The surface integrity of machined metal components is critical to their in-service functionality, longevity and overall performance. Surface defects induced by machining operations vary from the nano to macro scale, which cause microstructural, mechanical and chemical effects. Hence, they require advanced evaluation and post processing techniques. While surface integrity varies significantly across the range of machining processes, this paper explores the state-of-the-art of surface integrity research with an emphasis on their governing mechanisms and emerging evaluation approaches. In this review, removal mechanisms are grouped by their primary energy transfer mechanisms; mechanical, thermal and chemical based. Accordingly, the resultant multi-scale phenomena associated with metal machining are analyzed. The contribution of these material removal mechanisms to the workpiece surfaces/subsurface characteristics is reviewed. Post-processing options for the mitigation of induced surface defects are also discussed.

Surface integrity in metal machining - Part I: Fundamentals of surface characteristics and formation mechanisms

UV laser high-quality drilling of CFRP plate with a new interlaced scanning mode

Film cooling holes (FCHs) of nickel-based single crystal turbine blades were drilled by 532 nm Nd:YVO4 nanosecond laser in coaxial waterjet-assisted environment. Microstructure of the side wall of the FCHs was mainly investigated by means of transmission electron microscopy. The average thickness of heat affected zone (HAZ) around FCHs decreases with increasing of water flow rate. The main phase within HAZ evolves from β-NiAl to β-NiAl + γ-Ni with the increase in the water flow rate. Some γ-Ni particles in the HAZ twined along (111) plane. A small portion of the FCHs are free of HAZ when drilled by coaxial waterjet-assisted laser drilling at a laminar water flow rate ≥3.1 m/s. There are no processing-induced defects including HAZ, microcrack, and phase transformation around the FCHs when drilled at the water flow rate ≥5.1 m/s. The FCHs with high surface quality can be drilled by the coaxial waterjet-assisted laser drilling. Finally, effects of fluid water on drilling quality of the FCHs were discussed.

Coaxial waterjet-assisted laser drilling of film cooling holes in turbine blades

Dual-beam laser drilling process for thick carbon fiber reinforced plastic composites plates

Carbon fiber-reinforced polymer composites (CFRP) is a composite material with resin as matrix and carbon fiber as reinforcement. It has been widely used in aerospace, military products, and automotive industries. However, CFRP is prone to damage because of its complex anisotropy and low interlayer strength, so it is a typical difficult-to-process material. Water jet guided laser processing technology is a combination of laser and water jet processing technology, which has the characteristics of no wear, no contact, flexible processing, and potential advantages of reducing HAZ and increasing cutting depth. In this paper, the water jet guided laser processing technology is used to perform cutting experiment for CFRP processing of low damage and large depth. In the experiment, the influencing law of the process parameters such as laser power, CFRP feed speed and water jet speed on the cutting results is obtained; then the cutting thickness of 1 mm, 2 mm, 4 mm and 10 mm CFRP is realized by adopting the parallel path layered scanning method. Moreover, the influences of carbon fiber arrangement direction and laser cutting path on the CFRP cutting damage mechanism are analyzed for the first time, and three damage mechanisms (exposing, falling-off and pulling-out) are summarized, which will provide the reference for the high precision cutting of large thickness CFRP.

The cutting process and damage mechanism of large thickness CFRP based on water jet guided laser processing

Study on immersion waterjet assisted laser micromachining process

At present, waterjet-assisted laser processing technologies are disadvantaged by low coupling power and poor process reliability, which significantly affect processing efficiency and depth. To address these shortcomings, we propose herein a novel water-gas shrinkage-guided high-power laser processing (WSLP) technology. Firstly, the characteristics of the laminar flow and the light guiding of the water-gas coupled device are optimized. The laminar simulation results show that the water-gas contraction ratio and laminar flow length can be adjusted by changing the water/gas pressure and structural parameters. Secondly, light guiding simulation reveals with a 532 nm 1000W laser, the light guiding efficiency of the shrinkage interface can reach more than 95% within the range of the axial offset 22.1 mm, radial offset 0.62 mm and angular offset 15.8° of the laser focus. Compared with the traditional waterjet-assisted laser processing method, the anti-disturbance capability of the WSLP method is increased by 3.8 times in the axial direction, 2.3 times in the radial direction, and 1.5 times in the angle offset. Thirdly, the feasibility of the laser conduction and processing with this water-gas shrinkage method is verified by experiments. The formation conditions and the relationship of the water-gas laminar flow are investigated. The result shows that the laser coupling efficiency can reach 93% in the low power condition. The research can provide technical support for large depth laser precision machining, in the future.

Gas shrinking laminar flow for robust high-power waterjet laser processing technology

The synchronized laser and shaped tube electrochemical machining (Laser-STEM), a hybrid machining process that combined the advantages of electrochemical machining (ECM) and laser beam machining (LBM), has been proposed and studied. The mechanisms of Laser-STEM were studied theoretically and experimentally. Mathematical model has been developed to study the effects of laser-induced thermal effects on the electrochemical dissolution rate. The influences of electrolyte concentration and laser power on the laser attenuation coefficient have been studied. Results showed that the side gap could be decreased by 62.7% and the feeding rate could be raised by 108% when utilizing Laser-STEM with a proper laser power for drilling small holes, compared with that without laser assistance. Moreover, the performance of Laser-STEM has been investigated, in terms of laser power and pulsed voltage. Experimental results showed that the machining efficiency increased with higher laser power, pulse voltage, and feeding rate, and the precision could be improved with the higher laser power and feeding rate and a smaller pulsed voltage. Finally, small holes with a diameter of 1.25 mm and free of recast layer have been fabricated on the aluminum alloy workpiece of 5 mm in thickness.

Fabrication of deep and small holes by synchronized laser and shaped tube electrochemical machining (Laser-STEM) hybrid process

The invention discloses a water-jet guided laser processing device and system, and belongs to the technical field of laser processing. The water-jet guided laser processing device comprises a frame structure, a laser transmitting pipeline and a laminar flow assembly; the frame structure sequentially comprises a focusing chamber, a liquid chamber and a gas chamber from top to bottom; the laser transmitting pipeline is fixed into the liquid chamber in the propagation direction of lasers, and a window filter is fixed to the lower end of the laser transmitting pipeline; and a liquid inlet is formed in the liquid chamber, the laminar flow assembly is fixed into a first annular space formed by the laser transmitting pipeline and the liquid chamber to enable liquid entering the liquid chamber toform a stable laminar flow in the propagation direction of the lasers, and thus the lasers emitted from the laser transmitting pipeline are wrapped. According to the water-jet guided laser processingdevice, the total reflection efficiency of the lasers is improved, the coupling power between the lasers and the liquid is increased, thus the high-power coupled water-jet guided lasers are obtained,and the processing depth of the lasers is increased.

Water-jet guided laser processing device and system

The invention discloses a rotary-type laser processing device, application thereof, and a laser processing system and method. The rotary-type laser processing device comprises a supporting part and acontraction flow conduction device; liquid coupled with a laser is led into the supporting part; the contraction flow conduction device is arranged below the supporting part and communicates with thesupporting part; a liquid chamber and a packaging gas layer are arranged in the contraction flow conduction device; the packaging gas layer is arranged outside the liquid chamber; the cross section diameter of the liquid chamber is gradually decreased in the transmission direction of the laser to form a conduction end, and a spindle of the conduction end and a laser main laser shaft are inclined in an acute angle mode; and the contraction flow conduction device automatically rotates around the laser main laser shaft. On the other hand, the invention further provides application of the rotary-type laser processing device, and the laser processing system and method.

Rotary-type laser processing device, application thereof, and laser processing system and method

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