Minimizing Set-Up and Changeover Times
by John Kaverman
Maximizing machine efficiency means minimizing set-up, changeover and cycle times, especially in toda?sjust in tim? manufacturing environments. Here are four recommendations for increasing efficiency.
Adjust the height of your work and pads. Everyone adjusts the stoke distances for image pick-up and print, however many people overlook the height of the work and/or the pad. If you can move the work closer to the pads, or the pads closer to the work, you can reduce the required stoke distance and therefore the time necessary to pick up and transfer the image.
Use Z-axis indicators to minimize the time necessary to adjust worktable height. Z axis indicator is another name for the hash marks that you put on the adjustable height table and frame of the machine that correspond to different jobs. For example, lining up the indicator line on the work table with indicator line labeled A on the frame adjusts the height for one job, while alignment with indicator line B adjusts table height for another.
Use a pad holder that has adjustable height, or use spacers to bring the height of the pad to within a few millimeters of the cliché and/or part surface before it strokes to pick-up or transfer the image.
Some machine designs allow you to move the print head up and down in the Z-axis via a mounting post and positioning table. The ability to adjust the print head in relation to a stationary part conveying accessory enables the user to more easily reconfigure semi-automated systems so stoke distances are reduced to a minimum.
Use set-up cards. Each application is different, however too many people attempt to commit the parameters for each job to memory rather than write them down. Not only should you write down a description of Job A, B and C so you can use those indicators just mentioned but also, you should write down information like pad stroke adjustments, speeds in all axes of motion, speeds of part conveying accessories, and any delays that you might use.
Some machines have programmable memories that allow you to store the parameters for jobs. By selecting different saved programs, you can change the speed of motion in all axes, part conveying speeds, number of indexes and travel distances of part conveying accessories and print delays in all axes of motion. In addition, you can activate peripheral equipment such as corona treatment systems or dryers with the touch of a button.
Purchase a spare set of accessories. Having spare accessories will reduce machine downtime regardless of whether you are using an open inkwells or sealed ink cups.
If you are using an open inkwell, consider purchasing a spare doctor blade, holder ink spreader (and polymer cliché holder if applicable) in addition to the extra inkwell. That way one operator can remove and replace all the machine components that come in contact with the ink.
With sealed ink cups there are usually fewer parts that come in contact with the ink; however, replacing the cup(s) is still faster than cleaning. If you are using polymer clichés, do not forget to purchase spare cliché holders as well. That way, you can remove and replace the ink cups, polymers and cliché holders together, negating the need for removal of the polymers, cleaning of the holders, and mounting of new polymers.
While the cost of spare accessories may seem high at first glance consider how much money you will save by reducing changeover times. If you dont have a second operator available to clean the dirty accessories immediately upon removal from the machine, carefully place them in a sealed, airtight container with a rag dampened with thinner. The thinner in the rag will saturate the environment within the container preventing the ink from drying before your operator can clean it at the end of the shift.
Machines are now available on the market that offer a flexible cliché platform that allows you to align your polymer clichés via a pin register system, with the ability to use varying ink cup diameters and Y axis (front to back) locations. When you need to changeover, you simply unlock the entire platform, remove it from the machine, and replace it with another. When used in conjunction with that manufacturers digitally-controlled stepper motor, users can reduce changeover times to less than fifteen minutes, even in ten color applications.
Use templates to prepare polymer clichés. Using a tiny piece of film to make clichés can cost you money once you get to press. If you make a template showing the outline of the cliché, or at least one edge and two corners, and center your artwork in the same location each time prior to exposure, you will have far less adjustment to make once the cliché is in the printer.
If you are making your own films directly from your PC, just cut and paste your image into the template, duplicate the template and the image, and selectively delete to make your color separations. If you are using a process camera to make films, you might align smaller films to a cliché-sized template using an underlay for reference.
There are now pin register systems that allow you to punch your film positives to correspond with the holes in the clichés, allowing you to positively align your films to their respective plates in the exposure unit.
Every dollar spent now on speed and efficiency will have a cascading impact on the profitability and viability of your business in the future. The cost of labor in the U.S. will not decrease. Pressure from overseas markets will have a profound effect on your customer base. You must take advantage of the only edge available by embracing the equipment, materials and methods that help you not only survive, but grow a sustainable and profitable business in the future.
John Kaverman has over fifteen years of combined screen and pad printing process experience and is currently the national sales manager for Innovative Marking Systems of Lowell, MA. For more information, contact him at firstname.lastname@example.org or visit: www.padprinters.com.