Nozzle design and simulation of gas flow for the laser cutting process

Abstract

University ofTechnology, Inst. for High Power Beam Technology 2University Erlangen, Inst. for Manufacturing Technology AB STRACTIn the laser cutting process the gas flow is of main importance to remove molten material from the cut kerf. Changes in nozzle geometry, gas supply pressure and nozzle workpiece stand-.offdistance have a strong influence on the cut quality.The aim of the investigation is the numerical simulation of supersonic gas flow.Supersonic nozzles for laser applications are designed Which can be manufactured more easily and cost effective than conventionally used Laval nozzles. For the simulation wall friction is regarded and the flow field is calculated two dimensional and assumed turbulent. Normal jet impingement for the designed nozzles and underexpanded conic-cylindrical nozzles is compared at various nozzle stand-off distances and shows a more constant pressure on the workpiece for the designed nozzles.Furthermore supersonic effects in the cut kerf are investigated and compared with results from Schlieren photographs. The nonlinear pressure distribution inside the kerf indicates both the shock formation and detachment ofthe gas flow.In the presence of shock waves the existing equations in finite volume form have been modified, as they lead to wrong predictions both in the shock location and strength due to an incorrect inertia term in the momentum equations.

<title>Investigations of the gas flow of conic-cylindrical and supersonic nozzles in a laser cut kerf</title>

“…For a better understanding ofthe gas flow in the cut kerfwe investigated nornialjet impingement on a workpiece for various nozzle stand off distances 10,12 The maximum pressure on the workpiece strongly depends on the workpiece placement relatively to the shock waves ofthe corresponding free stream and shows sharp variations in case of the conic-cylindrical nozzle. The advantage of the designed supersonic nozzle is seen clearly 11: The pressure variation in the free stream due to frictional effects is weak and leads to a constant pressure on the workpiece for various nozzle standoffdistances up to 8 mm.…”

Laser Cutting: A Review on the Influence of Assist Gas

“…Behind the Mach disk, a region of subsonic flow ( M < 1) bounded above by a slipstream (slip line) emanating from the triple point, appears. Leidinger et al used a finite volume code to simulate the free stream that emerged from an underexpanded conic-cylindrical nozzle [25]. They determined that after crossing the MSD, the velocity and energy of the gas is reduced, and the stagnation pressure on the workpiece decreases (the reduction in pressure on the workpiece was first observed by Fieret et al [22]).…”

Simulation and experiment on standoff distance affecting gas flow in laser cutting

“…The pressure and velocity distribution in cutting slot with taper nozzle cutting workpiece vertically were illuminated by Leidinger and Penz [7], and the result was tally with schlieren photos. Mathematical model of laser cutting was brought up by Man et al [8,9], and the supersonic flow field in cutting slot and the effect of cutting parameters on cutting quality were analyzed in their study .…”