Since 1981 Rosenberg Ventilatoren GmbH (http://www.rosenberg-gmbh.com), located in Künzelsau-Gaisbach, has developed into an outstanding centre of the air movement and air handling industry by design and production of controllable external rotor motors. Rosenberg is a competitive medium sized company with around 1,400 employees worldwide and during the last 20 years, the Rosenberg Group has been complemented in Europe by several additional works in France, Italy, Hungary, Czech Republic and Germany.

With an annual production of about 120,000 fans, Rosenberg Ventilatoren GmbH currently exports 55% of the total company turnover and to keep the high quality of products, they aim to chase a continuous flow of information and good cooperation with their valued customers all the time. Furthermore, it is important to jointly achieve a continuous evolution of the quality of products.

The case study goes on to describe how they scan existing fan blades to generate CAD models.  And of course with XOR, the CAD models are editable because they have a full feature tree, with parent-child relationships (not just a bunch of imported surfaces):

As new project, they were looking for a solution provider who is able to measure a ventilator blade for qualified CAD modeling. The new project aims to create a precise CAD modeling for Highly-Effective Performance with lower noise and vibrations. It is always challenge for them to improve their products in terms of efficiency and noise and now they are quite keen to see new improvement with Rapidform XOR, the most comprehensive Scan-To-CAD application.

sigma3D (www.sigma3d.de), plays a role to serve the qualified CAD modeling using Rapidform XOR to Rosenberg Ventilatoren GmbH and Mr. Hubert Schwarz, Project Manager at Rosenberg is quite satisfied with the performance of Rapidform XOR. sigma3D uses a FARO laser scanarm for measuring, then imports it into Rapidform XOR to create a optimized polygon model in easy & quick way through “Mesh Buildup Wizard™”. This technology automatically processes the 3D scan data from multi-shot point clouds into a single qualified mesh. After that, to capture each geometry information interactively, Rapidform XOR is able to produce “Auto Segmentation” from the mesh model automatically based on feature region.

Of course, the real magic results come from what you do after you’ve gotten to a merged mesh.  The XOR technique of making CAD models for scan data is all about extracting design intent, then using real CAD tools (like extrude, revolve, loft, sweep, fillet, boolean and such) to build up a real CAD model that represents the scanned object.  This results in an “intelligent model”, meaning it’s feature-based and editable just like anything that can be designed in SolidWorks, Pro/E, NX, etc.  In the case of Rosenberg Ventilatoren’s fan blades, this means that they can improve upon an existing design and bring a new product to market in record time.

Generally, when you model a sheet metal body with finite thickness, you create one side and using offset command you can create the other side.

This modeling method is used to create a sheet metal body with thickness even when you have only its upper side surface. Then you can check the interference between inner side of the surface body and another part. However, if you have a surface body with some complex shape, it is not easy to create it using above mentioned method.

XOR helps you to easily convert a surface data to mesh in order to complete the inner shape from the converted mesh using offset operation. You can quickly create a surface body on the mesh using Auto Surfacing command and complete the whole shape connecting the inner and the outer surface body on the boundary of model.

Through this document, you will understand how to create a complex inner side of body from the existing design data using the Convert Body, Auto Surfacing commands.

Method

First of all, you need to prepare a mesh from the existing design data in order to apply the offset operation.
1. Go to Mesh mode and select Tools > Mesh Tools > Convert body in the menu. Click the Ok button.

The design data is converted to a mesh and the copied mesh data will be registered in the Model Tree as shown in the image below.

Now extract a curve along the boundary of upper body using Convert Entities command. Then extract a curve along the boundary of the converted mesh using Boundary command as well.

1. Go to the Mesh mode, select Tools > Mesh Tools > Offset in the menu

2. Select the Surface Method as offset method and input a thickness value in the Distance box

3. Choose offset direction using Flip button so that it is offset to the inside of the part

Note
You can choose offset direction by just clicking the (Flip) button. If you want to turn over the current direction to the opposite direction, click the Flip button and the copied mesh will be offset along the selected direction. Also if you click this button again, the offset direction will be reversed again.

4. Go to the 3D Mesh Sketch mode, or select Tools > 3D Sketch Entities > Boundary in the menu

5. Select the option Interactively-Split Curve Segments From Single Boundary and select an edge as Boundary. Then pick nodes to create partial boundary curves as shown in the image below

6. Go to the 3D Sketch mode, or select Tools > 3D Sketch Tools > Convert Entities in the menu

7. Extract a curve along the boundary of upper body using Convert Entities command as shown in the image below

8. Try to merge between the split splines using Merge command

Finally, connect the curves that are extracted from the upper side of body and the inner side of mesh using the Surface Loft command. You can also easily and quickly create an inner side of body from the mesh using Auto Surfacing command.

1. Try to execute the Surface Loft command. Click the Surface Loft button in the main toolbar

2. Select two sketch chains as Profiles and click the OK button

3. You can also create other lofting surfaces by the same way as shown in the image below

4. Try to apply Auto Surfacing command to the offset mesh. Click the Auto Surfacing button in the main toolbar

5. Select the mesh and set the value for No. Of Surfaces as shown in the image below

A surface body will be created on the offset mesh as shown in the image below

6. Try to execute the Sew command. Click the Sew button in the main toolbar

7. Select all surface bodies and click the next button

8. Click the OK button. The split boundaries of the surface bodies are sewed. Then you will get a solid model which has thickness as shown in the image below.

This technical tip will help you understand how to create a high quality fitting surface.

Step 1: Mesh Optimization

To get a high quality fitting surface, you will first need to prepare the mesh through some optimization processes. If the size of the poly-faces is regular and the resolution of the mesh is high enough, you will be able to fit a more ideal surface.

How to optimize a mesh to get a high quality fitting surface:

Note: XOR provides you with several methods to optimize a mesh from its current state, such as Healing Wizard, Fill Hole, Smooth, Enhance Shape, Optimize Mesh, etc.

If some abnormal faces and various defects exist in the mesh, you can easily find and clean them with the Healing Wizard command.
If some holes exist in the mesh, you can easily close them with the Fill Holes command.
You can also enhance the quality of the mesh using the Enhance Shape and Optimize Mesh commands.

1. Double-click the mesh, or click on the “Mesh” mode button in the Tool Palette, to enter Mesh Mode.

2. Click the “Healing Wizard” button or click Tools > Mesh Tools > Healing Wizard.

3. You can check which kinds of defects are in the mesh and how many there are, as shown in the image below.

4. Click the OK button

Note: The Healing Wizard automatically heals various defects in the mesh.

Folded Poly-Faces – If checked, folded poly-faces will be deleted.
Dangling Poly-Faces – If checked, you will remove any 2 or 3-sided open poly-faces.

Small Clusters – If checked, you can set a value for the Maximum Face Count In A Cluster; then all clusters (a group of connected poly-faces) that have less than the specified number of poly-faces will be removed.

Small Poly-Faces – If this is checked, you can input a value in the “Area Is Smaller Than” box, and poly-faces whose areas are smaller than this value will be removed.

Non-Manifold Poly-Faces – If checked, non-manifold faces and redundant poly-faces will be removed.
Crossing Poly-Faces – If checked, all the crossing faces will be removed. There are three methods: The Smooth method smoothly regenerates poly-faces around the crossing poly-faces. The Merge Poly-Vertices method merges poly-vertices around the crossing poly-faces. The Delete And Fill Hole method removes poly-faces around the crossing poly-faces and fills in the hole(s) there.

Small Tunnels – “Small tunnels” means that the poly-faces’ shape is constructed as a tunnel or handle. If Small Tunnels is checked, you can adjust the Poly-Face Count In Tunnel box. Then the tunnel faces whose number to the tunnel direction is shorter than this value, will be removed.

5. Click the “Defeature” button or click Tools > Mesh Tools > Defeature.

6. Select the Flat option as the “Method” and select a region to remove features and fill faces in that region, as shown in the image below.

7. Click the OK button.

Note: “Defeature” removes the selected poly-faces and fills in the space based on adjacent poly-face information.
If you want to re-form the feature after you generate whole surface body, you have to prepare a feature profile beforehand.
Another way to do this is, before Defeature operates, to copy the original feature into its own new mesh using Copy (Ctrl + C) and Paste (Ctrl + V). You will then be able to work with it later.

Note: You can fill faces in the missing area using “Fill Holes” or clicking Tools > Mesh Tools > Fill Holes.

8. Click the “Optimize Mesh” button, or click Tools > Mesh Tools > Optimize Mesh.

9. Select the “High Quality Mesh Conversion” option as the Method, and adjust the options as shown in the image below.

10. Click the OK button.

11. Check the result.

Step 2: Create Boundary Curves

Secondly, you can prepare boundary curves to create a fitting surface on the mesh. If the number of curve boundaries is 4 and the shape is a regular rectangular feature, you will get a better fitting surface.
Otherwise, a fitting surface will be twisted and have some self-intersection(s).

How to organize boundary curves to get a fitting surface:

Create 3D Mesh Sketch
• Create boundary curves which can keep the equilibrium of forces
• If the number of boundary curves is 4 and its shape is a regular rectangular feature, you will get abetter fitting surface, as shown in the image below.

• Even though you can keep that the number of boundary curves at 4, if its shape becomes suddenly narrow or twisted as shown in the image below, twisted and self-intersected faces could be created when the surface is generated.

Match Boundary Curves
• If possible, avoid “T-Junction” matching when you create curve networks
• If not, organize “T-Junction” matching so that the curve networks can keep the equilibrium of forces as shown in the image below.

• Other than the 4 sides of the curve boundary, others will create a trimmed fitting surface.
• If trimmed surfaces are neighbored with the same matching boundary, those will not be matched.
• Organize the curve network so that the surface matching conditions can be applied.

For Example:
Untrimmed Surface – Untrimmed Surface
Untrimmed Surface – Trimmed Surface – Trimmed Surface
Untrimmed Surface – T-junction matching – Untrimmed Surface

• If possible, setup the same number of control points in the each matching boundary of the surface patches to improve surface matching continuity.
• If possible, setup the boundary curves using appropriate control points to apply the fitting operation.

Create Curve Network
• If the shape is going sharp or dull, you can manage the number of curve boundaries according to the shape, as shown in the image below.

• If a fitting curve is not correctly put on the mesh, an accurate fitting surface cannot be created.
• In that case, increase the number of control points on the curve using the “rebuild” option

Step 3: Create a Boundary Fit Surface

Finally, you can create a fitting surface using the pre-defined boundary curves.
However, even if the curve networks are well organized on the mesh, the fit surface will be created a bit differently, according to the defined fitting options.

How to use options to get a high quality fitting surface:

Boundary Fit operation has been separated into 2 stages:
• In the first stage, you can set Mesh Curves, Curve Loops, and Loop options.
• In the second stage, you can define sharp edges to keep the sharpness at the boundary, as well as the number of control points in the surface to be created. This is shown in the image below.

1st Stage (Setup Curve Loops):
• Allow Hole (Boundary) – If this option is turned on, the surface will be created even though a hole exists inside the boundary of the curve, as shown in the image below.

• Allowable Convex Ratio – In the case that some feature(s) exist inside the loop, this option allows you to create a surface using a Convex Ratio.

2nd Stage (Adjust Fitting Options):
• Set Resolution – you can adjust the resolution of a surface patch via “Number of Control Points” or “Allowable Deviation.”
  • If possible, set the same number of control points along the U and V directions, as you can get a better surface body that way.
  • Using “Set Manually,” you can easily set the control points along the U and V directions of a surface patch, as shown in the image below.

• Set Sharp Edge – Use this option if a sharp area exists in a mesh, or if you need to keep the sharp feature on a surface body.
  A position matching operation will be applied to the boundary only.
  In this way, you can preserve the sharp edge in the surface body you’re creating and modify it whenever you want.

• Resample – If this option is turned on, the fitting area will be regularly simplified and a smoother surface will be generated.
  However, you can decide whether you turn the option on or not according to your particular application.
  If you want to generate a surface body as close as possible to the mesh (“as is”), even if the resulting shape would have positive or negative complex features like under-cut areas, turn off this option.

Create fit surfaces by drawing a patch network on the mesh:

As you can see below, there are some cases where the trimmed surfaces will produce a bad result. Specifically, the “Tangent Constraint On Boundary” option, which uses mesh normals to match continuity, sometimes gives a bad result.

(In General, you should avoid drawing patch boundary curves on the high curvature regions of a mesh.)

The following images are the result of a boundary fit rebuilt after optimizing the mesh (Optimize Mesh, then Enhance, thenSubdivide) and adjusting the curvature and size of the mesh.

You may see that the surface quality and continuity between patches are far better than before.

Therefore, the nearly class A quality of surfaces can be simply generated by mesh optimization (It takes only 1~2 min. in XOR)

It is especially indispensable when you match the continuity between patches using the “Tangent Constraint On Boundary” option.

(It’s better to optimize the triangles of meshes to be regular, even if meshes appear to be of good quality. In addition, making sufficiently dense meshes in proportion to the control points of the surface patches can help.)

To summarize briefly: 3G RE is the process of making a full CAD model from 3D scan data, using well-established solid and surface modeling techniques. It’s the way RE is done using Rapidform XOR. Second generation (2G) RE is the process of creating NURBS surface models that are fit onto scan data (specifically, optimized polygon meshes of scanned objects). First generaration RE is the process of tracing over 3D scan data to build splines that you then use to make lofts and sweeps.

Obviously we strongly believe the third generation approach is the best in most cases of mechanical reverse engineering. If what you’re scanning is completely freeform or organic, the 2G approach is usually the best. That’s why we offer Rapidform XOS.