Rusting workpieces
Close
Login to Your Account
Results 1 to 11 of 11
  1. #1
    Join Date
    Jun 2017
    Country
    FINLAND
    Posts
    12
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    0

    Default Rusting workpieces

    We have problems with rusting workpieces.
    Material is case-hardened steel 18CrNiMo7-6.
    Workpieces are in water only one hour and there will come little bit rust points to ungrinded surfaces, grinded surfaces are ok. This workpiece is for production so antirust system have to be very easy.
    We are using 1,6% of Buchem BP 10 Inhibitor in deionized water.
    Machine is Sodick ALC600G 2017.


    I there any other ways to get workpieces without rust?
    Attached Thumbnails Attached Thumbnails 32bc8599-f041-4807-a2a5-e5e57982f903.jpg  

  2. #2
    Join Date
    Mar 2019
    Country
    UNITED KINGDOM
    Posts
    145
    Post Thanks / Like
    Likes (Given)
    2
    Likes (Received)
    23

    Default

    Wax spray, we use
    lusin protect g31 chem trend,
    Itís strong enough to stick when roughing on full power jet.

    But if your problem is from corrosion or pitting on surfaces created in that machining operation then the conductivity and water condition will need to be adjusted. But Iíll admit Iím not 100% on ideal conditions

  3. Likes PegroProX440, Jim7511 liked this post
  4. #3
    Join Date
    Jul 2007
    Country
    UNITED KINGDOM
    Posts
    4,761
    Post Thanks / Like
    Likes (Given)
    2514
    Likes (Received)
    2311

    Default

    If you can, check the coolant on the other machining operations. Can you use a detergent wash before the EDM operation to remove ionic contamination from the parts?

  5. #4
    Join Date
    Sep 2018
    Country
    UNITED STATES
    State/Province
    Pennsylvania
    Posts
    49
    Post Thanks / Like
    Likes (Given)
    26
    Likes (Received)
    11

    Default

    Quote Originally Posted by KK80 View Post
    We have problems with rusting workpieces.
    Material is case-hardened steel 18CrNiMo7-6.
    Workpieces are in water only one hour and there will come little bit rust points to ungrinded surfaces, grinded surfaces are ok. This workpiece is for production so antirust system have to be very easy.
    We are using 1,6% of Buchem BP 10 Inhibitor in deionized water.
    Machine is Sodick ALC600G 2017.


    I there any other ways to get workpieces without rust?
    What is your Resistivity level at? I know on my Sodick AQ537L I tend to see more water marks/rust when my level is low around 55,000. If I am concerned about getting rust or water marks I tend to just wipe my parts in a light coat of oil before and after machining. Careful putting it on to0 much, I've seen it cause issues with sensor touch when picking up zero.

  6. #5
    Join Date
    Oct 2018
    Country
    UNITED STATES
    State/Province
    Oregon
    Posts
    42
    Post Thanks / Like
    Likes (Given)
    5
    Likes (Received)
    11

    Default

    We had an incident a few months ago, resistivity dropped below 50k and we suddenly had rust on parts that never rusted before. Check your deionizing bottle, we had to replace with a new bottle to get resistivity back in line.

  7. #6
    Join Date
    Dec 2015
    Country
    UNITED STATES
    State/Province
    Ohio
    Posts
    79
    Post Thanks / Like
    Likes (Given)
    30
    Likes (Received)
    22

    Thumbs up

    Quote Originally Posted by Luke.kerbey View Post
    Wax spray, we use
    lusin protect g31 chem trend,
    Itís strong enough to stick when roughing on full power jet.

    But if your problem is from corrosion or pitting on surfaces created in that machining operation then the conductivity and water condition will need to be adjusted. But Iíll admit Iím not 100% on ideal conditions
    Spray wax all the way

  8. #7
    Join Date
    Jun 2002
    Country
    CANADA
    State/Province
    British Columbia
    Posts
    2,543
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    1980

    Default

    Hi KK80:
    I agree with all who have advised checking the resistivity of the water, and the recommendation to wash the parts before they go into the wire EDM to keep from contaminating the water with coolant.

    I've stopped being a fan of using oils or waxes to avoid rusting...the oil slick that appears on the surface of the water makes me queasy, and I want the cleanest surface possible to touch off to.
    I used to just spray on a light coat of WD40 based on the recommendation of a service tech but I don't do that anymore.

    I have come to feel this way because I very foolishly once agreed to cut some stator laminations that had been epoxied together.
    The decomposing epoxy poisoned the water and contaminated the whole dielectric system including all the hoses and the inside of the chiller.
    I couldn't control the water conductivity anymore and I would trash a new resin bottle in an hour.
    It took weeks to get it fixed and cost a bundle.

    That episode cured me forever of just popping my block into the worktank without cleaning it first and making sure it's very clean.
    I now pop them in the ultrasonic cleaner and rinse them in running water whenever possible before they go in the worktank.

    Also if this is a new problem, check that the anti electrolysis circuitry is working.
    An easy way to check is to test cut a bit of titanium.
    If it turns blue around the cut edges you need to call in the service techs to fix the machine.

    Cheers

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

  9. Likes Milland, nlancaster, sfriedberg liked this post
  10. #8
    Join Date
    Jun 2017
    Country
    FINLAND
    Posts
    12
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    0

    Default

    Hello Sirs,

    Thank you of your comments.
    Our rusting problem solved by increasing resistivity of water to 90 000.
    In Sodick ALC600G machine standard value of resistivity is 50 000.
    What is effect to WEDM process when increasing value from 50 000 - 90 000?

  11. #9
    Join Date
    Mar 2019
    Country
    UNITED KINGDOM
    Posts
    145
    Post Thanks / Like
    Likes (Given)
    2
    Likes (Received)
    23

    Default

    Changing resistivity/conductivity will change the spark gap so effect accuracy but this will only be noticeable above and below a certain limits, the charmilles machine at work uses conductivity and A fluctuation of about 20% from optimal didnít appear to have any effect on our work

  12. #10
    Join Date
    Oct 2018
    Country
    UNITED STATES
    State/Province
    Oregon
    Posts
    42
    Post Thanks / Like
    Likes (Given)
    5
    Likes (Received)
    11

    Default

    Sounds like you need to check the resistivity probe with a stand alone tester. If the probe is mis reading, raising the set resistivity will just get you back into the normal range, but the problem will probably return. Probes can get dirty and possibly fail.

  13. #11
    Join Date
    Jun 2002
    Country
    CANADA
    State/Province
    British Columbia
    Posts
    2,543
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    1980

    Default

    Hi All:
    This all makes sense...when you make the water less conductive (more resistive), you strip ions out of it by running it through the DI bottle...the same ions that can promote galvanic corrosion.
    So (simplistically) less ions, less opportunity for rusting.

    So far, so good, but there are a couple of things to consider that some of you have already touched on.

    First, why did you have to strip out more ions from your water than normal... or did you actually do that?
    Some have pointed out that conductivity probes and the circuits they send signals to can stop working or malfunction.
    A simple and crude test is to short across the legs of the probe with a screwdriver...resistivity should fall to zero (conductivity rises to "infinity").
    That will tell you if the probe is basically working but it won't tell you if it's working correctly...for that you need to do as nlancaster recommends in post #10.

    Second, you have to ask how the extra ions got in there in the first place and why they are localized to the un-ground areas of the part and only in spots.
    I immediately suspect something in the heat treat cycle.
    If at any time the parts are immersed in molten salt during HT you will get this.
    If a furnace is contaminated you will get this.

    So it would be prudent to investigate the conditions during HT...it may be you can permanently solve your problem with a simple change to the pre-wire handling protocol.

    Last to Luke Kerby's comments in post #9:
    He is quite correct, the water conductivity will affect the dimensions of the part and here's basically how it works:
    The wire senses the gap voltage between wire and workpiece to hold the proper distance between wire and workpiece before it discharges.
    Conductivity too high and the discharge happens too early so the kerf around the wire is bigger.
    Conductivity too low, and the wire has to get too close to the workpiece before a discharge is triggered...the kerf is too small, cut debris can't escape and the wire starts breaking

    You can compensate for these effects by changing the wire offset values in the program...but that's a risky band aid to apply because it depends on maintaining the wrong conductivity to keep the workpieces coming out the correct size so all your wire offsets will be wrong for all jobs you run on the machine until you change the conductivity back to normal.
    Also with a failing resin pack (conductivity increasing), the parts will start to vary in size until you notice something's wrong...you cannot hold size on critical features.
    If you're already near the upper conductivity limit for an effective spark gap, when the gap continues getting bigger and bigger, the cut speed gets slower and slower as the sparks become less and less effective at blasting away a bit of the workpiece. (of course that's true regardless what conductivity you started with but starting at the upper limit makes it show up sooner and worse as the resin degrades)

    So I believe it is worthwhile to check all this out if you want to be able to rely on the intrinsic accuracy of the wire cut process.
    If you don't have to care about microns for your application, you can get away with it as is.

    Cheers

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

  14. Likes nlancaster, jz814 liked this post

Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •