Hard machining vs. carbon

[JIMMY]

Hi everybody,

I am going to be doing a study on Hard Machine vs. Carbon and if anybody can find any information on these subjects that would be great.

Thanks,

JIMMY

[MnotLyon]

I think you need to form your question a little better. Are you talking about machining hard steel vrs. Ram edm burning?

[JIMMY]

Sorry about that. I am doinf a study on hard machining vs. edm. I am trying to convince my company to do more hard machining than they do now. We already do a lot of hard machining but they still have edm in their head so I am trying to get imformation on the two.

[MnotLyon]

In my opinion, sometimes EDM is better. EDM will allow you to burn shapes that can't be cut conventionally. It can also reduce bench time if you're using a newer machine.

Of course, hard machining has it's advantages too. There is no expensive graphite to buy, or machine. That alone may eliminate the need for an expensive graphite mill. Tooling for EDM's can be costly as well. Ventalation can be an issue with larger machines. And, in some areas, the recast layer produced by an EDM my cause quality problems.


I build plastic injection molds. I can't imagine being able to eliminate my EDM for things like deep ribs, and square corners. Each job stands on its own, and each machine has it's place.

[JIMMY]

You are right I can not eliminate deep ribs and square corners. I just want to cut back on the amount of trodes that we make. Hard machining and edm are great combinations if done right.

[derekj308]

Hi Jimmy

I've done some research recently on high speed machining which includes techniques for machining pre-hardened steels. The goal for us at least is optimise the machine utilisation on both our EDM's and machining centres to reduce 'man hours' on machines. I came across 'negative stock allowance' which is an excellent way to reduce spotting time on a die and also increase venting and improves die life. Not practical on manuals but achieveable with precision machining centres. As far as reducing the amount of 'trodes you make HSM is an excellent starting point for your research but don't forget about standardising rib thicknesses, maximum cavity depth for a given cavity width, etc. If you give your product designers some written guidelines and list of standard tooling you keep you can reduce the amount of electodes you need to make.

Cheers

Derek

[derekj308]

Hi Jimmy

Try http://www.mmsonline.com/articles/040601.html
and http://www.mmsonline.com/hsm/

Cheers

Derek

[MrMold]

I have really reduced but not completely eliminated the amount of EDM work I do. Many companies I worked for in the past were more concerned with utilizing equipment than getting the job done.
Take sub gates for example. Some shops love to burn all their sub-gates. I machine a majority of them. Some companies hate to have a 100K EDM machine in their shop that sit there a majority of the time. And some companies hire specialized EDM operators instead of moldmakers, so they like to create work for them.
You can reduce alot of edm time by utilizing Micro tooling. I use 1/32" cutters and smaller all the time to save EDM time. The finish is usally outstanding and require little or no polishing.
Many times the methods I use are dependant on Machine utilization. Machining time isn't everything when you can run several machines at once. Anytime you can reduce Polishing and electrodes is a plus and don't forget the cost of some of the finer graphites. The newer EDM's are capable of pretty good finishes now, but any time I can avoid it. Carbon is a mess even with them best vaccum sytems.

[PeteZ28]

What kind of machine are you using for your hardmilling? Are you using a conventional machining center, or do you have a proper, high speed, high feed, rigid hardmilling machine?

If you have the proper equipment for hardmilling, by all means you should be looking for any excuse to get work in there and not the EDM. By the time you machine the 2-5 graphite electrodes you will need, not including setup time and the many hours of burn time, you can be done with it by hardmilling. In the process, you will be saving hundreds of dollars in graphite, and probably use the same amount if not less costly coated carbide endmills. Not to mention other sinker EDM consumables.

Even if the part has square corners or a deep rib, milling out 90% of it then going in with the EDM to finish the details is a huge time saver. For example, if you have a tight inside corner radius to finish deeper than and endmill will allow for the given radius, you can go in after milling with a few small, simple electrodes in the corners and burn out the remaining material in no time.

To me I cannot see why any company with hardmilling capability would even want to think about a sinker except as a last resort. In fact I think it's practicly going to become mandatory in the next few years if domestic moldshops want to survive, the cost and time benefits are just that good! Even the EDM companies are making or selling some type of hardmilling machine now. It's the way of the future and even they know it.

[JIMMY]

I have two YBM 640 YASDA hard milling machines. My company has been going through a slow transition from wanting to use edm rather than hard machine. I have new owners now and I am going to be putting together some information for them. They are going to be putting new machines in the shop and also installing robots as well. So I want to show them what Hard Machining and do. I cut .0002 tolerances all day and night with these machines.

[wmFlipper]

You go Jimmy, miss the place there.

[AlexBanich]

Just out of curiousity what is the minimum width that everybody is able to achieve with hard mills? To be exact if you were to make a slot what would be the minimum width you'd be able to achieve keeping a tolerance of say plus or minus .0002? My company is trying to move away from EDM and in to the new age of hard turning and milling. The problem is we are having a hard time convincing our management of this when they feel EDM is working well enough. As well the decision was made to hard turn on our conventional CNC lathe and we're running in to poor qualtiy finishes and other issues that have further delayed our progress. Does anybody also have any input on hard turning and milling of interupted cuts? Is there much in the way of burs? In what ways besides the typical getting it up and running exists in man hours? I apologize for the numerous questions but I just happened to stumble on to this thread and it hits right on the issues we are looking in to. Thanks for any information.