[4]

Machining gummy metals

[3]
[10] Like what you see?
Click here to donate to this forum and upgrade your account!

RJSakowski

H-M Supporter - Gold Member
H-M Supporter - Gold Member ($25)
Joined
Feb 1, 2015
Messages
3,388
Likes
3,881
#3
An interesting article. I will have to try it as well. It isn't intuitively obvious to me that a surface coating less than a mil thick would affect a .020" DOC.
 

MAKEITOUTOFWOOD

H-M Supporter - Silver Member
H-M Supporter - Silver Member ($10)
Joined
Dec 3, 2016
Messages
229
Likes
398
#4
Interesting. Thanks for posting.
 

markba633csi

H-M Supporter - Gold Member
H-M Supporter - Gold Member ($25)
Joined
Apr 30, 2015
Messages
2,668
Likes
1,381
#5
That IS interesting- i wonder if dykem works too? Better order a case :)
 

whimsnag

Swarf
Registered
Joined
Dec 25, 2015
Messages
5
Likes
4
#6
More pics here, but the paper is behind a paywall (not free): https://journals.aps.org/prapplied/a...lied.10.014009

An earlier paper was published in Proc Nat Acad Sci (free, as in speech and beer):
http://www.pnas.org/content/112/32/9828

From my limited understanding:
1. Gummy metals "bunch" (= large amplitude folding) at the cutter/material interface. This increases the cutting force needed to create the chip.
2. Coating the surface changes the fluid dynamics at the metal surface to induce segmentation of the "bunching" (way beyond my understanding). (Maybe the coating acts like a "chip break", or maybe it's a non-linear effect involving complex fluids and boundary layer effects that is beyond my comprehension.)

Where this might be useful immediately for us hobbyists is when tapping holes. After drilling, coat the holes with dykem/sharpie/glue stick before tapping. You could probably measure the torque needed with and without the coating using one of those "indicator"-style torque wrenches.

Looking back, I think I might have seen this long ago when machining OFHC copper. I could have sworn that the copper cut without a burr out at the first pass (after layout with Dykem) but then got worse after that first pass. But I just wanted to get the the part finished, so I did not with follow up additional tests. Also, I might be remembering it incorrectly -- that was long ago and far away.
 

pdentrem

Active User
Registered
Joined
Jan 28, 2011
Messages
1,948
Likes
447
#7
I use Trim sol as a line 50 ml in 450 ml of water. AppIied with a brush. I found plain jane HSS and uncounted carbide problematic.

DLC - Diamond Like Coating is new to me. We use it for other applications currently. Not turning jobs.
Cermet Inserts should work.
PVD inserts work and I have been using them for years.
CBN insert may work but I have not used on copper and similar metals.
 

whimsnag

Swarf
Registered
Joined
Dec 25, 2015
Messages
5
Likes
4
#8
I got a copy of the paper (incidentally, the electronic journal is free to public libraries -- the library just needs to register with the journal publisher).

It sounds like the mechanism is that the coating causes the nucleation and propagation of cracks in the sinuous (bunched) shear front; this causes the cut to break into chips, rather than bunch/pile up ahead of the cutter. Basically, the coating causing the formation of pinning points

Well, that's my understanding of the paper.

Other notables from the paper:
  • The surface coating results in an improved surface finish.
  • Cleaning aluminum with alcohol might be a bad idea: alcohol binds strongly with aluminum, and is believed to react with aluminum to form an alkoxide (chemical embrittlement).
  • It sounds like the research group used a lot of materials just lying around the office for the coating: glue sticks, Scotch tape, Sharpie, Gorilla glue, Dykem, and Liquid Paper correction fluid.
  • FWIW, the research group used Mobile 1 5W-30 as a machining lubricant.
 
[6]
[5] [7]
Top