Laser surface hardening is one of the effective methods to enhance the mechanical properties of localised surface area of engineering parts made of different types of steels and other metals like ultra-high strength steel etc. Laser surface hardening has many advantages over conventional hardening process like, self-quenching, very fast, control over energy input and localised hardening etc. In order to further improve the surface quality and mechanical properties of 30CrMnSiNi2A ultra-high strength steel parts fabricated by laser deposition manufacturing (LDM). The quenching modified layer was prepared on the surface of 30CrMnSiNi2A steel by laser quenching technology. This work presents the effect of different laser parameters on the surface morphology and mechanical properties of 30CrMnSiNi2A steel after laser hardening. The experimental data of OM morphology, microstructure, micro-hardness and wear property of hardened layer were analyzed by using the methods of range analysis. Effects of these parameters over the micro hardness of the surface are described. It has been found that, there is around 20% increase in hardness after laser hardening. It considerably debased the surface roughness and wear rate of LDM 30CrMnSi2A alloy parts, which has decreased by 53% and 57% than without laser surface hardening parts. Accordingly, industrial applications of laser deposition manufacturing 30CrMnSi2A alloy parts were supposed to be widened by this study.
Aiming at the problems of tool wear and poor consistency in the mechanical subtraction of Inconel718 nickel-based superalloy complex structural parts in the laser additive and subtractive manufacturing process. In this paper, the short pulse laser is used to perform precision subtractive processing of Inconel 718 superalloy continuous laser deposition manufacturing (LDM) parts. This paper focuses on the research of short pulse laser milling and scanning technology of Inconel718 LDM. Based on the Response Surface Method, the influence of process parameters such as scanning speed, hatch distance and scanning times on the shape accuracy of the inner channel, surface roughness, material removal rate and recast layer was explored. The optimal milling process parameters are obtained as follows: the laser power is 100 W, the scanning speed is 6000 mm / s, the scanning times are 800, and the hatch distance is 0.02 mm.
Carbon Fiber Reinforced 1Plastic (CFRTS) and TC4 titanium alloy have excellent properties such as high stiffness, fatigue resistance and corrosion resistance, which are widely used in aerospace and new energy vehicle manufacturing. Due to the great differences in physical and chemical properties between CFRTS and TC4 titanium alloy, the traditional bonding and riveting methods have the problems of aging and stress concentration. This study introduces the interface composite control process of “picosecond laser cleaning and plastic-covered”. Firstly, CFRTS was subjected to laser cleaning pretreatment to remove the surface epoxy resin. Secondly, laser was used to pretreat the surface microstructure of TC4 titanium alloy. A layer of 0.02 mm PA powder was spread on the surface of the microstructure and melted by laser to form a plastic-covered layer. Finally, the treated CFRTS and TC4 titanium alloys were welded by laser-assisted joining. Compared with the traditional cleaning technology, it was found that the carbon fiber was exposed obviously and the structure was complete on the CFRTS surface after picosecond laser cleaning, and the epoxy resin was removed completely. The porosity of the joint interface is reduced, and the weld morphology is better. The shear strength of CFRTS-TC4 titanium alloy joint is significantly enhanced, and the maximum shear strength is 6333 N.
The laser deposition manufacturing (LMD) is a free-form metal deposition process, which allows generating a prototype or small series of near net-shape structures. Despite numerous advantages, one of the most critical issues of the technique is that produced pieces have a deleterious surface finish which requires post machining steps. Mechanical machining method such as milling and grinding has been used to improve the surface quality of the laser additive manufacturing components. However, the mechanical machining method has some drawbacks such as tool wearing and narrow-area difficult to machining. In this paper, we demonstrate the capability of continuous wave (CW) in polishing rough surface of additive manufactured TiAl alloy. The surface morphology, microstructures, corrosion resistance, micro-hardness and wear resistance of samples were characterized using a laser confocal microscopy (OM), scanning electron microscope (SEM), electrochemical analyzer, Vickers hardness machine, and wear tester, respectively. Results revealed that the surface roughness more than 16.06 μm could be reduce to less than 1.76 μm through laser polishing process. It was also found that a hardened layer about 600μm was produced on the TiAl alloy surface after laser finishing. The microhardness of the sample was improved about 8% compared with the mechanical milling method.
Laser additive manufacturing (LAM) is a novel technology that uses high-energy laser beam to obtain high performance entities and coatings. However, in this process, it is difficult to control the microstructure of materials effectively by changing the laser parameters. Based on this situation, we proposed a method that using direct electrostatic field (DESF) to assist LAM process. In this paper, we investigated the changes in 316L microstructure after assisted by DESF, and discuss the effect of electrostatic field. Microstructures of the 316L stainless steel sample fabricated by this method were tested. The result showed the solidification direction and grain morphology was influenced by the direction and value of DESF obviously. While the ESF direction is opposite to the laser scanning direction, the grains in the longitudinal-section perform orderly growth and the directions are biased to the laser scanning direction. While the DESF direction is the same as the scanning direction, the original solidification direction is obviously changed and the direction tended to be opposite to the scanning direction.
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