First of all, from the analysis of ordinary 4A2S, the left and right movement of the machine head can not be done without the servo motor, plus the two A for feeding car and the machine head moving,just 4A. At this time, there are only two strokes of the top and the end of the die head in the up and down movement of the die changing, and the oil cylinder is also two strokes of the up and down oil feeding, which is exactly in line with this usage, so the two-layer die can be completed with 4A (Figure. 1).

Figure 1  4A-2S machine head

When it comes to 3S, it is necessary to consider that the distance of the machine head moving up and down is divided into three sections. Even if the cylinder stroke is controlled by the way of oil cutting off, the movement of the cylinder will not meet the requirements of production due to the accuracy problem. Therefore, due to the excessive stroke points of the mold with more than three layers, the servo motor can only be used to control the up and down movement.

Figure 2  5A-3S machine head