Depending on the materials being used, the structure, and the design of the window, the production process may be completed in various different ways, but can also can be easily divided into several basic stages. Firstly, the final frame for the window must be prepared. Various different components will require a wide range of different treatments, depending on the materials and functionality, which includes milling, gluing, assembling, cutting, trimming and welding. These individual processes are normally carried out in automated production plants. Often the materials involved range from pvc wood, reinforced steel, and composite materials. Once the frame is complete, the glass is used to fill the frame, and must be precisely fitted so that it can be correctly sealed.