# Effects of Solid Die Types in Complex and Large-Scale Aluminum Profile Extrusion
## 4 Results and Discussion
### The Transverse Weld of the Pocket Die and the Spread Die  
Pocket die and spread die are commonly used in billet-to-billet extrusion [9]. The pocket (or spreader) placed in front of the die orifice will control the flow and reduce the die deformation. It also acts as an element that controls the pressure needed for forming the transverse weld. Depending on the requirements of the customer, the part containing the charge weld may have to be removed with a high-quality product request.  
In practice, the length of the transverse weld can be determined according to the position of the so-called \"stop mark\" [37; 38] occurred after completion of the extrusion process of a billet. Figure 17 shows the stop mark, which is caused by the formation of friction between extruding material and bearing surfaces when stopping the ram.  
\begin{table}
\begin{tabular}{c c c c} \hline \multirow{2}{*}{**Max. Deflection of Dies (mm)(Mag)**} & \multicolumn{3}{c}{**Ram Speed (mm/s)**} \\ \cline{2-4}  & **1** & **5** & **9** \\ \hline Flat-face die & 0.17 & 0.18 & 0.19 \\ Pocket die & 0.12 & 0.12 & 0.12 \\ Spread die & 0.11 & 0.13 & 0.13 \\ \hline \end{tabular}
\end{table}
Table 6: Effect of ram speed on die deformation of solid extrusion dies.  
Figure 16: Die deformation: (**a**) Traditional flat die; (**b**) The pocket die; (**c**) The lower die of the spread die.  
Figure 18 shows the invasion (replacement) of the new material stream in the pocket and spread dies in different time steps. The initial interface of the transverse weld is flat (time step = 0 s)) and then gradually bent (see Figure 18a (time step = 8 s) and Figure 18b (time step = 30 s)). This figure also indicates that materials in the dead-metal zone are strongly influenced by sticky friction. The pocket extrusion process takes only 60 seconds, while the spread extrusion process takes 250 seconds to fulfil 100% new material.  
Figure 19 demonstrates the relationship between the length of the charge weld line and the percentage of new material simulated at the ram speed of 1 mm/s. It is worth noting that the average length of the charge weld for the spread die is twice that of the pocket die. This is because the material  
Figure 17: The appearance of stop mark and charge weld in the continuous extrusion of solid dies. The formation of a transverse weld and its length (\(L_{tw}\)) with distance from stop mark to starting position of charge weld (\(L_{s}\)), and distance from stop mark to the cut-off location at the end of charge weld (\(L_{c}\)).  
Figure 18: Progression of the charge weld in the dies: (**a**) The pocket die; (**b**) The spread die.  
volume in the pocket chamber is less than the spreading chamber, and the material in the dead zone is harder to wash off.  
Table 7 shows parameters related to the charge weld at different ram speeds of 1, 5, and 9 mm/s. Table 6 clearly shows that increasing extrusion speed leads to an increase in the length of the transverse weld in both dies. The charge weld lengths of the two dies are small at low extrusion speed (at ram speed of 1 mm/s). In particular, the increase rate in the weld length of the pocket die is much slower compared to that of the spread die. The weld length increases by about 221 mm for the pocket die, while it is 3243 mm for the spread die.