Určování fyzikálně - mechanických vlastností materiálu z jeho porušení kapalinovým paprskem

Abstract

Thesis are aimed at determination of correlation between material properties and effects of abrasive water jet, and it is in a direct relationship with solving of the project MPO 1H–PK2/22. There is a range of approaches to the evaluation of quality of surfaces created by the abrasive water jet, from the ones evaluating the roughness and waviness to the ones evaluating the convergence or divergence established on the surface of the cut during penetration of jet through material. The presented doctor’s dissertation describes the principle and use of a new method of measuring the typical quality characteristics of the cut. The method is based on establishing the scale of deviation of the abrasive water jet from the original direction due to the movement of the nozzle over the cut material and different qualities of the various materials. This scale is characterised by the so-called declination angle, the parameter which is monitored by the individual sorts of materials with different physical-mechanical qualities. Theoretical and experimental works have established the relationship between the parameters used with liquid jets and the qualities of the accessible tested materials. In the theoretical part I have discussed the scientific approaches of authors dealing with the problem of water jet and I have described their system of equations which enabled evaluation of the important parameters of cutting. I have focused in most detail on Hlaváč’s theory, as these theses are mainly based on, and I concentrated on the parameters of materials included in this theory. The effort to prove a direct correspondence between values of selected parameters and values of angles of declination demanded certain knowledge of the material structures. More detailed analyses of the structure and qualities are conducted at specific work stations that using mostly standardised directives, select and use a suitable method for determining of the required quality. The practical part is focused on two groups of materials – metals and rocks. Although both these groups include a large number of representatives in fact, only a limited number of materials have been incorporated into the experiments. They had been selected based on the requirements for cutting by the water jet and on the consequent evaluation of results aimed at prove of a possible correlation. I have also confronted their selected qualities obtained from various sources. A direct relationship connected to the measured declination angle is looked for being a predicative parameter of the quality of the cut surface. The acquired knowledge can lead to improvement of the efficiency and effectiveness of the cutting process itself and has been used for the development of the new CNC control program of machines of a new generation in the PTV spol. s.r.o. company in Hostivice.