This intake manifold was modified by someone and used to thin of material after modding the intake to make it a short runner.
Here is the problem,too thin of plate and it acts like a drum and under boost it balloons out and cracks the welds.

Intake set up on the JIG plate on the mill. I had to get pretty creative with the hold downs to clamp it to the JIG plate. I might drill and tap the JIG plate for the next intake for the clamp studs. I did not clamp it really tight as not to warp the manifold.

This is after a couple of passes with the cutter. I only took off about .015" at a time.

Just another pic.