If it`s only 0.4mm I think it`s just a piece of cake on a 4 flute HSS, on my experience I can even cut 1mm thick stainless steel sheet, by just using a 1/8 carbide bit single flute at feedrate 400 and plunge rate of 80 on 5 passes, sometimes 7 passes, depending on the sharpness of my installed tool bit, it gets dull in time after a couple of cuts, so in the beginning I make a CAM for 5 passes and for 7 passes, after 20 cuts I change the code for 7 passes to continue working and after a couple of cuts that`s the time I re sharpen hehe, sometimes laziness made me think further just to minimize the tool change
make sure to have a sacrificial plywood to avoid accidentally scraping your CNC table and to easily clamp your holding tabs in place.