Aviation Application Overview
Laser metal additive manufacturing technology plays a decisive role in the development of the aviation industry. Laser cladding technology can improve the surface hardness, wear resistance, corrosion resistance, and fatigue resistance of aerospace parts under harsh working conditions, increase the service life of materials, and can also be used to repair worn parts and save processing. cost. Laser metal 3D printing technology is applied to the rapid manufacturing of aircraft parts, which can reduce the manufacturing process of workpieces and improve the quality of parts. In foreign countries, major aerospace engine manufacturing companies such as GE, Rolls-Royce, and Prewitt have begun to develop the application of laser additive manufacturing technology in the molding, manufacturing, and repair of aerospace parts as early as the 1980s. Among them, is laser additive repair of high-pressure turbine blades It has been a mature technology for 20 years and is widely used in repairing turbine blade tips and deep cracks in commercial aircraft engines.
Laser additive technology is applicable to a wide range of material systems, including high-strength steel, aluminum alloys, nickel-based high-temperature alloys, cobalt-based high-temperature alloys, titanium alloys, etc. in aircraft and aero-engine maintenance. Laser additive technology is currently the most feasible technical method for additive repair of some engine hot-end components. At present, the development of laser additive repair processes for commonly used nickel-based high-temperature alloys, such as IN625, Waspaloy, IN718, IN738, etc., has been relatively mature. A large amount of literature data reports the microstructure and mechanical properties of repaired parts, as well as optimized Post-repair heat treatment plans. Direct laser metal deposition of nickel-based superalloys, after optimized heat treatment, has properties higher than castings and comparable to forgings.
According to the existing theory on the growth of oriented crystal structures in laser direct forming, a top-down ultra-high temperature gradient (up to 10^6K/m) is formed between the molten pool and the substrate during the laser direct forming process. Under the ultra-high cooling rate, the molten pool solidifies instantly (the solidification rate can reach 24mm/s), causing the microstructure of the cladding layer to exhibit a forced directional crystal growth pattern along the Z-axis. Therefore, the temperature gradient is the main driving force affecting the growth of oriented crystals. In order to obtain a well-oriented crystal structure, the bottom of the substrate must be convectively cooled to increase the temperature gradient. However, no matter what method is used to cool the substrate to increase the temperature gradient, The temperature gradient in the areas on both sides of the molten pool still does not follow the Z-axis direction. This is because it is in direct contact with the surrounding protective gas and transfers heat. The cooling rate is also very fast, causing the temperature gradient in the R direction to begin to affect the oriented crystal. The growth is affected, and with the continuous accumulation of heat during the forming process, the temperature gradient in the Z direction decreases, and the influence of the temperature gradient in the R direction becomes more and more obvious so that the growth direction of the oriented crystal is deflected and cannot be along the Z axis. Directional epitaxial growth ultimately affects the microstructure and properties of the entire formed part.

Temperature closed-loop control software introduction
In order to overcome the above-mentioned problem of temperature gradient deflection on both sides of the molten pool during the forming process of high-temperature alloys, the Huirui cladding system provides a method of induction heating to control the directional growth of high-temperature alloys directly formed by the laser. This method ensures that the entire molten pool area is in the solidification process. The positive temperature gradient along the Z direction is maintained, so that the formed part has a more complete oriented crystal structure that grows epitaxially along the Z axis.
The induction heating system uses high-frequency induction heating equipment, which can efficiently heat thin-walled structural parts. A high-performance two-color infrared thermometer is used to monitor the preheating temperature of parts in real-time, and the workpiece temperature can be accurately and stably measured in the temperature range of 600-1400°C. The angle and attitude of the thermometer can be adjusted through the software interface, making it easier to aim at the heated workpiece and achieve accurate measurement.
The picture below shows the temperature feedback control software independently developed by Huirui Company. It can adjust and control the induction heating power in real-time through the computer to stabilize the workpiece heating temperature within the range of +/-5℃ of the set temperature. Curves of different colors in the software interface curve represent respectively the set temperature value, the measured temperature value, and the heating power setting value.
The first stage of the curve is the open-loop control stage, where the heating power is constant and the temperature ramps up;
The second stage is the controller tuning stage, where the heating power and measured temperature oscillate and then converge;
The third stage is the stabilization stage, where the measured temperature stabilizes near the set stability.
After adopting temperature closed-loop control, reasonable heating, insulation, and cooling curves can be set according to the actual conditions of the material and workpiece to achieve a precise heat treatment process in the laser repair process. This process is very important for the repair of high-temperature alloys. The structure is regulated by precise temperature control to ensure that there is no cracking during the laser additive process. The ideal mechanical properties can be achieved without further heat treatment after laser additive.
The induction preheating closed-loop temperature control can also work simultaneously with the molten pool closed-loop control system to jointly ensure process stability and consistency.