RDWorks Learning Lab 227 Cutting 40mm Polyethylene Foam
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- čas přidán 30. 01. 2022
- About 3 years ago I used DOT mode to cut shapes in polyethylene foam packing material. It was not entirely successful because the bottom of the cut opend up witth a significant taper. My previous attempts were based on the traditional approach of experimenting with parameters to try and find values that minimised the taper.
During that intervening period I have come to understand fully the relationship between the laser beam, the lens and the way light interacts with materials. I no longer randomly hunt for successful cutting parameters but start off by trying to understand the properties of the material. From there I try to zoom in on lens and beam configurations that are sympathetic to the needs of the material.
This is a fairly quick revisit to cutting PE, to see if my new knowlegede can help decode the cutting mechanism that causes PE to cut in such an uncontrolled manner. - Věda a technologie
Nice video. It's always a delight to see a new episode.
From the point of view of material science it proves a lot; these foams are very "sincere" materials, where just a tiny modification of parameters makes a world of difference and lets us understand each piece of the puzzle. Looking forward to the next session!
I routinely cut things from 2lb density EPS foam on my CNC router. Wanting to eliminate the dust/chips, I did at least 50 tests trying to cut the foam on my laser. The taper or hourglass shaped result could be minimized, but for my needs, it never was good enough - however watching this video has sparked a renewed interest in trying again. If I remember correctly, on my Trotec 30 watt, when I changed the HZ setting, that also had an effect. I got some cuts that had hair-like connections still remaining, or at the other extreme, it increased the cut width and taper. Heat is the enemy of good cuts in EPS.
Hi
I also have my Tangerine Tiger , a 30watt RF machine that I created in a cheap attempt at discovering the "magic" that Epilog and Trotec try to portray for their technology. I spent several months experimenting and testing , only to find a complex technology that the big companies try to dumb down with a menu interface that poeple can understand. Hidden behind that facade, users do not get the opportunity to understand the technology. There will be a few people like yourself who break through that barrier and try to understand what's really happening.
You are quite right about too much heat being the enemy of PE. As I try to xplain in the video, a glass tube has the ability to change the beam shape from "sharp" to "blunt" by varying the current flow through the tube. That allows me a major mechanism for reducing the beam INTENSITY. There is no such mechanism with an RF tube. The RF tube only delivers ONE power....full power, whenever it is switched on. The beam is ALWAYS sharp because the current flow is fixed at the maximum allowable., The apparent control of power comes from the PWM duty cycle., the beam can never be blunted.
I have not tried cutting PE on the RF machine but knowing the damage mechanism and the RF machine's beam characteristics , I anticipate a losing battle. I MAY BE WRONG!!!! Your comment has made me curious to give it a try. I anticipate that the lowest frequency, VERY low power (duty cycle) and VERY slow speed will give me the best chance. A;lthough I have the option for dot (perforation) mode with my software if I cannot get a straight cut then that will not help me.. Although I have the opportunity to keep the cut temperature low with coaxial air assist into the cut, it seems that blowing the hot gas through the cut is the main cause of taper even when the power.is very low. A large orifice engraving nozzle seems the best strategy along with a long focus (soft) lens. I do have a 7.5" lens I could try.
Thanks again for the thought provoking comment.
Best wishes
Russ
@@SarbarMultimedia I just got a bundle of Fastcap brand Kaizen foam (same stuff, just fancy colors) and searched on Google for starting settings. Next thing I know, your video pops up!
I'm going to start with your suggestions and see where that leads me. If desired, I'll report back here.
Thanks for the perfectly timed video. Had I ordered the material when I should have, your video wouldn't have been available when I tried to start working on the project!
Sandy.
Your timing couldn't be more perfect.
I just ordered 2 each 48" x 96" x 1" sheets and I want to cut them with the laser to make some custom packing.
Thank you Russ!
Can you try cutting Ethylene-vinyl acetate (Eva Foam) 10mm+ ?
Sadly no. I ony have 3mm thick foam and that cuts very easily and cleanly with no special thought other than a few quick 25mm test squares to establish the fastest cutting speed. I always use full power (70 watts for me).
Best wishes
Russ
Great video , I learnt some interesting stuff in this one. Did you check out the PCB I made on my machine?
Hi Russ! Long time I havent seen your videos haha. As sadly I had to sell my CO2 laser while moving from California to Florida. Miss that machine a lot. I now have an interesting project that requires to cut relatively thick eva foam to shape. Since I no longer have my machine, I cant even try it, but I suspect I will also have problems with cutting it vertically due to focus loss. Was wondering maybe you tried to cut that type of foam before with a laser? I have seen people cut super deep and nice and vertically with CO2 lasers, but I assume they dont use a standard lens right? Came here to ask a pro basically :) Maybe I am looking for reasons to buy myself a CO2 machine again? :)) EVA foam i am looking to cut is 5-10mm thick basically.
Hi Vlad
EVA foam cuts easily and 10mm is not a problem. Any lens from 2.5", 4" to 7.5" will do the job.. I would use 2.5"
Welcome back to the mad laser cutting world!!
Best wishes
Russ
@@SarbarMultimedia thanks a lot for you advice! Thats exactly what I needed to hear! My previous machine was 600x400. I will probably be getting 1200x700 this time. 🤠👌🏻
@@VladOnEarth
Hi Vlad
Big machines are more difficult to manage as far a beam alignment. Bigger lengths means bigger refelction errors from mirrors so you will have be super precise with your setings. The other issue is beam divergence, Ok so it's only 3mm growth per metre. But a 5 mm beam at the back cormer bounces off mrror 2 and at the front opposite corner will be 1200+600 =1.8m X3 = a 5.4mm bigger diameter beam. A beam setup that cuts well at the back corner will be much less efficient when the beam grows to 10.4mm diameter at the front. Take a look at this video where I explain and demonstrate this problem. czcams.com/video/z8sNPtIIXZ4/video.html
If you need it for projects you have in mind then go ahead with your big machine but if it's just a "want" then think again. 600x400 is a great size these iproblems are hardly noticeable unless you are me and go looking for issues.
Good luck with your new venture. I feel sure we shal speak again.
Best wishes
Riuss
@@SarbarMultimedia thanks again Russ, I am aware of that potential problem, but last time when I had only 600mm machine, multiple times I ran into an issue where I simply couldnt use it because of size limitation. My understanding is that if i need something smaller to cut on a large machine, I can always use top right vorner of a platform to stay closer to a beam and only use the remaining platform when necessary. This in my mind should minimize the downside of using a longer beam, or am I wrong?
@@VladOnEarth
Hi Vlad
Your wisdom will alow you to optimize the capability of a bigger machine. Understanding that compromises may have to be made for certain big jobs is kowledge that manty big machine useres do not have. . You are returning to this crazy laser world with lots of previous experience but new challanges await.
Best wishes
Russ
I remember not using any lens at all. Keeps the beam parallel.
HI
You are nearly correct in that a glass tube laser beam grows at the rate of about 3mm per metre, so it's nearly parallel . But try and cut without a lens and you will finish up with a 10mm wide cut.
Best wishes
Russ
@@SarbarMultimedia my laser doesnt have a glass tube. Its one of those ceramic laser sources. No idea how the beam performance is compared to glass.
@@MrHighvolt
Hi
It's a coincidence that I am just working on a video that goes into this subject. I Also have another machine similar to the one you have. There is a big difference between a constant power glass tube system and an RF ceramic tube. .I built my own low cost version of one of those expensive RF machines to see if I could discover the "magic" claimed
by the marketing hype that surrounds this technology. You can follow my journey building that machine and the subsequent discoveries I made about the technology if you go to You Tube and search for Tangerine Tiger..
The problem with the RF technology is that you have no control over your beam. Let me explain. I have a 30 watt RF tube that actually delivers 38 watts, but that is what it ALWAYS delivers, there is no control of that wattage. Whenever the tube is switched ON it delivers 38 watts. However the control system for the tube is PWM (Pulse Width Modulation).which is basically a square wave electric signal that switches the tube ON and OFF at very high speed. You will have a frequency control for your tube and a %power control The frequency control sets the square wave speed and typically you will think of a square wave as being 50% high and 50% low. PWM control allows you to change this ratio. For example, my 38 watt tube running at 50% ON and 50% OFF appears to be doing 19watts worth of damage. If I change that ratio with the % power control to 99% then the tube is ON for 99% of each cycle and off for 1% ie I will then do 38 watts worth of damage (on average)
A graph of light intensity within you beam is NOT a horizontal straight line . Instead it is a Gaussian distribution( you may recognize it as a Normal or Bell Curve shape), There is very low intensity at the edge and high intensity at the centre. With an RF tube the peak intensity is FIXED. Every time the tube is ON the intensity distribution remains the same . It will be a very "sharp" or "pointed" beam as it leaves the tube. BUT the problem is that as I mentioned before, a laser beam is not naturally parallel. Your beam will grow at the rate of about 7mm per metre. Lens theory tells us that if you increase the size of the beam you can make it almost parallel. This means that it will perform uniformly across your table area.The problem is that increasing the beam size DECREASES its cutting ability, however it will be super at engraving. It depends on the beam expander that your manufacturer has used as to how much your beam has been castrated.
A glass tube perfomance is completely different. The beam is ON continuously but the shape of the INTENSITY can be varied from "sharp" at 99% to "blunt" at 10%. and that is what you see me doing in this video. I can further control the "bluntness" of the amplified intensity by using a long focus lens.
Take a look at this video that shows you how to SEE the performance of your beam. If you do try this with your machine set it to 99% power (frequency is not important) do one test at the corner nearest your tube and another at the opposite corner of your table. Are they about the same? They will definitely not be sharp like the video but more like my 15% "blunt" test.
For your foam cutting (I will be testing foam cutting with the RF machine soon) I would choose the longest focal length lens, set the % power as low as possible and the frequency as low as possible
Good luck
Russ
@@SarbarMultimedia Thanks for the explanation! The machine I have is a gravograph LS900. I only have power and speed control in the software, The only frequency that I can change is in the maintenance settings menu of the laser. It's currently at 10khz. I never played with this frequency. I think it is the PWM frequency of the tube. I'm not sure how increasing or decreasing this PWM freq would give me a certain advantage in some applications.
Trotec machines seem to be able to control this in their software. I've even seen recommendations for certain frequencies for certain materials.
Interesting stuff isn't it :)
Regards,
Wim
@@MrHighvolt
Hi Wim
I just had a quick look at the LS900 spec and like so many machines it can be veruy misleading, Yes this has an sir cooled RF unit that I suspect will be similar to this
www.cloudraylaser.com/collections/co2-laser/products/cloudray-rf-co2-laser-tube-cr30c-cr40c
This will be a generic Chinese design. If you can find a model number on it then there will be a spec sheet available. They normally allow modulation frequency from 0 to 25kHz and power 0- to 100%.
RF technolgy with its PWM control system is far from intuitive so they generally hide the complexity behind a menu system or maybe in your case special software. Without the experience of my glass tube machine and all the research I did to understand how it all works in detail, I would not have been able to decode and compare the two systems.
When I finished my first pass through of the RF system to see what performance an capabilities it offerd, I was to say the least unimpressed. There was non of the expected magic, just smoke and mirrors. The machine has remained swithed off for almost a year now. My everyday go-to machine is a 70 watt 6040 glass tube machine.
I am currently back on the RF machine because I am trying to transform it into something REALLY useful by ramping up it's cutting performance. I am sure you will have a beam expander fitted to the tube. I would be interested to know if it is a X3 or a X4.., A beam expander hides the poor beam divergance specification and creates a fairly uniform but low intensity beam over the whole table area. This is perfect for engraving but castrates cutting performance.
I cannot see anything in the machiine specification other than a claimed top speed of 2000mm/sec. I suspect that the machine is driven by DC servomotors.. Even with a max power system you will never be able to use this speed. I also nie it claimes a resolution of 50 to 1200dots per inch. Hmmm.......one day you may understand how impossible that 1200 is.
Good luck with your machine
Russ
Urethane foam is way easier. Nasty fumes though
ALL plastics are dangerous to different degrees if you excite them above their decomposition temperature. However dangerous is a misleading word. Almost every burnt product, plastic or oganic produces carbon monoxide and/or carbon dioxide. Breathed to excess and they kill..... but these are normal everyday gasses we live harmlessly with in small quantities. However there are toxic products of conmbustion that are really dangerous to our health in VERY small quantities. Research is the key to steering clear of REALLY dangerous materials like ABS , Urethane or PVC. Good extraction is the next key feature to minimise risks. There is one pretty good source to refer to for lots of material safety guidance .
wiki.atxhs.org/wiki/Laser_Cutter_Materials
Thanks for the comment and the opportunity to add a bit more detail
Best wishes
Russ
Hate to be nitpicky, but polyethylene can't decompose into carbon dioxide.
I am always happy with "nitpicky" because I as I have said many times, I am not a chemist and have to rely on research for my information. I had seen several sources that said that above a critical temperature atmospheric oxygen will bind with the carbon as it breaks from the hydrogen. There are many other chemicals genetated during the heating process but I was searcing for something that could cause the effects I was seeing. Expanding hot gas was the only real candidate and everywhere I reserached I was seeing CO and CO2 as decomposition products above 500 C
Here are just a few of my reference points, there were many others.
nvlpubs.nist.gov/nistpubs/Legacy/IR/nbsir85-3268.pdf
Edward Willhoft
Former Principal of Scientific Consultancy, ETGS.
Answered Mar 10, 2019
Unlike the linear HDPE, LDPE has a highly branched structure and is less thermostable than the former.
In the presence of air, as in normal combustion, a complex mixture of oxygen-containing organic compounds, in addition to saturated and unsaturated hydrocarbons is produced.
The toxic and odourless gas CO is produced as well as CO2. Both are the principal products of combustion. To a lesser extent other oxygen containing products are also produced during incineration and include acrolein, formaldehyde, formic, acetic and propionic acids
Lake Kubilius
Ph.D. in Chemical Engineering, 3+ years in chemical manufacturing
Answered Jan 28, 2016
Originally Answered: What are the gases released when we burn pure Polyethylene ?
There's no reason why pure polyethylene couldn't burn completely. In that scenario, there would be only two products: carbon dioxide and water.
On the other hand, a completely perfect burn is unlikely. In reality, the gasses coming off of it -- if you just tossed a brick on a campfire, for example -- would have a good bit in common with burning gasoline.
The exact details will depend strongly on the burn conditions. Carbon dioxide and water will be the big ones almost no matter what. There will likely be some carbon monoxide in there, followed by some short-length hydrocarbons that got away before being oxidized completely.
Vinay Reddy
B.E Civil Engineering, RV College of Engineering (2018)
Updated Mar 3, 2017
Originally Answered: What are the gases released when we burn pure Polyethylene ?
When we burn a pure polythene only carbon di oxide and water are the products. But there is nothing like pure polythene
Jitendra Goyal
Answered Sep 20, 2018
Originally Answered: What are the gases released when we burn pure Polyethylene ?
Polyethylene molecule contains carbon and hydrogen atoms only . Therefore burning it will produce largely carbon dioxide oxide and small amount of carbon monoxide.Burning of coal,paper and wood also produces these two gases.
Any additional information/references will be gratfully received.
Best wishes
Russ
@@SarbarMultimedia @SarbarMultimedia I looked at the first reference and it seems pretty clear that there are two separate reactions depending on the presence of oxygen. I'm thinking that probably the foam will decompose before it hits the ignition point and reacts with oxygen. But there's no guarantee that a significant reaction with oxygen is actually occurring. It would be worth doing a control test in an oxygen-free environment. If you have any nitrogen or argon lying around, this would be easy to do. If you don't, then you could light a few candles in the cutting area lol. But honestly, it is really important to know if additional energy is coming from the reaction with oxygen, or if this reaction is negligible. After all, a welding cutter works entirely via the reaction with oxygen and doesn't even require the heat from the acetylene (except for ignition).
Regardless, the term "thermal decomposition" of a material like polyethylene that doesn't have a boiling point implies that the reaction only has one reagent: itself. Combustion means that it is reacting with oxygen. I am not a chemist either, but I believe I am correct in this.
@@lazyman114
Hi Daniel
Thanks for your answer . There is a possibility that the air trapped in the foam is the real culprit if it gets too hot. The air itself will not heat up with the laser light but it may heat by conduction and cause the collateral damage. What ever the mechanism is , limiting the rate of energy input to the cut almost eliminates the collateral damage. These are all fascinating and intriguing problems.
Best wishes
Russ