Metal tools and implements – making – Blank or process – Die
Reexamination Certificate
1998-11-25
2001-01-30
Watts, Douglas D. (Department: 3724)
Metal tools and implements, making
Blank or process
Die
C076S107800, C219S121850
Reexamination Certificate
active
06178852
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally 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 or both of the dies 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, paperboard, cardboard, plastic film, metal foil, thin sheet metal, and the like.
U.S. Pat. No. 4,608,895 discloses a pair of rotary dies which are made from a cylindrical blank of tool steel which is hardened and then ground to produce a cylindrical surface before it is electrical discharge machined (EDM) to produce cutting blades on the surface of the dies with the desired geometry to cut the blanks. The cutting blades are formed on the rotary dies after the steel of the rotary dies is hardened to prevent the deformation which would occur if the cutting blades were formed and then the rotary dies were heat treated to harden the cutting blades. While these rotary dies have been sold commercially and performed satisfactorily for relatively high volume mass production operations, they are expensive and difficult both to manufacture and re-sharpen when they become worn or dull in use.
U.S. Pat. No. 5,575,185 discloses a pair of rotary dies having coacting cutting blades projecting generally radially outwardly from the main body of each rotary die. These rotary dies are formed of unhardened tool steel and the cutting blades may be formed by machining with conventional cutting tools. After the cutting blades are formed by machining, the cutting blades are hardened by heating to an elevated temperature with a laser and quenching them without substantially hardening the core or body of the workpiece and hence without distorting the core or body of the workpiece by heat treating it. Thus, this system obviates the need for EDM machining which reduces the cost to produce rotary dies.
However, conventional cutting tools tend to produce an undesirable offset or undercut when attempting to machine a cutting blade which extends generally radially outwardly from a rotary die cylinder. The undercut produces a cutting blade with a sharp edge or edges which wear quickly and may chip causing an unsatisfactory cut. Further, the blades with an undercut can cause a cut blank of material to become stuck on a cylinder interfering with the cutting of subsequent blanks and potentially jamming and damaging the cutting dies. Also, detailed portions of the cutting blades are difficult to form with conventional cutting tools and on average, 30% to 60% of the total machining time of cutting blades with conventional tools is spent forming such detailed portions as corners and cross-over portions.
SUMMARY OF THE INVENTION
A pair of rotary die cylinders having co-acting cutting blades formed by integral lands projecting generally radially outwardly from the main body of each cylinder and a method of making them by rough machining a tool steel workpiece with conventional cutting tools to form the general outline of the cutting blades and thereafter final machining and simultaneously heat treating the cutting blades with a laser to provide an accurately formed and hardened cutting blade. Preferably, the rough machining with conventional cutting tools and the final machining and heat treating by a laser are performed with the same machine tool, such as a computerized numerical control (CNC) machining center. Such a machining center permits rapid and accurate rough machining as well as accurate final laser machining of the cutting blades. The more accurate final machining accomplished by a laser produces a more accurately formed cutting blade and also simultaneously heat treats the blade with minimal distortion of the blade and without significant distortion of the core or body of the cylinder.
Objects, features and advantages of this invention are to provide a pair of rotary die cylinders with co-acting cutting blades which are easier and more accurately formed, can be initially rough formed with conventional cutting tools, are precisely formed into their final shape by a laser which simultaneously heat treats the cutting blade, can be heat treated and hardened without substantial distortion of the cutting blade or the die cylinder, provide a clean and accurate cut of a blank from a web of material, are of relatively simple design and economical manufacture and assembly and have a long in service useful life and may be formed by a method which is more accurate, faster, easier and less expensive than current methods of making the rotary die cylinders.
REFERENCES:
patent: 4473735 (1984-09-01), Steffen
patent: 4608895 (1986-09-01), Bell et al.
patent: 5061839 (1991-10-01), Matsuno et al.
patent: 5575185 (1996-11-01), Cox et al.
patent: 2013674 (1971-10-01), None
patent: 2752717 (1979-05-01), None
patent: 0191203 (1986-08-01), None
patent: 0228623 (1989-09-01), None
patent: 9729878 (1997-08-01), None
Atlantic Commerce Properties
Reising Ethington, Barnes, Kisselle, Learman & McCulloch, P.C.
Watts Douglas D.
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