Combine Bodies

You can combine multiple solid bodies to create a singled-bodied part or another multibody part. There are three ways to combine multiple solid bodies:
Add. Combines solids of all selected bodies to create a single body.
Subtract. Removes overlapping material from a selected main body.
Common. Removes all material except that which overlaps.
To use the Add or Common operation type:
Click Combine on the Features toolbar, or click Insert, Features, Combine.
The Combine1 PropertyManager appears.
Under Operation Type, click Add or Common.
Under Bodies to Combine, select the bodies in the graphics area, or select the bodies from the Solid Bodies folder in the FeatureManager design tree.
Click Show Preview to preview the feature.
Click OK .
To use the Subtraction operation type:
Click Combine on the Features toolbar, or click Insert, Features, Combine.
The Combine1 PropertyManager appears.
Under Operation Type, click Subtract.
Under Main Body, select the body to keep from the graphics area for Solid Body , or select the body from the Solid Bodies folder in the FeatureManager design tree.
Under Bodies to Subtract, select the bodies whose material you want to remove for Solid Bodies .
Click Show Preview to preview the feature.
Click OK .


For the body intersection multibody technique, you use the Combine feature and its Common option. Body intersection is a quick way to create complex parts with very few operations, which can result in faster performance. The operation takes multiple solid bodies that overlap one another and leaves only the intersecting volumes of the bodies. For most models that can be represented fully by two or three drawing views, this technique can be used by intersecting either two or three extruded solids. The extrusion sketches are the solid lines represented in the two or three views. The following example shows this technique with the intersection of two extrusions.
Front
Top
Isometric
To create the part described above, you begin with the base part:
And then select the Common option of the Combine feature to use only the overlapping material of the base part.
(fr.solidwork help)