Završna obrada metala bazirana na kotrljanju krutog alata

Abstract

Ovaj rad se bavi procesom završne obrade metala kotrljanjem kuglice po površini predmeta obrade. Razvijena su dva alata visoke krutosti: alat za obradu ravnih i cilindričnih površina i alat za obradu otvora. Teorijski je razmatran uticaj krutosti alata na parametre površinske hrapavosti a eksperimentalno je utvrđen uticaj parametara procesa obrade, inicijalne hrapavosti i definisana je optimalna trajektorija krutog alata. Krutim alatom sa kuglicom koja prodire u profil hrapavosti do predefinisane dubine penetracije se postiže optimalni kvalitet površine bez obzira na inicijalnu mašinsku obradu. Na osnovu analize kinematike glodanja je razvijen model hrapavosti koji je korišćen za FEM analizu. Numeričke simulacije i korišćeni model hrapavosti potvrđuju tvrdnju da se prodiranjem krutog alata do srednje linije profila hrapavosti postižu najbolji rezultati sa aspekta poboljšanja povrinske hrapavosti. Nakon analize unutrašnjih napona u predmetu obrade uspostavljena je zavisnost unutrašnjih napona po dubini otvrdnutog sloja i dubine penetracije kuglice. Osim toga, fenomen tečenja materijala sa vrhova neravnina je razjašnjen. Primarni cilj obrade alatom za obradu otvora je postizanje dimenzione i geometrijske tačnosti otvora. Korišćenjem specijalno konstruisanog krutog alata otvori su prošireni u proseku za 0.06 mm pri čemu su greške kružnosti i cilindričnosti drastično smanjene, posebno pri većim dubinama penetracije kuglice. Dodatno, površinska hrapavost je redukovana za 35%. FEM analizom je određena distribucija napona u predmetu obrade kao i zaostali naponi nakon obrade.

This paper is focused on the process of ball burnishing. Two high stiffness tools are developed: tool for processing of flat and cylindrical surfaces and tool for processing of openings. The influence of tool stiffness on surface roughness parameters was considered theoretically, while experimental investigation was conducted to define the influence of process parameters, initial surface roughness and optimal trajectory of stiff tool. The ball within the stiff tool system, which follow a predetermined depth of penetration into the roughness profile, very likely provide optimum surface quality, regardless of the initial machining. For the purpose of numerical simulations, a surface roughness model based on milling kinematics was used. Numerical simulations and the used roughness model support the claim that penetrating with a stiff tool up to the mean line of the roughness profile yields best surface quality. The analysis of internal stresses within the workpiece after ball burnishing allowed a relationship to be established between internal stress distribution along the depth of the hardened layer and ball penetration depth. Furthermore, the phenomenon of profile peak deformation is substantially clarified. The primary goal, when using tool for processing of openings, was to achieve dimensional and geometrical accuracy. Using a specially designed stiff tool, the openings were widened by 0.06 mm on average, while the roundness and cylindricity errors were drastically reduced, especially at greater ball penetration depths. In addition, the surface roughness was improved by 35%. FEM analysis was conducted to determine the stress field distribution in the workpiece, as well as to approximate the residual stresses after the ball burnishing.