Manufacturing Processes phần 3 pot

DRAWING 13-21

Tailor Welded Blanks (TWB) in Forming With the demand for

reducing both automotive structure weight and manufacturing costs

many new processes are being employed:

1. Different parts are formed separately and then joined by laser. Part

forming is independently optimized, followed by trimming and weld

assembly. Forming is easier but welding along curved lines is more

complex (Fig. 13.2.21a).

2. The blanks are welded, and then the panel is formed in one die.

Welding is simpler, but forming is considerably more complex.

Dimensional tolerances are better controlled (Fig. 13.2.21b).

3. Blanks of varying thickness are tailor-welded using laser tech￾niques to create a single blank that subsequently is formed into the

required geometry (Fig. 13.2.22). The forming process of TWBs is very

complex as the blank areas with different thicknesses flow differently

during the drawing operation.

4. Friction stir welding is used to create a single blank made of dif￾ferent materials or different sheet thickness. This composite blank is

then drawn to final geometry (Fig. 13.2.23).

Hot drawing above the recrystallization range applies single- and

double-action drawing principles. For light gages of plastics, paper, and

hexagonal-lattice metals such as magnesium, dies and punches may be

heated by gas or electricity. For thick steel plate and heat-treatable

alloys, the mass of the blank may be sufficient to hold the heat required.

High-Pressure Hydroforming of Tubes Tubes formed to various

cross sections and bent to various shapes are widely used in automotive

frames. There are a number of variants of this process (Fig. 13.2.24),

including forming under (1) tensile and compressive conditions,

(2) bending conditions, and (3) shear conditions. Each variant is intended

to impart a particular deformation to the tube by a predetermined

motion of the tools. Motions include axial compression due to tool

motion and circumferential expansion due to internal pressure. In high￾pressure forming, pressurized force can reach 35,000 tons. Lead times

can be very high due to the slow pressurization and depressurization

required for each forming cycle. These high pressures lead to metal

Fig. 13.2.20 Drawing of magnesium sheets at elevated temperatures. (a) Flow

stress of magnesium AZ61. [Chabbi, et al., 2000, Hot and Cold Forming Behavior

of Magnesium Alloys AZ31 and AZ61, in K. U. Kainer (ed.), “Magnesium Alloys

and Their Applications,” Wiley-VCH, D, pp. 621–627.] (b) Drawn AZ31B cups at

room temperature (left) and at 230C (right). (S. Novotni, Innenhochdruk￾Umformen von Belchen aus Aluminium-und Magnesiumlegierungen bei erhohter

Temperatur, Ph.D. thesis, Elrangen University, Germany.)

0

0

100

200

300

400

0.26

0.13

RT Homologous temperture

0.32

0.2 0.4 0.6 0.8 1

Degree of deformation

(a)

Deformation rate = 0.8 s−1

Flow stress, MPa

Mg AZ61

Fig. 13.2.21 (a) Many parts are formed separately and joined to form side

panels and pillars; (b) single blank is trimmed and then formed. (Source: Ruch

et al., Grobserienfertigung von Aluminumkarosserien, in K. Siegert, “Neuere

Entwicklungen inder Blechumformung,” MATINFO, Frankfurt, D, 2000).

0.70 mm

BH 260/370 0.70 mm

BH 260/370

1.20 mm

DP 100/1000

1.80 mm

DP 100/1000

1.50 mm

DP 100/1000

Fig. 13.2.22 Use of tailor-welded blanks in automotive side panels using

different materials of unequal thickness. (Source: Ultra Light Steel Autobody

Consortium, USA.)

FSW

F

Joint

Tool

Fig. 13.2.23 Use of friction stir welding to create a blank. (Source: The

Welding Institute.)

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