Geometric tolerance
The processed parts not only have dimensional tolerances, but also the actual shapes or mutual positions of the points, lines, and faces that make up the geometric features of the parts are inevitably different from the shapes and mutual positions specified by the ideal geometry. The difference in shape is the shape tolerance. The difference in mutual position is the position tolerance, collectively referred to as the tolerance of form and position.
The geometric tolerance term has been changed to the new term geometric tolerance according to GB/T1182-2008.
Includes shape tolerances and position tolerances. Any part is made up of points, lines, and faces. These points, lines, and faces are called features.
There are always errors in the actual elements of the back part relative to the ideal element, including shape and position errors. Such errors affect the function of the mechanical product and should be specified in the design and marked on the drawing in accordance with the specified standard symbols. Around the 1950s, industrialized countries had standard tolerance standards. The International Organization for Standardization (ISO) published the geometric tolerance standard in 1969 and the principle and method of geometrical tolerance detection in 1978. China promulgated the shape and position tolerance standards in 1980, including inspection regulations. Shape tolerances and position tolerances are referred to as geometric tolerances.
The following chart is useful for a more intuitive understanding of the concept of gold powder.
Measurement methods
Shape error
Refers to geometric errors that may occur during processing of geometric features such as points, lines, and faces on a part.
For example, when machining a cylinder, the diameter of each section of the shaft may be different, or the section of the shaft may not be round, or the axis may not be straight, or the plane may be warped inequality.
Position error
Refers to the error in the relative position that the structural elements on the part may produce during processing.
For example, the axis of rotation of the stepped shaft may have an offset or the like.
At present, there is a measurement method for efficiently measuring various shape and position errors, that is, the data acquisition instrument can be directly connected to various indication tables [3], such as a dial indicator, and the data acquisition instrument automatically reads the measurement data and performs data analysis. No need for manual measurement and data analysis, can greatly improve the efficiency of mechanical measurement.
Measuring instruments: deflection meter, dial indicator (or other indicator), data acquisition instrument
Measurement principle: The data acquisition instrument can read data from the dial indicator in real time, and calculate and analyze the shape and position error. Various shape and error calculation formulas have been embedded in our data acquisition instrument software, and no manual calculation is needed. The cumbersome data can greatly improve the accuracy of the measurement.
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