Abstract: In response to the many drawbacks of misjudgment, inability to quantitatively display machining errors, large number of templates, and high machining difficulty in measuring the position of the stop groove of linear bearings using a template, after exploration and analysis, a suggestion to switch to instrument measurement is proposed. Actual use has shown good results.
Keywords: Linear bearings; Stop groove; Axial positioning; Template; measuring method
The stop groove on the outer diameter of the linear bearing plays an axial positioning role during installation, ensuring that the bearing operates smoothly and without axial displacement under working conditions. Therefore, the accuracy of the machining of the stop groove position will directly affect the installation and use of the bearing, and the detection method to ensure the accuracy of the machining of the stop groove position is particularly important.
1. Current measurement methods and drawbacks
1.1 Measurement tools
The position and size of the stop groove on the outer ring of a linear bearing are usually measured using a template, as shown in Figure 1. The b in the figure represents the large norm; M is a small fan; The notch R is a mark on one side of the small sample, designed to facilitate the differentiation of large and small samples at any time during the use of the sample. There is one measuring point and one measuring surface for each of the large and small scales (as indicated by the dashed arrow in the figure).
Figure 1 Sample of the position of the linear bearing stop groove
1.2 Design and measurement principles of templates
1.2 The values of the large and small ranges (b and M) of the template shown in the design drawing 1 can be calculated by the following equation
B=Position dimension+upper deviation (1)
M=Position dimension+Lower deviation (2)
According to equations (1) and (2), it can be seen that the large range is the maximum value of the positional dimension, and the small range is the minimum value of the positional dimension.
1.2.2 Measurement principle of the template
The qualified machining of the position dimension of the outer ring stop groove of the linear bearing measured using the template in Figure 2 is determined by the light gap method.
1.2.2.1 Determination of qualified products
(1) When measuring the position dimension with the small scale of the template, the measuring point is precisely stuck on the edge of the stop groove near the bearing end face, but does not enter the groove (Figure 2 and partially enlarged image); When measuring the position dimensions using the large scale of the template at the same time, the measuring points of the template enter the groove, but there is a gap between the measuring surface and the side near the bearing end face of the groove. If there is light transmission, it is qualified (as shown in Figure 3 and local enlarged images).
(2) When measuring the position dimension using the small scale of the template, the measuring point falls on the outer diameter of the bearing end face near the stop groove, as shown in Figure 4; When measuring the position dimensions using the large scale of the template at the same time, the measuring points of the template enter the groove, and there is a gap between the measuring surface and the side near the bearing end face of the groove. If there is light transmission, it is qualified (Figure 3 and local enlarged images).
(3) When measuring the position dimension with the small scale of the template, the measuring point falls on the outer diameter near the stop groove on the side of the bearing end face (Figure 4). At the same time, when measuring the position dimension with the large scale of the template, the measuring point of the template enters the groove, but the measuring surface is close to the stop groove on the side of the bearing end face, and it is qualified if it is not transparent (Figure 5).
1.2.2.2 Determination of non-conforming products
(1) When measuring the position dimensions using the small scale of the template, if the measuring point enters the groove, it is not qualified.
(2) When measuring the position dimension with a large scale of the template, if the measuring point falls on the outer diameter of the side near the bearing end face of the stop groove, or just gets stuck on the edge of the side near the bearing end face of the stop groove, but does not enter the groove, it is considered unqualified.
According to the design principle of the template, there are three situations for the qualified products measured above. The first is the minimum value of the position dimension, the second is the middle value of the position dimension, and the third is the maximum value of the position dimension. There are two situations for non-conforming products, the first is when the position dimension is less than the minimum value, and the second is when the position dimension is greater than the maximum value.
1.2.3 Existing drawbacks
There are the following drawbacks to using a template for measurement:
(1) Due to the roughness of the workpiece in the machining process, burrs and dust affect the observation of the light gap, often leading to misjudgment. Especially in critical state, accurate measurement is more difficult. Sometimes, the position size is already smaller than the minimum value, but the burrs on the edge of the groove lift the sample, making it impossible for the measuring points and surfaces of the sample to enter the groove and mistakenly thinking it is qualified; Sometimes, if the position size is smaller than the maximum value, it is considered a qualified product. However, the burrs on the edge of the groove lift the sample, preventing the measuring points and surfaces of the sample from entering the groove and mistakenly thinking it is unqualified; Sometimes, the measuring points and surfaces of the sample have entered the groove, but due to the influence of dust, the light cannot be seen. Therefore, often after the final processing is completed, all interference and illusions are eliminated, and a lot of waste is returned, causing disputes between workers and inspectors.
(2) It can only qualitatively reflect whether the processing is qualified or not, and cannot quantitatively display processing errors.
(3) Each position dimension must have a dedicated template, and high requirements are placed on the machining accuracy, roughness and hardness of the measurement and positioning surfaces of the template, which indirectly increases the cost of bearings.
2. Improvement suggestions
2.1 Measurement methods
Given the aforementioned drawbacks of template measurement, it is recommended to use a height instrument for measurement. Figure 6 is a schematic diagram of measuring the position and size of the outer ring stop groove of a linear bearing using height instruments such as G203 and G204.
1- Bearing; 2- Levers; 3- lever bracket; 4- Instrument; 5- Instrument pillars; 6- Instrument measuring points; 7- Instrument workbench
Figure 6 Schematic diagram of measuring groove position using a height instrument
2.2 Measurement Principles
Taking the measurement of position dimension B=5.75+0.10 mm for linear bearing ZX203242A as an example, the following will be explained:
(1) Use specification 5 Calibrate the instrument with a height standard of 75 mm, so that the pointer of the instrument (dial gauge) points to zero. After calibration, the position size ranges from 0 to 0 The qualified range displayed on the instrument is 0-10 with a tolerance of 1 mm.
(2) When measuring the position and size of the bearing stop groove, as long as the value displayed on the instrument is within 0 to 10, it is considered a qualified product. When the instrument displays 0, the position size of the bearing is the minimum value, and when the instrument displays 10, the position size of the bearing is the maximum value.
Compared to the template, using instruments for measurement has the following advantages:
(1) The measured values are more accurate and simple and fast.
(2) The qualification of workpiece processing can be directly read from the instrument and the error value can be read out. If the workpiece processing is not qualified, the operator can accurately adjust the tool according to the out of tolerance value read on the instrument, thereby reducing the generation of waste.
(3) A height instrument can measure any position or size (as long as it is within the measurement range), with strong versatility. Height instruments are essential for production plants and do not need to be purchased separately; Although height standard parts are required for instrument calibration, the specifications of height standard parts in the production branch are relatively comprehensive. Even if special sizes need to be customized separately, the production of such height standard parts is relatively convenient; Convenient to use, with a longer lifespan and reduced measurement costs.
3. Conclusion
The measurement method for the position and size of the stop groove of linear bearings has been changed from template measurement to instrument measurement, which can make the measurement simpler, faster, and more accurate; Regardless of whether the workpiece is qualified or not, the instrument can accurately display the numbers, making it easier for workers to adjust the cutting tools and reducing the generation of waste products; After the improvement, the cost of designing, cutting, manufacturing, storing, and managing samples by dedicated personnel has been saved.
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Features:
magnetic, electric, and mechanic ABS
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Steel Material: GCr15/52100/100Cr6
Steel Type: Forged
Ball Grade: G10
Grease: Shell
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2024-03-15