Lena Trippe

Melt ejection during single-pulse drilling and percussion drilling of micro holes in stainless steel- and nickel-based superalloy by pulsed Nd:YAG laser radiation

Single pulse drilling and percussion drilling of micro holes (diameter 100 μm, depth 2 mm) with Nd:YAG laser radiation (pulse duration 100 - 500 μs) in stainless steel (X5CrNi18-10) and nickel-based superalloy (CMSX-4) are reported. The development of the hole geometry, especially the hole diameter depending on the focal diameter including caustics and the thickness of the melt at the hole wall, is investigated. The experimental results are compared to the calculations of a physical model describing the motion of the melt front, the phase boundary between liquid and solid. Closures resulting from melt in the hole are detected by recording the expansion of plasma using high speed photography (50000 fps). The quality of drilled holes, e.g. conicity, thickness of recast and closures, is investigated by metallography and optical microscopy. Timescales of physical processes as the onset of melting and vaporization, the time to stationary melt flow and geometrical scales like the hole depth, the closure depth and the hole diameter are determined experimentally and numerically.

Reconditioning of nickel base HPT blades and vanes used in aero engines and power plant gas turbines by combination of direct laser forming, laser metal deposition and laser drilling

Parts like HPT (High Pressure Turbine) blades and vanes with integrated complex shaped cooling channels cannot be repaired. The parts are replaced by new ones. The aim is to develop and implement a reconditioning chain to avoid scrapping of the part. The reconditioning chain covers the three different Laser Applications 1. Direct Laser Forming (DLF), 2. Laser Metal Deposition (LMD) and 3. Laser Drilling (LD) which are arranged in subsequent Processing Steps. The damaged volume of the blade or vane is replaced by a fitting patch with integrated cooling channels which is generatively manufactured by DLF based on CAD data acquired by digitizing and reverse engineering in a first step. The generated patch is joined into the remaining part of the blade or vane by LMD. The non open cooling channels are opened and in case of necessity reshaped by LD in the third step. Also the cooling channels damaged or destroyed in the joint zone patch-substrate by the LMD joining process within step 2 are reworked or inserted by LD in the third step. First results achieved within basic R & D of DLF, LMD and LD of relevant Nickel Base Alloys are presented.Parts like HPT (High Pressure Turbine) blades and vanes with integrated complex shaped cooling channels cannot be repaired. The parts are replaced by new ones. The aim is to develop and implement a reconditioning chain to avoid scrapping of the part. The reconditioning chain covers the three different Laser Applications 1. Direct Laser Forming (DLF), 2. Laser Metal Deposition (LMD) and 3. Laser Drilling (LD) which are arranged in subsequent Processing Steps. The damaged volume of the blade or vane is replaced by a fitting patch with integrated cooling channels which is generatively manufactured by DLF based on CAD data acquired by digitizing and reverse engineering in a first step. The generated patch is joined into the remaining part of the blade or vane by LMD. The non open cooling channels are opened and in case of necessity reshaped by LD in the third step. Also the cooling channels damaged or destroyed in the joint zone patch-substrate by the LMD joining process within step 2 are reworked or inserted...

Investigation of movement of the melting front to analyse the formation of hole geometry during single pulse drilling with Nd:YAG laser radiation

Single pulse drilling of micro holes (diameter 100 µm, depth<2 mm) in stainless steel (X5CrNi18-10) and nickel-base superalloy (CMSX-4) is performed by pulsed Nd:YAG laser radiation (pulse duration 100-500 µs). The movement of the melting front is investigated by metallography and optical microscopy. The formation of the hole geometry is compared to the spatial and temporal distribution of the pulse power. The processing limits regarding the aspect ratio (diameter: depth) are extended and the quality of drilled holes regarding recast layers in drilled holes, cylindricity, and defined conicity is extended.Single pulse drilling of micro holes (diameter 100 µm, depth<2 mm) in stainless steel (X5CrNi18-10) and nickel-base superalloy (CMSX-4) is performed by pulsed Nd:YAG laser radiation (pulse duration 100-500 µs). The movement of the melting front is investigated by metallography and optical microscopy. The formation of the hole geometry is compared to the spatial and temporal distribution of the pulse power. The processing limits regarding the aspect ratio (diameter: depth) are extended and the quality of drilled holes regarding recast layers in drilled holes, cylindricity, and defined conicity is extended.

Diagnosis and Simulation of High Speed Drilling

Laser drilling is a thermal ablation process being about to be widely applied in ablating and hole drilling applications, such as the drilling of filters, sieves or injection nozzles. This work describes advances in fundamental physical modeling, experimental diagnosis as well as time varying processes like drilling a prescribed hole shape. The laser drilling process is represented mathematically by a three-dimensional free boundary problem for the motion of two phase boundaries, namely, the solid-liquid and the liquid-vapor boundary. In drilling the mechanisms governing the shape of the drilled hole -still showing efficient melt removal -are identified experimentally and can be related to the processing parameters theoretically.