A device and method for cold spray impact strengthening of a part surface

Abstract

The application provides a part surface cold spraying impact strengthening device and a spraying strengthening method, which comprise a compressed gas tank, a heater, a gas feeding pipeline, a driving powder feeder, a driven powder feeder, a cold nozzle, a powder recovery cover and a powder recovery pipe; the cold nozzle is a special small-bore large-expansion-ratio contraction-expansion nozzle. The compressed gas tank, the heater, the gas feeding pipeline, the cold nozzle and the powder recovery cover are sequentially communicated; the driving powder feeder and the driven powder feeder are respectively arranged on two branches of the gas feeding pipeline, high-melting-point metal powder is contained in the driving powder feeder, the driven powder feeder is communicated with the powder recovery cover through the powder recovery pipe, residual powder is sucked and transported to the gas feeding pipeline; the cold nozzle is moved to spray the blade surface during spraying, fine strengthening treatment is realized on the local area of the part, the part does not need to be disassembled, other parts are not polluted, and the defect that the complex part needs to be disassembled before impact strengthening in the prior art is solved.

Description

Technical Field

[0001] This invention belongs to the field of aviation manufacturing and maintenance technology, specifically relating to a cold spray impact strengthening device and spray strengthening method for part surfaces. Background Technology

[0002] Many components in the aerospace field, such as aircraft engine blades and gears, are typically operated under cyclic stress conditions, making their fatigue behavior during service particularly important. Numerous flight accidents caused by fatigue fracture result in significant economic losses. Therefore, fatigue fracture is a pressing problem that needs to be solved in the development and service of aircraft structural components. To improve the reliability of parts under service conditions and extend their service life, a common method is to increase the strength of the parts through surface strengthening techniques without altering the quality of the base material.

[0003] Commonly used surface strengthening methods include laser strengthening, mechanical shot peening, and roll forming. Laser shock strengthening often requires a water-based constraint layer or an absorbent coating on the surface of the part to be strengthened. This process is not only complex but also prone to contaminating areas that do not require strengthening. Furthermore, the equipment used is expensive and cannot be moved.

[0004] Traditional mechanical shot peening has a centimeter-level spray range, resulting in a large dispersion of the shot. This makes it suitable only for overall strengthening of the entire part, not for precise strengthening of small, localized areas. Furthermore, for in-situ, non-destructive impact strengthening of parts, traditional mechanical shot peening easily causes shot contamination of other areas. Low-plasticity roll forming requires specialized tooling designed for the parts being strengthened, resulting in poor tooling versatility and difficulty in strengthening complex-shaped parts. Summary of the Invention

[0005] In response to the problems mentioned in the background art, the applicant considered designing a small nozzle suitable for shot peening areas in the mm range. However, for small-sized nozzle designs, if the nozzle size is too large, an expansion wave will be generated at the nozzle exit; if the size is too small, an arc wave will be generated at the nozzle exit. The generation of these two types of shock waves will consume the kinetic energy of the strengthening powder particles. The speed of the strengthening powder particles decreases when passing through the shock waves, making it impossible for the kinetic energy of the powder particles to generate sufficient residual compressive stress on the matrix, resulting in poor impact strengthening effect on the matrix.

[0006] Based on the above considerations, this invention proposes a cold spray impact strengthening device for parts. By designing a specific nozzle size and coordinating it with the shot peening size and distance, the strengthening metal powder does not generate shock waves at the nozzle exit, ensuring the acceleration effect of the strengthening metal powder. Through the cooperation of the cold nozzle and the powder recovery hood, it achieves fine strengthening treatment of local areas of the parts and powder recovery. No protective layer is required during the spray impact strengthening process, and it will not cause pollution to areas that do not need to be sprayed for strengthening. Furthermore, it can perform in-situ fine strengthening treatment of parts with different complex shapes without decomposition.

[0007] To achieve the above objectives, the technical solution provided by this invention is:

[0008] A cold spray impact strengthening device for part surface is characterized in that it includes a compressed air tank, a heater, an air delivery pipeline, an active powder feeder, a driven powder feeder, a cold nozzle, and a powder recovery hood.

[0009] The compressed gas tank contains inert gas;

[0010] The compressed air tank, heater, air delivery pipeline, cold nozzle, and powder recovery hood are connected in sequence;

[0011] The gas delivery pipeline includes two branches. One branch is equipped with an active powder feeder, and the high melting point metal powder located in the active powder feeder is transported to the branch by its own weight.

[0012] Another branch is equipped with a driven powder feeder, which is connected to the powder recovery hood through a powder recovery pipe. It can suck in the residual metal powder in the powder recovery hood and transport it to the air supply pipeline.

[0013] The nozzle is a contraction-expansion type nozzle, with the expansion section connected to the powder recovery hood inlet; the inner diameter of the large end of the expansion section of the cold nozzle is 6-8mm, and the expansion ratio is 3-4; the inner diameter of the throat located between the contraction section and the expansion section is 2mm-3mm.

[0014] Furthermore, the driven powder feeder draws residual metal powder from the powder recovery hood into the driven powder feeder through a negative pressure device installed inside it.

[0015] Furthermore, the metal powder is spherical or approximately spherical, with a particle size of 30μm-70μm.

[0016] Furthermore, the metal powder is aluminum oxide powder or silicon dioxide powder.

[0017] Furthermore, the powder recovery hood is trumpet-shaped, with the small end coaxially fixed to the outer wall of the cold nozzle expansion section, and the inner diameter of the large end being 1.5-3 times the outer diameter of the cold nozzle expansion section.

[0018] Furthermore, the distance between the large end of the powder recovery hood and the outlet end of the cold nozzle expansion section is 15mm-40mm.

[0019] Furthermore, the inert gas is argon.

[0020] The method for strengthening the surface of parts using the aforementioned cold spray impact strengthening device is characterized by the following steps:

[0021] Step 1: Perform pre-treatment on the surface of the parts before spraying;

[0022] Step 2: Place the metal powder in the active powder feeder, adjust the angle between the cold nozzle and the surface of the part to be 70° to 90°, and maintain a gap of 1cm to 10cm between the outlet end of the powder recovery hood and the surface of the part.

[0023] Step 3: Set the spraying impact strengthening parameters:

[0024] The gas pressure in the compressed air tank is 2MPa to 10MPa;

[0025] The heating temperature of the heater is 300℃~1000℃;

[0026] The powder feeding rate of the active powder feeder and the driven powder feeder is 100g / min to 800g / min;

[0027] Step 4: Spray the area on the part surface to be impact-strengthened.

[0028] Furthermore, in step 1, the specific process of pre-treatment of the part surface before spraying is as follows: first, use paint stripper to remove the protective paint on the part surface, then clean the oil stains on the part surface and dry it.

[0029] Furthermore, in step 4, when spraying the impact-strengthening area on the surface of the part, the nozzle moves in a zigzag pattern on the surface of the area to be strengthened, and multiple sprays are performed as needed.

[0030] The advantages of this invention are:

[0031] 1. This invention uses a shrink-expansion type small nozzle. By designing a specific nozzle throat inner diameter, expansion section large end inner diameter and expansion ratio, shock waves are not generated at the nozzle orifice, ensuring the acceleration effect of the enhanced powder particles. This enables effective control of the spraying area of ​​the enhanced area and fine enhancement treatment of local areas of parts, avoiding the drawbacks of existing mechanical shot peening which can only enhance the whole area but not the local fine enhancement.

[0032] 2. In this invention, by setting a powder recovery cover at the cold nozzle orifice and a driven powder feeder connected to the powder recovery cover, it is possible to eliminate the need for protective treatment of the blade surface during the impact strengthening process, and to prevent contamination of areas that do not require impact strengthening. This enables the recovery of residual powder from the first impact strengthening process, realizes the recycling of metal powder, avoids powder waste, and saves on impact strengthening processing costs.

[0033] 3. In this invention, the compressed gas is heated by a heater, so that the heated compressed gas can increase the powder temperature after entering the powder feeding pipeline. During impact strengthening, it can generate a thermal effect on the blade matrix, promote better plastic deformation, and thus improve the impact strengthening effect.

[0034] 4. The spraying strengthening device of the present invention has a simple structure and high mobility. The small-sized nozzle can not only achieve impact strengthening of narrow parts of the parts, but also be used for impact strengthening of local areas of parts with different complex shapes. No additional auxiliary tooling is required. It solves the drawback of existing methods that require the complex parts to be disassembled one by one before impact strengthening. It realizes the impact strengthening of parts without disassembly and movement, and is suitable for field operations under different environmental conditions. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the cold spray impact strengthening device of the present invention;

[0036] Figure 2 This is a schematic diagram of the cooling nozzle structure in this invention;

[0037] Figure 3 This is a schematic diagram of the microscopic plastic deformation of the substrate surface of a part after impact strengthening using the device of the present invention.

[0038] Explanation of reference numerals in the attached drawings: 1-compressed gas, 2-heater, 3-gas delivery line, 4-active powder feeder, 5-driven powder feeder, 6-powder, 7-cold nozzle, 701-contraction section, 702-expansion section, 703-throat, 8-powder recovery hood, 9-substrate, 10-impact reinforcement layer, 11-powder recovery pipe. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0040] To achieve precise spray coating strengthening treatment on the surface of parts, the present invention provides a cold spray impact strengthening device for the surface of parts, including a compressed air tank, a heater, an air supply pipeline, an active powder feeder, a driven powder feeder, a cold nozzle, and a powder recovery hood.

[0041] The compressed gas tank contains inert gas;

[0042] The compressed air tank, heater, air delivery pipeline, cold nozzle, and powder recovery hood are connected in sequence;

[0043] The gas delivery pipeline includes two branches. One branch is equipped with an active powder feeder, and the high melting point metal powder located in the active powder feeder is transported to the branch by its own weight.

[0044] Another branch is equipped with a driven powder feeder, which is connected to the powder recovery hood through a powder recovery pipe. It can suck in the residual metal powder in the powder recovery hood and transport it to the air supply pipeline.

[0045] The nozzle is a contraction-expansion type nozzle, with the expansion section connected to the inlet end of the powder recovery hood; the inner diameter of the large end of the expansion section of the cold nozzle is 6-8mm, and the expansion ratio is 3-4; the inner diameter of the throat between the contraction section and the expansion section is 2mm-3mm.

[0046] The device of this invention eliminates the need to protect non-coated areas during impact strengthening, prevents contamination of other areas, and enables the recovery and recycling of residual powder from the strengthening process.

[0047] Reference Figure 1 A cold spray impact strengthening device for part surface includes a compressed air tank 1, a heater 2, an air supply pipeline 3, an active powder feeder 4, a driven powder feeder 5, a cold nozzle 7, a powder recovery hood 8, and a powder recovery pipe 11.

[0048] The compressed gas tank 1 contains inert gas, and a heater 2 is installed between the outlet of the compressed gas tank 1 and the gas delivery pipeline 3. This allows the heated compressed gas to increase the temperature of the powder after entering the powder delivery pipeline. During impact strengthening, the compressed gas can generate a thermal effect with the part matrix 9, promoting better plastic deformation and thus improving the impact strengthening effect.

[0049] The gas delivery pipeline 3 includes two branches. One branch is equipped with an active powder feeder 4, in which high-melting-point metal powder is fed by its own weight. The other branch is equipped with a passive powder feeder 5 with a negative pressure device. The passive powder feeder 5 is connected to the powder recovery hood 8 located at the outlet of the cold nozzle 7 through the powder recovery pipe 11. It can draw residual metal powder in the powder recovery hood and the powder recovery pipe into the passive powder feeder, and then feed the metal powder into the gas delivery pipeline by its own weight.

[0050] The cold nozzle 7 is located at the outlet end of the air supply pipeline 3. The cold nozzle is a contraction-expansion type nozzle, with the contraction section connected to the air supply pipeline and the expansion section connected to the powder recovery hood. The inner diameter of the large end of the expansion section of the cold nozzle is 6-8mm, and the expansion ratio is 3-4.

[0051] To prevent the compressed gas from oxidizing the metal powder after heating, argon is used as the compressed gas.

[0052] Based on the properties of the blade material, the powder contained in the active powder feeder 4 is a spherical or nearly spherical high-melting-point metal powder with a particle size of 30μm-70μm. The hardness of the spherical or nearly spherical powder is better than that of the blade matrix.

[0053] Reference Figure 2 The cold nozzle 7 is a small-diameter, high-expansion-ratio contraction-expansion type laval nozzle with a two-stage columnar shape. It has a through-hole along its axis starting from the large end. The through-hole includes a contraction section 701 and an expansion section 702. The contraction section consists of a coaxially connected columnar hole and a conical hole. The diameter of the columnar hole is 20mm, and the diameter of the conical hole gradually decreases. The length of the contraction section is 30mm. The expansion section is a conical hole with a gradually increasing diameter. The diameter of the large end of the expansion section is 6mm-8mm, the expansion ratio is 3-4, and the length of the expansion section is 220mm. The specific design of the inner diameter and expansion ratio of the large end of the expansion section in this invention prevents the generation of shock waves at the cold nozzle exit end, ensuring the acceleration performance of powder particles during the spraying process. This achieves precise shot peening while improving the impact strengthening effect.

[0054] A throat 703 is provided between the contraction section and the expansion section. The throat 703 is a columnar hole with a diameter of 2mm-3mm, which allows the metal powder particles to reach the speed of sound in the throat, ensuring the acceleration performance of the particles when entering the expansion section.

[0055] The large end of the cold nozzle has an outer diameter of 30mm and is connected to the outlet end of the air supply pipeline. The small end of the cold nozzle has an outer diameter of 14mm and is threaded on its outer wall for threaded connection with the small end of the powder recovery hood 8. The small-diameter, high-expansion-ratio nozzle used in this invention enables precise strengthening of localized areas of components, avoiding the drawback of existing mechanical shot peening which can only strengthen the entire component and not provide precise localized strengthening.

[0056] The optimized cold nozzle is mounted on a robotic arm and moves via the robotic arm, allowing for high mobility. It can be applied to impact strengthening of local areas of components with different complex shapes without the need for additional auxiliary tooling.

[0057] The powder recovery hood 8 is trumpet-shaped, with one end being cylindrical and the other end conical. The inner wall of the cylindrical section is threaded and connected to the outer wall of the small end of the cold nozzle. The small end of the powder recovery hood has an M14*1.5 diameter and a thread length of 30mm. The diameter of the large end of the powder recovery hood is 1.5-3 times the outer diameter of the small end of the cold nozzle 7. The distance from the large end of the powder recovery hood to the outlet end of the expansion section of the cold nozzle is 15mm-40mm.

[0058] The method for spraying and strengthening the surface of a part using the apparatus of the present invention includes the following steps:

[0059] Step 1: Pre-treat the surface of the part to be reinforced. First, use paint remover to remove the protective paint on the surface of the part, and then use acetone to clean the surface of the part to remove the paint layer, coating, oil and foreign matter on the blade surface until the part substrate is exposed.

[0060] Based on the properties of the matrix material, select spherical or nearly spherical high-melting-point metal powders with a particle size of 30μm-70μm, and load the metal powders into the active powder feeder.

[0061] Step 2: Adjust the position of the cold nozzle so that the distance between its outlet end and the surface of the part is 2.5cm-14cm, and the angle between the cold nozzle and the surface of the part is 70°-90°; then install the powder recovery hood on the cold nozzle, and keep a gap of 1cm-10cm between the outlet end face of the powder recovery hood and the surface of the part.

[0062] Step 3, set the spraying impact strengthening parameters:

[0063] The gas pressure in the compressed air tank is 2MPa to 10MPa;

[0064] The heating temperature of the heater is 300℃~1000℃;

[0065] The powder feeding rate of the active powder feeder and the driven powder feeder is 100g / min to 800g / min;

[0066] Step 4: Spray the area on the blade surface to be impact-strengthened;

[0067] The cold nozzle is held by hand or by a robotic arm and moved zigzag across the surface of the part to perform impact strengthening.

[0068] After cold spraying for strengthening, check whether the coverage, appearance, and dimensions of the part surface meet the technical requirements. Depending on the desired strengthening effect, multiple spraying processes can be performed on the areas to be strengthened on the part surface.

[0069] The following example illustrates the process of using the device of this invention to perform cold spray impact strengthening on engine blades.

[0070] Example 1

[0071] The engine rotor blades are made of 2A02 aluminum alloy.

[0072] Step 1: Use paint stripper to remove the yellow protective paint from the blade surface, clean the oil stains on the blade surface with acetone, and then dry it.

[0073] Step 2: Select spherical aluminum oxide powder as the impact strengthening powder, with a powder particle size of 50 μm, and load the aluminum oxide powder into the active powder feeder 4.

[0074] Step 3: Mark the area to be reinforced on the blade. Select a cold nozzle with a diameter of 20mm in the constriction section, 2mm in the throat, and 6mm in the expansion section. Adjust the cold nozzle 7 to the starting point of the area to be reinforced, ensuring that the distance between the outlet of the cold nozzle expansion section and the blade surface is 14cm, and maintaining an angle of 90° between the cold nozzle and the blade surface.

[0075] Step 4: Select a horn-shaped powder recovery hood with a large end diameter of 21mm. Fit the small end of the powder recovery hood onto the outer wall of the cold nozzle expansion section, and maintain a 3cm gap between the large end face of the powder recovery hood and the blade surface. Connect the powder recovery pipe to the recovery hood.

[0076] Step 5: Select argon as the compressed gas, set the gas pressure to 4MPa, set the heater temperature to 600℃, turn on the active powder feeder 4 switch, and set the powder feeding rate to 300g / min; turn on the driven powder feeder 5 switch and set the powder feeding rate to 200g / min.

[0077] The handheld cold nozzle is moved in a zigzag pattern on the area of ​​the blade surface to be impact-strengthened, so that an impact-strengthened layer is formed on the blade surface.

[0078] The blades were inspected after being reinforced by cold spraying. The coverage, appearance, and dimensions of the blades after shot peening met the requirements of the drawings and specifications.

[0079] Example 2

[0080] The engine rotor blades are made of TC4 titanium alloy.

[0081] Step 1: Remove the yellow protective paint from the blade surface with paint stripper, clean the oil stains on the blade surface with acetone, and then dry the blade.

[0082] Step 2: Select spherical silica powder as the impact strengthening powder, with a particle size of 40μm, and load the silica powder into an active powder feeder.

[0083] Step 3: Mark the area on the blade that needs to be strengthened. Select a cold nozzle with an inner diameter of 20mm in the contraction section, a throat diameter of 3mm, and an inner diameter of 8mm in the expansion section. Adjust the cold nozzle to the starting position of the area to be strengthened so that the distance between the outlet end of the cold nozzle and the blade surface is 10cm, and keep the angle between the cold nozzle and the blade surface at 90°.

[0084] Step 4: Select a horn-shaped powder recovery hood with a large end diameter of 28mm. Install the powder recovery hood on the cold nozzle, ensuring a 2cm gap between the large end face of the powder recovery hood and the blade surface. Connect the powder recovery pipe to the recovery hood.

[0085] Step 5: Select argon as the compressed gas, set the gas pressure to 5MPa, set the heater temperature to 700℃, turn on the active powder feeder switch and set the powder feeding rate to 250g / min; turn on the driven powder feeder switch and set the powder feeding rate to 200g / min; hold the cold nozzle and move it in a zigzag pattern on the area to be impact-strengthened on the blade surface.

[0086] The blades were inspected after being reinforced by cold spraying. The coverage, appearance, and dimensions of the blades after shot peening met the requirements of the drawings and specifications.

[0087] Figure 3 This diagram illustrates the microscopic plastic deformation of the substrate surface after impact strengthening using the device of the present invention. Spherical aluminum oxide or silica powder particles, accelerated by a cold nozzle, impact the blade substrate 9 at extremely high speeds. Since the particle velocity does not reach the critical deposition velocity, the particles are rebounded by the substrate. The kinetic energy of the particles is dissipated through the plastic deformation of the substrate material. Due to the constraint of the undeformed substrate, the plastic deformation is insufficient, resulting in significant residual compressive stress within a certain depth range of the substrate. A work-hardened layer, the impact strengthening layer 10, is then formed on the substrate surface. This impact strengthening layer 10 effectively inhibits the generation and propagation of fatigue cracks, extending the fatigue life of the blade.

[0088] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the scope of the technology disclosed in the present invention, and such modifications or substitutions should all be covered within the scope of protection of the present invention.

Claims

1. A device for cold spraying impact strengthening of a part surface, characterized in that, Includes compressed air tank, heater, air delivery pipeline, active powder feeder, passive powder feeder, cold nozzle and powder recovery hood; The compressed gas tank contains inert gas; The compressed air tank, heater, air delivery pipeline, cold nozzle, and powder recovery hood are connected in sequence; The gas delivery pipeline includes two branches. One branch is equipped with an active powder feeder, and the high melting point metal powder located in the active powder feeder is transported to the branch by its own weight. Another branch is equipped with a driven powder feeder, which is connected to the powder recovery hood through a powder recovery pipe. It can suck in the residual metal powder in the powder recovery hood and transport it to the air supply pipeline. The nozzle is a contraction-expansion type nozzle, with the expansion section connected to the inlet end of the powder recovery hood; the inner diameter of the large end of the expansion section of the cold nozzle is 6mm-8mm, and the expansion ratio is 3-4; the inner diameter of the throat located between the contraction section and the expansion section is 2mm-3mm. The powder recovery hood is trumpet-shaped, with its small end coaxially fixed to the outer wall of the cold nozzle expansion section, and its large end having an inner diameter that is 1.5-3 times the outer diameter of the cold nozzle expansion section; the distance between the large end of the powder recovery hood and the outlet end of the cold nozzle expansion section is 15mm-40mm.

2. The cold spray impact strengthening device according to claim 1, characterized in that, The driven powder feeder draws residual metal powder from the powder recovery hood into itself through a negative pressure device located inside it.

3. The cold spray impact strengthening device according to claim 1, characterized in that, The metal powder is spherical or approximately spherical, with a particle size of 30μm-70μm.

4. The cold spray impact strengthening device according to claim 3, characterized in that, The metal powder is aluminum oxide powder or silicon dioxide powder.

5. The cold spray impact strengthening device according to claim 1, characterized in that, The inert gas is argon.

6. A method for spraying and strengthening the surface of a part using the cold spraying impact strengthening device according to any one of claims 1-5, characterized in that, Includes the following steps: Step 1: Perform pre-treatment on the surface of the parts before spraying; Step 2: Place the metal powder in the active powder feeder, adjust the angle between the cold nozzle and the surface of the part to be 70° to 90°, and maintain a gap of 1cm to 10cm between the outlet end of the powder recovery hood and the surface of the part. Step 3: Set the spray coating impact enhancement parameters: The gas pressure in the compressed air tank is 2MPa to 10MPa; The heating temperature of the heater is 300℃~1000℃; The powder feeding rate of the active powder feeder and the driven powder feeder is 100g / min to 800g / min; Step 4: Spray the area on the part surface to be impact-strengthened.

7. The method according to claim 6, characterized in that, In step 1, the specific process of pre-treatment of the part surface before spraying is as follows: First, use paint remover to remove the protective paint from the surface of the parts, then clean the oil stains on the surface of the parts and dry them.

8. The method according to claim 7, characterized in that, In step 4, when spraying the impact-strengthened area on the surface of the part, the nozzle moves in a zigzag pattern on the surface of the area to be strengthened and performs multiple sprays as needed.

Images