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Multiblade Hub Chatter

Experimenter
Experimenter

Hello Everyone;

 

I am working as a application angineer in a turbocharger company.

We produce aliminium impellers.

But on hub surface we suffer chatter problem.

How can I solve this problem.

Outer diameter of the impeller is 40 mm.

We use 39000 rpm and 35000 mmpm feedrates.

 

P_20180423_112740_1_HDR_p.jpg

Ergun KESKİN, CAD/CAM/DRAFTING Application Engineer, DP Manufacturing


Production: {NX11}

Development: Testing: {NX11}
10 REPLIES

Re: Multiblade Hub Chatter

Siemens Phenom Siemens Phenom
Siemens Phenom
I think the solution requires a few more inputs for our understanding.
What cutter are you using?
Cutter geometry and material?
Tool holder?
Clamping?

Maybe a reduced rake cutter? Maybe cutting too fast for your setup? Can the operator overuse the spindle speed and feed rate to get a better result?
Chatter is a black art to solve sometimes. I appreciate you also have production targets so it may not be straight forward. I’d start with cutter selection and profile. I’m guessing it’s longer than 6X it’s diameter.
Paul

Re: Multiblade Hub Chatter

Experimenter
Experimenter

We use carbide endmills and sometimes coated endmills. Usually R1_5 degree (tipangle 10) The material is a aliminum 7020 series. For impeller which has a outer diemeter of 50 mm we finish it at one time. We use shrinking method. We DMG Mori 5 axis simultaneous machine. But I think the problem is vibration. 

To reduce the chatter we change feedrates, spindle speed and stock amount.

Is there any procedure to solve this problem?

 

 

 

Ergun KESKİN, CAD/CAM/DRAFTING Application Engineer, DP Manufacturing


Production: {NX11}

Development: Testing: {NX11}

Re: Multiblade Hub Chatter

Siemens Phenom Siemens Phenom
Siemens Phenom

Hello @izmirliergun

Have you tried to put some lead/lag on the cutter in the direction of cut? trying to get away from milling with the nose of the tool may help. I would also dull the cutter a little, too sharp can cause chatter with long tools. Your setup seems fine. Are they 4 fluted endmills? Can you try a 3 flute endmill? 2 flutes sacrifice rigidity, 4 flute has less chip evacuation, 3 flutes is best I think for aluminium. Also cutters that have the flutes at equal angles around the axis(equal index) can tend to produce a natural harmonic effect and therefore chatter. Try and find a tool that has an unequal indexfor the flutes like these: http://www.monstertool.com/ProductData/variable-helix-end-mills-4-flute-radius.html

I've even tried things like putting a thin rubber sleeve or even heavy tape to wrap around the shank to try and absorb vibration or at least push the vibration to a different natural frequency.

Certainly speeds, feeds and depth of cut have the biggest influence but even then you can't remove chatter without some other unconventional strategies.

Sorry I don't have any magic answers.

Regards

Paul

 

Re: Multiblade Hub Chatter

Experimenter
Experimenter

 Thank you for your valuable response.

 

Now we are sure that using 3 flutes cutter have an effect on reducing chatter.

Also reducing the total lenght of the cutter have a positive effect.

But we even don't know about unequal index cutter so I will search on this.

I have been using neutral lead angle along the toolpath but will change to negative lead angle.

It means that the cutter lean backwards when it travel along the toolpath.

When we use neutral lead angle cutter go along a toolpath with an angle of 90 degree with the surface.

 

We are now working with cutter producers both local and international suppliers.

Also we started to work with academic personel from a local university.

 

It is somehow time consuming process but I will note data and  inform you about the improvements.

 

Best Regards.

 

 

 

 

Ergun KESKİN, CAD/CAM/DRAFTING Application Engineer, DP Manufacturing


Production: {NX11}

Development: Testing: {NX11}

Re: Multiblade Hub Chatter

Valued Contributor
Valued Contributor

Hi,

 

First thing to do must be being sure of workholding. 

 

You should use 3 flutes cutter, having unequal flute spacing will have good effect on the chatter issue.

 

I don't fully agree with "dull" tool for cutting, it depends on dullness of the tool though. A very dull tool will cause nothing but a headache for you.

 

Another possibility is using hammer test equipment, analyzing frequencies to avoid chatter zones, using "sweet spots" for cutting. Note this should be last resort as this is costly and hammer test must be done again whenever tool changes (even if you pull out same tool and use it again)

 

Tool stick-out must be minimum you can achieve, you said you are using heat shrink but I would use milling chuck for best rigidity (Use if holder is not gonna collide with workpiece, because these holder are big in diameter wise, not like heat shrinks.)

 

When these variables are its best, (workholding, toolholding) rest is about part stifness and toolpaths. You should try to maintain part stiffness while creating toolpaths. You might need to be creative.

 

 

Re: Multiblade Hub Chatter

Gears Legend Gears Legend
Gears Legend
Assuming that this is tool vibration.
Chatter is caused by the tool edge hitting the part at the tool assemblies natural frequency.
You can't simply say "use a 3 flute instead of a 2-flute" or "reduce the cutter length" It may well be that sticking out the cutter a few mm's more, might resolve the chatter.
Usually you will get the best result by finding the correct RPM. Feedrate has NO effect on preventing vibration, just the intensity of it.
Google for "cutter stability lobes" for more info
Patrick Delisse
KMWE - DutchAero
NX 12.0, TC 11.2, CAMPOST V22, Vericut 8.2, TDM 4.8
C#, VB, .NET

Re: Multiblade Hub Chatter

Siemens Legend Siemens Legend
Siemens Legend

From the software side I'd try to use the Min lead angle and set a positive value - the largest that would still end up with a continous path all allong the hub. somtime "pushing the material" can produce vibrarions. are you using Zig pattren or Zigzag? if it is Zigzag - do you see a difference between the vibration marks on the motion leading to trailing and the motion trailing to leading?

 

Yours

Eddy Finaro
NX CAM Product Manager
Siemens PLM

Re: Multiblade Hub Chatter

Siemens Phenom Siemens Phenom
Siemens Phenom

Hi @izmirliergun

Did you make any progress on removing the chatter from your machining? I had one other thought. Have you tried to use some spindle modulation? i.e. change the spindle speed at each line, randomizing the spindle speed to ensure you won't hit the natural frequency/resonance at any particular time during the cut.

Regards

Paul

 

Re: Multiblade Hub Chatter

Experimenter
Experimenter

Helo Paul;

 

At the moment our 5 axis impeller manufacturing process stopped.

But as soon as we start again to produce I will try some changes.

At the same time I am searching on the web about essays on this topic.

I think try error method is somehow time consuming.

If you are interested I can send you some of them. Also when I get more information and experince on this special applicationI will share 

Thanks.

 

 

Ergun KESKİN, CAD/CAM/DRAFTING Application Engineer, DP Manufacturing


Production: {NX11}

Development: Testing: {NX11}

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