Cutting 1/2" BB Ply with a brand new Whiteseide 2 flute down cut spiral carbide bit at 150ipm 18000rpm and the bit snapped in half? It snapped off right at the collet. I'm confused by this. I have cut at speeds quite a bit faster than this before with no issues and the bit was only about 1/8" into the plywood.

Anyone have any ideas about why this happened?

Machine is 1500x1500 C Beam extrusions with ballscrews and linear rails on all axes and a 2.2KW spindle.