Milling Marks from Wiper Inserts on 4140 Skim Cut

[Nerdlinger]

Hi Everyone,

I am skimming off .005" from a block of annealed 4140 with a nice Ingersoll face mill using wiper inserts @ 700SFM and .020ipt and getting some swirl marks. The attached picture does not quite show it, but there ARE swirls going both directions, so I do NOT think it is the perpendicularity of the spindle to the table. Also, it comes and goes AND it is not always a rhythmic pattern so I do NOT think it is just one insert sticking down or up a little more than the others.

I am doing it dry and just going right down the middle of the 1-3/4" wide block with a 2" cutter. Should I try to offset the cutter to the left a bit and do it in two passes? I was hoping to do it in one pass to minimize mismatch lines, but as long as it comes out in blasting/vibrating after heat treat we are good. In the meantime we are hand grinding the surface before vibrating and plating.

What causes that? Is it a sporadic built up edge that scrapes and then falls off so the next couple of cuts is good until it builds up again and then leaves another groove, etc? Maybe I need to increase the cutting speed?

Thank you for any help!

 

[Nerdlinger]

ummm, as I was just looking at the pic myself it appears that the "inner cutting diameter" of the inserts (since the wiper land is so long) never reaches the outside edge(s) of the part so maybe the chips don't break on the edge and instead get shoveled around and around and around? I noticed this because the swirl marks are complete circles on the face of the part and not reaching the outer edges. Does that make sense?

 

[dandrummerman21]

Yes.

 

[dandrummerman21]

with only .005 coming off, I'd probably try your current tool with only 1 wiper insert.

 

[Nerdlinger]

with only .005 coming off, I'd probably try your current tool with only 1 wiper insert.

Just to completely eliminate any effects of varying insert height?

 

[dandrummerman21]

I think it would just load up the one insert better than trying to load up all 4 or 5.

Maybe it wouldn't work. I dunno. But It's what I'd try.

In the olden days, they often used flycutters to achieve the nice finish.

 

[mhajicek]

You'll probably get better finish from 4140 prehard. Still cuts easy. Why use 4140 if it's going to be annealed?

 

[Nerdlinger]

You'll probably get better finish from 4140 prehard. Still cuts easy. Why use 4140 if it's going to be annealed?

You're probably right regarding the surface finish of prehard vs annealed, but prehard is not readily available in the shape we need. The material comes in annealed so it is soft for machining and then the part goes out to get hardened.

 

[dpolseno41]

You're probably right regarding the surface finish of prehard vs annealed, but prehard is not readily available in the shape we need. The material comes in annealed so it is soft for machining and then the part goes out to get hardened.

To what hardness? I much rather machine hardened 4140 versus soft.

 

[Nerdlinger]

If it was you guys would you rather use a smaller cutter (like the one I already have) and do it in two passes with a slight overlap OR get a cutter large enough to do it in one pass. I figger if I do it in two passes with each pass, say, centered over the edge of the material each insert would scrape away material for 1/2 turn

To what hardness? I much rather machine hardened 4140 versus soft.

52HRC In my experience that seems too hard to prefer over annealed, but maybe I'm living in the past? The other side of the part includes pockets and some 5-40 holes.

 

[plastikdreams]

Take the wiper out, run one pass forward and one back at same feed, speed, and height

 

[Nerdlinger]

Take the wiper out, run one pass forward and one back at same feed, speed, and height

This cutter uses four inserts and all are wipers.

EDP: 2917710 - Part Number: EF6J-02R01 - Series: EF6J Hi-Feed Finishing Face Mill

EDP: 2917710 - Part Number: EF6J-02R01 - Series: EF6J Hi-Feed Finishing Face Mill

www.ingersoll-imc.com

 

[nscele]

ummm, as I was just looking at the pic myself it appears that the "inner cutting diameter" of the inserts (since the wiper land is so long) never reaches the outside edge(s) of the part so maybe the chips don't break on the edge and instead get shoveled around and around and around? I noticed this because the swirl marks are complete circles on the face of the part and not reaching the outer edges. Does that make sense?

What about running the cutter offset to a side, so that the outside edge of the cutter just cleans up, pretty sure it is not the problem here but is it not better to run a face mill so that the cut is not completely centered, what I mean is that there is a side force on the tool pushing either left or right.
From your picture I am going with a built up edge, the rest of the surface looks flat so the inserts are all matched?

 

[Nerdlinger]

What ARE those sporadic scrape marks? A built-up edge that is being shoveled through the material? Maybe I'll try coolant...I've been running it dry...

 

[ManualEd]

IMO with such a small DOC, chips aren't big enough to get flung out nicely, and you're going to get chips stuck in the center cavity between the mill and the part.

Coolant should help flush them, and taking it in two passes might help clear them as well.
But two is more than one, and aint nobody got time for that.

 

[5 axis Fidia guy]

Soft 4104 tears very easy, I would try without a wiper insert myself.

 

[Orange Vise]

What ARE those sporadic scrape marks? A built-up edge that is being shoveled through the material? Maybe I'll try coolant...I've been running it dry...

Tearing or chip dragging.

Either way, it's not a simple problem to solve, i.e. not a simple parameters tweak.

Four solutions, in increasing order of added complexity but also increasing order of probability of success:
1. Use a second facemill and crank up the SFM by 50%. Light DOC: under 0.010". Dry.
2. Finish in the hardened state with a ceramic facemill. Again, light DOC, under 0.005" if possible.
3. Flip the part sideways in a rotary axis and finish with an endmill
4. Grind

 

[eKretz]

I thought I had already replied to this...but yes, USE COOLANT. Many of these types of marks are from chip scratching and/or BUE. Coolant will help lubricate and prevent scratching, and also help prevent material from sticking to the cutting tool. You may need to increase speed a bit with coolant, but may not. Give it a try and see what happens. If the finish is dull, bump the speed up until it brightens back up. With such a light cut you can crank it up pretty high in soft material. Do not remove inserts, totally unnecessary.

 

[vr6]

Nerdlinger, I supported when you first started running this cutter and inserts back in 2020, have you by chance picked up new inserts since then?

We changed the inserts to a press rake face because the older inserts at times, 1 would sit more proud then the others causing a scratch on the back side, the new insert design eliminates that issue

It was a running change so the inserts are still the same edp# and callout

 

[EMTech]

As others have said, coolant could help.

Air blast is another option.

Ground inserts with a sharper cutting edge might also help. With such a small depth of cut, the insert geometry and edge prep may be hindering the chip from breaking away cleanly.