Summary of precision testing knowledge of each part of the machine tool
1. For the guide rail of different shapes, which plane straightness errors should be controlled separately from each surface?
A: the common shapes of machine guide are rectangular guide and v-shaped guide. The horizontal surface of the rectangular guide controls the guide rail's straightness error in the straight plane. The two surrounding surfaces of the rectangular guide guide control the guide guide in the horizontal error straightness. V guide, because the guide is composed of two oblique surfaces, so the two oblique surfaces both control the straightness error in the straight plane, together also control the straightness error in the horizontal plane.
2. What are the common ways to check the straightness error of the guide rail?
Answer: the guideway straightness error commonly used inspection method has: research point method, flat ruler pull table contrast method, pad plug method, pull steel wire inspection view and level instrument inspection view, optical flatness instrument (self-collimation instrument) inspection view and so on.
3. What is point method?
Answer: when using a flat ruler to check the guide rail straightness error, the guide rail appearance is evenly coated with a layer of very thin red lead oil, the flat ruler is covered in the guide rail appearance, with the appropriate pressure to make short interval reciprocating movement for research point, and then take off the flat ruler, investigate the rail appearance of the research point distribution and research point the most sparse density. The point is evenly distributed over the whole length of the guide, which indicates that the straightness error of the guide has reached the corresponding precision requirement of the ruler. This method is called point method.
The flat ruler used in the research point method is a standard flat ruler, and its precision grade is selected according to the precision requirements of the guide rail inspected, usually no less than grade 6. The length is not shorter than the length of the guide rail under inspection (in the case of low precision requirement, the length of the flat ruler is 1/4 shorter than the guide rail).
4. Which types of guide rail straightness error inspection is applicable to the research point method?
Answer: choose scrape grind method to repair the straightness error of guide rail, choose grind point method mostly. Point method is often used for the inspection of shorter guide rail, because the flat ruler beyond 2000mm is easy to deformation, difficult to make, and affect the accuracy of measurement. Blow grind short guide rail, rail straightness errors usually by the ruler to ensure accuracy, together with the research point of density per unit area is must demand, and can be based on the precision of the machine tool needs and guide in the machine of the nature and importance of location, separation rule for every 25 mm x 25 mm research within not less than 10 to 20 points (that is, each party ideas within the number).
When using point method to view the guide rail straightness error, because it can not measure the error value of the guide rail straightness, so when there is a level, usually do not need to point method for final inspection. However, it should be pointed out that in the absence of measuring instruments (level, optical flatness meter, etc.), the selection of three flat ruler produced by mutual research method, can effectively meet the normal machine tool short guide rail straightness error inspection requirements.
5. Which plane straightness error is suitable for measuring the guide rail with the comparison method of flat ruler pull table?
A: the comparison method of flat ruler pull table is usually used to check the straightness error of short guide rail in straight plane and horizontal plane. In order to improve the stability of the measurement reading, the length of the pad iron moving on the inspected guide rail shall not exceed 200mm, and the touch surface of the pad iron and the guide rail shall be scraped with the inspected guide rail to make the touch excellent, otherwise the accuracy of the measurement will be affected.
(1) inspection method for straightness errors in the straight plane place the flat ruler working surface horizontally and place it around the guide rail to be inspected, the closer the better, so as to reduce the influence of guide rail distortion on measurement accuracy. Put one on the guide rail and guide with a good mat iron, will dial gauge fixed on the pad iron, make the dial gauge measuring head has two top care feet appearance, adjust the flat feet, make the reading of the dial gauge to care about feet two head looks flat, then move the pad iron, every 200 mm read numerical a dial indicator, dial gauge readings each one of the biggest difference is the guide rail straightness error in length. In measurement, in order to avoid the influence of scratch point, make the reading accurate, it is best to pad a gauge block under the gauge head of the micrometer.
(2) the way to check the straightness error in the horizontal plane is shown in figure 3-4. Put the working side of the flat ruler around the guide rail to be inspected, adjust the flat ruler, so that the reading on both sides of the outer appearance of the dry meter is equal, and the measurement method and accounting error method are the same as above.
6, the pad plug method is applicable to which guide rail straightness error view?
A: the pad plug method is suitable for viewing the plane guide after grinding and surface roughness is lower
The rail, on the plane guide to be inspected, put a standard flat ruler, at the two ends of the flat ruler are 2/9•L interval, with two equal height pad support under the flat ruler, the usage block and the feeler to check the space between the flat ruler working surface and the measured guide plane. If the straightness of the horizontal lathe guide rail service is (1000∶0.02) mm, that is, equal to the thickness of equal height pad plus 0.02mm gauge block or feeler, in the guide rail interval of 1000mm in any place can not be plugged in is qualified. Measurement of fine machine guide, should choose the high accuracy of the measuring block, so as to be more accurate measurement of the guide line error value.
This method can also use micrometer instead of feeler, but to increase the thickness of the block, so that the micrometer can enter the measurement.
7. What are the characteristics of the straightness error of the guide rail? What questions should be paid attention to when operating?
Answer: use the steel wire after tensioning as the ambition of the straight line, direct measurement of each section of the guide line constitute the plane straightness error line value. Like using a flat ruler table comparison method, is a line value measurement method.
This method can only check the guide rail in the horizontal line error. Put a 500mm length of iron pad on the bed guide rail and install a reading microscope with scale. The lens of the microscope should be aligned with the steel wire and placed in a straight position if necessary. At both ends of the guide rail, each fixed a small pulley, with a diameter of less than 0.3mm steel wire, one end fixed on the small pulley, the other end with a heavy hammer hanging. The weight of the hammer should be 30% ~ 80% of the breaking force. Then adjust both ends of the wire so that when the microscope is at both ends of the guideway, the wire and the cut line on the lens coincide. Write down the reading on the hand wheel of the moving dividing board on the microscope.
Move the pad iron and investigate the microscope every 500mm to see if the steel wire coincides with the marking line. If not, adjust the reading wheel on the microscope to make it coincide, and take down the reading. Measure the whole length of the guide rail and record the readings in sequence. Arrange the readings on the graph paper and plot the motion of the pad. The maximum coordinate difference between the motion curve on each 1000mm length and the connecting line at both ends is the straightness error on each 1000mm length. If the curve that forms is in convex or in concave line, most convex or most concave point occupies the coordinate difference value of join to both ends namely the straightness error on guide rail full-length. If what form is wavy fold line (be apart in horizontal coordinate axis both sides namely have a bit), choose to contain line method, take the coordinate difference value between the two parallel lines with the smallest interval, it is the straightness error on guide rail full-length.
8, guide straight error curve production should pay attention to what question?
Answer: when making the straightness error curve of the guide rail, the scale of the curve chart should be chosen to be moderate. If the scale is too large, it is inconvenient to make and correct. Size is too small, in the calculation of guide straightness error may be prohibited. Recommended in measurement, small machine when. 0 - x axis length of 200mm, long bed 200~400mm, expertise of the machine tool should not exceed 500mm. Once the length of the x axis is determined, the scale of the x axis can also be determined. In practice, the 0-x axis represents the interval of the iron pad of the level, which can be made according to 1:5 to 1:10, that is, the measurement interval of 200mm is indicated by 40 or 20mm. Z axis and y axis represent the accuracy error of the guide rail, which can be indicated by the coordinates of l~2.5mm from 1000∶1 to 2500∶1, that is, accuracy error l mu m. Extra fine machine tool guide rail (usually shorter), you can take 5000∶1, that is, 1 micron error with 5mm to indicate.
For example, when measuring the guide rail of a certain machine tool, the length is 1000mm, the specification of the level used is 0.02/1000, and the length of the iron pad of the level is 200mm. When the level is placed on the guide plane at 0~200mm section, the reading value is zero. When the level moves forward to the guide plane at 200~400mm section successively, the bubble in the level moves forward one grid, which is positive value, indicating that the guide plane in this section is skewed 0.004mm upward. When the level moves to the 400-600mm section of the guide plane, if the bubble of the level moves back and returns to the zero position, it indicates that the guide plane of this section is parallel to the guide plane of the 0-200mm section. Since the 200~400mm guide rail faces upward aslant, the guide plane of the 0~200mm section is parallel to that of the 400~600mm section, but it is not in the same plane. When the level moves to the 600-800mm section of the guide plane, the bubble in the level moves back one grid, which is a negative value, indicating that the guide plane of this section is downward skewed. In the end, the 800-1000mm level returns to zero again, and the measurement continues until the measurement of the entire guide rail stops. The curve formed by each line segment is called the guide rail straightness error curve (or tool movement curve).
9. What are the characteristics of errors in measuring the straightness of the guide rail with optical instruments?
A: the principle of error in measuring the straightness of a guide using collimators and active collimators (optical flatness) is based on the fact that the beam of light moves in a straight line. The advantages of optical instrument measurement are :(1) in the measurement process, the accuracy of the instrument is less affected by external conditions (temperature, vibration, etc.), so the measurement accuracy is higher; (2) it can not only measure the straightness error of the guide rail in the straight plane (not equal to the horizontal level), but also replace the straightness error of the guide rail in the horizontal plane measured by steel wire and microscope. Therefore, in the manufacture and repair of machine tools, has been widely used. However, as for the long guide rail measuring more than 10m, because the journey of the beam is long and the light energy is lost greatly, the image is not clear enough and cannot be directly measured. Instead, it is necessary to measure the length in sections.
10, single guide rail appearance distortion error should be how to view?
Answer: about the appearance of each guide rail shape, in addition to in the horizontal plane and the straight surface there are straightness requirements, in order to ensure that the guide rail and moving parts cooperate with outstanding, progressive touch rate, but also need to control the guide rail appearance distortion error, this demand for large guide rail is particularly important. In scraping, in order to measure the parallel between the guide rail error, as a benchmark measurement with the guide rail, but also to avoid severe distortion.
Single guide rail appearance distortion error inspection method: V type guide rail with V type level pad iron, flat guide rail pad iron, from the arbitrary end of the guide rail, moving the level pad iron, every 200 ~ 5001Am reading, the maximum algebraic difference of reading level, is the guide rail distortion error. The error requirements in the precision specification of the machine tool as a rule, the first rule in the scraping and grinding process.
11, what is the need for the plane error measurement of the machine tool platform?
Answer: machine tool work platform plane degree error of view method, in the past continue to use "two point method", namely use parallel flat ruler, thousand points table, etc. However, it does not conform to the flatness definition rules in the national standard of shape and position service. Currently, jb2670-82, the common practice of metal cutting machine tool inspection, points out that the inspection measurement of flatness errors is all the interval between the smallest two parallel planes according to the accommodating practice surface
It can be seen from this definition that the orientation of the bearing plane, which serves as the identification reference, also needs to be determined according to the principle of minimum conditions. So it is necessary to grasp all of the measured appearance of error, and then ability according to the principle of identification benchmark. In this way, it is necessary to divide measurement into two processes. Firstly, the height of an arbitrary ambition plane (measurement benchmark) is measured at several points on the external surface of practice, and then the error value corresponding to the definition can be calculated by means of benchmark transformation.
12. How to operate and identify flatness errors measured with indicators?
Answer: measure the flatness error with the indicator, and place the tested part on the flat plate with the support. The working surface of the flat plate is the measuring standard. In measurement, the three points farthest apart from the outside of the measured practice are usually adjusted to equal height with the flat plate (leveling), so the algebraic difference between the maximum and minimum readings measured by the indicator is the error value of flatness identified by the three-point method. It is also possible to adjust the height of the two ends of a diagonal line on the outside of the measured practice and the height of the two ends of another diagonal line. Therefore, the algebraic difference between the maximum and minimum readings measured by the indicator is the error value identified by the diagonal method. But this flat contrast difficult, can be measured by the wiring must be measured appearance, together with the record reading. Usually the algebraic difference between the maximum and minimum readings is used as the error value. If necessary, the readings of each measuring point can be processed according to the minimum condition to solve the error value.
13. What questions should be paid attention to when measuring flatness errors with horizontal instrument?
Answer: with level instrument measurement plane degree error is with natural level as measurement benchmark, measure should be guessed to practice appearance adjustment to approximate level first. Then the level is placed on the bridge board, and the bridge board is placed on the measured surface. The measured surface is measured point by point according to certain wiring, and the readings (grid number) of each measuring point are recorded together, and then the grid number is converted into line value. According to the measured reading (line value), after data processing, the flatness error can be obtained. This method can be used to measure the flatness of a large plane.
14, with self-collimator measurement plane error should pay attention to what question?
Answer: when measuring flatness error with self-collimator, place the self-collimator on the base other than the measured parts, place the reflector on the bridge board, and place the bridge board on the measured surface. In measurement, the self-collimator should be adjusted to approximately parallel to the measured surface. Then, by measuring the error of straightness and wiring according to meters, the readings of each measuring point on the diagonal are measured first, and then the readings of each measuring point on the other diagonal and each measuring point on other sections are measured, and these readings are converted into line values.
According to the measured reading (line value), the intersection point of two diagonals is used to determine the ideal plane that fits the diagonal law, and then the error value of flatness is solved according to the ideal plane. If necessary, the error value can be further solved according to the minimum condition. This method can be used without measuring the flatness of large plane.
15. How to identify flatness errors when measuring with flat crystals?
Answer: apply optical flat crystal to measure the plane. When measuring, stick the flat crystal on the measured surface. If the measured surface is concave or convex, the annular dry and band will appear.
If the dry and fringe are not closed, a slightly askew Angle between the optical flat crystal and the measured surface can be made to form an air wedge between the two. The error value is obtained by multiplying the ratio of the curvature of the dry and band by the ratio of the adjacent dry and band by half the wavelength. However, the errors identified by this method are replaced by straightness errors in practice.
The crystal used in the past can only measure the plane. These years with the flat crystal dry and instrument, the application of this instrument can also use the flat crystal dry and method to measure the larger plane.
