Tech Tips. Owosso Graphic Arts, Inc.

What is it?
Profile of a Good Thermal Kiss-Cut Die

Magnesium thermal dies are typically produced in two thicknesses. The most commonly used thickness for four-poster presses is 11 point (.153"). Then there is 18 point (.250"), typically used on clamshell presses. The size of thermal dies is only limited by your press size. Using our oversize die etching machine, OWOSSO can etch cutting images ranging from a single square inch to 10 feet long. Currently 30 inches is the maximum width.

Since etched magnesium thermal dies are produced photographically, care must be taken in preparing the film negatives, Ruby Lithes, etc. OWOSSO has to transfer your images onto the photosensitized magnesium by producing a fine-line negative using artwork in whatever format you supply. Please remember: a high quality initial image will yield higher-quality end products, and higher customer satisfaction. Today, the best quality fine-line negatives come from computer electronic imaging, which can produce consistent die lines. We offer computer-imaging services so that customers can send electronic orders via E-mail.

Obviously, the goal of using a thermal die is to precisely cut your customer's artwork. It's vital in matching this artwork to remember that heat (the thermal part of your die) expands all metals--including magnesium.

Magnesium expands approximately .25% at 290°F and .5% at 350°F. Higher temperatures will cause greater expansion. The Heat Expansion formula in Diagram #2 will help you, especially with critical registration.

If your job requires close registration, run a sample under actual conditions so that printing can be matched to the impression of the die registration. You can use carbon paper between the die and the counterboard underlay to create an impression of the expanded die.

Photoengraving demands craftsmanship. After the image is developed onto highly polished magnesium, every fine detail, every inch, must be inspected for broken lines, pinholes, or missing details. The magnesium is then etched in acid baths. Diluted nitric acid containing solvents and water is splashed against the image surface of the magnesium, etching away everything except the desired line image. The process has to be monitored for constantly changing acid concentrations, temperatures, and humidity, which all fluctuate depending on the amount of open areas of the image being etched.

All these factors influence the depth, shoulder angle, and cutting-edge width of a thermal die; whether it's a steep, sharp shoulder or sloping and wide. Please see Diagram #3.

Diagram #3

The cutting edge for 2 mil to 4 mil vinyl should have a surface of .002" to .004", depending on the boldness of the image, or if imprinted vinyl is being used. The regular etching depth is between .060"-.075" for basic cutting needs. More depth can be achieved for special cutting requirements. Please note that only the first .010-.012 inches will actually do the cutting of your vinyl. The remainder of the die's depth will help prevent scorching of your substrate and build up of melted vinyls. It will also help avoid slow downs in cutting speed, and will keep the vinyl away from the heated die.

We can help you get the best results if we know what you’re cutting. We can etch the dies deeper, or with steeper shoulders if necessary. Some examples of materials needing special attention are: preprinted, UV coated, static cling, and reflective vinyl.

Magnesium expands approximately .25% at 290°F and .5% at 350°F. Higher temperatures will cause greater expansion. The Heat Expansion formula in Diagram #2 will help you, especially with critical registration.