Eight Core Components of Injection Molds
Injection molds are key equipment for injection molding, whose structural design directly determines product precision, production efficiency and mold lifespan. The eight universally recognized core components cover key functional modules such as molding, gating, guiding and ejection, working synergistically to realize melt filling, cooling and demolding. Below are their core functions and practical details:
1. Molding Components (Cavity & Core)
These are the core parts that directly shape the plastic melt, consisting of cavity (for product outer surface) and core (for inner surface). Their dimensional accuracy is precisely calculated based on plastic shrinkage rate, and surface roughness matches product requirements (Ra≤0.02μm for high-gloss products, Ra≤0.8μm for regular ones). Made of wear-resistant steels like P20, 718H and S136, molding components for reinforced plastic products require nitriding or quenching to enhance surface hardness and wear resistance.
2. Gating System
It delivers molten plastic from the injection machine nozzle to the cavity, including sprue, runner, gate and cold slug well. The sprue is precisely aligned with the nozzle, designed with a 2°–4° taper for smooth melt flow and demolding. Runners are evenly distributed with circular or trapezoidal cross-sections to reduce pressure loss. Gates (spot, side or submarine types) determine filling speed and product appearance. Cold slug wells store cold melt at the flow front to avoid product defects.
3. Guiding & Locating System
It ensures precise alignment during mold opening and closing, preventing cavity-core misalignment and product rejection. Composed of guide pins, bushings and locating pins, it adopts a sliding fit (0.005–0.01mm clearance) with SUJ2 bearing steel material quenched for hardness. Large or high-precision molds add conical locating pins to further improve clamping accuracy, ensuring long-term guiding precision and wear resistance.
4. Ejection System (Demolding Mechanism)
It ejects cooled products from cavity or core, including ejector pins, rods, plates, guide pins and return springs. Ejector pins (1–5mm diameter) are evenly arranged to avoid product deformation; ejector plates suit large flat products, while elastic mechanisms prevent damage to thin-walled products. Return springs reset the system after demolding to ensure precise cavity-core fitting, with design balancing ejection force and product surface quality to avoid ejection marks or cracks.
5. Cooling/Heating System
It controls mold temperature to regulate melt filling, cooling and solidification speed, including cooling channels, heating rods and temperature controllers. Most plastics (ABS, PP, PE) require cooling, with channels 15–25mm from cavity surface and 1–3m/s water flow for uniform cooling. High-temperature plastics (PA, PPS) or melt flow improvement needs heating systems, with heating rods evenly placed and temperature controlled within ±2℃. Reasonable channel layout can shorten molding cycles by 20%–30%.
6. Venting System
It expels cavity air and melt volatiles to avoid burns, flow marks and short shots, including parting line vents, ejector pin clearances and insert vents. Vent depth is precisely controlled by plastic type (0.01–0.03mm for ABS, 0.03–0.05mm for PE), with 5–20mm width and 10–30mm length extending outside the mold. Auxiliary vents are added for complex cavities to ensure full gas exhaust while preventing melt flash.
7. Side Parting & Core-Pulling Mechanism
It handles products with side holes, undercuts or reverse buckles, consisting of angled pins, sliders, guide grooves, locking blocks and return springs. Angled pins (15°–25° tilt) drive sliders via clamping force for side core-pulling; locking blocks secure sliders during injection to prevent displacement; return springs reset sliders after mold opening. Design considers core-pulling distance, force and mold space to ensure stable operation.
8. Mold Base & Standard Parts
The mold base is the supporting structure for fixing functional components, including fixed/moving mold plates and retainers, made of S50C or 45# steel for sufficient strength and rigidity to avoid deformation. Standard parts (bolts, pins, springs, seals) comply with GB/T or ISO standards for interchangeability and reliability, reducing mold manufacturing costs and lead times as the foundation for stable mold operation.
