The necessity of monitoring the abrasive waterjet (AWJ) processes increases with the spreading of... more 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 t...
V technickem a přirodovědeckem výzkumu je velmi casto nutne znat hodnoty měrných povrchů prasků c... more V technickem a přirodovědeckem výzkumu je velmi casto nutne znat hodnoty měrných povrchů prasků ci sypkých hmot. Prvnim stupněm takoveho výpoctu je pak aproximace zrn některým geometrickým utvarem s hladkým povrchem, nejcastěji hladkou kouli. Nejenom samotna aproximace způsobuje chybu stanoveni měrneho povrchu a dalsich parametrů materialu. Při výpoctu měrneho povrchu prasku se dale nepřihliži k charakteru rozděleni pravděpodobnosti, kterým se rozměr castic prasků a sypkých hmot řidi. Jedna o logaritmicko-normalni rozděleni. V clanku je navrženan statisticka metoda zpřesňujici výpocet měrných povrchů prasků a sypkých hmot a jsou prezentovany take dalsi statisticke parametry těchto materialů.
The aim of the research was to investigate changes of abrasive grains on metals observing the ker... more 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 abr...
This paper presents an investigation of abrasive waterjet turning (AWJT). The purpose of the arti... more 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.
Measurements enabling the online monitoring of the abrasive waterjet (AWJ) cutting process are st... more 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 eff...
Material structure is one of the important factors influencing abrasive waterjet (AWJ) machining ... more Material structure is one of the important factors influencing abrasive waterjet (AWJ) machining efficiency and quality. The force measurements were performed on samples prepared from two very similar steels with different thicknesses and heat treatment. The samples were austenitized at 850 °C, quenched in polymer and tempered at various temperatures between 20 °C and 640 °C. The resulting states of material substantially differed in strength and hardness. Therefore, samples prepared from these material states are ideal for testing of material response to AWJ. The force measurements were chosen to test the possible influence of material structure on the material response to the AWJ impact. The results show that differences in material structure and respective material properties influence the limit traverse speed. The cutting to deformation force ratio seems to be a function of relative traverse speed independently on material structure.
Research performed by the author in the last decade led him to a revision of his older analytical... more 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 app...
Machining of materials through classical way, i.e. using conventional tools for turning, drilling... more 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.
The knowledge of the surface roughness is a very important parameter for machining techniques. Th... more The knowledge of the surface roughness is a very important parameter for machining techniques. The direct detection of surface quality is a problem of abrasive water jet technology, especially if used for turning, milling or grinding, where the surface is opened for detection. The topic of the paper is a theoretical and experimental investigation of certain optical methods and their utilisation for surface quality analyses. Methods are based on scanning by defocused laser beam. The methods are theoretically described and the most important theoretical results are discussed for wide scale of technical conditions. The experimental data are analysed from the point of utilisation of the methods for determination of roughness and waviness of surfaces prepared by abrasive water jets.
The necessity of monitoring the abrasive waterjet (AWJ) processes increases with the spreading of... more 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 t...
V technickem a přirodovědeckem výzkumu je velmi casto nutne znat hodnoty měrných povrchů prasků c... more V technickem a přirodovědeckem výzkumu je velmi casto nutne znat hodnoty měrných povrchů prasků ci sypkých hmot. Prvnim stupněm takoveho výpoctu je pak aproximace zrn některým geometrickým utvarem s hladkým povrchem, nejcastěji hladkou kouli. Nejenom samotna aproximace způsobuje chybu stanoveni měrneho povrchu a dalsich parametrů materialu. Při výpoctu měrneho povrchu prasku se dale nepřihliži k charakteru rozděleni pravděpodobnosti, kterým se rozměr castic prasků a sypkých hmot řidi. Jedna o logaritmicko-normalni rozděleni. V clanku je navrženan statisticka metoda zpřesňujici výpocet měrných povrchů prasků a sypkých hmot a jsou prezentovany take dalsi statisticke parametry těchto materialů.
The aim of the research was to investigate changes of abrasive grains on metals observing the ker... more 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 abr...
This paper presents an investigation of abrasive waterjet turning (AWJT). The purpose of the arti... more 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.
Measurements enabling the online monitoring of the abrasive waterjet (AWJ) cutting process are st... more 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 eff...
Material structure is one of the important factors influencing abrasive waterjet (AWJ) machining ... more Material structure is one of the important factors influencing abrasive waterjet (AWJ) machining efficiency and quality. The force measurements were performed on samples prepared from two very similar steels with different thicknesses and heat treatment. The samples were austenitized at 850 °C, quenched in polymer and tempered at various temperatures between 20 °C and 640 °C. The resulting states of material substantially differed in strength and hardness. Therefore, samples prepared from these material states are ideal for testing of material response to AWJ. The force measurements were chosen to test the possible influence of material structure on the material response to the AWJ impact. The results show that differences in material structure and respective material properties influence the limit traverse speed. The cutting to deformation force ratio seems to be a function of relative traverse speed independently on material structure.
Research performed by the author in the last decade led him to a revision of his older analytical... more 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 app...
Machining of materials through classical way, i.e. using conventional tools for turning, drilling... more 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.
The knowledge of the surface roughness is a very important parameter for machining techniques. Th... more The knowledge of the surface roughness is a very important parameter for machining techniques. The direct detection of surface quality is a problem of abrasive water jet technology, especially if used for turning, milling or grinding, where the surface is opened for detection. The topic of the paper is a theoretical and experimental investigation of certain optical methods and their utilisation for surface quality analyses. Methods are based on scanning by defocused laser beam. The methods are theoretically described and the most important theoretical results are discussed for wide scale of technical conditions. The experimental data are analysed from the point of utilisation of the methods for determination of roughness and waviness of surfaces prepared by abrasive water jets.
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Papers by Libor Hlaváč