Using wire EDM for cylinders production

[alexmit]

Cylinders for Piston Engines go through a final process of grinding and honing to achieve a surface finish that is fine enough to prevent as much friction as possible yet rough enough for holding engine oil for lubrication between the Cylinder and the Piston.
The required Surface Finish is around Ra 0.4 micro meters.
It is possible to achieve such surface finish with wire EDM (with no need for grinding and honing).
If anyone knows anything about the suitability of Wire EDM to create a good lubrication retention surface it will be of great help.

 

[SteamKing]

What happened to the piston rings?

 

[alexmit]

Nothing, I'm talking about replacing the traditional methods for cylinder production to wire EDM.

 

[pantaz]

Have you calculated how long it would take to wire-EDM a typical cylinder?

 

[xxChrisxx]

Have I missed something here?

Why would you want to wire cut a hole when blocks are cast?

 

[alexmit]

I havn't calculated how long it will take nor am I worried about it. My concern is about quality and functionallity.

 

[alexmit]

Chris you're right, blocks are cast and then go through final process of grinding and honing like I've mentioned. I don't want to do any honing, my idea is to wire EDM the cylinders and I have some thoughts that wire EDM will have some superior properties in terms of surface finish. I'm looking for an advice in that area.

 

[Ranger Mike]

As former Product Manager of a company that invented the Profilometer,,,used to measure Surface Texture parameters i am well versed on this subject.
There is no such thing as surface finish. Per ANSI B46 standards Surface texture is classified as Roughness, Waviness, Flaws and Lay. The Ra or Average Roughness parameter you state is just about worthless in controlling a particular metal products functionality. Traditional methods of final machining of a cast iron cylinder block ( engine case) has been developed to the point that minimum break in is required to seat the piston rings and yield maximum serviceability of the engine...max miles between rebuild..if ever.
You are correct in the requirement of oil retention of the cylinder walls. Super smooth walls will harm the ring sealing and foul spark plugs.
Todays piston rings need to ' run in " or seat to attain maximum sealing over the longest life span. To this end automotive manufacturers have developed Plateau honing to knock off peaks present on a surface but retain valleys for lube retention.
Knowing this you should research the various Surface Texture parameters ( over 140 at last count) and identify the ones currently used in manufacturing and compare these to those attainable with EDM. Good luck.

 

[alexmit]

Mike thank you for your reply,
I'm well aware of the standards for surface texture, I'm also familiar with the common practice parameters used for manufacturing of cylinders.
I also know that those parameters can be achieved using wire EDM.
However those parameters used to measure surface texture don't tell the whole story. Honning creates sort of valleys like you said while wire EDM creates sort of cavities while achieving the same parameters.
That's exactly what my question is about, the suitability of Wire EDM to create a good lubrication retention surface.

 

[Ranger Mike]

You are almost there. What you really need to do is measure the roughness profile of a suitable surface. This will graphically display the surface and you can see the shape. A total profile will in fact thel lthe whole story. It will be a squiggly line...Parameters are an attempt to qualify this surface numerically. To take the guess work out of describing one surface from another.

 

[alexmit]

Mike, I know I can manufacture an example and run any number of tests on it.
What I'm trying to do is figure out beforehand if anyone has any experience with something similar and can shed some light on the subject. All before I turn to spending lots of money on manufacturing and trials.

 

[xxChrisxx]

I forgot to make my post about this before. Aren't you asking the wrong question?
Rather than 'is it suitable' shouldn't you be asking why would EDM be better?

It's been a long time since I learned about manufacturing processes, so what I know may be out of date.

To get fine tolerances and good finish, EDM requires multiple small passes making it a very very long process to get a really good finish. The machines are also more expensive to run than the grinder. EDM's forte is producing complex shapes, which finishing a bore isn't.

What's the driver to move away from grinding?

 

[alexmit]

Hi Chris,
From what I've read about wire EDM today first or maybe second pass will give me the required result.
The driver is to do the whole thing in one shot rather then using multiple machines, while achiving better results in terms of oil retainment like I've mentioned before. The other advantage I'm looking for is to be able to manufacture complicated geometries like the Wankel engine Trochoid.