Marine crankshaft runout control and precise grinding method

Abstract

The invention discloses a marine crankshaft runout control and precise grinding method, which comprises the following steps of: firstly, providing a controllable stress release path for a crankshaft in a grinding process through a tip jacking force which is gradually reduced in stages; and secondly, adopting a center frame supporting scheme of step-by-step progressive from less to more, and changing a supporting point position combination in a key stage so as to expose and identify the original deformation and residual stress distribution of the crankshaft. And finally, creatively introducing an eccentric grinding compensation technology based on a run-out detection result, converting the run-out value of the main journal into an eccentric machining parameter of a numerical control grinding machine, and carrying out shape correction grinding on the non-supporting journal, so that the rotation reference of the crankshaft is physically reconstructed. According to the invention, the transformation from passive support to active control and from unified rigid positioning to segmented flexible adaptation is realized, and the machining precision, stability and production efficiency of the large crankshaft are obviously improved.

Description

Technical Field

[0001] The present invention relates to the field of large-scale precision machining, and particularly to a method for controlling the runout and precision grinding of marine crankshafts. Background Art

[0002] As the core power transmission component of a marine engine, the machining accuracy of a large marine crankshaft directly determines the operating stability, power output efficiency, and service life of the engine. The runout of the crankshaft is a key indicator for measuring its machining quality, including radial runout. If the runout exceeds the allowable range, it will cause severe vibration and increased noise during the operation of the marine engine, and even lead to serious failures such as excessive wear of the crankshaft and bearings, and failure of the seals, resulting in engine damage and threatening the safety of ship navigation.

[0003] Currently, fixed two-point steady rests or servo two-point steady rests are used for grinding large marine crankshafts. During the grinding process, at least two or more steady rests are used to always support the fixed main journals of the crankshaft until the crankshaft is precisely ground. However, there are defects in the grinding process. First, during the grinding process, the stress release steady rest of the crankshaft cannot make timely adjustments and still always supports according to the original settings. Second, the problem of wear and loss of the steady rest support blocks during the grinding process causes a change in the support center. Third, during the grinding process, the machine tool center point always presses the crankshaft with a single force, and the stress of the crankshaft cannot be released. Fourth, during the grinding process, the steady rest cannot accurately track in real time and cannot make adaptive adjustments according to the dimensional differences of different journals of the crankshaft, resulting in insufficient support stability, which in turn affects the accuracy of runout measurement and control, and the measurement and adjustment are out of sync. Summary of the Invention

[0004] To solve the above technical problems, the object of the present invention is to provide a method for controlling the runout and precision grinding of marine crankshafts; the specific technical solution is as follows: A method for controlling the runout and precision grinding of marine crankshafts, characterized by comprising the following steps: Step 1: Initial positioning and reference establishment stage; Clamp the crankshaft on the grinding machine, and the machine tool center point presses the crankshaft with a first pressing force F1; arrange a first group of steady rests to support on at least two main journals of the crankshaft; adjust the support to make the deflection of the crankshaft reach a first preset accuracy T1, and perform the first reference grinding. Step 2: Stress release and rigidity enhancement stage; Increase the number of steady rest supports to a second group, and at the same time reduce the pressing force of the machine tool center point to F2, and F2 < F1; adjust the support to make the deflection of the crankshaft reach a second preset accuracy T2, and perform the second pre-grinding; after this grinding, offline detect the runout and its phase of each main journal of the crankshaft, and record them. Step 3: Precision forming and runout evaluation stage; Increase the number of steady rests-support to the third group again. At the same time, reduce the top tight force of the machine tool center to F3, and F3 < F2. Adjust the support to make the deflection of the crankshaft reach the third preset accuracy T3, and perform the third forming grinding. After grinding, detect and record the runout of the crankshaft offline again. Step 4: Runout analysis and active correction decision-making stage; Judge whether the runout is qualified according to the detection results of Step 4. If it is unqualified, execute the active eccentricity correction process in Step 5. If it is qualified, enter the final precision grinding.

[0005] 2. A method for controlling the runout and precision grinding of a marine crankshaft according to claim 1, wherein the active eccentricity correction process described in Step 5 includes: (1) Support point position transformation and detection: Change the steady rests-support combination on the machine tool to the fourth group on the machine tool. The support point positions are different from those of the third group to reveal the deformation state of the crankshaft under different constraints. Adjust the deflection and grind under the top tight force F3, and then detect and record the runout in this state offline. (2) Generation of eccentricity compensation parameters: Analyze the detection results of (1). For the main journal that is not supported by the steady rest currently, map the magnitude of its runout to the stroke of eccentric grinding, and map the phase angle of its runout to the angular phase of eccentric grinding. Generate an eccentric machining program for the CNC grinding machine. (3) Benchmark reconstruction grinding: Adjust the steady rests-support to the fifth group, and perform eccentric compensation grinding on the main journal to be corrected determined in (2) to establish a new basis closer to the ideal axis. (4) Final precision grinding: Based on the new benchmark, adjust the steady rests-support to the sixth group covering all the main journals to be machined, and perform final precision grinding on all the main journals until the runout meets the requirements.

[0006] 3. A method for controlling the runout and precision grinding of a marine crankshaft according to claim 1 or 2, wherein the first top tight force F1 is dynamically determined according to the weight, material and length-diameter ratio of the crankshaft to ensure the balance of initial positioning rigidity and avoid excessive elastic deformation; the F1, F2, and F3 decrease step by step, and the decreasing ratio is set according to the stress release characteristics of the crankshaft material and the grinding allowance.

[0007] 4. A method for controlling the runout and precision grinding of a marine crankshaft according to claim 1 or 2, wherein from the first group to the third group of the steady rests-support groups, the number of supports gradually increases, and the selection of the support point positions added each time follows the principles of uniform span distribution, avoiding oil holes, and gradually stabilizing the flexural deformation.

[0008] 5. A method for controlling and precision grinding of marine crankshaft runout according to claim 2, characterized in that, in step five (1), the fourth set of support points and the third set of support points are offset from each other by at least one main journal distance in the axial direction, forcing the crankshaft to present different stress bending forms, thereby obtaining more comprehensive deformation information for eccentricity compensation calculation.

[0009] 6. A method for controlling and precision grinding of marine crankshaft runout according to claim 2, characterized in that, in step five (2), the eccentric compensation grinding technology is based on the eccentric grinding principle of crankshaft connecting rod journal, but is applied to the correction of form and position errors of main journal. The radial and phase programming of the grinding wheel feed path is performed by the CNC system to realize the directional removal of material in a specific direction of a specific main journal.

[0010] Working principle of a method for controlling crankshaft runout and precision grinding in marine applications: 1. Positioning Stage: The crankshaft is installed into the machine tool. The clamping force of the machine tool center is determined according to the weight, material, rigidity, and other properties of different crankshafts. If the clamping force is too small, it will cause positioning deviation, uneven grinding, and eventually scrap the ground crankshaft; if the clamping force is too large, it will cause crankshaft deformation and bending, grinding runout exceeding tolerance, and other problems. Therefore, it is necessary to select an appropriate clamping force according to the actual situation of the crankshaft.

[0011] 2. Gradual reduction of force: In each pre-grinding process, the clamping force is gradually reduced to allow the crankshaft to have a space for stress release during the grinding process, which helps to control the runout of the marine crankshaft.

[0012] 3. Gradually increase the center support: Start with 2 center supports in the initial pre-grinding and gradually increase to 5 center supports. The fewer center supports used initially, the more the original runout size and direction of the crankshaft will be exposed. As the center support is gradually increased in each grinding step, the grinding rigidity is gradually strengthened, and the crankshaft becomes more stable.

[0013] 4. Eccentric Grinding to Remove Runout: The runout is removed by grinding the connecting rod journal. The runout magnitude is equal to the eccentric stroke, and the runout direction (angle) is equal to the eccentric angle. This re-establishes a new support center to ensure that the runout meets the requirements. Beneficial effects

[0014] Compared with the prior art, the present invention has the following significant advantages: 1. Strong adaptive positioning capability: By adjusting the clamping force of the machine tool center and the number of center supports, the force and number can be adjusted according to the journal size and weight of different crankshafts to achieve stable positioning. It is compatible with various models of marine crankshafts, eliminating the need for additional tooling and reducing production costs. 2. Multiple grinding processes are used to reduce stress; the method of first tightening and then loosening, starting with less and then increasing, and multiple pre-grinding processes are used to remove runout. This method is easy to adjust, has high precision and speed, and improves production efficiency. 3. Easy to operate and highly practical; This invention is easy to operate and suitable for most grinding machines, both domestically and internationally, reducing the labor intensity of operators and making it highly practical. Attached Figure Description

[0015] Figure 1 A schematic diagram of a large marine crankshaft structure; Figure 2 This is a schematic diagram of the initial support state of the first group; Figure 3 This is a schematic diagram of the second set of support states; Figure 4 This is a schematic diagram of the third set of support states; Figure 5 This is a schematic diagram of the fourth group of support states; Figure 6 This is a schematic diagram of the fifth group of support states.

[0016] In the diagram: 1 - Main No. 1; 2 - Main No. 2; 3 - Main No. 3; 4 - Main No. 4; 5 - Main No. 5; 6 - Main No. 6; 7 - Main No. 7; 8 - Main No. 8; 9 - Main No. 9; 10 - Center frame; Detailed Implementation

[0017] The invention will be further described below with reference to the accompanying drawings, but it should not be construed that the scope of the invention is limited to the following embodiments. Various substitutions and modifications made based on ordinary technical knowledge and common practice in the art without departing from the spirit of the invention should be included within the scope of protection of the invention. Example

[0018] To validate this large marine crankshaft grinding process, final fine grinding of all main journals (Main No. 1 to Main No. 10) is required.

[0019] like Figure 1-4 As shown, a grinding method for controlling the runout of the main journal of a large marine crankshaft includes the following steps: Step 1: Initial Positioning and Baseline Establishment (1) Hoist the crankshaft onto the CNC crankshaft grinding machine, and align the center points of the headstock and tailstock with the center holes at both ends of the crankshaft; (2) All center frames are in the retracted state and do not participate in support; start the tailstock hydraulic system to tighten the crankshaft with a first tightening force F1=2000kg; this force is calculated based on the weight and rigidity of the crankshaft and is approximately the weight of the blank. (3) Move and lower the two center frames 10 to form the first set of supports. In this embodiment, the supports are selected on the main journals No. 4 and No. 6; the position of the support pads is precisely adjusted to avoid the lubrication holes on the journals; (4) Use a high-precision crankshaft gauge to measure the crankshaft deflection near the support point; adjust the crankshaft deflection value to within the first preset accuracy T1 = 0.01mm by finely adjusting the height of the center frame support block; (5) Under this stable condition, perform the first reference grinding; this grinding is rough grinding, the main purpose of which is to remove most of the machining allowance and, under the current center force and support conditions, initially establish a grinding reference center aligned with the machine tool axis.

[0020] Step Two: Stress Relief and Rigidity Enhancement; (1) Increase the number of central frames to enhance system rigidity; adjust the support of central frame 10 to the second group, that is, in this embodiment, add support for the main shaft journals of Main No. 2 and Main No. 8 to form a four-point support pattern of Main No. 2, Main No. 4, Main No. 6 and Main No. 8. (2) Simultaneously reduce the tailstock tip clamping force to the second clamping force F2=1500kg; it provides a controllable release space for the stress that may be redistributed inside the crankshaft due to the first grinding. (3) Use the gauge again to measure and adjust the four support points so that the crankshaft deflection is controlled within the second preset accuracy T2=0.01mm; (4) Perform a second pre-grinding to further remove excess material; (5) After grinding, remove the crankshaft from the machine tool and place it on an offline coordinate measuring machine or a special runout detection platform; accurately measure and record the magnitude and direction of the radial runout of all main journals.

[0021] Step 3: Precision forming and runout assessment; (1) Re-clamp the crankshaft back onto the machine tool and further increase the support of the center support 10 to the third group; in this embodiment, the support for the Main5 main journal is increased to form five support points: Main No. 2, Main No. 4, Main No. 5, Main No. 6, and Main No. 8; (2) Reduce the clamping force of the top again to the third clamping force F3 = 850 kg; at this point, the clamping force has completed the step-by-step reduction from 2000 kg to 1500 kg and then to 850 kg; (3) Fine-tune the five support points to ensure that the deflection reaches the third preset accuracy T3 = 0.01mm; (4) Perform a third forming grinding. After this grinding, the dimensions are close to the finished product requirements. (5) Perform offline jitter detection again to fully acquire and record jitter data in the current state.

[0022] Step 4: Fluctuation Analysis and Proactive Decision-Making; Analysis of the inspection report in step three revealed that the runout of journals such as Main1, Main4, and Main9 still exceeded the 0.03mm requirement specified in the drawing; therefore, it was determined that the active eccentricity correction process needed to be initiated.

[0023] Step 5: Active bias correction process; (1) Support point transformation and detection: Change the combination of the support of the center frame 10; change the support points from five points in the third group to three points in the fourth group: Main No. 3, Main No. 5, and Main No. 7. The purpose of this transformation is to allow the crankshaft to undergo elastic deformation under a different set of constraints, thereby exposing another side of its original deformation and stress distribution, and providing more comprehensive data for subsequent calculations.

[0024] The top clamping force is kept at F3, which is 850 kg; after adjusting the support to make the deflection qualified, the journal of the current support is lightly ground. After grinding, offline testing was performed again to obtain a runout distribution map under the new support condition; (2) Generation of eccentricity compensation parameters: Based on the comprehensive analysis of the detection data in step three and step five (1), the current center frame 10 supports Main No. 3, Main No. 5, and Main No. 7. Then Main No. 1, Main No. 2, Main No. 4, Main No. 6, Main No. 8, and Main No. 9 are unsupported journals to be corrected. Based on the magnitude and direction of the crankshaft main journal runout, an eccentric grinding method is used to remove the runout by grinding the connecting rod journal. That is, the runout magnitude is the eccentric stroke, and the runout direction (angle) is the eccentric angle. Modify the machine tool program to perform eccentric grinding on the main journals without center support in Main 1, Main 2, Main 4, Main 6, Main 8, and Main 9. The purpose of this grinding is to re-establish a new center.

[0025] (3) Reference reconstruction grinding: Adjust the center support position to the fifth group: Main No. 1, Main No. 2, Main No. 4, Main No. 6, Main No. 8, Main No. 9, that is, provide support for the journal to be corrected as determined in (2); Under this supported condition, the eccentric compensation grinding program generated for each journal is executed sequentially. (4) Final grinding: Based on the new benchmark established in the previous step, the support is redesigned and the center frame is adjusted to the sixth group to cover all the main journals that need final grinding, for example, by adopting a symmetrical six-point support layout.

[0026] Adjust the center support position to the main spindle journals No. 1, No. 2, No. 4, No. 6, No. 8, and No. 9. Use the new rotary center to grind the remaining main spindle journals, namely No. 3, No. 5, and No. 7. Final offline testing showed that the radial runout of all spindle journals was stable within 0.025mm, meeting the drawing requirement of ≤0.03mm.

Claims

1. A method for controlling the runout of a marine crankshaft and precision grinding, characterized in that, Includes the following steps: Step 1: Initial positioning and benchmark establishment phase; The crankshaft is clamped in the grinding machine, and the machine tool center clamps the crankshaft with the first clamping force F1. Arrange the first set of center support on at least two main journals of the crankshaft; Adjust the support to make the crankshaft deflection reach the first preset accuracy T1, and perform the first reference grinding; Step Two: Stress Relief and Rigidity Enhancement Stage; Increase the number of center support sets to a second set, while reducing the machine tool center clamping force to F2, and F2 <F1; Adjust the support to make the crankshaft deflection reach the second preset accuracy T2, and perform a second pre-grinding. After this grinding, the runout and phase of each main journal of the crankshaft were detected offline and recorded; Step 3: Precision forming and runout evaluation stage; The number of center support sets was increased to a third set, while the machine tool center clamping force was reduced to F3, and F3 <F2; Adjust the support to make the crankshaft deflection reach the third preset accuracy T3, and then perform the third forming grinding. After grinding, the crankshaft runout was detected and recorded offline again. Step 4: Jump Analysis and Proactive Decision-Making Phase; Determine whether the runout is acceptable based on the test results in step four; if it is not acceptable, proceed with the active eccentricity correction process in step five. If it passes the test, it will proceed to the final grinding.

2. The method for controlling and precision grinding marine crankshaft runout according to claim 1, characterized in that: Step 5, the active eccentricity correction process, includes: (1) Support point change and detection: Change the center support combination to the fourth group on the machine tool. The support point is different from the third group to reveal the deformation state of the crankshaft under different constraints; perform deflection adjustment and grinding under clamping force F3, and then detect and record the runout in this state offline; (2) Generation of eccentricity compensation parameters: Analyze the detection results of (1), for the main spindle journal that is not currently supported by the center frame, map the magnitude of its runout to the stroke of eccentric grinding, and map the phase angle of its runout to the angular phase of eccentric grinding; generate an eccentric machining program for CNC grinding machine; (3) Reference reconstruction grinding: Adjust the center support to the fifth group and perform eccentric compensation grinding on the spindle journal to be corrected as determined in (2) to establish a new basis that is closer to the ideal axis; (4) Final fine grinding: Based on the new benchmark, adjust the center support to cover the sixth group of all the main journals to be machined, and perform final fine grinding on all the main journals until the runout meets the requirements.

3. A method for controlling and precision grinding marine crankshaft runout according to claim 1 or 2, characterized in that, The first clamping force F1 is dynamically determined based on the weight, material, and length-to-diameter ratio of the crankshaft to ensure a balance between initial positioning rigidity and avoiding excessive elastic deformation; F1, F2, and F3 decrease in a stepwise manner, with the decreasing ratio set according to the stress release characteristics of the crankshaft material and the grinding allowance.

4. A method for controlling and precision grinding marine crankshaft runout according to claim 1 or 2, characterized in that, The number of supports in the central frame support group gradually increases from the first group to the third group, and the selection of each additional support point follows the principles of evenly distributed span, avoiding oil holes, and gradually stabilizing flexural deformation.

5. The method for controlling and precision grinding marine crankshaft runout according to claim 2, characterized in that, In step five (1), the fourth set of support points is offset from the third set of support points by at least one main journal distance in the axial direction, forcing the crankshaft to present different stress bending forms, thereby obtaining more comprehensive deformation information for eccentricity compensation calculation.

6. The method for controlling and precision grinding marine crankshaft runout according to claim 2, characterized in that, In step five (2), the eccentric compensation grinding technology is based on the eccentric grinding principle of crankshaft connecting rod journal, but is applied to the form and position error correction of main journal. The radial and phase programming of the grinding wheel feed path is performed by the CNC system to realize the directional removal of material in a specific direction of a specific main journal.

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