justify the existence of our manufacturing department
You need to show what the department contributes to the company, is that right? Do you need to write this report to show the value your department has for the company?
This has to be a persuasive essay. List 3 strong arguments about the importance of the department. Let each argument becme a paragraph. Then, go back and write an introduction. I'm sorry I have no example to give. I'm not sure yet if I correctly understand what you are trying to do. Who will read the report? The company executives?