Does Wire EDM change the temper or properties of metal?
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    Default Does Wire EDM change the temper or properties of metal?

    Hi I am fairly new to the wire EDM world.

    I have a Sodick vz300

    I have a customer asking me if wire EDM changes the temper/properties of the material. They also asked if it does change, how much into the part from the edge/cut area would it affect?

    Any info would really help.

    thank u.

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    There was a time when this was considered a problem, but that time is now long past.

    A rough and skim will leave a HAZ of a few "tenths" and as near no recast layer.

    A couple more skims will virtually eliminate them.

    I'm not sure what your customer's application is but:

    We regularly wire-edm punches, die blocks, forms, and other die components from tool steels that have been heat-treated to 55-65 Rockwell C with no problems in operation afterward.

    We regularly cut metallurgical test specimens for several customers.

    We also regularly cut the blade root profiles in gas and steam turbine disks. We are getting set to do several even now.

    We've also done flight hardware for a couple of customers.

    On early edm machines, both wire and sinker, the HAZ and recast layer would have prevented running these jobs but ...

    The modern controls and power supplies available today now make edm the preferred method in many of these cases.

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    Thank you very much, this info is very helpful.

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    Jay,

    fwiw: A good number of years ago, I cut quite a few titanium components for the mirror actuators on the James Webb Space Telescope. I had to cut a number of test articles which were run through a lab for SEM analysis, and everything passed with flying colors. The machine used was a 1995 Agie, so definitely not the latest/best in generators, but the right selection of wire and tech settings did the job well above the requirements.

    PM

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    Hello jay131,
    You asked a very good question. Although I'm not an expert on wire edm I have asked the same question regarding aircraft machining. Apparently, the practice of using edm for manned aircraft hardware is not accepted. For reasons unknown to me, metallurgist and aerospace engineers do not like what they see. Other than this, sinker/wire edm has proven to be a indispensable practice in the production of molds and dies.
    otrlt

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    Quote Originally Posted by otrlt View Post
    Hello jay131,
    You asked a very good question. Although I'm not an expert on wire edm I have asked the same question regarding aircraft machining. Apparently, the practice of using edm for manned aircraft hardware is not accepted. For reasons unknown to me, metallurgist and aerospace engineers do not like what they see. Other than this, sinker/wire edm has proven to be a indispensable practice in the production of molds and dies.
    otrlt
    Strange ... NASA and Lockheed have yet to complain about our work.

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    Quote Originally Posted by otrlt View Post
    Hello jay131,
    You asked a very good question. Although I'm not an expert on wire edm I have asked the same question regarding aircraft machining. Apparently, the practice of using edm for manned aircraft hardware is not accepted. For reasons unknown to me, metallurgist and aerospace engineers do not like what they see. Other than this, sinker/wire edm has proven to be a indispensable practice in the production of molds and dies.
    otrlt
    It's probably because if the re-cast layer is not removed, then there will be significant fatigue issues, leading to reduced life spans of parts. How much to remove, and whetehr the vendor did an acceptable job are issues.

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    Quote Originally Posted by triumph406 View Post
    It's probably because if the re-cast layer is not removed....

    In the year of 2016, most of the "recast layer removal" for aerospace work is pure legacy BS that the respective aerospace companies will not
    and cannot address at this time.

    +80% of my stuff is aerospace related, and most of my UOS tolerances are +/- .005.
    So please someone in the aerospace engineering industry explain to me why a .001-.002 max recast ( white or HAZ ) layer is an issue?

    Why can I wire EDM a surface that is cost prohibitive to manufacture in any other way, and yet, all other machining on the same part must be done by a "conventional" method?


    Sidenote: I also make a fair amount of ultrasonic related parts that are fully kosher to be cut by wire EDM.

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    Quote Originally Posted by SeymourDumore View Post
    In the year of 2016, most of the "recast layer removal" for aerospace work is pure legacy BS that the respective aerospace companies will not
    and cannot address at this time.
    Fatigue is not legacy BS. Recast is on the surface, and depending on the machine/process/setup etc can leave microcracks in the surface,so unless it's removed it can lead to stress problems. Just because the recast layer of .001-.002 is within the +/-.005 tolerance is meaningless.

    Instead of assuming it's acceptable, talk to a stress engineer at an aerospace company so he can set you straight.

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    Fellow Sparkies,

    By pure physics, all EDM machining is considered to be a thermal process! This means that some form of heat was generated during the machining process, which can alter a materials metallurgical structure (controlled or uncontrolled). This can result in changes to the material’s fatigue stress, hardness, and wear properties. As EDMers, the big kicker here is that you cannot see or measure a parts metallurgical quality when you pull a part out of the machine. Metallurgical analysis requires specialized equipment and often includes destructive testing (parts are sliced up to inspect a cross-section of material), and the areas of concern from a metallurgical standpoint are often found below the actual EDM'ed surface.

    The Aerospace industry closely monitors and restricts certain components from being produced by the EDM process, as the smallest imperfection in metallurgical quality can lead to part failure considering the repeated mechanical stress and thermal cycling many of these components are exposed to. The reason why metallurgical quality is of such high importance is due to the controlled predictive and repeatable component live cycle of any given part. The Aerospace industry has tested and determined key metallurgical factors that contribute to changes in the predictive life of a component, and they work to keep these parts well within established safe limits for operational service hours before they are pro-actively replaced. The 3 main metallurgical quality factors that are most often monitored are Recast, HAZ (Heat Affected Zone), and Micro-Cracking.


    Recast: Is the re-solidification of the work piece material back upon itself, and can be harder and more brittle than the parent material. This is the melted/eroded debris material re-adhering back on to the newly machined surface. If there is a large built-up or globules of recast, this can "chip" away and cause damage to other areas of the part or to other parts. If a surface has variations in its recast layer, the wear characteristics of that surface will also be uneven and unpredictable. Inspection of recast this is typically performed with high power microscopy (1000x magnification and greater) and destructive testing.

    HAZ: Is an annealed layer of material that is located below the surface or outer skin of the parent material. The inner core of the material immediately under the EDM'ed surface (say up to 0.020" or 0.5mm deep from the EDM'ed surface) may have a modified metallurgical structure when compared to the rest of the part. This could be a slight hardening or softening of the material in this very small area underneath the EDM'ed surface, and this change can alter the wear and fatigue stress properties of the material. HAZ inspection can be performed by high power microscopy through destructive testing of the part, and the affected depth of this layer can be determined through special hardness testing methods.

    Micro-Cracking: This might be the easiest to understand, as this is small cracks in the material on the outer surface. This can be the result of poorly controlled EDM discharge power, and is most often seen as cracks in the recast layer. Inspection for Micro-Cracks is performed with high power microscopy and also destructive testing, and it is critical to determine the depth of these cracks. The concern with the existence of any surface micro-cracking is that these cracks will grow and propagate with part stressing (mechanical & thermal cycling), and will result in unpredictable component failure.


    From a Wire EDM standpoint, most new machines do a good job in producing fine metallurgical quality with modern AC generators and adaptive power control technologies. The metallurgical quality that is produced on new machines is far superior to Wire EDM's that are 15+ years old, but these advances CANNOT eliminate Recast, HAZ, and Micro-cracking due to the thermal nature of the EDM process. Modern Wire EDM's have greatly improved and minimized the undesired material changes caused by HAZ and Micro-Cracking, but Recast will exist on ANY EDM'ed part. Any claims by any EDM manufacturer to "Virtually Eliminate Recast" are 100% false, as this would indicate a breach in the fundamental laws of physics!


    -Brian

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    Hi All:
    Further to the commentary on recast, microcracks and failure by crack propagation, there are sometimes counterintuitive reasons or un-obvious reasons why EDM may be accepted on some parts and not others or even in some places on a part and not others.

    My exposure is medical not aerospace, but the principle remains; what has been found in my domain for example, is that certain surface topographies will attract and retain biofilms with much more tenacity than others, and EDM finishes are sometimes problematic, even very fine ones.
    Never mind the issues around alteration of the local metal chemistry on the EDM cut surfaces and the implications for biocompatibility, and on and on.

    Unless you know intimately, what the part does and what bits are subjected to the relevant stressors and etc etc, you really cannot make disparaging remarks about the idiot who designed this or that part, or make a general case that a process should be OK for an application or not.
    That's supposed to be the job of the engineer; and even in this world where so many are hopelessly inexperienced but responsible for quite sophisticated designs, they still are usually better positioned to make these kinds of judgements than we are, unless they let us in to the design process early.

    I'm finding more and more, that this is indeed the case as bright young engineers are given responsibility way before they're ready and are looking desperately for some guidance.
    There's a lot to know, and they're mostly very receptive to input if it's framed so as not to trample on toes.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    www.vancouverwireedm.com
    Clarus Microtech Inc. | Facebook

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    Thank you, for all the info, its been very helpful.

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    Quote Originally Posted by Brian Pfluger View Post

    The Aerospace industry closely monitors and restricts certain components from being produced by the EDM process, .... The Aerospace industry has tested and determined key metallurgical factors


    The metallurgical quality that is produced on new machines is far superior to Wire EDM's that are 15+ years old...
    -Brian

    Brian, that's exactly the point!

    As far as I know, the latest revision of "controlled processes" specification that I need to work to is dated 12/16/97!

    Triumph
    Fatigue is not legacy BS
    AFAIK, there is no such thing as "thermal fatigue" when talking metals. ( perhaps some powder metals, certainly not alloys )
    And no, I did not in any way mean to suggest that there are no issues with strength as a result of EDM process, just that there should be a constant update and review
    of the specifications, using current available technology and not rely on test results from the 80-s.

    Brian is working for Makino, and they have done a very extensive research and testing with a variety of aerospace alloys specifically with that industry in mind.
    I have seen the document ( may even have it somewhere), and one would be quite amazed at the differences between today's technology vs. the ones from even 10-15 years ago.

    Marcus
    Unless you know intimately, what the part does and what bits are subjected to the relevant stressors and etc etc, you really cannot make disparaging remarks about the idiot who designed this or that part, or make a general case that a process should be OK for an application or not.

    Completely agree. I am not, nor do I want to be the designer.
    What I do not agree with however is the utter lack of discussion and interaction between manufacturing and engineering ( at least in my direct and indirect experience ) with regard
    to possibly re-evaluating a manufacturing method.
    I can give a few examples where such discussion COULD yield a drawing revision, except there is absolutely no mechanism available to any of us to do so.
    Most often any request to change certain process ( not only EDM, but any process ) results in one of two replies:

    a: We've always done it this way and see no reason to change it
    b: How are we ( the customer ) going to benefit from the change and who is going to pay the cost of the revision change?

    With that, case is permanently closed.

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    Since it was brought up, I've attached links below to (x2) Makino Webinars that captures the extensive Aerospace metallurgical testing that Makino performed back on 2007. This data has helped bring awareness to the Aerospace industry on the dramatic improvements that have been made in EDM technologies. Wire EDM IS being used more in production Aerospace applications, but this has all been on new parts programs. The way the Aerospace industry (and Medical industry) works is once a manufacturing process is fully tested and cerified, it CANNOT be change or altered. Any change to a certified process would require a full extensive re-evaluation testing of that component, which means a lot of time, money, and paperwork!

    Machine Tool Webinars and Events | Makino

    Machine Tool Webinars and Events | Makino

    - Brian

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    Brian, Marcus, all,
    Has there been any studies of post treatments to reduce some of the drawbacks of wire cutting? I'm thinking specifically of micro-bead blasting for compressive surface modification, as well as reducing the surface roughness that could facilitate biofilm accumulation. Also, is chemical milling ever done to remove the last few thousandths?

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    Quote Originally Posted by Milland View Post
    Brian, Marcus, all,
    Has there been any studies of post treatments to reduce some of the drawbacks of wire cutting? I'm thinking specifically of micro-bead blasting for compressive surface modification, as well as reducing the surface roughness that could facilitate biofilm accumulation. Also, is chemical milling ever done to remove the last few thousandths?

    Milland

    Don't know about other companies, but Pratt & Whitney's specification for EDM operation is PWA-97, which is titled:
    "Finishing by Electrochemical or Electrodischarge metal removal"

    That immediately includes chemical milling.

    As for bead blasting, believe it or not, it is probably a bigger no-no than EDM!

    Let me quote this from PWA-367, section 4:

    All glass bead, ceramic and steel shot peening process are prohibited, except glass bead peening may be used for deburring and cleanup, provided that a minimum of 0.030 in. of material is
    subsequently removed by mechanical means.
    Interestingly, the same spec. requires mechanical removal of .004 in for Wire, and .010 for conventional EDM operations.

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    Hi All:
    For those who prefer to read text rather than watch videos, here's a link to a Makino white paper on the process as it relates to aerospace.
    This may be of special interest to you, Jay131, because it answers your questions directly.

    Here it is:
    Aerospace Manufacturing, EDM for Aerospace, Aerospace Production | Radical Departures

    Interesting that HAZ has become essentially unmeasurable and recast is measured in low numbers of tenths.
    Interesting also, that sinker is still not quite as good as wire.

    Reading through it I really get your point, Seymour.
    It seems that the industry specifications have not kept up with the process improvements at all, and that your contention of brainless bureaucratic inertia is spot on.
    Must drive you nuts at times.
    I sympathize!!
    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    www.vancouverwireedm.com
    Clarus Microtech Inc. | Facebook

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    Quote Originally Posted by Brian Pfluger View Post
    Any claims by any EDM manufacturer to "Virtually Eliminate Recast" are 100% false, as this would indicate a breach in the fundamental laws of physics!


    -Brian
    Since virtually means
    "effectively, in effect, all but, more or less, practically, almost, nearly, close to, verging on, just about, as good as, essentially, to all intents and purposes, roughly,"
    they are claiming to have recast, so how are their claims false?

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    From the link to the Makino's own 1st webinar:

    Advanced EDM processes for Aerospace

    July 26, 2007

    The recast layer and Heat Affected Zone (HAZ) left on workpiece surfaces by the EDM process can be a problem in aerospace applications. Advancements in machine tool and generator design, along with spark generation technology, can reduce or eliminate both recast and HAZ. This Webinar will address these two key issues related to the aerospace use of EDM, and how today's EDM technology can be used effectively on exotic aerospace materials.

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    Quote Originally Posted by KilrB View Post
    From the link to the Makino's own 1st webinar:
    They did not use the weasel word "virtually" , so I can agree with 100% false.
    They used eliminate: remove, get rid of, put an end to, do away with, end, stop, terminate, eradicate, destroy, annihilate, stamp out, wipe out, extinguish.


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