Why are my layers separating?

Layer adhesion failures come from low temperature, too much cooling, or a nozzle that is too cold for the speed. Push nozzle temp up 5–10 °C, drop fan to 80% on the first 5 layers, and slow outer walls to 80 mm/s. Forgely PLA holds 50 MPa tensile when printed correctly — separation almost always traces back to under-extrusion.