Cutting Polystyrene Without Angel Hairs - 101

Written By Mark Batson Baril

This question was put out to a network of Tech Heads to find a fast cutting edge solution. We thought it would be fun to show the results just as they came in – one at a time.

We are cutting 24 mil Styrene (polystyrene) on a flat bed Bobst machine. The material gets angel hair hanging off the edge. Is this a characteristic of the stock or is there something we can do to eliminate the angel hair?

1. It is a common characteristic of styrene materials. We have experienced the same situations on many occasions because of the material and the way the die cuts it, bursts through the material and hits the bed harder than normal, thus dulling the die itself. (Tom with Larkin Industries)

2. This sounds like the same problem stuff we used to work with for promotional model airplanes. The best results are had with a special razor rule 1.5 points with an extreme 30 degree bevel angle, and about a 65RC Hardness. This is only made by one company I know of. I can't remember all the details but the trick seemed to be in the steep angle. (Mark Baril from Cut Smart)

3. Maybe I'm doing something wrong too, because I have always had trouble with fine hair on styrene. If you get a plausible answer back from someone, could you let me know? (John Mechetti from Mechmar Industries)

4. Without more details, it may be difficult to pin down the specifics of the problem, such as type of rule used, configuration of the part and spacing layout, ejection being used, etc. A quick answer however may be to glue a piece of mylar (.007) or hard oak tag stock (.010) on the cutting plate. This may remarkably improve the situation. (Allen Gurka)

5. We used to cut styrene on a hand fed platen press and found that the only way to eliminate angel hair was to use a very sharp die and cut with either something underneath (like paper) or to not cut completely through and then pull the part out of the web. Maybe others know better methods. (Fred Antonini from Cutcraft)

6. I have tried all kinds of cutting rule to get rid of the angel hair problem with diecutting polystyrene. We use Bohler Universal Supreme 45 degree cutting rule .937 2 pt. We also use a cutting rule called Mpower. This is made by Atlas Die in Elkhart, IN. This works the best so far. I went from 300,000 impressions to a million impressions on die re knives with the Mpower rule cutting .013” polystyrene. This has not gotten rid of all the angel hair; we still get some once in a while. I believe it is caused in the mixture of the plastic some how, because you will run one lot and have very little, if any, angle hair, and in the next lot it will be all over the sheet, but the Mpower rule helps to eliminate the angle hair and if you use a water jet rubber so the rubber is away from the knives this has helped a lot also. We use a T-75 tiger-x rubber. (Leo Moore from Master Tag)

7. Angel hairs are caused by dulling of the rule. If you have sharp rule, as it enters the material, and penetrate to a set depth, the material fractures the rest of the way. Much like splitting a log with an ax. However, when the rule dulls, you have a flat spot on the edge of the rule, as it penetrates the material it actually holds the material in place on both sides of the rule edge. As the material fractures there are two fracture lines through the material. This causes a small "hair" on the sides of the cut part. The hair becomes more pronounced as the rule keeps getting duller. There are three solutions that I know of on how to reduce the hairs:

1. Add heat to the tool which reduces the fracture point. Approximately 190 degrees. 2. Preheat the material to reduce the material rigidity. 3. Use extremely sharp rule reducing the stress of the material as the rule enters it. I have had good luck using Tsukatani 30 degree bevel with a ground and polished edge, however, Sandvik and National also make a similar rule that I am sure would work just fine. Standard rule is 42 degrees and that causes too much friction going through this type of material. (Randy Norman from Preco)

WOW....that's a lot of knowledge!
The common threads that may lead you to a solution in your shop include:

Know your material and your supplier so you get the same type of plastic every time.

Get yourself a very steep angle cutting edge knife to help penetrate the material.

Cut against a cutting blanket that will not dull the knives or spend some extra time in make-ready when cutting against steel.

Keep a close eye on tool maintenance. Does the job start with perfect results and deteriorate to angel hairs? If so work to keep the blades sharper or replace them more often.

Add heat wherever you can. To the tool or to the material.

Good Luck!