Abstract: We consider the extrusion of ribs on thin flat plates as a problem in the theory of plane strain for perfectly plastic-ringid materials. These assamptions imply that ι≥2(w+d), (Fig. 1), and that the effect of work hardening being distributed over the deformed regions.The problem is one of coining. The anthor is unaware of other solutions treated in the prosent manner, except a similar initial motion problem given in Ref. 15. However, if the thickness h of the plastic material is large compared to the width of the extruded bar d, the flow region will be concentrated around the die and this is the familiar problem of inverted extrusion (Ref. 16) has recently given an approximate solution to the present problem. His results are discussed in section 4.