CoBalt Chroma milling strategy

[Uliana]

Hello everyone.
We are about to start Cobalt Chroma milling in the lab on Imes Icore 450i milling machine. We have burs and metal discs. The only missing thing is a strategy. Can you guys share with me your strategy, please?

Thank you in advance.

 

[brayks]

Machining strategies and parameters are very much dependent on:

• Available CAM Software strategies
• Machine and fixture rigidity,
• Spindle torque
• Tool shank diameter

CoCr is extremely tough, if you expect to get any sort of tool life your smallest DoC (Depth of Cut) should be at least .1mm.

Generally speaking, ideally you want:

• Coated carbide tooling (TiSiN or TiAlN)
• Very rigid fixturting
• Tooling as short as possible
• Flood coolant

Not sure what tooling you have (6.0mm shank is best) but here are some guidelines/starting points (if abiding by above conditions):

Roughing/Semi-finishing
3mm ball nose DOC 0.18mm / step over 0.75mm @ 20,000 RPM/ 2,000 mm/m
2mm Ball nose DOC 0.1mm / step over 0.5mm @ 22,0000 RPM / 2,000 mm/m

Finishing
1.0 mm Ball Nose DOC 0mm / Step over 0.05mm @ 32,000 RPM / 1300 mm/m

Above may be too fast or agressive for your set-up (machine & fixture rigidity, tool shank size, tool coating, etc.) so slow it down (spindle, feedbrate). You will know if you need to.
​

Also,

• Make sure you are getting the chips/slurry out of from the machining area
• Always be climb cutting
• Machining from bottom, up is typically preferred
• Avoid plunging into material, arcing, ramping, helixing into and out of a cut instead.
• Use strategies that produces smooth tool path that produces uninterrupted paths that avoid sudden changes in direction (reference attached image.)
• Avoid intermittent cutting by running enough semi-finishing and/or semi-roughing operations with appropriate DoC, Step-over and stock allowance to assure a consistent amount of stock.is on the part (consistent stock thickness/scallop heights). Reference attached image.

Not sure if this is what you are looking for but maybe it will help....

 

[Uliana]

Machining strategies and parameters are very much dependent on:

• Available CAM Software strategies
• Machine and fixture rigidity,
• Spindle torque
• Tool shank diameter

CoCr is extremely tough, if you expect to get any sort of tool life your smallest DoC (Depth of Cut) should be at least .1mm.

Generally speaking, ideally you want:

• Coated carbide tooling (TiSiN or TiAlN)
• Very rigid fixturting
• Tooling as short as possible
• Flood coolant

Not sure what tooling you have (6.0mm shank is best) but here are some guidelines/starting points (if abiding by above conditions):

Roughing/Semi-finishing
3mm ball nose DOC 0.18mm / step over 0.75mm @ 20,000 RPM/ 2,000 mm/m
2mm Ball nose DOC 0.1mm / step over 0.5mm @ 22,0000 RPM / 2,000 mm/m

Finishing
1.0 mm Ball Nose DOC 0mm / Step over 0.05mm @ 32,000 RPM / 1300 mm/m

Above may be too fast or agressive for your set-up (machine & fixture rigidity, tool shank size, tool coating, etc.) so slow it down (spindle, feedbrate). You will know if you need to.
​

Also,

• Make sure you are getting the chips/slurry out of from the machining area
• Always be climb cutting
• Machining from bottom, up is typically preferred
• Avoid plunging into material, arcing, ramping, helixing into and out of a cut instead.
• Use strategies that produces smooth tool path that produces uninterrupted paths that avoid sudden changes in direction (reference attached image.)
• Avoid intermittent cutting by running enough semi-finishing and/or semi-roughing operations with appropriate DoC, Step-over and stock allowance to assure a consistent amount of stock.is on the part (consistent stock thickness/scallop heights). Reference attached image.

Not sure if this is what you are looking for but maybe it will help....

Thank you for your reply.

Do you have a ready strategy to share?

I just got to know from Imes Icore themselves, that Imes Icore 450i is not suitable for metal milling as the shaft is 3 mm and this milling will damage the spindel. Do have any opinion on this information?


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[CoolHandLuke]

the 450 is an old machine they dont make any more as far as i know. but the 350 is capable of CoCr milling, as well as titanium.

or if you feel adventurous, get the next best one, the 650 with magnetic guides, granite base, standalone unit, and schunk tribos clamping system and open tooling.

these newer machines have whats called "zero point" clamping systems to hold the material in the precise position, which the 450 does not have. this is very important for implants. Axsys machines employ a secure strategic material clamping system which is repeatable, even if it is not the expensive Zero point systems in place in imes machines.

 

[Uliana]

the 450 is an old machine they dont make any more as far as i know. but the 350 is capable of CoCr milling, as well as titanium.

or if you feel adventurous, get the next best one, the 650 with magnetic guides, granite base, standalone unit, and schunk tribos clamping system and open tooling.

To get a new machine it is a great option but not affordable. The thing is, that 450i been made to mill metal and now, after they sold machines, saying that they tried it and got bad results.. I wonder if anyone is using it for metal milling and the results are?


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[CoolHandLuke]

some people also say Yenadent makes good milling but its by far a machine not so widely known or used.

to say the 450 did metal poorly is going to come down to 4 variables

1. how the computer decided to run the machine, i.e. how the CAM software drove the axes. this is very important to get correct, and while some machines are more capable of utilizing their spindle horsepower, some machines are not. and so the CAM software must be programmed by a person familiar with milling the material in question or else bad results happen. i've seen first hand how that happens, and how bad it can be. sometimes, well i will go further and say most times, the strategy (the plan to attack) for the material is conservative, to the point that the machine takes 16+ hours to cut your big roundhouse implant framework, or does not employ the A and B axis to actively remove undercuts and leftover material.

2. the holding of the material. sometimes the clamping system does not apply enough clamping force, and due to no fault of the operator the material slips out of place and breaks a tool. hey, it happens. it especially CAN happen with Wet processing when there is Oil as a lubricant involved. it is also conditional that the material clamp does not slip when turning over for the underside. in older 450's it is documented (even documented here in this forum) how the material clamp has "play" where the abutment top side and bottom side (A+ and A-) are shifted by some microns, creating a kind of offset that distorts the abutment, and is most prevalently seen in abutments.

3. the power of the machine itself. look, some spindles even if they have 3 horsepower, do not have torque enough to cut hard materials. pushing the envelope with a hard material and an Air Powered spindle means driving air pressure up, and thats expensive and difficult to keep consistent.

4. machine rigidity. the vibration from cutting hard materials is most evident at high speeds, especially in a machine that has high mass, so even in the 650 (which i have) the granite slabs that hold the X Y and Z axis together contains well over 30Kg of mass, and for moving this mass at high speed you will need air ans servo motors with a lot of power. no matter how well the all-steel frame is constructed, that's enough inertia to put the whole machine into vibration so dampening that is a balancing act of underusing the power of the machine, and cutting with speed and precision.

something has to be sacrificed to give the best result. a machine with low mass in the X Y Z axis will require less power, and so may not have enough power to cut through a hard material.

CAN the 450 cut metal, sure. but HOW is a question really on you can answer. because 2 of the 4 above points rely on your ability as a machine operator to control the production.

 

[A. M.]

In my old place we had a 450. Milled a couple metal crowns and bridges.
It was good with the imes puck, and it was milled dry.
Did not work well with any other puck, and those were milled wet.
But we didn't mill a lot of metal with it, so I don't have that much experience...

 

[CoolHandLuke]

imes metal pucks? like supplied from germany ?

 

[Uliana]

In my old place we had a 450. Milled a couple metal crowns and bridges.
It was good with the imes puck, and it was milled dry.
Did not work well with any other puck, and those were milled wet.
But we didn't mill a lot of metal with it, so I don't have that much experience...

What pucks are exactly?


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[brayks]

Thank you for your reply.

Do you have a ready strategy to share?

I just got to know from Imes Icore themselves, that Imes Icore 450i is not suitable for metal milling as the shaft is 3 mm and this milling will damage the spindel. Do have any opinion on this information?


Sent from my iPhone using Tapatalk

I agree with this. I believe metal cutting was an option for these machines and may have included the available 6mm tooling. If this is true a new, stronger spindle MAY have been utilized. This is only speculation as their literature indicated 6mm tooling was available.

However as CHL indicated, there is much more to it than just tool diameter and spindle torque. motors, guideways, linear actuater specs (i.e. ballscrews, diameter, pre-load, etc.),machine rigidity, fixturing ,etc. all play an important role.

All this said, if a representative indicated it is not a good idea and you have 3mm spindle clamp diameter. I would say your machine is most certainly not suited for CoCr machining.

 

[A. M.]

imes metal pucks? like supplied from germany ?

What pucks are exactly?

Yes, imes CoCr ...
Just to show you guys:
http://shop.cap-us.com/cobalt-chrome-milling-disc/
http://www.imes-icore.de/fra/disque-d-usinage-coritec-cocr-alliage-non-precieux.html