Mechanical Machining Surface Treatment

Mechanical machining surface treatment:

1. Chemical polishing: A process method in which the surface of a workpiece undergoes chemical or electrochemical changes under the action of abrasives, chemical solvents, and other agents, thereby achieving the desired result.

2. Anodizing: A process in which an oxide film containing metal cations is applied to the surface of a workpiece and, under appropriate conditions, is oxidized into a colored metallic layer. The metal anodizing processes include electrolytic oxidation, chemical oxidation, and plasma oxidation, among others.

3. Sandblasting: A process technique that uses mechanical methods to create a fine, sand-like roughness on the surface of a workpiece, thereby enhancing its surface friction properties.

4. Electroplating: A process in which a thin metallic film is deposited onto the surface of a metal or alloy using chemical or electrolytic methods. Electroplating is a widely used and heavily applied surface treatment technique in hardware manufacturing.

The manufacturing precision of fine mechanical machining is high, and during use, the surface of the product remains smooth and polished. In other words, fine mechanical machining can significantly reduce the need for further mechanical processing, allowing these parts to be directly put into practical applications. The surface of finely machined components often features numerous light, circular depressions that are grayish-black in color. Before the equipment is cleaned, these depressions are filled with slag-like material. Such material, to varying degrees, can directly affect the quality of our castings.

Precision machining utilizes a cast iron material whose overall performance is comparable to that of steel. Thanks to its excellent properties, this material has been successfully employed in the casting of parts that are subjected to complex stresses and demand high strength, toughness, and performance. Ductile iron has now become the second most widely used cast iron material after gray cast iron. The phrase “replacing steel with iron” primarily refers to ductile iron.

The microstructural components of precision-machined cast iron are categorized into three types: ferrite, pearlite, and gray cast iron. The characteristic feature of gray cast iron is its flaky graphite structure. Ferrite plus pearlite—carbon (C) and silicon (Si) are elements that promote graphitization. To ensure that the cast iron achieves a gray-chip microstructure during casting without resulting in excessively large and coarse graphite flakes, the carbon and silicon contents must be carefully controlled within the range of 2.5% to 4.0% C and 1% to 2.5% Si. Elements such as Al, Cu, Ni, and Co can also promote graphitization in cast iron. On the other hand, carbide-forming elements like Cr, W, Mo, and V tend to degrade the mechanical properties and fluidity of cast iron.