Large-size Specification Three-cylinder Crankshaft Geometric Tolerance Measuring Device and Method

Abstract

The present invention relates to a device and method for measuring the form and position tolerances of a large-size three-cylinder crankshaft. The purpose is to solve the problem in the prior art that the measuring device cannot guarantee the correctness of the manufacturing dimensions of parts. The present invention compensates for the radius difference of the main shaft necks at both ends of the three-cylinder crankshaft by the height difference of the transition connecting plate, so that the measurement of the form and position tolerances of the three-cylinder crankshaft is more accurate and reliable. During measurement, the height difference of the main shaft necks at both ends when they are mounted on two V-shaped clamping blocks is first measured and calculated, and the corresponding transition connecting plates are processed according to the height difference. Then, the two V-shaped clamping blocks are correspondingly installed on the two transition connecting plates. The height difference of the two transition connecting plates just compensates for the height difference of the main shaft necks at both ends when they are mounted on the two V-shaped clamping blocks. Then, measurement is performed, and the product is judged to be qualified by comparing the actual measured value with the theoretical value. Compared with the existing method, the measurement results of this method are more accurate and the precision is higher.

Description

Technical Field

[0001] The invention relates to tolerance measurement of a three-cylinder crankshaft, and in particular to a device and method for measuring form and position tolerance of a large-size three-cylinder crankshaft. Background Art

[0002] High-performance diaphragm pumps for liquid medium transmission equipment in the fields of petrochemical and coal chemical industries. The power end of the equipment consists of a crankshaft, connecting rod, crosshead, piston rod, and piston to form a crank-connecting rod mechanism, such as Figure 1 As shown, the crankshaft consists of a main journal 01, a connecting rod journal 04, a connecting rod journal 04, a main journal 01, a connecting rod journal 04, a main journal 01, and a connecting shaft 05, all connected in sequence. With each crankshaft revolution, the pistons in the three crank-connecting rod mechanisms each complete a suction and discharge stroke. The angle between the three connecting rod journals is 120°, and the output flow rate pulsates over time according to a trigonometric function. Model 110 / 96 equipment has a maximum operating flow rate of 110 m³ / h and a maximum operating pressure of 96 bar. The power transmission crankshaft at the power end is a large, non-fully supported, integral, three-bend, three-support, special-shaped crankshaft. The performance parameters and operating principle of the equipment indicate that this transmission crankshaft is large in size, with a total length of 3400 mm, a maximum swing diameter of 760 mm, and a total weight of 2500 kg. The relative form and position tolerances of the crankshaft's main journal and connecting rod journal, as well as the angular tolerances of the three connecting rod journals, have a direct impact on the smooth movement of the equipment's motion mechanism. In order to ensure the design dimensions and form and position tolerance requirements of the parts, the finished parts require a set of dimensional measurement methods to ensure the correctness of the parts' manufacturing dimensions. Summary of the Invention

[0003] The purpose of the present invention is to solve the problem that the measuring devices and methods in the prior art cannot ensure the correctness of the manufacturing dimensions of parts, and to provide a device and method for measuring the form and position tolerances of a large-size three-cylinder crankshaft.

[0004] The technical solution adopted by the present invention is a large-scale three-cylinder crankshaft form and position tolerance measuring device, which includes a gantry milling machine and a lever dial indicator. The lever dial indicator is installed on the spindle of the gantry milling machine. The special feature of the present invention is that:

[0005] Also includes two sets of support components,

[0006] Each set of support components includes a transition connecting plate arranged on the working table of the gantry milling machine and a V-shaped clamping block arranged on the transition connecting plate;

[0007] The V-shaped clamping blocks on each set of support components have exactly the same structure;

[0008] The height difference between the two transition connecting plates is equal to the radius difference between the main journals at both ends of the three-cylinder crankshaft.

[0009] Furthermore, the lever dial indicator is installed on the main shaft of the gantry milling machine through a transition frame. The transition frame is in the shape of a connecting rod, one end of which is fixed on the main shaft of the gantry milling machine, and the other end is used to install the lever dial indicator.

[0010] Furthermore, the model of the gantry milling machine is GMC2060r2.

[0011] Based on the above-mentioned large-size three-cylinder crankshaft form and position tolerance measuring device, the present invention also provides a large-size three-cylinder crankshaft form and position tolerance measuring method;

[0012] Follow these steps to implement:

[0013] Step 1) Select an appropriate gantry milling machine based on the crankshaft diameter and length, and determine the three planes of the gantry milling machine coordinate system according to the right-hand Cartesian coordinate system principle, namely: XY plane, XZ plane, and YZ plane;

[0014] Step 2) Process two V-shaped clamping blocks and install them on the gantry milling machine worktable. Install the main journals at both ends of the crankshaft on the two V-shaped clamping blocks in a free state. Use the center line connecting the main journals at both ends as the crankshaft measurement reference centerline. Make the crankshaft measurement reference centerline parallel to the gantry milling machine worktable and the XY plane, and perpendicular to the YZ plane; measure the V-angles ∠abc and ∠efg of the two V-shaped clamping blocks;

[0015] Step 3) Select a micrometer based on the crankshaft diameter, use the micrometer to measure the dimensional error and shape error of the main journals at both ends, and record the main journal diameters at both ends to determine the main journal radius ab at one end of the crankshaft and the main journal radius ef at the other end;

[0016] Step 4) Based on the measured main journal diameter and the V-angles ∠abc and ∠efg of the V-clamping block, calculate the height difference ae between the centers of the main journals at both ends of the crankshaft when the crankshaft is tangent to the V-clamping block:

[0017] ae=ac+cg-eg;

[0018] Among them: ac=ab*sin∠abc,

[0019] cg=mf=bm*ctg∠bfm,

[0020] ∠bfm=∠efg=∠abc;

[0021] bm=(ab*cos∠abc)-(ef*cos∠efg);

[0022] eg=ef*sin∠efg;

[0023] Step 5) Processing two transition connecting plates, and processing the plane height difference between the two transition connecting plates to the ae value;

[0024] Step 6) Install the transition plate on the gantry milling machine workbench, install two V-shaped clamping blocks on the two transition plates respectively, and install the main journals at both ends of the crankshaft on the two V-shaped clamping blocks so that the distance between the center axis of the main journals at both ends and the bottom surface of the corresponding transition plate is equal;

[0025] Step 7) Measure the actual size of the crankshaft, calculate the error between the actual size and the theoretical size, and determine whether the measured crankshaft is qualified.

[0026] in:

[0027] Points a and e are the cross-sectional center points of the main journals at both ends of the crankshaft;

[0028] Points b and f are the tangent points of the cross section of the main journals at both ends of the crankshaft and the V-type clamping block respectively;

[0029] Points c and g are the intersections of the vertical diameter of the cross section of the main journal at both ends of the crankshaft and the horizontal line passing through points b and f respectively;

[0030] Points a, b, and c are on the cross section of the main journal at one end, and points e, f, and g are on the cross section of the main journal at the other end.

[0031] Furthermore, the step 7) specifically includes:

[0032] Step 7.1) Measure the coaxiality of the center axis of the crankshaft's intermediate main journal with the crankshaft's measurement reference centerline; measure the coaxiality of the center axis of the crankshaft's connecting shaft with the crankshaft's measurement reference centerline; measure the parallelism and position of the center axes of the three connecting rod journals with the crankshaft's measurement reference centerline;

[0033] Step 7.2) Calculate the error between the actual crankshaft size and the theoretical size based on the measured coaxiality, parallelism, and position;

[0034] Step 7.3) Determine whether the measured crankshaft is qualified based on the error.

[0035] Furthermore, steps 1) to 7) are performed once in the horizontal state and the vertical state of the gantry milling machine respectively, and the errors are calculated respectively, and the average value is taken.

[0036] Furthermore, in step 5), the flatness of the two transition connecting plates is 0.005, and the surface roughness is not greater than 1.6.

[0037] Furthermore, in step 6), the V-shaped surface runout of the V-shaped clamping block is no more than 0.003.

[0038] Furthermore, in step 2), the V-shaped clamping block is manufactured as a whole and then evenly divided into a pair, and the V-shaped surfaces on the same side are marked to ensure that the directions of the V-shaped surfaces on the same side are consistent when the V-shaped clamping block is positioned.

[0039] The beneficial effects of the present invention are:

[0040] The present invention provides a device for measuring the form and position tolerances of a large-size three-cylinder crankshaft. The device compensates for the radius difference of the main journals at both ends of the three-cylinder crankshaft by the height difference of the transition connecting plate, making the form and position tolerance measurement of the three-cylinder crankshaft more accurate and reliable.

[0041] The present invention's method for measuring the form and position tolerances of large-scale, three-cylinder crankshafts first measures and calculates the height difference between the main journals at both ends when mounted on two V-shaped clamping blocks. A corresponding transition plate is then machined based on this height difference. The two V-shaped clamping blocks are then mounted on the transition plates accordingly. The height difference between the two transition plates precisely compensates for the height difference between the main journals at both ends when mounted on the two V-shaped clamping blocks. Measurements are then performed again, and the product's conformity is determined by comparing the actual measured value with the theoretical value. This method provides more accurate and precise measurement results than existing methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a schematic diagram of the structure of the crankshaft;

[0043] 01-main journal, 04-connecting rod journal, 05-connecting shaft;

[0044] Figure 2 This is a front view of the device for measuring form and position tolerances of a large-scale three-cylinder crankshaft according to the present invention;

[0045] Figure 3 This is a side view of the form and position tolerance measuring device for a large-scale three-cylinder crankshaft according to the present invention;

[0046] Figure 4 This is a cross-sectional diagram of the crankshaft main journals at both ends mounted on the V-shaped clamping blocks in this embodiment. Figure 1 ;

[0047] Figure 5 This is a cross-sectional diagram of the crankshaft main journals at both ends mounted on the V-shaped clamping blocks in this embodiment. Figure 2 ;

[0048] Figure 6 This is a cross-sectional diagram of the crankshaft main journals at both ends mounted on the V-shaped clamping blocks in this embodiment. Figure 3 ;

[0049] Figure 7 This is a cross-sectional diagram of the crankshaft main journals at both ends mounted on the V-shaped clamping blocks in this embodiment. Figure 4 ;

[0050] Markings in the figure: 1-main spindle neck, 2-V-type clamping block, 3-transition connecting plate, 4-connecting rod neck, 5-lever dial indicator, 6-transition indicator frame, 7-gantry milling machine, 71-spindle, 72-work table. DETAILED DESCRIPTION

[0051] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. The crankshaft of the power transmission part of the diaphragm pump equipment has large dimensions and is heavy. Without special detection equipment, it is very difficult to measure, install and calibrate the parts. It cannot be detected by the general detection method for detecting small-sized crankshafts. In order to complete the measurement of large-sized diaphragm pump crankshafts without special large-sized measuring instruments, the first thing to solve is the problem that the general measurement means are difficult to calibrate due to the large dimensions and weight of the parts, and the second is to solve the technical problem of measuring form and position tolerances. In the absence of suitable special measuring instruments, the measurement of positional dimensional relationships can be carried out with the help of the X-axis, Y-axis, and Z-axis three-axis coordinate system of the gantry milling machine equipment and the lever dial indicator to measure the various relationships of the crankshaft's measured elements relative to the reference elements, and the measurement results are obtained by calculation and analysis of the collected data.

[0052] Example 1:

[0053] The structure of the large-scale three-cylinder crankshaft form and position tolerance measuring device of the present invention is as follows:

[0054] Combine Figure 1 、 Figure 2 As shown, it includes a gantry milling machine 7 with model GMC2060r2, a lever dial indicator 5 and two groups of support components. The lever dial indicator 5 can rotate with the vertical state and horizontal state of the main shaft 71 installed on the gantry milling machine 7; each group of support components includes a transition connecting plate 3 arranged on the work table of the gantry milling machine 7, and a V-shaped clamping block 2 arranged on the transition connecting plate 3; the V-shaped clamping block 2 on each group of support components is exactly the same in structure; the height difference between the two transition connecting plates 3 is equal to the radius difference of the main journal 1 at both ends of the three-cylinder crankshaft.

[0055] Preferably, the lever dial indicator 5 is installed on the spindle 71 of the gantry milling machine 7 through a transition frame 6. The transition frame 6 is in the shape of a connecting rod, one end of which is fixed to the spindle of the gantry milling machine 7, and the other end is used to install the lever dial indicator 5.

[0056] Example 2:

[0057] The present invention's method for measuring the form and position tolerances of a large-size three-cylinder crankshaft:

[0058] Follow these steps to implement:

[0059] Step 1) Because the crankshaft to be measured has large dimensions, with a total length of 3400mm and a maximum rotary diameter of 760mm, a gantry milling machine GMC2060r2 is selected for measurement. The worktable size of this equipment is 2000mmX6000mm, which meets the measurement size requirements of the crankshaft. At the same time, the main shaft of this equipment has both vertical and horizontal functions. Assuming the gantry milling machine is in vertical processing state, the three planes of the gantry milling machine coordinate system are determined according to the right-hand Cartesian coordinate system principle, namely: XY plane, XZ plane, and YZ plane. To ensure the detection conditions for the crankshaft to be installed and positioned on the gantry milling machine worktable for measurement, the center line of the crankshaft main journal must be parallel to the gantry milling machine worktable, and the line connecting the main journals at both ends must be parallel to the XY plane and perpendicular to the YZ plane.

[0060] Step 2) Due to the large size and weight of the crankshaft, the dial indicator calibration method cannot be used to meet the above measurement conditions. Therefore, a measuring tool can only be designed to meet the requirements of the above two measurement conditions. The crankshaft positioning is usually supported by a V-shaped clamping block 2. Therefore, two V-shaped clamping blocks 2 are processed and installed on the gantry milling machine workbench, and the main journals 1 at both ends of the crankshaft are respectively installed on the two V-shaped clamping blocks 2 in a free state. The outer diameters of the main journals 1 at both ends of the crankshaft are the same. Therefore, the center line connecting the center of the main journals 1 at both ends is the crankshaft measurement reference center line, so that the crankshaft measurement reference center line is parallel to the gantry milling machine workbench and parallel to the XY plane, and perpendicular to the YZ plane; Figure 4 As shown, measure the V-shaped angles ∠abc and ∠efg of the two V-shaped clamping blocks;

[0061] Step 3) The crankshaft being measured is a three-bend, three-support crankshaft, and the main journal 1 is a three-section discontinuous cylinder. The discontinuity of the machining of the main journals 1 at both ends may cause dimensional tolerance errors in the crankshaft outer diameter. In addition, the accuracy of the equipment used to machine the crankshaft may also cause machining errors in the roundness of the crankshaft main journal 1. These errors have a direct impact on the positioning accuracy of the crankshaft measurement datum. Therefore, a 300mm to 350mm outside diameter micrometer can be used to measure the dimensional error and shape error of the main journal 1, and the diameter of the main journal 1 can be recorded to obtain the radius ab of the main journal 1 at one end of the crankshaft and the radius ef of the main journal 1 at the other end of the crankshaft.

[0062] The measurement method is as follows:

[0063] like Figure 5As shown, the lever dial indicator 5 is used to measure the cylindrical surface of the crankshaft. After connecting the lever dial indicator 5 to the transition indicator frame 6, the transition indicator frame 6 is installed on the spring chuck of the machine tool spindle. According to the crankshaft outer circle measurement point a1 and the tooling installation position, the transition indicator frame is adjusted to select a suitable measurement rotation radius. The machine tool spindle is moved along the negative direction of the Z axis so that the head of the lever dial indicator 5 contacts the outer circle of the measured element for alignment. The lever dial indicator 5 is rotated along the spindle direction. When the pointer of the lever dial indicator 5 shows the highest point, the pointer of the lever dial indicator 5 is adjusted to zero; the lever dial indicator 5 is moved to the point b1 symmetrical to the point a1, where the Z-axis coordinate value remains consistent with the point a1 and the rotation radius of the lever dial indicator 5 is consistent with the point a1. The Y-axis coordinate of the machine tool is moved so that the head of the lever dial indicator 5 contacts the measured cylindrical surface of the crankshaft. At the same time, the transition indicator frame 6 is rotated with the spindle as the center, and the pointer of the lever dial indicator 5 is adjusted to the zero position. The above steps complete the alignment process of the lever dial indicator 5. According to the above alignment steps, under the condition that the rotary diameter measured by the meter head remains unchanged, and under the condition that each group of measured points symmetrical with respect to the Z axis is measured at the same height point on the Z axis, measure points a1, b1; c1, d1; e1, and f1 in groups in sequence (the more measuring points, the higher the measurement accuracy) for alignment measurement. After the alignment of each detection point is completed, read and record the coordinate value of the measured element relative to the machine tool coordinate system on the machine tool display screen. Add the absolute values of the data recorded for each group of measured points symmetrical with respect to the Z axis and divide them by 2. Record the calculation results. Then, calculate the average value of the calculated several groups of data, and the obtained data is the coordinate value of the center point of the measured element relative to the machine tool coordinate system in the Y-axis direction.

[0064] Therefore, according to the above measurement method, the coordinate coefficient values of each main journal and connecting rod journal relative to the machine tool are measured and calculated respectively, and the relative distances of each main journal and connecting rod journal in the Y-axis direction in the measurement coordinate system can be derived according to the coordinate values of the machine tool coordinate system.

[0065] Measurement and calculation of Z-axis data in the measurement coordinate system:

[0066] Install the lever dial indicator 5 on the machine tool spindle spring chuck, move the lever dial indicator to the highest point of the outer circle of one end of the crankshaft main journal and adjust the lever dial indicator 5 to zero, read the coordinate value of the highest point of the outer circle of one end of the crankshaft main journal relative to the machine tool coordinate system on the machine tool display screen and record it, move the machine tool spindle to the upper end of the highest point of the outer circle of the main journal at the other end of the crankshaft, move the machine tool Z axis to the zero position, read the coordinate value of the upper end of the highest point of the outer circle of the main journal at the other end relative to the machine tool coordinate system on the machine tool display screen and record it, add the coordinate values recorded by the lever dial indicator of the main journals at both ends of the crankshaft and calculate the average value, subtract the obtained value from the average value of the measured values of the radius of the main journals at both ends of the crankshaft, and the obtained value is the coordinate value of the measurement reference center point relative to the machine tool coordinate system in the Z-axis direction, move the machine tool spindle center to this coordinate point, clear the relative coordinate of the Z-axis on the machine tool display screen to complete the establishment of the Z-axis direction of the measurement coordinate system of the crankshaft. Therefore, according to the above measurement method, the values of the highest points of the main journals and connecting rod journals of each measured element in the Z direction relative to the crankshaft measurement reference in the measurement coordinate system are measured and the data is recorded. In this way, the data collection in the Z-axis direction of the measured element is completed. The relative distance between each main journal and connecting rod journal in the Z-axis direction in the measurement coordinate system can be derived by subtracting the corresponding measured value of the journal radius from the recorded data.

[0067] The measurement points in the Y-axis direction of the crankshaft are collected by grouping symmetrical points and multiple points, while the Z-axis direction only uses single-point collection. This is because the different contact points between the lever meter head and the measured cylindrical surface in the Z-axis direction will cause measurement errors, so only single-point collection is used in the Z-axis direction. The contact points of the lever meter head and the measured cylindrical surface in the Y-axis direction are in the same position and there is no measurement error, so the measurement points in the Y-axis direction are collected by grouping symmetrical points and multiple points.

[0068] Step 4) Figure 4 As shown in the figure, based on the measured main journal diameter and the V-angles ∠abc and ∠efg of the V-type clamping block, the height difference ae between the centers of the main journals 1 at both ends when the crankshaft is tangent to the V-type clamping block is calculated:

[0069] ae=ac+cg-eg;

[0070] Among them: ac=ab*sin∠abc,

[0071] cg=mf=bm*ctg∠bfm,

[0072] ∠bfm=∠efg=∠abc;

[0073] bm=(ab*cos∠abc)-(ef*cos∠efg);

[0074] eg=ef*sin∠efg;

[0075] Step 5) Processing two transition connecting plates 3, and processing the plane height difference between the two transition connecting plates 3 to ae value;

[0076] Step 6) Install the transition connecting plate 3 on the workbench of the gantry milling machine, install the two V-shaped clamping blocks 2 on the two transition connecting plates 3 accordingly, and install the main journals 1 at both ends of the crankshaft on the two V-shaped clamping blocks 2 so that the distances between the center axes of the main journals 1 at both ends and the bottom surfaces of the corresponding transition connecting plates 3 are equal; that is, the height difference between the two transition connecting plates 3 and the height difference between the two V-shaped clamping blocks 2 compensate each other.

[0077] Step 7) Measure the actual size of the crankshaft, calculate the error between the actual size and the theoretical size, and determine whether the measured crankshaft is qualified.

[0078] Finally, to reduce the error in the single Y-axis data, the GMC2060r2 gantry milling machine's spindle can be used in both vertical and horizontal positions. Adjust the gantry milling machine's spindle to the horizontal position and, following the aforementioned crankshaft measurement steps and calculation methods for the vertical position, collect data for the horizontal Y-axis data (and the vertical Z-axis) and the horizontal X-axis data (and the vertical Z-axis). This means performing steps 1) through 7) in both the horizontal and vertical positions of the gantry milling machine, calculating the errors and taking the average.

[0079] Crankshaft measurement data analysis and measurement conclusions: The data obtained by the above measurement steps and measurement data calculation method are classified and averaged to solve the position coordinates of the center point of the measured element of the crankshaft relative to the measurement coordinate system, such as Figure 6 As shown in the figure, data A, B, C, E, F, G, the connecting rod neck of the crankshaft being measured is divided into 4 angular directions of 120°, and the pitch circle diameter is ￠M, so the theoretical value from the diameter center of the three connecting rods to the diameter center of the measuring reference spindle is M / 2, as shown in the figure. Figure 7 As shown, the lengths of oa2, ob2, and oc2 can be calculated through the data A, B, C, E, F, and G; in Rt⊿a2oe2, ∠a2oe2=arctgE / C can be solved, and in Rt⊿c2of2, ∠c2of2=arctgA / F can be solved, so ∠a2oc2=∠a2oe2+90°+∠c2of2, and the angular error of the crankshaft processing can be solved by comparing the measured angular value ∠a2oc2 with the theoretical angular value 120°. Similarly, the measured angular values ∠b2oc2 and ∠a2ob2 can be calculated and compared with 120° to solve the other two angular errors of the crankshaft processing.

[0080] The connecting rod neck with the center point a2 is selected as the orientation reference for crankshaft measurement. The theoretical values of ∠c′of′ and ∠b′og′ can be calculated from the above-mentioned measured value ∠a2oe2 according to the 120° angular relationship of the three connecting rod necks. Then, the theoretical value M / 2 (oa2=ob2=oc2=M / 2) from the diameter center of the three connecting rod necks 4 to the diameter center of the main journal can be calculated from ∠a2oe2, ∠c′of′, ∠b′og′. Using the functional relationships Rt⊿a2oe2, Rt⊿c2of2, and Rt⊿b2om2, we can determine the theoretical values A′, B′, C′, E′, F′, and G′ of the crankshaft's measured element's center point relative to the measurement datum. By comparing these theoretical values with the actual measured values, we can determine the positional error of the crankshaft connecting journal relative to the measurement datum's centerline. The coaxiality of the intermediate main journal and connecting shaft relative to the measurement datum's centerline can be determined by calculating their coordinates using the aforementioned measurement steps and calculation methods. These values can then be compared with the coordinates of the crankshaft's measurement datum's centerline to determine the coaxiality error. The parallelism of the crankshaft connecting journal and main journal can be determined by directly measuring the cylindrical generatrix of the measured element using a lever dial indicator. The measured parallelism error is the parallelism error between crankshaft connecting journal 4 and main journal 1.

Claims

1. A method for measuring the form and position tolerances of a large-size three-cylinder crankshaft, characterized by: Follow these steps to implement: Step 1) Select an appropriate gantry milling machine based on the crankshaft diameter and length, and determine the three planes of the gantry milling machine coordinate system according to the right-hand Cartesian coordinate system principle, namely: XY plane, XZ plane, and YZ plane; Step 2) Process two V-shaped clamping blocks and install them on the gantry milling machine worktable. Install the main journals at both ends of the crankshaft on the two V-shaped clamping blocks in a free state. Use the center line connecting the main journals at both ends as the crankshaft measurement reference centerline. Make the crankshaft measurement reference centerline parallel to the gantry milling machine worktable and the XY plane, and perpendicular to the YZ plane; measure the V-angles ∠abc and ∠efg of the two V-shaped clamping blocks; Step 3) Select a micrometer based on the crankshaft diameter, use the micrometer to measure the dimensional error and shape error of the main journals at both ends, and record the main journal diameters at both ends to determine the main journal radius ab at one end of the crankshaft and the main journal radius ef at the other end; Step 4) Based on the measured main journal diameter and the V-angles ∠abc and ∠efg of the V-clamping block, calculate the height difference ae between the centers of the main journals at both ends when the crankshaft is tangent to the V-clamping block: ae=ac+cg-eg; Among them: ac=ab*sin∠abc, cg=mf=bm*ctg∠bfm, ∠bfm=∠efg=∠abc; bm=(ab*cos∠abc)-(ef*cos∠efg); eg=ef*sin∠efg; Points a and e are the center points of the cross-sections of the main journals at both ends of the crankshaft, respectively; points b and f are the tangent points of the cross-sections of the main journals at both ends of the crankshaft and the V-shaped clamping blocks, respectively; points c and g are the intersections of the vertical diameters of the cross-sections of the main journals at both ends of the crankshaft and the horizontal lines passing through points b and f, respectively; points a, b, and c are on the cross-section of the main journal at one end, and points e, f, and g are on the cross-section of the main journal at the other end; m is the perpendicular point of point f on line bc; Step 5) Processing two transition connecting plates, and processing the plane height difference between the two transition connecting plates to the ae value; Step 6) Install the transition plate on the gantry milling machine workbench, install two V-shaped clamping blocks on the two transition plates respectively, and install the main journals at both ends of the crankshaft on the two V-shaped clamping blocks so that the distance between the center axis of the main journals at both ends and the bottom surface of the corresponding transition plate is equal; Step 7) Measure the actual size of the crankshaft form and position tolerance, calculate the error between the actual size and the theoretical size, and determine whether the measured crankshaft is qualified.

2. The method for measuring form and position tolerances of a large-scale three-cylinder crankshaft according to claim 1 is characterized in that: The step 7) specifically includes: Step 7.1) Measure the coaxiality of the center axis of the crankshaft's intermediate main journal with the crankshaft's measurement reference centerline; measure the coaxiality of the center axis of the crankshaft's connecting shaft with the crankshaft's measurement reference centerline; measure the parallelism and position of the center axes of the three connecting rod journals with the crankshaft's measurement reference centerline; Step 7.2) Calculate the error between the actual crankshaft size and the theoretical size based on the measured coaxiality, parallelism, and position; Step 7.3) Determine whether the measured crankshaft is qualified based on the error.

3. The method for measuring form and position tolerances of a large-scale three-cylinder crankshaft according to claim 2 is characterized in that: Perform steps 1) to 7) once in the horizontal and vertical states of the gantry milling machine, calculate the errors respectively, and take the average value.

4. The method for measuring form and position tolerances of a large-scale three-cylinder crankshaft according to claim 3 is characterized in that: In step 5), the flatness of the two transition connecting plates is 0.005, and the surface roughness is not greater than 1.

6.

5. The method for measuring form and position tolerances of a large-scale three-cylinder crankshaft according to claim 4 is characterized in that: In step 6), the V-shaped surface runout of the V-shaped clamping block is no more than 0.

003.

6. The method for measuring form and position tolerances of a large-scale three-cylinder crankshaft according to claim 5 is characterized in that: In step 2), the V-shaped clamping block is manufactured as a whole and then evenly divided into a pair, and the V-shaped surfaces on the same side are marked to ensure that the directions of the V-shaped surfaces on the same side are consistent when the V-shaped clamping block is positioned.

Images