A few projects ago, we were asked to develop a solution for a very specialty cutting operation. The product was the basic earplug. The customer was the grand-daddy of all customers – yes, the US Government. As it turned out, in years past the US Gov hadn’t done much shopping around. On this one they were making up for lost time. This product had to be perfect and it had to be cheap. So off we went and started to brainstorm on the very best way to approach the cutting end of this project. Some of the constraints put on us included the following:
- The Shape – A basic 1/2" (12.7mm) diameter circle
- Quantities – 40 million per year.
- Material – Approx .750" (19mm) thick new specialty grade foam.
- Tolerances - ±.030" (.76mm)
- Quality – SPC at every # 5,000 part for all specifications
- Cleanliness – No debris or liquid contaminants allowed
- Target Price – Less than $.01 per part for just the cutting operation.
First ideas led us to extruding the foam and cutting it off as it came out of the extrusion process. This went nowhere when we found out that the only way the new material could be produced involved a curing process that could only be done over time in sheet form. Suddenly we were restricted to not only dealing with having to traditionally cut this products entire shape, we had to deal with the fact that the sheets were going to be at absolute maximum eight feet long by eight feet wide. This foam had an incredible ability to be squashed down to nothing and, over the course of about 30 seconds, fully expand to its original size. It also had a skin or denser layer on the top and bottom surfaces.
We started the die cutting experiments using a series of different types of punches. We realized that with this kind of quantity the tool would have to feed the finished parts through so all the operator would have to do was worry about cut quality and feeding the material. There would be no stripping or touching the product during the process. We tried long bevels and short bevels and serrated edges of all sorts of bevels and wall thickness. We tried male/female of several types and no matter the press or the cutting plate or the impression speed, or the type of tool, we kept coming up with the same result that made the product no good – The crushing effect, before the cut, made for a medium to large concavity on the cut edge of the part.
As we were reaching one day, for crazy ideas that may work, one of the people involved loaded a long bevel extra thin wall feed thru punch into the chuck of a Bridgeport milling machine. He started the machine and spun that punch at a medium RPM and made an impression in the foam. As miracles would have it, the cut result was perfect. We were on our way to a solution.
It turned out that this was not a new idea. We talked to several machinists about building a tool that could spin multiple spindles(punches), and found that it had been done before. What we needed was a multiple up tool (machine) that could accept a slotted specialty punch into its’ geared works. This machine would hold the punches in place and would make them spin while allowing the back end to be clear for ejection. It would also be mobile enough to allow an up and down motion for the impression through the foam. We decided that we would run two rows deep by about ten parts across and would create a step in the image in order to get the absolutely best yield from the material while moving the material the absolute minimum distance. By spinning the punches we found that there was almost no space needed between the parts to hold the web together. The material would have to be sliced into strips before the final cutting would happen and this would be done as a separate operation.
After several experiments to prove out the theory and factor out the bugs we had our final cutting numbers ready to bid. The final tooling cost, before the replaceable punches, was approx. $60,000.00 USD. The tool would be mounted in a standard punch press and the material would be fed in strips using a slightly modified standard clamp and draw air feed. There would be a special female cutting plate that would allow a cut that never bottomed out – meaning the punches would last millions of impressions. The process could create a new impression just about every two seconds and with a twenty up tool this meant that the process could cut around 36,000 parts per hour. At $150.00 US per hour the cutting price after tooling, set-ups and maintenance came in at less than half the target price and the parts were perfect.
As the tooling house, we had done our job, and had been paid for the expenses and the time we spent. The last time we heard about this job (we never did get to build it), the company that we worked for had bid the job but had lost the bid due to material costs. It turned out that the winning bidder had direct contacts and affiliations with the manufacturer of the material and had bargained for the better deal. The case most of the time with specialty cut products, especially in huge volumes, is that the expense and often the profit is buried somewhere in the material management end of the deal. The converting end of the product becomes inconsequential and in some cases becomes a give away just to sell the material. I found this to be both an interesting and frustrating experience. I hope that you have found it to be a technical stimulator!
We still don’t know exactly how they cut the ear plugs. I’m assuming that out there somewhere is a pretty wild looking tool that is just spinning its’ hours away cutting perfect parts that will protect tens of millions of ears worldwide.
Please contact Cut Smart if you would like more information on this subject.
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