1.create the cone
2.stop by turning the 2 degrees..middle point,Your cone, will now have a thin slit in it
3. convert the sheet metal , and now we can use Solidworks to convert the tube into sheet metal. Go to Insert -> Sheet Metal -> Bends and change the radius to the radius of the tube, and K-factor to 1.
5.The last thing you need to do is right click on the tube and click Flatten. Your tube should now be flat.