Ideas for making rounds

Discussion in 'Pro/Engineer & Creo Elements/Pro' started by dgeesaman, Feb 8, 2007.

  1. dgeesaman

    dgeesaman Guest

    I have lately made a few models where the rounds are driving me nuts.

    I'm modeling a cylindrical hub (axis = vertical) with smaller angled
    ears welded to it. See this pic: http://www.philamixers.com/pbt.asp,
    except that my ears are trapezoidal instead of rectangular, with the
    longer edge being at the outside.

    I'm to represent the welds with fillets (round features). To
    complicate the shape a little more, if you look at one of these ears
    it's trapezoidal, such that the wider end is away from the hub.

    Making rounds about the intersection of these features is tricky -
    since the edges of the ear feature are not rounded, the round feature
    doesn't turn the corners. Plus, the angle between the faces of the
    cylinder and ear continually change as you trace around their
    intersection, so the legs of the fillets are not the same length as
    the fillet turns the corner from one face to the next. I can
    sometimes make it work with transition sets or surface patching, but
    it's a huge time waster considering I just want smooth weld-like
    geometry for my Mechanica model.

    Any tips or advice are appreciated, whether it's tips for make the
    rounds work better, or maybe a better way to represent the welds
    altogether. I just want smooth, robust, good rounds for simulation.

    Dave
     
    dgeesaman, Feb 8, 2007
    #1
  2. dgeesaman

    Jeff Howard Guest

    I have lately made a few models where
    Dave,
    Can you post a sumpin' like it, native and / or neutral,
    somewhere (mcadcentral?).

    [I can read WF2 native, fwiw.]
     
    Jeff Howard, Feb 8, 2007
    #2
  3. dgeesaman

    David Janes Guest

    First, I thought the simulation stuff was generally done (Vince Adams,
    "Building Better Products Through FEA",
    http://www10.mcadcafe.com/aws/display_book.php?book_id=157) with the rounds
    turned off which was one of the reasons for advising they be done last.

    Second, I didn't see "realistic" in your list of criteria. I say this
    because no welder is going around sharp corners and leaving them sharp. So,
    if you say there's no radiuses on those corners, the automated MIG welder
    begs to differ. It will, whether you acknowledge it or not, round those
    corners. My recommendation, deferring to reality, would be to put variable
    rounds on those corners ~ zero at the top and full round at the bottom
    (problem is thinness of impeller section vs bead size). Then the round will
    go easily around the the entire welded intersection. Or approximate the same
    with a VSS or construct a curve on the impeller at the top of the bead, an
    end rounded curve on the shaft at the impeller/shaft intersection and some
    bead profile curves at the corners, then construct a boundary suface from
    these curves.

    David Janes
     
    David Janes, Feb 9, 2007
    #3
  4. dgeesaman

    Jeff Howard Guest

    Reading your reply was a smack on the back of the head I needed. I'd
    gotten lost trying to visualize the shape Dave was describing and
    never made it to "Mechanica model". If I were shell meshing something
    like that I might break the sharps and blend the root with
    'chamfer-ish' facet surfaces. Solid meshing and Mechanica are out of
    my league. Creating those root fillet (round feature) surfaces
    without radical boundary curvatures or singular / degenerate edges
    (either of which will drive the mesher nuts?) is not possible without
    first putting generous rounds on the vane / blade edges. Even then
    I'd create 'nice' boundary / trim curves and Boundary Blend or, maybe,
    VSS a conic arc between the hub and blade. I'll go back to my hole
    now, watch and see if I might learn from those that have something
    worthwhile to say. ;^)
     
    Jeff Howard, Feb 9, 2007
    #4
  5. dgeesaman

    dgeesaman Guest

    Hey wait I have that book. I haven't been thru it in a couple of
    years - I should skim it again.
    I have done this with some success - the failures relating to the
    variable radius rounds themselves, or not having enough space for
    them. I'm actually working on more complicated ear geometry with rib
    features, and the rounds tend to overlap/intersect a lot. Which is
    fine for welding, but hell for modeling.
    Just after posting this (of course) I did think of an elegant way to
    do this: I made a surface offset from the cylinder by the length of
    the weld leg, and did an intersect to make a curve. Then I offset the
    intersection curve of the ear and cylinder so that I traced the other
    leg. Then I boundary blended the curves.

    Dave
     
    dgeesaman, Feb 9, 2007
    #5
  6. I don't bother trying to fight with problematic rounds, as you say its a
    real time waster - just go straight to surfacing,

    Sean
     
    Sean Kerslake, Feb 12, 2007
    #6
  7. dgeesaman

    dgeesaman Guest

    While surfacing can make the geometry, I usually find a whole bunch of
    boundary blends bring their own misbehavior to the party.

    I guess I was looking for reassurance that rounds are some of the most
    time-intensive features in Pro/E. It seems I'm not alone.

    Dave
     
    dgeesaman, Feb 12, 2007
    #7
  8. I agree that resolving the issue with surfaces brings its own problems but I
    find these issues a little more transparent and the functionality more
    flexible to fine tune the surfaces and resolve them.

    Sean

    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Sean Kerslake
    Dept of Design & Tech
    Loughborough University
    LE11 3TU

    01509 228317
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     
    Sean Kerslake, Feb 13, 2007
    #8
  9. dgeesaman

    David Janes Guest

    The last element I thought (after going over this discussion) to add was the
    "accuracy factor". Accuracy comes up constantly as a factor in feature
    failures and other strange error messages. Setting absolute accuracy to the
    same value for the assembly and all its components alleviates many regen
    errors. The same can be said for curves and surfaces as well as import
    surface errors: many can be eliminated with adjusting accuracy or by
    switching from relative to absolute accuracy. I've eliminated many goem chks
    (including on imported models) simply by setting absolute accuracy to a
    correct value.

    David Janes
     
    David Janes, Feb 23, 2007
    #9
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