Machining method for two-section base of low-speed diesel engine

Abstract

The machining method for a two-section engine base of a low-speed diesel engine involves processing key components affecting the assembly accuracy of the main unit, such as the main bearing hole, thrust stop surface, damper mounting surface, and upper plane. Each section undergoes only rough machining, leaving machining allowance. The two sections are then directly fixed to leveling pads and connected as a whole, followed by finish machining at the same workstation. Adding process pin holes to the mating surfaces facilitates the connection of the engine base and the milling of the pin holes, while also solving the problem of insufficient worktable width and ensuring more secure and stable workpiece fixation. This method more reliably guarantees the overall assembly accuracy of the main unit and avoids irreversible impacts on the quality of the main unit.

Description

Technical Field

[0001] This invention relates to the field of machining, specifically a machining method for a two-section engine base of a low-speed marine diesel engine, and more particularly a machining method for a two-section engine base of a 9X92B ultra-large low-speed marine diesel engine. Background Technology

[0002] Generally, the engine base of a marine low-speed diesel engine is welded as a single piece. However, for some large low-speed diesel engines, such as the 9X92B marine main engine, due to their enormous size and weight (a single section weighs approximately 120 tons and is nearly 10 meters long), a two-section structure is used for the engine base. Like the integral engine base, the two-section engine base still uses welded steel structures, requiring segmented machining before assembly. The design and manufacturing method of the two-section engine base involves segmented machining followed by assembly, making it more difficult to guarantee precision than the integral engine base. Controlling the dimensional and positional tolerances at key assembly points is challenging, and the machining process is very difficult. Furthermore, issues such as misalignment between the two sections after connection and poor fit between the mating surfaces must be overcome. Otherwise, the overall assembly precision of the main engine will be affected, or leaks may occur, causing irreversible damage to the product quality of the main engine. Summary of the Invention

[0003] This invention addresses the difficulties in the original two-section engine base machining design drawings by providing a machining method for a two-section engine base of a low-speed diesel engine, which can more effectively and reliably ensure the overall machining accuracy of the two-section frame.

[0004] The technical solution of this invention is:

[0005] Instead of machining the two machine base sections separately as per the original design drawings, the two machine base sections are connected together in one assembly based on key positions and geometric tolerances that affect the assembly accuracy of the machine base. The key parts are machined simultaneously, which can more effectively ensure the overall machining accuracy of the machine base.

[0006] The low-speed diesel engine two-section base processing method of the present invention is characterized in that: the original design of two separately processed base sections is optimized to allow for processing of key parts such as main bearing holes, thrust bearing surfaces, damper mounting surfaces, and upper surfaces when processing a single section. The two base sections are leveled with equal height pads (10). Before each use, the equal height pads are milled into the same plane by a machine tool. Then, the base is directly fixed to the equal height pads by connecting the base plate (9) to the equal height pads through bolts (6), nuts (7), and adjusting pads (8). After the two base sections are connected into a whole, the main bearing holes, damper mounting surfaces, thrust bearing surfaces, and upper surfaces (5) of the two base sections are processed together. This can more reliably ensure the coaxiality of the main bearing holes, the perpendicularity of the bearing holes to the damper surfaces and thrust bearing surfaces, and the parallelism of the bearing holes to the upper surfaces. Ideally, when scribing the two machine base sections on the blank, the width dimensions of the two sections should be measured at two or more points at the same location for comparison. This will help check for misalignment during the scribing stage and ensure that the two machine base sections achieve the minimum misalignment tolerance. It is also advisable to add a process positioning pin hole (1) next to the original design pin hole on the mating surface of the two machine base sections for positioning during the initial connection of the two machine base sections.

[0007] More specifically, this invention relates to a machining method for a two-section engine base of a low-speed diesel engine. In the separate machining state, the main bearing cap holes, upper surface, thrust stop, and damper mounting surface of both engine base sections remain in a rough machining state. All machining items, such as the upper surface holes and grooves, are temporarily left unmachined. The remaining positions, including the main bearing cap mounting platform, are precision machined according to the drawings. When marking the two engine base sections on the blank, misalignment is checked during the marking stage by taking multiple points at the same location and measuring the width dimensions of the two Y-axis sections for comparison. Figure 1 This minimizes the misalignment between the two machine base sections.

[0008] After the first bottom surface work is completed, the contour pads are arranged on the gantry milling machine worktable, fixed to the worktable, and then milled flat to ensure that all contour pads are on the same plane.

[0009] After the rough machining at the second station is completed, the clamps of the two machine base sections are loosened, and the machine base is tapped around the circumference using a pressure bar to release the machining stress.

[0010] A process positioning pin hole (2) is added to each mating surface. During segmented machining, the pin hole is machined to a diameter 1 mm smaller than the given diameter. After connection, the two positioning pin holes are manually milled together to the given diameter. A process positioning pin hole is added next to the original design pin hole on the mating surface of the two machine bases for subsequent positioning connection of the two sections. The design pin hole is temporarily machined to a diameter 1 mm smaller than the given diameter and is not machined into a finished product.

[0011] On the gantry milling machine's worktable, rearrange the leveling pads and clamp them in place. Then, mill all the leveling pads flat, ensuring they are all on the same plane. Connect the two machine base sections into a single unit. Install the process locating pins, install all connecting bolts on the mating surface and tighten them. Then, manually mill the locating pin holes on the mating surface, adapt temporary locating pins according to the actual dimensions, and insert them into the pin holes for positioning.

[0012] Simultaneously machining the main bearing bore, thrust stop surface, damper mounting surface, upper surface, and all holes and grooves on the upper surface further ensures the coaxiality of the main bearing bore, the perpendicularity of the bearing bore to the damper surface and thrust stop surface, and the parallelism of the bearing bore to the upper surface, completing the overall machining of the machine base. In this way, the present invention can more reliably guarantee the coaxiality of the main bearing bore, the perpendicularity of the bearing bore to the damper surface and thrust stop surface, and the parallelism of the bearing bore to the upper surface. Attached Figure Description

[0013] Figure 1 This is a diagram showing the location of the inspection points for misalignment of the two sections of the engine base in the low-speed diesel engine according to the present invention.

[0014] Figure 2 This is a schematic diagram of the machining station for the bottom surface of the two sections of the low-speed diesel engine base according to the present invention.

[0015] Figure 3 The diagram shows the locations of four additional process pin holes added to the mating surface of the two sections of the low-speed diesel engine base in this invention.

[0016] In the diagram: 1. Added process pin hole; 2. Original positioning pin hole; 3. Bolt connection hole; 4. Bottom plate surface; 5. Top surface.

[0017] Figure 4 This is a schematic diagram of the two engine base sections of the low-speed diesel engine of the present invention connected as a single unit.

[0018] Figure 5 This is a schematic diagram of the base-specific leveling pad and clamping mechanism of the present invention.

[0019] In the diagram: 6. Bolt; 7. Nut; 8. Adjusting shim; 9. Base plate; 10. Special leveling shim.

[0020] Figure 6 This is a schematic diagram of the boring process after the two machine base sections of the present invention are connected as one unit.

[0021] In the diagram: 11. Thrust stop surface; 12. Main bearing hole; 13. Vibration damper mounting surface. Implementation

[0022] The following describes further embodiments of the present invention with reference to the accompanying drawings:

[0023] The present invention describes a machining method for a two-section base of a 9X92B low-speed diesel engine, as shown in the figure. The method involves determining the center line of the bearing hole during blank scribing, identifying the zero point of the workpiece in the X, Y, and Z axes of the workpiece coordinate system, checking for misalignment of the mating surfaces of the two sections, and comparing the Y-axis width dimensions of the two sections by taking multiple points at the same location. Figure 1 During the marking stage, check for misalignment to ensure that the two machine base sections are minimized.

[0024] At the first workstation, the two base sections are placed on the machine tool worktable with their bottom surfaces facing upwards. After setting the zero point of the workpiece, all finished products of the base plates (part 4) on both sides of the machine base are processed at this workstation.

[0025] On the worktable of the gantry milling machine, arrange the 9X92B type machine base special leveling pads (part 10), fix the leveling pads on the worktable, and then mill the leveling pads flat to ensure that all leveling pads are on the same plane.

[0026] In the second station, the two machine base sections are flipped 180° so that the base plate rests on the level pad. After alignment and clamping, each section is rough machined, including the upper surface (part 5), vertical mating surface, sliding block (part 11), main bearing hole (12), and all other machining parts. After rough machining, the clamping of the two machine base sections is loosened, and the machine base is tapped around its circumference using a pressure bar to release machining stress.

[0027] After stress relief, the two machine base sections are re-clamped and aligned, the workpiece zero point is reset, and the vertical mating surface and the connecting bolt holes on the surface are precision machined. The workpiece zero point is re-verified, the locating pin holes on the mating surface are precision machined, and process pin holes are set next to the locating pin holes originally designed in the drawings for subsequent positioning and connection of the two sections. A process locating pin hole (2) is added to each mating surface. During the segmented machining, it is machined according to the given diameter of the locating pin hole by 1mm. After connection, the locating pin holes of the two sections are milled together by hand to the given diameter of the finished product. The pin holes designed in the drawings are temporarily machined according to the diameter by 1mm and are not finished. The main bearing cover holes, upper plane, thrust stop, and damper mounting surface of the two machine base sections are still in the rough machining state. All machining items such as holes and grooves on the upper plane are not machined for the time being. The main bearing cover mounting table and other positions are precision machined according to the drawings.

[0028] According to the design requirements of the drawings, the main bearing cover was installed on the two machine base sections and connected, tightened and fixed to the machine base with hydraulic bolts.

[0029] On the worktable of the gantry milling machine, rearrange the 9X92B machine base-specific leveling pads and clamp them in place. Then, mill all the leveling pads flat to ensure that all the leveling pads are on the same plane.

[0030] The third station connects the two machine base sections into a single unit. First, place one section of the machine base onto a leveling pad, align it, and then clamp and secure it. Next, hoist the other section of the machine base onto the leveling pad, maintaining a small gap between the two sections. Using jacks and a leveling plate fixture, adjust the unsecured machine base along the X and Y axes. Adjust the X-axis until the mating surfaces are properly aligned, and adjust the Y-axis until the process pin holes are aligned, with a misalignment of less than 0.02mm. Then, install the process locating pins and all connecting bolts on the mating surfaces, tighten all bolts, and check that all mating surfaces are tightly fitted; a 0.02mm feeler gauge should not be able to penetrate. Finally, manually mill the locating pin holes designed in the drawing, adapt temporary locating pins to the actual dimensions, and insert them into the pin holes for positioning.

[0031] After connecting the two machine base sections into a single unit, the main bearing holes, thrust stop surface, damper mounting surface, upper surface, and all holes and grooves on the upper surface are machined simultaneously. This ensures more reliable coaxiality of the main bearing holes, perpendicularity of the bearing holes to the damper surface and thrust stop surface, and parallelism of the bearing holes to the upper surface. This completes the overall machining of the machine base.

[0032] After processing is completed, the machine base is lifted off the gantry milling table for final grinding and cleaning.

Claims

1. A method for machining a two-section base for a low-speed diesel engine, characterized in that: The original design of two separately machined machine bases was optimized to a single-section machine base. When machining the main bearing hole, thrust stop surface, damper mounting surface, and upper plane, machining allowance was left for key parts. The two machine base sections were leveled with equal height pads (10). Before each use, the equal height pads were milled into the same plane using a machine tool. Then, the machine base was directly fixed to the equal height pads by connecting its base plate (9) with the equal height pads through bolts (6), nuts (7), and adjusting pads (8). After the two machine base sections were connected into a whole, the main bearing hole, damper mounting surface, thrust stop surface, and upper plane (5) of the two ends of the machine base were machined together to ensure the coaxiality of the main bearing hole, the perpendicularity of the bearing hole to the damper surface and thrust stop surface, and the parallelism of the bearing hole to the upper plane. When the machine is being processed separately, the main bearing cover holes, upper plane, thrust stop, and damper mounting surface of the two machine bases remain in the rough machining state. All machining items of the upper plane holes and grooves are temporarily not processed. The remaining positions of the main bearing cover mounting platform are finely machined according to the drawings. When scribing the blanks of the two machine bases, the misalignment is checked during the scribing stage by taking multiple points at the same location and measuring the width of the two Y-axis sections for comparison, so that the two machine bases achieve a minimum misalignment. After the first bottom surface work is completed, the contour pads are arranged on the gantry milling machine worktable, the contour pads are fixed on the machine worktable, and then the contour pads are milled flat to ensure that all contour pads are on the same plane. After the rough machining at the second station is completed, the clamps of the two sections of the machine base are loosened, and the machine base is tapped around the circumference using a pressure bar to release the machining stress. An additional process positioning pin hole is added next to the original design pin hole on the mating surface of the two machine base sections for subsequent positioning and connection of the two sections; the pin holes in the drawing are temporarily machined with a diameter 1mm smaller and are not finished products. On the worktable of the gantry milling machine, rearrange the contour pads and clamp them in place; then mill all the contour pads flat to ensure that all the contour pads are on the same plane; connect the two machine bases into a whole; install the process positioning pins, install all the connecting bolts on the mating surface and tighten them; then manually mill the positioning pin holes on the mating surface; adapt the temporary positioning pins according to the actual dimensions and install them into the pin holes for positioning. Then, the main bearing hole, thrust stop surface, damper mounting surface, upper plane, and all holes and grooves on the upper plane are machined simultaneously to ensure the coaxiality of the main bearing hole, the perpendicularity of the bearing hole to the damper surface and thrust stop surface, and the parallelism of the bearing hole to the upper plane, thus completing the overall machining of the machine base.

2. The method for machining a two-section base for a low-speed diesel engine according to claim 1, characterized in that: When scribing the blanks of the two machine base sections, the misalignment is checked during the scribing stage by taking two or more points at the same location and measuring the width of the two sections for comparison, so that the two machine base sections achieve the minimum misalignment tolerance.

3. The method for machining a two-section base for a low-speed diesel engine according to claim 1, characterized in that: A positioning pin hole (1) is added next to the original pin hole on the mating surface of the two machine bases for positioning during the initial connection of the two machine bases.

4. The method for machining a two-section base for a low-speed diesel engine according to claim 1, characterized in that: After connecting the two machine base sections into a whole, the main bearing hole (12), the shock absorber mounting surface (13), the thrust stop surface (11), and the upper plane (5) are machined as a whole.

5. The method for machining a two-section base for a low-speed diesel engine according to claim 3, characterized in that: The contour pad is designed with T-slots. The machine base is fixed to the T-slots of the contour pad by bolts, rather than to the machine tool worktable, which reduces the requirements for the width of the machine tool worktable.

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