G'day JK,
I would NOT recommend 20 elements through the thickness in 3D unless you're dealing with very large thickness parts. For the most part in 3D the maximum I have used in 3D, is 12. I only use 20 laminates in Fusion and Mid-plane. To keep the 3D element aspect raitos to reasonable levels, if you went 20 elements through the thickness you would have to drive the element size so small that you will be talking millions of elements for the model, how many millions will depend upon what size parts you are talking about and the part thicknesses.
With your machine I would guess that a 2 million element model in 3D, F/P/W would probably take 24 hours, but you didn't indicate how many processors you have. If you don't have a multiple processor machine, it actually might be longer, but these are guesses. I would recommend you trying different levels of elements thru the thickness and determine what is needed for your level of analysis, because it will depend a lot on what you are trying to solve for with the program. As UI indicated before, if your only looking to find weld lines and pressure, number of gates needed, etc., then 6 or 8 elements in the thickness may be adequate for you.
Bob Sherman
Sr. CAE Analyst, RTP Company