Die Prozesskette zur Herstellung von bronzegebundenen Schleifwerkzeugen umfasst die Schritte Mischen, Einformen, Vorverdichten und Sintern. Die Konzeption und Optimierung dieser Schritte basiert bisher hauptsächlich auf implizitem Erfahrungswissen. Angesichts der großen Anzahl an vorhandenen Pulverpartikeln ist eine analytische Untersuchung der Herstellungsprozesskette nicht geeignet. Die numerische Simulation bietet eine kosten- und zeitsparende Alternative. In diesem Beitrag wird die Simulation der Prozesskette mithilfe der DEM- und FEM-Simulation vorgestellt. Manufacturing of bronze-bonded tools includes the steps of mixing, molding, pressing and sintering. The design and the optimization of these steps has so far mainly been based on experience. With regard to the large number of powder particles, an analytical investigation of the powder metallurgical processes is not suitable. Numerical simulation offers a cost and time saving alternative. In this article, the simulation of the process chain with the help of DEM and FEM simulation is introduced.
Die präsentierte Methode stellt eine Weiterentwicklung des Ritzprozesses dar. Das Ritzwerkzeug wird dabei aus einem Schleifwerkzeug herausgearbeitet. Somit wird der Einfluss der Bindung bei der Analyse des Einsatzverhaltens berücksichtigt. Das Belastungskollektiv je Schleifkorn wird damit bestimmt und für die zukünftige Auslegung von Schleifwerkzeugen genutzt. The presented method represents an advancement of the scratching process. The grain is attached to the scratching tool, which is manufactured on the basis of a real grinding wheel. Thus, the influence of the bond on the chip formation and wear behavior at the grain level is taken into account. A realistic single grain load can be determined and used for the design of grinding tools.
Für die Leistung und die Standzeit der Zahnräder im Getriebe sind die Oberflächen- und Randzoneneigenschaften der Zähne entscheidend. Die Kenntnis der durch den Schleifprozess erzeugten Temperaturen ist von besonderem Interesse, da thermische Schädigungen ein Bauteil für den Einsatz unbrauchbar machen. Die Messung von Temperaturen nahe der Kontaktzone ist aufgrund der gekoppelten Rotation von Werkstück und Schleifwerkzeug aufwendig. Eine werkstückseitige Messung bietet eine einfachere Lösung dafür, die auch die Untersuchung unterschiedlicher Werkzeuge erlaubt. Surface and subsurface properties of the gear teeth are crucial for the performance and service life of gears inside the gear train. The knowledge of temperatures generated by the grinding process is of particular interest, as thermal damage causes the gear to be unusable. The measurement of temperatures near the contact zone in this case is not trivial, due to the coupled rotation of workpiece and grinding tool. A measuring system attached to the workpiece offers a less complicated solution for this, and allows the examination of different tools.
Der Schneidstoff HSS (high-speed steel) ist neben den Hartmetallen industriell hoch relevant. Optimierungen der Werkzeuge erfolgten in den letzten beiden Jahrzehnten fast ausschließlich im Bereich des Hartmetalls und anderer hochharter Schneidstoffe. Eine angepasste Mikrogeometrie in Kombination mit multifunktionellen Schichten ermöglicht auch für Hochleistungsschnellarbeitsstahl eine deutliche Steigerung der Produktivität und somit der Ressourceneffizienz. Apart from tungsten carbide, the tool material high-speed steel (HSS) is widely used in industry, although optimizations of cutting tools have been carried out almost exclusively for tungsten carbide and other superhard tool materials in the last two decades. However, by optimizing the micro-geometry in combination with innovative multi-functional hard-coatings, high-speed steel tools also lead to a significant increase in productivity and resource efficiency.
In der Luft- und Raumfahrt werden höchste Anforderungen an die Belastbarkeit sowie Lebensdauer einzelner Komponenten gestellt. Bisherige Untersuchungen zeigen, dass insbesondere eingebrachte Druckeigenspannungen in der Werkstückrandzone aufgrund des erhöhten Widerstands gegen Rissbildung und -ausbreitung zu einer Lebensdauererhöhung von Turbinenschaufeln führen können. Mit dem Einsatz eines aerosolgelagerten Zangenwalzwerkzeug kann gezielt ein belastungsangepasstes Eigenspannungsprofil eingebracht werden. In aerospace industry highest demands are placed on the strength and durability of individual components. The present knowledge shows that especially compressive stresses in the subsurface lead to an increased lifetime of turbine blades, due to the enhanced resistance to crack initiation and propagation. An innovative aerosol mounted pincer rolling tool has been developed for the induction of individual residual stress profiles into such components.
Background Surgery is the main modality of cure for solid cancers and was prioritised to continue during COVID-19 outbreaks. This study aimed to identify immediate areas for system strengthening by comparing the delivery of elective cancer surgery during the COVID-19 pandemic in periods of lockdown versus light restriction. Methods This international, prospective, cohort study enrolled 20 006 adult (≥18 years) patients from 466 hospitals in 61 countries with 15 cancer types, who had a decision for curative surgery during the COVID-19 pandemic and were followed up until the point of surgery or cessation of follow-up (Aug 31, 2020). Average national Oxford COVID-19 Stringency Index scores were calculated to define the government response to COVID-19 for each patient for the period they awaited surgery, and classified into light restrictions (index 60). The primary outcome was the non-operation rate (defined as the proportion of patients who did not undergo planned surgery). Cox proportional-hazards regression models were used to explore the associations between lockdowns and non-operation. Intervals from diagnosis to surgery were compared across COVID-19 government response index groups. This study was registered at ClinicalTrials.gov, NCT04384926. Findings Of eligible patients awaiting surgery, 2003 (10·0%) of 20 006 did not receive surgery after a median follow-up of 23 weeks (IQR 16–30), all of whom had a COVID-19-related reason given for non-operation. Light restrictions were associated with a 0·6% non-operation rate (26 of 4521), moderate lockdowns with a 5·5% rate (201 of 3646; adjusted hazard ratio [HR] 0·81, 95% CI 0·77–0·84; p<0·0001), and full lockdowns with a 15·0% rate (1775 of 11 827; HR 0·51, 0·50–0·53; p<0·0001). In sensitivity analyses, including adjustment for SARS-CoV-2 case notification rates, moderate lockdowns (HR 0·84, 95% CI 0·80–0·88; p<0·001), and full lockdowns (0·57, 0·54–0·60; p<0·001), remained independently associated with non-operation. Surgery beyond 12 weeks from diagnosis in patients without neoadjuvant therapy increased during lockdowns (374 [9·1%] of 4521 in light restrictions, 317 [10·4%] of 3646 in moderate lockdowns, 2001 [23·8%] of 11 827 in full lockdowns), although there were no differences in resectability rates observed with longer delays. Interpretation Cancer surgery systems worldwide were fragile to lockdowns, with one in seven patients who were in regions with full lockdowns not undergoing planned surgery and experiencing longer preoperative delays. Although short-term oncological outcomes were not compromised in those selected for surgery, delays and non-operations might lead to long-term reductions in survival. During current and future periods of societal restriction, the resilience of elective surgery systems requires strengthening, which might include protected elective surgical pathways and long-term investment in surge capacity for acute care during public health emergencies to protect elective staff and services. Funding National Institute for Health Research Global Health Research Unit, Association of Coloproctology of Great Britain and Ireland, Bowel and Cancer Research, Bowel Disease Research Foundation, Association of Upper Gastrointestinal Surgeons, British Association of Surgical Oncology, British Gynaecological Cancer Society, European Society of Coloproctology, Medtronic, Sarcoma UK, The Urology Foundation, Vascular Society for Great Britain and Ireland, and Yorkshire Cancer Research.
Background Surgery is the main modality of cure for solid cancers and was prioritised to continue during COVID-19 outbreaks. This study aimed to identify immediate areas for system strengthening by comparing the delivery of elective cancer surgery during the COVID-19 pandemic in periods of lockdown versus light restriction. Methods This international, prospective, cohort study enrolled 20 006 adult (≥18 years) patients from 466 hospitals in 61 countries with 15 cancer types, who had a decision for curative surgery during the COVID-19 pandemic and were followed up until the point of surgery or cessation of follow-up (Aug 31, 2020). Average national Oxford COVID-19 Stringency Index scores were calculated to define the government response to COVID-19 for each patient for the period they awaited surgery, and classified into light restrictions (index 60). The primary outcome was the non-operation rate (defined as the proportion of patients who did not undergo planned surgery). Cox proportional-hazards regression models were used to explore the associations between lockdowns and non-operation. Intervals from diagnosis to surgery were compared across COVID-19 government response index groups. This study was registered at ClinicalTrials.gov, NCT04384926. Findings Of eligible patients awaiting surgery, 2003 (10·0%) of 20 006 did not receive surgery after a median follow-up of 23 weeks (IQR 16–30), all of whom had a COVID-19-related reason given for non-operation. Light restrictions were associated with a 0·6% non-operation rate (26 of 4521), moderate lockdowns with a 5·5% rate (201 of 3646; adjusted hazard ratio [HR] 0·81, 95% CI 0·77–0·84; p<0·0001), and full lockdowns with a 15·0% rate (1775 of 11 827; HR 0·51, 0·50–0·53; p<0·0001). In sensitivity analyses, including adjustment for SARS-CoV-2 case notification rates, moderate lockdowns (HR 0·84, 95% CI 0·80–0·88; p<0·001), and full lockdowns (0·57, 0·54–0·60; p<0·001), remained independently associated with non-operation. Surgery beyond 12 weeks from diagnosis in patients without neoadjuvant therapy increased during lockdowns (374 [9·1%] of 4521 in light restrictions, 317 [10·4%] of 3646 in moderate lockdowns, 2001 [23·8%] of 11827 in full lockdowns), although there were no differences in resectability rates observed with longer delays. Interpretation Cancer surgery systems worldwide were fragile to lockdowns, with one in seven patients who were in regions with full lockdowns not undergoing planned surgery and experiencing longer preoperative delays. Although short-term oncological outcomes were not compromised in those selected for surgery, delays and non-operations might lead to long-term reductions in survival. During current and future periods of societal restriction, the resilience of elective surgery systems requires strengthening, which might include protected elective surgical pathways and long- term investment in surge capacity for acute care during public health emergencies to protect elective staff and services. Funding National Institute for Health Research Global Health Research Unit, Association of Coloproctology of Great Britain and Ireland, Bowel and Cancer Research, Bowel Disease Research Foundation, Association of Upper Gastrointestinal Surgeons, British Association of Surgical Oncology, British Gynaecological Cancer Society, European Society of Coloproctology, Medtronic, Sarcoma UK, The Urology Foundation, Vascular Society for Great Britain and Ireland, and Yorkshire Cancer Research.
