Process and tool for grinding outer circle of crosshead pin shaft of low-speed diesel engine

Abstract

The invention belongs to the field of low-speed diesel engine crosshead pin shaft manufacturing, and particularly relates to a process and tool for grinding an outer circle of a low-speed diesel engine crosshead pin shaft. According to the tool, the large-diameter pipe thread is directly connected with the crosshead internal thread, the tool cone circle and the crosshead taper hole are attached and positioned, the datum circle is combined for alignment, datum unification of boring and grinding procedures is achieved, the tool cone angle on one side of the tool center through hole effectively protects the end face of the tool taper hole from being damaged, and the service life of the tool is prolonged. The coaxiality of a large-diameter pipe thread, a workpiece cone circle, a reference circle and a workpiece taper hole is controlled within 0.01 mm, and through group use and same-group identification matching, mixed use errors are avoided, the material of a tool is consistent with that of a workpiece, and the influence of thermal deformation difference on precision is reduced. The method has the advantages of being high in machining precision, low in cost, convenient to operate and the like, and the machining quality and efficiency of the crosshead pin shaft are remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the field of manufacturing crosshead pins of low-speed diesel engines, and particularly relates to a process and tooling for grinding the outer circle of crosshead pins of low-speed diesel engines. Background Art

[0002] The crosshead pin of a high-power low-speed marine diesel engine is a key component of the main engine, and its machining accuracy directly affects the operating performance of the diesel engine.

[0003] In the existing machining of grinding the outer circle of crosshead pins of low-speed diesel engines, the outer circle grinding of crosshead pins relies on the built-in center of the grinding machine. However, due to the large diameter of the 60-degree taper holes at both ends of the crosshead center, the existing centers cannot be adapted, and special imported centers need to be customized, with a cost as high as 150,000 yuan, resulting in poor economy. In addition, the machining accuracy requirements for crosshead pins are extremely high. The perpendicularity between the outer circle and the end face needs to be controlled within 0.02 mm, and the parallelism between the concave groove surface and the outer circle also needs to reach 0.02 mm. In the existing machining of grinding the outer circle of crosshead pins of low-speed diesel engines, the benchmarks for the boring and grinding processes are not unified, resulting in the accumulation of benchmark conversion errors during the machining process and making it difficult to meet the geometric tolerance requirements. At the same time, the tooling installation is cumbersome and the disassembly is inconvenient, further affecting the machining efficiency. Therefore, there is an urgent need for a special tooling with low cost, high precision and easy operation to solve the problems of poor benchmark unity, high machining cost and difficult accuracy guarantee. Summary of the Invention

[0004] In order to solve the problems of non-unified machining benchmarks, high machining costs and low accuracy in the existing machining of grinding the outer circle of crosshead pins of low-speed diesel engines, the present invention proposes a process for grinding the outer circle of crosshead pins of low-speed diesel engines, including the following steps:

[0005] S1: Machining the tooling:

[0006] Turn a through hole in the bar stock; turn a tooling taper hole and a tooling taper angle at one end of the bar stock; turn an external thread of a large-diameter pipe thread at the other end of the bar stock; machine a reference circle and an external hexagon on the outer circle surface at the tooling taper hole end; turn a workpiece taper circle at one end of the external hexagon.

[0007] S2: Pre-machining the crosshead:

[0008] Machine large-diameter pipe thread holes, crosshead taper holes and crosshead taper angles at both ends of the crosshead on a boring machine.

[0009] S3: Installing the tooling:

[0010] Screw the external threads of the large-diameter pipe threads of 2 identical toolings into the crosshead thread holes at both ends of the crosshead respectively, and tighten them with an internal hexagon wrench until the workpiece taper circles of the 2 toolings are completely fitted with the crosshead taper holes.

[0011] S4: Aligning the benchmark:

[0012] On the boring machine, after adjusting the position of the crosshead, fix the crosshead and machine the concave surface to the finished size.

[0013] S5: External cylindrical grinding:

[0014] Transfer the crosshead with the installation tooling to the CNC grinding machine. The headstock and tailstock centers of the CNC grinding machine are respectively inserted into the tooling taper holes of the two toolings.

[0015] Start the grinding machine and grind the outer circle of the crosshead with the reference circle of the tooling as the unified reference. During the process of grinding the outer circle of the crosshead, with the unified reference, the parallelism between the concave surface and the outer circle and the perpendicularity of the end face are < 0.02 mm.

[0016] According to the process for grinding the outer circle of the crosshead pin of a low-speed diesel engine described above, in S1: The workpiece taper hole is 60°, and the workpiece taper angle is 120°; the thread specification of the external thread of the large-diameter pipe thread matches the internal thread of the crosshead; the workpiece taper circle is 60°; the coaxiality of the large-diameter pipe thread, the workpiece taper circle, the reference circle and the workpiece taper hole is < 0.01 mm.

[0017] According to the process for grinding the outer circle of the crosshead pin of a low-speed diesel engine described above, in S2: The boring machine uses the crosshead end face as the reference and processes the large-diameter pipe thread holes and the crosshead taper holes at both ends in three stages: rough boring, semi-finish boring and finish boring. After each stage of processing, use an air gun to remove the chips and detect the aperture taper of the crosshead taper hole.

[0018] According to the process for grinding the outer circle of the crosshead pin of a low-speed diesel engine described above, in S3: The surface roughness of the contact surface between the tooling taper circle and the crosshead taper hole is Ra1.6; during the tightening process, force should be applied evenly to avoid deviation of the coaxiality between the tooling taper circle and the crosshead taper hole caused by eccentric loading.

[0019] According to the process for grinding the outer circle of the crosshead pin of a low-speed diesel engine described above, in S4: Adjust the position of the crosshead: Use a dial indicator to measure the upper generatrix and side generatrix of the reference circle of the tooling to make the accuracy of the horizontal direction and the axis direction of the reference circle ≤ 0.005 mm.

[0020] A tooling for the process of grinding the outer circle of the crosshead pin shaft of a low-speed diesel engine as described above. The tooling consists of 2 identical integral columnar structural parts, with a through-hole in the center of the tooling. One end face of the through-hole is successively machined with a tooling taper hole and a tooling taper angle. On the outer cylindrical surface at the other end of the tooling, there is an external thread of a large-diameter pipe thread. Between the external thread of the large-diameter pipe thread and the tooling taper hole and the tooling taper angle, there are successively a workpiece taper circle, an external hexagon, and a reference circle. The external thread of the large-diameter pipe thread is adapted to the internal thread of the crosshead. The tooling taper circle fits and positions with the crosshead taper hole. The reference circle is used to align the horizontal direction and the axial direction accuracy of the reference circle through a dial indicator during the boring process. The external hexagon is adapted to an internal hexagon wrench to tighten the tooling. The external thread of the large-diameter pipe thread, the tooling taper circle, the reference circle, and the tooling taper hole are coaxial. The tooling is used in pairs, and the outer diameter dimensions of the reference circles of the same set of tooling are the same and are marked with the same set identifier.

[0021] For a tooling for grinding the outer circle of the crosshead pin shaft of a low-speed diesel engine as described above, the tapered surface of the tooling taper hole is nitrided, and the hardness reaches HRC50 - 55.

[0022] For a tooling for grinding the outer circle of the crosshead pin shaft of a low-speed diesel engine as described above, the pitch diameter tolerance grade of the external thread of the large-diameter pipe thread is 6H, and the root chamfer of the thread is R0.3mm to eliminate stress concentration.

[0023] For a tooling for grinding the outer circle of the crosshead pin shaft of a low-speed diesel engine as described above, the material of the tooling is 45 steel, which is quenched and tempered to a hardness of HRC28 - 32, and is subjected to low-temperature aging treatment after processing, maintaining at 150°C for 6 hours to eliminate internal residual stress.

[0024] For a tooling for grinding the outer circle of the crosshead pin shaft of a low-speed diesel engine as described above, the perpendicularity between the side surface of the external hexagon and the axis of the reference circle is ≤0.01mm, and the side surface of the hexagon is electrolytically polished with a surface roughness Ra of 0.8.

[0025] The beneficial effects of the present invention are as follows:

[0026] 1. The tooling of the present invention directly connects the large-diameter pipe thread with the internal thread of the crosshead, and through the fitting and positioning of the tooling taper circle with the crosshead taper hole, combined with the alignment of the reference circle, the unity of the reference for the boring and grinding processes is achieved, ensuring that the parallelism between the concave groove surface and the outer circle and the perpendicularity of the end face both meet the requirement of 0.02mm.

[0027] 2. The tooling taper angle on one side of the through-hole in the center of the tooling of the present invention effectively protects the end face of the tooling taper hole from damage and extends the service life of the tooling.

[0028] 3. The external hexagon design of the tooling of the present invention is adapted to an internal hexagon wrench, simplifying the tightening operation and improving the installation efficiency.

[0029] 4. The coaxiality of the large-diameter pipe thread, workpiece taper circle, reference circle and workpiece taper hole of the present invention is controlled within 0.01 mm, and by using them in groups and matching the same-group identification, the mixing error is avoided.

[0030] 5. The tooling material of the present invention is the same as that of the workpiece, reducing the influence of thermal deformation difference on the accuracy.

[0031] The present invention has the advantages of high precision, low cost, convenient operation, etc., significantly improving the processing quality and efficiency of the crosshead pin. The tooling significantly reduces the processing cost and replaces expensive imported centers. Description of the Drawings

[0032] Figure 1 It is a schematic structural diagram of a tooling for grinding the outer circle of a crosshead pin of a low-speed diesel engine according to the present invention.

[0033] Figure 2 It is a schematic installation diagram of a tooling for grinding the outer circle of a crosshead pin of a low-speed diesel engine according to the present invention.

[0034] Figure 3 It is a cross-sectional view of a schematic installation diagram of a tooling for grinding the outer circle of a crosshead pin of a low-speed diesel engine according to the present invention.

[0035] Figure 4 It is a schematic diagram of the geometric accuracy of the crosshead.

[0036] In the figure: 1 - workpiece taper hole, 2 - workpiece taper angle, 3 - reference circle, 4 - external hexagon, 5 - workpiece taper circle, 6 - large-diameter pipe thread, 7 - through hole, 8 - crosshead thread hole, 9 - crosshead taper hole, 10 - crosshead taper angle, 11 - crosshead, 12 - tooling. Detailed Embodiments

[0037] Preferred Embodiment

[0038] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the drawings in the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present application.

[0039] As Figures 1 to 3 shown: In this embodiment, a process for grinding the outer circle of a crosshead pin of a low-speed diesel engine

[0040] S1: Processing the tooling:

[0041] Turn a through hole 7 in the bar stock; turn a tooling taper hole 1 and a tooling taper angle 2 at one end of the bar stock; turn the external thread of the large-diameter pipe thread 6 at the other end of the bar stock; machine a reference circle 3 and an external hexagon 4 on the outer cylindrical surface of the bar stock at the end with the tooling taper hole 1; turn a workpiece taper circle 5 at one end of the external hexagon 4;

[0042] S2: Pre-machining of the crosshead 11:

[0043] Machine the large-diameter crosshead threaded holes 8, the crosshead taper holes 9 and the crosshead taper angles 10 at both ends of the crosshead 11 on a boring machine;

[0044] S3: Installation of the tooling:

[0045] Screw the external threads of the large-diameter pipe threads 6 of 2 identical toolings into the crosshead threaded holes 8 at both ends of the crosshead 11 respectively, and tighten them with an internal hexagon wrench until the workpiece taper circles 8 of the 2 toolings are completely fitted with the crosshead taper holes 9;

[0046] S4: Alignment of the reference:

[0047] On the boring machine, after adjusting the position of the crosshead 11, fix the crosshead 11 and machine the concave surface to the finished size;

[0048] S5: External cylindrical grinding:

[0049] Transfer the crosshead 11 with the installed tooling to a CNC grinding machine, and the headstock and tailstock centers of the CNC grinding machine are respectively inserted into the tooling taper holes 1 of the 2 toolings;

[0050] Start the grinding machine, and grind the outer circle of the crosshead 11 with the tooling reference circle 3 as the unified reference; during the process of grinding the outer circle of the crosshead 11, with the reference unified, the parallelism between the concave surface and the outer circle and the perpendicularity of the end face are <0.02 mm.

[0051] In S1: The workpiece taper hole 1 is 60°, and the workpiece taper angle 2 is 120°; the thread specification of the external thread of the large-diameter pipe thread 6 matches that of the crosshead threaded hole 8; the workpiece taper circle 5 is 60°; the coaxiality of the large-diameter pipe thread 6, the workpiece taper circle 5, the reference circle 3 and the workpiece taper hole 1 is <0.01 mm.

[0052] In S2: The boring machine takes the end face of the crosshead 11 as the reference, and machines the large-diameter crosshead threaded holes 8 and the crosshead taper holes 9 at both ends in three stages: rough boring, semi-finish boring and finish boring. After each stage of machining, use an air gun to remove the chips and detect the hole diameter taper of the crosshead taper hole 9.

[0053] In S3: The surface roughness of the contact surface between the tooling taper circle 5 and the crosshead taper hole 9 is Ra1.6; during the tightening process, force should be applied evenly to avoid deviation of the coaxiality between the tooling taper circle 5 and the crosshead taper hole 9 caused by uneven load.

[0054] In S4: Adjust the position of the crosshead 11: Use a dial indicator to measure the upper busbar and side busbar of the tooling reference circle 3, and make the accuracy of the horizontal direction and the axis direction of the reference circle 3 ≤ 0.005 mm.

[0055] The tooling consists of 2 identical integral columnar structural parts, and there is a through hole 7 in the center of the tooling; on one end face of the through hole 7, a tooling taper hole 1 and a tooling taper angle 2 are machined in sequence; on the outer cylindrical surface of the other end of the tooling, an external thread of a large-diameter pipe thread 6 is provided; between the external thread of the large-diameter pipe thread 6 and the tooling taper hole 1 and the tooling taper angle 2, a workpiece taper circle 5, an external hexagon 4 and a reference circle 3 are arranged in sequence; the external thread of the large-diameter pipe thread 6 is adapted to the crosshead thread hole 8; the workpiece taper circle 5 is fitted and positioned with the crosshead taper hole 9; the reference circle 3 is used to align the accuracy of the horizontal direction and the axis direction of the reference circle 3 through a dial indicator during the boring process; the external hexagon 4 is adapted to an internal hexagon wrench to tighten the tooling; the external thread of the large-diameter pipe thread 6, the workpiece taper circle 5, the reference circle 3 and the tooling taper hole 1 are coaxial; the tooling is used in pairs, and the outer diameter dimensions of the reference circles 3 of the same group of tooling are the same and are marked with the same group identification.

[0056] The conical surface of the tooling taper hole 1 is nitrided, and the hardness reaches HRC50 - 55.

[0057] The thread pitch diameter tolerance grade of the external thread of the large-diameter pipe thread 6 is 6H, and the thread root chamfer is R0.3 mm to eliminate stress concentration.

[0058] The tooling is made of 45 steel, quenched and tempered to a hardness of HRC28 - 32, and subjected to low-temperature aging treatment after processing, keeping warm at 150 °C for 6 hours to eliminate internal residual stress.

[0059] The perpendicularity of the side surface of the external hexagon 4 to the axis of the reference circle 3 ≤ 0.01 mm, and the side surface of the external hexagon 4 is electrolytically polished, and the surface roughness Ra is 0.8.

[0060] The implementation steps of the tooling of the present invention are as follows:

[0061] Step 1: Tooling processing

[0062] Select a 45 steel bar and machine it into an integral structure by a CNC lathe. First, turn the central through hole 7, and machine a 60° workpiece taper hole and an adjacent 60° workpiece taper angle at one end; turn the external thread of the large-diameter pipe thread 6 at the other end, and its external thread specification matches the internal thread of the crosshead thread hole 8. Subsequently, machine the reference circle 3 and the external hexagon 4 on the bar, and turn a 60° workpiece taper circle at the end of the external hexagon 4. During the machining process, strictly control the coaxiality of the large-diameter pipe thread 6, the 60° workpiece taper circle 5, the reference circle 3 and the 60° workpiece taper hole 1 ≤ 0.01 mm. After completion, print a unique identification on the same group of tooling and ensure that the outer diameter of its reference circle is the same.

[0063] Step 2: Preprocessing of the crosshead 11

[0064] On the boring machine, machine the large-diameter pipe thread holes at both ends of the crosshead 11, the 60° crosshead taper hole 9 and the 120° crosshead taper angle. During machining, it is necessary to ensure the coaxiality of the large-diameter pipe thread holes 8 at both ends and the taper surface accuracy of the 60° crosshead taper hole 9 and the 120° crosshead taper angle 10. After completion, clean the thread holes and the taper surface to ensure no burrs.

[0065] Step 3: Installation of the tooling

[0066] Screw two toolings of the same group into the crosshead thread holes 8 at both ends of the crosshead 11 respectively, and tighten them with an Allen wrench until the 60° workpiece taper circle of the tooling is completely fitted with the 60° crosshead taper hole 9. During the tightening process, apply force evenly to avoid deviation of the coaxiality between the 60° workpiece taper circle and the 60° crosshead taper hole 9 caused by eccentric loading.

[0067] Step 4: Alignment of the reference

[0068] On the boring machine, use a dial indicator to measure the upper generatrix and the side generatrix of the reference circle 3 of the tooling, and adjust the position of the crosshead 11 so that the accuracy of the horizontal direction and the axial direction of the reference circle is ≤ 0.005 mm. After alignment, fix the crosshead 11 and machine the concave surface to the finished size.

[0069] Step 5: External circle grinding

[0070] Transfer the crosshead 11 with the installed tooling to the CNC grinding machine, and the headstock and tailstock centers of the CNC grinding machine are respectively inserted into the 60° workpiece taper holes 1 at the end faces of the two toolings. Start the grinding machine and grind the external circle of the crosshead 11 to the design requirements with the reference circle 3 of the tooling as the unified reference. During the grinding process, due to the unified reference, the parallelism between the concave surface of the crosshead 11 and the external circle of the crosshead 11 and the perpendicularity of the end face meet the requirement of 0.02 mm.

[0071] Disassembly and maintenance

[0072] After machining is completed, use an Allen wrench to loosen the tooling in the reverse direction, remove it, and clean the large-diameter pipe thread, the workpiece taper circle 5 and the workpiece taper hole 1, and check whether there is any damage to the workpiece taper hole 1. If wear is found, the accuracy can be restored by grinding the workpiece taper angle 2.

[0073] The tooling is made of the same material as the crosshead 11 to reduce the accuracy deviation caused by the difference in thermal expansion.

[0074] The workpiece taper angle 2 can disperse the impact force during loading and unloading and protect the workpiece taper hole 1.

[0075] The set of toolings must be strictly matched to avoid affecting the unity of the reference due to dimensional deviation.

[0076] During grinding, lubricating grease should be applied to the contact surface between the center and the workpiece taper hole 1 to reduce wear.

[0077] Through the above embodiments, this tooling has achieved low-cost and high-precision machining, significantly improving the production efficiency and quality stability of the crosshead pin shaft.

[0078] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes should be covered within the protection scope of the present invention.

Claims

1. A process for grinding the outer circle of a crosshead pin of a low-speed diesel engine, characterized in that: The following steps are involved: S1: Processing tooling: Turning through holes in bars; turning tooling taper holes and tooling taper angles at one end of bars; turning large-diameter pipe thread external threads at the other end of bars; machining reference circles and external hexagons on the outer cylindrical surface of the tooling taper hole end; turning workpiece taper circles at one end of the external hexagon; S2: Crosshead pre-machining: Processing large diameter pipe thread holes, cross head taper holes and cross head taper angles at both ends of the cross head on a boring machine; S3: Tooling installation: Screw the large-diameter pipe thread external threads of two identical tools into the crosshead threaded holes at both ends of the crosshead respectively, and tighten them with a hexagonal wrench until the workpiece cones of the two tools are completely fitted with the crosshead cone holes; S4: Benchmark alignment: On the boring machine, after adjusting the crosshead position, fix the crosshead and machine the concave stop surface to the finished product size; S5: Cylindrical grinding: The crosshead of the tooling is transferred to the CNC grinder, and the headstock and tailstock of the CNC grinder are respectively pushed into the tooling taper holes of the two tools; Start the grinder and grind the outer circle of the crosshead using the tooling reference circle as a unified reference. During the grinding of the outer circle of the crosshead, the reference is unified, and the parallelism between the concave block surface and the outer circle and the verticality of the end face are <0.02mm.

2. A process for grinding the outer diameter of a crosshead pin of a low-speed diesel engine according to claim 1, characterized in that: In S1: the workpiece taper hole is 60°, the workpiece taper angle is 120°; the thread specification of the large-diameter pipe thread external thread matches the crosshead thread hole; the workpiece taper circle is 60°; the coaxiality of the large-diameter pipe thread, the workpiece taper circle, the reference circle and the workpiece taper hole is <0.01mm.

3. A process for grinding the outer circle of a crosshead pin of a low-speed diesel engine according to claim 2, characterized in that: In S2, the boring machine uses the crosshead end face as a reference and processes the large-diameter pipe threaded holes and the crosshead taper holes at both ends in three stages: rough boring, semi-finishing boring, and finishing boring. After each stage of processing, an air gun is used to remove chips and detect the taper of the crosshead taper hole.

4. A process for grinding the outer circle of a crosshead pin of a low-speed diesel engine according to claim 3, characterized in that: In S3: the surface roughness of the contact surface between the tooling cone and the cross head cone hole is Ra1.6; the force needs to be applied evenly during the tightening process to avoid the coaxiality deviation between the tooling cone and the cross head cone hole caused by eccentric load.

5. A process for grinding the outer diameter of a crosshead pin of a low-speed diesel engine according to claim 4, characterized in that: In S4: adjust the crosshead position: use a dial indicator to measure the upper generatrix and the side generatrix of the tooling reference circle, so that the horizontal direction and the axial direction accuracy of the reference circle are ≤0.005mm.

6. The tooling for grinding the outer diameter of the crosshead pin shaft of a low-speed diesel engine according to claim 5, characterized in that: The tooling is composed of two identical one-piece cylindrical structural parts, with a through hole provided in the center of the tooling; one end face of the through hole is processed with a tooling tapered hole and a tooling tapered angle in sequence; a large-diameter pipe thread external thread is provided on the outer cylindrical surface of the other end of the tooling, and a workpiece taper circle, an external hexagon and a reference circle are provided in sequence between the large-diameter pipe thread external thread and the tooling tapered hole and the tooling tapered angle; the large-diameter pipe thread external thread is adapted to the crosshead threaded hole; the tooling tapered circle and the crosshead tapered hole are fitted and positioned; the reference circle is used to align the horizontal and axial accuracy of the reference circle through a dial indicator during the boring process; the external hexagon is adapted to an internal hexagonal wrench to tighten the tooling; the large-diameter pipe thread external thread, the tooling tapered circle, the reference circle and the tooling tapered hole are coaxial; the tooling is used in pairs, and the outer diameter size of the reference circle of the tooling in the same group is consistent and marked with the same group logo.

7. The tooling for grinding the outer diameter of the crosshead pin of a low-speed diesel engine according to claim 6, characterized in that: The conical surface of the tooling conical hole is nitrided and the hardness reaches HRC50-55.

8. A tool for grinding the outer diameter of a crosshead pin shaft of a low-speed diesel engine according to claim 7, characterized in that: The thread pitch diameter tolerance grade of the large-diameter pipe thread external thread is 6H, and the thread root chamfer is R0.3mm to eliminate stress concentration.

9. A tool for grinding the outer diameter of a crosshead pin shaft of a low-speed diesel engine according to claim 8, characterized in that: The tooling material is 45# steel, which is quenched and tempered to a hardness of HRC28-32, and is subjected to low-temperature aging treatment after processing, at 150°C for 6 hours to eliminate internal residual stress.

10. A tool for grinding the outer diameter of a crosshead pin of a low-speed diesel engine according to claim 9, characterized in that: The perpendicularity between the side surface of the outer hexagon and the reference circular axis is ≤0.01 mm, and the side surface of the outer hexagon is electropolished to a surface roughness of Ra0.8.

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