UDC 621.91.01 KNIVES FOR ROTARY DIES WITH VARIABLE GEOMETRY In almost all areas of modern machine-building production the use of CAD / CAM systems has been established. <...> A method for designing a new instrument - result of the rich experience of the author - rotary knifes with variable geometry along the cutting contour is analyzed. <...> INTRODUCTION Rotating dies (Fig. 1) are characterized with a significantly higher productivity than those working with fore- and- aft, thus have inculcated in a number of large-scale and mass production. <...> Band matrerial 2, of which pies are cut (Consider the case of machines for sanitary absorbents), passes between the rotary cutter 1 and a smooth drum. <...> One or more cutting edges with shape and size of the cut parts are developed on the rotary knifes (Fig. 1,b), called as well "figured". posed by the requirement to achieve high durability [3] regardless of the regrinding of the tools to restore their cutting ability. <...> MODELING OF ROTARY KNIVES OF VARIABLE GEOMETRY Study [8, 9] proves that to increase rotary dies duraa bility their knife must be of variable width b along the path of the cutter contour. <...> The value of b changes in a way that the area of contact patch in close vicinity of the intersection between the formation of the supporting cylinder and the path of the cutting edge (Fig. 2) to remain relatively constant regardless the angle which the tangent to the contour form with the formation of the cylindrical plane of the supporting drum, respectively the positioned normally to its axis. <...> It must be accounted that the cutting edge curve is closed and contact is realized simultaneously in two points. <...> Thus the changing width of the path will compensate for the changing angle of the tangent to the cutting edge, so that at a constant force of compression between the rotary knife and the smooth drum, the tension along the knife contour per unit of area will remain constant, hence the wear. <...> It is very important since a system fault, the die stops cutting and appears even when the cutting contour is in a section at a smaller radius (5 to 10 m µ) against the boards at both ends of the rotary knife. © Peter Hadzhiyski b Fig. 1 These tools are made with the use of machine tools with CNC [22]. <...> Dh the cutting (Fig. 3 <...>