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Technology Focus

Stripping Tool Design and Fabrication Considerations in Automatic Platen Diecutting

by Dan Witucki, Advanced Die Supplies

May-June, 2005

Stripping tool design should be a cooperative effort between the converter and his diemaker no matter whether that diemaker is internal or external. Some decisions are made by the converter and some by the diemaker. This division of labor is somewhat determined by the relationship of the converter with his diemaker and the trust that they have in each other.

Production planning
All job layouts are an X-Y matrix of one or more package designs on a two-dimensional paper surface. They can range from a one-up layout to a multiple assortment layout of various designs in a combination. Hopefully, the converter will have reviewed the particular job to determine the best layout in regards to the number of each design required for the greatest economy of production. Other factors to take into account would be printing bleeds, board utilization and the physical diecutting, stripping and blanking situations produced with the alternative layout choices.

The diemaker and/or converter will produce the CAD file and review the layout options to determine the best stripping method and the requirements to do so considering the cutting press type, the board type, the areas to be stripped and the impact of possible future blanking.

Will this job require only a female stripper unit (center unit), or will a combination of male and female strippers be required? Will this job require a front separator board or boards? Will this job require standard stripping or some sort of power/pressure stripping alternative?
 


CAD layout of die showing areas to be stripped.


Cutting die design to accept stripping option desired
At this point, the stripping knife locations are determined by what scrap areas are to be left in to assist in carrying the sheet through to the delivery section of the press and by what areas are to be removed in the stripping process.

If there are large pieces of scrap in the layout, it may be necessary to add bridges to the female stripping board to help the sheet span the large cut-out areas in the female stripper as the sheet is moved to the press delivery area. The cutting die will require additional scrap knives positioned over the areas that will correspond to the locations of the bridges on the female stripping board. These must also be added at this time.

Finally, at this time, the CAD layout file can now be completed by adding any kind of centerline notches, bolt-down holes, counterplate positioning holes, storage rack holes, identification information and anything else as requested by the converter.
 


CAD layout of Female stripper unit (center unit).


Stripping tool design options
Now we can begin with the design of the stripping tools. What are the cutting press specifications involved? Is this an SP or SPO press? Does this cutting press utilize centerline features? What are the exact press specifications? What is the required thickness of the female stripping board? What is the required total height of the male stripping unit? Does this cutting press require separator units and how many? Does this cutting press have lower stripping pins available? What is the physical condition of the cutting press?

Based on the cutting press specs, the stock being run, the length of the run and the intricacy of the scrap areas being removed, it is time to determine what type of stripping tools are best for this job.

The most common stripping option involves a female (center) stripping board with the use of upper and lower stripping pins. The approach involves the lowest tooling cost but considerable set-up time. This on-press set-up time can be greatly reduced using off-press pre-makeready equipment to allow the stripping pins to be set-up away from the press before the job is ready to run.

The next popular stripping option involves the use of a female and male stripping tool combination with or without adding lower stripping pins, depending on the diecutting equipment in use. This option results in an increase in tooling costs, but is useful when the job will be run repeatedly. It saves a lot of stripping pin set-up time. Some cutting presses require both male and female stripping combinations.

The third stripping option is to take the female/male stripping tool combination a step farther by building power/pressure-stripping tools. These hybrid-stripping tools are intended to eliminate completely the use of the lower stripping pins. They also can work in situations where the positioning of the lower pins would be too complex or cumbersome for the standard lower pin hardware available. Power/pressure stripping is the most expensive stripping option and generally is most useful in situations involving repeat runs.
 


CAD layout of Male stripper unit (upper unit).


Stripping tool design
Once the decision has been made about what stripping option will be best for this job, it is time to actually design the tools. It is best to start with the female (center) stripping tool. The female stripper design is essentially the job layout with the gripper area attached and the areas to be stripped cut away. The cut away areas are actually larger than the actual scrap pieces by a factor we will call the stripper offset. This is determined by the converter and the diemaker and is affected by the condition of the diecutting equipment. Poorly maintained equipment requires larger stripper offsets. The use of such equipment also restricts the option for the converter to use power/pressure-stripping tooling.

Once the female tool is designed using the appropriate offsets, the cutting press mounting holes, bridge locations and appliances must be designed as needed. The male stripping tool is designed using the appropriate offsets, but also includes the consideration of the male stripper construction. How will the areas that require stripping be built up on the male stripper? This decision affects the CAD design of this tool, as does the placement of air holes, foam stabilizing pads and mounting holes and appliances. Another factor to consider is whether any of the cut-out areas from the female stripping board will be used on the male stripper.

Finally, the separator tools must be designed using the standard cutting press specifications and stripping tool offsets as determined earlier.

CAD system considerations
The actual CAD processes used to design stripping tools may vary between CAD systems. Some CAD systems allow the user to produce macros to be used in repetitive situations to save CAD prep time by combining several CAD steps automatically in one simple command. Now the completed stripping tool CAD files are ready to be sent to the laser-cutting department.

Stripping tool fabrication overview
Most of the decision making in the stripping tool design process is done in the CAD prep stages of the tooling development. Stripping tool fabrication primarily consists of an assembly process. The laser cut components must be examined for quality, especially looking for board warp or weak areas on the female board. The assembly area needs to be well stocked with the tools and hardware necessary to fabricate a press-ready quality set of stripping tools.

Stripping tool assembly
The first step in the assembly process is to prepare the wood components. This involves the removal of all waste wood pieces as well as the removal of unsightly and dangerous nick bridges. The routing of the edges of the female and male stripping tools is next. The female stripping tool bottom edges require routing at a 45-degree angle to allow the scrap waste to easily pass through it. The top edges of the female stripping tool require a 15-degree rout where they are exposed to the sheet as it progresses across the female stripper. If the tools require any form of wood sealing or coating, it is done at this time.

All the hardware required for proper stripping is added at this time. Such hardware could include various T-nuts, spanner bridges, rear cut-off knife hardware and storage bolts. If a male tool is to be assembled, the built-up areas must also be added to the male baseboard. Male baseboards also require the addition of foam stabilizing pads.

Once all the stripping tool fabrication is complete, the stripping tools are now ready to be matched with the cutting die and are ready to go to the diecutting press.

This article was adapted from a past presentation and printed as an article in The Cutting Edge, a publication of the International Association of Diecutting and Diemaking. For more information on IADD, visit www.iadd.org.