+x+xI would consider a split mould that is silicone faced and supported by fibreglass backing mould too.
It's quite an involved and long process with flanging, silicone brushing and fibreglass, then repeating for the second side plus the silicone is quite expensive too.
I have some silicone split moulds I made for a car dash pad but I am having trouble with uploading anything at the moment!
Thanks for answer. Just to make sure I understand this right. Making a split mould with silicon face. Put the two (inner and outher) together and fill the hole thing with polyurethane?
Any suggestion of what kind of polyurethane to use?
That's right, I only say to use silicone since the back side of your part may have lots of details and these can possibly be cast ok as you will be able to flex the silicone off the new cast part? If there are any impossible bits you may be able to modify those bits with some plasticine before making the moulds.
You should plan which way up the casting pour will happen and consider a filling point and possible air venting too.
For the polyurethane there are loads of different grades that range from hard plastic like resins to others that are more like rubber. You need to pick the right one for you. Some suppliers of polyurethane resins will have a swatch of all the different resins so you can see and feel before you buy.
