A Steel Rule Die works like a cookie cutter. It is made using a razor-sharp "steel rule" that is cut, bent, and mounted in various substrates forming a stamping tool according to the desired shape. Substrates or "die boards" include plywood, acrylic plastic, aluminum, and steel sheets that are generally cut using computer aided design (CAD) and precision laser cutting machines.
Steel Rule Dies work by "knife cutting" parts out of material rather than shearing them as in male-female hard tooling. Occasionally unavoidable surface and cut edge effects may limit the viability in some applications. The most common of these are concave/convex edges or "hourglass effect." This is caused by the compression and extrusion of material as the die impression is stamped, especially on rubber and closed-cell sponge materials.
This all happens in a split second. The material "flows" under the pressure of the intruding force of the die before and during the cutting cycle. The die cuts straight through, but the momentary shift and subsequent recovery of the material once the part is ejected from the die leaves a concave rather than straight edge on a cross-sectional view. Because this is directly relative to the squeezing, stretching, and extruding of material under pressure, the "hourglass effect" increases with the softness and thickness of elastomer materials.
Other components of steel rule dies typically include machined punches for internal holes and ejection material (rubber or springs) mounted around cutting edges to clear cut material from the die area. When put together, the result is a precision tolerance knife-edged tool suitable for efficient production of a wide variety of part configurations and materials.
In general, die cutting is an inherently unidirectional process, making it a suitable means to produce two-dimensional shapes. While this process usually involves stamping parts out of flat rolled or sheeted materials, it can be combined with other methods for three-dimensional configurations in some cases.