yzr750 wrote:3d printing is not suitable to make molds that have to go in an autoclave, maybe sls if you can find one with a big enough footprint for a swingarm, but the resolution of those would require post machining anyway.
I know of one that's producing moulds here in Aus. for aluminium casting that would probably take a swing-arm (will take a four-cylinder engine cankcase, for sure), and yes, there is post-machining needed, though that's limited compared to conventional investment moulding techniques. It took over 9 months to develop a suitable printing medium and the guy isn't telling anybody what that is, atm anyway.
yzr750 wrote:Aluminium 7020 will not require heat treatment after welding, and is used in the construction of mtb frames without post processing, and does not suffer inordinately from stress fractures. I have used this alloy to construct my own motorcycle frames and swingarms without any problems whatsoever, and I currently use it in my business to manufacture rocket components, without post weld heat treat.
Fair enough - I assume you're using design techniques where high load paths don't cross weld lines. Do you pre-heat the component prior to welding? Aircraft construction practice almost always requires post-treatment to relieve the inter-granular stress between the weld pool and the parent metal, but 7020 is not an alloy I'm familiar with, I don't think it figures much in aircraft production.
Without hijacking this thread, you might like to check out:http://www.sciencedirect.com/science/article/pii/0010938X8590068X
for an analysis of the effect of welding on 7020. It appears that provided the ultimate load is fairly low, heat treatment is certainly not required ( as you say), but the inter-granular zone is susceptible to corrosion in wet conditions (and probably even worse in wet saline conditions: don't take yer motoGp bike for a ride on the beach!