3. Groove based workpiece data and geometry#


3.1. Overview#

This tutorial covers:

Working with workpiece related data that can be described by a 2 dimensional groove and a seam length


  • Opening and navigating through WelDX files (tutorial)

# download the example file for this tutorial

from util import download_tutorial_input_file


3.2. Plotting the specimen’s groove#

An important piece that will be part of most WelDX files is the specimen data. The complexity of a specimen can range from a single metal plate to complex 3 dimensional multi-part structures. In this tutorial, we will discuss specimen geometries based on a 2-dimensional cross-section that is extruded into 3d space.

First we open the example file and examine the workpiece information.

from weldx import WeldxFile

wxfile = WeldxFile("single_pass_weld.wx")
/home/docs/checkouts/readthedocs.org/user_builds/weldx/conda/latest/lib/python3.9/site-packages/asdf/asdf.py:340: AsdfWarning: File 'file:///home/docs/checkouts/readthedocs.org/user_builds/weldx/checkouts/latest/doc/src/tutorials/single_pass_weld.wx' was created with extension URI 'asdf://weldx.bam.de/weldx/extensions/weldx-0.1.1' (from package weldx==0.6.0), which is not currently installed
  warnings.warn(msg, AsdfWarning)
root (dict)
├─base_metal (dict)
│ ├─common_name (str)
│ └─standard (str)
└─geometry (dict)
  ├─groove_shape (VGroove)
  └─seam_length (Quantity)

The workpiece data of this particular file consists of two parts:

  • base_metal

  • geometry

The base_metal field contains information about the composition of the specimens material, which is not relevant for this tutorial. We are only interested in the geometry section that is further divided into:

  • groove_shape

  • seam_length

groove_shape describes the 2 dimensional cross-section of the specimen. We can already see, that it is of type VGroove. This object is based on the V-Groove described by ISO 9692-1. The norm specifies the shape of the groove by different shape parameters. We could now inspect the different parameter values and look up what meaning they have. However, this would be rather tedious. A much simpler way is to use the plot method of the groove object:

groove = wxfile["workpiece"]["geometry"]["groove_shape"]

Apart from the visual representation, the plot also contains all relevant information like the groove’s area and the ISO 9692-1 parameters.

3.3. Other cross-sections#

Not all specimens might have a cross-section that is described by a norm, or the norm it uses might simply be not considered in the WelDX API. For such cases, WelDX provides a more generalized class called Profile. It allows us to define arbitrary cross-sections based on simple geometric elements such as lines and arcs. So be aware, that you might get a Profile instead one of the available groove types out of a WelDX file. In fact, all groove types are based on the Profile class, and we can convert them with the to_profile method:

profile = groove.to_profile()

We can plot the content of a Profile the same way as we did before with the groove:


The only difference here is that we don’t get the additional, norm-related information.

3.4. 3d plot (matplotlib)#

We can also create a nice 3d plot from the groove and the seam length stored in the WelDX file. All we need for this is the Geometry class of WelDX. It can be created from a groove or profile and a length:

from weldx import Geometry, LinearHorizontalTraceSegment, Trace

t = Trace(LinearHorizontalTraceSegment(wxfile["workpiece"]["geometry"]["seam_length"]))
geometry = Geometry(groove, t)

Now all that remains, you might have guessed it, is to call the plot method:

HINT: Uncomment the code in the next cell to enable interactive plots in jupyter notebooks

# %matplotlib widget
<Axes3D: >

By default, the plot method shows us the triangulatad data. But you can also choose to only plot the control points. This can be achieved by setting the show_wireframe parameter to False:

<Axes3D: >

The density of the triangle mesh or the point cloud can be controlled py the parameters profile_raster_width and trace_raster_width. The first one sets the point density of the individual profiles, while the value of the second one influences, how many profiles are actually drawn. Both parameters need to be specified as pint.Quantity. You can simply import Q_ from weldx to use quantities or write them as unit string. Both methods are depicted in the code section below:

from weldx import Q_

    profile_raster_width=Q_(0.25, "mm"), trace_raster_width="17cm", show_wireframe=False
<Axes3D: >

As you can see, we now got only 3 densely rendered profiles. Try some other values to figure out which setting suits you most.

The last command also demonstrates two different ways to provide a Quantity to function that expects. We can either construct a quantity from a value and a unit like Q_(0.25, "mm") or we can combine value and unit in a string as 17cm. The second approach does not require us to import Q_ but it is limited to scalar values and only works for function parameters.

Another noteworthy thing we did in the last command is using length units of different magnitude (mm and cm). This is totally fine since weldx can handle all necessary conversions internally by utilizing the powerful Python package pint

3.5. 3d plot (k3d)#

In the previous section we learned how to generate simple 3d-plots from a groove and a seam length using the plot method. By default, plot relies on matplotlib as rendering backend. We have already mentioned before that this is not ideal for 3d renderings. Therefore, the weldx package offers an alternative for jupyter notebook users. You can select the k3d package as rendering backend as follows:


Now we got a nice 3d rendering of the geometry with a closed surface that we shift and turn as we like. However, because k3d uses equal axis scaling, we notice that the specimen appears to be rather slim. The reason for this is that the provided groove types only specify the shape of the groove and not the actual specimen width. But we can provide one during creation of the geometry using the width parameter. Note that this only works with groove types and not with a plain Profile.

geometry_2 = Geometry(groove, t, width="20cm")

Now lets plot the geometry again:

geometry_2.plot(profile_raster_width="5mm", trace_raster_width="16cm", backend="k3d")

3.6. Export 3d geometry into a CAD file#

The Geometry class also features a to_file method. It allows you to export the 3d data to different file formats like .ply or .stl. Using this function, you can inspect the geometry in a CAD program or model viewer of your choice:

    "weldx_geometry.stl", profile_raster_width="5mm", trace_raster_width="50mm"

The parameters profile_raster_width and trace_raster_width do have the exact same effect as in the plot method described before.

3.7. Conclusion#

In this tutorial we have learned that WelDX can store geometrical data in form of a 2d-cross section and an extrusion length. The 2d cross-section can either be of a specialized groove type or a more general Profile. Both can be visualized using the plot function and turned into an actual 3d geometry using the Geometry class. The Geometry class itself can also be rendered in a 3d plot and exported to a CAD compatible file format.

3.8. Further Readings#