Originally Posted by
peteeng
Morning Sus - I have gone off the idea of making grout/concrete parts 1) The material is not stiff enough in small machines that I am interested in 2) Moulds have to be made or you make steel shells. 3) Its difficult to post machine it unless you have access to stone masonry type machines 4) I still have to take it to a machinist to have the inserted lands machined 5) if I use ceramic aggregates to improve its stiffness it becomes nearly impossible to machine & these have not improved the stiffness in my tests. I would consider it if someone wanted a production machine like 1 per week, but then metal is viable at my machine sizes. If the machines are very big then cold casting makes sense.
The only material that I have been able to make that has a modulus greater than aluminium reliably is carbon fibre. I 've made E80 material in compression, tension and flexure in std modulus CF. Its costly and fiddly but a great solution.
So I come back to metals Aluminium, steel or cast iron the traditional material. For me aluminium works as I can machine it on my routers. But in production the cheapest path so far has been steel laser cut parts. If you need really thick parts they can be laminated. You may say what about damping? People harp on about damping but stiffness trumps damping. I have researched dynamic stiffness of machines enough now to know that no material is damp enough to solve the vibration issues in traditional CNC subtractive machines. There's been heaps of research and effort in this area and there are no material answers. The only answers lie in input shaping, active shaping and tap testing at present. These identify the vibration modes of the machine and you just stay away from those operational areas. Using tap testing, productivity improves 10x. So using the stiffest cheapest material is the way forward, then tap test your machine and your on your way. This means steel will be the obvious solution. Either billet machined, fabricated or self-assembled (bolted). If fabricated ideally use laser welding that may sidestep the stress relieve process.
Moving fwd commercial machines will 3D print their parts in metal (this is already occurring), use shaping in their control systems (which is occurring) and tap testing will become a std workshop practice (which is occurring)... unless additive overtakes subtractive in economics. Which in 5-10 years that will be the case... Then those fancy spiderweb designs that AI produce become easy to make and since they use 10X less material become viable to print... and printing is limitless in size... so hot casting will stop... when I'm 80 and in my dotage machines will look entirely different to how they look now...
So for me the conclusion is that laminated aluminium works for me its as damp as cast iron or composites and I can machine them on my routers. Once I get two more routers made I design a fully laminated aluminium mill.... Peter