Machining precision is the degree to which the actual dimension, shape and position of the surface of the machined part are in accordance with the ideal geometric parameters required by the drawing.The ideal geometric parameter, in terms of size, is the average size;In terms of surface geometry, it means the absolute circle, cylinder, plane, conical surface and straight line, etc.For the mutual position between the surface, it is absolutely parallel, vertical, coaxial, symmetrical and so on.The deviation value between the actual geometric parameters and the ideal geometric parameters is called machining error.
Introduction to machining accuracy
Machining precision is mainly used to produce products. Machining precision and machining error are terms to evaluate geometric parameters of machining surface.Machining accuracy is measured by tolerance grade. The smaller the grade value is, the higher the precision is.The machining error is represented by numerical value. The larger the numerical value is, the greater the error will be.Machining accuracy is high, machining error is small, and vice versa.
There are altogether 20 tolerance grades from IT01, IT0, IT1, IT2, IT3 to IT18, among which IT01 represents the highest machining accuracy of this part, and IT18 represents the lowest machining accuracy of this part. Generally, IT7 and IT8 are of medium machining accuracy.
The actual parameters obtained by any machining method are not absolutely accurate. From the function of the parts, as long as the machining error is within the tolerance range required by the parts drawing, the machining accuracy is considered to be guaranteed.
The difference between accuracy and precision:
1. Accuracy
The degree to which the measured result is close to the true value.The high accuracy of measurement refers to the small systematic error. At this time, the average value of measurement data deviates from the truth value less. However, in the case of data dispersion, the size of accidental error is not clear.
2. Precision
Refers to the reproducibility and consistency of the results obtained by repeated determination of the same standby sample.It is possible to have high precision, but the accuracy is inaccurate.For example, the three results obtained by measuring the length of 1mm are 1.051mm, 1.053 and 1.052, which are inaccurate though they are of high precision.
Accuracy means the accuracy of the measurement results, and precision means the repeatability and reproducibility of the measurement results. Precision is a prerequisite for accuracy.
The related content
1. Dimensional accuracy
Refers to the degree of conformity between the actual dimensions of the machined parts and the tolerance zone center of the dimensions of the parts.
2. Shape accuracy
Refers to the degree to which the actual geometry of the machined part surface conforms to the ideal geometry.
3. Position accuracy
Refers to the machining parts between the surface of the actual accuracy of the difference in position.
4. Correlation
Usually when designing machine parts and specifying machining accuracy, attention should be paid to control the shape error within the position tolerance, and the position error should be less than the dimensional tolerance.That is, precision parts or important parts surface, its shape accuracy requirements should be higher than the position accuracy requirements, the position accuracy requirements should be higher than the size accuracy requirements.