https://www.youtube.com/watch?v=XeeSsmsm9h0
lets say im making a mold exactly like this tutorial shows,but i want to make a pattern out from this mold with vacuum infusion.should i do anything different?the ionly thing im imagining to do is applying extra layers of coopling coat and some layers of chopped strand mat.have i thought it right?

Do you mean for the mould? The actual layup of the mould can be exactly the same as the video shows, no need to change anything. You will probably need to bag it in the same fashion as well, so you don't need to make the flanges bigger except where you need to place the infusion connectors. 

Infusion isnt going to be an ideal process though, you'll need plenty of spray adhesive to position everything and then resin is going to go everywhere and leave your mould covered with very sharp shards on the outside. Removing the mesh afterwards will be difficult too, though not impossible. For a one off it will work.

You would, but the mould would likely need a bit of clean up. The resin that will make its way onto the back of the mould will be extremely sharp and will cut any future bags to shreds, so you would need to grind it smooth again. You may find that any bolts you have to bolt the mould pieces together will also get covered in resin and become a problem as well, so you will want to take measures to stop that happening.

All in all, it's fine to do such a part with infusion, but it really isn't ideal at all, and I'm speaking from experience here. Youll find it tedious and you won't enjoy doing it if you are trying to make numeroua parts. If you are only doing one or two then fine, you put up with it. But for 30 or 40 pulls? No thank you. Parts like this are very much the reason I invested in a setup to move to pre-preg, and I haven't looked back since.

I have got a mould just like that (an airbox, 3 piece mould), and I made several parts with resin infusion. I didn't bag the whole mould, just the inside, like it was a one piece mould. The split flanges have sealing channels, which I prepare with tacky tape. The channels are inside of the bolting points (and there are a lot of bolts. When everything is put together, there are two points, where the sealing channel (and therefore the tacky tape) exits the mould. During the final bagging, I have to  take up this points wich the tacky tape / bagging film corner. After that, the bag should be absolutely tight, and the resin doesn't flow anywhere it isn't supposed to be.
I can't take a picture of the mould, because it is a customer project.
split mould infusion is absolutely an advanced process.

Just to expand on Oekmont's post with some photos, this is how you might go about that technique:

Layup the first half of the mould as normal, then when you do the next piece and remove the temporary flanges, use strips of sheet wax (slightly thinner than your tacky tape, so in this case my tacky tape is 3mm thick and I used 2mm thick sheet wax) on the solid flanges to create the channel (the joins between the wax strips can just be filled with filleting wax):









Once cured and demoulded, you'll be left with a channel on one side of your mould flanges whilst the other side will be solid:





It is important this channel is continuous all the way around the mould and finishes on the edges of your outer flanges, so that as Oekmont said you just run the tacky tape as normal on the edges of the mould and it meets up and seals with the tacky tape in the internal channels.Then before bolting your mould pieces together, you simply run tacky tape along the channels, and this seals the mould pieces together.




Then you can just layup and infuse as if it were a single piece mould.







Between pulls, you need to clean the tacky tape off the channels, which can be quite the task if the stuff you are using is anything like the Cytec stuff that I use. In all honesty, I don't know if this was much easier than simply grinding the excess resin off the outside of the mould after envelope bagging, but it did atleast use less vacuum bag and make the bagging process easier.

The other option is to not make the sealing channel, and just use automotive RTV silicone gasket between the mould flanges. This is also somewhat of a task to clean up between pulls, but it is my preferred method - it is just quicker and simpler and you don't need to spend the time building the channels into the mould. You do however need to be careful that you don't squeeze silicone into the joins of your mould, leaving you with a nicely encapsulated line of silicone on the seams of your finished parts!

All in all, it can be done and there's things you can do to make it work a bit better. But I haven't found any solution to make it as quick, neat and tidy as pre-preg.