Why does the file format of 3d printing model have to be STL and STP?

3D printing requires 3D stereogram. There are many formats of 3D stereogram, and the formats made by different software are different. For example, common 3D printing formats are: STL, STP, IGS, OBJ, BREP, MAX, 3DM, 3DS, X_T, SKP, SLDPRT, PRT, ASM, F3D, FBX, RVT, WIRE and so on. Different formats, other software may not open. In the same way, the 3D printer supports only a limited number of 3D stereogram formats. Nowadays, the most commonly used 3D stereogram formats for 3D printing are STL and STP. To some extent, these two formats are necessary for 3D printing(Different types of 3D Printing technologies and Processes)

The STL file format, invented by 3D Systems, is the standard trig language for 3D printers. All molding machines can receive STL file format for printing. When you move around or save STL files, all the surfaces and curves you design are replaced with mesh. The grid consists of a series of triangles that represent the exact geometry of your prototype.

STL files need to be watertight before they can be printed in 3d. The best explanation for water tightness is a volumetric solid without pores. You may be surprised to learn that even after you've designed the model, there may still be undiscovered holes in it. STL has become one of the industry standards of CAD/CAM system interface file format, and most modeling systems can support and generate such file format.

Although STL file format is simple, it can only describe the geometric information of 3d objects, and does not support the information such as color and material.

If without STL format, STP is ok as well. STP file is the 3d image data based on the ASCII format which conforms to the STEP application protocol ISO 10303-21 standard.

Currently, there are many formats to support quotation, such as listed above STL, STP, IGS, OBJ, BREP, 3DM, X_T, SLDPRT, PRT, ASM, F3D, FBX, RVT, WIRE can be quoted. Of course, as the article title says, it must be in STL and STP format, which will save you the trouble of printing.

Further reading.(What’s the difference between 3D Printing and CNC Machining?)(Which is better? CNC or 3D Printing?)