Good idea and i am interested about the process.
One thing that you should have in mind ( i have read it once in a Greek forum CNC HOBBY - CNC Mills, CNC Lathes, CNC Routers, Metal Casting, Servos, Steppers, Motion Control ) is that after Casting the aluminum shrinks according to a shrinking Factor. That Factor i think isnt stable as shrinking may be affected from humidity, temperature.... So that means that you cannot make by casting parts that have acurate dimensions near 0.1mm. Of course you can make your parts and then mill them to the dimensions that you want.

Good luck and keep trying