Injection molding flap demoulding
Injection molding flap-type demoulding is a special demoulding method for complex-shaped plastic parts (such as those with inner grooves, threads, or irregular protrusions). Its core principle is to achieve the smooth release of plastic parts from the mold through the coordinated movement of multiple detachable flap modules (also known as half blocks). Compared with traditional ejector pins and ejector plates, flap-type demoulding can effectively solve the demoulding difficulties caused by undercuts or deep cavities in complex-structured plastic parts. It is widely used in automotive parts, medical devices, home appliance accessories and other fields. The design and debugging of this demoulding method require extremely high mold precision. Any matching error between modules may cause scratches, deformation, or even failure to demold the plastic part. Therefore, it is crucial to have a deep understanding of its working mechanism and optimization points.
The structural composition and motion mechanism of a flap-type demolding system are fundamental to its smooth operation. A typical flap-type demolding mechanism consists of a flap module, a guide mechanism, a drive mechanism, and a positioning assembly. The flap module is the core component that directly contacts the plastic part. Depending on the part structure, it can be designed with two flaps, four flaps, or even multiple flaps. The module’s parting surface must precisely match the part’s contour to ensure a complete cavity when the mold is closed. The guide mechanism typically utilizes guide pins, guide sleeves, or inclined guide pins to ensure that the flap module moves along a preset trajectory during opening and closing, preventing interference between modules. Drive mechanisms are available in hydraulic, pneumatic, or mechanical transmissions (such as inclined slides and rack and pinion). Hydraulic drives are widely used in large molds due to their stable power and adjustable stroke. Positioning assemblies (such as locating pins and latches) ensure precise alignment of the flap modules during mold closing. Errors must be controlled within 0.01-0.02mm to prevent parting marks from forming on the part surface, affecting the appearance quality.
Part structure design significantly impacts the feasibility and efficiency of flap-type demolding. When designing a part with a flap-type demolding structure, careful consideration must be given to the choice of parting surface and the method of module separation. The parting surface should avoid the part’s exterior surface whenever possible. If it must pass through the exterior surface, a stepped or angled parting pattern should be employed to minimize the visibility of the parting line. Module separation should follow the “inside first, outside last” principle, prioritizing the smooth demolding of the inner undercut structure before considering the outer contour. For example, for a cylindrical part with internal threads, a four-part module can be split radially. The threaded portion is then released simultaneously with the module, and the part is then ejected using ejector pins. Furthermore, the part’s wall thickness should be evenly distributed to avoid deformation caused by uneven force on the modules. A draft angle of 0.5-1° at the module joint can reduce friction between the module and the part, minimizing the risk of scratches during demolding. If the part has deep ribs or bosses, avoidance structures should be added to the corresponding modules to ensure no interference during demolding.
Mold commissioning and parameter optimization are critical steps in ensuring the stability of flap-type demolding. During the mold trial phase, it is crucial to verify the synchronization and coordination of module movement. Inconsistent movement speeds among multiple modules can result in excessive localized stress on the plastic part, leading to cracks or deformation. The pressure parameters of the drive mechanism can be adjusted (for example, the hydraulic drive operating pressure should be controlled at 8-15 MPa) to ensure that the speed difference between the modules does not exceed 5%. The lubrication status of the guide mechanism should also be checked, and high-temperature grease should be regularly added to reduce friction during module movement. The demolding sequence is also crucial. Typically, the flap-type module is first radially moved outward 1-3 mm to disengage the undercut on the inside of the part. The ejector mechanism is then activated to eject the part from the module surface to avoid damage caused by concentrated demolding forces. Furthermore, the demolding speed should be adjusted based on the material characteristics of the part. For rigid materials such as ABS and PC, the demolding speed can be set to 50-80 mm/s. For flexible materials such as PP and PE, the speed should be reduced to 30-50 mm/s to prevent deformation and scrapping of the part due to stretching.
Common failures and maintenance measures for flap-type mold release require significant attention. Excessive clearance between modules is a common problem, leading to flash during mold closing and, in severe cases, even allowing melt to enter the gap between modules, causing mold release to become stuck. Regular inspection of the module parting surface for flatness is essential. Any deviation exceeding 0.03mm requires grinding and repair. Worn guide components should be replaced to ensure module linearity. Leakage or insufficient power in the drive unit can also affect mold release. Hydraulic drives require inspection of seals for aging and replacement of high-pressure seals every six months. Pneumatic drives require regular cleaning of the air path for moisture and impurities to prevent internal cylinder corrosion. Furthermore, wear on the module surface can lead to cosmetic defects in the plastic part. Weekly polishing is required to maintain a surface roughness Ra ≤ 0.8μm. For high-production molds, chrome plating or nitriding can be applied to the module surface to improve wear resistance and service life. Establishing a comprehensive maintenance system can effectively reduce the incidence of flap-type mold release failures, improving production efficiency and product quality.
