For all the models (not just sheet metal), do the following:
1. when clicking on the New Study command, select the Study Type and Mesh Type. Don't click OK yet.
2. in this dialog box, you also have Options button. Click on it.
3. under Results options, deselect Generate only Surface results (faster).
Now, do your simulation study and you will get iso surfaces insteas of contours.
If you already have the simulation completed, do the following:
1. exit the results display by clickin on Close Simulation Results first
2. right musue button click on the name of the simulation in the Simulation tree-view pane.
3. select the Modify Study command
4. in new dialog box, click on options button
5. turn off the Generate only Surface results (faster) option
6. run the simulation again by clicking on Solve
Your Iso display will give you now the surface display instead of contour.
And if you want this kind of behaviour all the time, you can go in Solid Edge options and under Simulation menu, you can disable the Generate only Surface results (faster) option.