1. Machining error
Machining accuracy refers to the degree to which the actual value of the forging geometric parameters (size, shape and mutual position of geometric elements, microscopic unevenness of the contour, etc.) conform to the design ideal value after machining. Machining error refers to the deviation of the actual geometric parameters from the design ideal value, the smaller the machining error, the higher the machining accuracy.
Machining error mainly has the following categories.
① Dimensional error: the actual size of the forged part after processing deviates from the ideal size. The ideal size is the average value of the maximum and minimum two limit sizes marked on the drawing, that is, the central value of the size tolerance zone.
②Shape error: refers to the difference (or deviation) of the actual surface shape of the machined forgings from the ideal shape, such as roundness, straightness, etc.
③ Position error: refers to the difference (or deviation) between the mutual position of the machined forging surface, axis or symmetry plane for its ideal position, such as the same axis degree, position degree, etc.
④ surface microscopic unevenness: microscopic geometric shape error consisting of smaller spacing and peaks and valleys on the surface of the forging after processing. Forging surface microscopic unevenness with surface roughness assessment parameter value.
Machining error is generated by many error factors of the process system. Such as the principle of the processing method error, forging mounting and positioning error, fixture, tool manufacturing error and wear, machine tool manufacturing, installation error and wear, machine tool, tool error, cutting process force, heat deformation and friction vibration, and the geometric error of the blank and the measurement error in processing.
2. Geometric tolerance
In order to control the processing errors and meet the functional requirements of forgings, the designer puts forward the corresponding processing accuracy requirements through the forging drawings, which are given in the form of geometric tolerance markings.
Geometric tolerance is the range of variation allowed for the actual geometric parameter values. Relative to various types of machining errors, geometric tolerances are divided into dimensional tolerances, shape tolerances, position tolerances and surface roughness indexes allowable values and tolerances of special geometric parameters of typical parts.
In modern production, the manufacturing process of a mechanical product often involves many industries and enterprises, some of which also require international cooperation. In order to meet the technical coordination requirements between each other, there must be a common compliance with the unified technical requirements of the specification.
The standard is to regulate the technical requirements of the regulations, is the common compliance in a certain range of technical basis. Standards are issued at different levels, in the world, the common compliance of enterprises is the international standard (ISO). China's standards are divided into national standards (GB), industry standards (such as machinery standards (JB)), local standards (DB) and enterprise standards. Local standards and enterprise standards are technical specifications developed in the absence of national standards and industry standards, and the need for uniform technical requirements in a certain range.
The scope of standards is very wide, involving all aspects of people's lives. According to the object, it can be divided into basic standards, product standards, method standards and safety and environmental protection standards.
