A method for preparing ultra-high-speed laser cladding coating on a piston rod of an ultra-large hydraulic cylinder

Abstract

This invention discloses a method for preparing an ultra-high-speed laser cladding coating on an ultra-large hydraulic cylinder piston rod, characterized by the following sequential steps: (1) Pre-cladding machining: The piston rod is mounted on a turning and grinding machine, the rod body is supported by a roller bracket, and the outer diameter is rough-turned and finish-turned in sections with the roller bracket as the interval; (2) Ultra-high-speed laser cladding: The tool holder is replaced with an ultra-high-speed laser cladding head, and ultra-high-speed laser cladding is performed in sections with the roller bracket as the interval, with seamless overlap between multiple cladding layers; (3) Post-cladding finishing: The grinding tool holder is started, the bearing bracket is replaced, and the coating is ground in sections to the final finished size, and the outer diameter is polished throughout. This method can obtain a uniform coating thickness on the surface of ultra-large parts, effectively solving a series of problems such as long process flow, insufficient subsequent machining allowance, stress cracking, powder rebound and splashing, and powder blockage of the cladding head.

Description

Technical Field

[0001] This invention relates to the field of surface engineering technology, specifically to a method for preparing an ultra-high-speed laser cladding coating for an ultra-large hydraulic cylinder piston rod. Background Technology

[0002] Ultra-large hydraulic cylinders are key core components in marine engineering equipment, construction machinery and other fields. Especially in marine working conditions with high salinity and high humidity, the cylinder piston rod is in a corrosive environment for a long time and the surface is subject to frequent reciprocating friction, which puts forward extremely high requirements for wear resistance and corrosion resistance. The performance of its surface coating directly determines the service life and reliability of the cylinder.

[0003] Traditional coating preparation processes have certain limitations: electroplating processes generate pollution, the coating is easy to peel off, and it is difficult to build ultra-large electroplating tanks, making it unsuitable for coating preparation on the surface of ultra-large hydraulic cylinder piston rods; thermal spraying processes result in porous coatings with weak corrosion resistance, and are prone to peeling and cracking, while also incurring high costs; traditional laser cladding technology has low working efficiency, and excessive heat input can cause problems such as localized decrease in the corrosion resistance of the coating and deformation of the substrate.

[0004] Ultra-high-speed laser cladding technology boasts advantages such as high efficiency, low cost, small heat-affected zone, and low coating dilution rate, making it particularly suitable for preparing coatings on the surfaces of rotating parts. However, currently, this technology is limited to applications in small and medium-sized parts, such as hydraulic supports for coal mining machinery and oil plunger pumps. For ultra-large parts, key challenges arise, including precision tolerances, stress cracking, and long-term operational stability. Summary of the Invention

[0005] This invention provides a method for preparing an ultra-high-speed laser cladding coating for an ultra-large hydraulic cylinder piston rod, effectively solving the following problems: a. Large-sized parts have large dimensional tolerances, and if the coating thickness is uneven, the coating is prone to wear through, exposure of the substrate, or lack of light during subsequent machining; b. The rod is long and requires multiple overlapping segments, resulting in a large amount of laser heat accumulation, which can easily lead to cracks if not properly controlled; c. The cladding time is long, and there are risks of powder blockage and ablation at the cladding head.

[0006] This invention is achieved through the following technical solution:

[0007] This invention provides a method for preparing an ultra-high-speed laser cladding coating for an ultra-large hydraulic cylinder piston rod, characterized by the following sequential steps:

[0008] (1) Machining before cladding:

[0009] a) The piston rod is clamped on a turning and grinding machine tool. One end is held by a four-jaw chuck, and the other end is tightened by a center. The rod body is supported by multiple roller brackets arranged at intervals of 3~5m.

[0010] b) Adopt a segmented machining strategy. First, rough machining is performed between the roller bracket support areas to make the outer diameter surface roughness Ra≤12.5μm;

[0011] c) After moving the roller bracket to the processed area, perform additional machining on the original support area;

[0012] d) Repeat the above segmented machining process for precision turning, so that the surface roughness Ra of the entire outer circle is Ra≤3.2μm;

[0013] (2) Ultra-high-speed laser cladding:

[0014] a) Install the ultra-high-speed laser cladding head, and adjust the nozzle position so that the working position of the cladding head is 10~15mm away from the tangent of the outer circle of the workpiece and H=tanθ·(L+R) away from the radial normal of the outer circle, where R is the radius of the outer circle and θ=5°~12°.

[0015] b) Perform surface degreasing and dust removal treatment;

[0016] c) Use a high-frequency induction preheating device to preheat the starting position of the cladding, and control the surface temperature of the workpiece to be ≥100℃;

[0017] d) A segmented cladding process is adopted to perform ultra-high-speed laser cladding between the roller bracket support areas. The process parameters include: laser power 4~6kW, spot diameter 2.5~3.8mm, and workpiece rotation linear speed 12~20m / min.

[0018] e) Perform segmented precision machining on the cladding layer, and machine a 30~40° transition chamfer at the end of the cladding layer;

[0019] f) After moving the roller bracket, perform additional cladding on the original support area and achieve seamless overlap of the old and new cladding layers through power gradient control;

[0020] (3) Finishing after cladding:

[0021] a) Use grinding to remove excess coating from the support area in sections;

[0022] b) Perform overall polishing to obtain a finished product with a surface hardness of 580~650HV and a corrosion resistance of 4200h neutral salt spray level 9.

[0023] Furthermore, the piston rod of the extra-large hydraulic cylinder has a diameter ≥ 0.5m and a length ≥ 10m.

[0024] Furthermore, in step 1.1, the integrated turning and grinding machine tool includes a turning tool holder and a grinding tool holder, the chuck is a four-jaw chuck, and the roller support is spaced 3~5m apart.

[0025] Furthermore, the width of the support area is greater than the width of the roller bracket roller and the width of the bearing bracket bearing.

[0026] Furthermore, the working position of the cladding head is at a vertical distance L = 10~15mm from the tangent of the outer circle, and at a vertical distance H = tanθ∙(L+R) from the radial normal of the outer circle, where R is the radius of the outer circle and θ is 5°~12°.

[0027] Furthermore, the preheating method is high-frequency induction preheating, the width of the heating coil is 200~400mm, the distance between the coil and the workpiece surface is 8~12mm, and the workpiece is kept rotating clockwise during the preheating process.

[0028] Furthermore, the ultra-high-speed laser cladding process parameters are as follows: laser spot diameter 2.5~3.8mm, laser power 4~6kW, workpiece outer diameter rotational linear speed 12~20m / min, spot movement speed along workpiece axis 0.8~1.2mm / r, powder-carrying argon flow rate 5~10L / min, protective argon flow rate 8~12L / min, powder spot convergence diameter 1.5~2.0mm, and powder feeding rate 50~60g / min.

[0029] Furthermore, the powder composition used in ultra-high-speed laser cladding is as follows: Cr: 18.0~20.0%, Ni: 0.5~2.0%, Mn: 0.1~0.3%, Mo: 0.4~1.0%, Nb: 0.1~0.3%, C: ≤0.2%, B: 0.8~1.0%, Si: 0.8~1.0%, with the balance being Fe; particle size range: D10≤15μm, D50≤45μm, D90≤70μm; Hall flowability ≤15s / 50g.

[0030] Furthermore, during the overlapping process, the time for the laser power at the initial emission position to increase from 0 to the set value is 500~1000ms, and the increase is linear.

[0031] Furthermore, the final product has a surface hardness of 580~650HV and a corrosion resistance of 4200h neutral salt spray level 9.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] a) This invention integrates multiple processes such as rough turning, fine turning, laser cladding, grinding, and polishing into one machine tool. The entire process only requires one setup, which shortens the production cycle, avoids the processing errors caused by repeated setups, reduces the subsequent machining allowance, and effectively reduces the risk of coating wear-through, exposure of the substrate, and loss of light.

[0034] b) The ultra-high-speed laser cladding process used in this invention is highly efficient, with a small machining allowance for the coating, saving more materials. The coating surface is smoother than that of traditional processes, and can be directly ground afterward, reducing a turning process and resulting in lower overall costs.

[0035] c) The piston rod of the ultra-large hydraulic cylinder has a large diameter and long stroke, and the continuous laser cladding operation time is long. This invention shifts the powder convergence point of the ultra-high speed laser cladding head by a certain angle and distance, and follows the rotation direction of the workpiece, so that the powder bounces and splashes to the side, avoiding the phenomenon of powder sticking and clogging in the ultra-high speed laser cladding powder feeding head.

[0036] d) The present invention adopts a high-frequency induction preheating method, and keeps the workpiece rotating during the preheating process to ensure that the workpiece is heated evenly, thus avoiding bending deformation caused by uneven heating and affecting the subsequent processing allowance.

[0037] e) Segmented cladding inevitably requires multiple cladding coating overlaps. Unlike cladding directly on the substrate, the overlap starts at the coating surface, which has higher hardness. Rapid laser energy impact can easily cause micro-cracks in the coating. In this invention, the preheating temperature is first ensured during the overlap process, and then the laser power is increased slowly and linearly to avoid energy impact and effectively reduce the risk of cracking. Attached Figure Description

[0038] Figure 1 A schematic diagram of mounting the piston rod on a turning and grinding machine.

[0039] Figure 2 This is a schematic diagram showing the position of the ultra-high-speed laser cladding head;

[0040] Figure 3 This is a schematic diagram of the chamfering process for the coating.

[0041] Figure 4 This is a schematic diagram of coating overlap.

[0042] Figure 5 This represents the coating thickness at different locations.

[0043] Reference numerals: 1. Headstock, 2. Bed, 3. Chuck, 4. Turning tool post, 5. Piston rod, 6. Roller support, 7. Grinding tool post, 8. Tail top, 9. Working position of cladding head, 10. Coating, 11. Coating finish turning chamfer, 12. Coating overlap area. Detailed Implementation

[0044] To more clearly illustrate the technical solution and features of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0045] A method for preparing an ultra-high-speed laser cladding coating for an ultra-large hydraulic cylinder piston rod, taking a Φ1.12×20m marine hydraulic cylinder piston rod as an example, requires a final surface coating thickness of 0.6mm, and is carried out according to the following steps:

[0046] (1): Machining before cladding

[0047] a) such as Figure 1 As shown, the piston rod blank is mounted onto the turning and grinding machine, with one end clamped in a four-jaw chuck and the other end pressed tightly against the center. The rod body is supported by four roller brackets with a center-to-center spacing of 4-5m.

[0048] b) The turning tool holder is equipped with a roughing tool head, and the outer diameter is roughed in sections to Φ1119.0mm with the roller bracket as the interval, and the surface roughness Ra≤12.5μm; the roller bracket has a roller width of 500mm and a support area width of 800mm;

[0049] c) Move each of the four roller brackets 1000mm toward the chuck, and rough machine the outer circle of the original bracket support area to Φ1119.0mm, with a surface roughness Ra≤12.5μm;

[0050] d) Replace the tool post with a precision turning tool head, and precision turn the outer diameter in sections to Φ1118.8mm with the roller support as the interval, and the surface roughness Ra≤3.2μm; the width of the support area is 800mm;

[0051] e) Move each of the four roller brackets 1000mm towards the tail end, and finish machine the outer circle of the original bracket support area to Φ1118.8mm, with a surface roughness Ra≤3.2μm.

[0052] (2): Ultra-high speed laser cladding

[0053] a) Replace the tool holder with an ultra-high-speed laser cladding head, such as Figure 2 As shown, adjust the nozzle position so that the working position of the cladding head is 15mm from the tangent of the outer circle and 100mm from the radial normal of the outer circle, and the angle θ between the line connecting the convergence point and the center of the outer circle and the radial normal of the outer circle is 10°.

[0054] b) Use alcohol to remove oil and dust from the piston rod surface;

[0055] c) Use high-frequency induction preheating to preheat the starting position of the cladding to above 100°C. The width of the heating coil is 400mm, and the distance between the coil and the workpiece surface is 10mm. Keep the workpiece rotating clockwise during the preheating process.

[0056] d) Set the ultra-high-speed laser cladding process parameters as follows: laser spot diameter 3.5mm, laser power 5.8kW, workpiece outer diameter rotational linear speed 15m / min, spot axial movement speed along workpiece 1.0mm / r, powder-carrying argon flow rate 6L / min, protective argon flow rate 10L / min, powder spot convergence diameter 2.0mm, and powder feeding rate 55g / min.

[0057] The powder composition used for ultra-high-speed laser cladding is as follows: Cr: 18.0~20.0%, Ni: 0.5~2.0%, Mn: 0.1~0.3%, Mo: 0.4~1.0%, Nb: 0.1~0.3%, C: ≤0.2%, B: 0.8~1.0%, Si: 0.8~1.0%, with the balance being Fe; particle size range: D10≤15μm, D50≤45μm, D90≤70μm; Hall flowability ≤15s / 50g.

[0058] Ultra-high-speed laser cladding is performed in segments with roller brackets as intervals, and the coating thickness is 1.0 mm.

[0059] e) Replace the tool post with a precision turning tool head, and precision turn the outer diameter to Φ1120.3mm in the area on the left side of the roller support (chuck direction), with a surface roughness Ra≤3.2μm and an area width of 800mm;

[0060] f) such as Figure 3 As shown, the coating at both ends of the roller bracket support area is precision machined with a 30° chamfer;

[0061] g) Move the roller carrier to the finishing area, replace the tool holder with the ultra-high-speed laser cladding head, and repeat steps a) to c).

[0062] h) Repeat step d) to perform ultra-high-speed laser cladding on the original roller bracket support area, seamlessly overlapping with the original cladding layer, such as... Figure 4 As shown;

[0063] The time for the laser power to increase from 0 to 5.8kW at the initial emission position is 1000ms, and the increase is linear.

[0064] (3) Machining after cladding

[0065] a) Start the grinding tool holder and grind the coating, excluding the roller support area, to the final finished size Φ1120.0 (-0.098, -0.203) mm;

[0066] b) Remove the roller bracket and replace it with a bearing bracket. Grind the coating of the original roller bracket area to the final finished size.

[0067] c) The outer circle of the piston rod is polished throughout.

[0068] Using the chuck end as the origin, samples were cut at 2m intervals, and the coating thickness was measured under metallographic conditions. The results are as follows: Figure 5 As shown, the coating thickness ranges from 0.58 to 0.63 mm, with an average thickness of 0.61 mm; the Vickers hardness of the coating is 588 to 655 HV according to GB / T4340.4-2009; and the corrosion resistance of the coating reaches level 9 of neutral salt spray after 4200 hours according to GB / T2423.17-2008.

[0069] 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 changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an ultra-high-speed laser cladding coating for an ultra-large hydraulic cylinder piston rod, characterized in that... Includes the following sequential steps: (1) Machining before cladding: a) The piston rod is clamped on a turning and grinding machine tool. One end is held by a four-jaw chuck, and the other end is tightened by a center. The rod body is supported by multiple roller brackets arranged at intervals of 3~5m. b) Adopt a segmented machining strategy. First, rough machining is performed between the roller bracket support areas to make the outer diameter surface roughness Ra≤12.5μm; c) After moving the roller bracket to the processed area, perform additional machining on the original support area; d) Repeat the above segmented machining process for precision turning, so that the surface roughness Ra of the entire outer circle is Ra≤3.2μm; (2) Ultra-high-speed laser cladding: a) Install the ultra-high-speed laser cladding head, and adjust the nozzle position so that the working position of the cladding head is 10~15mm away from the tangent of the outer circle of the workpiece and H=tanθ·(L+R) away from the radial normal of the outer circle, where R is the radius of the outer circle and θ=5°~12°. b) Perform degreasing and dust removal treatment on the surface; c) Use a high-frequency induction preheating device to preheat the starting position of the cladding, and control the surface temperature of the workpiece to be ≥100℃; d) A segmented cladding process is adopted to perform ultra-high-speed laser cladding between the roller bracket support areas. The process parameters include: laser power 4~6kW, spot diameter 2.5~3.8mm, and workpiece rotation linear speed 12~20m / min. e) Perform segmented precision machining on the cladding layer, and machine a 30~40° transition chamfer at the end of the cladding layer; f) After moving the roller bracket, perform cladding on the original support area and achieve seamless overlap of the old and new cladding layers through power gradient control; (3) Finishing after cladding: a) Use grinding to remove excess coating from the support area in sections; b) Perform overall polishing to obtain a finished product with a surface hardness of 580~650HV and a corrosion resistance of 4200h neutral salt spray level 9.

2. The method for preparing an ultra-high-speed laser cladding coating for an ultra-large hydraulic cylinder piston rod according to claim 1, characterized in that: The piston rod of the extra-large hydraulic cylinder has a diameter of ≥0.5m and a length of ≥10m.

3. The method for preparing an ultra-high-speed laser cladding coating for an ultra-large hydraulic cylinder piston rod according to claim 1, characterized in that: The integrated turning and grinding machine tool includes a turning tool post and a grinding tool post, the chuck is a four-jaw chuck, and the roller support is spaced 3~5m apart.

4. The method for preparing an ultra-high-speed laser cladding coating for an ultra-large hydraulic cylinder piston rod according to claim 1, characterized in that: The width of the support area is greater than the width of the roller bracket roller and the width of the bearing bracket bearing.

5. The method for preparing an ultra-high-speed laser cladding coating for an ultra-large hydraulic cylinder piston rod according to claim 1, characterized in that: The preheating method is high-frequency induction preheating. The width of the heating coil is 200~400mm, and the distance between the coil and the workpiece surface is 8~12mm. During the preheating process, the workpiece is kept rotating clockwise.

6. The method for preparing an ultra-high-speed laser cladding coating for an ultra-large hydraulic cylinder piston rod according to claim 1, characterized in that: The ultra-high-speed laser cladding process parameters are as follows: laser spot diameter 2.5~3.8mm, laser power 4~6kW, workpiece outer diameter rotational linear speed 12~20m / min, spot movement speed along workpiece axis 0.8~1.2mm / r, powder-carrying argon flow rate 5~10L / min, protective argon flow rate 8~12L / min, powder spot convergence diameter 1.5~2.0mm, and powder feeding rate 50~60g / min.

7. The method for preparing an ultra-high-speed laser cladding coating for an ultra-large hydraulic cylinder piston rod according to claim 1, characterized in that: The powder composition used for ultra-high-speed laser cladding is as follows: Cr: 18.0~20.0%, Ni: 0.5~2.0%, Mn: 0.1~0.3%, Mo: 0.4~1.0%, Nb: 0.1~0.3%, C: ≤0.2%, B: 0.8~1.0%, Si: 0.8~1.0%, with the balance being Fe; particle size range: D10≤15μm, D50≤45μm, D90≤70μm; Hall flowability ≤15s / 50g.

8. The method for preparing an ultra-high-speed laser cladding coating for an ultra-large hydraulic cylinder piston rod according to claim 1, characterized in that: During the overlapping process, the time for the laser power at the initial emission position to increase from 0 to the set value is 500~1000ms, and the increase is linear.

9. The method for preparing an ultra-high-speed laser cladding coating for an ultra-large hydraulic cylinder piston rod according to claim 1, characterized in that: The final product has a surface hardness of 580~650HV and a corrosion resistance of 4200h neutral salt spray level 9.

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