Development and Application of Conventional Laser Processing Technologies

With innovations and advancements in processing technology, conventional laser processing techniques such as drilling, cutting, and surface modification have all seen varying degrees of progress.

(1) Drilling

Early laser drilling employed the fixed-point impact method: a pulsed laser beam continuously processed a single location until the hole penetrated. This approach imposed limitations on both hole depth and diameter.

Following the practical application of high-repetition-rate YAG lasers, the trepanning method emerged. This technique employs specialized rotating optical heads or CNC-controlled circular trajectories to perform laser nesting processing. Not only does it eliminate diameter constraints, but the semi-open processing zone—enhanced by auxiliary gas blowing—facilitates melt evacuation, resulting in superior hole surface quality.

For components featuring numerous identical small holes, particularly rotary parts, the Drilling on the Fly method has been developed. Here, the laser processes one hole position per pulse. Regardless of whether the hole is completed, the workpiece rapidly moves (translates or rotates) to the next position during the pulse interval. This cycle repeats multiple times at the same location until all holes are processed. Its advantage lies in utilizing the laser pulse interval for hole displacement, significantly boosting processing speed. Current drilling rates reach tens of holes per second, with projections indicating potential for 500 holes per second (sub-millimeter apertures). The technological challenge lies in ensuring the laser beam reaches the target while the workpiece moves precisely into position, which is particularly difficult for non-uniformly distributed holes. CNC closed-loop control systems are employed. At higher drilling rates, to maintain circular hole shape, the laser beam must synchronize its movement with the part during the laser exposure time. Laser flight drilling has been applied in aerospace component manufacturing, with cooling hole processing in annular combustion chambers being a typical example. Additionally, at the leading edges of high-speed aircraft wings and engine inlets, airflow readily separates from the surface, generating increased turbulence and aerodynamic drag. To address this, laminar flow wing (nacelle) sleeves with air-intake functionality were designed. Their surfaces consist of 1mm-thick titanium alloy plates perforated with 12 million to 1 billion conical holes, featuring outer surface apertures of 0.06mm and with an inner surface aperture of 0.1mm and a hole spacing of 0.3–1mm. The micro-holes in the laminar flow wing cover were also created using the flying punch method.

For micrometer-scale aperture sieve holes, rapid scanning processing using excimer lasers or Q-switched YAG lasers (capable of processing thousands of holes per second) yields satisfactory results.

(2) Cutting

CO₂ lasers remain predominant for laser cutting in the near term. With increased device power, both cutting depth and speed have significantly improved. To enhance processing quality, high-pressure gas blowing (pressure reaching 1.6–2.0 MPa) is employed. A 3.4 kW CO₂ laser can cut 5–6 mm thick aluminum plates with smooth edges, leaving no slag residue on either side. Notably, dual-beam laser composite cutting achieves lower energy consumption. Figure 1 illustrates an experimental setup for dual-laser composite cutting. Tests demonstrate that combining a CO₂ laser (270W) with a KrF laser (30W) increases cutting speed by 30% and cutting thickness by over 40% compared to using a single CO₂ laser (300W) for carbon steel.

(III) Welding

Laser welding has long been applied in the instrumentation industry. Recent research focuses primarily on processing difficult-to-weld alloys such as high-temperature alloys, titanium alloys, aluminum, and magnesium in the aerospace sector; and deep penetration welding of thick and variable-thickness steel plates in the automotive industry.

The suspension of large passenger aircraft engine nacelles employs 2.5kW CO₂ laser welding technology. The compressor stator of the engine is constructed by laser-cutting blade holes followed by laser welding the blades to the outer ring, processed using a 2kW continuous-output YAG laser system achieving a welding speed of 7m/min.

In the automotive sector, laser welding's share has grown annually, evolving from joining identical materials in body panels to welding metal sheets with varying thicknesses and surface coatings. French company SCIAKY established a 6kW CO₂ laser processing station. Using a beam splitter, the laser beam is distributed to 12 stations for simultaneous spot welding, completing one part in 5 seconds. This not only saves 6 to 12 resistance spot welding robots but also reduces vehicle weight by 56kg by decreasing the overlap width.

The cutting edge of laser welding technology research involves two key areas. First, controlling plasma generated during high-power or ultra-high-power welding. This is achieved using lateral gas compression methods to press the plasma cloud into the seam formed by the molten pool, thereby improving its shielding behavior. Another direction involves employing fuzzy logic methods for intelligent control of the welding process. This is particularly significant for welding processes involving variable thicknesses and parameters.