Novel drill geometries for dry drilling of stainless steel

One completely new geometry and two modified chip breaker geometries were designed to increase the stability and reliability of the stainless steel dry drilling process. Experiments were performed and the results of individual tools were compared with a conventional solid carbide twist drill Gühring Ratio with a diameter of 5 mm. A matrix of three feed rates (0,03–0,07 mm/rev) and three cutting speeds (20–30 m/min) was designed for the cutting conditions. Precipitation-hardenable stainless steel 17-4 PH was chosen as a workpiece. During the experiment, the values of thrust force, spindle torque, temperature of the tool, surface roughness, chips morphology and chips division were recorded and compared with the reference tool. The results showed that compared to the reference tool A, the tool C - a multipoint drill with grooves through the cutting edge achieve approximately 4 % lower values of thrust force and 10–15 % lower values of spindle torque. Tool D with a step drill geometry achieve approximately 17 % lower values of thrust force and 10–15 % lower values of spindle torque and there is no chip clogging in the flute with C and D geometries. This effect is confirmed by the fact the spindle torque basically does not increase with the increasing depth of drilling. Tool B – new designed geometry achieve approximately 15 % lower values of thrust force and similar spindle torque values as the reference drill A. Tool temperature is a very important factor when dry drilling. Compared to the reference drill A, it was possible to achieve the tool temperature reduction of 20 % with the new geometry B, as well as with the multipoint drill C reduction by 26 % and with the step drill D reduction approximately by 30 %. All the modified drills also achieved a reduction in the surface roughness of the drilled holes. By 17 %, 35 % and 48 % lower surface roughness Ra was achieved with drills B, C and D. Chip morphology was significantly different for the tested drills. Conventional twist drills A and B generated helical short chips. While C and D twist drills with divided cutting edges generated ribbon snarled chips. Thanks to the reduction of cutting forces and temperature, it is possible to stably operate the drilling process with a higher cutting speed and feed rate, which leads to an increase in the efficiency and reliability of the machining process.Web of Science9252050

Technology of laser sintering of tool steel 1.2709

Tato bakalářská práce se věnuje technologii 3D tisku, zaměřuje se na technologii Direct Metal Laser Sintering (DMLS), snaží se zmapovat její silné a slabé stránky, doporučení pro návrh dílu, parametry procesu, vizi do budoucnosti. Práce se zaměřuje na konkrétní ocel, její vlastnosti, zpracování.This bachelor thesis examines 3D printing technology with a focus on Direct Metal Laser Sintering. Its aim is to explore its strenghts and weaknesses, design recommendations, process parametres and future vision. The main focus is on a specific type of steel, its properties and processin

Laparoscopic urinary bladder diverticulectomy combined with photoselective vaporisation of the prostate

INTRODUCTION: Pseudodiverticulum of the urinary bladder is mostly a complication of subvesical obstruction (SO). The gold standard of treatment was open diverticulectomy with adenectomy. A more contemporary resolution is endoscopic, in two steps: the first transurethral resection of the prostate (TURP), the second laparoscopic diverticulectomy (LD). AIM: To present a one-session procedure – photoselective vaporisation of the prostate (PVP) with LD. MATERIAL AND METHODS: From 1/2011 to 6/2014, 14 LDs were performed: 1 LD only, 1 with laparoscopic radical prostatectomy, 12 combined with treatment of benign prostatic hyperplasia (BPH), 4 cases of TURP and LD in the second period. In 8 cases, PVP and LD in one session were combined. These 8 cases are presented. 3D CT cystography was used as a gold standard for assessment of diverticulum. RESULTS: The mean age was 66.5 ±5.5 (57.3–75.1) years, the mean size of the diverticulum 61.8 ±22.1 (26–90) mm. The procedure starts in the lithotomy position. It includes PVP and stenting of the ureter(s). Changing of position and laparoscopy follows: four ports, transperitoneal extravesical approach. Photoselective vaporisation of the prostate was performed using the Green Light Laser HPS (1x) or XPS with cooled fibre MoXy (7x). The mean delivered energy in PVP was 205.1 ±106.4 (120–458) kJ. The mean time of operation was 165.0 ±48.5 (90–255) min. No postoperative complications were observed. One patient underwent TUR incision after 1 year for sclerosis of the bladder neck. CONCLUSIONS: Pseudodiverticulum of the urinary bladder (with or without SO) is a relatively rare disease. One session of PVP (Green Light Laser XPS, MoXy fibre) and laparoscopic (transperitoneal extravesical) diverticulectomy is the preferred method for treatment of subvesical obstruction due to BPH and bladder diverticulum at our institution

Porosity and microstructure of L-PBF printed AlSi10Mg thin tubes in laser shock peening

Laser powder bed fusion (L-PBF) has emerged as one of the most promising technologies for producing complex geometries that are difficult to achieve with other methods. However, its widespread adoption is hindered by issues such as deleterious microstructure, tensile residual stresses, and porous structure, mainly while working with aluminum alloys. To address these challenges, laser shock peening (LSP) offers a potential solution by mitigating the negative effects associated with aluminum L-PBF. This study investigates the impact of the important LSP parameters, namely energy, spot size, and overlap on L-PBF printed thin AlSi10Mg tubes. A total of 17 specimens were examined by varying the mentioned parameters at three levels each. The outcome of the study was evaluated in terms of residual stresses, porosity, microstructure and surface roughness. The results have shown significant improvements in residual stresses, where a maximum improvement of over 200% was observed and a decrease in porosity by 70%. Furthermore, the microstructure analysis revealed grain refinement and dislocation redistribution as material reactions, aligning with the observed microhardness increase. These findings demonstrate the viability of LSP as a post-processing method for demanding applications, effectively addressing the limitations of the L-PBF process

Influence on Micro-Geometry and Surface Characteristics of Laser Powder Bed Fusion Built 17-4 PH Miniature Spur Gears in Laser Shock Peening

Micro-geometrical errors, surface roughness, and surface integrity (microstructure, residual stresses, microhardness) play an important role in defining the quality of the gears as they directly affect their noise, vibration characteristics and service life during their use. In the present work, underwater laser shock peening (LSP) is employed to improve the quality of the laser powder bed fusion built 17-4 PH small-size spur gears (12 mm outside diameter). LSP was employed near the spur gear root, and effects were measured in terms of residual stresses, variation in microgeometry errors, surface roughness, porosity, microstructure, and microhardness. It was observed that LSP could impart compressive residual stresses up to 0.4 mm of measured depth, while the surface roughness has improved by 32%. Microgeometry and microhardness of gears showed minor variations. Additionally, LSP has shown an impact on the microstructure as the grain orientation was altered and grain size reduced by 15.6% due to shock wave transmission. The study paves the way to use LSP as a post-processing technique to modify the surface characteristics of LPBF-built miniature spur gears with minimal impact on the gear microgeometry