Femtosecond laser processing of fuel injectors - a materials processing evaluation

Technical Report · Sat Dec 16 00:00:00 EST 2000

DOI:https://doi.org/10.2172/15006882· OSTI ID:15006882

Stuart, B C; Wynne, A

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.

• Research Organization: Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
• Sponsoring Organization: US Department of Energy (US)
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 15006882
• Report Number(s): UCRL-ID-141346; TRN: US200412%%277
• Resource Relation: Other Information: PBD: 16 Dec 2000
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEFENSE
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ACCURACY
BEAM SHAPING
BOILING POINTS
CROSS SECTIONS
ENERGY TRANSFER
EVALUATION
GRAIN BOUNDARIES
HEAT AFFECTED ZONE
LASER-PRODUCED PLASMA
LASERS
NATIONAL SECURITY
PROCESSING
SOLID STATE LASERS
STAINLESS STEELS
VELOCITY