There are many bumps on the surface of things printed by 3D printer. What's the reason?

Let's show the picture which will more intuitive. The printing material is PLA. It's estimated that the temperature will not be too high, because I set the temperature at 190 degrees and the printing speed at 30. The bumps are the most serious at the corner.

No best answer

There are many reasons for this situation, but it can be roughly divided into two parts. The reasons should be analyzed according to the specific conditions of the machine:
1. The machine movement accuracy is not enough. (Dislocation leads to bulge)
2. The flow control accuracy is not enough. (Too many consumables are squeezed out in the convex part to cause the convex) Flow rate refers to the amount of material extruded by the extrusion head. This lack of accuracy can be divided into slicing software flow setting errors. The mechanical precision of the extrusion head is insufficient. The density of consumables is uneven.