Possibilities of 3D machining of materials by abrasive water jets

Machining of materials through classical way, i.e. using conventional tools for turning, drilling, milling, grinding and polishing, has some limits that can be overcome applying an abrasive water jet (AWJ). Therefore, some possibilities of 3D machining by AWJ placed on 6 axes robot have been tested. Programming of traverse speeds and tilting angles of cutting head was based on Hlaváč’s theoretical model. Low pressure pump has been used for tests. Because of very low pumping pressure, a selfdesigned and manufactured special mixing chamber was used in the experiments. The article deals with preliminary results and points at the direction of further research

Construction of The GPS device

Cílem této práce je návrh a realizace zařízení, zprostředkovávajícího komunikaci s GPS modulem iTrax300 a umožňujícího zobrazit jeho polohu na displeji. Práce pojednává o systému GPS, principech určení polohy a o standardizovaném formátu výstupních dat z navigačních systémů - protokolu NMEA 0183. Dále se zabývá jednotlivými kroky realizace navrhovaného zařízení od přesného vymezení požadavků po testování funkčnosti zhotoveného zařízení. Sestrojené zařízení zobrazuje GPS souřadnice, světový koordinovaný čas (UTC), datum, nadmořskou výšku a rychlost pohybu. Zařízení umožňuje zadat vlastní cílové souřadnic GPS, po jejichž zadání se na displeji zobrazuje směr a vzdálenost k cíli. Zařízení dále umožňuje ukládání trasy pohybu do paměti. Po propojení zařízení s PC přes USB rozhraní je možno uloženou trasu zobrazit v mapě.The goal of this thesis is a complete design and realization of a device that is able to communicate with GPS module iTrax300 and display the coordinates received from the module. The thesis deals with the GPS, localization principles and the standard communication protocol for navigation systems - the NMEA 0183 protocol. Futhermore it is dealing with the particular steps in the realization of the engineered device (from the specification of requirements at the beginning to the testing of its functionality in the end). The GPS coordinates, the Coordinated Universal Time (UTC), the date, the altitude and the speed on the ground can be displayed. There is also a possibility to put in any coordinates, the direction and the distance to the point are displayed afterwards. The device enables the track storage in the memory as well. The track is viewable while connecting the device and the PC through the USB interface.

Revised model of abrasive water jet cutting for industrial use

Research performed by the author in the last decade led him to a revision of his older analytical models used for a description and evaluation of abrasive water jet (AWJ) cutting. The review has shown that the power of 1.5 selected for the traverse speed thirty years ago was influenced by the precision of measuring devices. Therefore, the correlation of results calculated from a theoretical model with the results of experiments performed then led to an increasing of the traverse speed exponent above the value derived from the theoretical base. Contemporary measurements, with more precise devices, show that the power suitable for the traverse speed is essentially the same as the value derived in the theoretical description, i.e., it is equal to "one". Simultaneously, the replacement of the diameter of the water nozzle (orifice) by the focusing (abrasive) tube diameter in the respective equations has been discussed, because this factor is very important for the AWJ machining. Some applications of the revised model are presented and discussed, particularly the reduced forms for a quick recalculation of the changed conditions. The correlation seems to be very good for the results calculated from the present model and those determined from experiments. The improved model shows potential to be a significant tool for preparation of the control software with higher precision in determination of results and higher calculation speed.Web of Science1414art. no. 403

Výsledky průzkumu měkkýšů (Mollusca: Gastropoda, Bivalvia) v okolí města Blatná v jihozápadních Čechách

Results of the faunistic survey on molluscs in the vicinity of the town of Blatná (south-western Bohemia, Czech Republic) are presented. This research was carried out in 2004–2007 at 28 sites complemented by other older unpublished records. Altogether 87 species (76 gastropods, 11 bivalves) have been recorded that the freshwater molluscs represented the most abundant ecological group in this region (about 40% of all species recorded). However, the rare species (e.g. Aplexa hypnorum, Physa fontinalis, Pisidium obtusale) have been found usually in small water bodies while the majority of common freshwater molluscs was recorded predominantly in large and mid-sized ponds. The snail Gyraulus acronicus is the rarest freshwater species found only at one locality. Important proportion of investigated malacofauna consisted of wetland and floodplain species with rare elements such as Vertigo antivertigo, V. substriata, Euconulus praticola or even V. angustior, the former being protected in the whole Europe. Occurrence of this endangered species in the studied region represents one of the most important clusters of its populations in Bohemia. Only several forest species have been recorded, the species Acanthinula aculeata and Vertigo pusilla are of particular importance. Unique are finds of the steppe species Chondrula tridens on old slacking walls in the town of Blatná

Investigation of significant parameters during abrasive waterjet turning

This paper presents an investigation of abrasive waterjet turning (AWJT). The purpose of the article was to investigate significant parameters of the turning process and to evaluate their impact on the turning product. The influence of the traverse speed, the rotational speed, and the relative position of the jet to the specimen (lateral jet shift) were investigated. Based on the previous research done in this field, the multi-pass tangential turning method was selected. Rotational speed does not seem to have a significant impact on the AWJ turning process. However, the relative position of the jet is a key parameter for improving the efficiency of the process. Increasing the lateral jet shift causes the volume of the material removed to increase until the optimal impact angle is reached. These findings need to be extended in order to adjust AWJT. Without these improvements, a comparison of jet to traditional technologies is inappropriate.Web of Science1416art. no. 438

Analysis of several physical phenomena measured on the metallic materials cut by abrasive water jets (AWJ)

Cutting using an abrasive water jet is a complex process involving several physical phenomena. This research studies some of them, mostly the influence of selected variables on the measured forces and vibrations. The traverse speed represents one of the key parameters when cutting using the AWJ. In the presented research, a set of experiments was performed on twelve different metal samples, while the force sensor measured the exerted forces and accelerometers measured the vibrations. Ten different types of steel samples of the same dimensions were cut applying five different traverse speeds. The data obtained during these measurements show that an increase in the traverse speed leads to an increase in the measured forces and vibrations. An analogous experiment performed on bronze and duralumin samples of the same dimensions, having applied higher speeds to compensate for the difference in the material structure and properties, completes the presented data. The most important results of the research are that exerted forces in the z-axis are higher than those in the x-axis, whereas measured vibrations are higher in the x-axis. According to our research, the elemental structure, especially the carbide formation, affects the measured forces and vibrations substantially.Web of Science1521art. no. 742

Notes on the abrasive water jet (AWJ) machining

The aim of the research was to investigate changes of abrasive grains on metals observing the kerf walls produced by the Abrasive Water Jet (AWJ). The microscopy observations of the sidewalls of kerfs cut by the AWJ in several metal materials with an identical thickness of 10 mm are presented. The observed sizes of abrasive grains were compared with the results of research aimed at the disintegration of the abrasive grains during the mixing process in the cutting head during the injection AWJ creation. Some correlations were discovered and verified. The kerf walls observations show the size of material disintegration caused by the individual abrasive grains and also indicate the size of these grains. One part of this short communication is devoted to a critical look at some of the conclusions of the older published studies, namely regarding the correlation of the number of interacting particles with the acoustic emissions measured on cut materials. The discussion is aimed at the abrasive grain size after the mixing process and changes of this size in the interaction with the target material.Web of Science1422art. no. 703

towards intelligent autonomous sorting of unclassified nuclear wastes

Sorting of old and mixed nuclear waste is an essential process in nuclear decommissioning operations. The main bottleneck is manual picking and separation of the materials using remotely operated arms, which is slow and error prone especially with small items. Automation of the process is therefore desirable. In the framework of the newly funded European project ECHORD++, experiment RadioRoSo, a pilot robotic cell is being developed and validated against industrial requirements on a range of sorting tasks. Industrial robots, custom gripper, vision feedback and new manipulation skills will be developed. This paper presents application context, cell layout and sorting approach

Abrasive waterjet (AWJ) forces-indicator of cutting system malfunction

Measurements enabling the online monitoring of the abrasive waterjet (AWJ) cutting process are still under development. This paper presents an experimental method which can be applicable for the evaluation of the AWJ cutting quality through the measurement of forces during the cutting process. The force measuring device developed and patented by our team has been used for measurement on several metal materials. The results show the dependence of the cutting to deformation force ratio on the relative traverse speed. Thus, the force data may help with a better understanding the interaction between the abrasive jet and the material, simultaneously impacting the improvement of both the theoretical and empirical models. The advanced models could substantially improve the selection of suitable parameters for AWJ cutting, milling or turning with the desired quality of product at the end of the process. Nevertheless, it is also presented that force measurements may detect some undesired effects, e.g., not fully penetrated material and/or some product distortions. In the case of a proper designing of the measuring device, the force measurement can be applied in the online monitoring of the cutting process and its continuous control.Web of Science147art. no. 168

Abrasive waterjet (AWJ) forces - Potential indicators of machining quality

The necessity of monitoring the abrasive waterjet (AWJ) processes increases with the spreading of this tool into the machining processes. The forces produced on the workpiece during the abrasive waterjet machining can yield some valuable information. Therefore, a special waterjet-force measuring device designed and produced in the past has been used for the presented research. It was tested during the AWJ cutting processes, because they are the most common and the best described up-to-date AWJ applications. Deep studies of both the cutting process and the respective force signals led to the decision that the most appropriate indication factor is the tangential-to-normal force ratio (TNR). Three theorems concerning the TNR were formulated and investigated. The first theorem states that the TNR strongly depends on the actual-to-limit traverse speed ratio. The second theorem claims that the TNR relates to the cutting-to-deformation wear ratio inside the kerf. The third theorem states that the TNR value changes when the cutting head and the respective jet axis are tilted so that a part of the jet velocity vector projects into the traverse speed direction. It is assumed that the cutting-to-deformation wear ratio increases in a certain range of tilting angles of the cutting head. This theorem is supported by measured data and can be utilized in practice for the development of a new method for the monitoring of the abrasive waterjet cutting operations. Comparing the tilted and the non-tilted jet, we detected the increase of the TNR average value from 1.28 +/- 0.16 (determined for the declination angle 20 degrees and the respective tilting angle 10 degrees) up to 2.02 +/- 0.25 (for the declination angle 30 degrees and the respective tilting angle of 15 degrees). This finding supports the previously predicted and published assumptions that the tilting of the cutting head enables an increase of the cutting wear mode inside the forming kerf, making the process more efficient.Web of Science1412art. no. 330