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Prepress & Screen Making



I introduced the importance of prepress control in my November 2002 column. The premise was that screen printers allow outside influences to determine the ultimate outcome of a job when they accept digital files prepared by others. I would like to continue the discussion this month at a much deeper level by closely examining the role prepress control plays in <I>total quality management</I>.


I introduced the importance of prepress control in my November 2002 column. The premise was that screen printers allow outside influences to determine the ultimate outcome of a job when they accept digital files prepared by others. I would like to continue the discussion this month at a much deeper level by closely examining the role prepress control plays in <I>total quality management</I>.


Total quality management (TQM) results from the impressive work of Dr. W. Edwards Deming. His groundbreaking research and applications are the basis for the profound turnaround of the Japanese manufacturing industries of the 1950s, ’60s, ’70s, and ’80s. Every manufacturing industry has been affected by the achievements of this great pioneer, and international quality certifications like ISO 9000, 9001, and 9002 have directly evolved from his work.


One of the fundamental concepts that Deming proved, through the use of statistics and mathematics, was that 85% of the downstream variation in any process can be controlled by the first 15% of the process, starting with the conceptualization and design stage. His approach was to design products with the manufacturing process in mind, instead of figuring out how to produce the product after it had been designed and approved. By doing so, he moved control to the front end of the process where it could have the greatest impact on the process as a whole.


This concept hit home pretty hard for me as I thought about how frequently we have to figure out how to print an image conceived by a graphic designer or ad agency that has no understanding of the screen-printing process. Worse yet, what about all those times we have to "convert" numerous images delivered to support litho parameters that are inappropriate for our process? Virtually any of us involved in prepress deals with these situations on a weekly basis.


Deming’s TQM control principle involves creating a solid foundation that takes the entire process into account and thereby stabilizes subsequent steps. If we deliver perfectly prepared films and screens to the print production department, we will ensure smooth, predictable, and trouble-free printing. Spoilage will be minimal and materials consumption will be at the most efficient levels. Control means minimized variation. In screen-printing, consistent color, image quality, and efficiency are the fruits of process control.


When the prepress department treats the whole digital prepress sequence like a control function, we can stabilize 13 key variables of print production:


1. Image alignment 2. Press setup time 3. Color development  4. Primary and secondary moiré acute 5. Trapping  6. Color shifting during the run 7. Dot gain 8. Consistency within the run  9. Ink-film thickness  10. Ink consumption  11. Total ink limit  12. Piling 13. Press speed


In order to reach the point where there is minimal operator intervention in the process, managers and planners must learn how to front-load the system for stability. Concentrating on the first 15% of the overall printing process largely neutralizes the press operator’s role as a source of image quality adjustment.


This very important realization runs directly against the grain of how most press operators do their jobs. In the current state of the screen-printing industry, the majority of companies think of the press operator as the one who makes the jobs happen. The operators make all kinds of adjustments to get the image to the point where the customer is expecting it to be. The reality is that the press person should only be concentrating on image fit, ink-color density, and linear tone positioning. If prepress is handled correctly, these three functions will occur more or less automatically. As a result, we realize three benefits: printing becomes much more efficient, spoilage is reduced, and print quality increases.


Areas that we can affect


Careful attention to image construction, file preparation, film imaging, and screen imaging sets the foundation for a dramatic improvement of the overall printing experience. My approach has been to develop an equally careful understanding of each and every aspect of the production model. From this point, each type of on-press quality variation and failure is analyzed to determine if performance can be improved by changing the way prepress is handled.


To illustrate how we can reduce your overall cost to print a job by changing the way we work in prepress, we begin by looking at press setup, the first step past screenmaking. Accurate color-to-color alignment can be improved through the use of digital templating, pin registration, and image trapping. Underlying costs of film assembly are also reduced at the same time. A typical, traditional setup can range from 6-20 min per color (or more on larger presses). However, with a correctly designed process stream, setup times can be reduced to 30 sec-2 min per color, and sometimes less.


The goal of setup reduction is to minimize press adjustments solely to the level of image positioning and alignment. Squeegee angle, pressure, and speed, as well as screen off-contact and peel settings can remain constant. And by employing on-press pin registration, we can comfortably position images within &#177;0.002 in., largely eliminating the need to adjust micro registration.


<P>The savings and efficiencies continue when it comes time to print. Run-up and color development can be reduced to less than 10 sheets for graphics printing and less than six pieces for textile printers. This is accomplished by adhering to strict file preparation and separation parameters and using consistent screen tensions, emulsion thicknesses, open-area percentages, moir&eacute; controls, and dot-gain reduction strategies.


Prepress is used to control primary and secondary moir&eacute; generation, dot gain, and gray-balance stability. If uncontrolled, all of these require press adjustment, leading directly to nonbillable work for our operations. The only adjustment necessary beyond image fit should be bringing the ink film up to the specified density level. Tone and color transition are determined by prepress and will automatically fall in line through effective use of linearization.


Total ink consumption is also controlled by how the separations are produced, using a combination of black generation and total ink limit. By understanding the relationship between chromatic and achromatic gray balance, UCA, UCR, and GCR, we can reduce the amount of ink we use to less than 50% of the amount required in an uncontrolled workflow. For large-format graphics printers, this can save tens of thousands of dollars a year in materials.


Stability is the key concept to grasp during all steps past the prepress phase. For each step that is held constant, a variable is eliminated. Press personnel do not waste valuable billable time making redundant adjustments–they concentrate on quickly getting the job to "go" status and then maintaining the approved quality level from that point.


Eliminating variables adds benefits. When press operators maintain the same sequence of operations, they become extremely familiar with the key areas of interest that can change. It is much easier for them to identify variable performance when the number of potential adjustments is limited. From a management perspective, we can move from a point where every job on press is a new custom experience to one where exceptions are rare and are used to drive additional improvements.


Advantages to the organization


The advantages of adopting a TQM approach to prepress and production should be clear by now. In today’s competitive world, anything we can do to increase efficiency, while lowering total cost and improving overall quality, should be a primary goal. Sadly, the majority of companies I visit have little knowledge of this approach, much less any experience in its application. But those of us who familiarize ourselves with TQM and its application quickly realize its value from the way our net profitability multiplies.


The faster changeovers, improved running efficiency, reduced spoilage, and lower overall costs are only part of the value. All of these improvements result in more available hours for production, which translates to more net billable hours per month. And if the company is already profitable at this point and has covered its overhead and met its profit projections, the additional net profit flows directly to the bottom line. There is also intangible value added, such as improved confidence and morale among production workers and an improved reputation in the marketplace as the company delivers superior work, on time, at a competitive price.


As with most technical improvements to the screen-printing process, TQM will not happen overnight. It takes a commitment from upper management to start the process. Along the way, we encounter resistance from press operators who will feel threatened by the fact that we are eliminating the need for massive adjustments on every job. A significant amount of psychology is involved with managing the change that comes with the TQM approach. The technical changes amount to only a small percentage of the total organizational change. Everyone involved must clearly understand that priorities will be questioned to determine if they remain valid, so it’s important that we eliminate the potential fear associated with change.


Change requires overcoming inertia–the older a company, the more inertia it has built and the more difficult it is to change its direction. But by recognizing and overcoming the challenges involved with change at the very beginning of the process, we greatly improve the chances for a rapid transition to success and build a strong foundation for total quality management.





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