the grids. Then the "flash", or leftover material is machined out.
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Offline vaporcobra

Re: F9 Block 5 Updates, Discussions, and Speculations
« Reply #363 on: 12/11/2017 07:58 PM »
Crossposting from the Manifest thread.

Don't count your chickens before they hatch.  Although [10 reflights without refurb] is the design goal; they may not hit it with the first iteration [of Block 5].

That's almost besides the point. Even if Block 5 falls 50-70% short of the goal of 10 reflights without refurb, it would be absolutely paradigm-shifting. Remember, 10 flights sans refurb doesn't mention the more important goal, 100 flights with regular refurbishment. If a single booster is capable of flying even 10 times only with serious refurbishment after each recovery, it magnifies SpaceX's fleet by a factor of 10.

With 10 reflights per life and 6 weeks to refurb after each flight (worst-case realistic scenario), four boosters could conduct biweekly launches for 20 months. Three boosters could theoretically maintain a biweekly cadence for 15 months in the same conditions, but there is literally zero margin there for refurb delays.

At a more realistic present-day pace of manufacturing (10-20 Block 5 F9s per year) and with assumptions that Block 5 will manage at least 50% of its reuse goals (5 flights without refurb and 50 flights per booster), it is actually hard to fathom how significant a change it would be. The expendability paradigm is blinding, to say the least. The next focus, of course, will be cost and thus total reusability; BFR.
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