In 3D printing, due to the expansion of the heating material and the shrinkage of the cold material, residual stress accumulates in the part during printing, and the resulting force deforms the part and causes cracks, which weaken or tear the part, especially It is in metal. Researchers at Lawrence Livermore National Laboratory (LLNL) and the University of California at Davis are using laser diodes to solve this problem. The diode is a high-power laser borrowed from the LLNL National Ignition (NIF), which quickly heats the printed layer during construction. Its research was successfully published in Additive Manufacturing. By enabling researchers to reduce temperature gradients (difference between cold and hot extremes) and control cooling rates, the technology reduces the effective residual stress of metal 3D printed test components by 90%. John Roehling, the first author of the paper, said: In the metal field, it is really difficult to overcome these pressures. We have done a lot of work to change the scanning strategy to redistribute residual stress, but the basic method is to build Eliminate the parts when they are there so that there are no such problems. With this method, residual stress can be effectively eliminated, so that component failures do not occur during the construction process. For research, LLNL engineers and co-first author Will Smith built a small bridge-like structure with a 316L stainless steel laser powder bed (LPBF) process. Let each layer cure first, then illuminate the surface with a diode, starting with full power and then quickly reducing the intensity in 20 seconds. The result is like placing the part in the furnace after each layer because the surface temperature reaches about 1000 degrees Celsius (1832 degrees Fahrenheit). The legs of the finished product are thick and the overhanging part is very thin. The researchers can cut off one of the legs and analyze how much the weaker overhanging part moves. To measure how much residual stress is reduced, when the diode is used, the bridge is no longer deflected. The manufacture of these components works similarly to ordinary metal 3D printers, but the machine innovation of this research is that a secondary laser is used, which projects into a larger area and then heats the part - it rises rapidly The temperature is then slowly cooled in a controlled manner. When diodes were used, a tendency to reduce residual stress was found, as compared to the traditional practice of annealing parts in an oven. This is a good result and shows how effective the technology is. This method is a branch of a previous project. In this project, a laser diode (developed to smooth the laser in NIF) was used to print the entire metal layer 3d at a time. This method is superior to other common methods of reducing the residual stress of metal parts, such as changing the scanning strategy or using a heated build plate. Because this method is heated from the top, there is no limit to the height of the part. The researchers will next go into more in-depth research, turning their attention to increasing the number of layers per heating cycle to see if they can reduce residual stress to the same extent, try more complex parts, and use more quantitative techniques. Get a deeper understanding of the process. This technology can scale up. Because there is currently only a relatively small area to plan, there is still much room for improvement. By adding more diode lasers, you can add more heating area if anyone wants to integrate it into a system with a larger print area. More importantly, researchers will explore the phase transition of titanium alloys (Ti64). Typically, when built with Ti64, phase changes can cause the metal to become very fragile, causing the part to crack. If researchers can avoid this transition by slowly cooling the part, the material can be extended to aerospace standards.