Fig。 1。   The embossed pin head before and after the process。

The new design influenced the flow of the preform, resulting in lower tool stresses and preventing the folding problem。 Sun et al。 [18] studied the material flow behavior of magnesium alloy in the formation of hook, sidewall, and boss during the press forging of notebook cases。 They introduced methods to prevent the material from flowing outwards, which causes the geometrical defect。

The present paper intends to investigate the effect of punch and pin head features to geometrical defect。 This is important in order to ensure accurate assembly of the blade to the hubs, which could affect the performance of the propeller itself。 The paper begins with the embossing process overview of an aluminum alloy pin head, followed by the methodology of the study。 Afterward, the result is discussed, and the paper ends with conclusions。

2。Embossing process overview

The pin head of an Autonomous Underwater Vehicle    (AUV)

Fig。 2。  Final assembly of the blade to the hub of the propeller。

that could affect propeller performance is the twist angle; it also depends on the geometrical precision of the blade and the assembly accuracy [20]。

3。Methodology

The main objective of the study is to investigate the effect of some design parameters, namely, distance to the edge (DTE), punch diameter, and embossing depth to the unfilled region of the cold embossed pin head。 The current study also investigates the effect of a punch with taper to the formation of defects。 This process is considered an embossing process because the thickness of the resulted features, in this case, the pin head is not changed。 The nominal geometries of the pin head are shown in Fig。 2。 Here, several dimensions have to be taken into consideration because the accuracy of each parameter affects the assembly of the parts itself。 DTE and pin head diameter or cavity diameter are the two design parameters that influence the performance of the embossed part。 The size of the head is not considered as critical in this study because the geometry of the pin head diameter depends on the die cavity。 On the other hand, the DTE is further explored in this research。

The present study employs the finite element method to sim- ulate the material flow pattern of the workpiece during the cold forming process。 Theoretically, the governing equations for the solution of the mechanics in plastic deformation for rigid-plastic and rigid-viscoplastic materials involve equilibrium equations, yield criterion, constitutive equations, and compatibility condi- tions, which can be expressed as follows [21]:

blade is a special feature designed to ensure accurate assembly of the blade to the hubs。 It is crucial for an AUV to ensure accu- rate design and assembly for the purpose of saving of the power consumption [19]。 Fig。 1(a) shows the tooling and pin head emboss-

¸ ¸

˘ = o¯ ε¯˙ dV −

sp

tividS (1)

ing process, and Fig。 1(b) demonstrates the workpiece before and after the embossing process。 The pin head must be formed pre- cisely in order to avoid unwanted movement of the blade which may affect propeller performance。 One of the main    parameters论文网

where o¯  is the effective stress, ε¯˙  is the effective strain rate, Fi  rep-

resents the surface tractions, and ui is the velocity components。

The incompressibility constraint on admissible velocity fields in Eq。 (1) may be removed by using the penalized form of the

Fig。 3。  The FE model of the embossing process at initial position。