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Apprenticeship EDM knowledge

ChrisC_84

Plastic
Joined
Apr 4, 2020
Location
UK
Hi,
I wonder if someone can point me in the right direction please?
I'm an apprentice EDM operator and a part of my apprenticeship is that I need to answer some questions relating to EDM.
One of the questions is "Explain how the various types of materials will affect the feeds and voltage that can be used". I haven't got the faintest idea how different materials affect the process, I only know that they do. Is there anywhere I can go to read up about this?
Thanks
 
Chris,

I'd like to help you out…and its always a pleasure to help someone new coming into the trade!

Your question of “Explain how the various types of materials will affect the feeds and voltage that can be used” is somewhat difficult to explain, as I don’t fully understand the context and intended age of the EDM equipment the question is being asked about, but I will try my best.

General Response:
Different materials types (such as Aluminum, Tool Steels, and Tungsten Carbide) all require different EDM Generator values (On-Time, Off-Time, Amperage, Voltage) to machine with speed, precision, and most importantly process stability. The Electrode Size (Sinker EDM) and material thickness (Wire EDM) also impact the EDM Generator values, as these power levels must be reduced the smaller the machining area becomes. A materials metallurgical alloy make-up and subsequent electrical conductivity can also change the EDM discharge spark gap and machining efficiency.

Modern EDM’s do not operate with a set feedrate like CNC Milling or Turning machines, as EDM’s utilize automatic adaptive power controls to stabilize the EDM process. The adaptive power control monitors the EDM machining spark gap and maintains a precise and proper distance between the electrode and the work piece (these two NEVER touch during machining), and this gap distance is forever changing during EDM machining. The EDM process is inherently unstable, as the machine must disengage and re-engage from the part to establish and maintain a proper spark gap condition, so these is a lot of back-and-forth type motions that occur several thousand times per second within the spark gap. Modern EDM’s still utilize a common set of Generator Settings (On-Time, Off-Time, Amperage, Voltage), but these values become more like “target values” that the machine starts with and then automatically adjusts to optimize speed, precision, and stability.

For example, the EDM power levels and voltages are reduced when machining Tungsten Carbide materials when compared to Tool Steels. The setting changes are due in part to Tungsten Carbide’s higher electrical conductivity and higher melting point temperature of its chemical composition, and the lower power levels prevent damage such as thermal cracking to the Carbide material (Carbide is actually a pretty sensitive material to EDM). It is important to note that the EDM generator value changes are NOT related to the wok piece materials hardness! This means that the EDM process works equally well on a 30RC Steel part vs. a 60RC Steel part…the hardness does not affect the EDM settings values, but from a technical standpoint, hardened steels do technically EDM better because they have less impurities in them as a result of the heat treating process.

Have you learned and understand the basic EDM Generator fundamentals with On-Time, Off-Time, Amperage, Voltage, etc.? I hope the above information is helpful, and please let me know if you have any further questions.

Best of luck to you!

-Brian
 
Hi Chris,

The explanation of Brian is quite very good to understand how the process goes. Maybe in google you can find some info about it, typing EDM process or fundamentals. Also if you have the manual for the machine it explains everything...but is quite long to read..so take a large cup of coffee.

Best Regards.
 
Chris,

You've got a couple of experts providing you great information here. I will toss in one piece of info (from the trenches, haha) regarding feed rate: (I'll preface with saying that I have experience ONLY with wire edm, not sinker.)

In my experience, feed rate (and that is: "potential feed rate", since feed rate is not pre-determined with a "setting" on a wire edm machine) is just about directly related to material density. Gold cuts really really slowly, aluminum cuts really fast, other materials in between somewhere. It's a very "coarse" rule of thumb, but I've found it to be consistently true.

PM
 
Thanks for the responses. I think I can cobble together an answer to this question.

The question threw me for a loop when I saw that it was asking 'how' these materials affect the process. I work for a Carbide manufacturer so I haven't had much experience with different materials (cut a bit of steel on occasion). I haven't had much guidance with the machines either. The guy that was running them when I joined didn't seem to want to give up what he knew. Now he's gone and left me to work it out as I go.

Thanks again for the input, I'll be sure to return with other head scratchers.

Chris C
 
Hi Chris,

I might be able to help out. I wrote a lengthy (11-page each), 4-part series called "Toolroom Metallurgy" before Roger took over EDM Today magazine. Unfortunately, all articles previous to his acquisition are no longer available except within the printed issue itself. (All issues and articles since his management are available on our EDM Today website.)

"Toolroom Metallurgy" is an analysis of each material down to the molecular-level and an overview on how to EDM or WEDM them and why. I still have my final drafts of all them and can send them to you if you PM me your e-mail address.

Pt 1 - Ferrous alloys - all tool steels
Pt 2 - Ferrous and non-ferrous alloys - steels, steel alloys and non-ferrous materials
Pt 3 - Carbide-making
Pt 4 - Carbide-machining

Since you work for a carbide company and are actively wire-cutting, I would gratefully accept any updates or suggestions for improvement of the carbide sections.

Bud Guitrau
 
That would be very useful for my professional development.
I'll have a word with my boss about any suggestions regarding EDMing carbide
PM sent
Thanks Bud
 
"That would be very useful for my professional development"

I agree. One must never stop learning or can learn too much.

"I'll have a word with my boss about any suggestions regarding EDMing carbide"

Agreed also. Either they provide you with the knowledge, formal training and resources to successfully fulfill your job description, or they must recognize that you are instead, a pioneer on the frontier of their business-plan and should invest in your training and development, while recognizing and valuing your benefits and compensating you accordingly.

"PM sent"

Got it, thanks. You should have all 4 chapters in your morning e-mail and have a long-read with your morning tea. With your background and from what I have gleaned from your input and interest, I suggest you start with Pt 3 first, to better understand how carbides are made (if you didn't wholly know) and then why carbide behaves the way it does when EDM'ed (Pt 4).

"Thanks Bud["

Not at all, Chris and "You're welcome", for reaching out and asking in the first-place. (The only stupid question is the one that goes unasked" -- Ramon Bautista). I enjoy sharing my archives and experiences with anyone who is curious and wishes to learn and grow, because; "If you don't know, you can't grow." - Bud Guitrau

Please let me know what you think of this series and of any suggestions you might provide for improvement.

Bud Guitrau
 
Good morning BUd:
Are you willing to email me a copy of the series too?
I always value your knowledge and would love to learn.
Like all things worthwhile, I've found that the effort of learning always pays dividends, so if you're willing I'd be most appreciative.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Marcus, of course I can send you these. Glad to help. Will send to your Implant Mechanix address.

With a note to this thread's moderator, I have had numerous requests (through PM and LinkedIn), to send this out to several other PM members. I am happy to do this, but this could take an hour every day.

Instead, I would be happy to donate these papers (and more) to Practical Machinist where a simple download while member-browsing is possible. Is there such a library or archive?

Don't wanna sound grumpy, and I'd like to help everyone who are kind and curious enough to ask, but I'm just one guy who's recently retired (OMG, it's heaven!) and I don't need/want another job or the accompanying addiction or obligation to a computer and e-mail.

I see there is a "white-paper" area under the "Resources" button. I would be happy to upload my files for everyone's browsing if someone would tell me how.

PM, help me help you.

Bud Guitrau
 
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