CAD Packages

5

CATIA Data Transfer

In this Section:

• CAT Direct Connect Overview 94
• Transfering Alias to CATIA 95
• Transfering CATIA to Alias 110
• CAT Direct Connect Reference 112
• Supported Geometry and Data Mapping 130

CAT Direct Connect Overview

Alias CAT Direct Connect is a stand-alone utility that allows the exchange of 3D model data between Alias and CATIA using the CATIA/Alias neutral format CAI.

Software Requirements

• Version 4.2.0 of CATIA

• ALIAS SurfaceStudio, AutoStudio, Designer, or Studio

Workflows

Before transferring geometry between Alias and CATIA, you should consider the purpose of the transfer in order to plan an appropriate workflow. Two common workflows are:

• Geometry (describing mechanical components) is transferred from CATIA to Alias for concept design surfacing, then transferred back to CATIA.

• An Alias model is transferred to CATIA, and both Alias and CATIA databases are developed independently. Later, the modified Alias model is transferred again to CATIA, replacing the Alias geometry from the first transfer. In this scenario, all work done in CATIA on the first Alias model transfer will affect the new, modified geometry.

There are many variations on these two examples. Whatever the transfer scenario, you should carefully plan the transfer process, to ensure that the appropriate data is written out and is useful.

Transfering Alias to CATIA

This section describes the process of transferring an Alias model to CATIA:

• Creating the CAI file in Alias on page 95

• Importing the CAI file into CATIA on page 97

• Using a Skin in CATIA on page 101

• Working in CATIA with Geometry Imported from Alias on page 103

• Summary on page 108

Creating the CAI file in Alias

Follow these steps to create a CAI file in Alias for transfer to CATIA:

1

Select the object you want to export, to make it active.

2

Select File > Export > Active As-

3

The Save Active Options window appears. Select CATIA from the File Format menu under Basic Save Options.

If you want the comment file to be included with the CAI file, select Include Comments from the Save Options window. If you select Edit File Comments, a shell will be displayed in which you can create or update the comment.

The CATIA file comment is restricted to 70 characters per line and a maximum of 500 lines. However, because Edit Comment uses a user-defined editor, you are not bound by these limits when creating/updating the comment.

The file comment that is exported from Alias will be altered to conform to these restrictions if necessary. That is, lines over 70 characters in length will be wrapped and the comment will be truncated at 500 lines.

4

Click Save and specify the CAI file name. The file is now ready to be read into CATIA.

Importing the CAI file into CATIA

The following sections describe how to import Alias CAI files into CATIA, view them and prepare them to be used in downstream CATIA operations.

To import a 3D Alias file into CATIA and create useful geometry for the CATIA engineer, you must follow two main steps:

1

The Alias-created CAI file is read into CATIA, where a .model file is generated on import.

2

The model's surface geometry is converted into a skin, depending on available data in the Alias CAI file, by joining surfaces and trimmed surfaces (or faces). The skin can then be used for a variety of downstream processes in CATIA.

Step 1: Creating an Alias CAI file

Create the Alias CAI file as described previously in the section Creating the CAI file in Alias on page 95.

Step 2: Creating a CATIA model file

Everything imported from the Alias CAI file will be translated to make up the CATIA .model file.

Follow these steps to import the Alias CAI file into CATIA and create a model file:

Starting CATIA

1

Start the CATIA session. When CATIA is running, the following window and menu areas are displayed:

This main Graphics window is the area where you work with the model and its associated menus.

2

From the MenuBar select File > Open.

3

The Open window appears. Select the CAI option from the File Format menu.

The Open CAI File window appears:

4

Define the path to the directory containing the CAI files. Select the Info button to define the Header Information as well as to display the CAI file's physical characteristics.

You can either replace the model with the geometry being imported, or add the model being imported to the geometry in the current work session:

• Create a New CATIA Model. You replace the model in the current work session with the geometry in the .cai file being imported.

• Import in Active Model. The .cai file being imported will be added to the model in the current work session.

For more on the extended log file, see Extended Log File on page 121.

In the Conversion Options area you can specify if you want to use the CAI file's tolerances or generate an Extended Log File.

5

When the necessary parameters have been defined, select OK to open the converted CAI file.

For more on the log file, see Short Log File on page 119.

A log file documenting the conversion of the Alias CAI file to the CATIA Model file file_name.log_AC is generated, and can be found in the catusr directory.

The following window appears if the CAI file was successfully converted:

Changing a file name

You may want to change the name of a model file once you have opened it:

1

From the menu bar select File > File Manager > Rename. The File Selection Box-Rename is displayed, and you can select the file to be renamed.

2

The Rename window will be displayed. Type the new name for the file and select OK .

Step 3: Creating a Skin

Before using the imported Alias geometry in many of the downstream CATIA operations, a skin must be generated from CATIA face entities. A CATIA model file that has been generated from an Alias CAI file is made up of surfaces, curves and faces (trimmed surfaces). If the Alias geometry has been exported successfully as a shell, then a CATIA skin is automatically created. If a CATIA skin has not been generated automatically, you must create the logical links between faces.

To join faces into a CATIA skin, do the following:

1

From the Function menu select LIMIT2. Select the Skin option. At the prompt, select one of the faces that are adjacent to, or within, the set of faces you intend to use to create the skin.

2

With the face highlighted, select the Auto Search button to identify and select all other faces that can be included with the originally selected face and are also eligible to be used for skin creation.

Eligibility for selection using AutoSearch depends on the adjacent face's positional continuity in relation to the original face. If the order of faces being picked is ambiguous, or if a logical link between the faces does not exist, you may need to manually select the faces.

3

When the desired configuration of faces is highlighted, select the Yes button from the bottom right corner of the screen. A skin will be created (defined by all of the selected faces) and added to the work session in the present workspace.

Once you have created a skin from the available geometry, you can then define the skin as either a closed solid (volume), closed surface model, or an open surface model.

• Closed Solid - Geometry that describes a solid volume. Additional solid features can be added to the solid part and manipulated parametrically.

• Closed Surface Model - Multiple surfaces or faces which have been used to create a skin. A closed surface model can be converted to a closed solid by creating a shell from the surface model.

• Open Surface Model - Surface geometry in which some or none of the surface entities have topology relationships to adjacent surfaces.

Using a Skin in CATIA

Once the skin has been created, it can then be used for a variety of downstream applications:

• performing Finite Element Analysis (FEA) functions

• performing moldflow analysis

• creating solid imaging (SLA) files

• creating 2D and 3D drawing sets

• generating CNC toolpaths

• passing the model back to Alias for further design iterations.

Creating a Solid

For some downstream operations (for example, FEA and the creation of 2D and 3D drawings) you may be required to create solid geometry from the CATIA skin. This can be done using one of two techniques:

• assembling a series of skins and creating a solid, or

• offsetting a skin to create a solid.

Assembling a Solid

The skin that has been created can be "capped" to define a solid. You can then use this solid in boolean operations.

Offsetting to Create a Solid

You can perform this operation using the CATIA offset functionality (FORMTOOL > OFFSET, or SOLID > OFFSET).

There is no guarantee that the skin will meet all CATIA prerequisites for an offset. Underlying adjacent faces (and by extension, the surfaces) must not self-intersect during the offset. As well, the continuity between faces must be of a certain standard in order for CATIA to successfully offset the eventual skin.

Creating a Mesh

For creation of tessellated Solid Imaging files (such as .stl) you can create a mesh from the skin. Then, using the CATIA solid imaging functionality, offset the mesh to create a solid mesh. You can then send this file to the solid imaging technology operator for creation of the physical part.

Creating a Toolpath

From the skin, you can generate a toolpath to send to a CNC milling machine. This is usually the way in which prototype tooling is analyzed.

Working in CATIA with Geometry Imported from Alias

The following sections describe how to verify imported geometry for use in downstream processes such as offsetting and the creation of toolpaths.

Selecting geometry

In order to make the desired geometry type pickable, you may need to make the interior isoparms of the geometry visible. By default, the face boundaries are not displayed. Even if they were displayed, they would be positionally coincidental with the curve entities. You must modify the display configuration so that the curves are out of the way, then display the face boundaries and interior isoparms:

1

Use the Show/NoShow functionality to display the curves on the NoShow layer.

In order to select a face by clicking on it, the face's interior isoparms and boundaries must be displayed.

2

Select Function > Graphic > Mod Spec. You are prompted to select the elements for this operation.

3

Since you intend to display the boundaries and interior isoparms of all the faces in the currently displayed geometry, type "fac in the Dialog zone. The Face Attributes window appears and the geometry changes color to indicate that it is selected:

4

Configure the Face Attributes window so that the boundaries and isoparms are visible and pickable. To accept the selection, press the YES key in the bottom right corner of the screen.

The face entity's boundaries and isoparms are now visible and pickable.

Confirming Geometry Status

To confirm that the surface geometry imported from Alias exhibits a degree of curvature that allows it to be milled or offset, use the following two evaluation tools:

• Tools > Analyze > Curvature

• Analysis > Numeric

Using the Curvature function

1

Select Tools > Analyze > Curvature.

2

In the Curvature Analysis window, set the curvature to Limited.

3

Set the Minimum radius to 1.0.

4

Select the faces of the model by typing *fac. By displaying the shaded mode, you can see where the geometry of the model has a curvature radius greater than the input value.

5

If there are no areas displayed in red, continue to modify the curvature value to find the threshold of curvature for the model that has been imported.

Using the Numeric function

1

Select Function > Analysis > Numeric.

2

Select the surface.

3

In order to display the AlphaNumeric window, select Alt and the + key from the numeric keypad on the keyboard.

4

With the left mouse button, select the surface. With the middle mouse button, select the point on the surface where the information is required.

The AlphaNumeric window displays the pertinent information for the selected geometry.

You can continue to select multiple points to query using the middle mouse button, or select another surface using the left mouse button.

Meeting geometry requirements

All surface edges must be topologically matched before the geometry meets the requirements of either a Closed Solid or a Closed Surface Model.

In general, edges fail to match because of a mismatch in the topology of two or more adjacent faces, or because the maximum distance between two adjacent edges is greater then the current accuracy defined in CATIA. There may be a gap existing between the adjacent surface edges, or the edges may overlap to the extent that they are unable to be stitched.

You can fix this problem by lowering tolerances in Alias and recreating the Alias geometry before re-importing the file into CATIA. Alternatively, the re-intersection of surface geometry can be done in CATIA. By accessing the surface entities and retrimming them, you will re-establish a logical link between the faces and their edges.

Replacing Alias geometry in CATIA

A common workflow using Alias and CATIA together is one where you replace existing Alias geometry in a CATIA model file with updated Alias geometry. This workflow allows you to continue working in Alias, modifying a model that has already been passed over to CATIA.

When you want to update the CATIA database with the completed changes, the surfaces that have been modified are passed to CATIA as a CAI file. You import the new Alias geometry and then redefine the skin that includes the faces in question using the Limit2 > Skin > Create/Modify tool.

A skin is made up of adjacent faces that meet parameters such as positional and tangent continuity. If you want to make changes to a face or surface in Alias and then include that modified surface in the CATIA model, you only have to redefine the skin to its members. That is, this time you leave out the original face and include the new Alias-modified face. This way Alias geometry can be used to modify CATIA models at any point throughout the product development cycle.

To replace Alias geometry in CATIA:

1

Open the CATIA model file and then import the modified Alias geometry.

2

Select Limit2 > Skin > Modify. When prompted, select the skin that includes the face(s) to be replaced.

3

When you have picked the new set of faces (including the newly modified geometry), select the YES button. The skin is now defined by the set of faces that include the modified geometry.

4

If you want to create multiple skins from one skin, the same process can be used (a combination of Modify and Create ).

Alias/CATIA Geometry

The Curve Fit Distance is the tolerance to which trim boundaries are rebuilt to (or approximated). The default positional tolerance in CATIA is .1 mm, and the Alias Curve Fit Distance setting should be set to 0.01mm.

This Curve Fit Distance setting should normally be accurate. If you find that it is not resulting in Studio geometry that can be successfully used in CATIA , then experiment with the Curve Fit Distance-it can set to as low as 0.005 mm. This setting will enhance the success of post transfer processes, such as skinning, that are to be carried out once the geometry is in CATIA.

Whether you are creating a model, verifying a model, or debugging a translation, there are a number of Alias tools you can use to check the quality of the geometry you have created. The most useful tool is the Min/max measurement tool in the Locators menu, found within the Tool Palette. Use this tool to check the maximum distance between any two surface boundaries. (See NURBS Modeling in Alias for more information.)

Creating Shells for export in Alias

Creating a `skin' and offsetting (or creating solid geometry from imported Alias models) is a common workflow when integrating Alias and CATIA. When exporting the model from Alias, you must ensure that the geometry is built to the correct tolerance and that it can also be stitched. The stitching process in Alias identifies gaps between surfaces so that you can repair the appropriate geometry before writing the file out to CATIA.

During stitching, the surfaces are twinned. This means that the surface boundaries may be split to accommodate adjacent surfaces, and periodic geometry is detached into multiple surfaces. For this reason, you should save the Alias wire file before stitching so that if further modifications are required to be made to the Studio model, the construction history will be intact. (Stitched geometry saved to an Alias wire file cannot be unstitched to its original state.)

A typical workflow follows:

1

Stitch the surfaces to perform a visual check to confirm there are no gaps.

2

Undo the stitch operation.

3

Save the Alias wire file.

4

Stitch the surfaces again.

5

Export the stitched object to a CAI file.

Summary

Use the following summarized list of modeling practices discussed in this section as a quick reference guide if problems arise.

Before you create the model

• Units should be set to mm.

In the Construction Settings window:

• The Rational geometry flags should be toggled OFF.

Tolerances should be set as follows:

• Curve Fit Distance =.01 mm (lower as necessary)

• Curve Fit Checkpoints = 10

• Max Gap Distance = .01 mm (this value should remain the same as Curve Fit Distance)

• Trim Curve Fit =.005 mm (lower as necessary)

While you create the model

• Use degree 5 curves and surfaces to achieve curvature continuity between surfaces and successful data transfer.

• Surfaces should be overbuilt and trimmed back before export.

• Fillets and other detail geometry should be deleted from the Alias model before export. Fillets and detail geometry should be built in CATIA to improve the success of the transfer and give you parametric control of the fillet and detail geometry while using CATIA.

• Models should be transferred periodically from Alias to CATIA during construction to manage the quality of the model being created.

• The Alias model must be successfully stitched before export, but you should also periodically stitch the geometry to ensure that the model meets all tolerance requirements.

• Avoid using Attach and Join curve since these functions create multiknots in Alias geometry that are not supported by CATIA.

• Avoid using Skin and Patch functions between trimmed surface boundaries, since excessive amounts of data are created in the resulting surface. If Skin and Patch are used between trim boundaries, the resulting surfaces should be checked for multiknots before export.

• Use surface building tools such as Square and Birail to ensure and control curvature continuity between surfaces.

Transfering CATIA to Alias

This section describes the process of creating a CAI file in CATIA.

Creating the CAI file in CATIA

Follow these steps to create a CAI file in CATIA for transfer to Alias:

1

Select File/ Save As and under the File Format menu select CAI.

2

Specify the file name and select OK. The Save As CAI File window appears.

Under Conversion Options you can choose to include the CATIA Model Comment with the CAI file by making the appropriate selection from the File Format pull-down.

Also available is the ability to exclude geometry elements on the NO SHOW layer and the ability to write out an extended log file with the CAI file (see Extended Log File page 122 in the Reference section of this manual).

New in this release of the CAI functionality is the ability to filter the layers of the worksession. This will enable the user to simulate doing iterative updates by exporting only the layers that have changed geometry on them.

3

Select OK.

At this point the CAI file is created and a window appears with the status of the created file. If the CAI file was created successfully, it can then be read into Alias. If the CAI file was not created successfully, check the log file for more details