The protection process is based on the following two points: (1) The requirements on the chart. The number of parts that need to be protected is relatively small, and therefore it is easier to be negligent. It is often found only after the completion of the quality inspection. Therefore, it causes rework, and drawings must be read before processing. (2) Whether there is an opposite metal in the product. In addition to titanium, the surface of other black or non-ferrous metals must be protected. (Precious metals and rare metals are generally not possible as inserts or assemblies for aluminum parts.) This is not a standard for the designer. The operator can handle it by himself according to the process requirements.