One of the disadvantages of modern industrial technologies for laser three-dimensional printing is strong heating at the point of contact of the metal with the laser light beam. This heating melts the metal powder, but it also leads to the appearance of areas of internal mechanical tension and deformation of the workpiece. And all these things are practically impossible to predict, which makes it impossible to somehow compensate for them. However, a team of researchers from the University of Cambridge found a way to solve the problem described above. Using special holographic images generated by a computer using complex algorithms, it is possible to control the distribution of laser light energy in three dimensions, which avoids unnecessary heating of the manufactured part.
“Instead of using a single beam of light from a high-power laser, we use several beams of laser light that are focused in a special way at the desired point in three-dimensional space”, says Professor Tim Wilkinson, project manager, “This allows us to print parts in a more three-dimensional way, and avoid the occurrence of thermal deformation”.
The hologram used to print a three-dimensional object is calculated and changed by a computer at a speed of about a thousand times per second to improve control over the distribution of energy. At the same time, the algorithms that produce the control hologram take into account a number of subtleties, such as the properties of the materials used, optical distortions, current temperature, etc. “This holographic approach allows us to do things that were impossible to do before. There are certain types of structures that cannot be printed due to thermal deformations,” says Professor Wilkinson.
Now scientists have already created an experimental setup with three lasers, the rays of which are reflected from the silicon “microdisplay”, a thin layer of liquid crystals on the surface of a silicon chip, which acts as a controlled diffraction grating and changes the phase of the reflected laser light beam. And in the near future, Cambridge researchers plan to create a more advanced installation in which eight lasers will be used, with a total power of 200 W, which is enough to melt particles of aluminum powder.
In addition to checking the operation of liquid crystal microdisplays at this level of laser light power, scientists, with the help of a new installation, will work with metal powders with the addition of plastics and resins to improve the algorithms for composing control holograms. According to plans, a new and more powerful installation will begin to work in 2020, and this project, which should result in a fully operational industrial installation, will be completed by 2022.