TechTalk #10: Magnetic (Flexible) Dies

At Wilson, we’re always focused on the technical aspects of flexography. TechTalk is your quick snapshot of key topics in our industry. Let us know what you think.

Magnetic (Flexible) Dies

Magnetic tools have come a long way over the past few years. Most common materials can now be cut with a flexible tool. So how do I determine if I should buy a magnetic or solid tool? There are three primary criteria that should be considered to determine this.

1. Do I have the Magnetic cylinder of the right size to run this job?

To determine this, measure the repeat of one label or set of labels (length of label and space between labels). Then see if you have circumference of a magnetic cylinder that is evenly divisible by the repeat.

2. Do I have the correct undercut on the magnetic cylinder to cut this material?

A larger diameter will bend less than a smaller one. In the same example of the 2 around with a .125″ space, the diameter of the tool is 3.8993″. However, if you move it to 3 around, the diameter now becomes 5.8489″. At 1,200 lbs. on a typical 10″ machine, the 2-around tool will deflect .000091″ in the center. The 3-around tool will only deflect .000017″ in the center. This provides a more even die strike and longer-lasting die.

3. Do I have an extreme number of inches on the tool?

This can cause the steel not to adhere to the magnetic cylinder properly. As a general rule of thumb, the inches of engraving on the tool should not be more than three times the square inches of the plate. For example: A 2.00″ across x .375″ around rectangle. If we go 4 across and 20 around on a 80 teeth 10″ tool, the formula for figuring the inches of engraving is (2 * (2 + .375)) * 80 = 380″, the area of tool is 10″ across x 10″ around = 100 sq. in. 380″ is greater than 100″ x 3, so this tool would have an issue adhering to the roll. However, if we cut the number across down to 3 the engraving inches fall to 240″ which is now less than 3 x 100 and should not have issues when adhering.

As the undercut becomes greater than .019″ (i.e. .024″ or .030″) the probability of the 4 across die adhering properly is even less.

These are some general rules for flexible tools.