Surface treatment for “machining”

Machining Surface Treatment:

1. Chemical polishing: A process in which the workpiece surface 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 formed on the workpiece surface, resulting in a colored metallic layer under appropriate conditions. Anodizing techniques include electrolytic oxidation, chemical oxidation, and plasma oxidation, among others.

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

4. Electroplating: A process in which a metallic coating 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.

Precision machining delivers high manufacturing accuracy, resulting in products with smooth, polished surfaces. In other words, the finely machined components produced can often bypass many subsequent machining steps and be used directly in applications. The surfaces of precision‑machined parts typically exhibit numerous gray‑black, shallow, circular depressions; if these are not cleaned out prior to further processing, they become filled with slag, which can significantly compromise the quality of the castings.

Precision machining employs a cast‑iron material whose overall properties are comparable to those of steel. Owing to its excellent performance, it has been successfully used to cast components subjected to complex loading conditions, where high strength and toughness are required. Ductile iron has evolved into the second most widely used cast‑iron alloy, after gray cast iron. The notion of “replacing steel with iron” refers primarily to ductile iron.

The microstructural constituents of cast iron are classified into three types: ferrite, pearlite, and graphite‑bearing gray cast iron. The characteristic feature of gray cast iron is its flake‑like graphite. Ferrite–pearlite structures also occur. Carbon (C) and silicon (Si) are elements that promote graphitization. To ensure that the cast iron achieves a gray microstructure during solidification without developing excessive or coarse graphite flakes, its chemical composition is typically maintained within the ranges of 2.5–4.0% carbon and 1–2.5% silicon. Elements such as aluminum (Al), copper (Cu), nickel (Ni), and cobalt (Co) can also enhance graphitization. Conversely, carbide‑forming elements like chromium (Cr), tungsten (W), molybdenum (Mo), and vanadium (V) may reduce the mechanical properties and fluidity of the cast iron.