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UHMW milling HELP

AGCOTAY

By AGCOTAY,
in Industrial Forum

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AGCOTAY Newbie

AGCOTAY

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Looking for advice on milling attached part.

 

Specifically the internal dog bone shape; tool continues to break after packing occurs. I fully chain the shape and cut the perimeter. Note the call out, 0.222" is the distance from wall to wall of dog bone shape, tool used is 0.1875". I have used a range of F&S but the packing still occurs. I suspect the heat that is generated from the packing and RPM is causing a weak point. I would like advice on any and all attributes of what I'm doing. Please ask for more details if needed. I am not the originator of the program and would like to improve, I am waiting on an upcut 0.1875" mill. Currently using 15,000 RPM and 75 ipm feed rate.

I'm using a 4.0" L, 0.1875" dia. solid carbide router, 2 flute, straight O. 

 

 

GK81340.png

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Phillip herschknox Rookie

Phillip herschknox

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I machine a decent amount of UHMW parts. A .1875 endmill shouldn't really be breaking off. I would back down on the RPM a decent amount as you may be generating too much heat in the cut. Also make sure to be hitting the tool  with plenty of coolant or air blast to remove the packing of chips. If i wanted to be really conservative and make sure my tool didn't break I would use a contour ramp toolpath going about 5000 rpm and maybe 40 inches per minute. I don't know your tool stickout or setup so these numbers may be slower than necessary.

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crazy^millman Veteran

crazy^millman

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6 minutes ago, Phillip herschknox said:

I machine a decent amount of UHMW parts. A .1875 endmill shouldn't really be breaking off. I would back down on the RPM a decent amount as you may be generating too much heat in the cut. Also make sure to be hitting the tool  with plenty of coolant or air blast to remove the packing of chips. If i wanted to be really conservative and make sure my tool didn't break I would use a contour ramp toolpath going about 5000 rpm and maybe 40 inches per minute. I don't know your tool stickout or setup so these numbers may be slower than necessary.

The straight 2 flute 4" long is the problem. No where for the chips to go. I always used Aluminum uncoated endmills for machining UHMW and never had the problems they are running into. Coolant or high pressure air all the way to prevent sticking and/or melting of the material back into the cut. 

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Jobnt Proficient

Jobnt

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59 minutes ago, crazy^millman said:

The straight 2 flute 4" long is the problem. No where for the chips to go. I always used Aluminum uncoated endmills for machining UHMW and never had the problems they are running into. Coolant or high pressure air all the way to prevent sticking and/or melting of the material back into the cut. 

What he said, r.e. end mill type, chip evacuation and flushing are key.

Also, with UHMW (aka delrin), you cannot rough cut slowly. Don't baby it. It builds up too much heat even with good coolant flow. Chip loads in the .004 to .008 range work well for me using 3/16" 2 or 3 flute cutters just long enough to do the job at hand.

You should mind your approach/exit strategies as well, delrin chips easily when you break out of a corner. 

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jpatry Enthusiast

jpatry

Posted
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21 hours ago, AGCOTAY said:

Looking for advice on milling attached part.

 

Specifically the internal dog bone shape; tool continues to break after packing occurs. I fully chain the shape and cut the perimeter. Note the call out, 0.222" is the distance from wall to wall of dog bone shape, tool used is 0.1875". I have used a range of F&S but the packing still occurs. I suspect the heat that is generated from the packing and RPM is causing a weak point. I would like advice on any and all attributes of what I'm doing. Please ask for more details if needed. I am not the originator of the program and would like to improve, I am waiting on an upcut 0.1875" mill. Currently using 15,000 RPM and 75 ipm feed rate.

I'm using a 4.0" L, 0.1875" dia. solid carbide router, 2 flute, straight O. 

 

 

GK81340.png

My experience with UHMW, has been to use as sharp of tools as possible, rough with an upcut aluminum endmill, finish with a downcut, drill with 135deg split point HSS or specific aluminum geometry drills, sharpest possible geometry.

Chip load should be around .003 to .005

Harvey Tool has a whole line of plastic optimized endmills, they work very good.

 

As for surface footage, UHMW is very sensitive to heat and easily expands with said heat, so the moment your tool starts to smear, it will heat, swell, smear more, and heat more, resulting in a positive feedback loop of destruction, so it is best kept relatively low.

If your surface is looking fuzzy, your SFM is too high.

 

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jpatry Enthusiast

jpatry

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17 hours ago, Jobnt said:

Also, with UHMW (aka delrin)

UHMW is not Delrin, they are both excellent at wear resistance and are thus often used interchangeably for that purpose, but they are very different in machining characteristics and price, UHMW is cheaper.

UHMW is short for UHMWPE, or Ultra High Molecular Weight Polyethylene, whereas Delrin is Polyoxymethylene.

Basically, UHMW is Polyethylene but with longer spaghetti strings, this is what makes it such a pain to machine.

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AGCOTAY Newbie

AGCOTAY

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On 10/19/2023 at 6:37 AM, jpatry said:

My experience with UHMW, has been to use as sharp of tools as possible, rough with an upcut aluminum endmill, finish with a downcut, drill with 135deg split point HSS or specific aluminum geometry drills, sharpest possible geometry.

Chip load should be around .003 to .005

Harvey Tool has a whole line of plastic optimized endmills, they work very good.

 

As for surface footage, UHMW is very sensitive to heat and easily expands with said heat, so the moment your tool starts to smear, it will heat, swell, smear more, and heat more, resulting in a positive feedback loop of destruction, so it is best kept relatively low.

If your surface is looking fuzzy, your SFM is too high.

 

I have seen the fuzz. I received a lot of programs and are finding many issues with it. I am also using carbide straight wall, I think I have a few good starting points here. Thank you!

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