Journal of Materials Processing Technology 177 (2006) 600–603 Analysis of ﬂash formation in continuous rotary extrusion of copper T. Manninen a,∗ , T. Katajarinne b , P. Ramsay c a Helsinki University of Technology, Structural Mechanics, P.O. Box 2100, FIN-02015 TKK, Finland b Helsinki University of Technology, Processing and Heat Treatment of Materials, P.O. Box 6200, FIN-02015 TKK, Finland c Outokumpu Castform Oy, P.O. Box 60, FIN-28101 Pori, Finland Abstract Flash formation is an important technological issue in continuous extrusion of copper. Flash build-up has adverse machine loading effects and therefore the ﬂash must be shaved off from the wheel surface. This results in 5–25% material losses and extra costs from operator time spent clearing excess from the machine and disposal of the scrap. The present work aims to explain the mechanics of ﬂash formation in continuous rotary extrusion. An analytical model is developed for estimating the ﬂash shape and the amount of scrap based on geometrical factors and frictional properties. The proposed method is veriﬁed by comparison with experimental ﬁndings and with FE-simulation results. © 2006 Elsevier B.V. All rights reserved. Keywords: Continuous extrusion; Flash; Analytical model 1. Introduction Continuous rotary extrusion [2,3] was invented by Derek Green at the UKAEA in the 1970s. The principle of the contin- uous extrusion process is illustrated in Fig. 1. The machine has a revolving wheel with a circumferential groove. The feedstock is forced into the groove by means of a coining roll and driven down by friction. A ﬁxed shoe encloses the groove. Inside the shoe an abutment blocks the groove and forces the feed material into the expansion chamber and through a shape-giving die. A part of the feed material is extruded into the ﬂash gap between the shoe and the wheel. A small layer of material also circulates in the process as groove lining. Continuous rotary extrusion enables production of proﬁles and sections in virtually unlimited lengths. No pre-heating is required for the feedstock, and the production rate is high com- pared to traditional extrusion. Continuous extrusion is also an efﬁcient method for breakdown processing of cast grain struc- ture in aluminium and copper. The cast structure is transformed into equiaxial and ﬁne-grained one in a single pass. Flash formation in continuous extrusion resembles to that of closed die forging. Of necessity, there exists a gap between the revolving extrusion wheel and stationary shoe, and certain part of the feed material is extruded to the ﬂash gap. Flash build-up has adverse machine loading effects in copper extrusion, and ∗ Corresponding author. Tel.: +358 9 4513721; fax: +358 9 4513826. E-mail address: timo.manninen@tkk.ﬁ (T. Manninen). the ﬂash must therefore be shaved off from the wheel surface. This results in 5–25% material loss and extra costs from operator time spent clearing excess from the machine and disposal of the scrap. Therefore, ﬂash formation can be identiﬁed as one of the key technological issues of continuous extrusion. Typically, ﬂash formation is controlled by adjusting the ﬂash gap size. The size and shape of the ﬂash gap are, however, affected by bearing clearances, wheel eccentricity, machine deﬂection and local thermal expansions. Over the years the extruder design has been improved by numerous technologi- cal innovations aiming for better control of the ﬂash gap size [4,5]. Nevertheless, it is hard to specify the optimum ﬂash gap shape. Small gap settings producing less scrap increase surface wear and the risk of damaging the tooling. A number of experimental, analytical and numerical investi- gations of the continuous extrusion process have been presented since the late 1980s. However, ﬂash formation has not been prop- erly addressed in the existing investigations. The present work aims to explain the mechanics of ﬂash formation during steady state continuous extrusion. An analytical model is developed for estimating the ﬂash shape and the amount of scrap produced. The theoretical results are veriﬁed by comparison with experiments and numerical results. The simulations are discussed in detail in an accompanying paper [1]. 2. Analytical model In the present work, ﬂash formation is analysed based on a slab-theoretic approach. The approach is similar to that in 0924-0136/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2006.04.051