A Remedy for Slug Removal

The feed-through punch is a reliable low-cost solution. Making holes along with a typical die cut pattern is a very large part of materials converting. That cut-out center is usually considered as material to be discarded. However, getting rid of slugs can affect profit margin in a couple of instances—finding a way to reduce the manual and tedious labor often associated with it, and ensuring that there is a debris-free working area to reduce the occurrence of bad parts.   Gasket production is probably the most common example for removing slugs from the part. But it’s not the only industry with materials that require centers to be taken away. Certain foams, POP displays, ID cards and flexible circuits—to name a few—also are good candidates.   The only method for 100% slug removal is to invest in a male/female die. Its action forces the waste to make its way down through the female cavity for collection beneath the tool. The problem is that matched metal dies are expensive and beyond that, many presses won’t accommodate them. This is why the feed-through punch is far more popular for routine work. Although it doesn’t get the high marks of a Class A tool, a feed-through punch is quite dependable when you do your prep work.   How they work. There are different types of feed-through punches. A side-outlet punch, used most often for an on-the-board slug exit from a hole on its barrel is useful for clamshell and clicker presses, but does not satisfy the labor savings requirement or the avoidance of stray pieces getting back under the rule. On the other hand, a straight-wall feed-through punch is designed with an outside bevel and with an inside straight wall. This design allows the slug to be carried out of the web as it is die cut, and to the interior of the punch. Subsequent slugs are die cut and push the previously cut slugs up through the punch. For slugs to exit the punch, it must be mated to a backup board mounted on ground steel parallels so that the slugs come out of the back side. Granted that there is additional cost for adding the steel parallels to your steel rule die, but this cost compares favorably to the labor costs required to manually remove slugs or to the outlay for male/female tooling. Punch and substrate considerations. The material you are running needs to be about at least .010” thick. Although the inside surface of the punch is called a straight wall, there is a slight bevel on the inside to maintain its edge sharpness. That bevel is approximately .007” in height. Therefore the material thickness must be greater than .007” for a portion of the slug to make a close-fit above the bevel, for grabbing and lifting it out of the substrate. There are custom feed-through punches with a shorter inside bevel height, but custom-made can increase their cost. A “work-around” to be able to force thinner material up into the punch is to add an adhesive “button” of tape, approximately .010” thick, onto the cutting plate, such as a woven Teflon. Make one press cycle to cut through the tape and remove the excess, leaving the button. The button will push the material up an additional .010” allowing it to go past the inside bevel, ensuring that the slug is snugged inside the punch. In some cases, the type of material being cut calls for the inside of the punch to be back-bored to a slightly larger size. The reason for this is that slug material may create too much stacking pressure. It can even appear to act like ejection rubber, causing the slug to push back onto the substrate instead of advancing upward through the punch. Finally the punch must make a clean cut of the material. If there is any part of the perimeter of the slug that has not been cut, it will stay in the substrate. Would you like more information on this process? Preco is pleased to provide you with details for this topic or on other die cutting problems. Please go to our USA or global website link to find your nearest technical representative. If you're a Preco press owner, ask us about additional tips that will streamline the setup even further. Also, if this process will help someone else at your location, please pass it on. We’ll be happy to assist!  

  Photo credits: punches--AmeriKen; Die--Davis & Pierce   A Preco handles all kinds of tools, including Steel-Rule, Chem - Etch and Male/Female die configurations.     Learn More