Femtosecond laser processing of fuel injectors - a materials processing evaluation

Stuart, B C ; Wynne, A

Lawrence Livermore National Laboratory

关键词: Velocity;    National Security;    70 Plasma Physics And Fusion Technology;    Energy Transfer;    36 Materials Science;   

DOI  :  10.2172/15006882
RP-ID  :  UCRL-ID-141346
RP-ID  :  W-7405-ENG-48
RP-ID  :  15006882

美国|英语

来源: UNT Digital Library

【 摘 要 】

Lawrence Livermore National Laboratory (LLNL) has developed a new laser-based machining technology that utilizes ultrashort-pulse (0.1-1.0 picosecond) lasers to cut materials with negligible generation of heat or shock. The ultrashort pulse laser, developed for the Department of Energy (Defense Programs) has numerous applications in operations requiring high precision machining. Due to the extremely short duration of the laser pulse, material removal occurs by a different physical mechanism than in conventional machining. As a result, any material (e.g., hardened steel, ceramics, diamond, silicon, etc.) can be machined with minimal heat-affected zone or damage to the remaining material. As a result of the threshold nature of the process, shaped holes, cuts, and textures can be achieved with simple beam shaping. Conventional laser tools used for cutting or high-precision machining (e.g., sculpting, drilling) use long laser pulses (10{sup -8} to over 1 sec) to remove material by heating it to the melting or boiling point (Figure 1.1a). This often results in significant damage to the remaining material and produces considerable slag (Figure 1.2a). With ultrashort laser pulses, material is removed by ionizing the material (Figure 1.1b). The ionized plasma expands away from the surface too quickly for significant energy transfer to the remaining material. This distinct mechanism produces extremely precise and clean-edged holes without melting or degrading the remaining material (Figures 1.2 and 1.3). Since only a very small amount of material ({approx} <0.5 microns) is removed per laser pulse, extremely precise machining can be achieved. High machining speed is achieved by operating the lasers at repetition rates up to 10,000 pulses per second. As a diagnostic, the character of the short-pulse laser produced plasma enables determination of the material being machined between pulses. This feature allows the machining of multilayer materials, metal on metal or metal on ceramic where one material can be machined without damaging the next. Developed originally for the Stockpile Stewardship program of the Department of Energy, numerous industrial, medical and national security applications of the technology have emerged. The difference in machining ability of the ultrashort-pulse laser is dramatically illustrated in Figures 1.2 and 1.3. The clear presence of slag (resolidified molten material) is observable in Figure 1.2a where 1 mm thick stainless steel was cut with a 1 {micro}m solid-state laser. By changing the pulse duration of the laser to the ultrashort regime ({approx} 10{sup -13} to 10{sup -12} sec), material is removed without melting and the formation of slag. A cross section of holes drilled in 304 stainless steel (Figure 1.3) illustrates the lack of any heat affected zone or collateral damage in the remaining material. Note that the individual grain boundaries are intact up to the edge of the laser-machined surface.