material, which belongs to T6 state and possesses the diameter of 200 mm。 The chemical composition of 7A09 aluminum alloy is shown in Table 1。

Fig。 1。 Model of aluminum alloy rotating disk forging: (a) forward face; (b) backward face; (c) radial flow line and (d) circumferential flow line。

Fig。 2。  Flow chart of digitized design and manufacturing。

corresponding to  digitized  design  and  manufacturing  is  shown in Fig。 2。

3。1。CAD

According to three-dimensional (3D) model of the final work- piece, the 3D model of the cold forging of the rotating disk is established by means of CATIA software。 Subsequently, based on the 3D model of the cold forging, the 3D model of the hot forging is obtained by increasing the corresponding allowance。 According to the 3D model of the hot forging, the cavity profile of the upper die and the bottom die can be established by using Boolean operation module of CATIA software。 In the end, the 3D model of isothermal precision forging die is obtained, as shown in Fig。 3。

3。2。CAE

CAE is mainly based on finite element simulation of isothermal precision forming of the rotating disk forging。 According to the constutive model of 7A09 aluminum alloy, finite element simula- tion can be used for understanding the flow behavior of the metal material and predicting the defects of the forging during isother- mal precision forging。 As a result, the process parameters can be optimized by means of finite element simulation。 In the present study, DEFORM3D commercial finite element code is used to optimize the preform schemes。 Fig。 4 shows two preform    schemes,

in which one scheme is based on ring preform and the other scheme is determined as pentagram preform。

3。3。CAM

CAM lays a great emphasis on numerical control programming during machining of isothermal precision forging die。 It deals with planning cutter path, establishing cutter location file, modeling cutter locus and generating numerical code。 With the help of the computer, CAD and CAM can be integrated in order to implement the data exchange between CAD and CAM。

4。Constitutive behavior

4。1。Compression deformation behavior

Fig。 5 indicates the true stress–strain curves of 7A09  aluminum

alloy under compression at the strain rates ranging from 0。01 s−1 to 10 s−1  and at the temperatures ranging from 300 1C to 460 1C。

It can be found from Fig。 5 that 7A09 aluminum alloy is sensitive to the strain rates since the flow stress of 7A09 aluminum alloy increases with the increase in the strain rate in the case of the same deformation temperature。 Furthermore, at the strain rate   of

0。01 s−1, the stress–strain curves exhibit a characteristic of steady flow at the temperatures above 400 1C, while they are character- ized by work hardening at the temperatures of 300 1C and 350 1C。

However, in the case of the strain rate of 0。1 s−1, the stress–strain curves also possess a feature of steady flow at the temperature of

350 1C。 With the increase in the strain rate, in the case of the strain

rate of 1 s−1, the stress–strain curves are characterized by steady

flow even at the temperature of 300 1C。 It is very interesting that

when the strain rate increases to 10 s−1, the stress–strain curves fluctuate sharply before they exhibit the steady flow。 It is evident that there is a competition between work hardening and dynamic softening  during   hot   deformation   of   7A09   aluminum   alloy。 In general, work hardening results from the accumulation of the dislocations due to plastic deformation, while dynamic softening is attributed to the decrease in the dislocation  density  due to dynamic recovery or dynamic recrystallization [23]。 It can be generally accepted that the softening mechanism of dynamic recovery results from climb of edge dislocations, cross-slip of screw dislocations and counteraction of unlike dislocations。 How- ever, the softening mechanism of dynamic recrystallization is attributed to the annihilation of the dislocations due to nucleation and growth of new recrystallized grains。 The balance between working hardening and dynamic softening results in the steady flow of 7A09 aluminum alloy during hot deformation。 In general, dynamic recovery occurs at the low strain rates, as shown in Fig。 5 (a)–(c), while dynamic recrystallization arises at the high strain rates, as shown in Fig。 5(d)。 For example, in the present study, as compared  to  the  as-received  7A09  sample,  the  compressed 7A09