When we deal with processing every day, we often mention cnc machining v850 accuracy , but are you correct about the accuracy? Or is it rigorous? Let's take a look together!
Machining accuracy is the degree of conformity between the actual size, shape, and position of the surface of the processed part with the ideal geometric parameters required by the drawing! Ideal geometric parameters are the average size in terms of size; in terms of shape, they are absolute circles, cylinders, planes, cones, and straight lines; for mutual positions, they are absolute parallel, perpendicular, coaxial, etc. Symmetry and so on.
1. Dimensional accuracy
The degree of conformity between the actual size of the processed part and the center of the tolerance zone of the part size.
2. Shape accuracy
Refers to the degree of conformity between the actual geometric shape of the surface of the processed part and the ideal geometric shape.
3. Position accuracy
Refers to the actual position accuracy difference between the relevant surfaces of the parts after processing.
4. Mutual relations
Generally, when designing machine parts and stipulating the machining accuracy of parts, 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 surfaces of parts, the shape accuracy requirements should be higher than the position accuracy requirements, and the position accuracy requirements should be higher than the dimensional accuracy requirements.
The deviation of the actual geometric parameters of the part from the ideal geometric parameters is called the machining error. The size of the machining error reflects the level of machining accuracy. The greater the error, the lower the machining accuracy, and the smaller the error, the higher the machining accuracy.
1. Brief introduction of machining accuracy
Machining accuracy is mainly used for the degree of product production. Machining accuracy and machining error are both terms used to evaluate the geometric parameters of the machined surface. Machining accuracy is measured by tolerance grade, the smaller the grade value, the higher the accuracy; the processing error is expressed by the numerical value, the larger the numerical value, the greater the error. High machining accuracy means small machining error, and vice versa.
There are 20 tolerance levels from IT01, IT0, IT1, IT2, IT3 to IT18. If IT01 indicates the part has the highest machining accuracy, IT18 indicates the part has the lowest machining accuracy. Generally, IT7 and IT8 have medium machining accuracy. level. (We recommend that you pay attention to the "Mechanical Engineer" public account to grasp dry goods knowledge and industry information at the first time)
The actual parameters obtained by any machining method will not be absolutely accurate. From the perspective of the function of the part, as long as the machining error is within the tolerance range required by the part drawing, it is considered that the machining accuracy is guaranteed.
The difference between accuracy and precision:
1. Accuracy
Refers to the degree of closeness between the obtained measurement result and the true value. High measurement accuracy means that the system error is small. At this time, the average value of the measured data deviates less from the true value, but the data is scattered, that is, the size of the accidental error is not clear.
2. Precision
Refers to the reproducibility and consistency between the results of repeated measurements using the same kind of spare sample. It is possible that the precision is high, but the precision is not accurate. For example, the three results obtained by measuring using a length of 1 mm are 1.051 mm, 1.053, and 1.052, respectively. Although their precision is high, they are not accurate.
Accuracy represents the correctness of the measurement results, precision represents the repeatability and reproducibility of the measurement results, and precision is a prerequisite for accuracy.
2. Methods to improve machining accuracy
01
Adjust the process system
1) Trial cut method adjustment
Through trial cutting-measuring size-adjusting the amount of cutting tool-cutting-try cutting again, and so on until it reaches the required size. This method has low production efficiency and is mainly used for single-piece and small-batch production.
2) Adjustment method
The required size is obtained by adjusting the relative positions of the machine tool, fixture, workpiece and tool in advance. This method has high productivity and is mainly used for mass production. (We recommend that you pay attention to the "Mechanical Engineer" public account to grasp dry goods knowledge and industry information at the first time)
0
Reduce machine error
1) Improve the manufacturing accuracy of spindle components
The rotation accuracy of the bearing should be improved:
①Select high-precision rolling bearings;
②Using high-precision multi-oil wedge dynamic pressure bearings;
③Using high-precision hydrostatic bearings,
Should improve the accuracy of the accessories with the bearing:
①Improve the machining accuracy of box support holes and spindle journals;
②Improve the machining accuracy of the surface mating with the bearing;
③Measure and adjust the radial runout range of corresponding parts to compensate or offset the error.
2) Properly preload the rolling bearing
①The gap can be eliminated;
②Increase the rigidity of the bearing;
③Equalization of rolling element error.
Reduce the transmission error of the transmission chain
1) The number of transmission pieces is small, the transmission chain is short, and the transmission accuracy is high;
2) The use of reduced speed transmission is an important principle to ensure transmission accuracy, and the closer the transmission pair is to the end, the smaller the transmission ratio should be;
3) The accuracy of the end piece should be higher than that of other transmission parts.
Reduce tool wear
Before the tool size wear reaches the sharp wear stage, the tool must be re-sharpened.
