Example of gate layout for large-size plastic parts
In the injection molding of large automotive bumpers, the rationality of gate layout directly impacts part quality and production efficiency. A certain 1800mm long front bumper utilizes a multi-point gate layout with six gates located symmetrically at the ends, center , and transition points of the bumper’s curved surfaces. This layout allows the melt to simultaneously fill the cavity from multiple directions, shortening the melt flow distance and reducing pressure loss. The melt flow distance for each gate is controlled between 300-400mm, ensuring the melt fills the entire cavity before cooling. Fan-shaped gates are used as the gate type, with each gate measuring 30-40mm wide and 1.5-2mm thick. These gates allow the melt to diffuse rapidly after entering the cavity, reducing impact on the cavity surface and minimizing surface defects. CAE mold flow analysis software simulation shows that this gate layout keeps the melt filling time within 8-10 seconds, with uniform pressure distribution in each part and a maximum pressure difference of no more than 5 MPa, effectively avoiding warping and sink marks caused by uneven pressure.
The gate layout for large household appliance plastic parts, such as refrigerator side panels (1200mm x 800mm), must consider part flatness requirements. A combination of side gates and pinpoint gates is typically employed. Two side gates are located on either side of the side panel’s long edge. These gates, with a width of 20mm and a depth of 2mm, ensure rapid melt flow along the long edge. A pinpoint gate, with a diameter of 3mm, is located in the center of the side panel to supplement the melt in the center of the cavity and prevent underfilling caused by excessive flow distance. This layout, with side gates as the primary and pinpoint gates as the secondary, ensures more uniform melt filling, consistent cooling shrinkage, and part flatness tolerance within 0.5mm/m. Furthermore, the side gates are located on the non-exterior surface of the part, allowing gate marks to be removed later through trimming to ensure surface quality. Production experience has shown that this gate layout has reduced the scrap rate for refrigerator side panels from 8% to 3%, significantly improving production efficiency.
The gate layout for large plastic pallets (1200mm x 1000mm) requires careful consideration of melt flow and the part’s load-bearing capacity. Due to the complex structure of the pallet’s bottom, which features numerous reinforcing ribs and support legs, a combination of ring gates and latent gates is suitable. A ring gate with a diameter of 100mm and a width of 5mm is placed at the center of the pallet. This allows the melt to spread evenly from the center to the surrounding area, filling the reinforcing ribs at the bottom. A latent gate with a diameter of 2mm is placed at each of the four corners of the pallet, concealed within the support legs. These gates fill the complex corner structures and prevent melt stagnation. The ring gate significantly shortens the melt flow distance, ensuring that each rib is fully filled. The latent gate ensures molding quality in the corners, and the gate marks are concealed beneath the support legs, minimizing the appearance and usability of the pallet. This gate layout increases the pallet’s load-bearing capacity by 15%, while eliminating defects such as shrinkage cavities and bubbles on the bottom.
The gate layout for large medical device housings (such as CT machine housings, measuring 2000mm x 1500mm) requires extremely high surface quality and dimensional accuracy. A hot runner system combined with multi-point valve gates is typically used. Eight valve gates are evenly spaced around the edge of the housing, each controlled by an independent hot runner nozzle with a diameter of 4mm, enabling precise control of melt injection volume and timing. The hot runner system maintains a constant melt temperature during flow, preventing viscosity increases caused by temperature drops and ensuring smooth melt filling of all areas of the cavity. The valve gates can be closed promptly after the holding pressure ends to prevent melt backflow and minimize sink marks at the gate. The opening and closing times of each gate can be individually adjusted by the control system, optimizing the injection process based on the filling conditions of different areas of the cavity. For example, for thin-walled areas of the housing, the corresponding valve gates can be opened earlier to increase melt filling; for thicker-walled areas, the holding pressure time can be appropriately extended. This gate layout enables the surface roughness of the CT machine housing to be controlled below Ra0.8μm, and the dimensional accuracy reaches MT4 level, meeting the high-precision requirements of medical devices.
The gate layout for a large plastic water tank (500L capacity, 1500mm × 1000mm × 800mm dimensions) required consideration of the strength and sealing of the plastic part. Since the tank must withstand a certain amount of liquid pressure and must not leak, the gate layout was designed to avoid weld marks at stress-bearing locations. A single, large-point, 10mm-diameter, bottom-center gate was employed, allowing the melt to fill the entire cavity upward from the bottom center, maintaining a consistent melt flow and minimizing weld marks. To further minimize weld marks, an overflow chute was installed at the top of the tank to allow the final melt and gas to enter the overflow chute, ensuring full integration of the melt within the cavity. Furthermore, the large-point gate ensures sufficient melt flow, ensuring a filling time of 15-20 seconds, a holding pressure of 70% of the injection pressure, and a holding time of 30 seconds, resulting in a uniform wall thickness and the absence of shrinkage cavities and bubbles. The plastic water tank produced by this gate layout has passed the 0.5MPa water pressure test and has no leakage. Its service life is more than 5 years, meeting actual usage needs.
