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Technology Focus

Integrating the Graphic and Diecutting Processes

by Kevin B. Carey

May-June, 1998
The diecutting process is involved in a wide variety of graphic applications. From labels, presentation folders, and name plates, to cartons, circuit boards, and industrial components, diecutting provides one of the simplest, most flexible, cost effective and efficient manufacturing alternative available. Though they are used in a wide diversity of applications, diecut products share one common attribute - they have some form of graphic or printed information or instructions registered precisely and consistently to every part. The important words here are "precisely and consistently," as this simple task requires the integration of two very different processes.

Print and Diecutting Registration

When integrating the printing and dicutting processes, there are some important principles which must be recognized. Before the manufacturing process even begins, it is important to ensure the graphic image and the design to be diecut match each other precisely, that the print side of the material is oriented correctly to the die side of the steel rule die, the bleeds are properly positioned, and the "step and repeat" dimensions of any multiple print and die layouts are in sequence with each other. In most applications, the steel rule die cuts into the printed face of the material, and therefore, the die is a perfect mirror image of the graphic design.

Illustration 1

Clearly there are a number of factors which could undermine this match of print to die. These would include printing plate fabrication inaccuracy, print draw and flair, material shrinkage (this is particularly true on paperboard, fluted, and other cellulose based materials,) steel rule die fabrication variation, steel rule plywood dieboard shrinkage, and the variability of the press gripper/chain job substrate positioning systems.

The goal is perfect print-to-cut registration; however, it is also important to be able to detect which of the two processes has dimensional variation. One of the methods to ensure this degree of on-press synchonization between processes is to include register marks in the waste area of the printed sheet. These marks match specially shaped register knives inserted into the identical positions of the steel rule die layout which, when a diecutting impression is taken, cut into the printed register mark (See illustration 1.)

This is a simple and effective method of ensuring perfect registration between the printed image and the diecut design. Because the slightest variation can be detected immediately, it eliminates any misinterpretation of graphics/diecut design registration. In addition, it greatly simplifies the task of print/die alignment for the press operator. A variation on this theme uses "L" registration marks to achieve the same effect. In this application, the matching printed "L" shape and the "L" knives in the steel rule die are positioned at the edge of the material and aligned with the first gripper knife of the die. This has the advantage of enabling the same print/die alignment as the previously described register marks; however, the cuts in the diecut sheet can be used to both verify print registration and to verify the physical gripper and side lay accuracy of the printing and the diecutting press.

Illustration 2

The shape of the side guide marks used by the printer are another simple graphic modification which greatly simplifies the task of monitoring print-to-cut register for the press operator. In principle, this shape would be an "X." It should be positioned so the intersection fo the "X" mark aligns perfectly with the side lay edge of the sheet. This is an advantage to the diecutting team. If the print-to-print register is perfect, a single bar will appear on the side of the stack of printed sheets. If there is variation in either lateral direction, the side of the stack will show a double line, and the mark on the printed sheet will clearly define the direction of the misalignment (See illustration 2.)

Material Dimensional Volatility

These fundamental steps, taken to display and define the source of print-to-cut variability, are sound practices; but they deal with the symptoms of the problem and ignore the larger question of where the variation originates.

In making an assessment of variability sources, the substrate the image is printed on is a prime candidate for inspection. For example, any paper-based material is fabricated from a matte of cellulose fiber which is highly susceptible to moisture changes in the surrounding atmosphere. Since the air in the facility is usually drier than the material, paperboard and cellulose-based materials will gradually lose moisture, and therefore, shrink as they are processed. The degree of shrinkage will vary according to the amount of processing heat the materials are exposed to. To add a final variable to the mix, the degree of shrinkage will not be consistent in both directions, as shrinkage parallel to the grain direction will be more than twice the amount of shrinkage at right angles to the grain direction. This can be translated into a potential print-to-cut register problem in a long grain paperboard sheet where the cellulose fiber grain is at right angles of the printing machine direction.

This potential problem becomes more of an issue when you recognize the plywood die base the steel rule die is fabricated from is also a product composed mostly of cellulose fiber. Even though the grain direction of each veneer layer in the composite wood panel is rotated through 90 degrees, more than 60% of the grain is oriented in one direction. In addition, as the dieboard is lasercut to create the channels the steel knife will be inserted into, intense heat is generated and the cellulose rapidly loses moisture. Therefore, not only will the dieboard/steel rule die shrink during fabrication, the shrinkage will be twice as severe parallel to the grain direction of the top and bottom veneer layers (See illustration 3.)

In matching the steel rule die to the design, it is important to align the most critical dimension in the diecut part design at right angles to the grain direction of the top and bottom veneers of the dieboard. It is also important to align the most critical print-to-cut register requirement of the graphic image at right angles to the grain direction, and to integrate the impact of material shrinkage to this predictable steel rule die variable.

Illustration 3

Certainly, adjustments can and should be made to compensate for these potential variables. This may include adjusting the printed plate "step and repeat" dimensions, adjusting the packing of the print cylinder to control length, or adjusting the die design by adding a compensation amount into each design, enabling natural shrinkage to contract the finished die to the specified dimensions.

There are clearly a number of other factors which can undermine print-to-cut register. These may include:

  • Print flair and spread at the rear of the printed sheet.
  • Gripper/chain wear which can undermine positioning repeatability.
  • Heat induced contraction and expansion of the printed and diecut substrate.
  • Excessive tool lock-up pressure as the die is installed into the diecutting press.
  • Materials which are not flat and are distorted.
  • Growth in the steel rule die caused by too narrow slots holding the steel rule (which causes a "stacking" or expansion problem in the die.)
  • Excessive material distortion "draw" or contraction during the diecutting process.

Each professional in the process can anticipate and predict the degree of dimensional change in the materials, and can quantify those variables based on material type and the application the materials are used in. Their understanding of the principles of each process allows them to build compensation factors into the printing and diecutting tools based on material characteristics, image precision, design constraints, and processing distortion characteristics. The result is exceptional print-to-cut register performance.

Organizations may claim accuracy and precision in fabrication. Whether you are dealing with material manufacturers, printing technicians, diemakers and toolmakers, or the diecutting team, it is important to ask how inherent variability in each process, material and tool is anticipated and compensated for. Ask how these adjustments are integrated from print through diecutting to the finished product. Some discussion in the beginning of the process can save costly mistakes down the line.