A method and apparatus for laser cladding of structural components with online gas protection and radiation heating

Abstract

The application relates to a laser cladding method and device of an online gas protection and radiation heating structural member, which is a multi-process coupling forming process method based on heating and gas protection of a workpiece to-be-cladded area, reduces a temperature gradient in a cladding process, reduces and uniformly distributes internal stress of a cladding layer, simultaneously makes up defects of too small gas protection range of a powder feeding mechanism, and inhibits generation of defects such as cracks and pores in a cladding area. The device comprises a laser cladding head, a powder feeding mechanism, a protective cover, a radiation heating mechanism and an online gas protection mechanism. The cladding nozzle is provided with a protective gas structure and is provided with an air pressure sensor at a port to monitor an air pressure difference inside and outside the laser cladding device. The secondary protection gas pipes of the radiation heating mechanism and the online gas protection mechanism are installed on the periphery of the cladding nozzle through flanges and synchronously move with the laser cladding head to realize adjustable height of heat radiation, controllable heating speed and cooling speed, and the shell of the heating device is heat-insulated by heat-insulating ceramics. The application has practical application value for promoting local addition, strengthening and conformal cladding of large cast iron parts and molds, further realizes integrated forming of structural members, and has important significance.

Description

Technical Field

[0001] This invention belongs to the field of laser cladding forming and manufacturing. In particular, it relates to a laser cladding method and apparatus for online gas protection and radiation heating structural components. Background Technology

[0002] High-end equipment in fields such as aerospace, high-power engines, and hot stamping dies is developing towards greater complexity, lighter weight, integration, and whole-structure manufacturing. Key metal components are becoming increasingly larger, more complex in structure, and subject to more stringent performance requirements. Some special structures are difficult to manufacture using traditional casting and forging methods. Additive manufacturing technology, with its dimensional reduction and layered construction, can form arbitrary shapes and complex features, providing a new solution for manufacturing complex parts. However, in practical engineering applications, existing integral metal additive manufacturing struggles to balance high efficiency and low cost, becoming a bottleneck in the application of additive manufacturing. Furthermore, most parts do not require integral additive manufacturing.

[0003] The valve seats of an automotive engine are primarily used to seal the engine valves and withstand high temperatures and high-speed impacts. Traditional technology involves interference-fitting valve seat rings into the countersunk bores of the cylinder head. However, their wide and thick end design causes airflow pressure loss, affecting engine thermal efficiency. Furthermore, worn valve seat rings require replacement after prolonged use, resulting in material and energy waste. Laser cladding technology utilizes a high-energy laser beam as a heat source, acting on the substrate surface and the powder material to be clad. Employing a laser heat source with high focusing, precision, and energy density, it melts and solidifies the cladding material and substrate in a very short time, thus creating a cladding layer on the substrate surface. Laser cladding technology enables additive manufacturing of engine cylinder heads without the need for valve seat rings. The valve seats are directly machined into a smooth-flowing conical countersunk bore shape, and high-temperature wear-resistant powder material is directly deposited onto the surface of the countersunk bore through laser cladding. The cladding layer not only has better mechanical properties, but also enables a more superior air intake design to improve thermal efficiency and achieve energy conservation and emission reduction.

[0004] Most existing laser cladding equipment for engine valve seats uses a coaxial powder feeding method with a laser cladding head. The protective gas area is small and easily mixed with air due to the influence of external air. The presence of elements such as hydrogen and oxygen in the air leads to pores in the cladding layer. Furthermore, the high-energy-density laser beam acts on the substrate and the cladding material, resulting in rapid temperature changes and large temperature gradients in the molten pool. This generates significant thermal and residual stresses, as well as microstructural defects such as martensite and white iron structures that are prone to cracking. Consequently, the cladding layer develops cracks, uneven hardness, and other problems, leading to reduced performance and even deformation of the substrate. Summary of the Invention

[0005] With the development of high-power laser technology and additive manufacturing technology, laser cladding technology has gradually expanded from its original applications in surface modification and repair to the field of stereolithography, becoming one of the core processes in additive manufacturing. Laser cladding stereolithography technology has been successfully applied in aerospace, military, and other fields for high-end materials such as aluminum alloys, titanium alloys, and high-temperature alloys. However, most existing valve seat laser cladding equipment uses a coaxial powder feeding method with the laser cladding head. The protective gas area is small, and the cladding zone is easily affected by external air, leading to air contamination and porosity in the cladding layer. Furthermore, the high-energy-density laser beam concentrates on the substrate and cladding material, resulting in rapid temperature changes and large temperature gradients in the molten pool, leading to significant thermal and residual stresses. This, along with the formation of microstructures such as martensite and white iron, which are prone to cracking, causes cracks and uneven hardness in the cladding layer, reducing performance and even deforming the substrate.

[0006] To address the potential for air contamination and porosity in the cladding layer during laser cladding, this invention aims to isolate the cladding area from air by providing an online gas protection method. Since the flow rate of the protective gas inside a conventional protective shield is unstable, causing uneven blowing or non-uniformity of the protective gas and powder under sudden pressure changes, this invention aims to monitor and regulate the protective gas pressure at the powder outlet using a flow and pressure sensor, and to monitor and self-feedback adjust the incoming protective gas flow rate in real time, ensuring uniform and stable gas pressure within the protective shield, thus providing an online gas protection control system. Simultaneously, to address the issue of large temperature variations between the cladding area and the unheated substrate area caused by the concentrated action of a high-energy-density laser beam on the substrate and cladding material, potentially leading to significant thermal and residual stress during solidification, this invention aims to reduce temperature variations and residual stress by employing preheating before cladding and slow cooling after cladding to reduce the likelihood of crack formation, thus providing a method for radiation-heated structural components.

[0007] To address the issue of air easily getting into the cladding zone during laser cladding, leading to porosity in the cladding layer, this invention provides an online gas protection device. Furthermore, because the flow rate of the protective gas inside a conventional protective shield is unstable, causing uneven blowing or non-uniformity of the protective gas and powder under sudden pressure changes, this invention aims to monitor and regulate the pressure of the protective gas at the powder outlet using a flow and pressure sensor. It also provides real-time monitoring and self-feedback adjustment of the incoming protective gas flow rate, ensuring uniform and stable gas pressure within the protective gas shield, thus providing an online gas protection control system. Simultaneously, to address the problem of high-energy-density laser beams concentrating on the substrate and cladding material, resulting in significant temperature variations between the cladding zone and the unheated substrate area, potentially leading to substantial thermal and residual stress during solidification, this invention aims to reduce temperature variations and residual stress. It provides a device for heating structural components using a radiant heating mechanism, which reduces the possibility of crack formation by preheating before cladding and slow cooling after cladding.

[0008] This method and apparatus are adaptable to various cladding materials, structures, processes, and environments. During the cladding process, a radiant heating mechanism heats the cladding area, achieving preheating before cladding and slow cooling (insulation) after cladding, thus reducing temperature gradient changes in the cladding area. The protective cover is equipped with multiple pressure gauges. An inert protective gas is filled inside the cover, and real-time monitoring is achieved through flow and pressure sensors, enabling dynamic adjustment of the internal pressure to ensure constant consistency with the protective gas pressure of the powder feeding mechanism. An online gas protection control system supplies protective gas to the cladding area, monitoring pressure and flow changes through flow and pressure sensors and pressure gauges, and matching the protective gas pressure with that of the powder feeding mechanism. The protective cover, the online protective gas mechanism, and the protective gas of the powder feeding mechanism work together to provide a protective environment that isolates the cladding area from air. Compared with traditional laser cladding systems, the radiation heating mechanism prevents excessive temperature gradients caused by beam concentration, reducing the tendency for defects such as cracks in the cladding layer. The protective cover and external protective gas system increase the effective range of the protective gas between the cladding powder and the cladding zone, avoiding the possibility of air mixing in during laser cladding due to the insufficient protective gas range of the powder feeding device itself, which could lead to defects such as pores.

[0009] A laser cladding device for an online gas protection and radiant heating structure includes a protective cover, a laser cladding head, a powder feeding mechanism, a radiant heating mechanism, and an online gas protection control system. The laser cladding head is connected to a laser generator, with a cladding nozzle at its bottom. The powder feeding mechanism coaxially feeds powder with the laser generator, is integrated into the cladding nozzle, and carries a certain range of protective gas. The cladding nozzle is equipped with a pressure sensor to monitor, record, provide feedback on, and adjust the protective gas pressure at the powder cladding point. The moving shaft is equipped with a protective cover, which is also equipped with a pressure measuring instrument. The cover is filled with protective gas, which is monitored in real time to maintain a constant pressure, thus isolating the working area of ​​the laser cladding head from the air. The radiant heating mechanism and the online gas protection mechanism are mounted on the cladding nozzle end via a flange and move with the laser cladding head. The radiant heating mechanism is powered on to heat up, and the adjustable close-range radiant heating mechanism preheats the area to be clad and maintains a stable temperature, achieving controllable heating and cooling rates and reducing the temperature gradient at the start and end of the cladding process. The primary and secondary protective gas pipes of the online gas protection control system deliver protective gas to the area surrounding the powder feeding zone, compensating for the shortcomings of the powder feeding mechanism itself having too small a protective gas range, and ensuring stable gas pressure and no air in the powder zone and cladding zone.

[0010] The radiant heating mechanism is connected to the adapter block and flange via fastening screws. Its height is adjustable, and it is electrically heated. The outer shell is made of heat-insulating ceramic. During cladding, the heating device is 1-2 mm away from the surface of the structural component, ensuring effective radiant heating without damaging the workpiece surface. The heating temperature can be continuously adjusted via a temperature control system, ranging from 0 to 800℃, and is suitable for various process parameters, powder formulations, and matrix materials.

[0011] The aforementioned online gas protection mechanism connects the inlet ends of the primary and secondary protective gas pipes to an online gas protection control system. The secondary protective gas pipe is fixed to the flange of the cladding nozzle, while the primary protective gas pipe is secured to the protective cover via connecting bolts. The secondary protective gas pipe is equipped with a flow and pressure sensor, which delivers protective gas around the powder feeding area. The sensor monitors the gas pressure and flow rate, providing feedback to the protective gas control system for precise control of the flow and pressure. A pressure measuring instrument inside the protective cover monitors the internal gas pressure and provides real-time feedback to the online gas protection control system, adjusting the flow rate of the primary protective gas pipe. The online gas protection control system ensures that the protective gas pressure inside the protective cover and in the powder feeding area is balanced with the protective gas pressure of the laser cladding nozzle, thus preventing the possibility of air in the cladding area.

[0012] The protective cover is installed on the motion axis to ensure that the laser cladding head's light and powder output are not affected. The primary protective gas pipe is connected to the protective cover by connecting bolts, and is filled with protective gas to isolate the laser cladding head from the air. The protective cover is equipped with multiple air pressure measuring instruments to monitor the dynamic changes in air pressure inside the protective cover in real time and provide feedback and control in real time to ensure that the air pressure inside the protective cover is consistent with the protective air pressure of the cladding nozzle, achieving a gas pressure balance.

[0013] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0014] This laser cladding method and apparatus also requires an external laser generator, control system, and motion equipment. Before cladding the structural component, the radiant heating mechanism preheats the substrate material in the area to be clad for a certain period of time. Inert protective gas is introduced into the protective cover according to a preset formula, and the gas pressure is kept balanced and stable. After preheating, the motion axis drives the laser cladding head to move, the laser generator emits light, and the powder feeding mechanism starts feeding powder. At the same time, the online gas protection control system controls the pressure and flow rate of the protective gas through feedback signals from the pressure measuring instrument and flow pressure sensor, ensuring that the pressure is the same as and stable as the pressure of the protective gas in the preset formula and the cladding nozzle. After laser cladding, the radiant heating mechanism can provide a certain degree of heat preservation for the structural component.

[0015] After the entire cladding process is completed, the laser cladding head stops emitting light, the powder feeding mechanism stops feeding powder, the online gas protection control system stops working, the radiation heating mechanism is powered off and stops heating, and the moving equipment resets.

[0016] Compared with existing laser cladding technology for structural components, the advantages of this invention are as follows:

[0017] By preheating the structural components using an auxiliary heating mechanism, the heat consumption during the initial melting stage of the laser energy is reduced. This also prevents large temperature gradients in the base material caused by the concentrated laser beam energy, thus reducing the possibility of defects such as cracks and uneven forming in the cladding layer. With the help of a protective cover and an online gas protection control system, the range of the protective gas for the cladding powder is increased, eliminating the possibility of air mixing into the cladding area and causing defects such as porosity due to an insufficient protective gas range of the powder feeding mechanism itself. Furthermore, this method and device are integrated with the laser cladding head, achieving mechanization, automation, and low energy consumption, resulting in high-quality and high-efficiency manufacturing of structural components. Attached Figure Description

[0018] Figure 1 This is a schematic diagram illustrating the working principle of the method and apparatus of the present invention;

[0019] Figure 2 This is a side sectional view of the device of the present invention;

[0020] Figure 3 For the present invention Figure 1 Enlarged schematic diagram of device A.

[0021] In the diagram: 1-Motion shaft, 2-Protective cover, 3-Laser cladding head, 4-Clad head, 5-Radiation heating mechanism, 6-Powder feeding mechanism, 7-Flange, 8-Fasting screw, 9-Insulating ceramic, 10-Heating device, 11-Adapter block, 12-Primary protective gas pipe, 13-Secondary protective gas pipe, 14-Gas pressure measuring instrument, 15-Flow and pressure sensor, 16-Laser generator, 17-Connecting bolt, 18-Online gas protection control system. Detailed Implementation

[0022] The following detailed description, in conjunction with the accompanying drawings and specific implementation methods, provides a laser cladding method and apparatus for online protection and radiation heating structural components provided by the present invention. This invention is applicable to laser cladding of metal substrate structural components, and is particularly suitable for the laser cladding manufacturing of metal substrates for engine valve seats.

[0023] The following is combined with Figure 1 , Figure 2 and Figure 3 The steps of this laser cladding method are described in detail:

[0024] 1) During laser cladding, the motion axis 1 is equipped with a protective cover 2 and a laser cladding head 3. The powder feeding mechanism 6 is integrated into the cladding nozzle 4 and feeds powder coaxially with the laser source. The radiant heating mechanism 5 and the secondary protective gas pipe 13 are integrated onto the cladding nozzle 4 via a flange 7. The radiant heating mechanism 5 includes a heat-insulating ceramic shell 9 and a heating device 10, which are connected to the flange 7 via an adapter block 11 and fastening screws 8. The inlet end of the secondary protective gas pipe 13 is connected to the online gas protection control system 17, and the secondary protective gas pipe 13 is also equipped with a flow and pressure sensor 15. The primary protective gas pipe 12 is connected to the protective cover 2 via connecting bolts 17, and the protective cover 2 contains multiple pressure measuring instruments 14.

[0025] 2) Before laser cladding, the heating device 10 of the radiation heating mechanism 5 is powered on to preheat the structural parts to be clad for a certain period of time. Inert protective gas is introduced into the protective cover 2 and the flow rate and pressure of the protective gas are adjusted according to the cladding powder formula and the diameter of the cladding nozzle 4. The gas pressure of the online gas protection control system 18 is set and monitored and kept stable by the gas pressure measuring instrument 14.

[0026] 3) After preheating, the laser generator 16 emits light, the motion shaft 1 drives the laser cladding head 3 to move, and the bottom of the laser cladding head 3 starts to emit light at the cladding nozzle 4. The powder feeding mechanism 6 feeds powder synchronously. At the same time, the secondary protective gas pipe 13 introduces inert protective gas and controls the protective gas pressure and flow rate according to the feedback signal from the flow and pressure sensor 15, so as to ensure that the protective gas pressure is consistent with and stable with the cladding nozzle 4.

[0027] 4) After cladding is completed, the laser generator of the laser cladding head 3 stops emitting light, the powder feeding mechanism 6 stops feeding powder, and the radiation heating mechanism 5 maintains the temperature for a certain period of time based on the cooling rate of the structural components and the cladding layer calculated in the early stage. Finally, the radiation heating mechanism 5 is powered off and stops heating, the online gas protection control system 18 stops working, and the motion axis 1 resets.

Claims

1. A method of laser cladding of a structure with online gas protection and radiation heating, characterized in that, An inert protective gas is supplied around the cladding area and powder feeding area of ​​the laser cladding process, and the area around the cladding area is preheated and slowly cooled by a radiation heating mechanism. In the online gas protection control system (18), the protective gas pressure at the powder outlet is monitored and controlled by the flow pressure sensor (15). The protective cover (2) is filled with protective gas and monitored in real time. At the same time, the flow rate of the protective gas can be adjusted. The pressure inside the protective cover (2) is uniform and constant, which can reduce the phenomenon of uneven blowing or uneven distribution of protective gas and powder due to unstable gas pressure. The primary protective gas pipe (12) and the secondary protective gas pipe (13) of the cladding nozzle (4) deliver inert protective gas to the cladding area and the powder feeding area, isolating the gas in the working area of ​​the laser cladding head (3) from the outside air. The radiant heating mechanism (5) is powered on to raise the temperature of the heating device (10). The heating device (10) heats the area of ​​the structural component substrate to be laser cladding through the close-range thermal radiation effect, which can reduce the temperature gradient difference between the substrate material and the cladding layer material at the beginning and end of the cladding process. It makes up for the shortcomings of the small range of protective gas of the powder feeding mechanism (6), and at the same time ensures the stability of the gas pressure in the powder outlet and cladding area and the atmosphere of inert gas protection, so as to avoid the generation of porosity defects caused by air mixing into the molten pool during the cladding process. The laser cladding process for online gas-protected and radiant-heated structural components under multi-field action includes the following steps: 1) Before the laser cladding process, the radiation heating mechanism (5) is powered on to preheat the structural parts to be clad for a certain period of time. Inert protective gas is introduced into the protective cover (2) and the protective gas pressure and flow rate are adjusted according to the cladding powder formula and the diameter of the cladding nozzle (4). The gas pressure of the online gas protection control system (18) is set. The gas pressure inside the protective cover (2) is monitored and kept uniform and stable by the gas pressure measuring instrument (14). When the gas pressure changes, the flow rate of the introduced protective gas can be adjusted by the flow pressure sensor (15) to make the internal pressure uniform and stable. 2) After preheating, inert protective gas is introduced into the secondary protective gas pipe (13) and the online gas protection control system (18) controls the protective gas pressure and flow rate according to the feedback signal from the flow pressure sensor (15). When the environment is stable, the laser generator (16) connected to the laser cladding head (3) starts to emit light, and the powder feeding mechanism (6) feeds powder synchronously. The motion shaft (1) drives the laser cladding head (3) to move as a whole according to the set laser cladding process path, while ensuring that the protective gas pressure in the area around the cladding nozzle (4) is consistent and stable. 3) After the cladding is completed, the laser generator (16) of the laser cladding head (3) stops emitting light, and then the powder feeding mechanism (6) stops conveying powder material. The radiation heating mechanism (5) maintains and controls the cooling rate of the structural parts and the cladding layer for a certain period of time based on the cooling rate obtained from the previous calculation. 4) Finally, the radiant heating mechanism (5) is powered off and stops heating, the online gas protection control system (18) stops working, and the motion axis (1) is reset. The laser cladding device used in this laser cladding method includes a laser cladding head (3), a powder feeding mechanism (6), a protective cover, a radiation heating mechanism, and an online gas protection mechanism; Among them, the laser cladding head (3) is connected to the laser generator (16), the powder feeding mechanism (6) is coaxial with the laser cladding head (3) and realizes the coaxial feeding of the laser optical path and the powder, and the laser cladding nozzle (4) includes a gas protection structure. The online gas protection mechanism includes a primary protective gas pipe (12) installed inside the protective cover and a secondary protective gas pipe (13) installed at the cladding nozzle (4). The primary protective gas pipe (12) is connected to the protective cover (2) by connecting bolts (17). The primary protective gas pipe (12) and the secondary protective gas pipe (13) deliver inert protective gas to the cladding area and the powder feeding area. The inlet ends of the primary protective gas pipe (12) and the secondary protective gas pipe (13) are connected to the online gas protection control system (18). Among them, the secondary protective air pipe (13) is equipped with a flow pressure sensor (15), the motion shaft (1) is equipped with a protective cover (2), and the protective cover (2) is equipped with a pressure measuring instrument (14); The online gas protection control system (18) can ensure that the protective gas pressure inside the protective cover (2) and the powder feeding area is completely consistent with the protective gas pressure of the cladding nozzle (4), thereby isolating the air in the cladding area.

2. The laser cladding method for online gas protection and radiation heating structural components according to claim 1, characterized in that, The secondary protective gas pipe (13) of the radiant heating mechanism (5) and the online gas protection control system (18) is installed at the cladding nozzle (4) through the flange (7) and moves synchronously with the laser cladding head (3).

3. The laser cladding method for online gas protection and radiation heating structural components according to claim 1, characterized in that, In the online gas protection control mechanism, the primary protection gas pipe (12) is fixed to the protective cover (2) by bolts, and the secondary protection gas pipe (13) is fixed to the flange (7) of the cladding nozzle (4) to deliver inert protective gas around the powder feeding area; The gas pressure and gas flow rate are monitored by the flow and pressure sensor (15) and fed back to the online gas protection control system (18) in real time to accurately control the flow rate and gas pressure of the secondary protection gas pipe (13); A pressure measuring instrument (14) is installed at the air outlet on the edge of the protective cover (2) to monitor the internal air pressure of the protective cover (2) in real time and feed it back to the protective gas control system to control the gas flow of the first-level protective gas pipe (12).

4. The laser cladding method for online gas protection and radiation heating structural components according to claim 1, characterized in that, The protective cover (2) is installed on the motion shaft (1). The protective cover (2) has an opening to ensure that the light and powder output of the laser cladding head (3) are not affected. The primary protective gas pipe (12) is connected to the protective cover (2) by connecting bolts and filled with protective gas. The protective cover is equipped with multiple air pressure measuring instruments (14) to monitor the air pressure inside the protective cover (2) in real time and ensure that the internal air pressure is consistent with the protective air pressure of the cladding nozzle (4).

5. The method of laser cladding of a structure with online gas protection and radiation heating according to claim 1, characterized in that, The radiant heating mechanism (5) connects the fastening screw (8) to the adapter block (11) and the flange (7). The height of the heating device (10) of the radiant heating mechanism (5) is adjustable. The heating rate and cooling rate of the substrate and the cladding layer are controllable. It is electrically heated. The outer shell is made of heat-insulating ceramic (9). During cladding, the heating device (10) is 1-2 mm away from the substrate surface of the structural component to be clad, so as to achieve radiant heating while preventing scratches on the workpiece surface. The heating temperature can be continuously adjusted by the parameters of the temperature control system. The heating temperature range is 0-800℃, which is suitable for multiple process parameters, multiple powder formulations and multiple substrate materials.

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