Method for improving coating quality of laser cladding high-speed steel

Abstract

The invention belongs to the technical field of laser cladding, and particularly relates to a method for improving the coating quality of laser cladding high-speed steel. Comprising the following steps that 1, a rectangular laser spot is adopted, and high-speed steel powder is fed into the center of the long side of the rectangular laser spot through a powder feeding device; 2, a non-powder-feeding area in the rectangular laser spot is used as a heat source for preheating and delayed solidification of a molten pool; and 3, argon is blown to the two ends of the cladding area, staggered blowing is formed by the two air nozzles, and the liquid molten pool forms a rotary molten pool through staggered blowing. The device has the beneficial effects that the problem of low efficiency of traditional vibration, electromagnetic stirring and other technologies is effectively solved, the machining speed is remarkably increased, and the efficient treatment requirement of large workpieces is met.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of laser cladding, and particularly relates to a method for improving the quality of a high-speed steel cladding layer. BACKGROUND

[0002] The high-speed steel cladding layer is widely used in the fields of mechanical manufacturing (such as cutters and gear surface strengthening), die processing industry (improving the wear resistance of a die cavity), high-temperature wear-resistant and corrosion-resistant industry, steam turbine blade manufacturing, and aerospace field (enhancing the surface performance of parts) due to its high hardness, high wear resistance, and good thermal stability. These application scenarios have very high requirements for the quality of the cladding layer. However, during the laser cladding of the high-speed steel cladding layer with high carbon and high silicon content, defects such as pores and cracks are prone to occur. The existence of pores will weaken the compactness of the cladding layer and reduce its mechanical properties and corrosion resistance; cracks may expand during use, leading to failure of the cladding layer or even the substrate, and seriously affecting the service life and reliability of the workpiece.

[0003] Traditional techniques for dealing with the quality problems such as pores and cracks in the cladding layer include vibration, heating, and electromagnetic stirring during the cladding process, but their effects cannot effectively meet the requirements. For example, during the cladding process, the molten pool vibration technique is difficult to accurately control and may affect the cladding stability, and is not suitable for fatigue-sensitive, large / heavy workpieces; the method of heating the cladding layer after cladding is beneficial to the precipitation of pores, but has high energy consumption and it is difficult to ensure the uniformity of the temperature; the electromagnetic stirring of the molten cladding layer has complex equipment and high cost. More importantly, these techniques generally have low cladding efficiency and complex process, and for large / heavy and complex-structure workpieces, not only are the processing time-consuming, but also the equipment investment is large and the operation is complex, which cannot meet the requirements of high efficiency, reliability, and low cost in industrial production. Therefore, it is urgent to develop a method for solving the problems of pores and cracks in high-speed steel laser cladding, which has high efficiency, stable and reliable performance, strong applicability, and simple equipment. SUMMARY

[0004] The purpose of the present application is to provide a method for improving the quality of a high-speed steel cladding layer by laser cladding, which effectively solves the problem of cracks and pores in high-carbon and high-silicon cladding layers by laser cladding.

[0005] The technical solution of the present application is as follows: a method for improving the quality of a high-speed steel cladding layer by laser cladding, comprising the following steps:

[0006] Step 1: using a rectangular laser spot, feeding high-speed steel powder into the center of the long side of the rectangular laser spot through a powder feeding device;

[0007] Step 2: using the no-powder feeding area in the rectangular laser spot as a heat source for preheating and delayed solidification of the molten pool, respectively;

[0008] Step 3: Blow argon at both ends of the cladding area, and the two gas nozzles are staggered to blow gas, so that the liquid pool forms a rotating pool through staggered blowing.

[0009] The width of the rectangular laser spot is 3-5mm, and the length is 15-25mm.

[0010] The laser light output power is greater than 6000W.

[0011] The center staggered distance of the two gas nozzles is 3-5mm.

[0012] The argon gas flow is 5-20 SLM.

[0013] The staggered blowing structure realizes the following functions through argon gas flow:

[0014] (1) Rotating stirring pool, promoting gas discharge;

[0015] (2) Refining grains, inhibiting crack generation;

[0016] (3) Forming argon gas cover layer to prevent substrate oxidation.

[0017] The beneficial effects of the present application are that the present application effectively avoids the low efficiency problem of traditional vibration, electromagnetic stirring and other technologies, significantly improves the processing speed, and meets the efficient processing demand of large workpieces.

[0018] (1) High-efficiency cladding: the combination of the center point of the rectangular spot and the powder feeding point, together with the bidirectional staggered argon blowing, makes the molten pool metal rotate, promotes gas escape, avoids pore and crack generation, and produces grain refinement effect. Under the same cladding material and laser power, the X2 metal coating micro comparison before and after the application of the present application is shown in Figure 1 、 Figure 2 .

[0019] (2) Strong applicability: independent of the size or weight of the workpiece, especially suitable for surface strengthening of large and heavy workpieces, significantly improving the cladding efficiency, and widening the application scenarios of laser cladding technology.

[0020] (3) Reduce equipment investment cost: simplify the cladding equipment configuration, eliminate complex vibration or electromagnetic stirring device, reduce the cladding equipment investment and maintenance cost, and be more conducive to operation on site.

[0021] (4) Quality improvement: through the synergistic effect of preheating, delayed solidification and rotating pool, effectively reducing pores and cracks, improving coating density and mechanical properties, and prolonging the service life of the workpiece. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The effect comparison chart for inhibiting the crack in the overlapping area.

[0023] Figure 2 For the effect of refining grain contrast chart;

[0024] Figure 3 For a method of improving the quality of laser cladding high speed steel coating schematic diagram, show the rectangular laser spot, powder feeding position and tail argon nozzle structure, as shown.

[0025] Figure 4 For the present invention point powder and rectangular spot relationship schematic diagram, present the details of the powder into the rectangular spot long center. DETAILED DESCRIPTION

[0026] The present application will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0027] The equipment for implementing the method for improving the quality of laser cladding high speed steel coating mainly includes a laser, a powder feeder, a rectangular spot, a cladding head for coaxial powder feeding, a two-way argon or nitrogen nozzle, a mechanical arm for clamping the cladding head, etc.

[0028] A method for improving the quality of laser cladding high speed steel coating, comprising the following steps:

[0029] Step 1: A rectangular laser spot (width 3-5mm, length 15-25mm) is used, and high speed steel powder is sent into the center of the long side of the rectangular spot by a powder feeding device to form a circular powder spot. A laser with a power of 6000W-12000W is used.

[0030] The rectangular spot is formed by lens design to form a rectangular spot, which can be realized by the existing rectangular spot cladding head.

[0031] Step 2: The no-powder area in the rectangular laser spot is used as a heat source for preheating and delaying solidification of the molten pool, respectively, as shown. The laser spot has a high density of energy, which is irradiated to the workpiece surface, which is the heat source. It is equivalent to the heat treatment process before and after cladding, thereby further improving the cladding quality.

[0032] Step 3: Argon is blown at both ends of the spot, and the two gas nozzles are formed to blow gas in a staggered manner, so that the liquid molten pool forms a rotating molten pool.

[0033] Two gas pipes are connected with argon or nitrogen bottles, the end of the gas pipe is connected with a gas nozzle, the gas nozzle is installed on both sides of the cladding head, and the end of the gas nozzle is kept on both sides of the short side of the light spot, and the staggered blowing structure is arranged as shown in the schematic view. The center staggered distance of the gas nozzle is 3-5mm, and the liquid pool is formed into a rotating pool by staggered blowing. The structure has three functions, including 1) rotating agitation of the pool, promoting gas discharge and reducing pore formation; 2) grain refinement and crack prevention; 3) argon cover layer to prevent oxidation of the substrate within the light spot range. The argon flow is 5-20 SLM.

[0034] The specific implementation process of the present application is as follows:

[0035] Laser spot adjustment: according to the workpiece material and coating requirements, set the laser equipment parameters, generate a rectangular light spot with a width of 3-5mm and a length of 15-25mm, and ensure uniform distribution of light spot energy.

[0036] Cladding powder delivery control: start the powder feeder and deliver high-speed steel powder to the center of the long side of the rectangular light spot in a fixed-point manner, and the powder flow should be aligned with the center axis of the light spot to ensure the efficiency of powder melting.

[0037] Thermal process optimization: use the energy of the light spot on both sides without powder feeding to preheat the workpiece and delay the solidification of the pool, reduce the temperature gradient and the stress caused thereby, and reduce the risk of cracks.

[0038] Argon purging system: install staggered gas nozzles at both ends of the cladding area with a center distance of 3-5mm, open the argon purging, control the flow at 5-20 SLM, and make the pool metal rotate by staggered gas flow to promote gas escape and grain refinement.

[0039] Parameter coordination control: according to the coating thickness and hardness requirements, simultaneously adjust the laser power (6000-12000W), powder feeding speed (5-20g / min) and argon flow, to ensure the best matching of pool temperature, solidification rate and gas discharge efficiency.

[0040] By the above method, the problem of pores in high-carbon high-silicon high-speed steel laser cladding is effectively solved, the coating quality is improved, and the advantages of high efficiency, low cost and strong applicability are achieved.

[0041] Example 1: moderate parameter combination

[0042] Parameter setting:

[0043] Rectangular laser spot: width 4mm, length 20mm

[0044] Center staggered distance of the gas nozzle: 4mm

[0045] Argon flow: 12 SLM

[0046] Laser power: 6000W

[0047] Powder feed rate: 12g / min

[0048] Implementation process:

[0049] Powder is accurately fed into the center of the long side of the light spot. The preheating and delayed solidification of the substrate in the non-powder feeding area form a rotating molten pool with staggered argon gas flow.

[0050] Advantages:

[0051] Thermal process balance: The size of the light spot is moderate, the preheating and delayed solidification effect are balanced, local overheating or rapid cooling is avoided, and the risk of cracks is reduced.

[0052] Molten pool agitation is sufficient: 12 SLM argon flow with 4 mm staggered spacing, uniform molten pool rotation, high gas discharge efficiency, and porosity reduced by more than 60% compared to traditional methods.

[0053] Wide range of applications: Moderate parameters suitable for most high-speed steel coating scenarios (such as knives and molds), with dense coating and hardness (HRC 60-65) meeting industrial standards.

[0054] Example 2: High-efficiency parameter combination (biased towards high power and high powder feed rate)

[0055] Parameter settings:

[0056] Rectangular laser spot: width 5mm, length 25mm

[0057] Staggered distance between nozzle centers: 5mm

[0058] Argon flow rate: 20 SLM

[0059] Laser power: 8000W

[0060] Powder feed rate: 20g / min

[0061] Implementation process:

[0062] Large size light spot combined with high energy input, fast melting of powder, and high speed argon gas to strengthen molten pool rotation.

[0063] Advantages:

[0064] Improved cladding efficiency: 30% faster than Example 1, suitable for large area coating of large workpieces (such as heavy machinery gears).

[0065] Good molten pool fluidity: high argon flow rate enhances agitation, suppresses powder accumulation at high powder feed rate, and avoids inclusion of unmelted particles.

[0066] Excellent oxidation protection: complete argon gas cover layer, oxidation rate of substrate and molten pool <0.5%.

[0067] Example 3: Fine parameter combination (biased low power, low powder feed speed)

[0068] Parameter settings:

[0069] Rectangular laser spot: width 3 mm, length 15 mm

[0070] Misalignment distance of gas nozzle center: 3 mm

[0071] Argon flow rate: 5 SLM

[0072] Laser power: 6000 W

[0073] Powder feed speed: 5 g / min

[0074] Implementation process:

[0075] Small spot combined with low energy input, precise control of molten pool size, low speed powder feeding ensures sufficient powder melting.

[0076] Advantages:

[0077] Micro-precision machining: suitable for local strengthening of thin-walled parts (such as aerospace blades), with small heat-affected zone (≤0.5 mm), avoiding substrate deformation.

[0078] Significant grain refinement: long low-speed molten pool rotation time, grain size reduced by 40% compared to conventional methods, and coating toughness (impact toughness ≥15 J / cm 2 ) improved.

[0079] Negative examples outside the process parameter range and adverse consequences analysis

[0080] Negative example 1: spot width too small (2 mm, <3 mm)

[0081] Parameter deviation: rectangular spot width 2 mm, length 20 mm (other parameters normal).

[0082] Adverse consequences:

[0083] Insufficient preheating: the area without powder feeding is too small, the substrate is not effectively preheated, the temperature difference between the molten pool and the substrate increases (ΔT > 300℃), and thermal stress cracks are prone to occur at the interface.

[0084] Narrowing of molten pool: narrow spot leads to poor lateral flow of molten pool, powder is concentrated in the central area, and the edge un-melted defect rate increases (>15%).

[0085] Negative example 2: gas nozzle misalignment distance too large (7 mm, >5 mm)

[0086] Parameter deviation: gas nozzle center misalignment distance 7 mm, other parameters normal.

[0087] Adverse consequences:

[0088] Melt pool rotation failure: misalignment distance exceeds 5 mm, two argon gas flow action areas are separated, and a unified rotating melt pool cannot be formed, and gas retention rate increases (porosity > 8%).

[0089] Incomplete protection: argon gas coverage area deviates from the edge of the light spot, and the substrate is severely oxidized on both sides (oxidation layer thickness > 50 μm), which reduces the coating bonding strength.

[0090] Negative example 3: argon gas flow is too high (30 SLM, > 20 SLM)

[0091] Parameter deviation: argon gas flow is 30 SLM, and other parameters are normal.

[0092] Adverse consequences:

[0093] Melt pool disorder: high-speed airflow disperses the melt pool liquid metal, causing the melt pool to splash (splashing rate > 20%), and the coating surface roughness increases significantly (Ra > 3.2 μm).

[0094] Cooling too fast: excessive argon gas carries away heat, and the melt pool solidification time is shortened by 20%, and the gas cannot be discharged in time, and the porosity rate is increased by 3 times compared with the normal parameters.

[0095] Negative example 4: laser power is too low (200 W, < 3000 W)

[0096] Parameter deviation: laser power is 800 W, and other parameters are normal.

[0097] Adverse consequences:

[0098] Powder not fused: insufficient energy causes high-speed steel powder to be insufficiently melted (unmelted particles account for > 30%), coating hardness decreases (HRC < 55), and wear resistance is significantly reduced.

[0099] Insufficient heat input: preheating effect is missing, the melt pool and the substrate have a large temperature difference, and transgranular cracks occur in the coating.

[0100] Negative example 5: powder feeding speed is too high (25 g / min, > 20 g / min)

[0101] Parameter deviation: powder feeding speed is 25 g / min, and other parameters are normal.

[0102] Adverse consequences:

[0103] Melt pool overload: excessive powder input per unit time, the melt pool cannot completely melt the powder, and slag inclusion defects are formed (slag inclusion rate > 10%).

[0104] Energy distribution imbalance: powder absorbs a large amount of laser energy, substrate insufficient melting depth (<0.3mm), coating and substrate bonding force decreases (shear strength <50MPa).

[0105] Based on the above implementation case analysis, the implementation should be carried out strictly according to the technical solution described in the application.

[0106] Parameter synergy within the scope

[0107] The rectangular spot size, misaligned nozzle spacing, argon gas flow, laser power and powder feeding speed need to be matched within the scope of the patent. Through the closed-loop control of "preheating-melting-rotating degassing-delayed solidification", the gas hole suppression (≤2%), crack prevention (crack rate <0.5%) and high-efficiency cladding are realized.

[0108] Parameter failure mechanism outside the scope

[0109] Single or combined parameter over-limit will destroy the thermal balance or the molten pool flow field, resulting in defects such as gas hole, crack, oxidation, un-melted, especially for large workpieces or precision parts.

Claims

1. A method of improving the quality of a laser cladded high speed steel coating, characterized in that, The method comprises the following steps: Step 1: using a rectangular laser spot, feeding high-speed steel powder into the center of the long side of the rectangular laser spot through a powder feeding device; Step 2: using the powder-free area in the rectangular laser spot as a heat source for preheating and delaying solidification of the molten pool respectively; Step 3: blowing argon gas at both ends of the cladding area, and forming a staggered gas blowing structure with the two gas nozzles, so that the liquid molten pool forms a rotating molten pool.

2. The method of improving the quality of laser cladding high speed steel coating according to claim 1, characterized in that: The width of the rectangular laser spot is 3-5 mm, and the length is 15-25 mm.

3. The method of improving the quality of laser cladding high speed steel coating according to claim 1, characterized in that: The laser output power is greater than 6000 W.

4. The method of improving the quality of laser cladding high speed steel coating of claim 1 wherein: The center staggered distance of the two gas nozzles is 3-5 mm.

5. The method of improving the quality of laser cladding high speed steel coating of claim 1 wherein: The argon gas flow is 5-20 SLM.

6. The method of improving the quality of laser cladded high speed steel coating of claim 1 wherein: The staggered gas blowing structure realizes the following functions through argon gas flow: rotating and stirring the molten pool, and promoting gas discharge.

7. The method of improving the quality of laser cladded high speed steel coating of claim 1 wherein: The staggered gas blowing structure realizes the following functions through argon gas flow: refining grains and inhibiting crack generation.

8. The method of improving the quality of laser cladded high speed steel coating of claim 1 wherein: The staggered gas blowing structure realizes the following functions through argon gas flow: forming an argon gas covering layer to prevent oxidation of the substrate.

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