Ocena efektywności smarów plastycznych w aspekcie ich zastosowania w procesie głębokiego tłoczenia blach

W artykule przedstawiono badania tribologiczne dwóch smarów plastycznych (smaru maszynowego i Litomosu EP-25) przeprowadzone pod kątem oceny ich zdolności do pełnienia funkcji smaru technologicznego. Badania efektywności tych smarów przeprowadzono w dwóch etapach. Etap pierwszy obejmował wyznaczenie wskaźników efektywności na podstawie testów wykonanych na aparacie czterokulowym z kulkami o twardości modelującej twardość matrycy i tłoczonej blachy. Jako kryteria efektywności przyjęto obciążenie zespawania, zużycie i wskaźnik granicznego obciążenia zużycia. W etapie drugim przeprowadzono testy na prasie w sztywnej matrycy używając stempla o średnicy = 190 mm. Tu kryterium efektywności smaru była głębokość i maksymalna siła tłoczenia.

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A paper presents results of tribological tests of two plastic greases (a machine grease 2 and Litomas EP - 25) carried - out in order to estimate their ability to perform the function of the technological grease in the process of deep sheet - metal stamping. The tests of the greases effectiveness have been realized in two stages. The first stage comprised determination of the effectiveness factors basing on the tests conducted on four - balls apparatus with the balls of the hardness modeling the hardness of both the die and the metal sheet. The rotating ball was hardened to 62 HRC while stationary balls to 240 HB. The following factors were assumed as the effectiveness criteria: welding load FZ, wear rate of the stationary balls d and the indicator of the limiting wear load Goz. In the second stage the tests were carried - out by means of hydraulic press with the load of 2000 kN. The samples were in the form of rollers being stamped in the rigid die by the punch of diameter 190 mm. The samples were produced from the car body sheet E220BH with thickness of 0,75 mm. Here, the effectiveness criterion was depth and maximal stamping force as well as the surface outlook of the drawpiece. It has been found that the welding load FZ was equal to 450 daN and that it is by 120% bigger when compared to the force found for the machine grease. The similar differences occurred during the stamping trials. Destruction of the samples, in the presence of the machine grease, occurred on the depth of 24 mm, that is about 9 mm greater as without grease. It was easy to stamp the samples without the traces of destruction on the full depth of 69 mm at the presence of Litomas grease. The results to be found allow to conclude that the effectiveness of the plastic grease estimated on the four - balls apparatus with the balls modeling the die and metal sheet hardnesses does not differ essentially from that determined in the process of deep stamping. However, this statement necessitates, due to the small number of the greases as well as due to neglecting variation of p, v parameters, further tests.