Analysis of typical precision machined parts: plate machining

Part 1. Structural characteristics of plate parts

Plate parts are parts with a flat plate as the main body, usually consisting of threaded holes, small supporting surfaces, bearing holes, sealing grooves, positioning keys and other surfaces.

Part 2. Technical requirements for plate parts

(1) Dimensional tolerance plate parts are mainly divided into two categories: one is used as a inspection tool and is the standard for each measuring piece. Its surface precision is high, and the tolerance level is usually IT3~IT4. The requirement is to detect the difference level of the parts. At least 3 times; the other type of parts are used with large parts, and their surface tolerances are generally required to be IT5~IT6, which is one level higher than the large parts they match. (2) Geometric tolerances For the flatness, verticality, and parallelism of important surfaces such as the upper and lower surfaces, outer surfaces, and boss surfaces of plate parts, the errors should generally be limited to the dimensional tolerance range.
(3) Surface roughness The processed surface of the plate has surface roughness requirements, which are generally determined based on the performance and economy of processing, as well as the usage accuracy of the product. The surface roughness of inspection tool planes is usually Ra0.2~0.6μm, and the surface roughness of parts planes is Ra0.6~1.0um.

Part 3. Processing technology analysis of plate parts

For parts with higher precision requirements, roughing and finishing should be processed separately to ensure the quality of the parts. The processing of plate parts can generally be divided into three stages: rough milling (rough milling of the end face, rough boring), semi-finish milling (semi-finish milling of the end face, semi-fine boring, drilling and tapping of each threaded hole), fine milling and fine boring , sometimes in order to achieve very high surface quality and flatness requirements, a flat grinding process is required.

Part 4. Material selection for plate parts

(1) Materials of plate parts Plate parts are often made of cast iron. For plates that require high precision and good rigidity, 45 steel, 40Cr, or ductile iron can be used; for high-speed, heavy-duty plates, low-carbon alloy steels such as 20CrMnTi20Mn2B, 20Cr, or 38CrMoAI ammonia steel can be used.
(2) Blanks of plate parts After heating and forging of blanks such as 45 steel, the internal fiber structure of the metal can be evenly distributed along the surface to obtain higher tensile strength, bending strength and torsion strength. Castings can be used for large plates or plates with complex structures.

Part 5. Heat treatment requirements for plate parts

1) Before processing, forging roughness must be normalized or annealed to refine the internal grains of the steel, eliminate forging stress, reduce material hardness, and improve processability.
2) Quenching and tempering is generally arranged after rough milling and before semi-finishing milling to obtain good comprehensive mechanical properties.
3) Surface quenching is generally arranged before finishing, so that local deformation caused by quenching can be corrected. 4) Plates with high precision requirements must also undergo low-temperature aging treatment after local quenching or rough grinding.