hey any body can tell me how much thickness tolerence we can achieve by infusion?
Depends greatly on a number of factors including resin viscosity, vacuum level, fabric permeability. Not sure what typical numbers are. How wide are your tolerances?
also depends on infusion side vs. vent side…thickness, etc.
With double bag infusion you can reach a quite low variation in Vf, hence little thickness variation. In what kind of tolerances are you playing?
VAP and CAPRI are also other good ways of controlling thickness and FVF
Caulplates and membrane infusion as well, if you have good porting (vs, just on one side)
thanx all. I want to produce flat sheet around 1m X 2m in epoxy with some Carbon UD and BD layers. I am looking for Flatness within 0.2 mm
What is the overall thickness? Will you use infusion mesh or Dahltexx? Do they need to be flat on both sides?
I think if you need that tight of a tolerance, y ou will need to look into a closed mold, or caul plate and spacers. You will have to adjust your resin and fiber volume as you would for RTM. You can also try a center/4 side injection with a membrane (with opposite venting).
But 0.2mm might even go against the fiber tolerance, infusion or not! 
the overall thickness is 8 mm. I am going to use infusion mesh of 120 gsm. Need flatness on both side
They want to ultrasonic inspect at each 100 mm interval
I would highly suggest double bagging then. Due mechanics of fluid flow the inlet side will always be thicker than the vacuum side. The variation in thickness due to this is a function of the resin viscosity, I’m not quite sure if it’s significant for your resin but it’s something to note.
Also important is fiber construction. Wovens vary in thickness much more than UD or Multiaxials.
For smooth surfaces I recommend using Fibertex infusion mesh, or at elast their separating film.