**3.1. Design of thickening process for inner wall of cup parts**

The forming process and methods of typically double-layer cup with inner wall thickened by axial upsetting are introduced in this section.

As shown in Fig. 10a, the traditional metal forming method for manufacture double-cupshape part with thickened inner wall is that several partitions divided from the part is formed separately and assembled by the welding to a whole part. The part made by this method would decrease the mechanical performance of the part and production efficiency. In stamping-forging processing (see Fig. 10b), an initial blank is formed to a cup firstly by forward drawing. Then the bottom of the formed cup is drawn backward to form a doublelayer cup by powerful drawing. While backward drawing, the material of outside wall is pushed to the inner wall making the inner wall as thick as possible. Subsequently, the center hole is formed by piercing and the inner wall is straightened by flanging. Finally the inner wall of the cup is thickened by upsetting.

a) Traditional processing

Stamping-Forging Processing of Sheet Metal Parts 39

b) Stamping-forging processing

**Figure 10.** Scheme of forming process

38 Metal Forming – Process, Tools, Design

reaches the specified dimension.

**Figure 9.** Flywheel plate of car with outer wall thickening.

by axial upsetting are introduced in this section.

wall of the cup is thickened by upsetting.

After axial upsetting, four holes at bottom were formed by piercing.

**3. Thickening of inner wall of cup parts with axial upsetting** 

The forming process and methods of typically double-layer cup with inner wall thickened

As shown in Fig. 10a, the traditional metal forming method for manufacture double-cupshape part with thickened inner wall is that several partitions divided from the part is formed separately and assembled by the welding to a whole part. The part made by this method would decrease the mechanical performance of the part and production efficiency. In stamping-forging processing (see Fig. 10b), an initial blank is formed to a cup firstly by forward drawing. Then the bottom of the formed cup is drawn backward to form a doublelayer cup by powerful drawing. While backward drawing, the material of outside wall is pushed to the inner wall making the inner wall as thick as possible. Subsequently, the center hole is formed by piercing and the inner wall is straightened by flanging. Finally the inner

a) Traditional processing

**3.1. Design of thickening process for inner wall of cup parts** 

The flywheel plate manufactured by stamping-forging technology is shown in Fig. 9. It can be seen that there is no defect in forging surface, and the thickness of outer wall

5. Piercing

### **3.2. Material store-up for inner wall using reverse drawing**

In the forming of double-cup-shape part, the reverse cup-shape partition is formed by backward drawing to a certain height, which is prepared for subsequent thickening process. However, because it's difficult for the material of the outside wall flows to the bottom through the fillet, the backward drawing causes severe decrease in the thickness of inner wall. In order to improve stiffness of the inner wall and make the upsetting carried out latter more smoothly, the thickness of inner wall after backward drawing should be as thick as possible. Namely, it's necessary to store material during backward drawing.

As the required part could not be obtained by conventional backward drawing in one procedure, the process of powerful drawing in which a downward thrust is exerted on the outside wall to make metal flow to the inner wall is presented to get the thickened inner wall, as shown in Fig. 11. A pressure ring and a punch moves down and up, respectively, while the blank is clamped by blank holder. The die which is given an axial upside back pressure moves with pressure ring.

**Figure 11.** Diagram of thickening by powerful backward drawing
