Different finishes with same program, same material, same component.

Hi all.
Good day everyone.
I am new here & this is my first post.

I am sorry if someone has already posted this question which I am going to ask, I didn't find it.

I am using CNC Turning Centre with Fanuc Oi-Mate TD series.
The problem I am facing is about different finishes I am getting with same program, same material, same component.

I am making a component out of 28mm round bar of Mild steel(low carbon steel) material, in which drilling is done of 21.5mm & i have to bore it to 23.30mm final size. When making this component I am getting different finishes like sometimes superfine finish, sometimes fine finish with some lines & sometimes chatter. I tried almost everything like increasing/decreasing speeds & feeds, clamping pressure of chuck, changing inserts, flow of coolant but unable to find the solution to unwanted noise & different finish.

If anybody came across this problem & have solution to it, please help.

Details of component:
Bar Dia: 28mm
Bar length: 67mm
Bar length hanging out of chuck: 15mm
Drilling : 21.5mm
Boring: from 21.5-23.00mm
Final cut: 23.30mm (also increased/decreased the DOC)
Bore length: 45-46mm


Boring Insert CCMT09, nose radius: 0.4
Boring Bar Dia: 16mm
Boring bar hanging out of turret: 52mm

Any kind of help will be highly appreciated.

Thanks
Kusshal

When is it changing? Piece to piece? Bar to bar? What kind of steel exactly are you turning?

Pictures would help and are you running from full bars or sawed blanks?

HI Hazzert.

Its changing from piece to piece. Using Medium Carbon Steel – Composition of 0.29%-0.54% carbon, with 0.60%-1.65% manganese

Hazzert said:

When is it changing? Piece to piece? Bar to bar? What kind of steel exactly are you turning?

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Hi dualkit.
I am running sawed blanks, which are already drilled before loading on CNC.

Sorry pics not available at the moment. its a weekend here. Pics can be available on day after tomorrow.

Dualkit said:

Pictures would help and are you running from full bars or sawed blanks?

Click to expand...

How is the surface finish after drilling before boring? I've noticed on my manual lathe that any imperfections from one pass could be transferred to the next pass. Are you taking one boring pass from 21.5 to 23.0 mm or multiple passes?

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Hi Jay Fleming

There are imperfections after drilling & I am taking 2 passes from 21.5-23.0mm before the final 23.30 finish pass. I have also checked the bore before the finish pass i.e. on 22.90-23.0, the surface finish is fine & there is no noise while cutting, but when I take the finish pass, it makes unwanted sound & finish varies from piece to piece, sometimes its perfect as required, sometimes its fine but with some lines & sometimes its with chatter.

Jay Fleming said:

How is the surface finish after drilling before boring? I've noticed on my manual lathe that any imperfections from one pass could be transferred to the next pass. Are you taking one boring pass from 21.5 to 23.0 mm or multiple passes?

Sent from my HTC One using Tapatalk

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I had a similar random finishing problem with low carbon steel. I finally determined that it had to be chips randomly getting stuck between the insert and the piece on the finish pass. I cut the final DOC from one .25 mm pass to two .125 mm passes, and the problem went away. I think your .4 nose radius may be a little big for a .15 finish pass on mild steel. I rough cut with the .4 and finish with a .2 nose radius. I would try one rough pass (faster and better chips) and one or two finals at about .1 DOC with a .2 nose radius.

Gene

Is it possible that each blank you load is from a different bar?

May help to drop down a bar size, your easily taking enough cuts already to be able to do that with a 12mm CCMT06 size bar, the extra clearance will help you more than the slight loss in rigidity.

Std mild steels kinda soft and gummy, speed helps, but insert wise i find stainless style inserts are a bit sharper and help with the gummy ness more than the steel ones. Correct insert that could probably be done in one pass to size.

Hi Tungsten Carbide.

Thanks for your tip, I'll try this & take two finish passes & see if it solves my problem. If this doesn't solve then will try two inserts.

Tungsten Carbide said:

I had a similar random finishing problem with low carbon steel. I finally determined that it had to be chips randomly getting stuck between the insert and the piece on the finish pass. I cut the final DOC from one .25 mm pass to two .125 mm passes, and the problem went away. I think your .4 nose radius may be a little big for a .15 finish pass on mild steel. I rough cut with the .4 and finish with a .2 nose radius. I would try one rough pass (faster and better chips) and one or two finals at about .1 DOC with a .2 nose radius.

Gene

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No, its not possible.

Matt@RFR said:

Is it possible that each blank you load is from a different bar?

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Thanks, will check & try

adama said:

May help to drop down a bar size, your easily taking enough cuts already to be able to do that with a 12mm CCMT06 size bar, the extra clearance will help you more than the slight loss in rigidity.

Std mild steels kinda soft and gummy, speed helps, but insert wise i find stainless style inserts are a bit sharper and help with the gummy ness more than the steel ones. Correct insert that could probably be done in one pass to size.

Click to expand...

Hey dualkit,

Here is the pic of the component, with lines on one piece.

Dualkit said:

Pictures would help and are you running from full bars or sawed blanks?

Click to expand...