uhmw

can you use uhmw? what is the thickest material you can use in a 3d printer? i am making a cnc mill out of a commercial ink jet printer
i would like to use it for differant things.


thanks ratt

What, please, is "uhmw"?

The typical RepRap uses an additive fabrication process, so there is no limit in material thickness other than the build volume.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

I'm guessing uhmw is ultra high molecular weight somethingorother?
By thickness, do you mean viscosity?

UHMW I believe is the next step up from HDPE, another Polyethylene.

It looks impressive. I did not see any reference to meltingpoint in the Wiki article.

Quote

The weak bonding between olefin molecules allows local thermal excitations to disrupt the crystalline order of a given chain piece-by-piece, giving it much poorer heat resistance than other high-strength fibers. Its melting point is around 144 to 152 °C (291 to 306 °F), and, according to DSM, it is not advisable to use UHMWPE fibers at temperatures exceeding 80 to 100 °C (176 to 212 °F) for long periods of time. It becomes brittle at temperatures below −150 °C (−240 °F).

I believe one of the major issues with UHMW is is doesn't flow when it 'melts'? And if it does, it's no longer Ultra High Molecular Weight. Can anyone expand on this? As well as how toxic the fumes are perhaps?

Yeah, the molecular structure of UHMW is created as it is chemically formed. Reforming it through extrusion probably breaks those really long chains. It is listed as non-toxic.

UHMW is Ultra High Molecular Weight which is another form of polyethylene. It has great wear resistance and great for sliding applications. I buy it a lot from a place called Industrial Plastics. They have a website with more data and lots of pieces of material in many sizes.

[www.iplasticsupply.com]

If you are asking if you can machine UHMW with a CNC mill the answer is NO. Not unless you want to be incredibly frustrated. When cutting plastics it is best to use single fluted end mills but even with those it doesn't help. The UHMW just won't chip off so you end up with the dirtiest cut you've ever seen. The best plastics I've machined with my CNC router are HDPE, Acetal (delrin), and casted blocks of urethane resin.

I have to strongly disagree with tosjduenfs. I machine 1000s of squre feet of UHMW-PE every year on a cnc mill holding +- .005" and geting glass finishes. The key to to use 1 0r 2 flute solid carbide very sharp endmills and pushing hard with good coolant. My question is does anybody know if you can form UHMW in 3D printers?

I also am interested in using UHMW-PE. Unfortunately, it doesn't seem to be melt-processable. It just gets too viscous and the cooled result seems to be brittle. Here is a link to a forum where this has been discussed.

EDIT: quite conversely to that, I found this archived blog post by Zach according to which he succeeded in extruding UHMW-PE...so I guess it's time for experiments?

However, due to the excellent wear / self lubricating characteristics, I could imagine using this material as an integral structural / bearing solution, further simplefying the design and reducing parts.
As it is quite cheap, I will buy some sample piece(s) and experiment with it.

Edited 1 time(s). Last edit at 01/01/2013 06:17AM by uGen.

machinistmike Wrote:
-------------------------------------------------------
> I have to strongly disagree with tosjduenfs. I
> machine 1000s of squre feet of UHMW-PE every year
> on a cnc mill holding +- .005" and geting glass
> finishes. The key to to use 1 0r 2 flute solid
> carbide very sharp endmills and pushing hard with
> good coolant. My question is does anybody know if
> you can form UHMW in 3D printers?

What do you use for your "good coolant?

Thanks...

David

Have you any results for UHMWPE, what was a molecular weight for your samples?

Thanks,

Alexander

Ultra high molecular weight polyethylene) UHMW-PE has the same chemical structure as any other polyethylene and is polymerized by the same technology in low pressure reactors. Its molecular weight (MW) is simply 10 times larger than HDPE. The MW of HDPE is in the order of 300,000 and that of UHMW-PE is around 3 million. This makes is a material that is highly resistant to abrasion (used in truck lining, conveyor belts, etc.) and the best impact resistant among all polymers, even at low temperature. As mentioned above UHMW-PE does not flow above its chrystaline melting point, which makes it difficult to process when compared to regular PE, which can be injection molded and screw extruded. This polymer is prepossessed through compression molding or sintered (pressure and heat) or ram extruded (ram pushes resin (pressure) through an heated die (heat) in ordure to extrude a shape (can be simple or complex). A similar process to compression is called direct compression molding (DCM), which aims at molding a part by transferring the powder resin (UHMW-PE resin comes into a powder form as opposed to beads as with HDPE) into a horizontal mold by gravity. The mold has the shape of the part similar to what is being done with metal powder. The processed resin can definitely be machined with proper tooling. This has been done for years by numerous processors worldwide. The main reference for this resin is Ticona with GUR as their brandname. In NA they are based out of Florence, KY.

I've been looking for this product/service and I discovered this one uhmw material I'm not sure about the quality or the foundation of their offering. Has anyone have investigated this before? If you have any other available choices you know are worth the time to look at, please post them here. Many thanks!

Edited 2 time(s). Last edit at 09/20/2013 02:44PM by sukantha.

Quote
jcabrer
Yeah, the molecular structure of UHMW is created as it is chemically formed. Reforming it through extrusion probably breaks those really long chains. It is listed as non-toxic.

UHMW is Polyethelene.

It is a thermoplast, not a thermoset,

So you should be able to melt and extrude it.

I use UHMW a lot in a number of projects, it's very high wear resistant.

I don't know how well it would work as a 3D Printed material.

No, you can't really extrude it according to the information I collected (OK, maybe you can technically extrude UHMWPE, but you won't have much success printing it). The reason is that it requires a lot of pressure to properly bond together for some reason.
AFAIK, one processing option is sintering, albeit I guess that refers to sintering under a lot of pressure and not the laser sintering.

Anyone has any updated news on use of HMWPE or UHMWPE for 3D printing ?

Need your help to get through ith my industry analysis project based on UHMWPE. Kindly clock on the link and fill up this form
[docs.google.com]

Great posts so far, thanks to all above.

The big question is, will it flow? These guys (a German manufacturer?) say no, but that's their job I think.

One word that hasn't yet been mentioned here is annealing. According to a well sited Wikipedia page:

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Hoechst: Annealing (Stress Relief) of Hostalen GUR
When UHMWPE is annealed, the material is heated to 135 °C to 138 °C in an oven or a liquid bath of silicone oil or glycerine. The material is then cooled down at a rate of 5 °C/h to 65 °C or less. Finally, the material is wrapped in an insulating blanket for 24 hours to bring to room temperature.[8]

Controlling the cooling rate after you print a part in UHMWPE might be just as important as controlling the temp during the print.

Next, let's consider the concern over the pressure required to get UHMWPE to bond. First, I can't find a specific pressure, just lots of anecdotes. Second, I reckon that if you use a small nozzle (0.2mm or 0.3mm) and a wide diameter filament (2.85mm or 3mm) you can manage pretty high extrusion pressures just using your printer. This stuff, UHMWPE, has a high viscosity; what's that mean? That it should be easy to build pressure at a nozzle. I'm thinking slow print speed, medium height layers, and fat extrusion widths. Oh, and your extruder had better be able to generate an INCREDIBLE amount of torque (or other driving force) or I wouldn't bother trying.

Finally, in regards to concerns over affecting the molecular structure when we try to extrude this stuff out our printers, I must disagree with Jcabrer.

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jcabrer
Yeah, the molecular structure of UHMW is created as it is chemically formed. Reforming it through extrusion probably breaks those really long chains.

The long polymer chains in UHMWPE are produced in modern synthesis processes by exposing ethylene gas to Metallocenes. Older techniques, like the Ziegler-Natta mechanism which dates back to the 1950s, use other organometallic catalysts.Here is a link to a nice, old book on the subject.
I bring this up to point out that in order to change the molecular weight of the polymer you will have to cause a pretty dang serious chemical reaction. You will have to break carbon-carbon bonds to shorten the chains; which means you pretty much have to set it on fire.

Okay, so, now think about this from wikipedia:

Quote

It is made up of extremely long chains of polyethylene, which all align in the same direction. It derives its strength largely from the length of each individual molecule (chain). Van der Waals bonds between the molecules are relatively weak for each atom of overlap between the molecules, but because the molecules are very long, large overlaps can exist, adding up to the ability to carry larger shear forces from molecule to molecule. Each chain is bonded to the others with so many van der Waals bonds that the whole of the inter-molecule strength is high. In this way, large tensile loads are not limited as much by the comparative weakness of each van der Waals bond.

What's that mean? That one molecule of UHMWPE doesn't actually stick to other molecules of the same very well; but that doesn't matter because it's so dang long. Think about a woven-reed basket; the reeds don't stick to each other but they are long enough to hold each other in place quite well. Now image that the reeds are like a million times longer than that--that's kinda how UHMWPE holds together.

So, in order to reshape the plastic all we have to do is to make the Van Der Waals forces between the molecules negligible without breaking any carbon-carbon bonds within the molecules. I reckon that printing this stuff at about 130C will have little or no affect on the length of the chains.
Any significant heat-decomposition of the polymer is very, very likely to result in an obvious color change. I would also expect that decomposition could release organic vapors (ethane, ethylene, methane, CO2 if oxidation occurs) which has a will probably have a noticeable scent.

I think I'll try it. If the UHMWPE can be made to flow then it should work.

2Y passed since last comment.

@RickH Did you finally tried it? (someone)

This could be used to make really nice bearings