The stable operation of injection molds relies on the coordinated operation of eight core systems. Each system independently performs a specific function, yet they are interconnected to form a closed loop, directly determining the molding accuracy, production efficiency, and mold lifespan. Spline testing molds, as specialized equipment for material performance testing, emphasize standardization, high precision, and stability in their eight system designs, serving as a typical vehicle for understanding the core principles of molds. This article will analyze the core points of the eight core systems in conjunction with actual production scenarios and industry technology trends, focusing on the specific design requirements of spline testing molds.
I. Molding System
1. Core Function: As the core module of the mold, the precise fit between the cavity and core forms the inner and outer surfaces and geometric structure of the plastic part, directly determining the product's dimensional accuracy, surface quality, and mechanical properties. 2. Design Considerations: The clearance between the cavity and core must be controlled within 0.005-0.02mm to avoid overflow or sticking. Material selection must match the molding conditions; commonly used materials include P20 pre-hardened steel and S136 mirror steel, with a surface roughness Ra≤0.025μm.
3. Spline Test Mold Adaptation: Strictly adhere to GB/T 1040.2-2006 standard, with a cavity dimensional tolerance of ±0.01mm. Polished spline molds use S136 steel, with a surface polishable to Ra0.008μm, suitable for polymer material testing. Nitrided molds use 38CrMoAl steel, with a nitrided layer thickness of 0.2-0.4mm, suitable for high-temperature and high-wear scenarios.
II. Gating System
1. Core Function: Connects the injection molding machine nozzle and cavity, responsible for smoothly and evenly conveying molten plastic to the molding area, while simultaneously isolating cold material and transmitting pressure. 2. Design Considerations: Main runner cone angle 2°-6°, small end diameter 3-6mm; branch runners are mainly circular or trapezoidal, diameter 4.8-8mm, flow length difference ≤5%; gate type selected according to part characteristics, point gate diameter 1.5-2mm, fan gate diffusion angle 60-90°.
3. Spline Testing Mold Adaptation: Single-cavity molds use point gate design, distance between gate and spline end ≥5mm to avoid marks affecting testing; multi-cavity molds use balanced runners, length deviation of each cavity ≤0.5mm to ensure consistent spline performance; composite material spline molds add fiber guiding channels to prevent fiber breakage.
III. Ejection System
1. Core Function: After molding, the system uses mechanical force to smoothly eject the part from the cavity or core, ensuring no deformation or damage. 2. Design Considerations: Commonly used structures include ejector pins and push plates. Ejector pin diameter is 2-10mm, with a hardness ≥ HV800 after surface nitriding. The push plate ejection area ratio is ≥ 60%, suitable for deep-cavity, thin-walled parts. The ejection mechanism must be equipped with a pre-reset device to avoid interference with other systems.
3. Spline Testing Mold Compatibility: Use 3-5 ejector pins with a diameter of 2-3mm, with a clearance of 0.002-0.003mm to ensure uniform stress distribution. Ejector pin positions should avoid critical areas of the spline test to prevent stress concentration. For high-temperature conditions, ejector pins should be made of Inconel 718 high-temperature alloy.
IV. Cooling System
1. Core Function: Controls mold temperature through circulating media, shortens the molding cycle, ensures uniform cooling of the plastic part, and reduces dimensional deformation and internal stress. 2. Design Considerations: Cooling channel diameter 8-12mm, distance from product contour 1.5-2 times the channel diameter; zoned temperature control design, surface temperature difference ≤2℃; beryllium copper inserts can be used in high heat load areas, increasing thermal conductivity to 330W/m・K.
3. Spline Test Mold Compatibility: Polished mold water channel spacing 20-30mm, water temperature fluctuation ±1℃; nitrided mold water channel diameter increased by 1-2mm, equipped with high-temperature resistant seals; 3D printed conformal water channels are increasingly used in complex spline molds, improving cooling efficiency by 40%.
V. Guiding and Positioning System
1. Core Function: Ensures precise alignment of the moving mold and fixed mold during opening and closing, controls coaxiality deviation, prevents mold jamming or plastic part misalignment, and ensures molding stability. 2. Design Considerations: Four sets of guide pillars and bushings are used, with a tolerance of H7/g6 and a surface roughness Ra≤0.4μm; large molds are equipped with a central auxiliary guide, a conical positioning taper of 5-10°, and a positioning accuracy of ±0.005mm.
3. Spline Test Mold Adaptation: For polishing molds, the guide pillar and bushing fit accuracy is ≤0.005mm to avoid affecting the polishing accuracy of the cavity; nitriding molds have a 0.1-0.2mm allowance for nitriding layer processing; multi-cavity spline molds are equipped with an intelligent positioning monitoring module to provide real-time feedback on alignment deviations.
VI. Exhaust System
1. Core Function: Exhausts air and plastic decomposition gases from the cavity, preventing defects such as scorching, bubbles, and material shortage caused by trapped gas, ensuring smooth melt filling. 2. Design Considerations: The parting line venting groove depth should be 0.02-0.04mm, and the width 5-10mm; ventilated steel inserts can be used in deep cavity dead zones, with an air permeability ≥0.8L/(min・cm²); venting grooves must avoid critical molding surfaces.
3. Spline Test Mold Adaptation: Venting groove depth 0.03-0.05mm, one venting groove corresponding to every 10mm cavity length; for nitrided molds, due to the dense nitriding layer, the cross-sectional area of the venting grooves needs to be increased; venting structures must be installed at the junction of the spline cavity end and the weld line, with porosity controlled to <2%.
VII. Side Core Pulling System
1. Core Function: Holes, grooves, or undercut structures on the side of the molded plastic part are used to achieve core pulling and resetting actions via mechanical or hydraulic drive. 2. Design Highlights: The angled guide post drive angle is ≤25°; the hydraulic cylinder drive stroke accuracy is ±0.02mm; the slider surface is hard chrome plated or coated with DLC, with a friction coefficient ≤0.1; the angled ejector angle is accurately calculated using the undercut and ejection stroke.
3. Spline Test Mold Adaptation: For irregularly shaped test splines with grooves, a hydraulically driven slider is used, with the core-pulling speed controlled at 5-10mm/s; the clearance between the slider and the cavity is 0.008-0.012mm to avoid affecting the spline dimensional accuracy; wear monitoring sensors are provided for high-frequency use scenarios.
VIII. Mold Base Support System
1. Core Function: Supports and fixes various functional components of the mold, provides standardized installation interfaces, enhances the overall rigidity of the mold, distributes molding pressure, and facilitates mold maintenance and replacement.
2. Design Highlights: The mold base material is mainly S50C carbon structural steel; large molds use cast iron for enhanced rigidity; the template thickness is designed according to the cavity size and clamping force, with deflection deformation ≤0.01mm; equipped with standardized lifting rings and locating pins to adapt to injection molding machine installation requirements. 3. Spline Test Mold Adaptation: Single-cavity spline molds utilize lightweight aluminum alloy mold frames to improve mold change efficiency; multi-cavity mold frames are reinforced with ribs to ensure stability during mass production; modular design is becoming a trend, supporting rapid switching between 4-cavity and 8-cavity designs to adapt to different batch testing needs.
The synergistic optimization of eight core systems is the core direction of injection mold technology development. Currently, technologies such as 3D printing, CAE simulation, and intelligent monitoring are deeply integrated into each system, driving the transformation of molds towards high precision, intelligence, and green technology. The standardized design concept and precise control requirements of spline test molds provide important references for the design of complex plastic part molds. Mastering the design logic and adaptation principles of each system is key to both entry-level and advanced mold technology.
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