Chinese Journal of Lasers, Volume. 48, Issue 10, 1002201(2021)
Back Strike and Its Protection of Laser Machining of Microholes on Thin-Walled Cavity
Figures & Tables(22)
Fig. 1. Schematic diagram of back strike caused by fabrication of micro-holes on thin-walled cavity parts such as turbine blades using laser machining. (a) Turbine blade; (b) flat thin-walled cavity
Fig. 3. Schematic diagrams of laser processing methods. (a) Tap drilling; (b) trepan drilling; (c) scan filling drilling
Fig. 4. Schematic diagrams of cavity simulation of back strike protection experiment. (a) Triangular prism cavity; (b) quadrilateral prism cavity
Fig. 5. CTQ verification device for back strike protective materials. (a) Schematic diagram of device; (b) photos of device and the back strike
Fig. 6. Filling and removing experiments of water-soluble back strike protective materials. (a) Without filling; (b) filling PAM; (c) immersion in water; (d) after soaking for 8 h; (e) thin-walled cavity simulated piece after material is removed
Fig. 7. Microholes and back strike processed under different energy densities and cavity thicknesses. (a) 1 mm; (b) 3 mm
Fig. 10. Morphologies and sizes of back strike pit at different scanning speeds. (a)(b) 100 mm/s;(c)(d) 1000 mm/s
Fig. 13. Cross section of micro-holes in 7075 aluminum alloy tri-prism cavity unfilled with protective material and depth of back strike pit varying with drilling time. (a) Cross section of micro-holes; (b) depth of back strike pit varying with drilling time
Fig. 14. Depth of back strike pit varying with drilling time after 7075 aluminum alloy triangular prism cavity is filled with different protective materials. (a) Paraffin; (b) PUR; (c)(d) PAM
Fig. 15. Cross-section of 7075 aluminum alloy quadrangular cavity and its micro-holes and back strike. (a) 6 mm cavity; (b) 2.5 mm cavity;(c) 1 mm cavity
Fig. 16. Depth of back strike pit varying with processing time after 7075 aluminum alloy quadrangular cavity is filled with PAM for different flow velocity. (a) 1.5 m/s; (b) 2.0 m/s; (c) 2.5 m/s; (d) 3.0 m/s
Table 1. Chemical compositions of 7075 aluminum alloy (mass fraction)%
View tableTable 1. Chemical compositions of 7075 aluminum alloy (mass fraction)%
Cu Si Fe Mn Mg Zn Cr Ti Others Al 2.00 0.40 0.50 0.30 2.80 6.10 0.40 0.06 ≤0.15 Balance
Table 2. Physical and chemical properties of partial filling materials
View tableTable 2. Physical and chemical properties of partial filling materials
Material Melting point /℃ Boiling point /℃ Properties PUR 105--115 Unfixed Transparent, easy to discharge bubbles, and high viscosity after softening PAM Unfixed Unfixed Softening temperature is larger than 10 ℃; vitrification temperature is 188 ℃ Paraffin 47--65 >371 Insoluble in water; soluble in gasoline, acetone, etc. Graphite 3652 4827 Ignition point of graphite in air is 850--1000 ℃ SiO2 1650±50 2230 Abundant in production and low in price WC 2870 6000 High melting and boiling points
Table 3. Experimental parameters
View tableTable 3. Experimental parameters
Focal length of galvanometer / mm Energy density / (J·cm-2) Processing time /s Scanning speed / (mm·s-1) Focal shift /mm 160 31.067--64.596 10--60 100--2000 -2--2
Table 4. CTQ of for back strike protective materials
View tableTable 4. CTQ of for back strike protective materials
CTQ Fluid Colloid Solid Transparency Yes/no Yes/no Yes/no Fillability Porosity Porosity Porosity Removability Residual ratio Residual ratio Residual ratio Corrosivity Yes/no Yes/no Yes/no Self-sufficiency Yes/no Yes/no Yes/no Comprehensive Unsuitable/to be determined/alternative/optional/preferred
Table 5. Scanning speed and depth of back strike pit
View tableTable 5. Scanning speed and depth of back strike pit
Scanning speed / (mm·s-1) Depth of back strike pit 1 mm 2 mm 3 mm 4 mm 5 mm 6 mm 100 448.18 420.77 390.20 321.88 269.73 171.20 200 446.94 409.11 384.44 331.99 279.84 181.31 300 455.27 400.52 381.95 302.65 250.50 151.97 400 434.42 386.86 374.91 284.98 232.83 134.30 500 395.53 349.50 321.40 279.78 227.63 129.10 1000 379.09 339.36 316.01 273.82 221.67 123.14 1500 382.97 341.67 283.65 205.14 152.99 54.46 2000 375.33 321.82 288.72 183.86 131.71 33.18
Table 6. Preliminary CTQ verification results of back strike protective materials
View tableTable 6. Preliminary CTQ verification results of back strike protective materials
CTQ Colloid Colloid/solid Solid PUR PAM Paraffin Graphite SiO2 WC Transparency No No No No No No Fillability 3% porosity 1% porosity 2% porosity 2% porosity 5% porosity 3% porosity Removability 1% residual No residual 1% residual 1% residual 2% residual 1% residual Corrosivity No No No No No No Self-sufficiency Yes Yes Yes No No No Comprehensive Alternative Preferred Alternative Unsuitable Unsuitable Unsuitable
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Bin Wang, Yuezhuan Liu, Yufeng Wang, Wenwu Zhang. Back Strike and Its Protection of Laser Machining of Microholes on Thin-Walled Cavity[J]. Chinese Journal of Lasers, 2021, 48(10): 1002201
Paper Information
Category: Laser Micromachining
Received: Sep. 16, 2020
Accepted: Dec. 8, 2020
Published Online: May. 7, 2021
The Author Email: Wang Bin (wankoran@126.com), Zhang Wenwu (zhangwenwu@nimte.ac.cn)
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