Friday, September 10, 2010

Thin Foam Diecutting

Recently a manufacturer came to us with a production problem. It went something like this:

We have been over the edge with one particular job recently and could use some advice. We have a customer who has us diecut promotional models from 1/16" (1.587mm), fairly dense, polystyrene(foam cups are made of this). About ten different models are cut on separate steel rule dies. Each die runs the same part in up to a twenty on configuration. All the dies run between 1,000 and 2,000 inches of cut and are approx. 24" x 36" (610 x 918 mm). We use a 1 1/2 pt long double bevel rule and the dies are all rubbered solid with relieved areas in the bigger open spaces. We cut this job on a large clamshell type press and have had very good results cutting into a nylon (plastic) plate. Our problem is that we have run into one particular tool that just will not cut. Some areas will cut and others will not. We have made-ready forever on this job and feel like we know what we are doing, yet we get no where! Our diemaker has checked and rechecked the rule and says it is still good. The problem areas tend to be in areas of more rule concentration, some rules being as close together as 1/8" (3.175mm), yet similar situations have yielded better results. Help !

OK lets approach this with pure logic. Given your information filled question we can make a few assumptions;

Since you have run similar jobs before and had good results…

Tonnage Factor or what pressure your press is able to develop is adequate to get the job done. If you had not run similar jobs well, this would be extremely important to look at.

Die Materials meet the needs of the job at hand. A double long bevel ("razor rule") or sometimes even a micro-serrated rule usually will work great with this type of foam. Side-face rule may even work better for you in some areas depending on the shape.

Cutting Plate made of a dense and durable plastic such as nylon is well suited. We often recommend that diecutting, especially in long runs, be made as a steel blade onto a steel cutting plate, but foam is a totally different animal. If it works with the rest of your dies it should work with this one.

Areas to look at a little more closely are;

Ejection material - By rubbering a tool with a solid piece of ejection material many problems can be both eliminated and created. In this case where you have what sound like some very small areas you may be creating zones in which the foam cannot be easily compressed into. Remember the idea of ejection is to move freely with the stroke of the cut and then still have enough "kick" to remove that part. It may be worth trying a denser "gum type" rubber that fits your narrow areas ("areas of concentration" as you put it), more loosely. This will allow the ejector to move downward and still have the power to pop that part out. You could start by removing all the rubber. Can you get it to cut now? If so, then more than likely some experimenting with different materials for this one tool will yield good results.

Die Ruling can also be changed to incorporate side bevel rules in the area giving you problems. By taking the material being cut and pushing it towards larger open spaces rather than crushing it into the small slot, you can relieve pressure and perhaps gain some cutting power in that area.

Material Type - Are you sure the foam material you are purchasing is the same density and make-up as last time you cut for this customer. A slightly different material may knock out some of the earlier assumptions we made. I know this is a weak point, but in some situations you need to look at every angle!

The Impossible Image - We have certainly run across situations before where an image cannot be cut. In this case, where you have rules that are very close together compared to the thickness of the material, you may have to take a step back and look at the actual design of the part and the limitations of the die / press / material / etc... . Can the image be changed to eliminate the problem areas ? Will your customer kill you if you even suggest such a thing? Can this be avoided in the future by working with the designer of the part?

So logically, assuming that we have all the information correct, we have eliminated the tonnage factor, die materials, cutting plate problems and make-ready. Material type is a weak one so lets forget it for now. I would concentrate on ejection material problems first, die ruling second, and then as a last resort start talking and investigating problems with the design of the part vs. the capabilities of the process.

As it turned out in this case the ejection material was able to be changed enough to solve the problem. From that point on the diecutter became involved in the design process from the very beginning and new projects seem to be flowing smoothly.