Taking the Next STEP in NX

This article reviews the processes, options, and potential issues involving translations into and out of NX12 via the STEP format.

Overview

NX can read and write many different CAD data formats.  The methods for importing and exporting data, examining the quality of imported data, and repairing imported data are all fairly consistent but there are some differences between some of the specific CAD-specific procedures.

Translations can be run either from within NX (internal translators) or from outside of NX in a separate interface (external translators). These are generally run from a Windows (or other OS) command prompt.

When it comes to STEP translations, the experience I have with them is that they are usually effective, clean translations but the old saying, “Garbage in, garbage out” always applies. STEP came along a long time after the IGES format and was designed to handle more of today’s CAD data than IGES, which is probably 40-50 years old and was originally written to handle text, curves, and surfaces (sheet bodies) but not solids. And, of course, there are very few translation routines that can capture feature and parameter data. However, when using the Siemens Content Migration Manager® (CMM) products for a specific CAD program such as Ideas, Catia, and AutoCAD, those processes do have the capability to preserve not only feature definition but interpart associativity as well.

STEP Formats

Currently, there are 3 STEP formats available in NX12, STEP 203, STEP214, and STEP242.

• STEP 203 - Standard for Exchange of Product Model Data – better for model geometry (.stp and .step)
• STEP 214 - Standard for Exchange of Product Model Data – intended to be stored in pdm systems such as Teamcenter but will translate geometry equally as well as 203, better suited for CAM & related attribute data
• STEP 242 – will translate geometry as well as 203 but uncompresses from .stpx, .stpz, and .stpxz formats

Opening STEP Data Directly into NX 12

STEP files can be opened directly in NX12 just using the File→Open command and changing the “Files of type” filter:

• Select File→Import→STEP203, STEP214, or STEP242.
• Choose OK.

The translation is executed first and then the resulting .prt file is opened in NX. Note in the example below that the solid body, whether feature-based or not, is now a “Body” feature in NX, comprised of sewn surfaces.

If desired, the surfaces can be edited with Synchronous Modeling technology or just unsewn into individual surfaces:

This might be done, for instance, to remove a certain feature (group or region of faces) from the part and replace it with new, more intricate surface geometry or specific surface shapes copied from other portions of the model or from other parts.

Importing STEP Data Directly into NX

Regardless of which STEP protocol was used to create the STEP file, NX expects a file extension of .stp, .step, or the compressed formats .stpx, .stpz, and .stpxz.  It may be necessary to rename the file before NX will recognize it as a STEP file.

• Choose File→Import→STEP203, STEP214, or STEP242.

The import dialog appears.

• Click the Browse button and select the STEP file to import.
• Click OK to return to the import dialog.
• Set the options as desired for which object types are to be imported, which settings file to use, and what corrective operations are to be performed on the geometry before importing.

• Click OK to execute the translation.

NX begins the translation internally and an import status window displays the progress:

The objects are now translated into the equivalent NX objects, as defined in the settings in the import dialog as well as the settings file used for translation. In some cases, the translation settings files can be edited for specific results.

Exporting Out of NX 12

Taking a sample part containing a feature-based, parametric solid, Datum Planes, and some Sketches, the exported result can vary depending on the settings in the export dialog but there will rarely be any differences in shape of the geometry unless the B-spline Tolerance settings are modified.

STEP, based on ISO standard 10303, is becoming the preferred method for data exchange because it can handle solid models and non-geometric attribute information.  There are dozens of levels of STEP data exchange, called application protocols, targeted at data exchange for specific applications such as mechanical design, electronic design, systems engineering, and process planning.

• Select File→Export→STEP. A defaults file is read that will establish the initial settings for the translation.
• By default, the STEP file will have the same name as the original part file and be placed in a default directory. To change the name and directory, click the Browse button.  Navigate to a desired directory and enter a new part name.

• Click the Data to Export tab. By default, solids on any layer may be selected to translate. To translate curves, surface geometry, etc. check the appropriate entries in the list.

• In the Export menu drop-down, choose the Selected Objects option to select specific objects to be translated.
• To include color and layer attributes in the translation, click the Advanced tab. Check the Colors and Layers option.

• Click OK to begin the translation.

If you have modifed the part since opening it and begin the export process, NX12 warns the user of the modification and offers options in a popup alert:

• Choose Yes or Continue, as desired.

Parts with PMI

PMI (Product and Manufacturing Information) is a somewhat recent development in CAD, relative to the history of CAD, intended to move to a non-dependency on drawings and documentation. In NX12, the PMI application provides all the tools necessary to include this information in 3D space as view dependent objects and includes not only associativity to the model but inter-feature intelligence.

What we find in supporting NX STEP translations is that STEP itself is fully capable of translating and retaining the PMI data but that the downstream applications for which the STEP translation is being executed may not be able to handle the PMI definitions. It is important to update to the latest versions of those applications to enable the best capability.

Summary

It is important to understand that translating in general may not actually be necessary in all scenarios. Users should always communicate with those they are exchanging data with to understand the specific purpose for the data exchange and whether or not there may be more suitable or simpler solutions.

Just because Grandma always cut the ends off the beef roast before cooking it doesn’t mean you have to, too. Grandma only had an old, small roasting pan and the beef roast never fit!