venturi suction system

[rajanish]

hi
i am trying to design a venturi vacuum suction system for chip extraction for diamond turning operation. can anyone help in finding the formulae for suction power required, compressor power requirements etc?
regards,
rajanish

[ImanCarrot]

Hey! I thought I was the only Diamond Machinist here hehe!

I use one of these venturi extraction systems- when machining aluminium it clears the swarf in a big long thin strip- like tinsel.

I use a 1/2" diameter nozzle, the air pressure is about 60psi and the air hose is about 0.1" diameter. It works quite well untill it clogs, but I find that attaching a vacuum cleaner near to the output of the venturi system helps (obviously don't touch the venturi system with the vacuum cleaner- you know what vibration does to optical surfaces hehe). Also, having the spray mist coming from underneath the tool tip helps too.

Here's a piccy of it, not attached to the air line though.

[rajanish]

Hi Iman,
Thank you for your information. Would you please tell me how close you will keep that venturi to the machining zone since this also plays a role in sucking? i will be doing facing operation and my chips are going to be very fine like powder since i am machining brittle material not aluminum. and i am doing dry machining for my work piece
and it would be great for me if you know more about venturi design since i am planning myself to design my own rather than buying
thanks again
rajanish

[ImanCarrot]

Brittle material? I'm guessing Germanium? make sure you use the right tool- got to have a -25 degree top rake for Germanium, obviously if your facing you want a large radius tool to minimise tool wear.

To be honest I don't use the venturi system at the moment since I'm machining plastic I don't use it on Germanium either- I only use it on aluminium to get the swarf out of the way otherwise it all clogs up and gives a poor finish.

I've attached a quick sketch of the basics of the system for you in ACAD format


Oh, I generaly have the venturi pipe as close to the workpiece as I possibly can.

You mention not using any coolant... that is very unusual- what kind of finsih do you get please?

[rajanish]

its a optical material called KDP and applying diamond turning on this material. it is a not like other brittle materials like Ge, Si etc which are hard but is soft and brittle.
Having problems with chips on the surface and has a problem of 'Fogging' when a suitable coolant is used, that is why i use dry machining...
the surface finish i get is around 2 to 3nm....
trying to extract the chips during operation to eliminate the surface damage...

[rajanish]

by the way what is the that ashperic formula in the diagram...i couldnot understand

[ImanCarrot]

Sorry, my fault, the aspheric formula is used for when I'm designing lenses- it's nothing to do with the Venturi pipe sketch. I should have erased it.

I've never machined KDP, but I hear it's a non- linear crystal which is soluable in water- I suppose this could lead to problems with atmosperic moisture (fogging)? I also hear that the Top Rake needed is fairly steep at minus 40 odd degrees! I immagine this would introduce a conical error on the surface form?

[rajanish]

rightnow i am using only 0 rake tool maintaining undeformed chip thickness less than cutting edge radius which gives negative rake effect.....

it has been shown this condition achieves optical surfaces(ductile mode cutting) on brittle materials

[ImanCarrot]

Very interesting indeed. I've got a Germanium project coming up and they're teling me to use a minus 25 top rake tool.

Obviously I'd like to use a zero rake tool so that setting the tool height is easier.

[rajanish]

Hi Iman, are you working in diamond machining industry or a researcher? i am doing my research work on ductile mode cutting of brittle materials......its good to see sharing knowledge on this subject..
Do you machine Silicon also?

[ImanCarrot]

Manufacturing- I've been doing Diamond Machining for over 10 years

We're manufacturing hybrid aspheric lenses at the moment in high index plastic for night vision applications.

I have machined Silicon before at another company. However, the tool would only last a few components then we got tool wear and the typical "grey" surface associated with this.

Yep, it is good to share, I think I've only ever seen one other Diamond Machininst on these boards!

I would be interrested to know what depth of cuts and Feeeds/ Speeds you are using- I can't immagine they'd be too different from myself.

[rajanish]

we use depths of cut 0.1microns to 3 microns and feed rate around 2-5 microns......we do research on ductile mode cutting of brittle materials....theoretical and experimental.....perhaps you can check this site http://serve.me.nus.edu.sg/nanomachining/index.htm for more info..