Tool for grinding outer circle of crosshead pin shaft of low-speed diesel engine

Abstract

The utility model belongs to the field of low-speed diesel engine crosshead pin shaft manufacturing, and particularly relates to a 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] This invention belongs to the field of manufacturing crosshead pins for low-speed diesel engines, and specifically relates to a tooling for grinding the outer diameter of crosshead pins for low-speed diesel engines. Background Technology

[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 engine's operating performance.

[0003] Existing grinding techniques for machining the outer diameter of crosshead pins in low-speed diesel engines rely on the grinding machine's built-in centers. However, due to the large diameter of the 60-degree tapered holes at both ends of the crosshead, existing centers are unsuitable, requiring custom-made imported centers at a cost as high as 150,000 yuan, making it uneconomical. Furthermore, the machining accuracy requirements for the crosshead pins are extremely high; the perpendicularity between the outer diameter and the end face must be controlled within 0.02mm, and the parallelism between the concave surface and the outer diameter must also reach 0.02mm. In existing grinding techniques for the outer diameter of crosshead pins in low-speed diesel engines, the inconsistent datum between the boring and grinding processes leads to accumulated datum conversion errors during machining, making it difficult to meet geometric tolerance requirements. Simultaneously, the cumbersome installation and inconvenient disassembly of the tooling further impact machining efficiency. Therefore, there is an urgent need for a low-cost, high-precision, and easy-to-operate dedicated tooling to solve the problems of poor datum consistency, high machining costs, and difficulty in guaranteeing accuracy. Summary of the Invention

[0004] To address the problems of inconsistent machining datum, high machining costs, and low precision in existing grinding techniques for the outer diameter of crosshead pins in low-speed diesel engines, this invention proposes a fixture for grinding the outer diameter of crosshead pins in low-speed diesel engines. The fixture comprises two identical integral cylindrical structural parts, with a through hole at the center. One end face of the through hole is sequentially machined with a fixture tapered hole and a fixture tapered angle. The other end of the fixture has a large-diameter pipe thread on its outer cylindrical surface, with the large-diameter pipe thread sequentially positioned between the large-diameter pipe thread and the fixture tapered hole and the fixture tapered angle. The fixture includes a workpiece tapered circle, an external hexagonal prism, and a reference circle; the large-diameter pipe thread external thread is adapted to the crosshead internal thread; the fixture tapered circle is fitted and positioned with the crosshead tapered hole; the reference circle is used to calibrate the horizontal and axial directions of the reference circle during the boring process using a dial indicator; the external hexagonal prism is adapted to an internal hexagonal wrench to tighten the fixture; the large-diameter pipe thread external thread, the fixture tapered circle, the reference circle, and the fixture tapered hole are coaxial; the fixtures are used in pairs, and the reference circle outer diameter of fixtures in the same group is consistent and marked with a group identifier.

[0005] According to the above-described tooling for grinding the outer diameter of a crosshead pin of a low-speed diesel engine, the tapered surface of the tapered hole of the tooling is nitrided to achieve a hardness of HRC50-55.

[0006] According to the above-described tooling for grinding the outer diameter of the crosshead pin of a low-speed diesel engine, the thread pitch diameter tolerance grade of the large-diameter pipe thread is 6H, and the root chamfer is R0.3mm to eliminate stress concentration.

[0007] According to the above-described tooling for grinding the outer diameter of the crosshead pin of a low-speed diesel engine, the tooling is made of 45 steel, which is heat-treated to a hardness of HRC28-32, and after machining, it is subjected to low-temperature aging treatment, which is held at 150°C for 6 hours to eliminate internal residual stress.

[0008] According to the above-described tooling for grinding the outer circle of the crosshead pin of a low-speed diesel engine, the perpendicularity of the outer hexagonal side surface to the reference circle axis is ≤0.01mm, and the hexagonal side surface is electrolytically polished with a surface roughness Ra0.8.

[0009] The beneficial effects of the present invention are as follows:

[0010] 1. The tooling of the present invention adopts a large-diameter pipe thread and a crosshead internal thread for direct connection, and is positioned by fitting the tooling tapered circle with the crosshead tapered hole, combined with the reference circle for alignment, thereby achieving the standardization of the boring and grinding processes, and ensuring that the parallelism between the concave surface and the outer circle and the perpendicularity of the end face both meet the requirement of 0.02mm.

[0011] 2. The tooling cone angle on one side of the central through hole of the tooling in this invention effectively protects the end face of the tooling cone hole from damage and extends the service life of the tooling.

[0012] 3. The tooling of this invention features an external hexagonal design that is compatible with an internal hexagonal wrench, simplifying the tightening operation and improving installation efficiency.

[0013] 4. The coaxiality of the large-diameter pipe thread, workpiece tapered circle, reference circle and workpiece tapered hole of the present invention is controlled within 0.01mm, and the error of mixing is avoided by using them in groups and matching the markings of the same group.

[0014] 5. The tooling material of the present invention is the same as that of the workpiece, which reduces the impact of thermal deformation differences on accuracy.

[0015] This invention combines the advantages of high precision, low cost, and ease of operation, significantly improving the machining quality and efficiency of crosshead pins. The tooling significantly reduces machining costs and replaces expensive imported centers. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a tooling structure for grinding the outer circle of a crosshead pin of a low-speed diesel engine according to the present invention.

[0017] Figure 2 This is a schematic diagram of the tooling installation for grinding the outer circle of the crosshead pin of a low-speed diesel engine according to the present invention.

[0018] Figure 3 This is a cross-sectional view of a tooling installation diagram for grinding the outer circle of a crosshead pin of a low-speed diesel engine according to the present invention.

[0019] Figure 4 This is a schematic diagram of the geometric precision of the crosshead.

[0020] In the figure: 1-workpiece tapered hole, 2-workpiece tapered angle, 3-reference circle, 4-external hexagon, 5-workpiece tapered circle, 6-large diameter pipe thread, 7-through hole, 8-cross head threaded hole, 9-cross head tapered hole, 10-cross head tapered angle, 11-cross head, 12-tooling. Detailed Implementation

[0021] Preferred Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0023] like Figures 1 to 3 As shown: In this embodiment, a tooling for grinding the outer circle of a crosshead pin of a low-speed diesel engine includes: two identical integral cylindrical structural parts, with a through hole 7 at the center of the tooling; one end face of the through hole 7 is sequentially machined with a tooling tapered hole 1 and a tooling tapered angle 2; a large-diameter pipe thread 6 is provided on the outer cylindrical surface of the other end of the tooling, and a workpiece conical circle 5, an outer hexagonal body 4, and a reference circle 3 are sequentially arranged between the large-diameter pipe thread 6 and the tooling tapered hole 1 and the tooling tapered angle 2; the large-diameter pipe... The external thread of thread 6 is adapted to the crosshead threaded hole 8; the tooling tapered circle 5 is fitted and positioned with the crosshead tapered hole 9; the reference circle 3 is used to calibrate the horizontal and axial directions of the reference circle 3 by means of a dial indicator during the boring process; the external hexagonal body 4 is adapted to the internal hexagonal wrench to tighten the tooling; the external thread of the large-diameter pipe thread 6, the tooling tapered circle 5, the reference circle 3 and the tooling tapered hole 1 are coaxial; the tooling is used in pairs, and the outer diameter of the reference circle 3 of the tooling in the same group is consistent and marked with the same group mark.

[0024] The conical surface of tooling cone hole 1 is nitrided to achieve a hardness of HRC50-55.

[0025] The thread pitch diameter tolerance grade of the large-diameter pipe thread 6 external thread is 6H, and the root chamfer is R0.3mm to eliminate stress concentration.

[0026] The tooling is made of 45 steel, which is heat-treated to a hardness of HRC28-32. After processing, it undergoes low-temperature aging treatment and is kept at 150℃ for 6 hours to eliminate internal residual stress.

[0027] The perpendicularity of the outer hexagonal 4 side surface to the axis of the reference circle 3 is ≤0.01mm. The outer hexagonal 4 side surface is electrolytically polished, and the surface roughness is Ra0.8.

[0028] The tooling implementation steps of the present invention are as follows:

[0029] Step 1: Tooling Processing

[0030] 45# steel bar stock is selected and machined into a one-piece structure using a CNC lathe. First, the center through hole 7 is machined, and a 60° workpiece tapered hole and an adjacent 60° workpiece tapered angle are machined at one end. At the other end, a large-diameter pipe thread 6 external thread is machined, with its specification matching the internal thread of the crosshead threaded hole 8. Subsequently, a reference circle 3 and an external hexagon 4 are machined on the bar stock, and a 60° workpiece tapered circle is machined at the end of the external hexagon 4. During machining, the coaxiality of the large-diameter pipe thread 6, the 60° workpiece tapered circle 5, the reference circle 3, and the 60° workpiece tapered hole 1 is strictly controlled to ≤0.01mm. After completion, a unique identifier is printed on each tooling group, ensuring that the outer diameter of their reference circles is consistent.

[0031] Step 2: Pre-machining of the crosshead 11

[0032] Machining is performed on a boring machine, involving the large-diameter pipe threaded holes 8 at both ends of the crosshead 11, the 60° crosshead tapered hole 9, and the 120° crosshead tapered angle. During machining, the coaxiality of the large-diameter pipe threaded holes 8 at both ends and the taper surface accuracy of the 60° crosshead tapered hole 9 and the 120° crosshead tapered angle 10 must be ensured. After completion, the threaded holes and tapered surfaces must be cleaned to ensure no burrs.

[0033] Step 3: Tooling Installation

[0034] Screw the two fixtures in the same group into the crosshead threaded holes 8 at both ends of the crosshead 11, and tighten them with an Allen wrench until the 60° workpiece cone circle of the fixture is completely in contact with the 60° crosshead cone hole 9. During the tightening process, the force should be applied evenly to avoid uneven load, which would cause the coaxiality deviation between the 60° workpiece cone circle and the 60° crosshead cone hole 9.

[0035] Step 4: Baseline Alignment

[0036] On the boring machine, use a dial indicator to measure the upper generatrix and side generatrix of the reference circle 3 of the tooling, and adjust the position of the crosshead 11 so that the horizontal and axial directions of the reference circle are ≤0.005mm. After alignment, fix the crosshead 11 and machine the concave surface to the finished size.

[0037] Step 5: External cylindrical grinding

[0038] Transfer the crosshead 11 from the mounting fixture to the CNC grinding machine. The head and tailstock centers of the CNC grinding machine respectively insert into the 60° workpiece tapered holes 1 on the two end faces of the fixture. Start the grinding machine and grind the outer circle of the crosshead 11 to the design requirements, using the fixture reference circle 3 as a unified reference. During the grinding process, due to the unified reference, the parallelism between the concave surface of the crosshead 11 and the outer circle of the crosshead 11, as well as the perpendicularity of the end face, meets the requirement of 0.02mm.

[0039] Disassembly and maintenance

[0040] After machining, use an Allen wrench to loosen the tooling in the reverse direction, remove it, and clean the large-diameter pipe thread, workpiece tapered circle 5, and workpiece tapered hole 1. Check whether the workpiece tapered hole 1 is damaged. If wear is found, the accuracy can be restored by grinding the workpiece tapered angle 2.

[0041] The tooling is made of the same material as the crosshead 11, which reduces the accuracy deviation caused by thermal expansion differences.

[0042] The workpiece cone angle 2 can disperse the impact force during loading and unloading, and protect the workpiece cone hole 1.

[0043] The tooling in the group must be strictly matched to avoid affecting the consistency of the reference due to dimensional deviations.

[0044] During grinding, grease should be applied to the contact surface between the center point and the tapered hole 1 of the workpiece to reduce wear.

[0045] Through the above implementation methods, this tooling achieves low-cost, high-precision machining, significantly improving the production efficiency and quality stability of the crosshead pin.

[0046] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A tool for grinding the outer circle of a low-speed diesel engine crosshead pin shaft, characterized by, It comprises: 2 same integral columnar structural members, the tooling center is provided with a through hole; the through hole is sequentially provided with a tooling taper hole and a tooling taper angle on one end face; a large-diameter pipe thread outer thread is arranged on the outer cylindrical surface of the other end of the tooling, the large-diameter pipe thread outer thread and the tooling taper hole and the tooling taper angle are sequentially provided with a workpiece taper circle, an outer hexagonal body and a reference circle; the large-diameter pipe thread outer thread is adapted to the cross head thread hole; the tooling taper circle is positioned by being attached to the cross head taper hole; the reference circle is used to find the horizontal direction and the axial direction accuracy of the reference circle through the dial indicator in the boring process; the outer hexagonal body is adapted to the inner hexagonal wrench to tighten the tooling; the large-diameter pipe thread outer thread, the tooling taper circle, the reference circle and the tooling taper hole are coaxial; the tooling is used in pairs, the reference circle outer diameter size of the same group of tooling is consistent and is marked with the same group identification.

2. The tooling for grinding the outer circle of the crosshead pin shaft of a low-speed diesel engine according to claim 1, characterized in that: The taper surface of the tooling taper hole is treated by nitriding, and the hardness reaches HRC50-55.

3. The tooling for grinding the outer circle of the crosshead pin shaft of a low-speed diesel engine according to claim 2, characterized in that: The thread major diameter tolerance grade of the large-diameter pipe thread outer thread is 6H, and the thread root chamfer R0.3mm is used to eliminate stress concentration.

4. The tooling for grinding the outer circle of the crosshead pin shaft of a low-speed diesel engine according to claim 3, characterized in that: The tooling material is 45 steel, which is quenched and tempered to a hardness of HRC28-32, and then is subjected to low-temperature aging treatment after machining, 150℃ for 6 hours, to eliminate internal residual stress.

5. The tooling for grinding the outer circle of the crosshead pin shaft of a low-speed diesel engine according to claim 4, characterized in that: The perpendicularity of the outer hexagonal body side surface to the reference circle axis is ≤0.01mm, the outer hexagonal body side surface is treated by electrolytic polishing, and the surface roughness Ra is 0.8.

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