Cutting Polyethylene

[Andrea Weissenseel]

Hi all

has anyone experience in cutting Polyethylene (PE) ?

I have some 0.8mm thin material and I'm having problems cutting it. It seems to remelt together right after it's cut . I tried some different settings (without air, lower power, faster speed, etc.) but nothing seems to work.

Tips are appreciated

Cheers, Andrea

[Richard Rumancik]

Andrea, I haven't tried recently but I think your results are typical. Polyethylene is only a bit above wax as far as its molecular structure. It melts back on itself just as wax would and tends to re-weld the kerf with molten material. If you noticed the smell when it is cut, it will have a faint smell of a burning candle.

Although it can be possible to cut crude shapes the edges will generally look very poor. Sorry; I'm sure you did not want to hear this.

Polypropylene is one step higher than polyethylene but it still won't cut all that well.

[Mike Null]

As Richard said, you have a challenge. I would boost the air assist as high as you can and lower the hertz and see if you get any improvement. Also try focusing a couple of mm below the surface.

[Andrea Weissenseel]

Thanks for the answers so far, even if it all doesn't sound too positive

I'll give a try with the air assist tomorrow and see what happens.

Mike - do you really mean to focus below the material ? Thickness of the material is < 1mm

My next idea was using PP but Richard already gave the answer to that also.

Andrea

[Eric Edgette]

I think Mike means to focus in closer to the material as if the focal point were below the surface.

[Alexander Stein]

I have done a little of this and have had similar results with the re-melting of the parts back together. what I was doing to try to prevent the "re-melt" is to use our air compressor with an "air flow" gun attachment (a little thing that shoots air from your air hose) I then tried to follow the cutting with this air gun to force more air to the cut lines than the air-assist possibly could. This seemed to work pretty well in keeping the parts separated though due to the laser loosing focus from the top of the part to the bottom my tolerances from the top part to the bottom part were not as accurate as they could of been...

so I guess my recommendation would be to try to add additional air into the cuts while the laser is cutting.....


hope that helps!

[Mike Null]

Andrea,

I'm sorry, I misread the thickness in your original post as being 8mm. Forget that recommendation.

[Michael Hunter]

Andrea

I have done quite a lot of 1mm thick high density polyethylene on my 60W Epilog.

I run 100% power, 30% speed and 5000Hz (maximum frequency/ppi).
This puts lots of heat into the cut so that the air assist can blow the molten plastic away before it sets again.

My biggest problem is that the molten plastic flows over the back of the sheet and sets there, making a "lump" by the cut line. On some sheets I have been able to protect the surfaces with masking tape, but on the latest stuff (which had a rough surface) the tape would not stick, so my customer had to live with the "lumps".

Flareups are a big worry (particularly with the protection tape on) and I have found it best to split the jobs into sections so each cut is far away from the previous one.

Hope this helps

[Richard Rumancik]

Andrea - if you have the option of changing material, did you look at PETG? I can't say for sure it is available in 0.8 mm but that would be about .032" so it's possible you can find it. It won't cut like acrylic but it just might work, depending on your appearance requirements. I have cut it in the past; it raises a bit on the edges and maybe turns a bit white but it will cut far better than PE.

[Stuart Orrell]

Just a thought...I haven't tried this but.....If you did drop the part out of focus and apply more power, would this give a larger width of cut and reduces chances of the material welding back together?

[Brian Robison]

I've rastered some bottles in the past and it gave an interesting effect. I was amazed at the amount of power needed for PE.

[Andrea Weissenseel]

In the meantime, I had some pretty good results with PP (polypropylen) by lowering the PPI settings

Andrea

[Martin Reynolds]

Andrea - if you have the option of changing material, did you look at PETG? I can't say for sure it is available in 0.8 mm but that would be about .032" so it's possible you can find it. It won't cut like acrylic but it just might work, depending on your appearance requirements. I have cut it in the past; it raises a bit on the edges and maybe turns a bit white but it will cut far better than PE.

Here's some PETG. It cuts very well, once you get the settings dialed in. It does leave white dust after cutting. It is tough stuff - those are cold bends.

http://iobium.com/IMGP0149.JPG