**2.2.4 Addendum design**

The shape of a sheet metal automobile panel is typically complex and irregular, resulting in difficulty achieving uniform forces on the die face during drawing operations. To solve this problem, an addendum is introduced that uses various section curves (Fig. 10) to make forces uniform. Additionally, the convenience of subsequent operations is also a concern and can affect the choice of section type.

Fig. 10. Common section types

The design of an addendum requires determination of the trimming position, section type, and its size. Fig. 11 provides a detailed explanation of Fig. 10(b). A 3–5mm line is usually extended from the product-in face to avoid cracks from bending. An addendum is typically shaped like stairs to facilitate trimming. The bending angle of an addendum should be as small as possible.

Fig. 11. Stair-like section curve
