Polishing method for laser additive high-speed steel surface hardness fluctuation ≤ 5HRC

Abstract

The invention belongs to the technical field of surface processing, and specifically relates to a polishing method for laser-added high-speed steel with a surface hardness fluctuation of ≤5HRC. The surface of the laser-added high-speed steel is laser polished and plasma polished successively, the roughness Ra of the laser cladding coating is ≤100μm, and the hardness is 55-65HRC; the polishing temperature during laser polishing is 350-400℃; the laser polishing adopts a pulsed laser, the pulse duty ratio is ≤40%, the pulse frequency is ≤30kHz, the wavelength is 3-6μm, the laser energy density distribution is uniformly distributed, the laser spot is a rectangular spot or a line spot, and when the laser spot is a rectangular spot, the spot size is 1-1.5mm×3-5mm; during the plasma polishing, the plasma spot is a rectangular spot with a size of 0.5-1mm×2-4mm, the surface roughness of the laser-added M2 high-speed steel is significantly reduced, and the hardness fluctuation is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of surface processing, and specifically relates to a polishing method for laser additive high-speed steel with a surface hardness fluctuation of ≤5HRC. Background Art

[0002] The surface roughness of the cladding layer prepared by ultra-high-speed laser cladding is lower than that of the conventional laser cladding layer, but there are still uneven grains on the surface during the additive process. If the uneven grains on the surface of the cladding layer are not treated, the uneven grains will change the laser absorption rate of the roller surface during the next round of laser cladding manufacturing, which will seriously affect the dynamic spreading consistency of the hot capillary flow of the high-temperature melt during laser forming, directly leading to the fluctuation of the surface hardness of the additive layer ≥10HRC.

[0003] During the laser additive manufacturing process, the surface roughness of the M2 high-speed steel cladding layer is Ra ≥ 50μm, and the temperature of the additive layer is high, so conventional electrochemical polishing and electrolytic polishing cannot be used. If used, the M2 high-speed steel additive layer will undergo quenching and cause cracking. In order to improve the performance of cold-rolled work rolls manufactured by laser cladding, it is necessary to develop efficient technology to remove the uneven grains on the surface of the cladding layer and realize the synchronous polishing of the surface of the M2 high-speed steel additive layer of the cold-rolled work roll manufactured by laser cladding.

[0004] To achieve synchronous polishing of M2 high-speed steel in ultra-high-speed laser cladding additive manufacturing, the following technical difficulties are faced: ① Online polishing will cause roller vibration, affecting the forming accuracy, and thus affecting the surface hardness fluctuation of the additive layer>5HRC; ② Online polishing of coarse grains is difficult, which can easily cause very difficult synchronization, resulting in the surface hardness fluctuation of the additive layer>5HRC. At present, synchronous polishing technology has not been applied in ultra-high-speed laser cladding additive manufacturing of M2 high-speed steel additive layers. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a polishing method for laser-added high-speed steel with a surface hardness fluctuation of ≤5HRC, which significantly reduces the surface roughness of the laser cladding coating and reduces the hardness fluctuation.

[0006] The embodiment of the present invention provides a polishing method for laser additive high-speed steel surface hardness fluctuation ≤ 5HRC, laser polishing and plasma polishing are performed on the laser cladding coating successively, the roughness Ra of the laser cladding coating is ≤ 100μm, and the hardness is 55-65HRC;

[0007] The polishing temperature during laser polishing is 350-400°C;

[0008] The laser polishing adopts pulsed laser, the pulse duty ratio is ≤40%, the pulse frequency is ≤30kHz, the wavelength is 3-6μm, the laser energy density distribution is uniform, the laser spot is a rectangular spot or a linear spot, and when the laser spot is a rectangular spot, the spot size is 1-1.5mm×3-5mm;

[0009] After laser polishing, the polishing temperature during plasma polishing is 120-150℃ for areas with surface hardness lower than the average and surface hardness fluctuation of 5-8HRC; the polishing temperature during plasma polishing is 450-500℃ for areas with surface hardness higher than the average and surface hardness fluctuation of 5-8HRC;

[0010] During the plasma polishing, the plasma spot is a rectangular spot with a size of 0.5-1 mm×2-4 mm.

[0011] The “×” before and after are the length, width or width and length of the rectangle respectively.

[0012] In one of the embodiments, the laser cladding coating is a laser cladding coating coated on the surface of a rolling roller. Preferably, the material of the laser cladding coating is M2 high-speed steel powder.

[0013] In one embodiment, the laser polishing is performed using two oppositely disposed laser beams with the same frequency, and the plasma polishing is performed using two oppositely disposed plasma beams.

[0014] In one of the embodiments, the position of the laser polishing is controlled, and the distance between the position of the laser polishing and the position of the laser cladding is 120-260 mm.

[0015] In one embodiment, laser cladding is performed again after the laser polishing and plasma polishing.

[0016] In one embodiment, the laser power P of the laser polishing is 400 W, the scanning speed V is 15 mm / s, and the polishing time is 3 min.

[0017] The polishing method of the present application can solve the problems caused by online polishing. Online polishing generally causes roller vibration and affects the forming accuracy. The present invention proposes to use two laser beams or plasma beams for synchronous polishing in opposite directions to offset the vibration caused by polishing. However, it does not mean that conventional polishing methods can solve the vibration problem. The present invention can solve the vibration problem and reduce the roughness. The key points are: ① The laser is in pulse form and is polished in opposite directions at the same frequency, otherwise the vibration problem caused by the opposite synchronous polishing cannot be offset; ② Laser polishing is the first rough polishing, and the key is to offset the vibration and improve the polishing efficiency. Therefore, the pulse laser band is 3-6μm, which can well achieve Ra≥50μm before polishing of the M2 high-speed steel surface and Ra≤20μm after polishing; ③ The laser spot mode must be a rectangular spot or a line spot, and the energy density must be evenly distributed, and cannot be a Gaussian distributed energy density, otherwise the polishing effect is extremely poor, and the requirements of Ra≥50μm before polishing of the M2 high-speed steel surface and Ra≤20μm after polishing cannot be met; ④ The laser spot size cannot be too large, otherwise the polishing effect is extremely poor, and the appropriate spot size is 1-1.5mm×3-5mm, especially the spot size width cannot be greater than 2mm.

[0018] After using two laser beams for synchronous polishing as the rough polishing process, two plasma beams for synchronous polishing are used as the fine polishing process. It is particularly important to note that laser polishing and plasma polishing cannot be turned on at the same time, otherwise the vibration problem caused by polishing cannot be offset. In addition, the plasma spot size is 0.5-1mm×2-4mm, especially the spot size width cannot be greater than 1.5mm, otherwise it will cause the surface polishing finish fluctuation standard deviation of the additive layer to be greater than 3μm.

[0019] Since the M2 high-speed steel additive layer formed on the surface of the cold-rolled work roll requires a hardness of ≥60HRC and a uniform surface hardness fluctuation of ≤5HRC, the key is to control the temperature caused by polishing to be lower than the martensite transformation point temperature, otherwise the surface hardness of the M2 high-speed steel will decrease, which can be controlled by using online cooling technology. However, if the surface temperature of the M2 high-speed steel is too low, the polishing effect and polishing efficiency will be reduced. The appropriate surface polishing temperature of the M2 high-speed steel additive layer is 350-400℃. Since the first laser polishing will cause the temperature to rise, and the subsequent plasma polishing will result in a higher temperature, a temperature detector is required to monitor whether the polishing temperature is maintained between 350-400℃. Once the polishing temperature is exceeded, the online cooling technology should be adjusted immediately to solve it, otherwise the surface hardness uniformity of the M2 high-speed steel additive layer will be greater than 5HRC.

[0020] Since the polishing temperature near the working position of the ultra-high-speed laser cladding head is greater than 400°C, the polishing head needs to be ≥120mm away from the working position of the laser cladding head, but not ≤260mm, otherwise the polishing temperature will be ≤350°C. In order to achieve the polishing effect of the surface hardness fluctuation of the additively manufactured M2 high-speed steel ≤5HRC, the polishing position temperature of the additive layer on the surface of the cold-rolled work roll should be selected for polishing at 350°C. This is because the polishing process will further cause its temperature to rise. If the polishing position of 400°C is directly selected for polishing, it is extremely difficult to maintain the polishing temperature in the range of 350-400°C. The stable maintenance of the temperature during the polishing process is an important factor in determining the surface hardness fluctuation of the additively manufactured M2 high-speed steel ≤5HRC. In order to well control the polishing temperature of the cold-rolled work roll surface, an online cooling method is introduced to flexibly control its temperature to maintain it in the range of 350-400°C. For the online polishing of this ultra-high-speed laser cladding additive manufacturing process, it is generally not thought of controlling the temperature, let alone controlling it at 350-400°C.

[0021] The embodiment of the present invention provides a polishing device with a surface hardness fluctuation of laser-added high-speed steel of ≤5HRC, comprising a laser polishing machine and a plasma polishing machine. Before polishing, the roughness Ra of the laser cladding coating is ≤100μm, and the hardness is 55-65HRC; the polishing temperature during laser polishing is 350-400℃;

[0022] The laser polishing adopts pulsed laser, the pulse duty ratio is ≤40%, the pulse frequency is ≤30kHz, the wavelength is 3-6μm, the laser energy density distribution is uniform, the laser spot is a rectangular spot or a linear spot, and when the laser spot is a rectangular spot, the spot size is 1-1.5mm×3-5mm;

[0023] After laser polishing, the polishing temperature during plasma polishing is 120-150℃ for areas with surface hardness lower than the average and surface hardness fluctuation of 5-8HRC; the polishing temperature during plasma polishing is 450-500℃ for areas with surface hardness higher than the average and surface hardness fluctuation of 5-8HRC;

[0024] During the plasma polishing, the plasma spot is a rectangular spot with a size of 0.5-1 mm×2-4 mm.

[0025] In one of the embodiments, there are two laser polishing machines, which are disposed opposite to each other, and there are two plasma polishing machines, which are disposed opposite to each other.

[0026] In one of the embodiments, the position of the laser polishing machine is controlled, and the distance between the position of the laser polishing machine and the position of the laser cladding is 120-260 mm.

[0027] The beneficial effect of the present invention is that, taking the laser cladding coating of M2 high-speed steel as an example, by adopting the polishing method of the present invention, the surface hardness fluctuation of the additively manufactured M2 high-speed steel is ≤5HRC, and the surface roughness of the M2 high-speed steel additive layer before polishing is Ra≥50μm, and after polishing, it reaches Ra≤10μm; the standard deviation of the fluctuation of the polishing finish of the additive layer surface is ≤3μm, which is significantly better than the general polishing method.

[0028] The present invention uses pulsed laser and plasma composite polishing with appropriate pulse width and size to achieve synchronous polishing, and performs opposite polishing at the same frequency to offset the problem of vibration caused by opposite synchronous polishing affecting the forming accuracy. At the same time, the rough polishing problem is solved by first turning on the laser polishing, then turning off the laser polishing, and then turning on the plasma polishing to solve the fine polishing problem. At the same time, combined with the online cooling technology, the online polishing temperature is maintained in the range of 350-400℃, thereby achieving the effect of the surface hardness fluctuation of the additively manufactured M2 high-speed steel ≤5HRC.

[0029] The present invention is to achieve the polishing effect of laser additive manufacturing M2 high-speed steel surface hardness fluctuation ≤ 5HRC, which requires the following steps and technical parameters:

[0030] 1. The surface roughness of the M2 high-speed steel additive layer must be Ra≤100μm, because the surface roughness is proportional to the surface hardness fluctuation. If the surface roughness Ra>100μm, the surface hardness fluctuation will be>5HRC during the layer-by-layer laser additive process, which will make it difficult to make the surface hardness fluctuation of the high-speed steel additive layer ≤5HRC even with conventional online polishing. This is a necessary condition and is also a problem that is easily overlooked.

[0031] 2. After laser polishing, the surface hardness of the additive layer is lower than the average value and the surface hardness fluctuation is greater than 5HRC. In the area where the hardness fluctuation is ≤8HRC, the polishing temperature of the area is controlled within the range of 120-150℃, and plasma polishing is performed to increase its surface hardness value, thereby reducing the hardness fluctuation to ≤5HRC. This kind of low hardness but large hardness fluctuation in the region is also conditional, and not all large regional hardness fluctuations can be solved by polishing.

[0032] 3. For areas where the surface hardness of the additive layer is higher than the average value after laser polishing, the surface hardness fluctuation is greater than 5HRC, and the hardness fluctuation is ≤8HRC, the polishing temperature of the area is controlled within the range of 450-500℃, and plasma polishing is performed to reduce the surface hardness value, thereby reducing the hardness fluctuation to ≤5HRC. This is to say, this kind of low hardness but large hardness fluctuation in the region is also conditional. Not all large regional hardness fluctuations can be solved by polishing.

[0033] 4. Since laser polishing is used to solve the rough polishing problem, and plasma polishing is used to solve the fine polishing problem, the problem of excessive regional hardness fluctuation of M2 high-speed steel can only be solved before plasma polishing.

[0034] 5. Use two laser beams or plasma beams to synchronously polish the surface of the cold rolling work roll to offset the vibration caused by polishing. The laser is in pulse form, but it must be polished in the same frequency. To offset the vibration problem caused by synchronous polishing, the pulse duty cycle must be ≤40% and the pulse frequency must be ≤30kHz. Both indicators need to be achieved at the same time.

[0035] 6. The above parameters are only applicable to M2 high-speed steel with a surface hardness between 55-65HRC, and can solve the problem of surface hardness fluctuation ≤5HRC. If the surface hardness is not within this range, the above parameters cannot be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a structural schematic diagram of the present invention.

[0037] In the figure, 1 is a cladding head, 2 is a cooling piece, 3 is a laser polishing machine, and 4 is a plasma polishing machine. DETAILED DESCRIPTION

[0038] Example 1.

[0039] A laser cladding coating polishing method, wherein the laser cladding coating is located on the surface of a roller, such as Figure 1 As shown, the roller is clad with a laser cladding coating under the action of the cladding head 1. The preparation method of the laser cladding coating is as follows: a Cr12MoV roller is selected as the base material, the size is Φ100mm×2800mm, the roller is a forged part, the surface hardness is 58HRC~60HRC, the cladding material is M2 high-speed steel powder, and the particle size distribution is 30-50μm. The powder feeding method is three-way coaxial powder feeding outside the light, the protective gas and the powder feeding gas are nitrogen (purity 99.9%), the gas flow rate is 15 L / min, the laser power P is 2500W, the scanning rate V is 15mm / s, the spot diameter D is 1.4 mm, and the powder feeding rate is 6.5g / min.

[0040] The performance of the laser cladding coating was tested, and the roughness Ra was 50~80μm and the hardness was 56~64HRC.

[0041] After cladding, the roll passes through a cooling member 2, two laser polishing machines 3 arranged opposite to each other, and two plasma polishing machines 4 arranged opposite to each other in sequence.

[0042] The laser cladding coating of the roller is laser polished and plasma polished successively, wherein the laser polishing is performed by using two laser beams arranged opposite to each other, and the plasma polishing is performed by using two plasma beams arranged opposite to each other. The position of the laser polishing is controlled, and the distance between the position of the laser polishing and the position of the laser cladding is 200 mm.

[0043] The temperature of the laser polishing position is detected and controlled to be 350°C. The control method is to adjust the cooling force of the cooling member 2. The cooling member 2 is set at 100 mm away from the laser cladding position, and the cooling source is 40% pure liquid nitrogen.

[0044] The laser polishing adopts pulsed laser, the pulse duty cycle is 30%, the pulse frequency is 30kHz, the wavelength is 5μm, the laser energy density distribution is uniform, the laser spot is a rectangular spot, and the spot size is 1.5mm×4mm;

[0045] After laser polishing, the polishing temperature during plasma polishing is 130°C for areas with surface hardness lower than the average and surface hardness fluctuation of 5-8HRC; the polishing temperature during plasma polishing is 480°C for areas with surface hardness higher than the average and surface hardness fluctuation of 5-8HRC;

[0046] During the plasma polishing, the plasma spot is a rectangular spot with a size of 0.5 mm×2.0 mm.

[0047] The laser power P of laser polishing is 400 W, the scanning speed V is 15 mm / s, and the polishing time is 3 min.

[0048] The performance of the laser cladding coating after plasma polishing was tested, and the average roughness Ra was 10μm, and the surface hardness fluctuation was ≤5HRC. It can be seen that polishing significantly reduced the surface roughness and improved the smoothness and hardness uniformity.

[0049] Comparative Example 1

[0050] Compared with Example 1, the difference is that the temperature of the laser polishing position is controlled to be 200° C., and the rest is the same as Example 1.

[0051] The performance of the laser cladding coating after plasma polishing was tested, and the roughness Ra was 22μm, and the surface hardness uniformity was 7HRC. It can be seen that polishing significantly reduced the surface roughness and improved the finish and hardness uniformity.

[0052] Comparative Example 2

[0053] Compared with Example 1, the difference is that the laser polishing uses a pulsed laser with a pulse duty cycle of 50%, a pulse frequency of 40 kHz, and a wavelength of 2 μm. Other differences are the same as Example 1.

[0054] The performance of the laser cladding coating after plasma polishing was tested, and the roughness Ra was 30μm, and the surface hardness uniformity was 11HRC. It can be seen that polishing significantly reduced the surface roughness and improved the finish and hardness uniformity.

[0055] Comparative Example 3

[0056] Compared with Example 1, the difference is that the laser energy density distribution is Gaussian distribution, and the rest is the same as Example 1.

[0057] The performance of the laser cladding coating after plasma polishing was tested, and the roughness Ra was 25μm, and the surface hardness uniformity was 9HRC. It can be seen that polishing significantly reduced the surface roughness and improved the finish and hardness uniformity.

[0058] Comparative Example 4

[0059] Compared with Example 1, the difference is that the laser spot is a rectangular spot with a spot size of 2 mm×6 mm, and the rest is the same as Example 1.

[0060] The performance of the laser cladding coating after plasma polishing was tested, and the roughness Ra was 15μm, and the surface hardness uniformity was 8HRC. It can be seen that polishing significantly reduced the surface roughness and improved the finish and hardness uniformity.

[0061] Comparative Example 5

[0062] Compared with Example 1, the difference is that during the plasma polishing, the plasma spot is a rectangular spot with a size of 2mm×5mm, and the rest is the same as Example 1.

[0063] The performance of the laser cladding coating after plasma polishing was tested, and the roughness Ra was 18μm and the surface hardness uniformity was 20HRC.

[0064] Comparative Example 6

[0065] Compared with Example 1, the difference is that the polishing temperature during plasma polishing is 350° C., and the rest is the same as Example 1.

[0066] The performance of the laser cladding coating after plasma polishing was tested, and the roughness Ra was 28μm and the surface hardness uniformity was 24HRC.

[0067] It can be seen that controlling the parameters of laser polishing and plasma polishing can significantly reduce the surface roughness and improve the smoothness and hardness uniformity.

[0068] A person skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of protection of the present application is limited to these examples. In line with the concept of the present application, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of different aspects of one or more embodiments of the present application as described above, which are not provided in detail for the sake of simplicity.

[0069] One or more embodiments of the present application are intended to cover all such substitutions, modifications and variations that fall within the broad scope of the present application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of one or more embodiments of the present application should be included in the protection scope of the present application.

Claims

1. A polishing method for laser-assisted high-speed steel with a surface hardness fluctuation of ≤5HRC, characterized in that: The laser cladding coating is successively subjected to laser polishing and plasma polishing, wherein the roughness Ra of the laser cladding coating is less than or equal to 100 μm, and the hardness is 55-65 HRC; The polishing temperature during laser polishing is 350-400°C; The laser polishing adopts pulsed laser, the pulse duty ratio is ≤40%, the pulse frequency is ≤30kHz, the wavelength is 3-6μm, the laser energy density distribution is uniform, the laser spot is a rectangular spot or a linear spot, and when the laser spot is a rectangular spot, the spot size is 1-1.5mm×3-5mm; After laser polishing, the polishing temperature during plasma polishing is 120-150℃ for areas with surface hardness lower than the average and surface hardness fluctuation of 5-8HRC; the polishing temperature during plasma polishing is 450-500℃ for areas with surface hardness higher than the average and surface hardness fluctuation of 5-8HRC; During the plasma polishing, the plasma spot is a rectangular spot with a size of 0.5-1mm×2-4mm; The laser polishing is performed by using two laser beams arranged opposite to each other, and the two laser beams are of the same frequency. The plasma polishing is performed by using two plasma beams arranged opposite to each other.

2. The polishing method according to claim 1, characterized in that: The laser cladding coating is a laser cladding coating coated on the surface of the roller.

3. The polishing method according to claim 2, characterized in that: The material of the laser cladding coating is M2 high speed steel powder.

4. The polishing method according to any one of claims 1 to 3, characterized in that: The position of the laser polishing is controlled, and the distance between the position of the laser polishing and the position of the laser cladding is 120-260 mm.

5. The polishing method according to any one of claims 1 to 3, characterized in that: After the laser polishing and plasma polishing, laser cladding is performed again.

6. The polishing method according to any one of claims 1 to 3, characterized in that: The laser power P of the laser polishing is 400 W, the scanning speed V is 15 mm / s, and the polishing time is 3 min.

7. A polishing device for laser-assisted high-speed steel with a surface hardness fluctuation of ≤5HRC, characterized in that: Including laser polishing machine and plasma polishing machine. Before polishing, the roughness of laser cladding coating is Ra≤100μm, and the hardness is 55-65HRC; the polishing temperature during laser polishing is 350-400℃; The laser polishing adopts pulsed laser, the pulse duty ratio is ≤40%, the pulse frequency is ≤30kHz, the wavelength is 3-6μm, the laser energy density distribution is uniform, the laser spot is a rectangular spot or a linear spot, and when the laser spot is a rectangular spot, the spot size is 1-1.5mm×3-5mm; After laser polishing, the polishing temperature during plasma polishing is 120-150℃ for areas with surface hardness lower than the average and surface hardness fluctuation of 5-8HRC; the polishing temperature during plasma polishing is 450-500℃ for areas with surface hardness higher than the average and surface hardness fluctuation of 5-8HRC; During the plasma polishing, the plasma spot is a rectangular spot with a size of 0.5-1mm×2-4mm; There are two laser polishing machines, which are arranged opposite to each other. There are two plasma polishing machines, which are arranged opposite to each other.

8. The polishing device according to claim 7, characterized in that: The position of the laser polishing machine is controlled, and the distance between the position of the laser polishing machine and the position of the laser cladding is 120-260 mm.

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