Precision machining requirements for precision parts
Date：2018-8-7
The exact location of the points, lines and surfaces on the precision machined parts is in accordance with the ideal position. According to GB/T1182-1996, there are 8 items for evaluating position accuracy, such as parallelism, perpendicularity, inclination, coaxiality, symmetry, position, circular jump and full jump. Positional accuracy is controlled by position error, and the tolerance of each item is divided into 12 precision grades. The actual value of diameter, length and surface distance of machined parts is close to the ideal value. Dimensional accuracy is controlled by dimensional tolerances. Dimensional tolerance is the allowable variation of the size of parts in machining. When the basic dimensions are the same, the smaller the dimensional tolerances, the higher the dimensional accuracy. National Standard GB/T1800.2-1998 stipulates: Dimensional tolerance is 20 tolerance grades, namely IT01, IT0, IT1, IT2, IT17, IT18. IT denotes standard tolerance, the grade code of tolerance is denoted by Arabic numerals, from IT01 to IT18, the precision decreases in turn, and the tolerance value increases in turn. The degree of conformity between the actual shape of the line and the surface and the ideal shape after machining. According to GB / T1182 - 1996, there are six items to evaluate the shape accuracy, such as straightness, flatness, roundness, cylindricity, line profile and surface profile. Shape precision is controlled by shape tolerance. All shape tolerances are divided into 12 precision grades except roundness and cylindricity, which are divided into 13 precision grades. The 1 is the highest and the 12 is the lowest.
