What it takes to make a mirrored part with flatten capabilities in SolidWorks
There are two ways to make an opposite hand version of a part; a good way and a not so good way. The “not so good” way is to put the part in an assembly and use mirror components to create it. The only thing I do not like about this method is that you have to create an assembly file to make this happen. The final result is the same either way you go with it.
The other way that most people may not know about is through Insert>Mirror Part in the part file. Usually this option is grayed out. To make it available you must preselect the Plane/Face you wish to mirror about, then go to Insert>Mirror Part. SolidWorks will then ask you what you want to include in the new mirrored part. The item you must check is “Break link to part”.
That is the only way you will get the full functionality of the sheet metal features in your new part.
If you do not check it then all you will get is the solid body in the new part.