Electronic Engraving

Paul D. Fleming III, Paper Engineering, Chemical Engineering and Imaging

Electronic engraving methods may be electromechanical or laser. With the electromechanical device the cylinder is engraved with a diamond stylus. With the laser engraver the material is ablated away with a high power laser. Originally these were driven directly from a scanner. Now they are driven directly from digital files as just another output device on the network. Of course scanning may still have to be done, but some of that can be at another site.

Electromechanical engraving can generate cells of different sizes depending on how deeply the stylus intrudes into the metal. Thus, for a given stylus the cell depth and cell opening are not independent. The cell spacing is chosen so that the diamonds nestle between the cells of the preceding row.

For the largest volume cells a small cell wall must be maintained to support the doctor blade. Different screen angles are obtained by varying the size vertically and horizontally. Generally yellow and black are printed at 45°, cyan is printed at 30° and magenta is printed at 60°.

Examples of cells engraved by the Daetwyler GRAVOSTAR electromechanical engraver is shown at the top right. Laser engravers have a great deal of flexibility in cell sizes, shapes and depths. The most common laser engraved cell is circular shaped. A round dot cell gives enhanced ink release. Some samples from the Daetwyler LASERSTAR are shown below.

For a comparable printing density, the depth is only two thirds of that of an electromechanically engraved cell. Less cell depth of course means thinner galvanic platings, and less plating time. Moreover, for a required printing density, finer screens are possible. Laser-engraving combines the precision of digital engraving and the advantages of depth-variable gravure. With a cell diameter almost constant in shadow areas and highlights, good vignettes can be produced.