The common structural characteristics of machined parts are mainly determined by their type. Different functions of parts have different emphases in structural design, directly affecting the machining process and precision control. The following are the core structural features of four typical types of mechanical parts:
Shaft parts: The main body is a rotating body with a length-to-diameter ratio greater than 1. Commonly, stepped shaft structures are used, containing multiple shaft segments of different diameters (such as support journals and mating shaft segments). Key structural features include keyways, threads, relief grooves, and center holes. High coaxiality, cylindricity, and surface finish are required to ensure precise fit with bearings and gears.
Disc/sleeve parts: The overall shape is a flat rotating body or a short cylinder, with the radial dimension greater than the axial dimension. Typical examples include flanges, bearing sleeves, and end caps. Structurally, they often have a central through hole, evenly distributed bolt holes, sealing grooves, and flanges. Strict requirements are placed on the coaxiality of the inner hole and outer circle, and the perpendicularity of the end face to the axis. Machining accuracy is easily affected by deformation due to clamping forces.
Box-type parts: These have the most complex structure, often being hollow shells with internal cavities to support and house transmission components. Typical features include multiple sets of high-precision bearing holes, mounting planes, reinforcing ribs, cast fillets, and connecting screw holes. Positional accuracy (e.g., parallelism, perpendicularity) between holes and between holes and reference surfaces is a key focus of machining. The blanks are often castings, requiring coordinated multi-process machining.
Gear-type parts: The core structure is an involute tooth profile. Based on axial relationship, they can be classified as cylindrical gears, bevel gears, and ring gears. Tooth surface accuracy (pitch, tooth profile, tooth direction error) directly affects transmission smoothness and noise. Structurally, they are often integrated into shafts (shaft gears) or mounted independently (disc gears), requiring extremely high precision in heat treatment deformation control and finishing (e.g., grinding, honing).
