The principle of an automatic elbow welding machine is as follows:

1. Elbow positioning: Firstly, the elbow to be welded is placed on the working table of the welding machine and secured in the correct position using fixtures or other positioning devices. This ensures the accurate positioning of the elbow during the welding process.

2. Weld seam preparation: Before welding begins, some preparations are carried out on the elbow, including cleaning the welding surface, removing oxides, and using appropriate tools for chamfering or groove preparation.

3. Welding power setup: Based on the type and specifications of the welding material, the appropriate welding current, voltage, and other welding parameters are set. The selection of these parameters depends on the welding method used and the characteristics of the welding material.

4. Automatic welding: Once the preparations are completed and the welding parameters are set, the automatic welding machine starts executing the welding operation. It typically uses one or more welding methods such as TIG welding, arc welding, laser welding, etc. The welding machine automatically controls the movement of the welding torch and the output of the welding power according to the preset program to achieve the connection of the welding joint.

5. Inspection and quality control: After the welding is completed, the automatic welding machine usually carries out some inspection and quality control steps to ensure that the quality of the welded joint meets the specifications. This may involve checking the appearance, dimensions, and detecting any welding defects in the weld seam.

It should be noted that the specific principles of an automatic elbow welding machine may vary depending on the model and manufacturer. The above steps provide a general description to help understand its working principle, but the actual situation may vary. In practical applications, there may also be additional features and control systems involved to enhance automation and welding quality.