Generally speaking, stainless steel has the highest hardness, followed by cast iron, copper, and finally aluminum. The processing of ceramics, plastics, and other materials belongs to the processing of non-metallic materials.

1. Firstly, there is a requirement for the hardness of the data. In some cases, the higher the hardness of the data, the better. However, it is limited to the hardness requirements of the processing machine parts. The processed data should not be too hard, as it may be difficult to process if it is even harder than the machine parts.

Secondly, the raw materials should be moderately soft and hard, at least one level lower than the hardness of the machine parts. At the same time, it also depends on the purpose of the processing equipment and the reasonable selection of materials for the machine parts.

In short, there are still some requirements for raw materials in fine mechanical processing, and not all raw materials are suitable for processing. For example, materials that are too soft or too hard are not necessary for processing, while the latter cannot be processed.

So, the most basic thing is to pay attention to the density of the raw materials before processing. If the density is too high, it is equivalent to a high hardness. If the hardness exceeds the hardness of the machine parts (lathe turning tools), it is impossible to process. Not only will it damage the parts, but it will also cause danger, such as cutting tools flying out and injuring people. So, generally speaking, for mechanical processing, the hardness of the raw materials should be lower than that of the machine tool in order to be processed.