## 3 Results
### Alternation of Injection of Two Materials  
Both the HDPE engraving inserts, and the extraction plates, have hydraulic movements, four in total: two type-1 cylinders for the inserts and two type-2 cylinders for the extraction plates, as shown in Figure 13. Type-2 cylinders are designed to perform the extraction movement. They are more robust components because they are exposed on the outside of the mold, and are different from type 1 cylinders, which are inside the mold. Thus, type-1 cylinders are more compact and adjusted to the movements of the inserts. Figure 11: Horizontal extractors (section view). Figure 12: Technical drawing of the lifters with 4\({}^{\circ}\) inclination (sectional view). The two type-2 cylinders, responsible for advancing and withdrawing the extraction plates, use the back plate on the extraction side as a fixed base, and the rest are fixed to the extraction plates. Thus, when the piston advances, the cylinder causes the plates to rise by 45 mm, which is necessary for extracting the parts. A similar process occurs in type-1 cylinders. However, they are attached to the engraving plate on the extraction side and cause the mechanism to move, in which, as the pistons of these cylinders' advance, the two HDPE engraving inserts rise by 4.7 mm (Figure 14), leaving free the space to now be injected with the HDPE component. Type-1 and type-2 cylinders' advance and retract similarly, but at different stages of the injection cycle. Type-1 performs the backward movement when injecting HDPE, after injecting PP. Then, type-2 performs the forward movement of the components responsible for the extraction needed for them to function, followed by the reverse movement. After the type-2 cylinders retract the extraction plates, the type-1 cylinders remove the inserts. At the same time, the mold is closed by the injection machine, starting a new injection cycle. Type-1 cylinders have a maximum pressure capacity of 500 bar and a minimum of 80 bar, being able to press a force of 1025.1 kg in the advance and 715.02 kg in the return (for a diameter of 40 mm). Thus, even with additions, due to the friction and pressure loss of the hydraulic pump itself, with these cylinders operating at 80 bar, these pressures are expected to be more than sufficient for advancing and retracting the 1.41 kg of each one of the engraving inserts responsible for molding the HDPE components. Figure 14: Hybrid hydraulic/mechanical movement of HDPE engraving inserts. Figure 13: Hydraulic structure with type-1 and type-2 cylinders positioning. In the most advanced position, the injection pressure of PP laterally affects the insert. The hydraulic supports this pressure because the force is applied vertically. When the hydraulic is in the backward position, the vertical injection pressure (from HDPE) already affects the insert, but since it is in the resting position, it is mechanically supported, and so can easily resist the pressure applied to it. Thus, hydraulic cylinder type-1 (simple) requires only the minimum pressure (standard). Type-2 cylinders share the same maximum and minimum pressure limits (500 and 80 bars, respectively). Considering the two extraction plates, it is necessary to move a mass of 74.02 kg, plus about 6.3 kg of the components and the friction that they cause. Even so, the sum of these portions does not justify the need for high pressures, since the hydraulic performs a forward load in the order of 2050.02 kg and a backward load of 1430.04 kg for a diameter of 40 mm. Thus, a pressure of 160 bar is sufficient, within the limits of the cylinder. The extraction plates have more functionality than the extraction of the injected parts. Because they are plates of considerable dimensions (with about a 74 kg load), they require an element that guides their movements in a precise and independent way. The solution was to add four guide plates, one in each corner.