Secondary demoulding is used because the plastic parts need to be forced to demould
In the field of injection molding, some plastic parts have special structures that make it difficult to remove them smoothly by conventional one-time demolding. In this case, the secondary demolding process becomes a key solution. Forced demolding is usually suitable for cases where the plastic parts have deep undercuts, undercuts or complex internal cavity structures. Such structures will cause the plastic parts to fit tightly with the mold cavity or core after the mold is opened. If forced to demold in one time, it is very easy to cause deformation, cracking or even damage to the plastic parts. For example, some cylindrical plastic parts with inner flanges will have their inner flanges firmly stuck to the core. When ejected in one time, the flanges are under concentrated force and are likely to tear. Secondary demolding applies the demolding force in steps, first loosening the plastic part from the core or cavity, and then completely ejecting it. This effectively disperses the stress during the demolding process and ensures the integrity of the plastic part.
The design of the secondary demolding process requires targeted planning based on the structural characteristics of the plastic part. First, the sequence of the two demolding operations and the distribution of forces must be clearly defined. Typically, the first step involves slightly lifting the part from the core, creating a slight gap between the part and the core, thereby breaking the vacuum or friction between them. The second step is to completely eject the part from the mold. For example, for a box-shaped part with a deep cavity, the first step involves using a push plate to lift the bottom of the part 1-2 mm, breaking the tight fit between the part and the cavity wall. In the second step, an ejector pin is used to completely eject the part. During the design process, the mold’s guiding mechanism must also be considered to ensure the precise and orderly nature of the two demolding operations, avoiding any jamming or uncoordinated movements.
There are various mold structures that can achieve secondary demolding, including spring-type secondary demolding, hydraulic cylinder-driven secondary demolding, and inclined guide column-type secondary demolding. Spring-type secondary demolding relies on the elastic force of a spring to achieve the first demolding. When the mold is opened to a certain distance, a limit device triggers the second demolding action. This structure is simple and low-cost, and is suitable for plastic parts with low demolding forces. Hydraulic cylinder-driven secondary demolding uses a hydraulic system to precisely control the force and stroke of the two demolding operations. It is suitable for large or complex plastic parts and can provide stable and adjustable demolding force. Inclined guide column-type secondary demolding uses the coordination of inclined guide columns and sliders to achieve step-by-step demolding through inclined surface transmission during the mold opening process. It is reliable and widely used in the production of small and medium-sized plastic parts.
The two-stage demolding process requires careful attention to numerous details in practical applications to ensure production efficiency and part quality. The demolding force should be determined based on factors such as the part material, structural dimensions, and cavity surface roughness. Excessive force can easily damage the part, while too little force prevents smooth demolding. The two demolding strokes must be designed appropriately: the first stroke should loosen the part, while the second stroke should ensure complete release. Furthermore, the mold’s ejector mechanism should possess excellent rigidity and wear resistance to withstand the repeated motions of long-term production. Lubrication should also be ensured to minimize component wear and extend the mold’s life.
With the continuous development of the injection molding industry, secondary demolding processes are undergoing continuous optimization and innovation. The use of new drive devices, such as servo motors, makes demolding more precise and controllable, adapting to the production needs of different plastic parts. Intelligent sensor technology monitors the force and stroke during the demolding process in real time, providing timely feedback and parameter adjustments to improve production stability. The rational application of secondary demolding processes not only solves the demolding challenges of complex plastic parts but also provides an effective way to improve product quality and reduce production costs. It plays a vital role in injection molding production in the automotive, electronics, and medical device industries.
