Yes, you are right there is an option to Lock and Unlock field but it is uniform across all sheets. Now, to make it dynamic based on sheet selection, we need to use Triggers option available under sheet properties. It is like performing set of given tasks while selecting and leaving sheet. Follow below steps to perform it:
Step 1: Select Sheet --> Go to Sheet Properties --> Triggers --> Select (OnActivateSheet/ OnLeaveSheet). In your case select onActivateSheet because you want to lock filed when user navigate to Product, Operation and Manpower Sheet.
Step 2: Click On ADD action --> ADD --> below you have action type and related actions you want to perform.
Step 3: In your example, select Action Type as “Selection” and “Lock field” as Action, click on Ok.
Step 4: Provide the name of field which you want to lock and press Ok and Apply. Similarly you can define triggers for rest of sheet.
- Lock field for Product, Operation and Manpower
- Unlock field for Summary and Competition
Hope this helps!