One of the challenges regarding widespread use of parts made from alloy steel is their time-consuming polishing process. A rough freeform surface of part has been often expected to be polished rapidly up to a smooth surface finish. The focus of this study is to develop a fast polishing method of freeform surface by using dual-beam lasers. The dual-beam laser system consists of continuous laser (CW) and pulsed laser based on a five-axis CNC device. In this study, a series of experiments of CW laser polishing present the effects of different spot irradiation on surface topography, then the combination trajectory of zigzag and square waveform of pulsed laser is explored to realize a “melting peak for filling into valley” (MPFV) method. The polishing experiment on a semisphere of S136H steel polished by dual-beam shows that a rough semisphere surface was rapidly polished from initial state value of Sa (=877 nm) to post-polished value of Sa (=142 nm), and the polishing efficiency is as high as 2890 cm²/H.

Continuous-wave (CW) lasers are widely used in laser polishing, but with CW laser polishing, it is difficult to reduce the surface roughness to 0.2 µm from an original value exceeding 1.0 µm. The aim of this study is to develop an innovative method of laser polishing assisted by a steady magnetic field to overcome that bottleneck and produce smoother surfaces. Two experiments confirm the hypothesis that the molten pool overflows during melting peaks to flow into valleys in CW laser polishing, resulting in secondary roughness that causes the aforementioned quality bottleneck. To either reduce or eliminate this secondary roughness, a steady magnetic field is used during CW laser polishing to suppress the overflow of the molten pool. A three-dimensional surface profiler, a scanning electron microscope, and a nanometer indentation tester are used to characterize and analyze the microstructure and properties of the materials. The experimental results show that the Lorentz force due to the steady magnetic field plays an important suppression role in reducing the secondary roughness.

To increase the surface quality of the high-strength maraging steel metal materials, a new method of executing the additive manufacturing process and subtraction polishing process of maraging steel metal materials was studied. The mechanical properties of maraging steel metal materials before and after laser powder bed fusion (LPBF) polishing were compared and analyzed. The influence of laser parameters on the formability of high-strength MS metal materials was studied, with MS additive parts successfully prepared. The initial surfaces had roughness values of 6.198–7.92 μm. The metal additive manufacturing parts were polished with double laser beams. Confocal microscopy, scanning electron microscopy, and X-ray diffraction were used to obtain the microstructure and phase composition of the microstructures. The microhardness of high-strength maraging forming parts by using a microhardness tester and the mechanical properties were analyzed. The results showed that the surface roughness was considerably reduced to lengthen the service life of the high-strength MS metal materials from an initial roughness of Sa = 6.3 μm to Sa = 0.98 μm, with the surface hardness increased and the martensite content decreased after using double-laser-beam polishing.

To effectively improve the cutting quality of sapphire and optimize ultrafast picosecond laser cutting technology, this paper presents a new numerical simulation method and an experimental study of the ultrafast double-laser cutting of sapphire materials. The optimal cutting technology and the numerical simulation of the temperature field of the ultrafast picosecond laser cutting of sapphire were designed independently. The principle is based on double-laser-beam cutting using an ultrashort pulse and a CO₂ beam; the ultrashort pulse is focused on the material through a laser filamentous cutting head and perforated, and it moves at a speed of up to 200 mm/s to form the desired cutting line. Then, a CO₂ beam is used for heating, and the principle of heat bilges and cold shrink causes the rapid separation of products. Furthermore, an SEM tester was used to characterize and analyze the microstructure and properties of sapphire materials. A microscope was used to analyze the composition of the cutting micro-area and explore the general mechanism of laser cutting sapphire. The results showed that the proposed method greatly improves efficiency and precision; in addition, the chipping size of sapphire is less than 4 μm.

One of the challenges regarding the application of laser polishing in injection mold manufacturing is to eliminate the tensile residual stress on a polished cavity surface without the extra expenses of an annealing vacuum furnace. This study aims to develop a fast laser annealing method using a dual-beam laser system by which a mold cavity can be laser-polished and then laser-annealed. Fourteen mold steel specimens were laser-polished by a dual-beam laser, resulting in a roughness reduction from the initial state, Sa 1.11 μm, to Sa 0.16 μm, a smoother surface finish. A numerical simulation of laser annealing using the current CW laser was implemented to optimize the laser annealing parameters to guide the experiment of CW laser annealing. XRD measurement results showed that the tensile residual stress dropped from an initial 638 MPa to 10 MPa in an annealing cycle time of 40 min at 750 °C; therefore, fatigue cracks or stress corrosion cracks (SCC) on the mold cavity will no longer occur. Confocal microscopy, X-ray diffraction, and scanning electron microscopy were used to obtain the microstructure and phase composition of the microstructures, demonstrate that laser polishing and laser annealing by a dual-beam laser is a fast and effortless technique which can be effectively employed in injection mold manufacturing.