**2.3. Application**

In this section, an application of axial upsetting is presented. The application object is flywheel plate used in self-changing gearbox. The dimensional drawing and three dimension model of

part are shown in Fig. 7 and Fig. 8, respectively. It can be seen from figures that the flywheel plate is a cup type part with large diameter, 273.3 mm, while the wall thickness is 11 mm, and the bottom thickness is 10mm. The corner between wall and bottom is very small, inner round radius is 5 mm and outer round radius 2.5 mm. Moreover, there is one center hole and three auxiliary holes at the bottom of cup. The part material is 45 high quality carbon steel, which will has good mechanical properties after quenching and tempering.

Stamping-Forging Processing of Sheet Metal Parts 37

The thickening ratio of flywheel plate is 1.1. According to thickening ratio criterion, the wall thickness can be upset to designed value in one pass. So, the flywheel plate can be manufactured by sheet stamping-forging technology. Taking 10 mm circular plate as blank, firstly is drawn to a cup with uniform thickness, then the wall of cup is thickened to 11 mm

In order to decrease deformation stress, the warm forming was used in drawing and upsetting processes. Generally, the warm forming is a technology carried out at temperature between room temperature and recrystallization temperature, during which the

The stamping-forging processes are as follows: blanking, heating, drawing, finishing inner

Due to the thickness of bottom is 10 mm, the circular blank with 10 mm thickness is chosen. The diameter of blank is 337.8 mm calculated by constant volume principle. To obtain high quality circular blank, fillet edge dies with small clearance between punch and die was used for blanking. The dimensional accuracy reached grade IT9-IT11, and

The electric resistance furnace full of protective atmosphere was used for heating the blank in order to reduce oxidization. The blank was heated to 800-850 °C and hold for

A 1000 kN mechanical press was employed to carry out the drawing process. The key process parameters, such as radius of punch and die, were determined by empirical

As blank thickness larger than 6 mm, the radius of punch can not less than 1.5-2 times of the thickness. In this application, the radius of punch must larger than 15-20 mm. So,

the radius of punch was chosen as 15 mm to reduce the amount of finishing.

(2 ~ 4) (2 ~ 4) 10 20 ~ 40 *<sup>d</sup> r t* = = ×= *mm*

where *t* is the thickness of blank (mm). In this application, the radius was 20 mm.

An 8000kN mechanical press was used to finish inner corner and upset the wall. After the inner corner was ironed by a punch with 5 mm radius, the side wall was upset to desired dimension while the bottom of cup was clamped. Because the relief cavity reduces upsetting force significantly, the relief cavity method was adopted in this application.

The radius of die was determined by the following empirical equation:

deformation stress of material is significantly lower than that at room temperature.

by axial upsetting.

1. Blanking

2. Heating

3. Drawing

principle.

corner and axial upsetting, piercing.

the surface roughness was Ra3.2-0.8 μm.

4. Finishing inner corner and axial upsetting

30 minutes. Meanwhile, the dies were heated to about 200 °C.

**Figure 7.** Dimensional drawing of flywheel plate.

**Figure 8.** Three dimensional model of flywheel plate.

Due to the part has different thickness in the wall and the bottom, and a small corner radius, traditional drawing process can not obtain desired part. If employing machining, the material usage is very low about 35%. Moreover, machining will cut streamline, which may lower mechanical properties. If the bottom and the wall are formed, respectively, and then combined to a complete flywheel plate by welding, the weld seam has a harmful effect on mechanical properties, which may not satisfy the performance requirement.

The thickening ratio of flywheel plate is 1.1. According to thickening ratio criterion, the wall thickness can be upset to designed value in one pass. So, the flywheel plate can be manufactured by sheet stamping-forging technology. Taking 10 mm circular plate as blank, firstly is drawn to a cup with uniform thickness, then the wall of cup is thickened to 11 mm by axial upsetting.

In order to decrease deformation stress, the warm forming was used in drawing and upsetting processes. Generally, the warm forming is a technology carried out at temperature between room temperature and recrystallization temperature, during which the deformation stress of material is significantly lower than that at room temperature.

The stamping-forging processes are as follows: blanking, heating, drawing, finishing inner corner and axial upsetting, piercing.

1. Blanking

36 Metal Forming – Process, Tools, Design

part are shown in Fig. 7 and Fig. 8, respectively. It can be seen from figures that the flywheel plate is a cup type part with large diameter, 273.3 mm, while the wall thickness is 11 mm, and the bottom thickness is 10mm. The corner between wall and bottom is very small, inner round radius is 5 mm and outer round radius 2.5 mm. Moreover, there is one center hole and three auxiliary holes at the bottom of cup. The part material is 45 high quality carbon steel, which

Due to the part has different thickness in the wall and the bottom, and a small corner radius, traditional drawing process can not obtain desired part. If employing machining, the material usage is very low about 35%. Moreover, machining will cut streamline, which may lower mechanical properties. If the bottom and the wall are formed, respectively, and then combined to a complete flywheel plate by welding, the weld seam has a harmful effect on

mechanical properties, which may not satisfy the performance requirement.

will has good mechanical properties after quenching and tempering.

**Figure 7.** Dimensional drawing of flywheel plate.

**Figure 8.** Three dimensional model of flywheel plate.

Due to the thickness of bottom is 10 mm, the circular blank with 10 mm thickness is chosen. The diameter of blank is 337.8 mm calculated by constant volume principle. To obtain high quality circular blank, fillet edge dies with small clearance between punch and die was used for blanking. The dimensional accuracy reached grade IT9-IT11, and the surface roughness was Ra3.2-0.8 μm.

2. Heating

The electric resistance furnace full of protective atmosphere was used for heating the blank in order to reduce oxidization. The blank was heated to 800-850 °C and hold for 30 minutes. Meanwhile, the dies were heated to about 200 °C.

3. Drawing

A 1000 kN mechanical press was employed to carry out the drawing process. The key process parameters, such as radius of punch and die, were determined by empirical principle.

As blank thickness larger than 6 mm, the radius of punch can not less than 1.5-2 times of the thickness. In this application, the radius of punch must larger than 15-20 mm. So, the radius of punch was chosen as 15 mm to reduce the amount of finishing.

The radius of die was determined by the following empirical equation:

$$r\_d = (2 \sim 4)t = (2 \sim 4) \times 10 = 20 \sim 40 mm$$

where *t* is the thickness of blank (mm). In this application, the radius was 20 mm.

4. Finishing inner corner and axial upsetting

An 8000kN mechanical press was used to finish inner corner and upset the wall. After the inner corner was ironed by a punch with 5 mm radius, the side wall was upset to desired dimension while the bottom of cup was clamped. Because the relief cavity reduces upsetting force significantly, the relief cavity method was adopted in this application.

#### 5. Piercing

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

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 reaches the specified dimension.

Stamping-Forging Processing of Sheet Metal Parts 39

b) Stamping-forging processing

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

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

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

possible. Namely, it's necessary to store material during backward drawing.

**Figure 10.** Scheme of forming process

pressure moves with pressure ring.

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

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