Metal tools and implements – making – Blank or process – Die
Reissue Patent
1998-11-19
2001-09-18
Rada, Rinaldi I. (Department: 3724)
Metal tools and implements, making
Blank or process
Die
C076S107800
Reissue Patent
active
RE037366
ABSTRACT:
FIELD OF THE INVENTION
This 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 INVENTION
For 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 associated outer face at an obtuse included angle. When the line of severance subtends more than a quandrant, the cutting edge transfers from one side edge to the other of the coacting lands at a pair of cross over sections each having an outer face which is substantially narrower than the outer face of the adjacent portion of the land. To enable proper registration of the coacting lands to cut a web, the pair of die cylinders can be relatively shifted both axially and in rotational phase with respect to each other.
The die is made from a cylindrical blank of tool steel which is hardened and ground to produce a cylindrical surface before it is electrical discharge machined (EDM) to produce the lands with the desired geometry thereon. To produce the desired accuracy and geometry of the lands, they are EDM machined in the hardened cylindrical workpiece utilizing a negative electrode, which is preferably cylindrical with grooves machined in the periphery thereof with a generally V-shape cross section for forming the lands of the die cylinders.
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.
SUMMARY OF THE INVENTION
A pair of rotary die cylinders having coacting severing blades formed by integral lands projecting generally radially outwardly from the main body of each cylinder and having in cross section, an outer face and a pair of spaced apart side faces at least one and preferably both of which are essentially perpendicular to the outer face or its chord. A perpendicular side face and the outer face intersect to define a cutting edge on the land, and preferably the other edge is chamfered. To facilitate disengaging the cut blank from the dies, preferably each coacting pair of cutting lands has an associated elongate ejector land located adjacent to them and within the perimeter of the line of severance of the cut blank. The ejector land is integral with the die cylinder having the cutting land disposed outside the cut plank and cooperates with the other cutting land (inside the cut blank) to flex the blank.
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.
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M. L. Murphy et al., “The Rapid Manufacture of Metallic Components by Laser Surface Cladding”,Laser Assisted Net Shape Engineering Proceedings of the LANE'94,vol. II, Meisenbach Bamberg 1994, pp. 803-814.
Cox William Allen
Pfaff Alan Rae
Ashley Boyer
Bernal International, Inc.
Rada Rinaldi I.
Wood Herron & Evans LLP
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