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Flowdown Calculator

The Flowdown Calculator is an advanced engineering tool used to evaluate the radial stackup and manufacturing feasibility of your catheter design. It dynamically calculates the required dimensions of each layer to ensure proper clearances and tolerances during the build process.

Flowdown Visualizer​

The visualizer provides a dynamic, scaled cross-sectional representation of the catheter's layer stackup.

  • Exploded: Displays the catheter layers in their pre-reflow state, illustrating the necessary manufacturing clearances and gaps between layers prior to lamination.
  • Final: Displays the catheter in its final consolidated state, as it would appear after the heat shrinking and reflow process.

Design Grid​

The Design Grid allows for detailed inspection and modification of each layer's pre-reflow dimensions.

  • Layer Properties: Displays the Name, Type, and Material of each layer as defined in the Catheter Setup tab.
  • Dimensional Controls (ID, Wall, OD):
    • Linked (Auto) Mode: By default, layers are "linked" (indicated by the chainlink icon). In this mode, the software automatically calculates the ideal nominal dimensions to maintain the required manufacturing clearances and final reflowed dimensions.
    • Unlinked (Custom) Mode: Clicking the link icon disables the automatic calculation, allowing you to input custom dimensions (ID, Wall, or OD). Custom dimensions are intended to allow the user to round the input to the nearest available extrusion dimension for that layer. Any resulting changes will automatically cascade and update the layers external to the edited layer to maintain the proper spacing and a valid catheter geometry based on the custom value.
  • Tolerance (Tol): Enter the expected manufacturing tolerance for each layer to evaluate its impact on the cumulative tolerance stackup.

Layer Editing Constraints

To ensure physically realistic designs, certain layers have dimensional constraints when customized:

  • Braid, Coil, and Pullwire layers: Allow custom Inner Diameters (IDs) to be set, but their wall thicknesses are strictly fixed based on their defined wire/lumen dimensions.
  • Mandrel: Modeled as a solid core; the ID is locked.
  • Polymer, Liner, and Heat Shrink layers: Allow full customization of both ID and wall thickness.

Flowdown Metrics & Reporting​

At the bottom of the window, key summary metrics are displayed to evaluate the overall build.

  • Nominal Design OD: The ideal, auto-calculated outer diameter of the pre-reflowed catheter stackup. Note that this measurement intentionally excludes the outermost Heat Shrink layer, reflecting the dimensions immediately prior to lamination.
  • Custom Final OD: The expected outer diameter of the pre-reflowed stackup based on any custom dimensional overrides you have applied, displayed alongside the total cumulative tolerance stackup (±).
  • Min Shrink Ratio: Calculates the minimum required heat shrink recovery ratio to fully encapsulate the catheter, including a 15% margin to maintain required compression force. If this ratio exceeds 2.0, the value will highlight in red, indicating that the required recovery exceeds standard off-the-shelf capabilities and a highly specialized heat shrink may be necessary.
  • Revert to Nominal: Resets all unlinked layers back to their default auto-calculated nominal dimensions.
  • Export:
    • Export to Excel: Generates a comprehensive spreadsheet detailing the layer stackup, dimensions, tolerances, and gaps for procurement or engineering review.
    • Export to PDF: Generates a formatted, printable report of the complete flowdown configuration.