Deep Drawing
Embossing
Deep drawing is a stamping process that forms flat blanks into open hollow parts. It can also process prefabricated open hollow parts to reduce their diameter and increase depth through further stamping.
Embossing is completed in a single stamping operation, with no strict control over material thickness changes. It is commonly used to enhance the surface strength of sheet metal. Also known as bulging forming, embossing can create features of different heights on sheet metal. Bridge-shaped embossments can serve as clips for fastening.
Circular deep drawing is the most widely used type. For other forms of deep drawing, uniform deformation along the circumferential direction is required. This process features simple molds, fast production and high yield rate. Regardless of the shape, abrupt changes to the circumferential outline shall be avoided.
The depth of circular deep drawn parts is subject to restrictions, as shown in the figure below. Excessively deep drawing will easily cause material rupture.
A deep drawn part generally has three types of fillets: bottom fillet, top fillet and outline fillet. As shown in the figure, the root fillet R1≥T, the top fillet R2≥2T, and the outline corner fillet R3≥4T.
Figure 4-19 Corner Fillet Transitions for Deep Drawn Parts
The diagram shows the minimum radius requirements for different fillets in a deep drawn part:
R1≥T (bottom corner radius)
R2≥2T (side wall fillet radius)
R3≥4T (outer corner transition radius)
Where T represents the sheet metal thickness.
The deep drawing process of sheet metal cannot guarantee high dimensional accuracy. Since deep drawing is usually carried out in multiple passes, the wall thickness of sheet metal will change. Only either the internal dimension or external dimension can be precisely controlled for such parts.
The embossing depth H≤3T. Excessive depth will lead to cracks on embossments.
The taper angle of embossing α≥15°. A relatively large taper ensures smooth forming.
Figure 4-20 Depth and Taper of an Embossed Protrusion
H: Embossing depth
α: Taper angle of the embossed sidewall
The corner radius of the embossing outline shall follow the standard for deep drawing, namely R≥4T.
The distance between embossments, between an embossment and the sheet metal edge, or between an embossment and bending features shall satisfy E ≥ 2T.
Tip:The embossed bulge is too close to the bent edge, interfering with the bending process
Figure 4-21 Distance Between Embossed Feature and Bent Edge
a) Original design: The embossed feature is too close to the bent edge, which affects bending operation
b) Improved design (with a spacing E reserved between the embossed feature and the bent edge)
