COMBINING PROCESSES TAKES THE STRESS OUT
We have recently been asked to die cut a very small (.500" x .500" / 12mm x 12mm) intricate part that has, within the image, two .020" (.50mm) holes. The material is a .010" (.250mm) coated and printed Kapton and the final parts must be completely stripped of all waste and must have no remaining debris, slivers, scratching, burrs or contaminants. And yes - we must locate accurately to the twenty-five on printing per sheet. It’s a small cutting area with lots of little holes. The question is, what is the best type of punch to use to get our interior holes to be debris free and accurate to ±.002" (.051mm) for diameter and on center location? The quantities are fairly low – less than 5,000 parts (200 sheets) per month.
We’re going to go out on a limb on this one and make a final suggestion that is a little out of the ordinary. It involves stepping outside the normal realm of production and combining two processes to make a perfect part. First though, let’s talk about the challenges with the part you have described in your question. Kapton is a tough material to cut through with any type of die or punch and when you require tolerances of ±.002" (.051mm) the project automatically swings away from crush cutting of any kind. Crush cut punches used in steel rule type dies are out of the question from an accuracy standpoint as well as a final cleanliness standpoint because they will, by their very nature, cause some debris to be left over after the cut and cannot be made to cut to the accuracy needed here on a long term basis, especially when cutting against steel. If the outside perimeter of the part has the same requirements as the holes we can eliminate even a combo die (Crush Cut and Matched Metal) for this project. Making that assumption the entire project starts to look like one headed for a matched metal tool – maybe…
The no burr requirement is a flag, the tight tolerancing is another flag, and the non-contamination factor is a big flag even when we go to a hard tool, because of the small holes. The abrasiveness of the Kapton and the static that will build during handling will make the process of cutting and clearing the holes difficult and far away from full proof. Just keeping the male pins sharp enough to make a perfect cut will become a project in and of itself not to mention how much effort will be needed to keep fifty of them all working well enough to pass the final test on twenty-five out of twenty-five parts. It can be done but with great difficulty and this dilemma leads us to a final possible solution that is a little harder to manage from a manufacturing standpoint but will yield perfect parts.
Combine high speed CNC drilling with a final perimeter die cut.
What the drilling will do, that die cutting won’t, is make the hole cutting part of the process full-proof. Sandwiching the sheets to be cut between layers of sacrificial material will guarantee a contamination free part because all debris will be removed during the cut and nothing will be allowed to touch the final parts. Accuracy is assured and burr free cutting is no problem at all. Slug removal problems associated with static and dull tooling is also eliminated with drilling. What is added to the process is one more step and one more location of the sheet to the CNC machinery, but in this particular case we feel the extra time will be well spent and the break-even point compared to cutting the entire shape, including the holes, with a tool will take place somewhere around the first sheet! Even if you used matched metal tooling for the entire part, the decision would probably be made to use some type of a progressive / two hit tool that would involve a secondary location anyway. The other problem drilling creates for many commercial die cutters is that they have no CNC drilling capabilities in-house and will have to outsource this part of the process. Again we say, a small price to pay for the reduction in stress this solution should bring to the project.
This doesn’t really answer your direct question of what type of punch is best for this project, because we believe that any type of punch would be far from ideal in this case. Good luck!
Please contact Cut Smart if you would like more information on this subject.
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