Method of making rotary cutting dies

Abstract

A method of making a pair of rotary die cylinders with lands having coacting cutting edges which cut blanks from a web of material passing through the nip of the rotating dies. In cross section each land has an outer face and a pair of spaced apart side faces which are parallel to each other and perpendicular to the chord of the outer face to provide a clean cut and facilitate release of the cut blank from the cutting blades as it emerges from the nip of the dies. The die cylinders are journalled for rotation by recesses with frusto conical locating surfaces in their opposed ends. Each die cylinder is made by machining the recesses in the opposed ends of a generally cylindrical workpiece of tool steel and then utilizing the recesses to locate and orient the workpiece relative to a cutting tool to produce a cylindrical surface on the workpiece concentric with the axis of the recesses and then to machine away portions of the periphery of the cylindrical surface to form the cutting blade lands thereon. After machining is completed the cutting blade lands may be hardened by heat treating utilizing a laser beam directed onto the lands to heat them at an elevated temperature so that upon quenching they are hardened without any substantial hardening and resulting distortion of the core or body of the workpiece.

Description

FIELD OF THE INVENTIONThis invention relates to rotary die cutting of blanks from thin sheets or webs of material, and more particularly to improved rotary cutting dies and a method of making them.BACKGROUND OF THE INVENTIONFor many years, a pair of superimposed rotary dies with cutting blades on one of both cylinders have been used to cut blanks from a thin web of material passing through the nip of the dies. Typically, the thin web is of a material such as paper, paper board, cardboard, plastic film, metal foil, thin sheet metal and the like.U.S. Pat. No. 4,608,895 discloses a pair of rotary die cylinders with integral complementary cutting blades thereon which coact to sever a web of material passing through their nip. Each severing blade has an elongate land projecting generally radially outwardly from its cylinder and having in cross section an outer face and spaced apart depending side faces inclined towards each other at an acute included angle, and each inclined to its assoc...

AI Technical Summary

Benefits of technology

The rotary die cylinder is made by machining in the opposed ends of a tool steel workpiece, which is preferably generally cylindrical, a pair of recesses each having a bore with a frusto conical locator surface tapering inwardly with both the of the bores lying essentially on the same common axis of rotation. The tapered bores are used to accurately locate the workpiece while machining a peripheral cylindrical surface on it which is concentric with the common axis of rotation. Utilizing the recesses and frusto conical surfaces, the workpiece is located and oriented relative to a cutting tool to machine away material from the periphery of the workpiece to form the cutting blade lands and any ejector lands. Subsequently, the machined cutting lands are hardened by heat treating utilizing the tapered bores to locate and orient the machined workpiece relative to a laser to direct its beam of electromagnetic energy onto the cutting blade lands to heat them to an elevated temperature from which they are cooled to harden them without substantially hardening the main body of the cylinder.

Objects, features and advantages of this invention are to provide a pair of rotary die cylinders with coacting cutting blades thereon which have a substantially longer useful life in service, require a substantially lower cutting force requiring less power to drive the cylinders and produce less load thereon, substantially reduce the likelihood of cut blanks being caught, trapped or hung up in the die cylinders, having cutting blades which are easier, faster and more economical to resharpen after becoming dull in use, a substantially longer in service useful life, and rotary die cylinders and a method of making them which are significantly less expensive, may be made by machining with conventional cutting tools, enable the cutting blades to be hardened after being formed, and are relatively quick, easy, inexpensive and requires less capital investment to make them.

Problems solved by technology

While these die cylinders have been sold commercially and performed satisfactorily for relatively high volume mass production operations, they are expensive and difficult both to manufacture and resharpen when they become worn or dull in use.

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