The reasons why CNC machining centers have fast processing speed and smooth surface can be mainly attributed to the following aspects:

1. Accurate CNC system control: CNC machining centers use advanced CNC systems, which can accurately control the cutting parameters during the processing, such as cutting speed, feed speed, cutting depth, etc., to ensure the stability and processing quality of the processing process.

2. High-speed spindle and cutting tools: The spindle speed of CNC machining centers can reach a very high level, and the cutting tools equipped also have high hardness and high wear resistance, which can maintain the sharpness of the cutting edge during high-speed cutting, thereby improving the processing speed and processing quality.

3. Reasonable cutting parameter selection: In the CNC machining process, selecting appropriate cutting parameters is crucial to ensuring processing quality and improving processing speed. By adjusting parameters such as cutting speed and feed speed, the cut marks and burrs generated during the cutting process can be controlled, so that the surface of the workpiece is smoother.

4. Advanced processing technology and polishing technology: CNC machining centers can use advanced processing technology and polishing technology, such as milling, grinding, polishing, etc., to further improve the smoothness and precision of the workpiece surface. These technologies can remove burrs, scratches and other defects on the surface of the workpiece, making the surface of the workpiece smoother and more delicate.

5. Appropriate cutting fluid and coolant: In the process of CNC machining, the use of appropriate cutting fluid and coolant can effectively reduce the cutting temperature and cutting force, reduce the heat and wear generated during the cutting process, and thus improve the processing speed and processing quality.

In summary, there are many reasons why the CNC machining center has a fast processing speed and smooth surface, including precise CNC system control, high-speed spindle and cutting tools, reasonable cutting parameter selection, advanced processing technology and polishing technology, and appropriate cutting fluid and coolant. These factors work together to enable the CNC machining center to achieve an efficient processing process while ensuring the processing quality.