Steel Rule Die-Cutting
Steel Rule Die Cutting
Steel rule die cutting is a common and inexpensive way to cut a shape out of a sheet material like foam, paper, cardboard, rubber, plastic, cork, or fiberglass and is often viewed as a cookie cutting process. Most standard cardboard boxes and packages are made using this relatively straightforward technique. In addition to cutting out shapes, it can be used to create creases, perforations and slits.
The most common and simplistic steel rule cutting die is constructed out of three components: a die board (flat base or substrate), steel rule cutting blade and rubber ejection.
The flat base or substrate that is usually made out of high-grade and high-density plywood; the plywood is usually composed of hardwoods, such as maple, and is free from voids or other imperfections. Some special dies may require aluminum or steel substrates.
The die-maker cuts and bends precisely positioned slits into the substrate by duplicating the shape of the part to be die cut either by jigsaw or more commonly today, with a laser (That is why Chinese Engineers call Steel Rule Die Cutting as “ Laser Cutting- die”. The steel rule itself is essentially an elongated razor blade made out of hardened steel.
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The cut is called a kerf and the width is slightly smaller than the width of the cutting rule so that it holds the cutting rule tightly in the board. The sharp steel cutting rule is bent into the shape of the part to be die cut and pounded into the die board kerf with a soft faced die mallet.
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The final step in creating the die involves the addition of ejection rubber.
An important aspect to remember is that steel rule die cutting is not a shearing process but a displacement process.
The leading edge cuts the surface but as it is forced further into the material, the blade pushes the material apart along the cutting edge until it fractures and separates. Harder materials like film and paper actually fracture and are completely cut before the blade fully penetrates. Soft materials on the other hand do not fracture. The cutting action occurs when the compressive load of the material exceeds the force needed to begin cutting edge penetration. A dull die will require more force and compression that can lead to finished part distortion with soft materials and fuzzy or rough bur edges on rigid materials.
The right ejection and amount is a critical factor in the long-term accuracy and life of the cutting die. Ejection can also cover the entire cutting die called full ejection or spotted in specific locations around the cutting rule.
Rubber ejection is used to push the die cut part out of the cutting die. It is available in many different forms and firmness. Rubber pads are adhered to the substrate to help eject the material after it is cut. Without the inclusion of ejection rubber, the material may tend to get stuck amongst the steel rules.
There are all sorts of steel rule. The rule itself comes in a variety of thicknesses that are chosen based on the particular application.
Once the die maker has completed the steel rule die, it is immediately ready for production. The die is attached to the top platen of a die cutting press that will provide the force required for the job. Smaller presses may provide 20 tons (18,000 kg) of force, whereas larger ones give over 150 tons (135,000 kg).
The material to be cut is positioned below the die and then the press is actuated. If registration is an issue, the material is positioned against a stop or in a locating nest. The cutting edges of the steel rule penetrate through the material until they come into contact with the bottom platen; the press then reverses and the cut part is exposed. In some applications, a softer material is placed below the material to accept the cutting surfaces of the steel rule. When cutting paper, however, the cutting is performed against special steels designed for the purpose.
Perforations and creases are made with special rule that is positioned on the same die as the cutting rule. Creases sometimes require a secondary die called a matrix, which is positioned on the opposite side of the press and is aligned with the creasing rule; when configured properly, very crisp creases can be created in all sorts of materials. Sometimes, heated platens are used when plastic parts are being fabricated to improve the quality of the creases and cuts.
In high-volume die cutting operations, fully automatic machines are used. In these machines, the material to be cut is automatically fed into the press and located in the proper position. The steel rule die is pressed through the material and the pressure is released. The cut piece is removed along with any scrap material, and the next piece is indexed to repeat the process.
Simplicity and low tooling costs make steel rule die cutting a popular manufacturing process when cutting materials into a useable finished shape. This is a relatively inexpensive and effective way of cutting soft sheet goods.
Compiled by David Zou