HDPE tooling for best surface finish

[Svdharma]

I am doing prototype work in HDPE which requires thicknessing down a lot of sheet stock (usually taking around 1/16" off both sides of 24 x 24 sheets). We just put a deposit on a cnc router with a 2.2kw ISO20 spindle for these parts. We need a fast cycle time and a very good surface finish on the faces, so I was thinking something like a 1.5" face mill or a 1" indexable endmill would be a good investment. This spindle should have a usuable speed range of between 6,000 RPM and 24,000 RPM with constant torque of around 0.8NM across that range, and the rest of the machine is configured to handle very high feed rates and acellerations. I was wondering if anyone has any ideas about the best tooling for this facing operation?

 

[plastikdreams]

For thicknessing down hdpe on a router I'd use a desizing bit with a sharpness count of at least rB320, the higher the better. Don't get wolfram cutters get high carbon tool steel hardened to as much as possible.

 

[kenton]

I would go with tooling designed for aluminum. I suspect you will be fighting the material moving and stress relieving.

 

[Vancbiker]

For thicknessing down hdpe on a router I'd use a desizing bit with a sharpness count of at least rB320, the higher the better. Don't get wolfram cutters get high carbon tool steel hardened to as much as possible.

Don’t you worry that a desizing bit can withstand the crazy high 7 in/lb of torque on the OP’s spindle????

 

[triumph406]

and a very good surface finish on the faces,

Good luck, one reason why I typically no bid HDPE work

 

[Scruffy887]

How much is in a Schit Ton? Thousands of pounds of HDPE processed every month. AB tools shear hog with honed inserts for aluminum. Those are on all of our CNC machines. You can also Google "spoil board cutters". Spoil board cutters are not too expensive, not too robust if you buy cheap ones. But better ones like Onsrud can do the job. Those cutters take 12 x 12 or 15 x 15 square screw on inserts with 4 edges. I have them and use them on phenolic once in a while because inserts are cheaper. But for production I use AB. Your results may vary.

 

[706jim]

How thick are those sheets? Below a certain value (relative to the sheet width) that stuff is going to warp like crazy once milled and stress relieved.

 

[plastikdreams]

Don’t you worry that a desizing bit can withstand the crazy high 7 in/lb of torque on the OP’s spindle????

Well I considered that, it's just something the op is gonna have to figure out and deal with...shouldn't be too much trial and error.

 

[mhajicek]

You're planning on doing a ton of 24" x 24" sheets, and you got a 20 taper spindle? That doesn't seem like the best choice to me, unless you're then going to be carving a bunch of tiny details into those sheets. For just facing those sheets, I'd rather put them in a machine with a 40 or even 50 taper, and fly-cut them in a single pass.

 

[Svdharma]

You're planning on doing a ton of 24" x 24" sheets, and you got a 20 taper spindle? That doesn't seem like the best choice to me, unless you're then going to be carving a bunch of tiny details into those sheets. For just facing those sheets, I'd rather put them in a machine with a 40 or even 50 taper, and fly-cut them in a single pass.

Indeed, I will be carving tons of tiny details. Current cycle time is 2 hours per side.

I have tried a spoilboard tool from amana. It works OK, but I figured the square corners are not ideal for feed rate or surface finish.

I was also thinking shear hog. Any idea what SFM a shear hog wants to run at in HDPE? Will determine the diameter I choose.

Warping is not an issue as long as thickness is correct, the parts are pressed flat in service.

 

[mhajicek]

I was also thinking shear hog. Any idea what SFM a shear hog wants to run at in HDPE? Will determine the diameter I choose.

The shear hog will run as fast as you can spin it, short of ripping the inserts off with centripetal force. The limiting factor will be when the HDPE starts to melt. Air blast or coolant will help with this. You'll also be able to run higher RPM with higher feed, since more heat will be coming off in the chips.

 

[Svdharma]

I am thinking more in terms what SFM will get the best surface finish.

We should be able to keep the feeds high enough to to avoid melting at any realistic spindle speed. I kept the spindle small because I wanted to keep the gantry mass low, everything else is oversized. I think we will be able to run around 700 IPM and pull around 1.2g's of acelleration.

I like the shear-hog so far, but I would also be willing to drop a grand on a fancy high feed face mill if that would have any advantages.

 

[crossthread82]

Datron monoblock mcd facemill?

 

[Scruffy887]

HDPE does not have melting problems with sharp tools. I have HSS endmills in use since 1999 WTF! Anyway, tomorrow I will post what I run and I run what I need. But I can run crazy finishes if I want to. I run Shear Hogs because of the production speed but also run them in aluminum and other plastics. I prefer spoil board cutters for phenolic because the inserts are cheaper and phenolic ruins them fairly fast. I am not saying it is the best, saying the very sharp inserts work for me and no need to look elsewhere. Not remembering feeds but do limit 3" dia to 10,000 rpm simply because there is no advantage to a higher RPM, and I want to limit the ejection speed of a part that gets loose from the vacuum chuck.
We did have minor heat issues when drilling 16xD. Minor and solved 20 years ago.

 

[Donkey Hotey]

We used to do sizing of polyurethane sheet material on a vacuum hold-down table. We used 4-flute, coated 1/2" endmills. Anything bigger and the long cuts imparted too much force into the material. It wants to lift, stretch and push the sheet around.

Remember: you're only holding this down with vacuum and as the material gets thinner, it has less and less resistance to the material grabbing and lifting up, or tearing. Big diameter cutters have longer engagement distances and more tendency to rub on the trailing edge of the climb cuts. We did a constant engagement spiral, maybe 33% stepover, all the RPM and ran the FPT around 0.004".

 

[Scruffy887]

Indeed, I will be carving tons of tiny details. Current cycle time is 2 hours per side.

I have tried a spoilboard tool from amana. It works OK, but I figured the square corners are not ideal for feed rate or surface finish.

I was also thinking shear hog. Any idea what SFM a shear hog wants to run at in HDPE? Will determine the diameter I choose.

Warping is not an issue as long as thickness is correct, the parts are pressed flat in service.

What is the final thickness? Makes a huge difference in cutter choice.

 

[plastikdreams]

Not to change things too much but I'm gonna play with a huge chunk of 15-5...way easier than hdpe

 

[Bluejeep]

Koroloy Rippermill is my go to in hdpe . Exkenna has them back on his website https://latheinserts.com/shop-1/ols/categories/ripper-mill

 

[TeachMePlease]

I might be thinking too far out of the box here... But this sounds like a surface planer would do it quickly and easily, as a first op before going on the router?

 

[Scruffy887]

I might be thinking too far out of the box here... But this sounds like a surface planer would do it quickly and easily, as a first op before going on the router?

Surface planer can have serious issues if final pass is on thin material because it can get bent up into the cutterhead and bad things happen. I have done this and results are not good. There will be snipe. About 5 years ago the stock we received over 1.55" was rotary planed 2 sides. Think 50"+ fly cutter. Final thickness needed for better answers. Removing 1/16 from each face is not a problem. But material spec of some sizes is +- 10%. Sadly, they stopped rotary planing because they preferred to run UHMW through the machine and wanted to add the clean swarf back to make more UHMW sheets. The change of material required far too many hours of cleaning between runs.
BTW, I have run HDPE through a Wenig 5 head molder with awesome results. Planer not so good.