Dejan Movrin

One Contribution to the Friction Investigation in Bulk Metal Forming

One Contribution to the Friction Investigation in Bulk Metal Forming Friction is resistance to relative motion when one body slides over another. In metal forming operations, both sheet metal and bulk metal forming, friction is undesirable but also unavoidable occurrence. It has negative impact on main process parameters as well as on workpiece quality. In order to obtain accurate results in metal forming experiments or simulations, the precise value of friction has to be known. In this paper several methods for friction evaluations, such as ring test, forward bar extrusion, backward - forward hollow extrusion, twist extrusion are presented and analyzed. A new double backward extrusion model is proposed. Prilog Istraživanju Fenomena Trenja u Tehnologiji Zapreminskog Plastičnog Deformisanja Trenje je pojava koja nastaje usled relativnog kretanja jednog tela u odnosu na drugo. U tehnologijama plastičnog deformisanja trenje predstavlja nepoželjan, ali u isto vreme i neizbežan fenomen. Trenje ima negativan uticaj na sve glavne parametre procesa, a takođe i na sam kvalitet radnog komada. Kako bi se dobili tačni rezultati u eksperimentima i simulacijama kod plastičnog deformisanja, neophodno je veoma dobro poznavanje pojave trenja u datim uslovima. Za kvantifikaciju trenja razvijeni su brojni modeli, od kojih su najviše u primeni Coulomb-ov model, model konstantnog trenja i generalni model trenja. Svaki od ovih modela ima svoje područje primene. Postoji nekoliko razvijenih tehnika za određivanje veličine trenja. Neke od njih su prikazane u radu: sabijanje prstena, istosmerno istiskivanje, kombinovano šuplje istiskivanje, istiskivanje sa rotacijom, itd. Takođe je u radu predložen i novi metod za određivanje veličine trenja (dvostruko suprotnosmerno istiskivanje). U ovom metodu, obradak je istisnut pomoću specijalnog žiga sa otvorom kroz sredinu. Na taj način materijal teče i kroz centralni otvor i između žiga i matrice. Količina materijala koji protekne kroz centralni otvor je u korelaciji sa veličinom trenja koja vlada u procesu (što veće trenje, to više materijala proteče kroz otvor). Na bazi ove činjenice konstruisan je etalon dijagram, koji omogućava određivanje veličine trenja u konkretnim uslovima

Material formability at cold upsetting of cylinder by different plates as a base for metal forming technology design

Upsetting of cylinder by flat dies is one of the elementary bulk metal forming operation. But, upsetting of cylinder can also be performed by the dies different than flat, which influences the stress-strain state and material formability. This paper describes the formability analysis at cold upsetting of cylinder and hollow cylinder by different plates (flat plates, hollow plates and hollow plates whit concentric channels). The aim of this investigation is determination of influences of die and workpiece geometry on stress-strain state and material formability. The obtained results are integrated in formability limit diagram, which represents relationship between limit strain (ϕe1) and stress indicator (s). Experimental investigations have been performed on steel specimens C4146 (EN: 100Cr6). The determined diagram is a base for metal forming technology design, as it enables to predict damages of material structure during plastic deformation.

Spiral inductor fabricated by 3D additive manufacturing

This paper presents spiral inductor fabricated by 3D additive manufacturing. The inductor was made with conductive epoxy silver based paste which was injected in spiral channel fabricated in polylactide (PLA) substrate (model) using additive manufacturing technology. The fabricated structure has value of effective inductance around 415 nH, maximum quality factor around 12 and outer dimension diameter 24 mm. The prototype results show good characteristics of 3D additive manufactured spiral inductor and demonstrate an innovative approach to fabricate low-cost, passive devices such as an inductor.