Robot precision

    Hello,

    I recently started machining a section out of a part for tensile tests.

    I cut two dogbone shaped pieces and they need to be as accurate as possible obviously. I cut 2 pieces out of the same part, 1 is a vertical section and 1 is a diagonal section.

    When I cut the vertical section it comes out with a great finish, it measures at exactly 8mm which is what we need, but the diagonal piece is different. The edge finish is wavy and measures 7.9mm at one edge and 7.65mm at the other side.

    Is there something you guys can think of that would be causing I’m the diagonal piece to cut so much worse than the vertical? (Left is diagonal section)

    The problem is your using a Robot instead of a CNC :biggrins: .



    I would guess 1 is worse due to how the joints are loaded.


    Make sure your fixture and clamping is as rigid as possible. Make sure your cutter is short and stout. Use a good quality bit. Keep the robot as tight to the fixture as possible.


    What are you using for a cutter, feeds, and speeds?

    Haha, yeah I know this is very not ideal. I'm working with a lot of spare parts trying to do the best I can. :winking_face_with_tongue:
    I got a 1/4" carbide 4 flute bit (extends about 3/4" past collar), 25,000rpm air spindle (self regulating so i cant adjust its RPM), moving at 8mm/s. The fixture is about 7ft away from the robot so not max reach but not very close.


    I'm about to get a 2 flute 1/4" carbide bit though.

    Is this a single pass or multiple? Are you conventional milling or climb? Conventional is recommended if you lack rigidity.

    Quote from Beek

    Is this a single pass or multiple? Are you conventional milling or climb? Conventional is recommended if you lack rigidity.

    It's a 3mm thickness part, doing multiple pass of .6mm each. After getting all the way through I do a final clean up cut that takes .4mm off of each side. And doing conventional milling

    Interesting enough I just milled the mirror image part and both the vertical and the angle piece came out really clean.

    The 3rd one is the bumpy one, you may be able to see in image, all others are a clean cut edge.


    HawkME, If I have an opportunity to move the fixture I will, and definitely plan to get the 2 flute bit.

    There's a lot of possible factors here. The simple fact is, robots aren't made to withstand external forces while moving -- they don't have the rigidity of CNC machines. And with a robot's more complex kinematics, a milling path that works perfectly at one position in the robot's work envelope may have serious issues if that program is duplicated only 6 inches away. Robot arms also have "sweet spots" where all the axes line up in just the right (wrong?) way, or multiple axes have to reverse direction at the same time due to a linear motion.


    The first thing I would try is add a spring pass -- basically, run the final path twice, with no modifications. This gets used a lot even in CNC machines to really nail finish and tolerance.

    Is there any way to slow your spindle down to get your chip load up some? If you do purchase a 2 flute, make sure it is optimized for aluminium cutting.

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