Laser Machining of Southern Pine

In a factorial experiment, with two replications the variables were: Wood moisture content: dry (avg. 12 pct.) wet (avg. 70 pct.); Wood specific gravity: low (avg. 0.45); high (avg. 0.54); Direction of cutting: along the grain, across the grain; and Workpiece thickness: 0.25 inch; 0.50 inch; 1.00 inch. When samples were cut with an air-jet-assisted carbon-dioxide laser of 240 watts output power, the maximum feed speed at the point of full penetration of the laser beam differed with workpiece thickness, wood specific gravity, and moisture content. Maximum feed speed decreased with increasing workpiece thickness in both wet and dry samples; the trend was curvilinear. For a given thickness, slower feeds were required for wet than for dry wood. In wet wood, maximum feed speed was unrelated to specific gravity. For dry wood, slower speeds were required when cutting wood of high density than wood of low density. When cutting along or across the grain, the kerf produced by the laser beam was narrower (avg. 0.012 inch) than that of conventional saws. Kerf width was unrelated to cutting direction, moisture content, and specific gravity, but it increased with increasing workpiece thickness. Kerfs were 0.009, 0.012, and 0.015 inch wide for samples 0.25, 0.50, and 1.00 inch thick. Scanning electron micrographs showed that laser-cut surfaces, while blackened, were far smoother than sawn surfaces. There was little damage to wood structure, but carbon deposits were evident on cell walls and in lumen cavities. Visual inspection indicated that the degree of charring increased with increasing workpiece thickness and was greater for dry than for wet wood. Loose char was easily removed with compressed air or by light brushing.

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