In Odoo, developing an approval process involving both a manager and a department manager typically requires customization using the Odoo framework. The exact steps and implementation may vary based on the specific version of Odoo you're using and your business requirements. However, I can provide you with a general outline of how you might approach this process:

1. Define the Workflow:- Identify the specific modules (e.g., Sales, Purchase, HR) where you want to implement the approval process.

- Determine the conditions under which approval is required, such as order amount exceeding a certain limit, specific products being ordered, etc.

2. Custom Fields:- Create custom fields on the relevant model(s) to store approval status and related information. For example, you might add fields like "Approval Status," "Manager Approval," "Department Manager Approval," etc.

3. Configure User Roles:- Make sure the users are assigned appropriate roles to distinguish between regular users, managers, and department managers.

4. Workflow Actions:- Create a custom workflow using Odoo's Workflow Editor (Studio) or define it in Python code.

- Define different states for the workflow, such as "Draft," "Pending Manager Approval," "Pending Department Manager Approval," "Approved," and "Rejected."

5. Workflow Transitions:- Define transitions between the states. For instance, when a user submits a record, it might transition from "Draft" to "Pending Manager Approval."

6. Notifications:- Configure email notifications to inform the relevant users (managers and department managers) about pending approvals.

7. Record Access Control:- Set up record access control so that only the appropriate users can see and interact with records in certain states.

8. Automated Actions (Optional):- Implement automated actions triggered by certain events, like updating the approval status when a manager or department manager approves a record.

9. Custom Logic (Python Code):- If the approval logic is complex, you might need to write custom Python code to implement it. This could involve evaluating conditions, checking user roles, and updating approval fields.

10. Testing:- Thoroughly test the approval process in different scenarios to ensure it functions as expected.

11. User Training:- Train your users on how to use the new approval process and any changes made to the system.

Remember that implementing such a process may require technical expertise and familiarity with Odoo's framework. If you're not comfortable with customization, you might consider hiring an Odoo developer or consulting with an Odoo implementation partner.

Please note that the specifics of your implementation can vary based on your Odoo version and your exact requirements. Always make sure to have proper backups and follow best practices when customizing your Odoo instance.