Modelo para la identificacion de los errores de excentricidad en fresado periferico estudio de la influencia de los errores de excentricidad en el acabado superficial de las piezas fresadas

Resumen

in machining environments with expensive labour costs (as ours) the cutting conditions selection for machining operations can no "longer be made by the traditional "trial and error" method because the. costs are too high. instead the computer simulation of machining operations (which isa part of the so called virtual Machining) seems to be a promising alternative. A key feature in virtual Machining is the development of software for the accurate simulation of machining entities such as: tool trajectories, machined surface topography, stress strain and temperature distribution in the tool and in the workpiece during machining. And for it models have to be developed. in this PhD thesis an innovative model for machined surface topography simulation is presented. The model is only val i d for machining operations where process stiffness is sufficiently high that dynamics effects on the process can be neglected without noticeable error. The model simulates surface roughness and shows the presence of roughness heterogeneity bands which can be detrimental to the aesthetic appearance of the workpiece especian y in sectors such as Mould and Dies. The heterogeneity bands appear as a result of the presence of the overall tool eccentricity error. This is the sum of three different errors: a) the tool radial eccentricity error (the distance between the tool axis and the main spindle axis assuming that they are parallel), b) the tool tilt error and c) the tool grinding error (differences between the different teeth edge radius in each sección of the milling tool) which is generated in the process of tool sharpening. This thesis compri ses five chapters. in chapter the historical background of the study of the effects of tool eccentricity in peripheral milling on the surface roughness generation is presented as well as the thesis objectives. ln chapter 2 an innovative the model for the surface roughness generation is presented The model demonstrates that the bands are generated as a consequence of the overall eccentricity error and therefore that any accurate surface roughness simulation depends on the degree of accuracy of the three aforementioned errors. But the first and the second errors are very difficult to measure with the state of the art equipment. On the other hand the third one is easier to measure but in order to do it a methodology has to be developed. For this error measurement, an innovative methodology (that employs a Roundness measuring machine) is developed in Chapter 3. This methodology has been implemented on tools from three different suppliers and the results show that grinding errors are present along the teeth edge helix. The suppliers never menti on this errors but in this chapter is shown that their valúes can be as big as the sum of the parallel axis offset and the tilt errors and therefore they can no longer be neglected in the future roughness generation models. After the development of the method for grinding errors measurement, the next issue addressed in the thesis consists on the estimation of accurate and reliable parallel axis offset and tilt errors, however this a very difficult task as it was stated before, but since the surface topography is thoroughly defined when the valué of three error is known, in the development a the thesis a new approach is proposed. lt consists of the estimation of the valúes of the parallel axis offset and tilt errors based on the knowledge of the grinding errors of a particular milling tool and the real surface roughness of a workpiece machined by that milling tool. This is addressed in Chapter 4 and it consists on solving the inverse problem of the one addressed in chapter 2. if the cutting conditions are elected process dynamics is kept , results of this strategy are in reasonable agreement with experiments, therefore the developed strategy gives the valúes of the parallel axis offset and tilt errors of a particular mili tool with reliab