In multiple-stage cold forging using a parts-former machine, lubricant oil is needed on the ends of billets after cropping. The oil is trapped by a squeeze action and it is sometimes supplied from valleys of roughness serving as oil pits. Naturally, the surface roughness on the billets must affect lubrication, but data on surfaces of practical billets is not sufficient for estimating the lubrication condition for designers of tools and processes. The authors sampled some practical billets in two typical kinds of multiple-stage cold forging. Changing distributions of surface roughness and the contact ratios are exemplified.
KudoH.ShinozakiK.Attempts for reducing friction in cold extrusion of metals (in Japanese). J. Jap. Soc. Technol. Plast., 1968, 9(90), 466–475.
2.
AzushimaA.YoneyamaS.YamaguchiT.KudoH.Direct observation of microcontact behavior at the interface between tool and workpiece in lubricated upsetting. Ann. CIRP, 1996, 45, 28–33.
3.
SobisT.EngelU.GeigerM.A theoretical study on wear simulation in metal forming processses. J. Mater. Processing Technol., 1992, 34, 233–240.
4.
OyaneM.OsakadaK.The mechanism of lubricant trapping under dynamic compression. Bull. Jap. Soc. Mech. Engrs1969, 12, 149–155.
5.
WilsonW. R. D.WalowitJ. A.An isothermal hydrodynamic lubrication theory for hydrostatic extrusion and drawing processes with conical dies. Trans. ASMEJ. Lubr. Technol., 1971, 93, 69–74.
6.
WilsonW. R. D.An isoviscous model for the hydrodynamic lubricant of plane strain forging processes with flat dies. Trans. ASME J. Lubr. Technol., 1974, 95, 539–547.
7.
MahdavianS. M.A refined analytical model for hydrodynamic lubrication of cold extrusion and its comparison with experiment. Trans. ASME J. Lubr. Technol., 1982, 104, 46–52.
8.
BayN.WanheimT.Contact phenomena under bulk plastic deformation condition. In Proceedings of the 3rd International Conference on Technology of plasticity, 1990, 4, 1677–1691.
