Precision Surface Machining Technology
Compilation of monographs
Research progress of laser cleaning technology for typical materials
ZHAO Haichao;SONG Qiliang;WANG Rui;QIAO Yulin;MA Yufan;SUN Chuanwei;Army Armored Corps Academy;[Objective] Compared to traditional cleaning technology i.e. mechanical and chemical cleaning, laser cleaning technology has advantages such as being pollution-free, consumable-free, and non-damaging to the substrate.[Method] The mechanism and classification of laser cleaning technology were elaborated. The research and application status of laser cleaning technology on surface cleaning of materials i.e. stones, aluminum alloys, titanium alloys,magnesium alloys, and carbon steels were summarized. [Result] The development prospects of laser cleaning technology were discussed. [Conclusion] As an efficient and environmentally friendly surface treatment technology, laser cleaning has broad application potential in fields such as aerospace, shipbuilding and marine engineering, and precision instrument manufacturing.
Step-by-step process for ablation and polishing of mold steel surface by picosecond laser
ZHU Shengwang;JI Chenglong;WANG Chengjin;WANG Zhiwen;[Objective] The deep scratches generated during the manufacturing process of tire molds need to be removed to reduce surface roughness. [Method] A picosecond pulsed laser was employed for a step-by-step ablation and polishing test. The scratches on mold surface were removed by laser ablation and laser polishing successively. The optimal process parameters were explored by designing an orthogonal test for laser ablation and single-factor experiments for laser polishing. [Result] By laser abrasion at laser fluence 0.11 J/cm~2, scanning rate 10 mm/s, and scanning spacing 0.01 mm, scratches with a depth of about 38 μm were effectively removed, and the material removal mechanism was identified as ablation vaporization. In the second step of laser polishing at laser fluence 0.39 J/cm~2, scanning rate 1250 mm/s, and scanning spacing 0.018 mm, the surface roughness(Ra) of the material was reduced from(1.404 ± 0.132) μm to(99 ± 18) nm with a total reduction rate of 92.9%, and the laser polishing mechanism was characterized as shallow surface remelting. The surface microhardness was increased from(235.9 ± 17.3) HV to(316.3 ± 6.5) HV after the two-step laser treatment. [Conclusion] This step-by-step laser ablation and polishing process can produce a smooth, scratch-free, and high-hardness 35 steel surface, which facilitates the release process in subsequent vulcanization process.
Multilevel texturing of 304 stainless steel by combination of chemical etching and laser processing and its tribological properties
WENG Wenfeng;WAN Peng;CAO Dahua;LI Wenxuan;JIA Dan;[Objective] Aiming at the problem that the surface micro-and nano-structures prepared by laser processing are prone to be worn and damaged under external mechanical force, a method combining chemical etching and laser processing was proposed to construct multilevel texture on surface of 304 stainless steel. [Method] Chemical etching was conducted initially to form primary texture on 304 stainless steel, followed by laser processing to create secondary texture with an area density of 20%. The microstructure, composition, phase structure, and microhardness of 304 stainless steel after multilevel surface texturing were studied. The effect of surface texture shape on the tribological properties of 304 stainless steel under edible oil lubrication was also studied. [Result] Some regularly arranged convex points were formed on surface of 304 stainless steel after chemical etching, and its average friction coefficient was decreased by 16%. The 304 stainless steel underwent remelting and hardening after further laser processing, forming droplet-like spots with a diameter of about 55 μm. The microhardness was increased to(205.4 ± 36.2) HV, and the average friction coefficient was decreased. When the surface texture constructed by laser processing was square, the 304 stainless steel had the lowest average friction coefficient of 0.085, demonstrating the best wear resistance and friction reduction performance. [Conclusion] Stable multilevel textures can be constructed on surface of stainless steel by combining chemical etching and laser processing, which helps promote the application of stainless steel materials in the field of wear resistant, friction reducing, and non-stick fields.
Electrolytic polishing of 316L stainless steel sintered at high temperature
ZHANG Shuo;LIANG Xiao;SHU Chunhui;ZHU Qingqing;ZHAO Xuetong;YAN Ailin;WANG Zhenwei;WANG Yu;[Objective] The formation of a compact gray-black oxide film on the surface of stainless steel after high-temperature sintering adversely affects its subsequent processing and application. Therefore, corresponding measures needs to be taken to remove the oxide film. [Method] The 316L stainless steel subjected to high-temperature oxidation was treated by etching and pickling prior to electrolytic polishing. The pickling solution composition and process conditions were optimized through orthogonal test and single-factor experiments. The effects of current density and temperature during electrolytic polishing on the surface roughness and corrosion resistance of 316L stainless steel were studied in detail. Additionally, changes in surface profile and microstructure of 316L stainless steel after different processing steps were compared. [Result] The pickling solution composition and process conditions were optimized as follows: hydrochloric acid 220 mL/L, sulfuric acid 70 mL/L, metal salt X 60 g/L, temperature 70℃, and time 6 min. The suitable current density and time for electrolytic polishing was 50 mA/dm2 and 85 s respectively. After being treated under the optimized conditions, the surfaceof 316L stainless steel was uniform and smooth with a surface roughness(Ra)of 0.326 2 μm, and its corrosion resistance was significantly enhanced. [Conclusion] The oxide film on surface of high-temperature oxidized 316L stainless steel can be effectively removed through etching and pickling as pretreatments before electrolytic polishing, not only reducing the surface roughness, but also significantly improve its corrosion resistance.
Electrolytic polishing of nitinol cardiovascular stent
WANG Yali;LI Zhiyong;ZHANG Wei;YU Yazhou;CHAI Mingxia;[Objective] The surface quality of nickel–titanium alloy(NiTi) components prepared by selective laser melting(SLM) technology is often poor with partially melted powders attaced to its surface. Therefore, appropriate surface treatment is necessary. [Method] Nitinol cardiovascular stent manufactured by SLM technology was electrochemically polished in an electrolyte composed of sodium chloride and ethylene glycol. The effects of voltage,temperature, and polishing time on the surface roughness of nitinol cardiovascular stent were studied. The surface morphology, chemical composition, and surface wettability of the stent electrochemically polished under the optimized conditions were analyzed. [Result] The electrochemical polishing process parametrs were optimized as follows: voltage 25 V, temperature 28 ℃, and polishing time 25 min. The surface of the nitinol stent became smooth and uniform with a surface roughness Sa of 0.31 μm after being polished under the optimized conditions. The water contact angle of nitinol stent was increased to 103.5°, indicating that its hydrophobicity was improved. [Conclusion] Electrochemical polishing can significantly improve the surface quality of nitinol cardiovascular stents manufactured by SLM technology, thereby enhancing their biocompatibility.