Demonstration 5
Creating an Assembly; Boolean Operations
Introduction
This demonstration shows some of the functions available in the Assembly module, including positioning of part and model instances and using Boolean operations.
Part 1: Creating an Assembly
The first part of the demonstration focuses on assembling the cart shown in Figure D5–1.
Figure D5–1. Cart assembly
1. Open the model database file Demos/cart.cae in Abaqus/CAE. Examine the parts in the model using the Model Tree.
2. Copy Model-1 to new models named sub1 and sub2. These will be used to create subassemblies of the different components.
Wheel/axle subassembly:
1. Expand the container for the sub1 model.
2. Double-click Instances in the Model Tree (underneath the Assembly container), and instance the axle of the cart.
3. Instance the part bg_wheel, and create a coaxial constraint between the ID of the wheel and OD of the axle. Apply a face-to-face constraint between the wheel face and an axle face with an offset of 2.
4. Similarly, position a second instance of the part bg_wheel. The final subassembly is shown in Figure D5–2.
Figure D5–2. Wheel/axle subassembly
Body/mount subassembly:
1. Expand the container for the sub2 model.
2. Double-click Instances in the Model Tree (underneath the Assembly container), and instance the body of the cart.
3. Create a “dependent” datum point shown in Figure D5–3 using the Create Datum Point: Enter Parameter tool. The location of the point is noted in the figure. This datum point will be used to position the first instance of the mounts.
Figure D5–3. Datum point position
4. Create an instance of the mount, and position it by translation. Select the point at the center of the top edge of the mount as the starting point for the translation vector, as shown in Figure D5–4. Select the datum point on the cart as the ending point of the translation vector. This positions the mount, as shown in Figure D5–
5.
Figure D5–4. The starting point of the translation vector Select this point
Position at ¼ of the way along the edge
Figure D5–5. Subassembly: body and single mount
5. Create a 2 2 linear pattern of the mount instance ( ). Select the edges indicated in Figure D5–6 as the pattern directions. Use an offset of 36 for direction 1 and an offset of 40 for direction 2. If necessary, flip the pattern directions. The final subassembly is shown in Figure D5–6.
Figure D5–6. Body/mount subassembly Edge defining
direction 1 Edge defining
direction 2
Root assembly:
1. Create a new model named root. This model will be used to assemble the subassemblies.
2. Double-click Instances in the Model Tree (underneath the Assembly container).
In the Create Instance dialog box, select Models as the type and select sub2, as shown in Figure D5–7. Click Apply.
Figure D5–7. Instancing a model
3. Similarly, create an instance of the sub1 model. Toggle on the option to Auto- offset from other instances.
4. Create a coaxial constraint between the OD of the axle and the ID of one of the rear mounts.
5. Translate the wheel/axle instance 5 units in the negative Z-direction to center it with respect to the body.
6. Similarly, position a second instance of the sub1 model with respect to the forward mounts.
7. The final assembly appears as shown in Figure D5–8.
Figure D5–8. Root assembly
Modify the wheel/axle subassembly:
1. In the Model Tree, expand the instance named sub1-1 and click mouse button 3 on bg-wheel-1. From the menu that appears, select Switch to part/model context. You are automatically switched to the Part module of the sub1 model and the part bg-wheel is displayed in the viewport. Edit the part to decrease its outer radius to 7.5. Note the effects on the root assembly, as shown in Figure D5–
9.
Figure D5–9. Cart assembly with smaller bg_wheel radius
2. In model sub1, replace the instances of bg_wheel with instances of sm_wheel. The modified cart assembly is shown in Figure D5–10.
Figure D5–10. Cart assembly with sm_wheel
3. Right-click sub1 in the Model Tree and select Edit Attributes.
4. Review the settings in the Model Instances tab as shown in Figure D5–11. This tab controls whether constraints, connectors, and/or interactions are copied along with the model when it is instanced.
Figure D5–11. Model attributes
5. Save the database as demo_assy.cae.
Part 2: Boolean Operations
The second part of the demonstration focuses on assembling a Ball Grid Array built from unit cells (each cell represents a single solder joint). The model is depicted in Figure D5–
12.
Figure D5–12. Unit cell (left); Ball Grid Array (right)
1. Import the part Demos/boolean_demo.sat.
2. Define a part-level set named TopCircle containing the circular region on the top of the part, as shown in Figure D5–13.
Tip: Use the selection options toolbar to limit the selection to Faces.
Figure D5–13. Part-level set
Solder ball Circuit board
Chip
3. Define a part-level surface named Center on the solder ball (the barrel-shaped region in the center of the part), as shown in Figure D5–14.
Figure D5–14. Part-level surface
4. Create dummy material and section properties and assign them to the part.
5. Create an instance of the part.
6. Define an assembly-level set named TopFace containing the top of the part, as shown in Figure D5–15.
Figure D5–15. Assembly-level set
7. Create a 3 3 linear pattern of the part instance ( ). Select the edges indicated in Figure D5–16 as the pattern directions. Use an offset of 42 for both directions, as shown in Figure D5–17.
Figure D5–16. Offset directions
Figure D5–17. Linear Pattern dialog box
8. Merge the parts ( ). Name the new part Grid and choose the options to Delete the original part instances and Retain the intersecting boundaries.
9. In the Model Tree, expand the Sets and Surfaces containers underneath the Assembly.
Direction 1
Direction 2
10. Examine the part-level set and surface definitions to confirm that they have indeed been propagated to the new part. The part-level sets appear as shown in Figure D5–18.
Figure D5–18. Part-level set and surface after merging parts
11. Examine the assembly-level set definition. You will notice that it was not propagated to the rest of the part instance. This is by design. The assembly-level set is a feature of the part instance, not the part itself. When the part was patterned, the new instances were copies of the original part. Thus, only the original instance was associated with the assembly-level set. The new instances did, however, inherit the part-level set and surface definitions. As shown earlier, these were retained when the part was merged. The assembly-level set is retained, however, for future use. It appears as shown in Figure D5–19.
Figure D5–19. Assembly-level set after merging parts
12. Switch to the Property module and make the part Grid visible. Confirm that all regions of the part have inherited the section definitions.
