Creating a Producibility for Braiding

You can create a producibility for braiding.

This task shows you how to:

Start the Producibility

You can enter the basic parameters for the braiding simulation.

The centerline defines the path of the guide along the mandrel. A temporary centerline is computed to accelerate calculations, avoiding some recalculations. To avoid failures resulting from slanted ends of the mandrel or sudden jumps in the mandrel surface, points are added between existing points until a smooth line is created without changing the shape, within tolerance. The automatic extension of the centerline goes far enough beyond the end of the mandrel to allow the tows to get to the end of the mandrel and achieve the target angle.

The simulation runs along the x-axis of the rosette referenced by the ply. It can be reversed in direction as braiding machines often make multiple passes to build up the material thickness.

Starting Length and Finishing Length allow the user to modify the begin and end of the guide compared with the ply boundaries. Positive values create an extension.

The Guide Diameter must be sufficiently large to clear the ply surface.

The Carrier Rotation Speed is fixed for a typical braiding machine, while the angle of the braided fibers depends on the Mandrel Speed. Usually, the mandrel has varying cross sections while the braiding angle is kept approximately constant, so that a varying mandrel speed is usually required (See Edit Mandrel Speed).

  1. From the Producibility, Flattening and Splicing section of the action bar, click Producibility for Braiding and select a ply.
    Composites Braiding verifies that the ply is tubular and has one start and one end contour.
  2. Select a Propagation Type.

    By default, Braiding (Geometrical) is proposed.

  3. Still in the Home tab, select the Braid Path that is, the travel path of the braiding head.

    It is usually the centerline of the components.

    • It must be a single curve.
    • It must cover the entire surface, and even more to define a starting and finishing length.

    1. Either select an existing braid path.
      Its name is displayed in the dialog box.
    2. Or click Generate.
    • The braid path is created as Centerline under a body named after the ply.
    • The curve representing the braid path is smoothed to avoid sharp bumps that would reduce the quality of the resulting braid.
    • The name of the braid path is displayed in the dialog box.
    • The default values of the Machining Parameters are updated.
  4. Specify an orientation curve that allows the rotation fo the braiding tool relatively to the component.

    Selecting an orientation curve adds a head angle in the speed table. If you do not specify an orientation curve, the Z-Axis is taken as the starting position of the mandrel.

  5. Optional: Select the Reverse direction check box.
  6. Enter the values of the Machining Parameters.
    1. Starting Length

      Distance before the start of the ply, where the simulation starts. Its default value is 50 mm.

    2. Finishing Length

      Distance after the end of the ply, where the simulation ends. Its default value is 50 mm.

    3. Guide Diameter

      Internal diameter of the guide. Its default value is 1.5 times the Maximum Diameter. However, try to follow the practice of manufacturing and use a guide ring that is a close fit to the component. Using an overly large ring can cause convergence issues with the solution on parts with curvature.

    4. Carrier Rotation Speed
    5. Mandrel Speed, either as a fixed value, or as variable values in the Edit Mandrel Speed dialog box.
    6. Select the Show Path check box to display the braid head path as a pair of helices, and verify the consistency of the guide diameter and speed values.

      Anti-clockwise and clockwise tows are displayed in different colors.

  7. Click ... to enter variable mandrel speeds. In the Edit Mandrel Speed dialog box, enter a Target Angle and a Segment Spacing.

    • Editing the mandrel speed splits the braid axially into multiple segments, with a constant speed over each segment.
    • You can edit the position between each segment, defining the theoretical contact position on the surface.
    • By default, the Target Angle is the angle of the ply, usually 45 deg.
    • Based on a calculation of the braiding simulation that includes the effect of the lead of the carrier over the contact point, a nominal speed is calculated analytically. After a simulation is run, the average angle at each position is calculated and the difference to the Target Angle stored as an Angle Correction.
    • Optimize Speed recomputes the speed by adding the Angle Correction to the Target Angle. Using this "reverse engineering" process, you can determine an optimized speed profile to achieve an angle profile.

    1. Click Create to create the variable speeds.
      They are displayed in the work area and in the dialog box.

    2. Click Import to import them from an xml or a csv file.
    3. Click Clear to erase existing value.
    4. Repeat as required.
    5. Right-click anywhere in the table to add or delete rows.

    A verification informs of possible problems and proposes actions.

Specify Material Parameters

You can specify material parameters.

The complete braiding material consists of braid tows wound in a clockwise and a counterclockwise directions around the mandrel, and optional axial tows.

By default, the braid tow material is the material referenced by the ply, with the original width and thickness appended to the material. The material parameters of tow width and thickness can be overridden to investigate the sensitivity of results to material parameters. The number of braiding tows, typically between 18 and 36, is half the number of carriers. If the Axial Tow Ratio is 1, the number of axial tows is equal to the number of clockwise tows and to the number of anti-clockwise tows.

  1. Go to the Material tab to update material parameters.

    1. Braid Tow Material: Taken from the materials defined in the Composites Parameters.
    2. Num Braiding Tows: Number of braiding tows in each direction, defined by the braiding computer, and equal to half the carriers of the computer.

      By default, Num Braiding Tows is 18.

    3. Braiding Tow Width: Nominal cured width at the expected fiber volume fraction.

      By default, it is the width of the selected material, but it is editable.

    4. Braiding Tow Thickness: Nominal cured thickness at the expected fiber volume fraction.

      By default, it is the thickness of the selected material, but it is editable.

    5. Axial Tow Ratio: Ratio of axial tows/braid tows.

      Possible values are:

      • 1 for tri-axial braid
      • 0 for bi-axial braid (Axial Tow Material, Axial Tow Width, Axial Tow Thickness are disabled).

    6. Axial Tow Material: Taken from the materials defined in the Composites Parameters.
    7. Axial Tow Width: Nominal cured width at the expected fiber volume fraction.

      By default, it is the width of the selected material, but it is editable.

    8. Axial Tow Thickness: Nominal cured thickness at the expected fiber volume fraction.

      By default, it is the thickness of the selected material, but it is editable.

    9. Fiber Volume Fraction: Fiber volume fraction to use to compute the thickness.
  2. Click Estimate Dimensions.
    • Thickness information for cross-sections along the mandrel is computed (minimum, maximum and mean values). The computation is based on the target braid angle, tow dimension, number of tows and local perimeter of the mandrel.
    • The range of perimeters is displayed, for an early indication of the suitability of the design for use as a mandrel in braiding.

Update the Thickness

You can update the thickness. This method uses the thickness defined for the material, not the effective one.

  1. Select the With thickness update check box to activate it.
  2. Select the type of computation.

    • Constant Thickness
    • Core Sampling
    • User or Automatic Constant Offset

  3. Select the elements to process, Full Stacking or Ply group only.

Fine-Tune the Simulation

You can fine-tune the simulation using the Advanced Parameters

The Axial Step is used to define the maximum length of steps when exporting the piecewise linear mandrel path curve.

The Tessellation Sag and Step control the tessellation on which the simulation is run. The Sag represents the maximum distance from the surface to an element, while the Step limits the maximum size of an element.

Fiber Interaction invokes algorithms to account for the interaction between fibers in an empirical way, stabilizing the simulation.

The Centerline Orientation options force the guide to follow the centerline, or to keep a constant alignment with the tangent at the midpoint.

In the Advanced Parameters tab, enter the required values:
  1. Axial Step: Spacing between guide curve data points when exporting the braid path, given as a percentage.
  2. Tessellation Sag: Distance between the mesh and the surface used to generate the tessellation used in the simulation and exported in the layup file.
  3. Tessellation Step: Maximum allowed length of an element used to generate the tessellation used in the simulation and exported in the layup file. Setting a smaller value gives a better approximation to the component shape, at the expense of slower simulation.
  4. Select the Fiber interactions check box to verify the interactions between fibers at each crossing point, and reposition the fiber. However, it is more time consuming. Using this means that where fibers cross over other fibers, they are pulled toward the surface.
  5. Select the Perturb Helix check box to compute perturbation effects.

    The braiding simulation assumes the fiber between the guide ring and the mandrel is straight. However, the tow does not follow a straight line from guide ring to mandrel, but a curved (segmented) path due to the contact with the fibers going in the opposite direction. With a cylindrical mandrel, this curvature is the same at all points around the mandrel. With non- cylindrical mandrels the curvature varies, related in some way to the distance between the mandrel and the guide ring.

    A quick solution to the problem is to calculate the amount by which the tow angles need to be adjusted to account for the varying frictional affects when the mandrel is not cylindrical based on the variation in number of fibers crossed and use this to correct the fiber angles. A scaling factor is added to tune the magnitude of the effect as it depends on surface finish of the fibers, which is not accounted for in the calculations.

    If the check box is not selected or if the value is 0, perturbation effects are not calculated. A value of 1 uses the values as calculated.

  6. Select the Centerline orientation.

    • Follow braid path tangent (default option).
    • Follow braid path midpoint. With this option, the mandrel is translated without being rotated. To be used when there are sharp direction changes in the component, causing the tow threads to overlap.

Manage the Results

You can take export results to files that will help programming the robots supporting the mandrel.

Note: Results are updated dynamically when input variables are modified.

  1. From the list, select the Result to verify.

    • Axial Deviation
    • Clockwise Deviation
    • Anticlockwise Deviation
    • Clockwise Angle
    • Anticlockwise Angle
    • Coverage
    • Separation
    • Thickness
    • Concavity
    • Pertub Ratio allows to adjust the scaling factor to get the required effect on large aspect ratio mandrels.
    • Perimeter (Requires Ruled surface Display)
    • No Result

  2. Define the Warning and Limit values that define the visualization transitions between red, yellow, and blue.
  3. Select the elements where the results are displayed (multiselection is allowed).

    • Clockwise tow
    • Anticlockwise tow
    • Axial tow
    • Surface
    • Labels
    • Ruled surface

  4. Select an additional action.

    For more information on export, see Preparing for Import/Export of Files.

    • Producibility Inspection: In the dialog box that appears, braided fiber results are displayed. They can be considered as core samples for producibility results. For each point, you can retrieve the material, total thickness, expected and actual direction and the delta between them, as well as the local rosette. The results can be exported.
    • Export guide path: The data describing the guide path is written to an XML file. This file aims at programming the robots supporting the mandrel.
    • Export to Layup that writes out the standard layup file that can be used to transfer Composites definitions to other packages.
    • Export results as a .csv file for locations along the guide path. The values are the average for a ring of points at each location along the guide path.
    • Inspect Angles exports the variation in angle around the perimeter at a chosen location on the mandrel to allow comparison of simulation with experimental results.
      • Select a point. It is projected onto the closest point on the centerline.

        A plane normal to the centerline is created at this point.

        A line is created at the intersection of the plane with the mandrel surface.

        100 points are created on this line.

      • Or a line. 100 equally spaced points are created on this line, then projected on the mandrel surface. A set of 100 closest points is created on the surface.
      • Enter the storage path to export the result .csv file. It looks like this.
        Note: Point gives the position of 100 evenly spaced points around the perimeter.
        Coordinate Point Ratio CW Ratio ACW Clock-wise Anti-Clock-wise Perturbed Clock-wise Perturbed Anti-Clock-wise
        (376.843 19.910 -13.811) 1 0.779 0.779 -48.002 45.82 0 0
        (376.843 19.518 -15.228) 2 0.853 0.853 -46.544 45.975 0 0
        (376.843 18.864 -16.544) 3 0.855 0.855 -45.38 46.107 0 0

  5. Enter a name for the geometrical set, and press Keep all visible fibers to do so.