Surface and Solidification Knowledge in Mechanical Machining

The surfaces of finely machined parts often exhibit numerous light, circular depressions that are grayish-black in color. Before the equipment is cleaned, these depressions become filled with slag-like material, which can significantly affect the quality of our castings.

Fine machining is convenient and helps save materials, thereby conserving resources during operation. While many casting methods are limited to producing relatively simple castings, another advantage of fine machining is its ability to produce complex castings.

There are many issues that need to be carefully considered during precision machining. This is because the molten steel used in this process has relatively poor fluidity. To effectively prevent defects such as insufficient casting or cold shuts during machining, the wall thickness of precision-machined parts must not be less than 8 mm.

The solidification method for precision mechanical machining is as follows:

1. Intermediate Solidification: The solidification of most alloys lies between layer-by-layer solidification and mushy solidification.

2. Slurry Solidification: The alloy has a wide crystallization temperature range. During a certain period of solidification, no solid layer forms on the finely machined surface; instead, the solidification zone extends throughout the entire cross-section, initially appearing as a slurry and then gradually solidifying.

3. Layer-by-layer solidification: In metals and eutectic alloys, there is no solidification zone during the solidification process. The liquid and solid phases at the cross-section are clearly separated by a distinct boundary. As the temperature decreases, the solid-phase layer continuously thickens, while the liquid-phase layer continuously thins, with the middle region remaining unaffected.