I have a 1996 astro van...when i go to start and turn ignition it makes this real bad grinding sound? could it be the flywheel or the starter ?

Hello rywatson.

It could be either.
Often a misaligned starter or worn starter bushings will cause premature ring gear wear.
Also make sure that your starter bolts are tight before proceeding further.
If it is tight you will need to inspect the starter drive gear and the flywheel for worn or missing teeth.
There will be 3 areas where the flywheel stops most of the time.
You will need to rotate it to check them.
If the flywheel is ok replace the starter assembly. Most GM replacement starters come with shims.
Install it without the shim to begin and add one if the starter doesn't sound "right".

If you need further assistance with your issue, ask me here in a comment.
Thank you for using FixYa.
KL

It could be either the flywheel or the starter.
If it's grinding, don't try it again until you've removed and examined the starter and flywheel. If the starter solenoid isn't fully engaging the bendix, it will cause the gear to grind; replace or rebuild the starter if that's the case.
But you should examine the flywheel to see if it is seriously damaged from the problems you've had. Put a mark on the flywheel using a magic marker, then examine the flywheel as you slowly turn the engine by hand. (make certain that the ignition is off when you do that, you don't want anything bad to happen to your hand.) The mark on the flywheel will indicate when you've been able to examine the all of the teeth on the starter ring.

It is possibly that the bedix in the starter is not able to push the gear out to make contact with the flywheel. The first step is to remove the starter and visually inspect the teeth of the flywheel. If they are worn in that spot that the flywheel will need to be replaced. If the teeth look good a new starter should take care of the problem.

Most of the time its the starter and the flywheel is fine. However repeatedly try to start the vehicle when it makes the grinding noise can ruin the flywheel.