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Is the electrodischarging the only method to drill holes on hard materials?

04/08/2008 12:57 PM

I need to drill a little hole on a hard steel (heat treated). I do not want to change their microstructure that consist of Martensite (around 80% in area) and Austenite (around 20% in area). Hardness around 63 Rockwell C.

Is there another method than the electrodischarging way?

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#1

Re: Is the electrodischarging the only method to drill holes on hard materials?

04/08/2008 11:04 PM

What is your diameter to depth ratio?

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#6
In reply to #1

Re: Is the electrodischarging the only method to drill holes on hard materials?

04/09/2008 8:42 AM

dia= 6 mm (0.24")

depth= 25 mm (1")

dia/depth= 0.24

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#8
In reply to #6

Re: Is the electrodischarging the only method to drill holes on hard materials?

04/09/2008 8:54 AM

Carbide, diamond, laser should drill, depending on the tolerances and finish you need.

Also durability of the cutting tool is to be taken in consideration depending on the quantity of holes you need.

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#10
In reply to #8

Re: Is the electrodischarging the only method to drill holes on hard materials?

04/09/2008 9:07 AM

Thanks for your comment...Carbide and diamond are not alternatives...I tested with them...

I would like to know more about the laser method....at present the tolerances and finish are not being considered....The electrodischarging method is too slow...

thanks, again

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#2

Re: Is the electrodischarging the only method to drill holes on hard materials?

04/08/2008 11:23 PM

You may use diamond drills if it it is not too deep

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#3

Re: Is the electrodischarging the only method to drill holes on hard materials?

04/09/2008 12:38 AM

Why do you have both Martensite 80% and Austenite 20% in the area?

WHat Material is this?

MArtenisite should be at least 90-95%. No retained austenite?

What is the steel?

milo

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#7
In reply to #3

Re: Is the electrodischarging the only method to drill holes on hard materials?

04/09/2008 8:47 AM

It is an special steel that I need to develop...high Carbon and other special elements...

My target in this is 80% Martensite and 20% Austenite...

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#14
In reply to #7

Re: Is the electrodischarging the only method to drill holes on hard materials?

04/09/2008 9:42 AM

Goodluck.

Maintaining martensite and austenite simultaneoously in those ratios should prove to be a challenge.

milo

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#4

Re: Is the electrodischarging the only method to drill holes on hard materials?

04/09/2008 7:13 AM

A carbide drill should do the job. If not, then diamond would cetainly do it. Laser is another way to go. You want to use a Q-switched laser that ablates the material without changing the microstructure. To accomplish this, the laser needs to deliver high peak power and low average power.

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#9
In reply to #4

Re: Is the electrodischarging the only method to drill holes on hard materials?

04/09/2008 8:55 AM

Carbide and diamond drills are not alternatives...I tested with them..

Q-switched laser sound interesting..

Could you help me with some electronic paper to know more on this method? the address of a good web page? How is the device? Is it very expensive?...

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#5

Re: Is the electrodischarging the only method to drill holes on hard materials?

04/09/2008 7:39 AM

Depending on the size of hole and accuracy needed, abrasive waterjet may be an option.

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#11
In reply to #5

Re: Is the electrodischarging the only method to drill holes on hard materials?

04/09/2008 9:13 AM

dia= 6 mm (0.24")

depth =25 mm (1")

at present, the accuracy is not a problem...

How does the waterjet work? where can I find technical information (good technical information)?

Thanks for your comments...

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#13
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Re: Is the electrodischarging the only method to drill holes on hard materials?

04/09/2008 9:42 AM

INFORMATION ON ABRASIVE WATER JET IS AVAILABLE FROM FLOW INTERNATIONAL, OMAX, JET EDGE, THREE OF THE MANUFACTURERS OR THE MAGAZINE TOOLING ENGINEERING.

A through hole of the size you are talking about can be done but the bore would be rough. We do it all the time and a hole this size is fine for a bolt hole in a flange but for a pin or other precision hole it would not be suitable. It does however leave the material unchanged metalurgicaly. ( if that's a word)

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#15
In reply to #13

Re: Is the electrodischarging the only method to drill holes on hard materials?

04/09/2008 9:50 AM

It is now!

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#17
In reply to #13

Re: Is the electrodischarging the only method to drill holes on hard materials?

04/09/2008 9:57 AM

Thanks Morgan 23...

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#12

Re: Is the electrodischarging the only method to drill holes on hard materials?

04/09/2008 9:22 AM

Abrasive water jet. Any other method (now that the part has been heat treated) will change the near-surface metallurgy, which will leed to surface fracture and crack propagation. If there was a error during the manufacturing, lets say someone forgot to drill the holes, be careful. If the hole is used to secure the part or its relevance is structural then I would re-due them. If not then abrasive water jet will serfice.

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#16
In reply to #12

Re: Is the electrodischarging the only method to drill holes on hard materials?

04/09/2008 9:53 AM

Thanks for your comments...

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#18

Re: Is the electrodischarging the only method to drill holes on hard materials?

04/09/2008 10:02 AM

Hi,

search for ECM or electrochemical machining,

you need a metallic tube as an electrode,

a pump to have a lot of fluid pumped through,

the fluid being conductive, most people use sodium-nitrate to ensure good conductivity,

a feed mechanisms to bring the tube to a low (but never touching) distance to your workpiece,

a DC power-supply with 5 to 50 V and a lot of amperes (giving rate of dissolution),

a big tank or pool to cool down the heated fluid and oxidise by air contact the 2valent iron and other elements and separate the resulting mud.

This is the basics.

You will need in theory 96400 Ampere x seconds to dissolve 1 Val (molecular weight divided by valence =2 for iron) that is 28g of iron. But in reality you will need twice or three times this Charge.

You will need a very fast (microseconds) short circuit protection that is feasible (long cabling, high current) only by active short-circuiting and then shutdown because any metallic contact will trigger a partial meltdown of electrode and workpiece.

You will need a gap servo to ensure 100┬Ám gap between tube and workpiece.

You will need a voltage that is determined by the resistance of the fluid (very dependent on concentration and temperature) and some volts extra for the electrochemical action and the cabling losses.

I tried a very small bore (0,2mm) with a primitive arrangement but using a glass tube and a gold wire as an electrode and sulfuric acid as electrolyte - this is used to bore the cooling holes into modern aircraft turbine blades.

There are machines and installations available.

This process is used in fabrication of drop forge tools, for chocolate molds, and many more difficult to machine parts.

No wear on electrodes, but may be corrosion if not used.

This is the one and only process that does not influence the surface composition -!

Have success and please report here what you achieved.

RHABE

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#19
In reply to #18

Re: Is the electrodischarging the only method to drill holes on hard materials?

04/09/2008 11:12 AM

Thanks RHABE...I think, you are Chemical Engineer

What about the drilling rate (rate of dissolution)? how much is the expected time to drill one hole with 6mm dia and 25mm depth...? I know that depends on settings (and chemistry of steel)..but what is the "normal" range of dissolution rate?..

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#20

Re: Is the electrodischarging the only method to drill holes on hard materials?

04/13/2008 10:20 PM

http://www.nolansupply.com/supercut.asp?supercategory=Drills+-+Die+Drills

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